Solutional Landforms in Quartz Sandstones of the Sydney Basin Robert Arthur Wray University of Wollongong
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1995 Solutional landforms in quartz sandstones of the Sydney Basin Robert Arthur Wray University of Wollongong
Recommended Citation Wray, Robert Arthur, Solutional landforms in quartz sandstones of the Sydney Basin, Doctor of Philosophy thesis, School of Geosciences, University of Wollongong, 1995. http://ro.uow.edu.au/theses/1981
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Solutional Landforms in Quartz Sandstones of the Sydney Basin
A thesis submitted in fulfilment of the requirements for the award of the degree
DOCTOR OF PHILOSOPHY
from
The University of Wollongong
by
Robert Arthur Lassau WRAY B.Com., G.Dip.Sci., B.Sc (Hons.)
School of Geosciences (Geography) 1995 ii
This work has not been submitted for a higher degree at any other University or Institution and, unless acknowledged, is my own work
Robert A. L. Wray iii
ABSTRACT Solutional landforms have been described for over one hundred years from limestone terrains and are termed karst. In many tropical regions landforms of similar morphology but on highly siliceous sandstones and quartzites have also recently been identified. The similarity of these features in morphology and in genetic solutional processes to those on limestone has prompted recent calls for these quartzose landforms to also be regarded as true karst.
Although not unknown in temperate latitudes, these highly siliceous solutional landforms have been most commonly studied in present-day tropical regions, or areas believed to have been tropical in the recent past. This concentration of research in hot-wet areas, allied with the long held assertion of the insolubility of silica, especially quartz, led to a belief that tropical climatic conditions are necessary for karstic solution of these rocks. However, some of these quartzose solutional landforms are known in areas of temperate climate where there is little evidence for prior tropical climates. A comprehensive worldwide review of these landforms, and the processes involved in their formation, has not previously been conducted and forms the basis from which this study stems.
The Sydney Basin in southeastern Australia has had a stable temperate climate for much of the Cainozoic with no evidence of tropical climate. The highly quartzose Permo-Triassic sandstones of this area have little carbonate, but nevertheless display a wide range of landforms morphologically similar to those both on limestones and also tropical quartzites. These include large bedrock towers, grikes, caves, smaller solution basins and runnels and even widespread silica speleothems. This study describes the morphology of this suite of landforms in detail, and provides a comparative analysis of these sandstone forms to those reported from quartzites of tropical areas and also their limestone analogues. Microscopic and chemical analyses are then utilised in examining the poorly understood natural processes responsible for their formation. The process of sandstone solutional weathering in the Sydney Basin is also compared with that reported from the tropics, demonstrating very little difference in either the form or magnitude of attack between these two climatically distinct regions. No previous studies have examined the wide range of solutional features found on quartz sandstones in one region of a climate comparable to Sydney, nor of the processes involved in the genesis of these forms. iv
ACKNOWLEDGMENTS Many people have assisted in the preparation of this study, and without their help it would not have evolved into the form which it now is. Thanks must be given to all these people. The University of Wollongong provided financial assistance with APRA research funding, and also the use of the resources of the Geography Department.
Most importantly I must thank my parents, for without their constant love, compassion, tolerance and interest, this study could not have been completed, nor the author always remained sane. My brother also provided much assistance, more than he knows, both in the field, with the statistics, and just generally being interested.
To my Supervisor A. Professor R.W. Young and also Dr A.R.M Young is also owed an eternal debt of gratitude, not only for investing over three years of interest in this project, for help in the field, but also being in the unlucky position of having to read many of the earlier drafts of this thesis.
Other people have also been dragged around in the field during this research. Some have enjoyed the time (and why not, this is the best part of the World), but others haven't (sorry about surveying in the sun for 8 hours on a 40+° C day Brendan). Jason and Brett Moule both provided much assistance in the field, as did Brendan Brooke, Alice Turkington, and Judy Carrick. Lynne McCarthy, Karen Wilkinson and Filiz Bensan all provided a memorable days assistance. Now you won't have to run and hide if I ask if you want to go on a bushwalk.
The Staff of the Geography Department at the University of Wollongong have all also had an impact on the genesis of this thesis. Many have shown interest and engaged in interesting discussion on this topic over the last few years. Some warrant special mention; Jacqueline Shaw, for just being herself, always seeming calm in a crisis, and continually helpful and understanding. John Marthick for helping with new spells and general Black Magic when the computer misbehaved. Richard Miller for advice and assistance in cartography. Dr Bryan Chenhall with XRD, Dr Aivars Depers with optical microscopy, Mrs Penny Williamson for photographic assistance and Mr David Carrie for thin sections, all in Geology also provided much appreciated assistance, as did Mr Nick Mackie for SEM help in Materials Engineering.
Associate Professor Ken White must also be thanked for stimulating discussion and critical comments. Likewise, the assistance of Dr Julia James for water chemistry analyses is also much appreciated.
My fellow Postgrads (Brendan Brooke, Steven Tooth, Rainer Wende, H.Q Huang, Lynne McCarthy, Ali Rassuli, Richard Walsh, David Kennedy, and Alice Turkington) were all very helpful and understanding. Thanks for the help. V
TABLE OF CONTENTS
Abstract iii Acknowledgments iv Table of Contents v List of Figures ix List of Tables xi List of Plates xiii
Chapter 1. The Problem of Sandstone Solutional Landforms 1.1. Introduction 1 1.2. Research Strategy 4 1.3. Aims of this Study 6 1.4. Structure of this Study 7
Chapter 2. Solutional Weathering of Siliceous Sandstones - A Review 2.1. The Genetic System of Karren Forms 9 2.2. Tower Karst 13 2.3. Solutional Caves 18 2.4. Dolines and Shafts 29 2.5. Grikes 33 2.6. Drainage Runnels 34 2.6.1. Rillenkarren 35 2.6.2. Rinnenkarren, Rundkarren, and Decantation Rills 35 2.7. Solution Basins 37 2.8. Solution Notches 40 2.9. Silica Speleothems 41 2.9.1. Silica Speleothems from Non-Sandstone Caves 41 2.9.2. Sandstone and Quartzite Speleothems 42 2.10. General Conclusions 46
Chapter 3. The Sydney Basin 3.1. Introduction 48 3.2. General Geology of The Southern Sydney Basin 49 3.2.1. Geographic and Structural Boundaries of the Sydney Basin 49 3.2.2. Intra-Basin Structure 51 3.2.3. Evolutionary Sequence of the Southern Sydney Basin 52 3.3. General Characteristics of Sandstones Studied 53 3.3.1. Southern Region Shoalhaven Group 53 3.3.1.1. Snapper Point Formation 56 3.3.1.2. Nowra Sandstone 57 3.3.2. Blue Mountains Plateau Grose Sub-Group 57 3.3.2.1. Burra-Moko Head Sandstone 58 3.3.2.2. Banks Wall Sandstone 59 3.3.3. Central Region-Hawkesbury Sandstone 60 3.4. General Geomorphology 62 vi
3.5. Rates of Landform Change 67 3.6. Climatic and Vegetational History 71
Chapter 4. Quartz Sandstone Solution Basins 4.1. Introduction 76 4.2. Basin Distribution 77 4.3. Data Collection 77 4.3.1. Limitations with Data 78 4.4. Sampling Sites 79 4.5. Morphometric Analysis 82 4.5.1. Basin Size 85 4.5.2. Basin Shape 91 4.5.3. Basin Walls 95 4.5.4. Basin Floors 98 4.6. Relationships Between Morphometric Parameters 101 4.7. Morphometric Relationships Between Sample Sites 108 4.7.1. Differences Between Sites 109 4.7.2. Reasons for Differences Between Sites 114 4.8. Sandstone Hardness and Basin Preservation 116 4.9. Basin Age 118 4.10. General Conclusions 120
Chapter 5. Towers and Grikes 5.1. Introduction 123 5.2. Sandstone Towers 123 5.2.1. Tower Morphology 125 5.3. Structural and Lithological Constraints on Tower Formation 141 5.3.1. Central and Southern Study Area 141 5.3.2. Newnes Plateau Pagodas 148 5.4. Grikes 154 5.5. Conclusions 164
Chapter 6. Sandstone Runnels 6.1. Introduction 166 6.2. Types of Runnels 166 6.3. Runnel Morphology 171 6.4. Distribution of Runnels 176 6.5. Sandstone Hardness and Runnel Development 187 6.6. Conclusions 188
Chapter 7. Sydney Basin Sandstone Caves 7.1. Introduction 191 7.2. Subterranean Conduits 191 7.3. Sandstone Caves 206 7.4. Features Adjacent to the Study Area 211 7.5. Conclusions 212 vii
Chapter 8. Speleothems of the Sydney Basin Sandstones 8.1. Introduction 214 8.2. Silica Flowstone 215 8.3. Silica Stalactites 220 8.3.1. Conical or Cylindrical Stalactites 220 8.3.2. Coralline Silica Stalactites 227 8.3.3. Silica'Popcorn' 244 8.4. Silica Stalagmites 245 8.5. Speleothem Carbonate, Organic Matter and Water Content 249 8.6. Formation of Silica Speleothems 252
Chapter 9. The Chemical Weathering of Quartz Sandstone 9.1. Introduction 258 9.2. Silica Solubility and Chemical Kinetics 259 9.3. The Solubility of Silica 259 9.4. Naturally Occurring Pure Silica 260 9.4.1. Solubility of Natural Forms 261 9.4.2. The Effects of pH 262 9.5. External Influences 264 9.5.1. Metal Ions 264 9.5.2. The Effects of Organic Acids 265 9.5.3. Salts 267 9.5.4. Organic Interactions - Plants and Fungi 268 9.5.5. Temperature 269 9.5.6. Flushing Rate 270 9.6. The Locus of Chemical Attack 271 9.7. Conclusions 274
Chapter 10. Water Chemistry 10.1. Introduction 277 10.2. Sampling Methods 278 10.3. Results 280 10.3.1. Range of Naturally Occurring pH within this Study Area 282 10.3.2. Range of Naturally Occurring Dissolved Silicon in this Area..287 10.3.3. Relationships of Dissolved Silicon to pH 287 10.3.4. Dissolved Iron 290 10.3.5. Relationships of Dissolved Iron to Dissolved Silicon 291 10.3.6. Relationships of Dissolved Oxygen to Dissolved Silicon 293 10.4. Comparisons with Dissolved Silica in Other Areas 294 10.5. Conclusions 296 viii
Chapter 11. Quartz Etching and Silica Solution in the Sydney Basin 11.1. Introduction 298 11.2. Occurrence of Quartz Etching 301 11.3. Etching Type and Intensity 301 11.4. Conclusions 315
Chapter 12. Summary, Discussion and Conclusions 12.1. Introduction 318 12.2. Summary of Findings 319 12.3. Discussion: Significance of the Sydney Basin Sandstone Solutional Landforms 327
Bibliography 331
Appendix 1. Solution Basin Morphometric Data by Field Site 361 Appendix 2. Results of the Kruskal-Wallis and Multiple Comparison Tests 372 Appendix 3. Dissolved Iron, Silica, Oxygen and pH Determinations from Basins and Steams 379 ix
LIST OF FIGURES
Figure 2.1. worldwide distribution of previously reported sandstone and quartzite solutional landforms 11
Figure 3.1. Geographic and structural boundaries of the Sydney Basin 50 Figure 3.2. Stratigraphic nomenclature for the southern Sydney Basin 54 Figure 3.3. Surface outcrop of the major quartz sandstone units of the Sydney Basin 55 Figure 3.4. Reconstruction of changes in precipitation and vegetation in southwestern Australia from the Eocene to the Pleistocene 74
Figure 4.1. Location of solution basin study sites on the Hawkesbury and Nowra Sandstones and the Snapper Point Formation 80 Figure 4.2. Multi-site comparison of Hawkesbury Sandstone basin size parameters 88 Figure 4.3. Multi-site comparison of Nowra Sandstone basin size parameters 89 Figure 4.4. Multi-site comparison of Snapper Point Formation basin size parameters 90 Figure 4.5. Basin width/length ratios of Hawkesbury, Nowra and Snapper Point Formation Sandstones 94 Figure 4.6. Previously reported relationships of length, width and depth of sandstone solution basins 102 Figure 4.7. Width/length relationships of local sandstone solution basinsl03 Figure 4.8. Depth/length relationships of local sandstone solution basins 104 Figure 4.9. Width/depth relationships of local sandstone solution basins 105
Figure 5.1. Location of studied Sydney Basin towers and grikes 124 Figure 5.2. Locations of towers and grikes on the Nowra Sandstone and on the Snapper Point Formation at Jervis Bay 126 Figure 5.3. Detailed distribution of pagodas on the Newnes Plateau 136 Figure 5.4. Azimuth orientations of towers at Monolith Valley 143 Figure 5.5. Fracture pattern and tower alignments in the Nowra Sandstone at Monolith Valley 144 Figure 5.6. Profiles of two small pagodas close to the Glow Worm Tunnel Road 152 Figure 5.7. A generalised model for the development of Newnes Plateau pagodas 153 Figure 5.8. Distribution of grikes along the shore of Jervis Bay from Honeymoon Bay to Dart Point 158 Figure 5.9. Variability in grike orientation between Honeymoon Bay and Dart Point 159
Figure 6.1. Location of runnel study sites on the Hawkesbury and Nowra Sandstones and the Snapper Point Formation 167 x
Figure 6.2. Plan-forms, long-profiles and cross-sectional shapes of runnels on the quartzose equivalent of the Illawarra Coal Measures at Kanangra Walls 172 Figure 6.3. Plan-forms, long-profiles and cross-sectional shapes of runnels on the quartzose equivalent of the Illawarra Coal Measures at Kanangra Walls 173 Figure 6.4. Plan-forms, long-profiles and cross-sectional shapes of runnels on the Hawkesbury Sandstone at Wingecarribee River 174 Figure 6.5. Distance/depth relationships of runnels on some Sydney Basin sandstones 175
Figure 7.1. Locations of studied caves and speleothems on Sydney Basin quartz sandstones 194 Figure 7.2. Underground flow in the Nowra Sandstone along a tributary of the upper Endrick River 203 Figure 7.3. Underground flow in Deep Pass Canyon 203 Figure 7.4. Subterranean flow of the Endrick River through the Nowra Sandstone 205 Figure 7.5. The Hilltop Natural Tunnel 207 Figure 7.6. Sketch of Rocky Creek Cave 210 Figure 7.7. Tiger Snake Canyon Cave 210
Figure 8.1. Bundanoon Cave stalactite S.E.M E.D.A.X. spectrum 225 Figure 8.2. X.R.D trace of the Bundanoon Cave stalactites 226 Figure 8.3. S.E.M E.D.A.X traces of the Deep Pass Cave stalactite 234 Figure 8.4. Tiger Snake Canyon Cave stalactite S.E.M E.D.A.X. spectra 238 Figure 8.5. X.R.D trace of the Deep Pass Cave stalactites 241 Figure 8.6. X.R.D trace of the Fortress Creek stalactites 242 Figure 8.7. X.R.D trace of the Tiger Snake Canyon Cave stalactites 243 Figure 8.8. X.R.D trace of the Fortress Creek stalagmite 248
Figure 9.1. Relationship of the solubility of silica to pH 263
Figure 10.1. Range of measured pH of basins and streams within this study area 286 Figure 10.2. Range of measured dissolved silicon in basins and streams of this study area 288 Figure 10.3. Relationship of dissolved silica to pH in streams and basins 289 Figure 10.4. Range of measured dissolved iron in streams and basins in this study area 291 Figure 10.5. Relationship of dissolved iron to dissolved silicon in streams and basins in this study area 292 Figure 10.6. Relationship of dissolved oxygen to dissolved silicon in streams and basins in this study area 293 xi
LIST OF TABLES
Table 2.1. Classification of solutional microforms on limestone 12
Table 3.1. Annual average climatic data for the study area 72
Table 4.1. Summary of morphometric characteristics of studied quartz sandstone solution basins 86 Table 4.2. Basin shape for Hawkesbury Sandstone basins 91 Table 4.3. Basin shape for Nowra Sandstone basins 92 Table 4.4. Basin shape for Snapper Point Formation basins 92 Table 4.5. Wall characteristics of Hawkesbury Sandstone basins 97 Table 4.6. Wall characteristics of Nowra Sandstone basins 97 Table 4.7. Wall characteristics of Snapper Point Formation basins 98 Table 4.8. Floor characteristics of Hawkesbury Sandstone basins 99 Table 4.9. Floor characteristics of Nowra Sandstone basins 99 Table 4.10. Floor characteristics of Snapper Point Formation basins 99 Table 4.11. Spearman's Rank Correlation coefficients corrected for ties for Hawkesbury Sandstone basins 106 Table 4.12. Spearman's Rank Correlation coefficients corrected for ties for Nowra Sandstone basins 107 Table 4.13. Spearman's Rank Correlation coefficients corrected for ties for Snapper Point Formation basins 107 Table 4.14. Results of the Kruskal-Wallis Tests for Hawkesbury and Nowra Sandstones and Snapper Point Formation basins 109 Table 4.15. Multiple Comparisons of Hawkesbury Sandstone basins 110 Table 4.16. Multiple Comparisons of Nowra Sandstone basins 111 Table 4.17. Multiple Comparisons of Snapper Point Formation basins 111 Table 4.18. Hardness of sandstone surfaces and basin floors at various sites related to the degree of relative basin development 117 Table 4.19. Uranium/Thorium age determinations for the Bonnum Pic ferricrete 121
Table 5.1. Comparative hardness of towered and non-towered Nowra and Hawkesbury Sandstone from corrected Schmidt Hammer readings 146 Table 5.2. Hardness of Newnes Railway and Temple of Doom pagodas from corrected Schmidt Hammer readings 151
Table 8.1. Locations of well-developed flowstones 216 Table 8.2. Loss on ignition of silica speleothems 250
Table 10.1. Some previous chemical analysis of river waters from the Illawarra Plateau region 280 Table 10.2. Dissolved silica and iron determinations from the Avon Dam catchment 281 Table 10.3. Water chemistry of Hawkesbury Sandstone waters 282 Table 10.4. Surface water dissolved silica concentrations from the Huntley- Robertson district 283 xii
Table 10.5. Results of chemical analysis of water samples in this study submitted to Biological and Chemical Analytical Services (BACAS), with additional field Si, Fe, DO and pH determinations 284 Table 10.6. Results of chemical analysis of water samples conducted by Dr J. James, Department of Chemistry, University of Sydney 285 xiii
LIST OF PLATES
Plate 4.1. Large irregular flat-bottomed basins in the Snapper Point Formation at Blackall Rocks 83 Plate 4.2. Triangular, flat-floored basin at Point Perpendicular, Snapper Point Formation 83 Plate 4.3. Two large, shallow, intersecting basins in the Snapper Point Formation at Point Perpendicular 84 Plate 4.4. Rounded and irregular flat-bottomed basins in the Snapper Point Formation shore platform at Honeysuckle Point, Jervis Bay 84 Plate 4.5. Extremely irregularly basined shore platform at Honeysuckle Point, Snapper Point Formation, Jervis Bay 87 Plate 4.6. Small and medium-sized irregular flat-bottomed basins on the Nowra Sandstone at Monolith Valley 93 Plate 4.7. Medium-sized basins actively lowering the summit of a Monolith Valley tower 93 Plate 4.8. Irregular shallow basins on the very exposed Nowra Sandstone summit of Pigeon House Mountain 96 Plate 4.9. A chain of flat-floored basins cascading down a Nowra Sandstone pavement along the upper Endrick River 96 Plate 4.10. Shallow flat-floored circular basins on the Hawkesbury Sandstone at Bonnum Pic. 100 Plate 4.11. Several basins intersecting to form a larger irregular basin in the Hawkesbury Sandstone at Carrington Falls 100 Plate 4.12. The largest basin found in this study in the Hawkesbury Sandstone at Bonnum Pic 119
Plate 5.1. Type 1 towers at Monolith Valley isolated from the valley-side cliffline by generally box-like, joint-aligned corridors 128 Plate 5.2. Type 1 towers at Monolith Valley, with Type 2 towers along the cliffs in the centre distance 128 Plate 5.3. Monolith Valley Type 2 towers clustering along valley sides and integral components of the valley-side cliffs 130 Plate 5.4. Type 3 towers at Monolith Valley 130 Plate 5.5. Towers beside the upper Endrick River surrounded by heavily basined pavements 132 Plate 5.6. Cone-like or rounded pyramidal towers at Bulee Ridge 132 Plate 5.7. Small towers at Bulee Ridge 133 Plate 5.8. Hawkesbury Sandstone towers and pavements at Bonnum Pic 133 Plate 5.9. Higher level pagodas at Black Fellows Hand Rocks 137 Plate 5.10. Lower level pagodas at Black Fellows Hand Rocks 137 Plate 5.11. Pagodas at the Temple of Doom 139 Plate 5.12. Tower field on a hillside near the Old Coach Road 139 Plate 5.13. Surveyed pagoda near the Glow-worm Tunnel Road 150 Plate 5.14. Surveyed pagoda near the Glow-worm Tunnel Road 150 Plate 5.15. Grikes on the westward dipping Snapper Point Formation platforms at Honeymoon Bay 155 Plate 5.16. Grikes at Honeymoon Bay 155 XIV
Plate 5.17. Parallel grikes at Whale Point 156 Plate 5.18. Complex grike network at Honeysuckle Point 156 Plate 5.19. Interior view of a lm wide Honeymoon Bay grike 161
Plate 6.1. Series of linear Wandkarren on the walls of a Nowra Sandstone tower at Monolith Valley 178 Plate 6.2. Runnels draining over a cliff edge at Monolith Valley 178 Plate 6.3. A complex group of interconnecting runnels at Monolith Valley resulting in a 'Tray of Loaves' 179 Plate 6.4. A group of runnels beside the upper Endrick River which either drain from vegetation or have a direct rainfall water source 179 Plate 6.5. A complex runnelled pavement amongst the towers beside the upper Endrick River 181 Plate 6.6. Shallow decantation runnels at Pointers Gap 181 Plate 6.7. Detail of the opaline rims of the runnel shown in Plate 6.7 182 Plate 6.8. Decantation runnels on the Nowra Sandstone at Pointers Gap 182 Plate 6.9. A multi-headwater runnel at Kanangra Walls 184 Plate 6.10. Decantation runnel on the side of a Hawkesbury Sandstone tower at Bonnum Pic 184 Plate 6.11. Large tower-summit decantation runnel colonised by small trees at Bonnum Pic 186 Plate 6.12. Large 1.5m wide runnel draining the summit of a Black Fellows Hand tower 186
Plate 7.1. Network of interconnected tubes and other voids within the sandstone above Tiger Snake Canyon Cave 195 Plate 7.2. Entrance of a 10cm diameter tube in the Hawkesbury Sandstone at Bonnum Pic 195 Plate 7.3. Long stains issuing from the mouths of tubes on the walls of Nowra Sandstone towers at Monolith Valley 197 Plate 7.4. Detail of the tubes shown in Plate 7.3 197 Plate 7.5. Remnants of a subterranean drainage network on pedestals above the Hawkesbury Sandstone slopes of a Bonnum Pic tower 199 Plate 7.6. Detail of a section of the tube network shown in Plate 7.5 199 Plate 7.7. Spring in the wall of Bungleboori Creek canyon on the Newnes Plateau 204
Plate 8.1. Cross-section photomicrograph of the Tiger Snake Canyon Cave flowstone 218 Plate 8.2. Cross-section photomicrograph of the Wandian Rd flowstone 218 Plate 8.3. S.E.M image of a stalactite from Bundanoon Cave 222 Plate 8.4. Enlarged S.E.M image of Plate 8.3 of a stalactite from Bundanoon Cave, showing the silica flecks and some desiccation cracking 222 Plate 8.5. Long-section photomicrograph of a Bundanoon Cave stalactite 224 Plate 8.6. Enlarged long-section photomicrograph of the Bundanoon Cave stalactite of Plate 8.5 224 Plate 8.7. Coralline stalactite from Tiger Snake Canyon Cave 229 Plate 8.8. A cluster of coralline stalactites from Tiger Snake Canyon Cave 229 XV
Plate 8.9. Clusters and individual coralline stalactites on the roof of Tiger Snake Canyon Cave 230 Plate 8.10. S.E.M image of the irregular surface of a stalactite from Deep Pass Canyon Cave 233 Plate 8.11. Higher magnification of Plate 8.10 S.E.M image of the irregular surface of a stalactite from Deep Pass Canyon Cave 233 Plate 8.12. S.E.M image of a cross-section through a stalactite from Deep Pass Canyon Cave 236 Plate 8.13. S.E.M image of a cross-section through a stalactite from Tiger Snake Canyon Cave 236 Plate 8.14. Long-section photomicrograph of the Deep Pass Cave stalactite 237 Plate 8.15. Long-section photomicrograph of the Tiger Snake Canyon Cave stalactite 239 Plate 8.16. Cross-section photomicrograph of the Tiger Snake Canyon Cave stalactite 239 Plate 8.17. Stalagmites in Tiger Snake Canyon Cave 246 Plate 8.18. Long-section photomicrograph of the Fortress Creek stalagmite 247 Plate 8.19. Enlarged long-section photomicrograph of the Fortress Creek stalagmite 247 Plate 8.20. Large phytokarst carbonate stalactites from Palona Cave, Royal National Park 251
Plate 11.1. Thin-section micrograph of Snapper Point Formation sandstone from a grike wall at Honeymoon Bay (TS 12035) 303 Plate 11.2. S.E.M image of the Snapper Point Formation within a grike at Honeymoon Bay 303 Plate 11.3. S.E.M image of Snapper Point Formation from within a grike at Honeymoon Bay showing intense etching of quartz overgrowth 304 Plate 11.4. S.E.M image of the Snapper Point Formation at Honeymoon Bay showing intense etching of detrital grains and quartz overgrowth edges and faces 304 Plate 11.5. Fine grained Snapper Point Formation sandstone at Blackall Rocks (TS 12032) 307 Plate 11.6. Embayed overgrowths and sutures at Blackall Rocks resulting from clay degradation 307 Plate 11.7. S.E.M micrograph of sutured, interlocking but still highly permeable Nowra Sandstone at Monolith Valley 308 Plate 11.8. Widespread non-selective corrosion on grain surfaces and edges of overgrowths at Monolith Valley alongside uncorroded overgrowth faces 308 Plate 11.9. Thin-section micrograph (TS 12037) of the Monolith Valley Nowra Sandstone showing illustrating widening of contacts between grains, even between overgrowths 309 Plate 11.10. Thin-section micrograph (TS 12037) of the surface of the Monolith Valley Nowra Sandstone 309 Plate 11.11. Thin-section micrograph (TS 12036) of the surface of the upper Endrick River Nowra Sandstone 311 Plate 11.12. Thin-section micrograph (TS 12040) of the surface of the Nowra Sandstone at Bulee Ridge 311 xvi
Plate 11.13. S.E.M micrograph of unweathered Banks Wall Sandstone from the Clarence Road quarry 313 Plate 11.14. Higher magnification of Plate 11.13 313 Plate 11.15. Thin-section micrograph (TS 12042) of the surface of the Old Coach Road sandstone 314 Plate 11.16. Thin-section micrograph (TS 12044) within an iron-cemented sandstone layer at Black Fellows Hand 314 1
CHAPTER 1. THE PROBLEM OF SANDSTONE SOLUTIONAL LANDFORMS
1.1. INTRODUCTION
The detailed study of the large-scale calcareous solutional landforms, or karst, underlying much of eastern Europe began several hundred years ago
(reviewed in detail by Shaw, 1992), blossomed during the early to mid decades of this century, and developed into a highly structured field of research (eg.,
Sweeting, 1972, 1981; Jakucs, 1977; Jennings, 1985; Ford and Williams, 1989). It was perhaps unfortunate, though, that most early definitions of karst landforms, and still many today, were essentially restricted to carbonate bedrock because it was not long before a range of similar landforms on non- carbonate rocks was identified. But these non-carbonate landforms, whilst often identical in size, shape, and apparent formative process to their limestone analogues, were generally dismissed as pseudo-karst; that is to say, only a scientific curiosity and not worthy of detailed study. Even when solutional processes were later demonstrated as being a causative agent in the genesis of many of these forms in siliceous rocks, most geomorphologists and geologists, following conventional wisdom, were loath to change their outlook (Tschang, 1961; Feininger, 1969; Loffler, 1974; Marker, 1976; Vitek,
1979; Pouyllau and Seurin, 1985; Watson and Pye, 1988; Osborne and
Branagan, 1992; Yanes and Briceno, 1993).
During the last fifty years, and especially the last two decades, this paradox of the occurrence of solutional landforms on some of the most insoluble of rocks has become increasingly difficult to ignore. Very large, demonstrably solutional, landscapes on quartzites and quartz sandstones have been 2 discovered and systematically examined in many tropical regions. These landforms range over several orders of magnitude in size, from large karst towers to microscopic dissolution pits, and clearly exhibit an almost identical morphology to that of their carbonate relatives. Moreover, large scale solution of various types of silica including quartz, is clearly critical to their development. The great solutional assemblages in the quartzites of the
Roraima (White et ah, 1966; Urbani and Szczerban, 1974; Chalcraft and Pye,
1984; George, 1989; Briceno and Schubert, 1990) or the sandstones of central Africa (Mainguet, 1972) and northern Australia (Young, 1986, 1987, 1988), must now be included along with Tower and Cockpit Karst as major features of tropical landscapes.
The recognition of these large and complex, undoubtedly solutional, landform assemblages has also cast a cloud over many commonly accepted definitions of the term 'karst' itself. Karstic landforms are now seen to be not solely restricted to carbonate rocks, nor even to specific landform types; therefore the older lithologic- or morphologic-based definitions are now inappropriate. In recent years several wider ranging process-based definitions have been proposed (Sweeting, 1972; Grimes, 1975; Bogli, 1980; Ford, 1980;
Jennings, 1983, 1985; Twidale, 1984). For example, Sweeting (1972, p.5) states that "the sinking of water and its circulation underground is the essence of the karst process. This process is dominated by a chemical (solutional) activity, and true karst landforms result largely from the action of one erosive process, namely solution", whilst Ford (1980, p.345) notes that "true karst forms are distinguished from pseudokarst forms by the necessity of rock solution. True forms may be excavated entirely by aqueous solution, or other processes may contribute largely to their dimensions; but where this latter applies, solution plays an essential precursor or 'trigger role' ". Probably the most succinct and 3 useful definition is that of Jennings (1983, p.21), who remarked that karst is the "process, solution, which is thought to be critical (though not necessarily dominant) in the development of the landforms and drainage characteristics" of an area. This definition incorporates the essentials of the older karst definitions, but avoids their limitations. It is this definition of karst which is used in this study.
Although the recognition of solutional landforms in quartzose rocks has been a major advance in the study of karst in general, systematic investigation of them is still constrained by theoretical aspects of limestone geomorphology, especially by the supposedly key role of climate. A review of the studies of quartzose solutional landforms shows parallels to the limestone karst studies nearly half a century earlier when far too much emphasis was placed on type examples in classifying landforms as diagnostic of certain climates, without a really thorough investigation of the variability within or between climatic zones. Indeed, Williams (1978) argued that recent ideas of climatic geomorphology as applied to karst are too simplistic, that "despite these decades of climatically oriented karst research, this approach can claim little success in explaining karst landforms" (Williams, 1978, p.259). One such example is that of limestone Tower Karst, which was first recognised and studied in tropical regions (e.g. Lehmann, 1936), and then became entrenched as a 'tropical karst' form. More recently (e.g. Brook and Ford, 1976, 1978), similar limestone tower forms were recognised in extra-tropical, even sub polar, regions. Although, as Jennings (1981) warned, climatic effects cannot be simply dismissed, instances like this show the shortcomings of climatic determinism. Similarly, the recognition and investigation of quartzite and sandstone karst began in tropical regions, where once again a climatically- deterministic genetic model was developed, and has since repeatedly been 4 employed. Thus long-term tropical climates (either contemporary or assumed in the past) are regarded as critical for the genesis of these quartzite or sandstone karst (e.g. White et ah, 1966; Chalcraft and Pye, 1984; Pouyllau and
Seurin, 1985; Busche and Sponholz, 1992).
The most biting attack on climatic determinism in the study of quartzose karst has come from Young and Young (1992), who in a world-wide review point out that such features are by no means limited to the tropics, nor that can their distribution be simply attributed to the former extent of tropical climates. Moreover, they argue that until the morphology and formative process of such features in extra-tropical areas are known in detail, a climatically-based classification amounts to nothing more than premature generalisation.
1.2. RESEARCH STRATEGY
Providing an account of solutional features developed in quartzose sandstone in a humid-temperate land is the key concern of the present study. However, while the main English-language book on sandstone geomorphology (Young and Young, 1992) prompted the aim of this study, its French counterpart (Mainguet, 1972) provided the basis for the methodology employed.
Two distinct research strategies were possible at the outset of this study. It could have been a very much in-depth study of a few selected aspects of the solutional removal of silica. But, given the state of the research into siliceous karst in general, and into the landforms of the Sydney Basin in particular, a broader research strategy seemed the more desirable. In short, the range of such solutional features in the Sydney Basin needed first to be determined. It 5 was thus the role of solution in the development of landscapes of the Sydney
Basin which was chosen.
Mainguet (1972) went some distance in this direction in applying Huraulf s
concept of "paysage regionaux" (regional landscapes) to sandstones. Hurault's
major contribution was to detach the concept of a morphogenetic system from
climatic determinism. While emphasising the need to understand the
manner in which individual features form part of a total regional assemblage,
he pointed out that each of these features can be described and explained in
terms of processes without forcing them into a climatic explanation, although
climate past and present need to be considered (Hurault, 1967). The value of
this type of approach has also been demonstrated by Twidale (1982) in his
analysis of granitic terrain when he used the topography itself as the basis for
classification.
A similar applications of Hurault's principles can be made in a study of the
quartz sandstone solutional landforms of the southern Sydney Basin in
south-eastern Australia. Preliminary investigation of the sandstones of this
large region shows that, even though the climate has been essentially cool-
temperate since the Early Tertiary, surface features of these rocks are
remarkably similar to those described from tropical quartzite karst, and even
parallel landforms found on most limestones. Further, topographic, climatic
and lithologic variability have lent their influence in variations of surface
landforms across the study region, and this is clearly reflected in the
distribution of both large-scale and small-scale solutional landforms. 6
No comparably detailed study of solutional landforms on quartzites or quartz
sandstones in a similar temperate climatic region elsewhere in the world can
be cited. And indeed, except for Mainguet's (1972) study of regional sandstone
landforms in sub-tropical Tchad, no other study has yet covered as diverse a
range of sandstone landforms, or examines such a large area, as carried out here.
1.3. AIMS OF THIS STUDY
In the context of the prime aim and general methodology of this study, three main issues are addressed;
1) There has been a general neglect of the paradox of solutional or etch forms on some of the most resistant of rocks mimicking in both appearance and scale those on the most soluble. Are these solutional forms found on the
Sydney Basin quartz sandstones, and if so, how do they compare to those on
more soluble carbonate rocks? Is there a comparable role of solution in landform development upon quartz sandstones?
2) Previous work aimed at resolving this paradox has had an
overwhelming tropical emphasis; study has been almost exclusively concentrated to tropical regions or to areas believed to have been tropical in
the past. Are the solutional landforms of the temperate Sydney Basin, where
the climate has been similar for at least 10 million years, comparable in type,
form and scale to those described from quartzose rocks of the humid tropics?
3) Detailed study of tropical quartzites and quartz sandstones reveals intense weathering of silica, even quartz. Is silica significantly mobile in the
Sydney Basin environment, and how and from where is silica liberated? By 7 what processes is this silica removed from the Sydney Basin sandstones, and do these weathering processes differ markedly to those in the tropical sandstone and quartzite karst?
Various field and laboratory methods have been employed, including detailed field surveying and descriptive analysis, optical and Scanning Electron Microscopy, chemical analysis and other laboratory techniques to help resolve this perplexing paradox and more fully understand the development of these
landforms.
1.4. STRUCTURE OF THIS STUDY
This study consists of two major components. The first concentrates on morphology. It begins, Chapter 2, with a comprehensive review of the scientific literature pertaining to solutional landforms on quartzites and
quartzose sandstones around the world. Although an emphasis is placed
upon English-language sources, sources in other languages are not neglected.
Notwithstanding the work of Young and Young (1992), no such comparable
worldwide review of similar silica-based solutional landforms has previously been published.
From this worldwide examination of sandstone solutional landforms, the
study then proceeds to an examination in detail of the sandstones of the
Permo-Triassic Sydney Basin and solutional landforms developed on them
(Chapters 3 to 8). As much of the Sydney Basin is rugged, almost inaccessible terrain, the entire area could not be studied in detail, and observations have been confined to several of the Basin's larger quartz sandstone units.
Nonetheless, observations seem representative of solutional landforms over 8 the entire region. No previous studies of the types, distribution, and extent of solutional landforms in this study region have been conducted, and there are few comparable studies worldwide
The second major component concentrates on process. It begins with a review of the complexity of silica chemistry (Chapter 9), and proceeds to the study of the basic process, solutional weathering of silica, in the study area (Chapters 10 and 11). This examination of process is of paramount importance to show
whether solution is in fact critical in the genesis of these landforms.
Furthermore, such an analysis of solutional weathering can be utilised in a comparison with tropical quartz karst to ascertain what differences, if any, exist in weathering styles between the tropics and temperate regions.
In the final chapter the results of the description and analysis are reviewed,
and their implications to the study of silicate karst in general discussed. 9
CHAPTER 2. SOLUTIONAL WEATHERING OF SILICEOUS SANDSTONES - A REVIEW
2.1. THE GENETIC SYSTEM OF KARREN FORMS
There has been no previous systematic comparison of limestone and sandstone karst, nor even a detailed review of the range of solutional landforms on quartzose rocks. However, as these landforms and their related solutional processes have been reported from sandstones under a wide latitudinal and climatic range (Figure 2.1), the need for such a review and comparison is pressing. Moreover a survey of small as well as large features is required because, as was emphasised long ago by Hettner (1927, English translation, Hettner, 1972), small landforms often provide the key to understanding large ones. The immediate difficulty encountered in this task is that the complex manner in which the Earth's surface is moistened by precipitation and drainage water results in an almost infinite range of possible pathways for rock solution, and as
Bogli (1980, p.53) emphasised the consequent "multiplicity of possible karren forms makes a morphological system endless".
Bogli (1960) was the first to approach the systematic classification of limestone solutional landforms by erecting a genetic typology of small scale karren forms
(for an English translation see Bogli, 1981). By karren Bogli meant all minor forms of corrosion on limestone and dolomite (Bogli, 1981). He considered the circumstances by which water contacts the limestone surface to be critical, and grouped karren into three major classes; those formed by "free, unhampered 10 run-off, those that form under partial cover, and those formed on a limestone area that is completely covered" (Bogli, 1981, p.78). These three groups include all forms of surface karst, but "associated with them are three further groups; cave karren, surf-zone karren, and lacustrine karren" (Bogli, 1981, p.78).
Within these three main groups are initial or basic forms, and subsequent forms, "which develop as basic forms in one group and then come under the influence of conditions of other groups and are modified" (Bogli, 1981, p.78). Furthermore, individual forms combine to create complexes of forms in which several karren combine to constitute a new, generally larger, clearly characterised, overriding or inclusive unit. "Individual forms and complexes of forms are collected into groups of complexes, and these are units" (Bogli, 1981, p.78) that are major forms, like karren fields or tower karst assemblages. Bogli's typology, shown in Table 2.1 (with some minor additions), has been adopted with minor modification by most karst geomorphologists (e.g. Bogli, 1960; Sweeting, 1972; Bogli, 1980;
Sweeting, 1981; Jennings, 1985; Summerfield, 1991).
Since such a well ordered, and generally accepted, genetic typology of limestone solutional forms is available, it provides a ready means of considering solutional forms in the wider context of non-carbonate bedrock. This chapter focuses on application of this classification to solutional landforms on highly quartzose rocks, especially quartz sandstones. It begins with the largest landforms and proceeds to the smallest. 3 0009 03155283 4 E 2 e s o > " « u — § J So •" tn • 60 8-g o> -E •a «5 8-a .e >^ •£ =a (a uto •g 8 c _ i- E XI o •a £ 01 c n O o > -O ot E u 5 ay; El01 w 1.32 S X> ra ~ O >^ _ B •2 tn jo s % 3 IJ >
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2.2. TOWER KARST
"A tower karst landscape consists of residual hills, normally of carbonate rocks, scattered across a surface of low relief. ... Chinese geomorphologists distinguish
'fenglin' or 'peak forest' landscapes of individual isolated towers on a plain from
'fengcon' or 'peak cluster', which comprises groups of residual hills emerging from a common bedrock base and often incorporating closed depressions between the clusters of peaks" (Williams, 1987, p.454). Outside China these forms, known as Tower Karst (Turmkarst) and Cone Karst (Kegelkarst), have been recognised for many years (Lehmann, 1936). However the origin of these bedrock towers, often many hundreds of metres high, remains problematic
(Jennings, 1985).
Tower karst has traditionally been regarded as characteristic of karst processes in
the wet to humid tropics and sub-tropics, for it is these regions where most
investigation of tower karst has been conducted (Lehmann, 1936; Jennings and
Bik, 1962; Corbel and Muxart, 1970; Jennings, 1972; Day, 1978; Williams, 1978;
McDonald, 1979; Zhang, 1980; Yuan, 1981; Drogue and Bidaux, 1992, and others).
Brook and Ford (1976, 1978), however, presented convincing evidence for
limestone tower karst forming in sub-polar northern Canada, thereby
questioning the validity of tower formation as a wholly tropical karst process.
Observations such as these led Jennings (1985, p.121) to state that "the traditional
climatic geomorphological approach has had to be re-examined and it is
becoming more evident that tower karst formation is controlled more by
structure than was ever thought before." Furthermore, the discovery of tower
karst in its most characteristic form within quartzites, for example in China by
Yuan (1981) and in Venezuela (White et al, 1966) led him to conclude that 14
"structure may predominate even over lithology and hence even over specific solutional processes" (Jennings, 1985, p. 123).
Probably the best documented examples of sandstone tower karst, or 'ruiniform' landscapes (Mainguet, 1972) is in the Roraima area of southern Venezuela. Some of these towers are graphically illustrated in the photographs of George (1989).
Briceno and Schubert (1990), Chalcraft and Pye (1984), Pouyllau and Seurin (1985),
Urbani (1977), White et al. (1966), Zawidzki et al. (1976), Briceno et al. (1990) and
Yanes and Briceno (1993) describe large sandstone and quartzite towers in the
Roraima which conform to the definition of tower karst in all aspects. Most of these authors argue for true karst processes in the formation of these landforms.
Numerous large flat-topped table mountains, or tepuis, of the Precambrian
Roraima Group orthoquartzites surrounded by precipitous cliffs, often nearly a kilometre high, soar above a sea of dense jungle. Weathering and erosion has transformed the summits of the mesas into chaotic labyrinths of intricately carved quartzite, vast tower and doline fields, poljes and innumerable smaller karst landforms. The summits of these almost inaccessible mesas are commonly mist shrouded and experience very high rainfall, most averaging 2800 to
7500mm precipitation annually (Chalcraft and Pye, 1984). Some surface runoff flows directly over the rim of the tepuis spectacularly plunging hundreds of metres to the forests below in the highest waterfalls in the world (Briceno and
Schubert, 1990); Angel Falls, the highest, has a single uninterrupted drop of over
986m (Pouyllau and Seurin, 1985). But the most striking aspect of these tepuis are the tower fields, doline fields and caves on the summits, which bear unquestionable testimony to the solution of the quartzites. As Yanes (1993, p.341) 15 points out the morphology of the table mountain summits conforms to the definition of a karst morphology because it is characterised by chaotic block accumulations, walls, arches, and towers, tower fields, depressions, caves, and residual forms. And it has been proposed by Martini (1982) that chemical weathering, together with the constant removal of detritus has produced a karst like topography on the table mountain summits.
Yet the Roraima Quartzite is a highly chemically resistant rock. It is typically an
orthoquartzite, becoming locally arkosic with about 5% feldspar, consisting
mainly of a red, medium grained sandstone. While often deeply weathered on
the surface, beneath the weathered zone the rock is often nearly white and very
well cemented. The grains are well rounded, cemented with quartz, and often
have quartz overgrowths (White et al., 1966). Similarly, Chalcraft and Pye (1984,
p.324) found silica to be the main cementing agent, chiefly in the form of
optically continuous overgrowths, with over 95% of the clastic grains quartz with
minor amounts of feldspar, mica and heavy minerals. It is thus undoubtedly
silica that is being removed in solution, not a carbonate cement.
Yanes and Briceno (1993, p.343) also attribute the development of these karst-like
structures in the Roraima meta-sandstones to the chemical weathering of the
siliceous cement and feldspar grains, followed by mechanical removal of sand
grains under vadose conditions. They believe that this process leads to a
progressive arenisation of the rock along zones of weakness such as joints and
bedding planes. 16
The photographic evidence from the numerous reports on the Roraima area certainly shows that the major fracture systems exert a prominent control on the landforms. Briceno and Schubert (1990, p.131) demonstrate that the underground landforms there are also intricately sculptured "by solution of the siliceous cement of the quartzite", and contend that one of the most important dynamic modelling processes is the widening of the fractures by chemical weathering of the quartzite cement, accompanied by mechanical removal of the rock fragments and grains (Briceno and Schubert, 1990).
The long exposure of the Roraima quartzites to sub-aerial weathering may be a key factor in the development of this karst. Yanes and Briceno (1993) argue that karstification has gone on there for ~70 Ma.
Although probably being the best documented instance of quartzose tower karst, Roraima is by no means the only occurrence of such features. Twidale (1987a) reports sandstone towers and domes from the Vila Velha region of southeastern
Brazil, and Mainguet's superb 1972 comparative study of the sandstone topography of the Ennedi region of Chad, central Africa, provides further instances of large and often complex sandstone towers and domes upon which the action of natural waters has played a critical formative role. Solution of silica seems also to have played the critical role on the development of dome-shaped towers up to about 50m high in the Entrada Sandstone of the Colorado Plateau
(D. Netoff, pers. comm., 1993). Indeed some of these towers have pits deeper than 8m sunk in their summits. 17
Notwithstanding the fine Venezuelan and African examples, probably the best and largest number of examples of tower karst in quartz sandstone found anywhere in the world are in northern Australia. Jennings (1979, 1983) described
large areas of the Proterozoic Arnhem Land Plateau quartz sandstones, especially
at the 'Ruined City', as being chopped up by meshes of corridors and canyons, in
parts reduced to towers jumping out of the plains (Jennings, 1983). Percolation of water down and along joints during a long period of sub-aerial weathering has removed much of the quartz cement which bound the rock. Later erosion of this
weathered rock, dominantly along the major joints, has resulted in the formation of subsurface pipes and a general 'ruiniform' relief. Springs issuing
from small tubes along bedding planes and numerous large closed depressions
attest to a perseverance of this underground drainage to the present day. Jennings (1983) insisted that the 'Ruined City', and presumably the similar landscapes, such as the 'Lost City' (Johns, 1994), in much of the Arnhem Land Plateau, are attributable to processes where solution "is thought to be critical (but not necessarily dominant) in the development of the landforms and drainage
characteristics" (1983, p.21), and thus true karst.
Of comparable scale to the examples in Arnhem Land, the Bungle Bungle Range in the Kimberley Region of Western Australia is also an extremely impressive example of tower karst. Young (1986) demonstrates that, despite a lack of subsurface drainage, intense etching and solution of silica, clearly demonstrated
by microscopic analysis, has been critical in the formation of this landscape, and
that the terrain is thus karstic. Solution of the quartz cement and detrital grains
of these Devonian sandstones has been so intense that large blocks of the rock
can be sheared with hand pressure. The interlocking network of component 18 grains has, however, resulted in the sandstone retaining a high compressive strength allowing it to stand in steep faces, turrets and sinuous aretes (Young,
1986, 1988). Young emphasises the striking similarity of this terrain to the tower karst terrain described from limestone in the West Kimberley by Jennings and
Sweeting (1963).
Twidale (1956) also noted unusual quartz sandstone "bee hives" or small towers in northern Queensland. These small convex towers, about 6m in height and 3m in diameter are formed in quartzose horizontally bedded sandstones, and have a morphology similar to that seen in many of the Arnhem Land and Kimberley towers.
2.3. SOLUTIONAL CAVES
Formation of caverns is the most commonly accepted indicator of extensive
solutional activity. In limestone, a well-documented sequence of reactions
results in the direct removal in solution of soluble rock (see for example, Jakucs (1977), Bogli (1980) or Jennings (1985)). No comparable direct solution occurs in silicate rocks (Yariv and Cross, 1979). Instead more complex solutional and other weathering processes are involved, followed by removal of weathered material
by meteoric waters. Solution kinetics of the numerous forms of silica, and the
associated total equilibrium solubilities, vary widely, but all are much lower than
those of most limestones (Krauskopf, 1956; Yariv and Cross, 1979).
Given the low solubility and solution rates for quartz rich rocks (Section 9.4.1), limestones and other highly soluble rocks were long believed the sole location 19 for large karst cave systems, and only recently has this idea been seriously questioned. While admittedly none of the known caves in sandstone, quartzite or other non-calcareous rock attain the size or length found in the larger limestone caves, they are nonetheless comparable in size to the vast majority of smaller limestone caves. They are thus significant, and often very impressive, karst features.
The most imposing cavernous quartzite and sandstone region in the world is again undoubtedly Roraima. The frequency and development of cavernous features within these highly quartzose rocks far exceeds that reported from any other region in the world (Tate, 1938; White et al, 1966; Colvee, 1973; Urbani and Szczerban, 1974; Urbani, 1976; Szczerban et al, 1977; Chalcraft and Pye, 1984;
Pouyllau, 1985; Pouyllau and Seurin, 1985; George, 1989; Briceno and Schubert,
1990; Urbani, 1990a). And again for an excellent photographic essay on this area see George (1989).
The runoff that does not cascade over the massive cliffs of the Roraima mesas rapidly finds its way underground, draining through extensive series of chaotic fissures, canyons, blind valleys, sinkholes and caves. Such is the scale of this karst landscape that the largest depressions are poljes (Briceno and Schubert,
1990). Like the surface morphologies, the subsurface drainage pattern is controlled by major fracture systems and lithological contacts within the quartzites (Briceno and Schubert, 1990). The water that proceeds underground via the myriad of sinkholes finds its way by large and intricate, often joint and bedding controlled cavern systems. The caverns have been formed by the mechanical removal of sand from the sandstone following partial solution of the 20 siliceous cement (Briceno and Schubert, 1990), and flow from them re-emerges on the vertical walls of the table mountains, generally several hundred metres below the summits.
Notwithstanding the efforts of South American researchers during the last 20 years only a tiny number of these cave systems have yet been explored and documented. A complex passage system over 400m long with phreatic tubes of up to 20m diameter has been reported within Cerro Autana, 650m up this 800m high mountain (Colvee, 1973; Urbani and Szczerban, 1974; Urbani, 1976). Geomorphological evidence suggests that this cave is not only significant for its large size, but that it is also the oldest known cave in the world, apparently having formed during a period of phreatic activity in the Precambrian (Colvee,
1973). It is thus far older than any known limestone cave.
Other cave systems in quartz sandstone and quartzite are reported from this region of South America. Urbani and Szczerban (1974) briefly describe several active river caves, including one in Territorio Amazonas, which passes through
Guanay Mountain to emerge 800m from where it sinks, and another resurging
over 1 000m from its sink (Urbani and Szczerban, 1974). The Sarisarinama
Plateau in nearby Bolivar State has numerous large shafts and caves, one 1 352m
in length, in hydrothermally weathered Roraima quartzites (Zawidzki et al, 1976). Szczerban (1977) also reports numerous caves in Bolivar State, the caves and dolines of the Meseta de Guaiquinima being linked by an underground
stream nearly 2km long. Chalcraft and Pye (1984), Pouyllau and Seurin (1985),
George (1989) and Briceno and Schubert (1990) also report large active underground drainage systems and abandoned caves in this area. 21
Urbani (1990b) compiled a bibliography of caves in the Precambrian non- carbonate rocks of the Venezuelan Guiana Shield, and recently reported (Urbani,
1993) that Sima Auyantepuy Noroeste in Venezuela is 2 500m long and 370m
deep, making it (at the time) the deepest, and longest known quartzite cave in
the world. Similar karst hydrology and caves exists over the border on the nearby
Guyana Plateau (Urbani, 1977), and in the Rio Claro region of lowland Brazil
(Wernick et al, 1977), where joint-controlled sandstone caves more than 300m
length have been explored. Other sandstone caves have been reported from mid-
eastern Brazil by Karmann (1990).
Recent reports from Ibitipoca, near Rio de Janeiro, Brazil, describe very large
sandstone and quartzite caves. Bromelias Cave, with a surveyed length in excess
of 2 650m, is the longest quartzite cave in the world (Gilney Raymundo Damm,
Universidade Federal do Rio de Janeiro, pers. comm., 1994). Explorations in the
region, although still no more than preliminary, have revealed more than 35
sandstone caves in excess of 500m length, at least 2 of which are much more than
1 000m in surveyed length. This is undoubtedly the highest concentration of
long quartzite caves known anywhere in the world.
The Roraima and nearby regions of tropical and sub-tropical South America are
by no means exceptional, for active river caves and other caves in sandstones
have also been described from other continents.
Caves had been reported from thick bedded Upper Cretaceous sandstones of
humid tropical southern Nigeria since near the turn of the century (Talbot, 1912, 22 and Wilson and Bain, 1928, quoted in Szevtes, 1989), but it was not until recent investigations by Szevtes (1989) that accurate descriptions of these caves became available. Sixteen horizontal caves are listed by Szevtes (1989), many of which have been surveyed. Some contain active streams and several are associated with deeply incised canyons. The longest is Ogbunike Cave, a complex 350m multi level sandstone maze that records a. long period of cave and canyon development. Water flowing out of this cave emanates from joints and bedding planes. Oduru Cave is the most impressive in the region (Szevtes, 1989), and apparently follows a fault. Water from a large sandstone plateau drains by way of a canyon to sink at a 10m high and 3m wide entrance to this cave; 150m further on the stream re-emerges from the canyon wall. There are several entrances and at least one underground tributary feeding Oduru Cave. A different type of development is found in Ogba Ihunabo (Two Faced Cave) which sinks into 150m of cave at the end of a blind valley. The cave eventually sumps, but the waters reemerge in a large spring cave. Bedding planes are seen to be important in the development of this cave also (Szevtes, 1989). Egboka and Orajaka (1987) and Mbanugoh and Egboka (1988) also describe sandstone caves from Nigeria, some with running streams.
Like the Roraima quartzites, in the Nigerian examples the cementing material is mainly ferruginous and siliceous, and the carbonate content is subordinate
(Szevtes, 1989). It is the cementing silica, not the carbonate, that is undergoing solution. The weathered sandstones are more friable and their erosion results in cave formation. 23
Busche and Erbe (1987) and Busche and Sponholz (1988, 1992) in their landmark papers on North African sandstone karst clearly demonstrate that present-day wet tropical regions are not the only locations where significant sandstone caves are found. These authors report hundreds of closed scarp-foot drainage depressions and numerous small phreatic caves in the hyper-arid (20mm precipitation per annum) Sahara of Niger, northern Africa. The caves are relict and apparently formed during wetter periods in the mid-Tertiary, although the scarp-foot depressions are believed to have been active until the Pliocene. Small sub-horizontal to sub-vertical karst tubes a few centimetres in diameter are often exposed in cliff walls, and gush water after heavy rain, thereby proving the existence of a well developed subterranean network of karst passages in the sandstones. Although the total number of accessible caves is rather small, the sandstones of the area are completely riddled with small inaccessible passages;
"the total number of karst vessels exceeds that of most limestone areas" (Busch and Sponholz, 1992, p.10).
Mainguet's (1972) comparative study of sandstone terrain of seasonally dry tropical Tibetsi region of Tchad, supported the findings of Busche and Erbe (1987) and Busch and Sponholz (1988, 1992), and stressed the importance of underground water movements controlled by lithologic and structural weaknesses within sandstones. The occurrence of caves and pipes in the sandstones of Tchad prompted Mainguet also to state that "they are as common in sandstone as in limestone" (1972, p.113). Several caves in Devonian sandstones are described by Mainguet (1972), most revealing some structural control. Other karstic phenomena are also found in this area including dolines and gouffres (shafts) (e.g. Mainguet, 1972, Planche XXII, p.126). 24
Extensive cave systems are by no means limited to regions in the hot wet tropics, or to regions which have had such climates in the relatively recent geologic past, for sizeable sandstone caves occur in the worlds wetter temperate regions. The supply of water would appear to be as important in the formation of sandstone caves as it is in limestone caves, but hot temperatures are not essential.
Caves have been long known to occur in the sandstone and quartzites of the Table Mountain sandstone of the Cape Peninsula, South Africa. Especially at Kaulk Bay a large number of extensive sandstone caves have developed in which solutional processes appear to have been critical. In many places the
quartz sandstone has been "eroded into weird shapes" and many streams drain
underground through extensive caves (P. Swart, South African Speleological
Society, 1994, pers. comm.). Marker (1976, p.8) also reports "an exceptionally high
density of pseudokarst caves" at Kaulkbay (sic) Mountain. She notes that, while some are mere vertical fissures intersecting an enlarged bedding plane, others are complex, extensive, network caves at considerable depth below the surface. Marker also comments that the plan forms of such caves are similar to phreatic
karst caves in that they are usually sub-horizontal, and most show evidence of
active vadose enlargement along a preferred joint. Cave walls are scalloped and,
as on the surface, differential weathering is apparent within certain beds or bands
which are selectively eroded.
The Black Reef Quartzite of the Eastern Transvaal, also displays distinctive karst dolines and a number of extensive cave systems (Martini, 1979, 1982). Martini
described this rock as an "orthoquartzite with quartz very largely predominant.
Feldspar may be frequent, but only locally ... no carbonates have been observed in 25 the unweathered samples" (Martini, 1979 p.115, 118). Two extensive cave systems have developed there. The Southern System consists of two large complex dolines and other "less characteristic" depressions, beneath which are at least 17 caves, several with large chambers. Bedding planes are the dominant control on the cave development, and result in passages being wider than their height.
Passage size also varies considerably along the strike, passing rapidly from passages too small for human transit to large spacious chambers. The largest of these is 60m x 25m and 15m high" (Martini, 1979, p.118). Nearly all the caves are active, and in about 70% of the passages water flows even in the dry seasons. The
Northern System is less mature and displays a less well developed karst system. Dolines are relatively small, but the cave system, although smaller, has the same general morphology as the Southern System.
Further occurrences of well developed and often extensive cave systems have been reported in this part of Africa (Marker, 1976; Martini, 1979, 1981; Twidale,
1980; Jennings, 1983). Martini reports Magnet Cave in the Eastern Transvaal to be
2 490m in length with large chambers (Martini, 1990, 1994), but other large caves are also found there, one with a chamber 80m high (P. Swart, South African
Speleological Society, pers. comm., 1994).
Special mention must be made of the recently discovered quartzite caves of Zimbabwe (Aucamp and Swart, 1991). At Turret Towers in the cool temperate Chimanimani Highlands, on the border of Zimbabwe and Mozambique, the deepest quartzite caves on the African continent are found. These caves are essentially vertical compared to the dominantly horizontal passages of many of the worlds other sandstone caves. Deep weathering of the faulted quartzite has 26 resulted in the development of many large jungle filled dolines, several with enterable caves. Bounding Pot attains a surveyed depth of 190m, whilst in the adjacent doline the series of chambers and shafts in Jungle Pot plunges vertically
to 250m (Aucamp and Swart, 1991). More recent exploration at Chimanimani has
shown a newly discovered cave Mawenge Mwena, also on Turret Towers to be 350m deep (P. Swart, South African Speleological Society, pers. comm., 1994). The
later is currently southern Africa's deepest cave, and if one discounts the collapse
shaft of Sima Auyantepuy Noroeste (-370m) of Bolivar, Venezuela, it is the worlds deepest true sandstone cave.
Large number of limestone caves, but few caves in sandstone have been reported from Europe. Only two known reports of sandstone caves have been found in Britain. Mullan (1989) reports one small, apparently phreatic, cave in sandstone, lm wide, 0.6m high 9.6m long in the Fell Sandstone of the Northumberland region, northern England. Although Mullan believed the cave was not formed
by solution, it is hard to envisage other mechanisms that would produce such
phreatic-like development. Reeve (1982) reports small natural caves in sandstone at Ightham, Kent. Caves in sandstones and other quartz-rich
sedimentary units have been reported from areas of eastern and southern
Europe, notably Czechoslovakia (Vitek, 1982a, 1982b, 1982c; Balatka and Sladek, 1983; Mitter, 1983; Musil, 1983; Zimerman, 1984).
Some caves in European sandstone had been listed as the longest in the world
(Courbon et al, 1989, quoted in Truluck, 1991), but they are developed in
calcareous sandstone or in thin limestone layers sandwiched between the 27 sandstone. Since their origin is clearly linked to the dissolution of carbonate, they are no longer classified as quartzite-sandstone caves (Martini, 1994).
Australia is an arid continent but possesses large areas of quartz sandstones, many of which have notable sandstone cavern systems. Cavernous sandstones,
streamsinks and resurgences in the northern regions of Australia have been documented since the time of the first white explorers. For example, Grey (1841,
quoted in Jennings, 1983) recorded several sandstone river caves in his
explorations of the North Kimberley region apparently not since re-visited.
Indeed only recently have detailed explorations and documentation of sandstone
caves been made in northern Australia.
Jennings (1979, 1983) described several large sandstone caves in monsoonal northern Australia. Whalemouth Cave, near Turkey Creek in the East
Kimberley is an active river passage about 220m long and 120m deep with an impressive exit 60m high and 45m wide. Yulirienji Cave excavated in the Upper
Proterozoic quartzose Hodgson Sandstone south of Roper River, Arnhem Land,
is a large rounded remnant of a former river cave 50m long by 8 to 10m wide and 1.5 to 4m high (Jennings, 1979).
Reports of large caves in the Hodgson Sandstone at the 'Ruined City' south of Roper River, Arnhem Land, prompted exploration by Jennings (1979) but none
were found. Nevertheless "there were many small tubes where small streams
flowed out of joints and bedding planes in the wet season" (Jennings,1979, p.826).
Sandstone caves near Nabarlek in Northern Arnhem Land were also reported by 28
Jennings (1979). Jennings (1979, p.825) was convinced that the agent responsible for the excavation of these caves and other karst forms in northern Australia was flowing water, "water is the prime sculptor ... it dissolves the natural (quartz) cement and removes separated sand."
Many other sandstone caves are also known in the seasonally dry tropics of northern Australia. White (1967, quoted in Jennings 1984) and Mulvaney (1965) report enterable caves in Arnhem Land and southern Queensland, several of which have intermittently active streams. Archaeologically famous Kennif Cave has over 100m of passage and is fed by water issuing from small tubes (Joyce, 1974).
Galloway (1967), R.W. Young (pers. comm.), A.R.M. Young (pers. comm.), G.C.
Nanson (pers. comm.) and others, all describe dozens of caves in the quartz rich
Precambrian Kombolgie Sandstone of Arnhem Land. Sandstone cliffs at Cannon Hill, Noorlangie Rock, Mosquito Man and the Labyrinth are all riddled with caves, many of which exceed many tens of metres in length, but unfortunately, little detailed documentary work has yet been done on the caves of this spectacular region of Arnhem Land.
Temperate Australia also has solutional caves in sandstones and other siliceous
rocks, and Shannon (1975) documented three active cave passages at the unconformity between granite bedrock and overlying indurated and duricrusted
colluvial sand sheets in the Bananna Range of central Queensland. 29
2.4. DOLINES AND SHAFTS
Dolines, or similar closed drainage depressions, have only rarely been reported from sandstones. Mainguet (1972) noted several in Tchad, but in the Millstone
Grit of Wales there are vertical walled shafts and "flat bottomed basins (which are) generally completely closed without external drainage. Their average length is 100m, with the long axes following the strike" (Battiau-Queney, 1984, p.235).
These basins are completely independent from any organised surface drainage pattern, were not glacially carved, and have been linked to the weathering of the sandstones (Battiau-Queney, 1984).
Thomas (1954) attributed many of these depressions in the South Wales
Coalfield to collapse into voids within the underlying Carboniferous limestone.
Battiau-Queney (1984) found, however, that in no case could depressions within the Grit be unequivocally linked to collapse in pre-existing underlying limestone caves, and in a number of cases concentration of water into the depressions in the Grit had actually acted toward cave development in the underlying limestone. Battiau-Queney (1984) argued that the area had suffered a long subaerial evolution which "favoured a powerful chemical weathering" (p.299), possibly under a hot wet tropical climate. Furthermore, she concluded that the sharp lithologic boundaries and regular jointing within the Grit have resulted in the quartzite being extensively, although irregularly, weathered with "a massive loss of silica coming directly from the solution of quartz. ... A massive sound bed may be preserved above a completely decayed one ... Instability resulting from these variations may lead to a sudden collapse. It is significant that many sinkholes have vertical quartzite walls: they reflect the collapse process along vertical joints" (Battiau-Queney, 1984, p.238). 30
Complex assemblages of dolines also occur in the Entrada Sandstone of the
Colorado Plateau, U.S.A. (Netoff and Shroba, 1993). These depressions, up to 18m deep, are analogous to solution dolines, but no cave systems have been found beneath. There are no obvious lithologic or structural controls, but several of these pits have long axes in excess of 50m.
In the thick jungles of the Roraima and Sarisarifiama Plateau, Venezuela
(Urbani and Szczerban, 1974; Dyga et al, 1976; Zawidzki et al, 1976; Gesner and
Mehl, 1977; Szczerban et al, 1977; Urbani, 1977; Pouyllau, 1985; Pouyllau and
Seurin, 1985; George, 1989), and in nearby Guyana (Urbani 1977) and Brazil
(Wernick et al, 1977; Brichta et al, 1980), huge vertically walled shaft dolines
150m to nearly 400m deep and 100 to 400m wide, have formed from collapse
precipitated by chemical solution of quartzites and other siliceous rocks. In places
these siliceous rocks have undergone localised hydrothermal solution and
alteration. Urbani (1974) argued that, as large springs spout from cliff walls near
the shafts, huge cave systems must exist below the shafts.
The size of these Venezuelan sinkholes is quite astounding. Of the world's dozen
deepest sandstone/quartzite caves (Truluck, 1991), ten are shafts of the
Sarisarifiama Plateau. The deepest, Sima Auyantepuy Noroeste, is reputedly
-370m deep (Urbani, 1993), and all ten attain depths in excess of 200m. These
collapses are of a comparable size to the largest collapse shafts found in
limestones, of which El Sotano, Mexico, is 412m deep (A. Warild, pers. com.). 31
The furnas of Parana State, Brazil (Bret, 1962), are vertically walled shafts with deep lakes. The No.l furna is circular in plan, 50m in diameter and 112m deep, the lower 48m water filled. These collapses which are developed within sub- horizontal Devonian sandstone and are believed to result from subjacent collapse into voids excavated in presumed underlying limestones (Bret, 1962).
Jennings (1984), however, suggested that, in the light of the evidence from nearby Venezuela, the furnas might also result from solution, cave formation and roof collapse entirely within the sandstones themselves. If this is the case, they should presumably be regarded as cenotes, or water filled dolines.
Hayes (1900) also describes two shafts or "solution sinks" (p.228) over 50m deep, in quartzite in Alabama, U.S.A., and proposed that the beds in which they occur have been faulted over beds of limestone, and the material which originally occupied the depressions had fallen into underground cavities in the limestone through which it was carried off by flowing water. As there is, however, no evidence given in this old report for the presence of limestone below the quartzites, it seems possible that these shafts may be similar to those already described and formed primarily from the solution of the quartzite.
The Kombolgie Sandstone of the Arnhem Land Plateau also contains large doline fields formerly attributed to load casts (Needham, 1978), which more recently, considering the local abundance of sandstone karst, have been reinterpreted as solutional in origin (A. R. M. Young pers. comm., 1992, and J. F.
Nott pers. comm., 1995). 32
The lateritised western Sturt Plateau of the Northern Territory (Twidale, 1987b) is also littered with dolines and sinkholes believed to be formed by the processes of silica and silicate solution. The Mullaman Beds in which the sinkholes are formed are siliceous, and meteoric waters infiltrating along fractures could have dissolved the rock creating voids or zones of low density into which the country rock has collapsed (Twidale, 1987). Alkaline groundwaters, perhaps facilitated by various biogenic factors, are proposed to have aided in the solution of the quartz and silica in the bedrock. Although current dissolved silica levels are not excessively high, Twidale thought that even slow solution could achieve impressive results over a long period of time (Twidale, 1987, p.47). "Given time, silica is significantly soluble, particularly in certain environments. The effects are most obvious where the weathering is localised by structural factors" (Twidale,
1987, p.53), a fact so often overlooked by those who have dismissed solution of quartz and silicates.
The process of subjacent solution of limestone has repeatedly been employed to account for many collapse features in numerous non-calcareous rocks world wide, even when no evidence for underlying limestones has been found (Hayes,
1900; Gesner and Mehl, 1977; Brichta et al, 1980). It is interesting to note that the majority of these shafts are found to only penetrate quartzites, sandstones and other highly siliceous sedimentary rocks. The Big Hole near Braidwood, New
South Wales, is a well known case in point. This roughly circular 110m deep,
30m to 50m diameter, shaft in Devonian quartz sandstones and conglomerate is located on top of a wooded hill. A pool is found at the base of the hole, which is perched 20m above the Shoalhaven River less than 1km to the west. The Big
Hole was studied by Jennings (1966, 1967, 1983) who attributed it to subjacent 33 limestone solution and collapse into the resulting void. Although limestone is found in several locations within a few kilometres, no evidence for limestone has been found in the vicinity or in rubble at the shaft base.
2.5. GRIKES
The widening of joints (grikes or kluftkarren (Bogli, 1960; Jennings, 1985)) by
solution are a moderately common occurrence on limestones where the
inherent planes of weakness within the rock channelise the flow of water, which
in turn promotes their own growth and widening. Grikes also occurs in quartz
sandstones.
In the Roraima quartzites long, narrow, deep slots or crevasses were examined
and photographed by Tate (1938) on the summit plateau of Auyan-Tepui,
Venezuela. Many of these slots appear to be joint controlled (see for example
Figure 6, p.458). Similar slots were also described from the Roraima by White et
al (1966). Further description of these cleft networks were given by George (1989).
Excellent photographs, notably those on pages 546-7 and 560 of George's paper
illustrate the grike networks characteristic of many of the Venezuelan tepuis.
Numerous fissures generally 6 to 15m in depth, but up to 30m deep are described
from a supposedly limestone plateau at 1 600m elevation in central Thailand
(Odell, Undated). Field examination of these 'Bogaz' has shown them to be in
sandstone, not limestone (J. Dunkley, Canberra Speleological Society, pers.
comm., 1993). These slots are usually about 30m in length, but the connection of
several grikes by natural tunnels has resulted in lengths of 200m being reached. 34
Ford and Williams (1989, p.392) also make passing mention to grikelands developed on sandstones in environments as diverse as the dry mountain ranges of the Australian and U.S.A deserts and the sandstones along crestlines in the subpolar, periglacial Mackenzie Mountains of Canada.
Frye and Swineford (1947) described networks of solution groves or troughs on sandstones in Kansas. These slots range from less than 1cm in width and depth to about l/3m width and several metres depth. In contrast to findings elsewhere, these examples show no correlation with joints and other structural features of the rock (Frye and Swineford, 1947) and were thus not grikes per se.
2.6. DRAINAGE RUNNELS
Small drainage channels formed by aqueous dissolution as meteoric waters flow across a rock surface are known by many names, the most common of them being karren, lapies, gutters, rills or runnels. Their occurrence on carbonate rocks has been studied in much detail; they have been classified by size and mode of origin (Bogli, 1960; Sweeting, 1972; Jennings, 1985); they have been attributed to varied formational processes (Ford and Lundberg, 1987); and they have been subjected to extensive morphometric analysis (Dunkerley, 1979, 1983; Goudie et al, 1989; Gil-Senis, 1992). However, although they are known to occur also on basalt (Palmer, 1927), granite (Tschang, 1961, 1962; Wall and Wilford, 1966), quartzite and sandstone, far less attention has been given to their occurrence on non-carbonate rocks. 35
The following review of their occurrence on quartzose rocks applies Bogli's grouping of those runnels that are formed by the direct action of sheetflow, for example rillenkarren, and the larger group of those that are a consequence of channelised water flowing across a surface from an external source
(rinnenkarren, rundkarrean and decantation forms) (Bogli 1960).
2.6.1. Rillenkarren
Rillenkarren are small V and U shaped suites of straight channels of regular form and dimension that head at the crest of steep sided bare rock slopes and extinguish down slope. They are formed by sheet flow of rainwater that falls directly onto the rilled surface (Bogli, 1960). There has apparently only been one previous report of rillenkarren on quartzose sedimentary rocks. Robinson and Williams (1992, p.426) describe "a strange micro-topography of sharp-crested ribs or ridges" on quartz sandstones of the Atlas Mountains in Morocco as bearing "a somewhat similar appearance" to rillenkarren. They are equivocal, however, as to the origin of these features. Robinson and Williams question whether they form in the same manner as rillenkarren because they occur where rain-beat is unexceptional, and believe that they may develop beneath winter snow drifts by carbon-dioxide charged melt waters, or were formed by percolating water charged with organic acids beneath a former soil cover.
2.6.2. Rinnenkarren, Rundkarren, and Decantation Rills
Unlike rillenkarren which begin at the crest of the slope, rinnenkarren head where sheet flow down the slope breaks into linear streams. Rinnenkarren are much bigger than rillenkarren, generally 12 to 50cm wide, are separated by distinct interfluves, have sharp channel rims and rounded bases and increase in 36 depth and width down slope. True rinnenkarren form subaerially throughout their development (Ford and Lundberg, 1987).
Rundkarren are rounded solution runnels which in limestone generally form beneath a cover of soil or other material (Bogli, 1960, 1980; Jennings, 1985; Ford and Lundberg, 1987). They are similar in size to rinnenkarren, and may deepen down slope (Ford and Lundberg, 1987). Lengths are variable and dependant on the volume of water available, length and gradient of slope, rock texture and amount of cover removed. Rundkarren are much more rounded in section than
rinnenkarren, and commonly display dendritic or meandering plan forms on low angle surfaces. On higher angle slopes they tend to be sub-parallel (Sweeting,
1972).
Much more varied in morphology, scale and distribution than either
rinnenkarren or rundkarren are dissolutional rills formed by decantation or
overspill processes where the solvent is supplied from an up slope store, such as
a patch of soil or vegetation, rather than from direct precipitation (Ford and
Lundberg, 1987). Water from this store flows either perennially or intermittently
down the bare rock slope, into which it corrodes a channel below the overspill
point.
These features are by no means limited to carbonate rocks, for runnels and
'gutters' on granite outcrops in both Australia and Zimbabwe have been
repeatedly discussed by Twidale (1963,1974,1976,1982,1984b), who has argued for
an evolution dominated by "moisture attack in the subsurface, and specifically to 37 solution" (Twidale, 1976, p.376) at the weathering front. Many other authors
(Schwinner, 1936; Bulow, 1942; Blank, 1951; Rasmusson, 1959; Reynolds, 1961;
Dragovich, 1968; Hedges, 1969; Watson and Pye, 1988) have all attributed rill shaped dissolution forms on granites, micro-granites, mica-schist, amphibolites and other crystalline rocks to sub-aerial solution by channelled water.
Excellent examples of various rinnenkarren, rundkarren or decantation runnels are also found on many sandstones and quartzites, but reports of this are rarer than on granites. Robinson and Williams (1992) discuss shallow channels or gutters up to 100mm wide and 10mm deep inset into sloping sandstone pavements in Morocco (See Photo 6, p.426). They argue, however, that "there is not evidence to suggest the channels developed beneath a soil cover and it would seem more likely that they formed subaerially" (Robinson and Williams,
1992, p.425). In South Africa, Marker (1976) reported sequences of basin or
"kamenitza-like hollows" (p.8) drained by runnels on the quartzites and metamorphosed sandstones of the Transvaal. White et al (1966) similarly reported frequent grooves and intermediate ridges (Rinnenkarren) with a groove to ridge relief of 25 to 50cm, on the tops of the mesas and buttes of the Roraima.
Pouyllau and Seurin (1985) provide further illustration of runnel formation in the quartzites and sandstones of the Roraima, and Mullan (1989) also reported rundkarren on the Fell Sandstone, Northumberland, England.
2.7. SOLUTION BASINS
Solution basins, pans, gnammas, weathering pits, Opferkessel or rock tanks, are the various local names for the several types of small rock depressions in silicate rocks. Although aspects of the basin forming processes still remain obscure, there 38 is little doubt that they are produced dominantly by the solutional action of standing water; "The action of water is evident to the eye though not easily described" (Ormerod, 1859, quoted in Dzulynski and Kotarba, 1979). They are here collectively termed solution basins, and are analogous to the solution basins found on limestone outcrops (variously termed tinajitas, kamenitza or just solution pans).
Solution basins are depressions of varying size and shape found inset into outcrops of solid rock, are fed by rainwater, and may hold this water for long periods after rain. They may be near circular to oval in plan, but are more commonly of irregular shape. Floors of the basins are flat, gently hemispherical
or irregular in section, and they are bordered by walls which may be from gently
sloping to vertical or undercut. In the bottom of many basins is retained a residuum left from the weathering process, and often a thin layer of silt, moss,
lichen or plant litter. They are only rarely found on steeply dipping surfaces. Smith (1941) discovered that the largest basins on limestone were located where surfaces were flattest, finding none on slopes inclined more than 20 degrees from the horizontal, but in Brazil Branner (1913) found solution basins developed on
granite slopes as steep as about 45 degrees. Branner further observed that the
basins were more abundant on the lower slopes than on the hill crest, attributing
this concentration to the larger volume of run-off on the lower slopes and the
more vigorous disturbance of the water in these lower slope basins.
Where the topography allows basins are sometimes found in chains, generally cascading down slope, and often connected by a shallow channel or spillway.
Also, where several basins form in close proximity, as they enlarge they often 39 breach their intervening walls thus coalescing to form a larger, amoeboid basin.
Several basins may even occur nested inside one another in sequential development but not always consequent upon the lowering of the spillway.
Solution basins are by no means limited to carbonates, for they have been reported in numerous siliceous rocks. The most commonly reported lithology has been granite (Ormerod 1859; Twidale and Corbin 1963; Dahl 1966; Hedges
1969; Dzulynski and Kotarba 1979; Twidale 1984), but other lithologies including granodiorite (Branner, 1913), syenite (Branner, 1913; Udden, 1925), diabase
(Briceno and Schubert, 1990), basaltic lavas (Wentworth, 1944), lateritic duricrust
(Bowden, 1980; McFarlane and Twidale, 1987; Twidale, 1987a), as well as certain schists and other metamorphics (Fuller, 1925; Dahl, 1966).
The reports of basin development in highly siliceous quartz sandstone and quartzite are numerous. They have been found in the U.S.A (Howard and
Kochell, 1988), South America (White et al, 1966; Pouyllau, 1985; Pouyllau and
Seurin, 1985; George, 1989; Briceno and Schubert, 1990), in Africa (Marker, 1976;
Busche and Erbe, 1987; Cooks and Pretorious, 1987), in Europe (Haberle, 1933;
Franzle, 1971; Backhaus, 1972; Vitek, 1979a, 1979b) and in Australia (Twidale,
1980, 1984a). These rocks, being dominantly quartz, often provide little in the way of the more 'soluble' minerals so often relied upon to explain basin formation.
Few direct measurements of the sizes of sandstone solution basins are available, but the general reports indicate that they range in size from several centimetres to several metres in diameter and may be up to several tens of centimetres deep 40
(Franzle, 1971; Schipull, 1978; Cooks and Pretorious, 1987). They are generally much wider than they are deep. Smaller basins are by far the more common, but
very large examples are sometimes found, dimensions of which must often be
expressed in several tens of metres.
2.8. SOLUTION NOTCHES
Solution notches (Bogli, 1980; Jennings, 1985) are a further solution form, found
where soil borders on a very steep or vertical rock surface. They are common in
limestone areas where the rock becomes undercut by waters rich in biogenic C02. In cone and tower karst areas of the humid tropics, cliff-foot caves occur which
are over-sized enlargements of solution notches (Bogli, 1980). See also Plate 12 of Jennings (1985) for a good example.
Solution notches in the form of flared slopes on granite tors and slopes have
been described numerous times, notably by Twidale and Corbin (1963) and
Twidale (1976,1977a, 1977b, 1980, 1982, 1984b), who attributed them to sub-surface
weathering of fresh rock by the solutional action of water at the weathering front.
Subsequent stripping of the soil and regolith has exposed these flared slopes.
Flared slopes with solution notches are also seen developed upon some
sandstones, but are rarer than those on granites. Twidale (1980) reports notched
slopes on Clarens Formation sandstones of South Africa. Twidale (1984a, 1987b)
also observed that the sandstone outcrops on the karstic Tindal Plain, Northern
Territory, Australia, display well developed "mushroom or hoodoo rocks (and) flared boulders and slopes" (1984, p. 100) attributable to the chemical action of 41 groundwater, and Harrell and Twidale (1989) described grooves formed at a sandstone-granite contact in Okalahoma, U.S.A, by groundwater weathering similar to flared slopes.
2.9. SILICA SPELEOTHEMS
Speleothems are secondary deposits of various rock forming minerals, most
common within caves, especially limestone caverns. Calcite is by far the most
abundant, gypsum less common, and a vast range of secondary minerals has
been identified. Hill and Forti (1986) provide the definitive reference of cave
minerals. Deposition of these minerals occurs under a range of physical and chemical conditions, both vadose and phreatic, resulting in a wide variety of speleothem types, the most common of these being flowstones, stalactites and stalagmites. Sweeting (1972), Ford and Cullingford (1976), Bogli (1980), Jennings
(1985), Hill and Forti (1986), Ford and Williams (1989), and others delve into the
details of speleothem development. In contrast, it is generally believed that
speleothem deposits in non-carbonate caves are quite rare, and there are
relatively few references to speleothems within caves in granite, basalt lava, and sandstone.
2.9.1. Silica Speleothems from Non-Sandstone Caves
Silica speleothems are known to assume a variety of forms which mimic
carbonate speleothems including anthodites, blisters, boxwork, coralloids, crusts,
flowstone, stalagmites, stalactites, columns and even helictites (Hill and Forti,
1986). Anderson (1930) examined 4 to 7cm long opal stalactites and stalagmites within a number of lava tubes in Northern California, and Swartzlow (1935) and Swartzlow and Keller (1937) also found erratic, or coralloidal, opal in other 42
Northern Californian basalt caves. Further opaline speleothems have been described in lava caves in a number of other localities; White (1976), and Hill (1976) in the U.S.A., Bartrum (1930) and Cody (1980) in Auckland, New Zealand, and Webb (1979) in southeast Queensland. Webb and Finlayson (1984) investigated the detailed morphology and chemical composition of opaline cave
coral and flowstone in two granite boulder caves in the Girraween National
Park, southeast Queensland, and Finlayson and Webb (1985) presented a highly
detailed study of amorphous silica speleothems.
Silica stalactites have also been recorded in limestone caves. Deal (1964) described
'Scintillites', spectacularly red coloured helictite-like quartz speleothems from
the USA, and Broughton (1974) reported stalactites of fine-grained chalcedony in
limestone caves of Wyoming, USA, and cristabolite, sometimes replacing
gypsum (Broughton, 1971), is also widely reported in the U.S.A (Ford and
Cullingford, 1976; Ford and Williams, 1989) and also in Argentina (Siegel et al, 1968).
2.9.2. Sandstone and Quartzite Speleothems
Silica speleothems also occur in caves in sandstone and quartzites worldwide,
and provide clear evidence of their solutional genesis. Again it is the cavernous
quartzites of northern South America where this speleothem type has been studied in the greatest detail.
The first reports of flowstones and stalactites in the Roraima quartzites were by
White et al. (1966, p.311) who found on a thin coating of opal flowstone on the
wall of a small fissure cave, providing evidence for the solution and later 43 redeposition of silica. They also reported (p.312), "a dense quartzite with a coating of white-grey flowstone which forms some rudimentary stalactites." Little subsequent investigation of these silica speleothems was undertaken for almost a decade until the introductory review by Urbani and Szczerban (1974) heralded a time of resurgence of cave exploration and karst research in the Roraima. Laffer
(1973, quoted in Urbani and Szczerban, 1974) had noted the formation of iron oxide speleothems within a cave in the 'Iron Formations' rocks of the Imataca
Formation near the Tocoma River, and further silica and iron-based stalactites, stalagmites and flowstones were soon after discovered (Zawidzki et al, 1976) in the caves and shafts of the Sarisarifiama Plateau. At the later site hydrothermal
alteration of the quartzites was believed to be important in the formation of the
caves, and X-ray diffraction identified numerous speleothem forming minerals
within the caves. Opal was found forming stalactites up to 10 cm long,
flowstones and different types of crusts and coral-like shapes (Zawidzki et al,
1976, p.36). Large goethite stalagmites several metres high (an excellent example
from the Sima de la Lluvia is illustrated in Figure 4, p.35 of Zawidzki et al, 1976),
were also discovered together with more unusual mineral stalactites, including
Lithiophorite (LiMn3Al209-3H20).
Detailed petrographic, chemical, XRD and SEM analysis of stalactites, stalagmites
and coralloid speleothems from Cerro Autana Cave was undertaken by Urbani
(1976), and revealed a composition of opal, length-fast chalcedony, and calcite
showing concentric growth banding. These deposits were thought to originate
from direct precipitation of the opal and calcite from alkaline waters at room
temperature, with the chalcedony representing recrystallisation of the opal. 44
Some components were believed to have originated from the breakdown of feldspars in arkose horizons within the quartzites.
Urbani (1977) also reported siliceous stalactites in caves near Kumerau Fallas, and in almost all other caves in the Roraima Formation In 1990 he compiled a bibliography of published literature on speleothem and cave minerals found in the Precambrian non-carbonate rocks of the Venezuelan Guyanan Shield
(Urbani, 1990b).
Flowstone stalactites from Mount Roraima were analysed by Chalcraft and Pye (1984) using SEM and XRD techniques, and were found to differ from those previously described. Examination of the flowstone material in thin section showed it to posses a porous texture and to consist of detrital sand grains loosely cemented by cristobalite, tridymite and authigenic quartz (Chalcraft and Pye,
1984) instead of the opal-A matrix found by most of the earlier researchers.
The excellent examination of the geomorphology of the Gran Sabana by Briceno and Schubert (1990) provided further reference to the speleothems of the regions cavernous orthoquartzites. "In some small galleries, speleothems of amorphous
silica were found, forming small stalactites (2cm) and 'popcorn'-type structures"
(Briceno and Schubert, 1990), p.138).
There have been few studies of silica speleothems in sandstone caves outside
South America. Martini (1979, 1982), working in temperate South Africa described small stalactites composed of limonite from the cavernous Black Reef 45
Quartzite. Opal 'popcorn' was also found, as well as a dark, partly organic, flowstone. Other speleothems were, however, poorly developed. Evans (1964) reported the occurrence of silica stalactites in Cornwall, England, but gave few other details, and Porter (1979) noted opaline stalactites and coral on sandstones of the Lee Formation in Virginia, U.S.A.
Reports from the sandstones of northern Australia have indicated the widespread occurrence of silica-based speleothems (Jennings, 1979; R.W. Young pers. com., 1992; G.C. Nanson pers. com., 1992; R. Wende, pers. com., 1994), but few detailed studies have been published. In Kakadu National Park, Watchman
(1990, 1992) analysed numerous silica skins, or flowstone, using SEM, XRD, IRS and petrology, finding silica and a wide range of other minerals including various compounds of calcium, silica, sulphur, aluminium, magnesium and potassium.
Silica speleothems have also been briefly reported in the sandstone overhangs and caves of the Sydney region, but silica is not the only important speleothem- forming mineral in solution here, as various iron compounds are also active agents. Lassak (1970) observed the presence of small stalactites of laminar limonite and opal on several of the quartz sandstone units. A. R. M. Young
(1987) also noted the common occurrence of iron-rich stalactites and tuff as, and provided the only notable description of local silica-based stalactites. She described them as "small (up to 10mm long) stalactites ... (on) ... the roofs of inactive caverns in quartzose Narrabeen Group sandstones in the Blue
Mountains ... consist only of silica with no associated iron oxides" (A.R.M.
Young, 1987, p.965) Her findings contrast with those of Lassak (1970), who 46 postulated alternating precipitation of silica and iron oxide. Mention was also
made of local silica speleothems by Young and Young (1991) but no further
details were given.
Stalactites are not the only speleothems reported from the quartz sandstones of the Sydney Basin region. Watchman (1990, 1992, 1994) conducted detailed
petrographic and SEM study of silica skins, or thin flowstones, from a number of
quartz sandstone locations, including Gnatalia Creek near Wandandian, and
nearby Tianjara Creek, both within the Nowra Sandstone.
Speleothems from non-carbonate caves are undoubtedly not as rare as commonly believed. On the contrary, the unusual and often complex chemistry
of many of these makes them all the more interesting.
2.10. GENERAL CONCLUSIONS
The weight of evidence for solutional karren forms, and indeed entire
landscapes with a fully integrated karstic network, on highly quartzose (and
some crystalline) rocks is overwhelming. Natural waters are undoubtedly capable, and without doubt are actively reducing, bedrock of a wide range of compositions by solutional processes. But, unlike carbonates, the removal of material from sandstones and quartzites is not wholly in solution. Solutional
processes are seen to prepare the rock; solution of matrix, silica cement, or both,
reduces the strength or resistance to erosion of the rock. Martini (1979) has called
this interaction of process 'arenisation'. The arenised rock is less competent, and
much more susceptible to mechanical removal of sand grains or other 47 component material than would be otherwise unweathered bedrock. Thus whilst processes other than true solution contribute largely to the dimensions of these sandstone landforms, "solution plays an essential precursor or 'trigger' role" (Ford, 1980, p.345), and thus they must be regarded as solutional and even karstic for as Jennings (1983, p.21) argued that solution needs to be "critical (but not necessarily dominant) in the development of the landforms and drainage characteristic of karst."
It is also clear that the standard typography of surface and underground
landforms developed by Bogli (1960) for limestone karren can easily be applied,
almost without exception, to landforms on highly quartzose sandstones and
quartzite. The typography applies to morphologically similar forms, at the same
scale, and even over a similar range of scales. Thus, not only the application of a system of morphological classification developed for limestone terrains, one of the most soluble rock types, but also the specific genetic process involved, namely solution, are both seen to be easily transferable to landforms commonly
located upon quartzose rocks, regarded by many to be amongst the most insoluble. 48
CHAPTER 3. THE SYDNEY BASIN
3.1. INTRODUCTION
As the history of the study of landforms in the Sydney Basin has been reviewed elsewhere (Scott, 1977; Young, 1978; Young and Twidale, 1993) it will not be repeated here. However several salient points highlighted by those reviewers that are especially relevant to this study do need emphasising.
Firstly, despite the criticism by Carne (1908) early this century, geomorphological accounts of this region have almost completely ignored the lithological and structural characteristics of the major sandstones which dominate so much of this terrain. Lip service was paid to 'structure' in the Davisian sense of the term, but only recently (Young, 1978, 1983; Young and Young, 1988) was attention directed to the variable geomorphological
properties of the sandstones. Secondly, the variability of landforms across the
Basin, especially the variability of slope and valley morphology, was virtually ignored. Thirdly, an overwhelmingly Davisian interpretation of morphology
emphasised the 'youth' of the rugged plateau terrain (e.g. Andrews, 1910; Taylor, 1958; and Browne, 1969). Recent chronological research (e.g. Wellman and McDougall, 1974; Young, 1974; Young and McDougall, 1982; Young and
McDougall, 1985) has shown that, contrary to earlier opinion, this landscape is
of great antiquity and that geomorphological change is remarkably slow.
Fourthly, the recognition of laterites around Sydney led to the longstanding
dominance of the idea of tropical climates during much of the Tertiary
(Woolnough, 1927; Browne, 1969). This idea too is now known to be
completely unfounded (Kemp, 1978; Bird and Chivas, 1989; Young et al, 1994). It is these four issues on which this chapter is focused. 49
Not all of the major sandstone outcrops of the region could be studied because some of them are under the Sydney urban area, and others are in extremely rugged and virtually inaccessible terrain. Nonetheless, the examples considered are drawn from variable environmental settings scattered widely over the Basin, and thus do give a representative picture of the region as a whole.
3.2. GENERAL GEOLOGY OF THE SOUTHERN SYDNEY BASIN 3.2.1. Geographic and Structural Boundaries of the Sydney Basin
The Sydney Basin, which is one of the major structural features of eastern Australia, has well-defined geographical and structural boundaries (Figure
3.1). These structural boundaries are believed to have developed over a long period beginning with the Early Permian Hunter-Mooki Thrust System during the Hunter Orogeny, and culminating with the final major tectonic movements during the Late Triassic (Herbert, 1980a). Sedimentation within the Basin was actively controlled by this orogenic activity. Extensive uplift and warping, largely completed by Early Tertiary times, resulted in minor deformation of the sediments, but did not lead to significant change in basin structure (Herbert, 1980b).
The unconformable western edge of the Sydney Basin extending from the southern limit of the Basin at Durras, near Batemans Bay, northward through
Marulan and Lithgow, and thence into the Gunnedah Basin is a depositional or erosional contact rather than a structural feature (Bembrick et al, 1973).
The Permo-Triassic sediments of the Sydney Basin thin westward and unconformably lap onto the Palaeozoic granites and highly folded metamorphic rocks of the Lachlan Fold Belt along what appears to be the REFERENCE
——— Unccnlornm
.---.. A»u<3 cc'*l3•'*",,; »o'cmics -.thin i-e :tc!m
Monoct'ne ir>.no direction ;f -iC
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Tnfuji -,nc--«T direction ?i -:;
Boundtrv V r = 5>"
F"3*iiiar ./"c:"Oip
Structural '.*_;:•• lien —t— Syncime 1 J Figure 3.1. Geographic and structural boundaries of the Sydney Basin. Source: After Herbert and Helby (1980), Figure 1.2, p.7. 51 stable margin of the Late Carboniferous-Early Permian craton. Many Early
Permian sandstone outliers extend a small distance westward of this boundary, indicating that stripping of the cover during the Mesozoic has resulted in an eastwards contraction of the boundary. Less is known of the offshore southeastern boundary of the Sydney Basin. Seismic evidence suggests the Basin extends to the continental shelf, and probably to the continental slope (Mayne et al, 1974), and may even be rifted (Carey, 1969).
Much, however, remains uncertain about this extremity (Bembrick et al, 1980).
3.2.2. Intra-Basin Structure
The Sydney Basin may be further subdivided into a series of internal secondary structural units (structural plateau, secondary depositional basins and tectonic units) (Figure 3.1). The geomorphology of the region is markedly controlled by structural and depositional variations between these units.
The Blue Mountains Plateau, and its northward extension the Newnes Plateau, which are separated from the Lachlan Fold Belt by the regional unconformity, form the western section of the Sydney Basin. The Blue
Mountains/Newnes Plateau is delineated from the Cumberland Basin to the east by the Lapstone Monocline-Nepean-Kurrajong Fault system (Branagan and Pedram, 1990), and extends southward from the Mt Coricudgy Anticline until it merges with the Illawarra Plateau. The Illawarra Plateau is itself bounded to the northwest by the Nepean Fault, on its northern side by the Nepean Monocline, and to the south by the 'Shoalhaven Low' which is an ancient river channel incised into the basement approximating the course of the Shoalhaven River from near Marulan to the coast near Callala (Bembrick et al, 1973). 52
South of the Illawarra Plateau is the Sassafras Plateau, the southern limit of which is an east-west basement discontinuity, the 'Tallaterang Low', where a sudden thickening of sediment occurs. The southernmost structural unit of the Sydney Basin is the Boyne Mount Plateau divided from the Sassafras
Plateau by the 'Tallaterang Low', and extending southward to the coast near
Durras. The western boundary of all these plateaux is the regional unconformity with the Palaeozoic fold belt rocks.
The northeastern part of the Basin is the Hunter Dome Belt, bounded by the
Hunter-Mooki Thrust to the north and a basement fault to the southwest
(Bembrick et al, 1973). South of the Hunter Dome Belt is the Hornsby Plateau, bordered to the south by the Hornsby Warp and Cumberland Basin, and to
the west by the Lapstone Monocline and Blue Mountains Plateau. South of
the Hornsby Warp and bordered to the west by the Lapstone Monocline and
to the south by the South Coast Warp and Woronora Plateau is the
Cumberland Basin. The Woronora Plateau is separated from the Illawarra
Plateau by a set of tensional structures reflected in thickness of sediment and
facies change (Bembrick et al, 1973).
3.2.3. Evolutionary Sequence of the Southern Sydney Basin
The Sydney Basin contains numerous series of fluvial, marine clastic and
volcanic strata. These range in age from Carboniferous to Holocene, but the
overwhelming majority were deposited during Permian and Triassic times.
Devonian and Carboniferous sediments occur at depth in the north-eastern
rim, and may also be present at depth beneath the Hunter Valley (Bembrick et
al, 1973). In the study area, however, Carboniferous sediments are of very
limited extent. For the main part Permo-Triassic sediments rest 53 unconformably on an eroded Palaeozoic basement of granite and metamorphic rocks and Late Devonian sedimentary sequences.
3.3. GENERAL CHARACTERISTICS OF SANDSTONES STUDIED
The stratigraphic relationships of the sediments of the southern Sydney Basin are shown in Figure 3.2. This study is only concerned with a number of the
Basin's more extensive massive quartzose sandstones, especially the Triassic
Hawkesbury Sandstone, the Triassic Grose Sub-Group, the Permian Nowra Sandstone and the Lower Permian Snapper Point Formation. Numerous lithic or tuffaceous sandstone units are not discussed. The surface outcrop of these sandstones is shown on Figure 3.3.
3.3.1. Southern Region Shoalhaven Group
The Shoalhaven Group, which dominates the southern extremity of the
Basin, consists of a thick sequence of shallow marine, interbedded quartzose conglomerates, sandstones and siltstones which dip at 1° to 2° to the northeast. The older marine sandstones of the Shoalhaven Group are best exposed south of Nowra, where they comprise the Sassafras and Mt Boyne plateaux. They thin rapidly westward from a thickness of about 1 000m at the
coast to only 45m on the unconformity at Tallong 50km inland (Herbert,
1980b). Constituent formations either merge or 'wedge out' to disappear at varying distances westward, but the older sandstones are also seen in outcrop along the western edge of the Blue Mountains and Illawarra Plateaux.
The Conjola Sub-Group contains the oldest sandstone units of the
Shoalhaven Group. This Sub-Group has been divided into the Wasp Head,
Pebbly Beach and Snapper Point Formations in the coastal and southern parts 54 55
*. *. '.*','Grose .' u • •••,*. in Sub-Group ra 1- H Hawkesbury • .••. • Sandstone
Nowra c ra Sandstone
VE- c- Snapper Point * • Formation
0 10 20 30 40 50 i i i •
Figure 3.3. Surface outcrop of the major quartz sandstone units of the Sydney Basin. Inland outcrops of Snapper Point Formation are poorly mapped and not all are shown. Source: After Sydney 1:250 000 Geological Sheet SI 56-5 and Wollongong 1:250 000 Geological Sheet SI 56-9. 56 of the area, but not further north where these units appear to merge (Gostin and Herbert, 1973). These Formations vary markedly in their topographic extent, and it is the Snapper Point Formation, which records the maximum transgression of the Early Permian sea onto the ancient craton (Herbert,
1980b), which is of concern here.
The Mid-Permian Upper Shoalhaven Group includes the Nowra Sandstone
and sandstones of the Berry Formation. These sandstones extend west to near Tallong and Kanangra Walls (Figure 3.3), almost as far as the Snapper Point Formation. They dominate the surface outcrop upon the Sassafras Plateau.
33.1.1. Snapper Point Formation
The Snapper Point Formation is the most extensive of the lower Shoalhaven
Group in outcrop, being subordinate only to the Nowra Sandstone in total
Group outcrop. It is strikingly displayed on many of the massive cliff lines of the Clyde Valley and Budawang areas, Jervis Bay, and on the lower cliffs of the coastal escarpment south of Ulladulla (Figure 3.3). The Formation progressively thins westward, from 170m thick at the coast, to several tens of
metres at Kanangra Walls (Gostin and Herbert, 1973). It is a dominantly
westward coarsening fine to coarse highly quartzose marine sandstone. Pebbly
sandstone is also common, as is some siltstone and conglomerate (Gostin and Herbert, 1973; Herbert, 1980b).
These sands were deposited in a shallow marine environment above wave
base (Gostin and Herbert, 1973), although the western basal conglomerates
were probably deposited in fluvial (possibly fluvioglacial) systems (Herbert,
1972; Herbert, 1980b). The Formation dips eastward at 3° to 4°, but 57 crossbedding measurements indicate a predominance of north to northwest movement of material by longshore currents (Gostin and Herbert, 1973).
Large erratic boulders are common and have prompted suggestions of ice rafting (Gostin and Herbert, 1973; Herbert, 1980b). The quartzose material
comprising the Snapper Point Formation probably had its provenance in the
south and west (Herbert, 1980b).
3.3.1.2. Nowra Sandstone
In areal extent, the Nowra Sandstone is the predominant member of the
Shoalhaven Group, and the most prominent cliff-forming member of the
Permian sequences within the region. It is a regressive-transgressive
middle/upper shoreface to foreshore sand (Le Roux and Jones, 1994), and
crossbedding within it is suggestive of deposition by northerly longshore
currents from a southerly source.
Detailed petrographic descriptions of the Nowra Sandstone are few, and the
Sandstone itself has only recently being discussed in any detail by Le Roux
and Jones (1994) It is generally a grey to yellow, fine to coarse arenite, with
numerous pebbly beds and a few bouldery beds. The Nowra Sandstone
becomes more silty toward the west, where it is difficult to distinguish from
the sandy facies of the overlying Berry Siltstone. Fisher (1972, quoted in
Herbert and Helby, 1980) found particular difficulty in distinguishing between
these two units in the western Shoalhaven River Gorge.
3.3.2. Blue Mountains Plateau Grose Sub-Group
The Late Permian-Early Triassic Narrabeen Group overlies the Permian
Illawarra Coal Measures, and outcrops in both inland and coastal regions
north of Wollongong. For much of the area of its outcrop the Narrabeen 58
Group forms a plateau surface and is not overlain by younger sedimentary rocks. Much of the Blue Mountains west of Woodford, the rugged country of the Wollemi National Park, and many of the cliffs and plateau of the
Burragorang Valley are composed of Narrabeen Group sandstones (McElroy,
1969). Within the study area, it is in the spectacular cliffed walls and plateau of the western Blue Mountains that the most impressive outcrops of
Narrabeen Group sediments are found.
On the Blue Mountains and Newnes Plateaux the Narrabeen Group has been
subdivided into three Formations, the Caley Formation, Grose Sandstone and Burralow Formation (Crook, 1956). Holland (1974), however, proposed the
elevation of the Grose Sandstone to Sub-Group status with the former Members acquiring Formational status. The cliff forming Grose Sub-Group is composed of two major sandstone Formations, the Burra-Moko Head and Banks Wall Sandstones, and several red-bed units, the Mount York and Wentworth Falls Claystones (Goodwin, 1969; Goldbery and Holland, 1973;
Holland, 1974; Bembrick, 1980). Palaeocurrent and palaeoenvironmental
indicators suggest that the Grose Sub-Group are "fluvial (braided) sands"
(Bembrick, 1980, p.145).
3.3.2.1. Burra-Moko Head Sandstone
The Burra-Moko Head sandstone is the most dominant cliff forming
sandstone in the western Blue Mountains. It has well developed vertical
jointing and varies in thickness from 30m on the westward margin to over
175m at Kurrajong Heights near the eastern edge of the Blue Mountains
Plateau. The dominant lithology is a medium to coarse-grained, cross-bedded quartz to quartz-lithic sandstone, and whilst claystone horizons are common,
thick claystone beds are rare (Goodwin, 1969; Bembrick, 1980). The Burra- 59
Moko Head sandstone is more quartzose than the underlying Caley Formation sandstones. The bedding is usually massive and the matrix rich in clay minerals rendering the sandstone friable (Goodwin, 1969). Ironstone concretions are very common, although not as abundant as in the overlying
Banks Wall Sandstone (Goodwin, 1969).
3.3.2.2. Banks Wall Sandstone
The Banks Wall Sandstone forms the upper cliffs and the plateau surface over much of the western Blue Mountains Plateau north of Lawson, and as far south as Lake Burragorang. It is separated from the Burra-Moko Head
Sandstone by the 9 to 12m thick Mt York Claystone (Goldbery, 1969; Goldbery and Holland, 1973). This sandstone is generally quartzose with a small percentage of lithic fragments. Cross-stratification is common. Numerous lenticular claystone units occur throughout, and increase toward the base. The matrix is rich in clay minerals which renders the sandstone friable, at times extremely so. This friable rock is sometimes quarried for building sand
(Department of Planning, 1990). Ironstone bands are extremely prevalent, and are oriented sub-parallel or at random to the bedding. These bands are highly indurated and resistant, exerting a major influence on the erosion of the rock, often leading to unusual shapes.
The maximum measured thickness of the Banks Wall Sandstone in the western Blue Mountains is 115m, but it thickens eastward attaining 244m at
Kurrajong Heights (Bembrick, 1980). In the western Mountains several small remnants of the Hawkesbury Sandstone are found conformably overlying the
Banks Wall Sandstone. Toward the east, the Burralow Formation appears between the Banks Wall and Hawkesbury Sandstones, conformably overlying the Banks Wall Sandstone. 60
The Narrabeen Group also outcrops extensively on the coast to the north of
Sydney, on the coast to the south of Sydney, and along the Illawarra
Escarpment (Bowman, 1971) where it is overlain by the Hawkesbury
Sandstone. The sequence of coastal Narrabeen Group sediments is similar to that of the Blue Mountains, they are not studied here.
3.3.3. Central Region-Hawkesbury Sandstone
The Middle Triassic Hawkesbury Sandstone is a flat lying, highly crossbedded quartz sandstone of about 20 000 km2 outcrop. It is this impressive cliff- forming sandstone that dominates the landscape within a 100km radius of Sydney, outcropping over much of the Illawarra Plateau, lower Blue Mountains, Hornsby Plateau, Woronora Plateau and Cumberland Basin, except where it is overlain by the shales of the Middle Triassic Wianamatta
Group.
The depositional environment of the Hawkesbury Sandstone has been much debated because of a relative absence of fossils. It has been interpreted as of shallow marine, lacustrine, estuarine, and even aeolian origin (Osborne, 1948; Bembrick et al, 1987). Detailed investigation of depositional structures within the unit now suggest a fluviatile origin (Standard, 1969), with a braided alluvial environment proposed more recently (Conaghan and Jones, 1975;
Conaghan, 1980; Jones and Rust, 1983). All stratigraphic indicators are consistent with a low sinuosity fluvial environment. Overbank deposits are extremely rare.
The thickness of the Hawkesbury Sandstone is variable. It attains a thickness of 232m in the centre of the basin (Bembrick et al, 1987), but thins to only 30m at the southern extremity (Standard, 1969). In the upper Blue Mountains, 61 most of the Hawkesbury sandstone has been stripped. Minor outcrops have been preserved under small Miocene basalt cappings, the largest and thickest being at Mt Tomah (52m), but is also under basalt at Mts Hay, Banks, Bell,
Irvine and Wilson (Goldbery, 1969).
Like most other southern Sydney Basin sediments the Hawkesbury
Sandstone dips at an average of only a few degrees. Steeper dips are found, for example on the Lapstone Monocline, but these are very localised.
As a direct consequence of its outcrop surrounding the largest urban area in Australia, the composition and engineering properties of the Hawkesbury
Sandstone have been well studied, certainly much more so than any other
sandstone within the study region. Lithologically, the Hawkesbury consists of about 95% quartz sandstone, with the remaining 5% fine sandstone/siltstone
laminite, and siltstone and claystone interbeds of limited and localised extent. The sandstone varies from white to light brown and is very fine to coarse grained, but the majority is medium grained (Goodwin, 1969).
Petrographically, "The sandstone is comprised primarily of subangular quartz
grains with an argillaceous matrix and some siderite cement. Secondary silica
occurs mostly as overgrowths around grains ... The degree of overgrowth
development is variable and has an important bearing on the strength and stiffness properties of the material ... Siderite is sometimes found in sufficient
quantity to bind quartz grains together. The spaces between the quartz grains
contain sericite and clay. Where the degree of overgrowth is small, many of
the grains are separated by the argillaceous materials resulting in lower
strength and greater compressibility. While the secondary silica does not act as 62 a true cement SEM studies show that true cementation is quite widespread"
(Pells, 1977, p.10).
Analysis of widely spaced samples from the whole outcrop shows the general composition of the Hawkesbury Sandstone to be as follows: Detrital Grains,
Quartz 68%, Others (rock fragments and clay pellets 15%, 1% feldspar and 1% mica) 4%; Matrix Clay 20% (70% Kaolinite, 20% Illite); Secondary Silica 6% and Siderite 2% (Standard 1969, p.412). As Pells (1977) pointed out, however, considerable variations in composition may occur even over one site.
Smooth quartz and rarer lithic pebbles up to 60mm in diameter are common, as are gravel layers up to 50mm thick at the base of sandstone beds. The sandstone is often iron-stained. Siderite usually weathers to limonite near the surface producing concentric orange 'Liesegang Bands' caused by the migration of iron-rich groundwater (Bembrick et al, 1987), although, unlike the Banks Wall Sandstone, concentration of iron into thick resistant bands is uncommon. Where iron-staining is absent, the sandstone is sometimes quite friable (Goodwin, 1969).
3.4. GENERAL GEOMORPHOLOGY
The general geomorphology of the sandstone lands around Sydney has only been discussed in any detail by Young and Young (1988). It can best be
categorised in terms of the repetition of three landform sub-types: gently dipping plateau summits and upland valleys; cliff lines; and valley sides and
floors. There are, however, marked variations in morphology of each of these three types across the region. 63
Trends in the major landforms of the region are a reflection of the geologic structure. Uplift and broad warping with some faulting, produced structural plateaux which reached their present elevations by at least the Early to Mid
Tertiary (Wellman and McDougall, 1974; Young, 1978). This uplift, allied with the original depositional geometry of the Basin, produced an elongated, asymmetric, saucer-like regional structure, the centre of which is a Triassic- shale capped rolling lowland known as the Cumberland Plain. Around the
Cumberland Plain the sedimentary rocks rise gently to the north and south, but more steeply to the west, to form a number of structural plateaux or
'ramps' encircling and dipping inward toward the Cumberland Plain. These structural plateaux, notably in the Hawkesbury Sandstone, rise to the north
(the Hornsby Plateau), south (the Woronora and Nepean Plateaux and
Illawarra Plateau), and to the west (the Blue Mountains and Newnes
Plateaux) (Figure 3.1). The Hornsby Plateau rises from near sea level to an altitude of between 100 and 200m, whereas to the south the Woronora and
Nepean Ramps rise gently from sea level to merge with the Illawarra Plateau which itself attains 850m altitude near Robertson. The Blue Mountains rise more steeply westward from the Lapstone Monocline-Nepean/Kurrajong
Fault System to attain 1094m. Further south the same ramp-like structural influence can clearly be seen in the Sassafras Plateau formed on the gently dipping Nowra Sandstone. This plateau originates near sea level at Nowra and rises at only about 1 degree toward the southwest to peak at 860m.
Where these plateaux are mainly cut from a single stratigraphic unit, generally a resistant sandstone, the summits are commonly a relatively narrow series of flat-topped ridges. These ridges are flanked by broad benches commonly linked to differential weathering of various beds within the sandstone (Young and Young, 1988). Major streams have cut deep, cliffed 64 valleys. Smaller streams on the plateaux surfaces often flow through broad, low gradient, sediment filled swampy depressions (Holland, 1974; Young,
1986). These swampy dells, which are best developed on the Woronora, Blue
Mountains, and some parts of the Sassafras Plateaux, retain a perched water table providing low, but persistent, discharges. Where patches of shales or basalt overly the sandstone, the summit ridges tend to be broader (Young and
Young, 1988).
On the Blue Mountains and Newnes Plateaux, carved mostly from the
Narrabeen Group sediments, major rivers have excavated deep gorges.
Sections of the Grose River, for example, are 400 to 500 metres below the plateau surface. Holland (1974, 1977) demonstrated how deep incision and headward retreat of small nickpoints from the major clifflines along claystone beds of the Narrabeen Group has led to the entrenchment of the lower reaches of many creeks draining the plateau into extremely narrow slot canyons many tens of metres deep and hundreds of metres long. Even where the creeks tumble over high waterfalls, deep incision has resulted in a large local relief above the falls (Young and Young, 1988). Stratigraphic and structural control on the slot canyons is well displayed, but the geomorphology of these canyons has not been described in any detail.
Claystone beds in the Hawkesbury, Nowra and Snapper Point Formation sandstones are rarer than in the Narrabeen Group, thus slot canyons are rarely if ever found on the other plateaux of the region.
The major cliffs of the Blue Mountains valleys are the sandstones of the
Grose Sub-Group below which long ridges in the lower Narrabeen Caley
Group sediments and Permian Coal Measures and shales are formed. These 65 in turn sit atop cliffs in the Permian Shoalhaven Group sandstones and in the westernmost valleys, hilly terrain in Devonian granite.
Another outstanding feature of the Newnes Plateau is the development of large tower, bee-hive or pagoda shaped outcrops on the ridges and clifflines,
and have not previously been described. Their morphology is controlled by
small scale variations in lithology. Some scattered pagodas are also found in
the Blue Mountains north of Katoomba, but are poorly developed. Different
sandstone tower or bee-hive formations also occur on the Nowra Sandstone
at a number of locations on the Sassafras Plateau, and also at a few locations
on the Hawkesbury Sandstone of the Illawarra Plateau.
The Sassafras Plateau is for the most part carved in the Nowra Sandstone.
Large outcrops of the overlying silty to sandy Berry Formation and the
underlying Snapper Point Formation sandstone also occur, and impart major
control in the form of broad flat plateaux, isolated flat topped mesas, long,
high, clifflines, and pronounced structural benching (see Young and Young,
1988, Plate 1). The profiles of the valley sides below the major cliffs of the
Sassafras Plateau are controlled by lithologic variations. The valley slopes
below the Nowra Sandstone are a gentle to steeply angled bench formed in
the underlying Wandrawandian Siltstone, whilst below this bench are the
more resistant sandstone cliffs of the Snapper Point Formation. The valley
floors are carved in the underlying folded basement rocks.
The pattern of landforms on the Illawarra, Woronora and Hornsby Plateaux
is different from those described above. The valleys are cut in the Hawkesbury
Sandstone and not as deep. Consequently, the valley sides are generally cliffed 66 or of steep gradient. Valley bottoms are often narrow and rugged. Along the
Illawarra Escarpment, cliffs in the Hawkesbury Sandstone cap a sequence of benches and minor cliffs cut in the Narrabeen Group sediments and ridges cut in the Coal Measures sediments. This pattern of benching changes southward as Permian volcanic sandstones and extrusive lavas become increasingly more prominent in the escarpment (Young and Young, 1988).
Undoubtedly the most scenic and spectacular landforms in the region are these large sandstone cliffs, often several hundred metres high. These are best displayed in the Snapper Point Formation and Nowra Sandstone clifflines of the Clyde and Shoalhaven valleys and in the Kanangra-Boyd area. Other prominent cliffs are cut in the Narrabeen Group and Hawkesbury Sandstone
along the Illawarra Escarpment and in the sea cliffs near Sydney, and in the upper Narrabeen Group in the Blue Mountains, Newnes Plateau and
Burragorang areas.
A common occurrence is the erosion of the clifflines by shallow but extensive
taffoni and caves. These caves rarely extend more than a few metres into the
cliffs, but may extend horizontally along the cliff line for many tens, even
hundreds of metres. They are often concentrated along particular layers
within the rock, but occur at all stratigraphic levels. Caves are seen most
clearly on the exposed cliffs, but contrary to popular belief are not formed by
the erosive action of the wind, as can be readily demonstrated by the
occurrence of large numbers of identical caves in very sheltered and heavily
vegetated locations. Young and Young (1988, p.19) provide an alternate
explanation, "While hydration of clay in the matrix of sandstone may be a
contributing factor, the mobilisation of iron and silica by water moving
through the rock is of far greater importance ... The primary cause ... seems to 67 be salt weathering ... (by) a chemical etching of quartz grains promoted by the presence of chloride". Further evidence of the role of salts in cavernous weathering was provided by Young (1987).
Subsurface water movement is also important on all the plateaux, where seepage water is clearly seen emerging from joints and bedding planes, particularly near cliffs, and at nickpoints along streams. Seepage is also seen emerging at the contacts of impermeable claystones and more permeable sandstones. However, as Mainguet (1972) noted at sites overseas, flow patterns within sandstones are often complex, and seepage often emerges from two-dimensional non-point sources close to summits (Young and
Young, 1988). Tuff as and stalactites of minerals dissolved from within the sandstones, commonly very high in silica and/or iron, are commonly seen at the resurgence of these seepage waters at bedding planes, along joints or under overhangs. Opaline silica stalactites and flowstones are also very common. This movement of water from the plateau surface and upland valleys is not confined to surface flow, as subsurface movement is also important.
3.5. RATES OF LANDFORM CHANGE
Traditional belief has been that the major landform structures of the Sydney
Basin resulted from widespread peneplanation during the Miocene followed by minor uplift during the Pliocene and major uplift with contemporaneous canyon cutting by the major rivers at the close of the Tertiary (e.g. Andrews,
1910; Browne, 1969; King, 1969). Recent investigations have, however, revealed that "large sections of the upland surfaces (of south eastern
Australia) originated in the Mesozoic; many of the shallow valleys incised into these surfaces range in age from Eocene to Miocene, and in many cases 68 canyon cutting began no later than the middle of the Oligocene" (Young, 1983, p.221).
The topographic position of widespread small patches of Tertiary basalt, dated by K-Ar techniques, provides the key to the antiquity of the region's
landforms. Young (1977, 1980, 1981, 1982, 1983, 1985) and Young and
McDougall (1983,1985) have used these basalts to repeatedly demonstrate the
great age of the landforms both in the plateau regions of the Southern
Highlands and along the adjacent coastal lowland. They considered that some
upland surfaces originated in the Late Mesozoic, but that many others were
well developed by the early Tertiary (Young and Bishop, 1980; Young, 1981),
see also Nott (1990) and Wray et al (1993). The last major phase of uplift must
have commenced before or early in Tertiary times (Young and McDougall,
1985) as the onset of major canyon cutting was well under way by the mid-
Oligocene (Nott, 1990) and even by the Mid-Eocene (Young, 1977, 1983, 1985).
Headward extension of canyons is the main form of change in this landscape.
Not only were the other major topographic character of the region developed
early into the Tertiary, but many aspects of the landscape have been altered
surprisingly little since then (Young, 1983; Wray et al, 1993). "Rates of change
here, whether measured by distance of scarp retreat or by amount of valley
cutting, are much lower than those widely regarded as modal in the spectrum
of geomorphic change" (Young, 1983, p.224). This conclusion is supported by
estimates of rates of scarp retreat of the coastal plain at Ulladulla, valley
incision in the canyon of the Endrick River, and of stripping of the Blue
Mountains Plateau. The estimates for these rates were found to only be 6 to
10% of the average denudation rates proposed elsewhere. Schumm (1963), for
example, gives denudation rates for the United States ranging from 30.5m per 69 million years to 91.4m per million years, whilst Ahnert (1970) quotes rates that range from 16 to 165m per million years for lowland Europe and the
U.S.A.
Dating of low-level coastal basalts near Ulladulla by Wellman and McDougall (1974) demonstrated the great antiquity of the coastal lowlands, and the slow
rates of landform modification within the region. The uplift of the high
plateaux of the Sydney Basin had attained its present height by early Tertiary
times, and with the foot of the coastal escarpment lying only 4.5 km west of
the westernmost dated basalt (average age 29.7 ±0.5 Ma), the escarpment can
have retreated at an average rate of no more than 170 m per Ma since the Mid-Oligocene (Young, 1983).
Similarly, dated basalts on the Sassafras Plateau west of the coastal escarpment
demonstrate that cliff retreat in the major river canyons has also been remarkably slow. In the Endrick Valley average rates of cliff retreat relative to
Eocene basalts were found to be only 28m per Ma or 18m per Ma, much lower than the average of 1km per Ma quoted for similar climates elsewhere (Young, 1983). Rates of vertical incision on the plateau surface are also much
lower than quoted elsewhere. Eocene basalt was erupted onto the plateau
surface at Sassafras, and extended over 150m down into adjacent valleys
indicating the extent of local relief at the time. Stream incision here since the Eocene is in the order of 0.2 to lm per Ma, and slope retreat only 12 to 25m per
Ma, virtually identical to that of the Endrick Valley downstream (Young and
McDougall, 1985). 70
Low rates of denudation also have been determined elsewhere in the study area. Although the canyons of the Grose, Cox's, Wollangambie and the
Wolgan Rivers, are all incised 300 to 600m below the Blue Mountains and
Newnes Plateaux surface, Miocene basalt cappings at several places are seen to rise only a small distance above the contemporary plateau. At Mt Tomah, immediately north of the Grose Valley, 81m of Miocene basalt (14.6 ±0.4 Ma
(GA3462) (Wellman and McDougall, 1974)) overlies Triassic shales and
Hawkesbury Sandstone. The base of the basalt is only 70m above the general local level of the plateau, 850 to 950m, therefore the maximum rate of lowering of the plateau surface at Mt Tomah since the Miocene has occurred at 4.7m per million years. Basalts of similar ages are seen nearby, 5km east of
Mt Wilson 16.3 ±.4 Ma (GA3461), another 17.7 ± 0.7Ma, and a third 4km east of
Mt Wilson 17.6 ±0.7 Ma (GA3460) (Wellman and McDougall, 1974), giving equivalent rates of stripping. Major river canyon cutting has, however, been much faster. The Grose River canyon, over 720m deep below the base of the basalt at Mt Tomah and 680m below the basalt at Mt Banks, may have been cut at up to 49m per million years. This rate of erosion is much more than those calculated by Holland (1974, p.192-193) for the Grose Canyon, 12.2m per million years, and 24.4m per million years for the Jamieson Valley, but is based on the assumption the canyon did not exist at the time of basalt eruption. It must be therefore be regarded as a maximum. Holland (1974) also calculated the minimum average rate for lowering of the hanging valleys near Katoomba at 1.3m per million years.
Thus it is apparent that average rates of landform lowering in this region are very slow, and even the faster rates of erosion associated here with major canyon cutting are still low compared with many similar regions overseas. 71
3.6. CLIMATIC AND VEGETATIONAL HISTORY
The climate of the Sydney region is humid temperate (Koppen's Cfa-Cfb). Temperature and rainfall variations across the Basin are presented in Table
3.1. These variations result from variations in elevation, proximity to the ocean, and rain shadow effects. Frosts are a normal winter occurrence in the higher areas, and winter snow falls occasionally occur on the higher parts of the Illawarra Plateau and upper Blue Mountains.
Natural vegetation is currently dominated by dry Sclerophyll eucalypt forest over most of the Sydney Basin. Protected valleys and slopes often host wet
Sclerophyll and even localised rainforest communities. Much of the area has been cleared for pasture and urban areas, but National Parks and Water
Catchment encircle Sydney preserving natural bush in a large portion of the region.
As the origins of the major geomorphic structure of the present landscape has been shown to have been well developed by Mid Tertiary, and in many cases even by earliest Tertiary times, the role of climatic change in shaping the landforms of the region must also be considered. Of particular importance to an assessment of sandstone karst is the traditional view, based largely on the occurrence of laterites around Sydney (Woolnough, 1927; Browne, 1969), that the area was subject to a tropical climate during much of Tertiary times. 72
Mean Annual Mean Annual Mean Annual Location Elevation Maximum Minimum Precipitation m °C °C mm
Katoomba 1030 16.6 8.0 1412 Newnes Forest 1050 16.9 5.9 1057 Centre Lithgow 950 18.0 6.4 863 Wentworth Falls 900 17.2 7.4 1342 Sydney 42 21.5 13.6 1212 Parramatta Nth 60 23.0 12.3 935 Richmond 20 23.6 10.6 799 Camden 70 23.5 9.9 794 Picton 171 22.8 8.8 813 Moss Vale 686 18.3 7.5 990 Wollongong 19 21.6 13.4 1420 Nowra 109 21.3 11.2 1153 Jervis Bay (Point 85 20.0 13.7 1247 Perpendicular) Nerriga 630 19 6.7 773
Table 3.1. Annual average climatic data for the study area. Source: Bureau of Meteorology (1988).
Recently, however, U/Th dating of many of these ferruginous weathering deposits around Sydney has shown that they formed not during the Tertiary, but during the late Pleistocene. Young et al (1994) clearly demonstrated that iron-manganese concretions and crusts from a wide range of locations around
Sydney, formed not under the tropical conditions widely attributed to this type of weathering, but rather under a cool temperate climate when average temperatures may have fallen 5°C below their present levels (Galloway, 1965; Colhoun, 1991).
There are other, much older, laterites in the region, some of them dating from the earliest Tertiary and even from the Cretaceous (Bird and Chivas,
1993). Nevertheless Bird and Chivas (1988, 1995) also demonstrate that stable oxygen-isotope ratios these profiles are indicative of conditions cooler than 73 those of the present day. Early-Permian kaolinitic clays from eastern Australia
indicate formation under conditions unlikely to have been warmer than cold
to cool-temperate. Pre mid-Tertiary clays also have 8 O ratios consistent with
weathering under a humid and cool to cold climate, whereas clays of post
mid-Tertiary age have 8 O isotopic compositions similar to that of the
present (Bird and Chivas, 1989). No evidence was found for clay formation
under climates warmer than present. These weathering deposits therefore
confirm that there has been very little change in the isotopic composition of
meteoric waters, and thus climate, in Australia since the mid-Tertiary.
Changes in oxygen isotope composition from the Permian to the Present are
also consistent with generally increasing temperatures over this period as
Australia drifted northwards from the much higher latitudes it inhabited for
much of its post-Palaeozoic history. Thus, from geochemical evidence, there
has been an remarkable longevity of humid temperate conditions, with a
general increase in temperature, in eastern Australia during Tertiary times,
and not a cooling from previous tropical conditions.
Fragmentary pollen evidence has also allowed several authors to assemble
palaeoclimatic data for this region for much of the Cainozoic. Kemp (1978)
argued for cool, wet temperate, but not tropical, climates in this region from
the Palaeocene to the close of the Miocene. Evidence for such a cool wet
temperate climatic regime at Bungonia just south of the study area during the
late-Eocene was also provided by Truswell and Owen (1988) and Nott (1990).
A pronounced temperature drop (Kemp, 1978) was then recorded during the
Oligocene, and the close of the Miocene was heralded by "an intense and
sudden chilling ... leading to marked precipitation decrease in much of
Australia" (Kemp, 1978, p. 170). 74
Martin (1991) also argued for cool wet climates in much of the Upper Lachlan
River and nearby southeastern New South Wales from the Late Eocene to
Mid Miocene. Climate during this period was relatively stable, apart from a steady but gradual decrease in precipitation under the influence of decreasing sea levels (Figure 3.4). A short return to more pluvial conditions at the opening of the Pliocene was correlated with a brief return to higher sea levels, and thence an abrupt drying phase brought on by falling sea levels during the mid-Pliocene.
PALYNOLOGICAL 1OC H VEGETATION PRECIPITATION EP DIVISION 3 LE1S1 Aster acaae/Paaceas Open UJ Upper Myrtacaas Wet sclerophyll z V ". UJ Nof/io/atjus'gyrnno sperm Halnlore3t I ^ o s? ~ o ~ Marked r J Wet sclerophyll dry season 10 0. Lower Myrtaceaa
1
UJ c z T. bellus < UJ >- o §20" ZJ o J 2 2 Halnlorsst ^ P. tuberculatus Ul z 30 Ul u a a 1i a \ - ui- 40 z Middle W. asperuj Ul 1 r— i— \. o 1000 o mm/pa UJ
Figure 3.4. Reconstruction of changes in precipitation and vegetation in southeastern Australia from the Eocene to the Pleistocene. Source: Martin (1991), Figure 4, p.186. 75
Major eustatic fluctuations during the Pleistocene then ensured the perseverance of relatively dry cool to moist temperate climates during the
Quaternary. Singh (1985) demonstrated substantial climatic shifts at nearby
Lake George during the Quaternary, with alternating periods of cool dry and
warm moist climate. However, A.R.M. Young (1986) studied the upland
swamps 300 to 500m above sea level on the Woronora Plateau near
Wollongong and found that plant fossil and pollen evidence gave no
indication that the environment of the plateau has changed substantially
during the Late Pleistocene or Holocene.
The general climate of the study region has thus been cool and moist for most
of the Pleistocene and the latter part of the Tertiary. The early-Tertiary was
cool and wet, but cool-temperate for the entire Quaternary, and most of the
latter Tertiary. The tropical weathering regimes so often regarded as necessary
in the process of silica solution have been demonstrably absent here during
the Cainozoic, and probably since at least the early Permian. This area is thus
ideally suited to the study of solutional processes on quartz sandstones under
temperate regimes. 76
CHAPTER 4. QUARTZ SANDSTONE SOLUTION BASINS
4.1. INTRODUCTION
Although it is generally agreed that the solutional activity of natural waters is very significant in the formation of small rock basins (Section 2.7) and many complex processes have been advocated in explaining them (e.g. Twidale and
Corbin (1963), Hedges (1969), Alexandrowicz (1989)), few detailed reports of solution basins in quartz sandstone have been published, and the detailed genetic processes involved remain unclear. The lack of empirical data on basins has imposed major constraints on our understanding of the formation of these features, for until our understanding of the basic morphometry of these basins is more complete it is difficult to fully comprehend their genesis.
Basins are very common on the major sandstones of this region, and their small size and discrete forms lend themselves far more readily than the other solutional forms studied here to detailed descriptive and morphometric analysis. To this end an examination of a large number of solution basins was conducted during this study as it was envisaged that detailed examination and comparison of basins found across a wide range of topographic and stratigraphic locations would provide a comparative baseline data set from which an understanding of their morphometry and formative processes could be derived. No comparable set of data has been previously compiled for basins in either sandstone or, surprisingly, given the numerous references to basins in the karst literature, limestone. 77
4.2. BASIN DISTRIBUTION
Solution basins on sandstones are distributed throughout the southern
Sydney Basin across a wide range of physiographic and climatic zones including marine, coastal plain and plateau. They occur in large numbers on all the major sandstones, except the Grose Sub-Group in the western Blue
Mountains and Newnes Plateaux where basins are generally very poorly developed and in concentrations too low to permit intensive study. Basins are more widespread on the Hawkesbury Sandstone in the eastern Blue
Mountains, suggesting that this variation is related to geological effects; basins are poorly developed on sandstones of the clayey Upper Narrabeen sandstones, but more common on the quartzose Hawkesbury Sandstone.
A similar scarcity of basins is found on parts of the Sassafras Plateau, but in other sections of the same area basins and runnels are very common and exceedingly well developed. The reasons for this variable distribution appear to be that the silty Berry Formation, which overlies the Nowra Sandstone and caps the slightly higher areas of the Sassafras Plateau, is not suitable for the development of these features, whereas the underlying quartzose Nowra
Sandstone is very suitable.
4.3. DATA COLLECTION
As basins occur on almost every outcrop of Hawkesbury, Nowra and Snapper
Point Formation sandstones within the study area, a range of sites could be chosen to give a representative impression of the total region (Figure 4.1). These study sites include areas of both very good, average, and poor basin development. 78
Measurement of the basic morphometric characteristics including length, average width, and average depth of 459 basins were made in the field with a tape-measure and straight edge, and recorded to the nearest 1cm. This data set is four times larger than the total number of previously published observation of basin size. Measurements were kept, as far as possible, orthogonal (90°) to each other. The general basin plan-form and the configuration of the walls and base were also noted. For statistical purposes, where possible at least 30 individual basins were chosen by a random-walk technique at each site, or if 30 basins were not available, all available basins were measured. Basins, the size or shape of which were obviously grossly influenced by joints, indurated layers or other factors within the bedrock were not measured.
Uniaxial compressive strength of a number of the surrounding rock pavements was measured with a Type-L Schmidt Hammer. At least 10 individual readings were made at each pavement, and the mean of these
readings, adjusted for gravitational effects on the inclination of the hammer, taken as the average rock strength. Samples of bedrock were collected for
laboratory analysis and samples of standing water within numerous basins
was also collected for analysis (Chapter 10).
4.3.1. Limitations with Data
It must be noted at the outset that several limitations are inherent within the
data set. Firstly, the great variability of basin shape limits the significance of
measurements of this type as basins of irregular plan, or variable depth
cannot be fully described by three measurements alone. However, because of
the requirement for a sufficiently large sample set to see significant trends and 79 the often difficult field access, it was not feasible to take more detailed multi dimensional measurements.
Another problem was defining the actual size of many poorly-defined basins.
For example, the basin rim often merges with the surrounding outcrop with
no well defined boundary. Where possible in cases such as these, and where other measurements could not be taken, visual projection of a regular arc connecting better defined sections of wall was used. Failing this, if the basin
contained water the highest consistent water mark was taken as the basin rim
on the assumption that this high water mark would represent a
contemporary basin-full state.
Despite these limitations these data can be usefully applied in understanding the general morphometry of basins within the study area. It should also be noted, in passing, that in the studies by Franzle (1971), Schipull (1978) and Cooks (1987) (Sections 2.7, 4.6) no discussion of similar measurement
problems was presented.
4.4. SAMPLING SITES
Sixteen sites upon outcrops of the Hawkesbury, Nowra and Snapper Point Sandstones scattered over a large area were selected for detailed investigation of solution basins, the locations of which are shown in Figure 4.1. The degree
of basin development is not the same at each site, nor are the total number of
basins seen. Access to the Hawkesbury Sandstone was easier than for the
Shoalhaven Group sandstones which are located in much more rugged
regions, and so nine sites for detailed study were chosen on the Hawkesbury, 80
u " H£| rz "u. Hawkesbury :':'::'lSandston e Nowra c Sandstone
u C- • • •Snapper Point • • Formation
.• Whale Point 0 10 20 30 40 50 i i i i i i
Figure 4.1. Location of solution basin study sites on the Hawkesbury and Nowra Sandstones and the Snapper Point Formation. Basins on the Blue Mountains Plateau were not of sufficiently great a number to permit study in that area. 81 but only three on the Nowra Sandstone and four on the Snapper Point
Formation.
Most of the nine Hawkesbury Sandstone study sites are located near rivers or ridges because much of the surrounding region is covered by Triassic shales or deep soil cover. Care was taken so that none of the basins near rivers could have been influenced by fluvial action during their formation, and thus be
'potholes' of erosive rather than solutional origin. These potholes are common but are not studied here.
Box Vale is located a few kilometres west of Mittagong beside Nattai Creek
(G.R. 620 862, Mittagong, 1:25 000, 8929-II-S) and is a site typical of basin development on the Hawkesbury Sandstone, as are the two sites along the
Nepean River, Maldon Weir (G.R. 815 125, Picton 1:25 000, 9029-IV-S) and
Maldon Bridge, about 0.7km downstream (G.R. 819 128, Picton 1:25 000, 9029- IV-S). At Carrington Falls, east of Robertson (G.R. 849 660, Kangaroo Valley, 1:25 000, 9028-IV-S), hundreds of basins have developed, but iron levels within the Sandstone here are higher than at many other localities. Two sites are on the Bargo River, a major tributary of the Nepean River; Mermaids
Pool is a large, deep, pool above a waterfall (G.R. 795 085, Picton 1:25 000, 9029-
IV-S), while the Bargo River site (G.R. 798 080, Picton, 1:25 000, 9029-IV-S) lies
400 to 500m further upstream. The Weeping Falls site is in a similar bedrock valley setting beside Sheepwash Creek near Mittagong (G.R. 674 862, Mittagong, 1:25 000, 8929-II-S). Both the Mt Keira (G.R. 015 923, Wollongong, 1:25 000, 9029-II-S), one of relatively poor basin development, and the Willow
Vale (G.R. 671 870, Mittagong, 1:25 000, 8929-II-S), one of very well developed basins, are located on bedrock pavements above sandstone cliffs or upon the plateau well away from any rivers or creeks. 82
On the small flat, but highly exposed Nowra Sandstone summit of Pigeon
House Mountain (G.R. 514 847, Milton, 1:25 000, 8927-II-N) are a number of well developed basins. Several kilometres westward is the rugged Monolith
Valley (G.R. 443 920, Corang, 1:25 000, 8927-III-N) where basins are extremely well developed. To the north of Pigeon House scattered basins are found on the Tianjara Plateau.
Basins on the highly quartzose Snapper Point Formation were studied at three coastal and one inland location. The coastal sites, all on Beecroft
Peninsula, are at Honeymoon Bay (G.R. 971 182, Currarong, 1:25 000, 9027-1-
N), Whale Point on the northern seaward side of the Peninsula (G.R. 018 244,
Currarong, 1:25 000, 9027-I-N), and at 85m altitude close to the lighthouse at
Point Perpendicular (G.R. 998 142, Currarong, 1:25 000, 9027-I-N). Large and well developed basins were also studied on the remote sandstone pavements at Blackall Rocks (G.R. 36 13, Bindook, 1:25 000, 8929-IV-S) close to the western edge of the Sydney Basin.
4.5. MORPHOMETRIC ANALYSIS
Solution basins in sandstones of the Sydney Basin range in plan from almost perfectly circular, to oval, or coalescing oval, with minimal departure from the circular or elliptic form, but are usually amoeboid or irregular in outline.
This irregularity can in places be attributed to the coalescing of a number of individual basins, to the influence of joints and other external factors, but mostly there is no obvious control on irregularity. The long axis of basins, best seen in the elliptical examples, possesses no preferred orientation. 83
Plate 4.1. Large irregular flat-bottomed basins in the Snapper Point Formation at Blackall Rocks.
Plate 4.2. Triangular, flat- floored basin at Point Perpendicular, Snapper Point Formation. 84
Plate 4.3. Two large, shallow, intersecting basins in the Snapper Point Formation at Point Perpendicular.
Plate 4.4. Rounded and irregular flat-bottomed basins in the Snapper Point Formation shore platform at Honeysuckle Point, Jervis Bay.
^k^*^ 85
Some basins have well defined outlet notches or low points on their rims, especially those on gently sloping surfaces, but a large proportion of those examined on near horizontal surfaces have no definite outlet. Spillways or runnels (Chapter 6), frequently well defined, indicate the path of water overflowing the basins, and on sloping rock pavements chains of basins connected by spillways are commonly found (Plate 4.10).
Hedges (1969), in a major review of siliceous rock solution basins or Opferkessel, asserted that nested or basin-in-basin solution forms had not been reported in the literature, but Frye and Swineford (1947), in one of the papers reviewed by Hedges, reported nested sandstone basins in central
Kansas. Nested basins of a range of sizes are certainly quite common on the
Sydney Basin sandstones.
4.5.1. Basin Size
Summary statistics for the length, width and depth of basins on the
Hawkesbury, Nowra and Snapper Point Formation Sandstones are shown in
Table 4.1, and detailed site data appear in Appendix 1. The range of sizes for the various sites are shown in Figures 4.2 to 4.4, and indicate that in all three basin axis there is a tendency toward smaller rather than larger sizes.
On the Hawkesbury Sandstone most basins are less than 150cm in length, but at several locations basins of 200 to 300cm in length, and even 500 to 800cm, can be found. However on the Nowra Sandstone, whilst most basins are also less than 150cm overall length, only a very small number of basins exceeded
150cm in length. 86
Location Rock n Min Max Mean S.D. Variance Kurt- Skew- Range osis ness Length Blackall Rocks Pss 30 20.00 430.00 149.27 94.02 8840.69 1.57 1.09 410.00 Pt. Perpendicular Pss 30 5.20 441.00 85.26 107.16 11483.22 5.10 2.24 435.80 Honeymoon Bay Pss 30 7.00 184.00 51.86 43.21 1866.74 2.62 1.65 177.00 Whale Point Pss 30 16.00 66.00 39.33 14.37 206.57 -0.92 0.40 50.00
Pigeon House Psn 32 12.00 165.00 49.25 32.03 1025.68 4.75 1.97 153.00 Monolith Valley Psn 31 7.00 150.00 48.55 42.43 1800.39 0.73 1.29 143.00 Tianiara PI. Psn 31 23.00 281.00 83.52 59.98 3361.52 4.02 1.85 _ 258.00
Bargo River Rh 31 16.00 770.00 104.48 134.72 18148.79 21.08 4.33 754.00 Box Vale Rh 30 15.00 143.00 55.43 35.28 1244.94 1.00 1.30 128.00 Carrington Falls Rh 30 19.00 222.00 86.30 57.67 3326.15 0.52 1.07 203.00 Maldon Bridge Rh 28 8.70 270.00 80.90 73.41 5389.07 1.98 1.64 261.30 Maldon Weir Rh 20 8.00 160.00 40.80 39.63 1570.38 5.31 2.39 152.00 Mermaids Pool Rh 30 6.00 500.00 52.03 90.18 8132.86 22.56 4.55 494.00 Mt Keira Quarry Rh 25 10.80 136.00 41.30 31.47 990.64 1.83 1.35 125.20 Weeping Falls Rh 30 10.00 200.00 67.97 45.40 2060.93 1.38 1.28 190.00 Willow Vale Rh 21 10.00 113.00 34.91 27.62 762.61 3.12 1.87 103.00
Width Blackall Rocks Pss 30 20.00 330.00 106.00 72.59 5268.69 1.61 1.20 310.00 Pt. Perpendicular Pss 30 4.00 333.00 46.99 65.30 4263.58 12.69 3.22 329.00 Honeymoon Bay Pss 30 5.80 129.00 32.73 29.54 872.77 3.55 1.96 123.20 Whale Point Pss 30 10.00 58.00 27.33 10.91 118.99 1.06 0.94 48.00
Pigeon House Psn 32 9.00 105.00 35.06 18.10 327.54 6.20 1.95 96.00 Monolith Valley Psn 31 5.00 130.00 35.26 29.48 869.06 2.08 1.42 125.00 Tianjara PI. Psn 31 13.00 110.00 53.94 26.21 686.80 0.00 0.72 97.00
Bargo River Rh 31 11.00 470.00 55.45 80.42 6466.99 25.46 4.85 459.00 Box Vale Rh 30 9.00 70.00 34.07 19.19 368.41 -1.29 0.38 61.00 Carrington Falls Rh 30 9.00 175.00 52.90 33.35 1112.02 4.99 1.71 166.00 Maldon Bridge Rh 28 3.80 210.00 53.48 46.42 2155.06 3.76 1.73 206.20 Maldon Weir Rh 20 5.50 102.00 25.78 23.41 548.07 5.90 2.39 96.50 Mermaids Pool Rh 30 5.00 187.00 29.30 37.03 1371.53 11.64 3.22 182.00 Mt Keira Quarry Rh 25 10.40 55.40 27.62 15.41 237.55 -1.06 0.58 45.00 Willow Vale Rh 21 6.00 77.00 23.55 17.87 319.45 3.43 1.88 71.00 Weeping Falls Rh 30 5.00 110.00 38.07 24.84 616.82 1.42 1.24 105.00
Depth Blackall Rocks Pss 30 5.00 75.00 25.33 18.72 350.51 0.82 1.16 70.00 Pt. Perpendicular Pss 30 2.50 37.00 9.29 8.86 78.58 2.02 1.66 34.50 Honeymoon Bay Pss 30 2.20 26.00 8.44 6.41 41.04 1.49 1.60 23.80 Whale Point Pss 30 2.50 17.00 5.37 3.22 10.38 5.46 2.23 14.50
Pigeon House Psn 32 1.00 14.00 7.47 3.08 9.50 -0.26 0.13 13.00 Monolith Vallev Psn 31 3 15.00 8.40 3.70 13.66 -1.12 0.38 12.00 Tianjara PL Psn 31 3.00 35.00 14.06 8.41 70.73 0.26 1.07 32.00
Bargo River Rh 31 2.00 53.00 13.23 12.72 161.91 3.73 2.00 51.00 Box Vale Rh 30 1.00 105.00 16.43 25.67 658.87 7.61 2.80 104.00 Carrington Falls Rh 30 3.00 20.00 9.80 4.04 16.30 0.14 0.52 17.00 Maldon Bridge Rh 28 2.00 67.00 19.34 16.19 262.00 2.08 1.35 65.00 Maldon Weir Rh 20 1.20 14.00 6.31 3.18 10.11 0.24 0.51 12.80 Mermaids Pool Rh 30 1.00 32.00 8.07 8.63 74.50 1.83 1.69 31.00 Mt Keira Quarry Rh 25 1.00 20.40 7.40 5.61 31.51 0.55 1.16 19.40 Weeping Falls Rh 30 2.00 30.00 8.03 5.51 30.31 8.00 2.39 28.00 Willow Vale Rh 21 0.50 33.00 6.12 7.51 56.44 8.67 2.87 32.50 - Total= 459 Table 4,1. Summary of morphometric characteristics of studied quartz sandstone solution basins. Rh = Hawkesbury Sandstone, Psn = Nowra Sandstone, Pss = Snapper Point Formation. 87
Plate 4.5. Extremely irregularly basined shore platform at Honeysuckle Point, Snapper Point Formation, Jervis Bay. Scattsrgram • 700 •
600 •
• 500 • + o ' f 400. i 300 • X * 200 "I • • 1 + t • * 100 • * « 1 1 1 a i 1 to E i 3 It £ 3 s 5 s
Scattergram
100 • +
80 • § + t 60- + •o S t * 40 J t + i i • 20 • • • 1 0 - 1 i + i i 1 S i 1 *
Scattergram
• 100 • •
80 •
E 4 u € 60 • + Q t * 40 • • x i i • 20 • 4 t t • i * 0 • 1 1 i i 1 1i
Figure 4.2. Multi-site comparison of Hawkesbury Sandstone basin size parameters. 89
Scattergram 300
Pigeon House Tianjara Plateau
Scattergram
4 120 - 4 t 100 • + E + • ° 80 • + B t+ • 5 + «,- 4 t -• 4 4 ! * 40 • 4
20 - i i | i i i 4 *
Pigeon House Monolith Valley Tianjara Plateau Location
Scattargram
Tianjara Plateau
Figure 4.3. Multi-site comparison of Nowra Sandstone basin size parameters. 90
Scattergram
Honeymoon Bay Whale Point Point Perpendicular Blackall Rocks Location
Scattergram
Honeymoon Bay Whale Point Point Perpendicular Blackall Rocks Location
Scattergram
4 70 - 4 60 . 4 4 E50- o 1-40- O •* * 30- 4 20 - 5 I 4- * 10 - i !* i i Honeymoon Bay Whale Point Point Perpendicular Blackall Rocks Location
Figure 4.4. Multi-site comparison of Snapper Point Formation basin size parameters. 91
Although most basins on the Snapper Point Formation were also below
150cm length, many larger basins, some to 450cm length, were seen. Similarly,
most basins had dimensions of less than 100 to 150cm in width and 30cm in
depth, but again as can be seen in Figures 4.2 to 4.4, there are some exceptions.
4.5.2. Basin Shape
Basin shape area was found to be highly variable, and difficulty in description
was thus encountered. The sedimentological literature contains many papers on numerically describing 'shape' or 'form' (e.g. Barrett (1980)), but while many of these methods are based on three orthogonal measurements, none were found appropriate for describing the shape of the basins. As a result,
eight general classes of basin plan-form shape were recognised empirically.
Field results are shown in Tables 4.2 to 4.4
Box Carrington Maldon Maldon Bargo Mermaids Mt Weeping Willow Vale Falls Bridge Weir River Pool Keira Falls Vale n 30 30 28 20 31 30 25 30 21 Oval 4 13 4 3 18 - 3 8 4 (13%) (43%) (14%) (15%) (58%) (12%) (27%) (19%) Irregular 9 - 4 4 - 2 4 2 5 Oval (30%) (14%) (20%) (7%) (16%) (7%) (24%) Circular 7 3 8 5 1 25 12 4 6 (23%) (10%) (29%) (25%) (3%) (83%) (48%) (13%) (28%) Irregular - - 5 2 - - 3 6 1 Circular (18%) (10%) (12%) (20%) (5%) Highly 10 2 7 5 10 3 2 9 5 Irregular (34%) (7%) (25%) (25%) (33%) (10%) (8%) (30%) (24%) Square ------Tri - - - - 1 - - - - angular (3%) Rounded - 12 - 1 1 - 1 1 - Rectangle (40%) (5%) (3%) (4%) (3%) Table 4.2. Basin shape for Hawkesbury Sandstone basins. 92
Pigeon House Monolith Tianjara Plateau Valley n 32 31 31 Oval 13 15 9 (40%) (49%) (29%) Irregular Oval 4 1 5 (13%) (3%) (16%) Circular 12 12 12 (38%) (39%) (39%) Irregular Circular 1 - - (3%) Highly Irregular - - - Square 1 2 2 (3%) (6%) (6%) Triangular 1 1 2 (3%) (3%) (6%) Rounded - - 1 Rectangle (3%)
Table 4.3. Basin shape for Nowra Sandstone basins
Honeymoon Bay Whale Point Point Perpendicular Blackall Rocks n 30 30 30 30 Oval 11 16 13 3 (36%) (53%) (43%) (10%) Irregular Oval 8 1 2 10 (27%) (3%) (7%) (33%) Circular 5 9 11 9 (17%) (30%) (36%) (30%) Irregular Circular 2 - - 2 (7%) (7%) Highly Irregular 2 2 2 6 (7%) (7%) (7%) (20%) Square 1 2 - - (3%) (7%) Triangular 1 - 2 - (3%) (7%) Rounded - - - - Rectangle
Table 4.4. Basin shape for Snapper Point Formation basins
As a result of this great diversity of shape, width-length ratios as a general indication of roundness (Figure 4.5) are also highly variable, and show no discrete clustering. On the Hawkesbury Sandstone width/length ratios range
from 1.00 for a number of almost perfectly circular basins, to only 0.275 for a
very elongate basin at Willow Vale. Similar width-length ratios for the
Nowra Sandstone basins are also highly variable, but again show no
clustering, ranging from 1.00 for several almost perfectly circular basins, to only 0.079 for one very elongate basin at Tianjara. Those on the Snapper Point 93
"i. :vJJ
Plate 4.6. Small and medium-sized irregular flat-bottomed basins on the Nowra Sandstone at Monolith Valley. Note pebble-sized weathering residue on floor of basin.
Plate 4.7. Medium-sized basins actively lowering the summit of a Monolith Valley tower. Note weathering residue of pebble-sized clasts on I floor of basin. Univariate Scattergram 1.1
1
.9 +1SD .8 •C Ui
_i Mean 1 * -1SD + 4
• * * *• +4
Observations
Width/length ratios of Hawkesbury Sandstone basins. Mean 0.648, Standard Deviation 0.186.
Univariate Scattergram 1.1
1-1 SD *• 4 ^#— 4 * •» •'*•" S .9 * J. 4 + •** 4 *r • --af-^tj*-*- Mean | .7 * + • *. t i ,6 • 4 4 -1 SD .5 —!— .4 4 4 .3 .2 .1 0 Observations
Width/length ratios of Nowra Sandstone basins. Mean 0.765, Standard Deviation 0.195
Univariate Scattergram 1.1
+ 1 SD g .8 rr £ .7 Mean
4 •* *.*» 5 -5 -1 SD •» +•* •* * .4
.3 *4 *
.2 Observations
Width/length ratios of Snapper Point Formation basins. Mean 0.678, Standard Deviation 0.189
Figure 4.5. Basin width/length ratios of Hawkesbury, Nowra and Snapper Point Formation Sandstones. 95
Formation sandstone also range from almost 1.00 to only 0.236 for a very
elongate basin at Honeymoon Bay. The Nowra Sandstone mean is slightly
higher than both of the other sandstones, and the Standard Deviation also
slightly greater, indicating that on the Nowra Sandstone basins are slightly
more rounded than those on the other sandstones.
4.5.3. Basin Walls
Like the shape in plan, basin cross-sectional form is greatly varied (Tables 4.5
to 4.7). Walls curve up from the base in one or more of several ways, and like
basin shape these have here been empirically classified; walls may either rise
at only a shallow angle (less than about 20°), they may rise more sharply, or they may be vertical or even undercut and overhang the basin floor. Many basins have a combination of wall types around their circumference. The zone where the walls of the basin merge with the surrounding rock surface may be either a sharply defined rim (commonly seen in those basins with
steep and especially overhanging walls), or a convexo-concave zone of
transition from pavement surface to basin wall with no clearly defined
boundary (Plates 4.6 and 4.9).
On sloping surfaces, basin cross-sections may not always be symmetrical;
many examples are seen where walls are steeper, and even overhanging, on
the higher or up-slope side of the basin, but only gentle to steep on the lower
or down-slope side (e.g. Plate 4.10). These cross-sections are in a down-slope
direction triangular in shape and inset into the sloping rock slope. Twidale and Corbin (1963) found similar examples in granite, "The smaller ones
commonly have overhanging sidewalls but the larger examples invariably display smooth convexo-concave sidewalls and bear a strong resemblance to
armchairs or miniature cirques" (p.5). 96
jfw ,jBtt?i -?*^ti
Plate 4.8. Irregular shallow basins on the very exposed Nowra Sandstone summit of Pigeon House Mountain.
Plate 4.9. A chain of flat-floored basins cascading down a Nowra Sandstone pavement along the upper Endrick River. 97
Dzulynski and Kotarba (1979) also found many examples of these 'armchairs' in granites in Mongolia which differed "from ordinary pans in having semi-
amphitheatrical shapes and fanning out side walls" (p.176), and they are
generally larger than most basins. These 'fanning out side walls' on the
downslope side of the basin are important, they differentiate armchairs from
basins inset into slopes which retain a 'proper' plan form but have a
triangular section solely as a result of the slope. Armchairs of this type in a
range of sizes, are seen widely within sandstones of the study area.
Box Carrington Maldon Maldon Bargo Mermaids Mt Weeping Willow Vale Falls Bridge Weir River Pool Keira Falls Vale n 30 30 28 20 31 30 25 30 21 All 20 9 11 14 24 19 18 20 10 Gentle (66%) (30%) (39%) (70%) (78%) (62%) (72%) (66%) (48%) All 1 6 4 5 1 2 2 4 Steep (2%) (20%) (14%) (25%) (3%) (7%) (8%) (14%) All 9 15 10 3 3 4 7 Vertical (30%) (50%) (36%) (10%) (10%) . (14%) (34%) 1/2 Gentle 2 1 1 2 3 1 2 1/2 Steep (7%) (5%) (3%) (7%) (12%) (3%) (9%) 1/2 Gentle, 1/2 Vertical . . . 1/2 Steep, 1 2 1 1 2 1/2 Vertical (3%) (7%) (4%) (3%) (9%) All 1 1 - 1 2 1 Overhung (2%) _ (4%) (3%) (7%) (4%) _ _ Table 4.5. Wall characteristics of Hawkesbury Sandstone basins.
Pigeon House Monolith Tianjara Valley Plateau n 32 31 31 All 4 4 3 Gentle (12.5%) (13%) (10%) All 13 13 9 Steep (40%) (42%) (29%) All 4 7 7 Vertical (12.5%) (23%) (23%) 1/2 Gentle, 1 1 3 1/2 Steep (3%) (3%) (10%) 1/2 Gentle, - 1 2 1/2 Vertical (3%) (6%) 1/2 Steep, 9 4 4 1/2 Vertical (28%) (13%) (13%) All 1 1 3 Overhung (3%) (3%) (10%) Table 4.6. Wall characteristics of Nowra Sandstone basins. 98
Honeymoon Whale Point Point Blackall Bay Perpendicular Rocks n 30 30 30 30 All 4 9 9 2 Gentle (13%) (30%) (30%) (6%) All - 4 4 - Steep (13%) (13%) All 9 - 14 14 Vertical (30%) (47%) (47%) 1/2 Gentle, 2 2 1 - 1/2 Steep (7%) (7%) (3%) 1/2 Gentle, 4 4 1 - 1/2 Vertical (13%) (13%) (3%) 1/2 Steep, 3 - - - 1/2 Vertical (10%) All 8 11 1 14 Overhung (27%) (37%) (3%) (47%)
Table 4.7. Wall characteristics of Snapper Point Formation basins.
4.5.4. Basin Floors
Unlike the great variability in plan and cross-sectional form, basin floors in
this study area are of two characteristic morphological types (Tables 4.8 to 4.10); generally either flat or hemispherical (concave-up). However, basins
with irregular floors are also sometimes seen, as are compound irregular
forms with smaller basins inset into their floors (cf. Hedges, 1969).
Twidale and Corbin (1963), following Wentworth (1944), proposed that "those (basins) that are semi-circular in cross-section, with a large depth relative to
maximum diameter, are called pits; those with flat floors and a small
depth/diameter ratio are pans. ... Pans are by far the most common. ... Pans are
usually very much shallower than pits" (Twidale and Corbin, 1963, p.3).
Difficulties with this classification were encountered here, inasmuch that many basins which possess a base of hemispherical form most often lack the high depth/diameter ratio necessary for recognition as a pit. Similarly, many
flat bottomed basins have a depth /diameter ratio greater than 0.5, even close
to or exceeding 1.0, and are therefore not readily classified either as pits or
pans. Hemispherical bottomed pits are like flat-bottomed pans in almost all
other respects. 99
Flat floored basins are the more common at virtually all sites within this study area; only at Mermaids Pool and Pigeon House are hemispherical based
basins the dominant form. This predisposition for a flat floor may in some
instances be explained in the exploitation of bedding surfaces within the
sandstone as basin floors. This is especially true at Weeping Falls where 97%
of all basins have flat bases which all appear to correspond with cross-bed
surfaces, and at Bargo River where all flat bottoms also appear to correspond with cross-bed surfaces. Nonetheless, in the majority of cases bedding or cross bedding surfaces does not appear to be responsible for the development of flat
basin floors.
Box Carrington Maldon Maldon Bargo Mermaids Mt Weeping Willow Vale Falls Bridge Weir River Pool Keira Falls Vale n 30 30 28 20 31 30 25 30 21 Hemisp 7 3 13 8 2 16 9 1 - herical (23%) (10%) (46%) (40%) (6%) (53%) (36%) (3%) 23 24 15 12 27 12 15 29 21 Flat (77%) (80%) (54%) (60%) (87%) (40%) (60%) (97%) (100%) - 3 - - 2 2 1 - - Irregular (10%) (6%) (7%) (4%) Table 4.8. Floor characteristics of Hawkesbury Sandstone basins.
Pigeon House Monolith Tianjara Valley Plateau n 32 31 31 20 7 10 Hemispherical (62.5%) (23%) (32%) 12 22 20 Flat (37.5%) (71%) (65%)
- 2 1 Irregular (6%) (3%)
Table 4.9. Floor characteristics of Nowra Sandstone basins.
Honeymoon Whale Point Point Blackall Bay Perpendicular Rocks n 30 30 30 30 Hemisph 9 - 12 - erical (30%) (40%) 17 30 18 30 Flat (57%) (100%) (60%) (100%) 4 - - - Irregular (13%)
Table 4.10. Floor characteristics of Snapper Point Formation basins. 100
Plate 4.10. Shallow flat-floored circular basins on the Hawkesbury Sandstone at Bonnum Pic.
Plate 4.11. Several basins intersecting to form a larger irregular basin in the Hawkesbury Sandstone at Carrington Falls. 101
4.6. RELATIONSHIPS BETWEEN MORPHOMETRIC PARAMETERS
Very little dimensional analysis of sandstone rock basins has previously been conducted. Franzle (1971) measured basins in sandstone at Fontainebleau,
France, Schipull (1978) measured basins in the quartz sandstones of the Colorado Plateau, and Cooks and Pretorius (1987) measured basins in sandstone and greywacke of the Clarens Formation, northwestern Transvaal.
The measured variables are the same as those investigated here, namely length, width and depth, and these previous results are presented in Figure 4.6. Basins of similar and larger size range than these have been recorded during this study, and also from other unpublished work (D. Nettoff, pers. com., 1992).
These three previous studies suggested strong positive correlations between basin width and length, with r2 values of 0.99 (Franzle, 1971), 0.95 (Schipull, 1978) and 0.92 (Cooks and Pretorius, 1987). Individually, the relationships between length and depth are also, in at least two cases, very strong (0.44, 0.81, and 0.97, respectively). Not so obvious, however, is the association between the three studies as Figure 4.6 clearly shows. The South African and
Fontainebleau basins are similar but display a greater range of length and depth than their Colorado counterparts. The similarity in width/length characteristics between these three areas on opposite sides of the world is notable, as is the similarity of depth/length within each group. But whilst the
French and South African basins are of similar depth/length characteristics, those from Colorado are generally larger and shallower (Figure 4.6). 102
j.ou •
0 0 Franzle, 1971 *• + Schipull, 1978 j& A Cooks and Pretorius, 1987 1- 1.00 • #t, ;4&i€ °°0 A «° 0.10 • AAA*£- A A A A A
U.U 1 " ' 0.01 0.10 1.00 10.00 Length m.
Scattergram of Depth/Length
10.00
o Franzle, 1971 + Schipull, 1978 - Cooks and Pretorius, 1987 1.00 - O
O ° AA
CD Q A **£^ A o -K**-1- 0.10 •: o coo J7 ^ A A *A i I A A 4-M-1-4 4-4- 4. 44-444-*- +-Mi-•»-» f -t »•«•
0.01 1 1 r—r-i-m-r 0.01 0.10 1.00 10.00 Length m. Figure 4.6. Previously reported relationships of length, width and depth of sandstone solution basins. Note log scale. After Franzle (1971), Schipull (1978) and Cooks and Pretorius (1987).
Graphs of the same parameters (Figures 4.7 to 4.9) provide a ready means of comparing the basins in this region with those reported elsewhere. They also facilitate comparison between basins on the various local quartz sandstones. Scattergram of Hawkesbury Sandstone Basins Split By: Location
•+ Willow Vale x A Box Vale a Carrington Falls • o Maldon Bridge 1.00 - a Maldon Weir _tftf*- X Bargo River ajrty^*^ • Mermaids Pool mitflnc? • Mt Keira A 0.10 i A Weeping Falls Ad*S[$?& •
0.01 - 0.01 0.10 1.00 10.00 Length m.
Scattergram of Nowra Sandstone Basins Split By: Location 10.00
4 Pigeon House * Monolith Valley a Tianjarra Plateau 1.00 • "-.+ f^V*A DD
0.10 ^
0.01 0.01 0.10 1.00 10.00 Length m.
Scattergram of Snapper Point Formation Basins Split By: Location 10.00
•* Honeymoon Bay A Whale Point ° Point Perpendicular 1.00 • C Blackall Rocks E
5 t**^' 0.10 •""J1 • a fin a
0.01 i i ^.^T^^—.— i i i i i i II i II ^-^.^^^ 0.01 0.10 1.00 10.00 Length m.
Figure 4.7. Width/length relationships of local sandstone solution b Scattergram of Hawkesbury Sandstone Basins Split By: Location 10.00 4- Willow Vale A Box Vale m Carrington Falls 0 Maldon Bridge 1.00 - A * 0 Maldon Weir H Bargo River • Mermaids Pool • Ml Keira 0.10 A Weeping Falls
0.01 0.01 0.10 1.00 10.00 Length m.
Scattergram of Nowra Sandstone Basins Split By: Location 1 0.00 "
4 Pigeon House Monolith Valley a Tianjarra Plateau 1.00 •
a" D D
0.10 i A At 2 •*£"" " A 4- 4- D
0.01 - 0.01 0.10 1.00 10.00 Length m.
Scattergram of Snapper Point Formation Basins Split By: Location 10.00
4 Honeymoon Bay * Whale Point a Point Perpendicular 1.00 - O Blackall Rocks E a. Q 4 4 fa* £T* - 0.10 A ** ^ *>$&?*
0.01 ^" 9 W< I • ^^^^^^^—^-^^-^ 0.01 0.10 1.00 10.00 Length m.
Figure 4.8. Depth/length relationships of local sandstone solution basins. Scattergram of Hawkesbury Sandstone Basins Split By: Location 10.00
*• Willow Vale 1.00 ' *> Box Vale B Carrington Falls E *?,•A . X A " "I»&1^ X & Maldon Bridge 5 • Maldon Weir x Bargo River 0.10 i , • Mermaids Pool • Mt Keira A Weeping Falls
0.01 0.01 0.10 1.00 10.00 Depth m.
Scattergram of Nowra Sandstone Basins Split By: Location 10.00 '
1.00 • 4-A '
0.10 : .A we f Pigeon House A Monolith Valley • Tianjarra Plateau
0.01 —1——i—i—•—i-^-^— 0.01 0.10 1.00 10.00 Depth m.
Scattergram of Snapper Point Formation Basins Split By: Location 10.00
Av« 1.00 : * "4.
E 5 4- Honeymoon Bay 0.10 - n • „ * A Whale Point • °4- a • Point Perpendicular O Blackall Rocks
0.01 II I I I I • I I I I I • l|" I I I I I I I I 0.01 0.10 1.00 10.00 Depth m.
Figure 4.9. Width/depth relationships of local sandstone solution basins. Length Width Depth Box Vale Length - 0.915* (p=0.0001) 0.544* (p=.0034) Width 0.915* (p=0.0001) - 0.642* (p=.0005) Depth 0.544* (p=.0034) 0.642* (p=.0005) - - Carrington Falls Length - 0.883*(p=0.0001) 0.364** (p=0.0482) Width 0.883*(p=0.0001) - 0.258 (p=0.1594) Depth 0.364** (p=0.0482) 0.258 (p=0.1594) -
Maldon Bridge Length - 0.941* (p=0.0001) 0.742* (p=0.0001) Width 0.941* (p=0.0001) - 0.695* (p=0.0003) Depth 0.742* (p=0.0001) 0.695* (p=0.0003) -
Maldon Weir Length - 0.847* (p=0.0002) 0.525** (p=0.0221) Width 0.847* (p=0.0002) - 0.775* (p=0.0007) Depth 0.525** (p=0.0221) 0.525** (p=0.0212) -
Bargo River Length - 0.897* (p=0.0001) 0.370** (p=.0428) Width 0.897* (p=0.0001) - 0.520* (p=0.0044) Depth 0.370** (p=.0428) 0.520* (p=0.0044) -
Mermaids Pool Length - 0.897* (p=0.0001) 0.561* (p=0.0025) Width 0.897* (p=0.0001) - 0.609* (p=0.001) Depth 0.561* (p=0.0025) 0.609* (p=0.001) -
Mt Keira Length - 0.955* (p=0.0001) 0.401** (p=0.0494) Width 0.955* (p=0.0001) - 0.386 (p=0.585) Depth 0.401** (p=0.0494) 0.386 (p=0.585) -
Weeping Falls Length - 0.882* (p=0.0001) 0.718* (p=0.0001) Width 0.882* (p=0.0001) - 0.683* (p=0.0002) Depth 0.718* (p=0.0001) 0.683* (p=0.0002) -
Willow Vale Length - 0.941* (p=0.0001) 0.713* (p=0.0014) Width 0.941* (p=0.0001) - 0.662* (p=0.0031) Depth 0.713* (p=0.0014) 0.662* (p=0.0031) - Table 4.11. Spearman's Rank Correlation coefficients corrected for ties for Hawkesbury Sandstone basins. * Significant at a = 0.01 ** Significant at a = 0.05 107
Length Width Depth Pigeon House Length - 0.879* (p=<0.0001) 0.575* (p=0.0015) Width 0.879* (p=<0.0001) - 0. 658* (p= 0.0003) Depth 0.575* (p=0.0015) 0. 658* (p= 0.0003) -
Monolith Valley Length - 0. 862* (p=<0.0001) 0.768* (p=<0.0001) Width 0. 862* (p=<0.0001) - 0.641* (p=0.0005) Depth 0.768* (p=<0.0001) 0.641* (p=0.0005) -
Tianjara Plateau Length - 0. 839* (p=<0.0001) 0.676* (p=0.0002) Width 0. 839* (p=<0.0001) - 0.699* (p=0.0002) Depth 0.676* (p=0.0002) 0.699* (p=0.0002) - Table 4.12. Spearman's Rank Correlation coefficients corrected for ties for Nowra Sandstone basins. * Significant at a = 0.01 ** Significant at a = 0.05
Length Width Depth Honeymoon Bay Length - 0.885* (p=0.0001) 0.477** (p=0.0102) Width 0.885* (p=0.0001) - 0.565* (p= 0.0024) Depth 0.477** (p=0.0102) 0.565* (p= 0.0024) -
Whale Point Length - 0.699* (p=0.0002) 0.351 (p=0.0585) Width 0.699* (p=0.0002) - 0.329 (p=0.0768) Depth 0.351 (p=0.0585) 0.329 (p=0.0768) -
Point Perpendicular Length - 0.953* (p=0.0001) 0.701* (p=0.0002) Width 0.953* (p=0.0001) - 0.626* (p=0.0008) Depth 0.701* (p=0.0002) 0.626* (p=0.0008) -
Blackall Rocks Length - 0.926* (p=0.0001) 0.707* (p=0.0001) Width 0.926* (p=0.0001) - 0.697* (p=0.0002) Depth 0.707* (p=0.0001) 0.697* (p=0.0002) - Table 4.13. Spearman's Rank Correlation coefficients corrected for ties for Snapper Point Formation basins. * Significant at a = 0.01 ** Significant at a = 0.05
Non-normality of basin size distributions necessitated the use of non- parametric statistical techniques, with comparisons at individual sites being
made using non-parametric Spearman's Rank Correlation, presented in
Tables 4.11 to 4.13. 108
Comparison of the Spearman's Rank Correlation r^ values with the clustering of the data of Figures 4.7 to 4.9 indicates that very significant relationships between basin length, basin width, and basin depth are seen within this study area. These data are also closely comparable to the few previously published studies with basin dimensions of an identical order, and again with strong positive correlations between basin width and length. The relationships between length and depth are also in many cases moderately
strong in this area, but there is a wider range than in the overseas examples.
4.7. MORPHOMETRIC RELATIONSHIPS BETWEEN SAMPLE SITES
It is evident that significant relationships exist in basin dimensions at the level of individual study sites, but it remains to be seen if such relationships
occur on the regional scale. Moreover, as these sites are scattered over a range of environmental conditions, from tidal marine to sub-littoral heath, and from moist coastal forest to closed dry-sclerophyll forest nearly 100km inland, a comparison of sites is useful in ascertaining the processes involved in basin
development.
Before being able to test if basins on each of the sandstones are statistically
similar, one must first determine if significant differences exist between samples on the same sandstones, because if they do, comparison across
sandstones may not be possible. Use was made of the Kruskal-Wallis non-
parametric analysis of variance test to determine for differences in basin length, width and depth between the sample localities within each of the sandstone groups. 109
Hawkesbury H Corrected for Probability of Conclusion #0.05,8 Sandstone Ties Being Random Length 52.230 15.507 <0.0001 Reject H0 Width 38.541 15.507 <0.0001 Reject H0 Depth 34.241 15.507 <0.0001 Reject H0
H0 = All basins belong to the same Population, a = 0.05.
Nowra H Corrected for Probability of Conclusion #0.05,2 Sandstone Ties Being Random Length 13.567 5.991 0.0011 Reject HQ Width 14.141 5.991 0.008 Reject HQ Depth 14.511 5.991 0.0007 Reject H0
H0 = All basins belong to the same Population, oc = 0.05.
Snapper Point H Corrected for Probability of Conclusion Formation Ties #0.05,3 Being Random Length 34.080 7.815 <0.0001 Reject H0 Width 38.335 7.815 <0.0001 Reject H0 Depth 42.280 7.815 <0.0001 Reject H0
H0 = All basins belong to the same Population, a = 0.05. Table 4.14. Results of the Kruskal-Wallis Tests for Hawkesbury and Nowra Sandstones and Snapper Point Formation basins.
The results of the Kruskal-Wallis test are shown in Table 4.14 and show that in all cases, highly significant differences exist within the group of sample sites for each variable on each sandstone. For each variable at at least one site upon the same sandstone, the mean basin length, width or depth was found to be significantly different. If was then necessary to determine where these significant differences occurred, and why.
4.7.1. Differences Between Sites
A non-parametric Tukey-type multiple comparison technique (Zar, 1984) was employed to establish between which site or sites basin characteristics differed. 110
These results are shown in tabular form in Tables 4.15 to 4.17, and in detail in
Appendix 2.
Hawkesbury Sandstone Basin Lengths Site 9 4 6 7 1 3 8 2 5 9 - V V V V V X X X 4 - V V V V V X X 6 - V V V V X X 7 - V V V X X 1 -
V = Belong to the same Population. X = Do not belong to the same population a = 0.05. 1= Box Vale, 2=Carrington Falls, 3=Maldon Bridge, 4= Maldon Weir, 5= Bargo River, 6= Mermaids Pool, 7= Mt Keira, 8= Weeping Falls, 9= Willow Vale.
Hawkesbury Sandstone Basin Widths Site 9 6 4 7 1 8 5 3 2 9 - V V V V V V V X 6 - •J V >l >l V -j X 4 - V V V V v X 7 - V V V V X 1 - V V V V 8 - V V V 5 - V V 3 - V 2 -
V = Belong to the same Population. X = Do not belong to the same population a = 0.05. 1= Box Vale, 2=Carrington Falls, 3=Maldon Bridge, 4= Maldon Weir, 5= Bargo River, 6= Mermaids Pool, 7= Mt Keira, 8= Weeping Falls, 9= Willow Vale.
Hawkesbury Sandstone Basin Depths Site 9 6 4 7 8 1 5 2 3 9 - V V V V V X X X 6 - V V V V V V X 4 - V V V V V V 7 - V V V V V 8 - V V V V 1 - V V V 5 - V V 2 - V 3 -
V = Belong to the same Population. X = Do not belong to the same population a = 0.05. 1= Box Vale, 2=Carrington Falls, 3=Maldon Bridge, 4= Maldon Weir, 5= Bargo River, 6= Mermaids Pool, 7= Mt Keira, 8= Weeping Falls, 9= Willow Vale. Table 4.15. Multiple Comparisons of Hawkesbury Sandstone basins Ill
Nowra Sandstone Basin Lengths Site Monolith Valley Pigeon House Mt. Tianjara Plateau Monolith Valley - V X Pigeon House Mt. - X Tianjara Plateau -
V = Belong to the same Population. X = Do not belong to the same population a = 0.05.1= Pigeon House Mt., 2=Monolith Valley, 3=Tianjara Plateau. Nowra Sandstone Basin Widths Site Monolith Valley Pigeon House Mt Tianjara Plateau Monolith Valley - V X Pigeon House Mt - X Tianjara Plateau - V = Belong to the same Population. X = Do not belong to the same population a = 0.05.1= Pigeon House Mt., 2=Monolith Valley, 3=Tianjara Plateau. Nowra Sandstone Basin Depths Site Pigeon House Mt Monolith Valley Tianjara Plateau Pigeon House Mt - V X Monolith Valley - X Tianjara Plateau -
V = Belong to the same Population. X = Do not belong to the same population a = 0.05.1= Pigeon House Mt., 2=Monolith Valley, 3=Tianjara Plateau. Table 4.16. Multiple Comparisons of Nowra Sandstone basins
Snapper Point Formation Basin Lengths Site Whale Point Honeymoon Bay Point Blackall Rocks Perpendicular Whale Point - V V X Honeymoon Bay - V X Point - X Perpendicular Blackall Rocks -
V = Belong to the same Population. X = Do not belong to the same population a = 0.05. Snapper Point Formation Basin Widths Site Honeymoon Bay Whale Point Point Blackall Rocks Perpendicular Honeymoon Bay - V V X Whale Point - V X Point - X Perpendicular Blackall Rocks -
"V = Belong to the same Population. X = Do not belong to the same population a = 0.05. Snapper Point Formation Basin Depths Site Whale Point Point Perpendicular Honeymoon Bay Blackall Rocks Whale Point - V V X Point - V X Perpendicular Honeymoon Bay - X Blackall Rocks -
V = Belong to the same Population. X = Do not belong to the same population a = 0.05. Table 4.17. Multiple Comparisons of Snapper Point Formation basins 112
These results indicate a number of interesting features. Firstly, the order in which the various sites appear in the ranking is generally similar for each of the three basin axes, especially for the Hawkesbury and Nowra Sandstones.
This follows from the high correlations demonstrated earlier. With respect to
the Hawkesbury, the Willow Vale basins always have the lowest ranked mean length, width or depth. Next lowest are Mermaids Pool and Maldon Weir for both width and depth, but this order is reversed for length (the
differences in ranked average length are very small) (Appendix 3). Following
this is Mt Keira then either Box Vale or Weeping Falls. The order of the
remaining highest mean rank sum groups is more variable, but is composed
of Carrington Falls, Bargo River, and Maldon Bridge.
Significant differences between ranked site means were found on the Hawkesbury Sandstone for all three basin axes. In respect to basin length, it is
apparent that Bargo River and Carrington Falls are significantly different (a =
0.05) from almost half the other sites (Willow Vale, Maldon Weir, Mermaids Pool, and Mt Keira) (Table 4.15). Weeping Falls is only different to Willow
Vale, but these two sites are however, not significantly different to the remainder of the sites where the ranked mean basin lengths come from the
same population. A subsequent multiple comparison test indicated that basin lengths at Bargo River, Carrington Falls and Weeping Falls are not
significantly different (a = 0.05).
With respect to ranked mean basin width, only Carrington Falls is
significantly different to any of the other eight sites, but only just so from Mt Keira. All other sites do not significantly differ from one another at a 95%
confidence level. 113
For basin depth, three sites again differ from the other six. Maldon Bridge is significantly different to both Willow Vale and Mermaids Pool, whilst both
Carrington Falls and Bargo River are only different to Willow Vale. All other basins belong to the same Population. A further Kruskal-Wallis Test indicated that Maldon Bridge, Carrington Falls and Bargo River, whilst they differ from the other sites, are themselves from the same population (a = 0.05).
On the Nowra Sandstone (Table 4.16) it is immediately obvious that, although the ranked means of the three basin axis at both Pigeon House and Monolith
Valley are statistically similar, the Tianjara Plateau basins do not belong to the same population. The ranking of the site means shows that for both length and width Monolith Valley basins are smaller than those at Pigeon House, but the Pigeon House basins are shallower than their cousins at Monolith
Valley. The differences between these two sites are not great. The Tianjara Plateau basins are, on average, significantly longer, deeper and wider than
those at both Pigeon House and Monolith Valley. Repetition of these
statistical tests omitting the Tianjara Plateau data (in this case by the Mann- Whitney U Test) showed that again neither the Pigeon House nor Monolith
Valley data differed significantly at the 95% confidence level.
A similar trend to that seen on the Nowra Sandstone was seen for Snapper
Point Formation basins (Table 4.17), with only one site, Blackall Rocks, being
significantly different in all three variables to all others in this group.
Repetition of the Kruskal-Wallis test without the Blackall Rocks data showed conclusively that the basins from Honeymoon Bay, Whale Point and Point
Perpendicular came form the same population, and even at a = 0.01 length and width for these three sites are not significantly different. 114
4.7.2. Reasons for Differences Between Sites
It is indeed interesting that there is not more variability in basins dimensions on the three sandstones across the study region, and this indicates that basin dimensions are not random. But the reasons for those differences which do exist are not obvious.
The Hawkesbury Sandstone is remarkably uniform over its outcrop, and no immediately obvious lithological differences are apparent, except at Carrington Falls where there is much induration by iron. All Hawkesbury
Sandstone sites experience similar climatic conditions with essentially the
same vegetative conditions and similar temperature and precipitation. The
physical locations of the basins also does not appear to be a controlling factor. Examination of the data for the most variable sites, Bargo River and Carrington Falls, indicates a small number of basins with much greater lengths and widths than the remainder of the sites (Figure 4.2). While the
disparate size and form at the latter site may be caused by the effects of iron
induration, no such induration occurs at the Bargo River site.
On the Nowra Sandstone basins on the Tianjara Plateau are significantly
different to those at both Pigeon House and Monolith Valley, and this difference seems not just a result of the small data set. On the sampled sites
on Tianjara Plateau, at Pointers Gap (G.R. 594 944, Milton, 1:25 000, 8927-II-N) for instance, Nowra Sandstone pavements have been exposed from beneath
swampy vegetation. The rock surface is very highly pitted and very irregular
with poorly defined drainage channels covering much of the surface, but
clearly recognisable basins are rare. Further north on the Plateau at G.R. 564
985 (Tianjara, 1:25 000, 8927-I-S) numerous basins were examined on an
extensive flat pavement, partly covered with heath and sedge, that again was 115 very irregularly weathered, and at G.R. 558 006 (Tianjara, 1:25 000, 8927-I-S) a number of additional basins were found amongst open forest bordering the plateau edge. The Monolith Valley and Pigeon House sites displayed completely different weathering suites, and a substantially greater number of localised solution forms such as basins. The retarded development of basins at
Tianjara may be due to an accelerated lowering of virtually the entire pavement surface caused by the low pH and abundant organic acids seeping from the thick cover of sedge and heath.
The only statistical difference seen in the data for the Snapper Point
Formation (Table 4.17) is that between Blackall Rocks and the three coastal
sites at Jervis Bay. The sandstone at Blackall Rocks is finer and has a higher proportion of iron minerals and clays than that at Jervis Bay. Two other likely reasons for the differences need to be considered. Firstly, as the rate of denudation of the inland bedrock surfaces is slower than that in the littoral zone basins thus have a much longer time period in which to develop before
being eroded. Secondly, and perhaps more importantly, solutional weathering
of quartz is enhanced by increased salinity along the coast (Chapter 8).
Environmental effects are also supported by variations in the distribution of
basins at Jervis Bay. Basins are most numerous just above tidal limits, where the effects of salt spray are high, but decrease proportionally with distance into
the vegetated regions behind the platforms. Emery (1946) found a similar shoreward decline in the number of basins in carbonate-cemented sandstone
at littoral sites and attributed it to different stages of development. At Jervis
Bay, however, basins on isolated outcrops and boulders behind the shore are
generally just as well developed as those on the platforms. The decline in
basin numbers at the rear of the shore platforms here seems due not to any
inherent variation in age, but to a general masking of the rock surface by
sandy sediments and vegetation. 116
Sharp basin rims and other angular surface features are also well displayed in the supra-tidal zone close to the shore where salt-laden water is plentiful, but
drains off much of the surface (and into the basins) relatively quickly. In the
tidal zone where the rock surfaces are covered by water for a significant period
of time, more rounded basin rims and other surface features are the norm, and probably attributable to a more widespread and even solutional attack.
4.8. SANDSTONE HARDNESS AND BASIN PRESERVATION
Sandstone hardness, as tested with a type-L Schmidt Hammer, appears to be a
significant influence on the occurrence of solution basins (Table 4.18), but this
relationship is not clear.
'Excellent' basin development occurs in areas of slightly harder sandstone, albeit with high within-site variability, than those locations with 'Good' basin
development, which are themselves slightly harder than sites with only
'Moderate' development. The poorest sites were found to have the softest sandstones. The Grose Sub-Group sandstones of the Blue Mountains display a
regionally very poor basin development, but curiously, included both the softest and hardest sandstones seen in the study area. The high matrix clay
content of these sandstones (Section 11.3) is believed to be important here in the degree to which voids within the rock are filled (the higher the
permeability the softer the rock), and whether the sandstone is grain-
supported (harder) or matrix-supported (softest). Regardless of the uniaxial
compressive strength, these sandstones are all very friable and thus are believed to erode by granular disintegration at too rapid a rate for basin
development. There are, however, some exceptions. For example, no basins
occur on the Nowra Sandstone pavements north of the The Jumps' (G.R. 398
215, Nerriga, 1:25 000, 8927-IV-N) despite rock hardness being greater than 117
Schmidt Relative Degree Sandstone Location Comments Hammer Std. of Basin Rebound Dev. Development Narrabeen Darling General Surface 24.1 1.4 Poor Banks Wall Causeway Katoomba General Surface 10.1 0.0 Poor Glow Worm General Surface 37.7 6.4 Poor Tunnel Road Temple of Doom General Surface 29.8 2.8 Poor
Hawkesbury Bonnum Pic General Surface 20.7 2.1 Poor-Moderate Bundanoon General Surface 32.2 1.4 Moderate Carrington General Surface 33.2 1.4 Excellent Falls Basin Floors 33.5 3.5 Excellent Mermaids Pool General Surface 30.0 1.4 Good General Surface 33.8 1.4 Good Basin Floors 30.7 3.5 Good Basin Floors 34.5 0.0 Good Maldon Weir General Surface 29.9 0.7 Moderate General Surface 30.9 0.0 Moderate General Surface 32.3 0.7 Moderate General Surface 28.4 1.4 Moderate General Surface 29.6 0.0 Moderate General Surface 27.5 2.8 Moderate Weeping Falls General Surface 24.5 2.8 Moderate Willow Vale General Surface 27.8 2.8 Good-Excellent Wingecarribee General Surface 34.7 0.0 Excellent Kiver Basin Floors 35.6 0.0 Excellent
Nowra Boyd Lookout General Surface 26.7 2.8 Poor 12 Mile Road General Surface 28.6 4.9 Poor Monolith General Surface 22.8 0.0 Excellent Valley Pavement 2km General Surface 31.6 0.0 Very Poor north of The Jumps' Upper Endrick General Surface 24.4 2.1 Excellent River
Snapper Point Blackall Rocks General Surface 32.1 4.2 Excellent Formation Basin Floors 30.6 0.7 Excellent Honeysuckle General Surface 35.8 2.8 Excellent Point Intensely Etched 31.7 6.7 Excellent Surface Basin Floors 33.8 5.6 Excellent Intensely Etched 32.7 9.2 Excellent Basin Floors Table 4.18. Hardness of sandstone surfaces and basin floors at various sites related to the degree of relative basin development. Average of multiple readings and corrected for gravitational effects.
other 'Poor' sites and similar to 'Moderate' to 'Excellent' sites. Monolith
Valley and the Upper Endrick River are also unusual in that they both display excellent basin features, but are on one of the softer sandstones. While these exceptions cannot be ignored, it does seem that, as the harder sandstones are 118 more resistant to general surface denudation, basins which have developed on them have a longer time in which to grow than do those on softer sandstones before being eroded away by general lowering of the surface.
4.9. BASIN AGE
The ages of solution basins have almost never before been determined because materials suitable for absolute dating are usually absent and at best provide a minimum age for these features. Small basins have formed in large boulders of Snapper Point Formation sandstone at Jervis Bay overturned by a tsunami (R.W. Young and E. A. Bryant pers com., 1994). These basins are about 10cm in length, and only quite shallow. 14C dating of shells on a transported boulder indicates that this tsunami event occurred at 1700 years
B.P. (R.W. Young, pers com., 1995). Basins upon the boulders must therefore have developed since this event, but because of the small number of basins on them no further inference can be drawn about actual rates of formation.
Uranium/Thorium techniques (Short et al, 1989) were also used to date two iron-rich crusts developed within basins. A 10 to 30cm thick massive, iron- rich ferricrete within the largest basin in the Hawkesbury Sandstone at
Bonnum Pic (Plate 4.12), proved too old to date (Table 4.19). The hard, impervious nature of this ferricrete suggests it was a closed system with respect to U/Th, and therefore the disequilibrium age of >350 Ka is acceptable.
A 1cm thick ferricrete which lines, and obviously postdates, a large basin above the streambed at Lizard Creek (G.R. 031 130, Appin, 1:25 000, 9029-I-S) was also analysed by the U/Th technique. An age of 33.5 +9.1 -8.5 Ka was yielded by this sample. These two dates are significant because they show that some basins have grown at very slow rates. Furthermore, the second of them 119
0) to • ^4 o 43 4-1 Cfl <44-H1 T3 O
CO
fr 4a 3 Oi 43 4a 4-i OenI u 44 • ciH CO >> rt £ t>0 cc rt 43 (3 d 4-1 • i-H nS 44-o3> • cl-C 44 O, H3 O CO S3 4-1 A M-c MoH 0) 4-1 O C 0) l-l T3 .-4 CO 1-1 4-1 xs to M-0c) $3 01 ctf (50< 43 4-1 0 43 01 bO PH 43 *4 6 0) 43 r-l 3 4->1 T)M tic «S 0) O S3 4-> .»—i ffl CO CO I—1 4-1 n3 PH rt4 a 120 shows iron mobilisation during the cooler conditions of the Last Glacial (Section 3.6). Lab no. 230Th/234u 234TJ/23STJ Age Corrected Corrected (ka) LH3628 1.5374 0.80418 Not Obtainable Table 4.19. Uranium/Thorium age determinations for the Bonnum Pic ferricrete. 4.10. GENERAL CONCLUSIONS Small rock basins have been reported from numerous locations world wide on granites and other siliceous rocks, but only rarely from areas of quartz sandstone. Four times more basin data from sandstones were collected during this study than has been previously published. The basins of Sydney Basin sandstones range in size over several orders of magnitude, from less than lcm in length, width or depth, to over 10m length, 5m width and 1.2m depth. Much larger basins are also sometimes found, but the smaller basins are by far the most common. Basins were also found to be highly variable in plan-form, ranging from almost perfectly circular to extremely irregular. No basin shape, or group of shapes, was found to be dominant over the area, indeed, no shape class was seen to occur in more than about half the basins at any one site. Shapes of basin in this area therefore apparently develop at random. Unlike the form in plan, wall or floor characteristics of the basins, although quite variable, do concentrate in a small range of types. Walls tend to be either gently angled, steeply angled or vertical, but composite forms are not uncommon. Basin floors are almost always either flat or hemispherical. 121 Classification of basins into 'pits' or 'pans' grounded on basin morphology by Twidale and Corbin (1963) does not seem applicable in this region. Several conclusions can be drawn from the statistical analysis of the size parameters of basins in this area. Firstly, basins here are of comparable sizes to those few sandstone basins examined elsewhere around the world. Relationships between the size parameters of the basins here and elsewhere are also similar. Secondly, the morphometric variables examined here are highly correlated. Spearman's Rank Correlation coefficients of length versus width are all greater than 0.699, most appreciably more so, and are all significant at the 99% confidence level. Length and depth are also highly correlated, mostly at 99%, and width and depth are generally significant at 95% confidence. Thirdly, although it seems that, because of these high correlations, differences in individual factors within sites are minimal, analysis of variance of means between sites on individual sandstones showed significant differences at the 95% confidence level. Generally, however, only one site in each group was found to be different from the others, and these differences are generally explainable in terms of site-specific lithologic, vegetative, or chemical conditions. Because of significant variability within the three sandstone sample groups, variability between sample groups was not examined. Thus, it has been demonstrated here that quartz sandstone solution basins express a morphological similarity over a range of scales, and, apart from only a few localised and explainable exceptions, across a wide variety of regions. Similarity of form across this study area, and indeed apparently worldwide, suggests a widespread similarity of genetic process. Because the action of 122 solution in the formation of these basins is undeniable, investigation must therefore be made of the chemical composition of basin waters, and also the processes by which these waters react with the sandstone bedrock to achieve these characteristic forms. These important issues are considered in Chapters 10 and 11. 123 CHAPTER 5. TOWERS AND GRIKES 5.1. INTRODUCTION Preferential solutional weathering of both regional and local bedrock fracture networks (faults and joints) is a major process in many terrains, but it is in limestones that this process produces some of the most dramatic of scenery, namely Tower Karst. This same joint widening process operates in the formation of grikes, but at roughly an order of magnitude lower. Both these large towers and smaller grikes have been reported in quartz sandstones in tropical latitudes (Section 2.2 and 2.5) but are also present in the Sydney Basin. 5.2. SANDSTONE TOWERS In several localities south of Sydney numerous series of towers, aretes and cones, often closely resembling those of the Bungle Bungle Range of the Kimberley (Young, 1986) or parts of Arnhem Land (Jennings, 1979; Johns, 1994) are cut from the Permian Nowra Sandstone (Figure 5.1). South-west of Sydney some outcrops of the Hawkesbury Sandstone also display tower and dome-like forms, and towers, locally known as 'pagodas', are widespread amongst the Upper Narrabeen sandstones of the northern Blue Mountains and Newnes Plateau. Although moderately well known and very scenic, none of the towers or pagodas of the study area have previously been described in detail in the geomorphic literature other than by Young and Young (1988, 1992). Numerical analysis of sandstone towers in this region, like that by Day (1978) on residual limestone hills in Puerto Rico, was not attempted for the 124 •m^r?-:. .OldCoach Road • ^V^W-"••.•.•.•• • • Glow Worm Tunnel Road frn-\£:::>\:'•'•'•'• •'•'• •;:•'.:•'•£> ••'•Ti •. BlackFellowsHand • - ^ ' \' '<-'iV'' • •'•'•'•& ''•'•'•TTJ." <..«u,u # Templeof Doom .•/.••..;:•.•.•• :y. \ ^v•^'•\^'•^^•^'•^•••-•.^•v.'•'.••'•v•^§'•^•••>•-• •' Lithgow - Grose u in Sub-Group in ra V- H Hawkesbury • :•*:• Sandstone Nowra c Sandstone ra u Snapper Point C- • • * Formation • * TN Honeysuckle Point Bulee Ridge •„ 0 10 20 30 40 50 i i i i i i upper Endrick River • Monolith Valley' 0 Figure 5.1. Location of studied Sydney Basin towers and grikes. 125 following reasons: detailed surveying in often highly inaccessible terrain was beyond the resources of this study; high precision mapping from air photos was not possible because of the small scale of the available photographic coverage and the obscuring effects of vegetation; and the frequently asymmetric form of many of the local towers further complicated morphometric analysis in that formal definition of individual tower dimensions was often difficult. Although not at sufficiently large scale for detailed analysis, the aerial photographic coverage was nonetheless adequate in some areas for basic mapping to be undertaken. 5.2.1. Tower Morphology Undoubtedly some of the best local examples of what Mainguet (1972) termed 'ruiniform' relief are to be found in the Budawang Range at the southern end of the Sydney Basin, west of Ulladulla (Figure 5.2). Here, deep, narrow river gorges have cut back into the Nowra Sandstone surface of the Sassafras and Mt Boyne Plateaux leaving numerous isolated sandstone mesas, the surfaces of which are rimmed by impressive cliffs. At Monolith Valley (G.R. 443 920, Corang, 1:25 000, 8927-III-N) a large mesa of Nowra Sandstone has been dissected into a complex maze of towers, rocky spires, aretes, broad pavements and scrub-filled valleys spectacularly perched many hundreds of metres above the Clyde River. The summit plateau is flat to gently undulating, but as the irregularity, and degree of dissection, increases toward the edges, this undulating terrain merges into a highly eroded and very angular tower and turret morphology, which in turn gives way to more continuous cliff lines. The residual sandstone towers line the 30m to 60m high cliffs encircling the main Valley, and similar towers are found lining many clifflines elsewhere in the area. 126 Bundanoon upper Endrick River • iO km '<*? 4 Monolith Valley Pigeon House Ulladulla Figure 5.2. Locations of towers and grikes on the Nowra Sandstone, and on the Snapper Point Formation at Jervis Bay. Source: Map after Le Roux and Jones (1994), Figure 3, p.193. 127 Young (1986) found that many clusters of towers and turrets at the Bungle Bungle Range of the Kimberley region "show a superficial resemblance to Mainguet's 'system emousse-ruiniform'" (p.192) where rounded towers dominate, but he also emphasised that the degree of dissection over much of the Bungle Bungle Range also seems rather typical of tower (kegel) karst. In many instances the resemblance of these sandstone towers to similar forms in limestone is uncanny. This is also the case at Monolith Valley, but, whereas the towers and flat-floored valleys of the Bungle Bungle Range display almost no control by joints (Young and Young, 1992), the development of the towers surrounding Monolith Valley has been strongly constrained by a mesh of major joints. The Nowra Sandstone at Monolith Valley is near horizontally bedded, fine to medium grained with occasional pebbly layers, and a joint spacing of about 5 to 50m is most prevalent. Localised small-scale undercutting of individual beds is very common, and at major bedding planes may extend for hundreds of metres along the cliffs (Plates 5.1 and 5.2). This erosion is, however, mostly very localised and on the scale of only a few centimetres height and depth. Occasional larger taffoni weathering caves are seen, but are not common. Long channel-like radial drainage runnels are very common on the walls of all towers and cliffs in this region, and are discussed in Chapter 6. Three broad types of towers can be recognised at Monolith Valley. Towers of the first type are isolated from the general cliffline of the main valley side, generally box-like, joint-aligned corridors (Plates 5.1 and 5.2). These towers tend to have very steep (> =60°) and even overhung sides, all of which are of a similar height and thus impart a general morphological symmetry. Some of the larger towers have flat summits but the smaller ones are usually quite 128 Plate 5.1. Type 1 towers at Monolith Valley isolated from the valley-side cliffline by generally box-like, joint-aligned corridors. Major bedding planes on the tower walls can be traced for long distances. Most summits are usually quite rounded toward the edges, and the cliff-foot break of slope is either very sharp or merges into a gently sloping bedrock pediment. Plate 5.2. Type 1 towers at Monolith Valley, with Type 2 towers along the cliffs in the centre distance. Note the basins and runnels on the foreground pavements. 129 rounded. Most tower summits, indeed almost all cliffs in the area, are rounded toward the edges (Plates 5.1 and 5.2). It is probable that many Type 1 towers initially have flat summits, but that they become progressively rounded as the towers are lowered by erosion. The second type of tower is not isolated, but is instead clustered along the valley-side walls, being integral components of the valley-side cliffs (Plate 5.3). Again, erosion along joints is the isolating process, but these towers are normally smaller than the first type. Side-walls of this second type vary from vertical or overhanging, to declivities as low as about 30° on their middle and upper slopes. The various sides of each individual tower are of differing heights, imparting a morphological asymmetry. Summits are more rounded and cone-like than on most of the isolated towers. In many cases vegetation, shrubs and small trees have colonised the lower angle cliffed sections of these towers. The third type of tower at Monolith Valley is a long, narrow, arete-like feature forming bedrock ribs or ridges which project from the plateau surface and terminate above the lower clifflines (Plate 5.4). Walls of these ribs are very steep to vertical, while the summits vary from flat to highly rounded and gradually decline in altitude from the mesa surface. The ends of these ribs finish abruptly at the plateau edge cliffs. There does not appear to be any altitudinal trend in flat or rounded summits in any type of tower here. Although adjacent towers often share similar summit levels, the summits do not correspond to any distinct stratigraphic level at the area-wide scale. The summits of the largest towers are often vegetated by shrubs or small trees, but in most they consist of bare rock. Basins 130 I SK^ Plate 5.3. Monolith Valley Type 2 towers clustering along valley sides and integral components of the valley-side cliffs. Side-walls of these towers vary from vertical or overhanging to as low as about 30°. In many cases shrubs and small trees have colonised the lower angle cliffed sections of these towers. Plate 5.4. Type 3 towers at Monolith Valley. Long, narrow, arete-like ribs or ridges which project from the plateau surface and terminate above the lower clifflines. Walls of these ribs are very steep to vertical, while the summits vary from flat to highly rounded and gradually decline in altitude from the plateau surface. 131 and other surficial weathering forms are exceedingly common on these rocky summits, and are actively lowering the towers. A number of other valleys and clifflines within about 15km north and northwestwards of Monolith Valley also display a similar, though generally less well developed, ruiniform topography. For example, along the upper Endrick River near G.R. 485 048, (Endrick, 1:25 000, 8927-IV-S), there are a number of smaller towers of Nowra Sandstone which are similar to the first two types of towers described from Monolith Valley (Plate 5.5). However, towers on Bulee Ridge (G.R. 388 132, Nerriga, 1:25 000, 8927-IV-N) 22km northwest of Monolith Valley (Plates 5.6 and 5.7) display a very different general morphology, but are once again clearly related to preferential weathering and erosion of the local joint set. They have formed along a ridge crest, and are not immediately surrounded by turreted clifflines. Furthermore, they are generally much smaller than those at Monolith Valley, and individual tower side-slopes are of much gentler angle, imparting a much more cone-like or rounded pyramidal form than many of those towers further south. A horizontal step-like topography of tower side-slopes is also common at Bulee Ridge (Plates 5.6 and 5.7). These steps are clearly related to variations in bedding, for, as Bulee Ridge lies closer to the westward margin of the Basin, there are numerous coarser sand and pebbly beds in the sandstone. Very steep to near vertical 'bulges', approximately every metre, correspond with major fine to medium sandstone beds, whereas the intervening horizontal grooving corresponds with the more pebbly or coarser sandy beds. The average vertical spacing of the horizontal grooves or undercuts is about 1 metre. 132 Plate 5.5. Towers beside the upper Endrick River surrounded by heavily basined pavements. Plate 5.6. Cone-like or rounded pyramidal towers at Bulee Ridge. Weathering and undercutting of regular coarser beds have led to the step-like topography of these towers. 133 Plate 5.7. Small towers at Bulee Ridge. Note the abrupt tower-foot break of slope. Plate 5.8. Hawkesbury Sandstone towers and pavements at Bonnum Pic. 134 Outcrops of the Hawkesbury Sandstone also display characteristic tower-like forms. The best example found in this study is at Bonnum Pic beside the Wollondilly River, west of Mittagong (G.R. 475 040, Hilltop, 1:25 000, 8929-11- N). Here outcrops of thinly bedded Hawkesbury Sandstone outcrops are cut into numerous small towers and rounded dome-shaped pavements (Plate 5.8). The towers at Bonnum Pic are less distinct and much more rounded than those further south. Their sides are commonly very steep to vertical in their lower sections, but generally much less steep and without vertical walls toward their summits. Slick-rock slopes are prevalent. The Hawkesbury Sandstone here has only minor pebbly lenses, but is highly crossbedded and quite friable, unlike most outcrops of this rock. This is the only large exposure of its type on the Hawkesbury Sandstone found during this study, although much smaller outcrops occur nearby and at Bundanoon. The northern Blue Mountains, and particularly the Newnes Plateau, display a wide array of tower-like landforms which are undoubtedly more numerous than those at the southern end of the study area. Indeed, along the north western margin of the Sydney Basin almost every exposed outcrop of Grose Sub-Group sandstones has been intricately carved into complex sequences of aretes, turrets and towers, separated by labyrinthine narrow, straight or winding valleys or parallel 'streets'. Atop the smaller valley-side cliffs and bare sandstone outcrops, towers locally known as 'pagodas', are very common. These features are strikingly similar to those of the Bungle Bungle Range and the Keep River area of the western Kimberley (Young 1986, 1987, 1988), both morphologically and in their clustering up hillsides. (R.W. Young, pers com.). These towers also mimic the Ruined City of Arnhem Land (Jennings 1979, 1984) and the 'beehives of northern Queensland (Twidale, 1956). 135 Pagodas are generally conical in shape, often with four or more sides, and commonly rounded. They differ most notably from the Nowra Sandstone towers at the southern end of the Basin, in that iron-indurated beds in the sandstone are very common and play a critical role in shaping the pagodas. These iron-stone layers are normally 0.25 to 3cm thick, and generally flat to gently dipping, but great local variations, and even bizarre almost circular shaped structures are common. As some iron sheets follow the bedding but others cut it at high angles, they are not a depositional feature, but their exact mode of origin is still unclear. Individual layers can commonly be traced for many tens of metres. Selective iron induration of joints is commonplace but vertical spacing between layers is variable. On two adjacent towers along the old Newnes Railway (G.R. 408 165, Cullen Bullen, 1:25 000, 8931-III-N) (Plates 5.13 and 5.14) that appeared representative of their type, average iron layer spacing was 0.41m (o = 0.27m) and 0.37m (e> = 0.27m) respectively. Many pagodas have formed along the westwards facing cliffs northwards of Lithgow, and at Black Fellows Hand Rocks (G.R. 316 095, Cullen Bullen, 1:25 000, 8931-III-N) (Figure 5.3) four major levels of pagodas can be seen. The highest of these pagodas at Black Fellows Hand Rocks are found on the ridgelines above the local 10 to 50m deep valleys, and appear to be the oldest. They are commonly degraded, and are apparently in the later stages of denudation. Some of the highest pagodas have partly collapsed, and there are fallen sandstone blocks scattered about them. Towers in this top level are generally smaller than those at lower levels. They are from 3m to 10m in height to 20m long. Towers in the second level, 15 to 20m downslope, are larger, better developed, more regular in shape and show little evidence of collapse (Plate 5.9). Immediately below them, and perched atop the valley side cliffs, are a further set of extremely well developed towers 5 to 50m in height, and usually about 5 to 30m long (Plate 5.10). A further set of 136 £ 0 1 2 3 4 5 Km Figure 5.3. Detailed distribution of pagodas on the Newnes Plateau. Source: After Wallerawang 1:100 000 topographic map, 8931 (Royal Australian Survey Corps, 1977), and extensive field investigation. 137 I - '*"•* •*»' Plate 5.9. Higher level pagodas at Black Fellows Hand Rocks. These towers are surrounded by low-angle sandstone pediments visible in the right foreground. late 5.10. Lower level pagodas"at Black Fellows Hand Rocks. Note the stepped topography imparted by the resistant iron layers. 138 immature or incipient towers up to about 4m high are developing at the base of the cliffs within some of the valleys. None of the valleys at Black Fellows Hand Rocks contain any distinct stream channel, and are filled with sand wash and thick scrub. Close by Black Fellows Hand Rocks another extensive suite of large pagodas and sandstone pavements, colourfully named the 'Temple of Doom', outcrop horizontally for several hundred metres, and for over 100m vertically down a hillside (G.R. 332 087, Cullen Bullen, 1:25 000, 8931-III-N) (Plate 5.11). The sandstone here is stratigraphically the same as that at Black Fellows Hand Rocks, but outcrops higher up this hillside have a distinctly smaller number of ironstone layers than the sandstone lower on the hillside. This variation has a major influence in the development of the turrets. Higher towers are quite rounded with very steep to vertical sides up to 10m high, whilst the lower towers are several times higher and have numerous projecting ironstone layers. Exquisite suites of towers stacked one atop the other at many levels up hillsides and bounded on the lower side by vertical to overhanging cliffs 10m to 50m high, are also found alongside the Old Coach Road near G.R. 420 187 (Ben Bullen, 1:25 000, 8931-IV-S) (Plate 5.12). These are morphologically the same as those a,t Black Fellows Hand and the lower pagodas at Temple of Doom. Another excellent field of pagodas between 5 and 20m high in similar iron-layered sandstone is located along the old Newnes Railway line. Two small pagodas were examined here in detail (Plates 5.13 and 5.14, Figure 5.6). Towers are not only very common across the valley sides and ridgelines here, but many large, dome-like towers with more angular pagodas upon their 139 *4 -.51- 1 '• -? V:^.— —.. >* Tfti s ^*" :,, 1 i^r^^* H P jm ..: rfj $0i ( ! J / / 1 / r . - PW^ ; - l ^* •H Plate 5.11. Pagodas at the Temple of Doom. Note the abrupt tower-foot break of slope. Plate 5.12. Tower field on a hillside near the Old Coach Road. 140 summits are found across a large expanse of the plateau surface westward towards the Wolgan Valley (G.R. 40 16, Ben Bullen, 1:25 000, 8931-IV-S). While towers are so well developed on extensive low angle bedrock slopes on the Newnes Plateau, high cliffs along the adjacent Wolgan Valley have no towers whatsoever. Their absence is apparently due to an obviously extensive undercutting and collapse of these cliffs. The pagodas, on the other hand, appear to be an upland valley phenomenon. In contrast to the Wolgan cliffs, there is little evidence for large-scale contemporary collapse of cliffs or towers in any of the areas studied. Despite the apparently precariously balanced nature of some towers (Plate 5.2), they appear to be essentially stable topographic forms, moreover, neither Jennings (1979) nor Young (1986) found widespread evidence for mechanical collapse of similar sandstone towers in northern Australia. On the contrary, as Young and Young (1993) emphasised, the morphology of the towers, and especially the frequent basal buttressing, imparts a general mechanical stability. Young (1987, p.211) also argued that "Not only are the towers ... mechanically stable, they are erosionally stable forms. The symmetrically domed towers are particularly so, for they minimise concentration or erosive energy by dispersing runoff radially". The radial shedding of runoff is clearly evident upon the cliffs and towers in the Sydney Basin, especially in the development of runnel forms (Chapter 6). This shedding of water from the tower crest and walls accentuates weathering and erosion at the foot of the slope, a reinforcement or positive- feedback mechanism (Twidale et al, 1974) leading to a continued growth of the tower. 141 The break of slope at the junction between valley side and the base of all the study areas towers is usually very sharp (Plates 5.1, 5.7, 5.11), as is often the case with limestone towers. This break of slope either occurs as an abrupt change of near vertical bedrock cliff to sandy valley fill, or, as a rapid transition from near-vertical cliff to bedrock pediment of low to medium declivity (Plates 5.1, 5.9). Small cliff-foot caves, like those which encircle many limestone towers (Jennings, 1976), are sometimes seen around the bases of some sandstone towers. These caves are never formed, as is the case with some limestone towers, by streams draining into openings at the tower foot, but seem rather to be the result of granular disintegration, presumably in a similar fashion to the widespread honeycomb weathering of local cliffs and boulders (Young, 1974, 1987; Young and Young, 1988). Weathering in these caves is undoubtedly enhanced by complex pore-water flow within the sandstones (Conca and Astor, 1987; Young, 1987). Other cliff-foot caves or hollows can be seen surrounding local towers, and, like those around many limestone towers and are interpreted as solution notches due to subsoil solution just beneath the soil surface at the active three-fold junction of atmosphere, rock, and soil (Jennings, 1976; Twidale, 1980). 5.3. STRUCTURAL AND LITHOLOGICAL CONSTRAINTS ON TOWER FORMATION 5.3.1. Central and Southern Study Area The processes by which sandstone towers in this area develop are controlled by a combination of deep weathering and selective erosion of the regional and 142 local joint network, small scale lithological variability within the sandstones, and the geotechnical properties of weak sandstone. Variation in these three factors is well illustrated in the differences between Monolith Valley, Bulee Ridge and Bonnum Pic, although at all three localities the sandstones are highly jointed and relatively thinly bedded. But these differences are especially highlighted in the contrasts between the Newnes Plateau pagodas and the towers in the southern sections of the study area. Both Mainguet (1972) and Jennings (1983) demonstrated the importance of accelerated weathering and erosion along joints within sandstones in tropical regions where widening of intermeshing system of joints often results in ruiniform landscapes "cut up by corridors and broad plaza, with flat floors gently declining ... down the dip of the rocks and aligned along a predominant joint set in that direction" (Jennings, 1979, p.825). It is unmistakably the same process that is occurring here, with an almost identical result, but without the tropical conditions. Young and White (1994) used satellite imagery techniques to examine the control of drainage on the Sassafras Plateau by fracture patterns, and found that the largest sets were expressed clearly on the surface outcrop of the Nowra Sandstone, and to some extent on the Snapper Point Formation. Mapping of the long axes azimuth's of 163 towers of all types at Monolith Valley from air photos clearly showed the constraints placed upon the topography by this fracture pattern. Tower long axes were entered into classes of 10° range (Figure 5.4) showing pronounced concentrations of azimuth occurring between N10°W and N20°E with a further, less dominant, set aligned between N80°E and N130°E. These tower orientations are similar to the larger regional fracture lineations identified but Young and White (1994), 143 and in fact nearly all of the bedrock ribs or Type three towers have the strike of their major axis between N10°W and N20°E in close accord with the local joint fracture pattern. The pattern of the towers in Monolith Valley and surrounding areas is clearly linked to the local fracture pattern of the Nowra Sandstone (Figure 5.5). Lines of erosion (valleys and residual towers) clearly show the rectilinear joint-controlled (diaclase) patterns which are characteristic of the well developed ruiniform type (e.g. Maingnuet 1972, Planche LXV). It is this preferential weathering and erosion of these fractures which has resulted in such a striking landscape. Figure 5.4. Azimuth orientations of towers at Monolith Valley. Radius of outer circle is equivalent to 30% of readings. This undoubted control by jointing in tower morphology at Monolith Valley also explains why the distribution of towers over the area is not more 144 Figure 5.5. Vertical air photograph of Monolith Valley. Note the pronounced fracturing of the Nowra Sandstone, and the influence of this on the formation of the numerous residual towers. The prominent lower cliffline is formed in the Snapper Point Formation. North is up, and the approximate scale is 1:25 000. 145 uniform; towers occur where the Nowra Sandstone is highly fractured, where these fractures have been deeply weathered, and where sufficient hydraulic gradient exists to remove the weathered sandstone by vadose flow. Where the intensity of this fracturing is less, or where there is a superficial cover of Berry Formation, as is the case on much of the Sassafras Plateau to the north, weathering and subsequent erosion of fracture zones with the formation of towers is less likely. The distribution of towers is also controlled by the variations in resistance of the sandstones. Testing with a Type-L Schmidt Hammer showed that the Nowra Sandstone in the towers fields at Monolith Valley, the upper Endrick River and Bulee Ridge is much weaker than outcrops further to the northeast where towers have not developed (Table 5.1). The more rapid widening of joints in the softer sandstones, in contrast to the minimal widening of them in the harder sandstones, seems to be critical to the development of towers. However, as microscopic examination of the softer sandstones reveals numerous overgrowths which show that these sandstones were once well-cemented (Chapter 11), differences in the history of weathering across the region also seem to be important. In this regard it seems significant that the higher plateau areas near Monolith Valley have been exposed since at least the Eocene (Young and McDougall, 1985). Variable rock resistance also seems to have controlled variations in tower morphology. The Monolith Valley sandstone is considerably softer than that at Bulee Ridge. The Schmidt Hammer readings at Bulee Ridge also demonstrated a very distinct difference in hardness between the coarser and more friable sandstone beds of the grooves (average rebound readings of 19.0, 0=4.2), and the finer, stronger, material forming the bulges (average rebound readings of 146 28.0, a=1.4) (Table 5.1). The differences in uniaxial strength of the beds may be a contributing factor in this great hardness variance, but these differences in Schmidt Hammer rebound values may also be indicative of greater void spacing in the coarser beds, and thus higher permeability. Indeed, in numerous instances, seepage or vegetative indicators of water seepage originate from major grooves on the tower sides, indicating that they are eroded slightly more easily than the rest of the rock (see also Pickard and Jacobs (1983) and Young and Young (1993)). The distinct rounding of the Bulee Ridge towers thus appears to be a result of the small-scale undercutting of closely spaced bedding planes (Young, 1987). n Hardness Std. Dev. Non-Towered Nowra Sandstone Boyd Lookout 12 26.7 4.1 Flat Rock Creek 25 40.1 4.9 Non-Towered Hawkesbury Sandstone Lizard Creek 17 28.0 3.6 Wingecarribee River 14 34.7 0.0 Mermaids Pool 12 30.0 1.41 Towered Nowra Sandstone Monolith Valley Southeast wall 6 21.7 1.4 North end of valley 12 23.5 0.0 Upper Endrick River Pediment between 11 24.4 2.1 towers Bulee Ridge Top of towers 10 28.4 1.4 Tower side bulge 10 28.0 1.4 Towers side groove 10 19.0 4.2 Towered Hawkesbury Sandstone Bonnum Pic Tower side 7 20.7 2.1 Table 5.1. Comparative hardness of towered and non-towered Nowra and Hawkesbury Sandstone from corrected Schmidt Hammer readings. 147 The spacing of vertical joints at Bulee Ridge is about lmto 2m on average with many of these joints transecting several beds, whilst others do not. Major joints intersect at approximately 90°, and this orthogonal jointing has led to the quite regular 'egg-box' layout of the towers. These joints are vertical preferential zones of concentrated groundwater weathering, as are the horizontal coarser bedding planes or pebble stringers. As already seen, such variations in permeability between beds are responsible for stepped topography on the Bulee Ridge towers. However, at Monolith Valley the alternating finer and coarser sandstone or pebbly beds are less common than at Bulee Ridge, the Nowra Sandstone is thinly bedded and thus, as these partings are closely spaced, the slopes also become rounded. An identical process is seen in the thinly bedded Hawkesbury Sandstone at Bonnum Pic. The sandstones in the recessed partings is generally indistinguishable from that on the adjacent slope, except maybe for minor changes in permeability. A similar trend was reported from the rounded towers of the Bungle Bungle Range by Young and Young (1992). Young and Young (1992) also thought that rounded surfaces on friable rock can generally be explained in terms of the critical declivity for the transportation of eroded debris. Howard and Kochel (1988) found that the slickrock slopes of the Colorado Plateau are essentially the result of granular weathering and erosion and the peeling of thin ( 'weathering-limited', in that the rate of removal of eroded material is far higher than the rate of debris production. R.W. Young (1987) found that the towers of the Bungle Bungle Range also seemed to be controlled largely by the detachment of grains, exhibiting a consistent mid-slope angle of around 64°, consistent with the high internal angle of friction of the closely interlocking grains. Further, 148 Young and Young (1992, p.46) also state that "the convexity of the summits of the towers (of the Bungle Bungle Range) may well be the result of reduced normal stress, because of the progressive decrease in overburden near the summit, which allows a more ready detachment of individual grains". The influence of these same processes is also supported by field evidence from this study, for weakly cohesive grains can easily be brushed from the surfaces of the Monolith Valley and Bonnum Pic towers, most eroded material is moving as individual grains, and the most rounded portion of these towers are the upper slopes above much steeper mid and lower slopes. 5.3.2. Newnes Plateau Pagodas While joints play an important role in the shaping of the Newnes Plateau pagodas, it is one that is less important than that at Monolith Valley or Bulee Ridge. Whilst excavation of joints are undoubtedly important in the initial stages of pagoda genesis, the final results are clearly more of an erosional form. These pagodas thus differ from the towers at the southern end of the Basin in that they are not directly the result of widened joints. In many instances, partially open or indurated joints can be seen to cut through a tower without any significant influence on the towers shape. At Black Fellows Hand Rocks, for example, a major iron indurated joint cuts vertically through the middle of one tower and thence cross two intervening gaps to bisect another two towers. Another example is to be seen on a large tower complex beside the old Newnes Railway which is crossed by two major essentially N-S joints. It is obvious in the field that these joints are not being widened to any appreciable extent, rather, in many cases the rock on one side of the joint has been lowered and the other less denuded side remains several metres higher. 149 Relatively regular spacing of the ironstone layers results in a 'staircase' like surface on most exposed rock outcrops, thereby imparting the characteristic morphology of the pagodas. Breakdown, erosion and undercutting of the sandstone on the pagoda sides occurs between the iron-layers. Most of the surface breakdown of the sandstone is granular, but on the pediments of the towers flaking and spalling of larger sandstone lumps is common. As this is currently occurring with no evidence of recent fire, the process does not necessarily appear to be fire induced, as was argued by Selkirk and Adamson, (1981). The more resistant iron-stones tend to eventually break off in thin, rectangular, sheets, and are commonly seen scattered across the pagoda surface. Detached grains of weathered sand are not common on the surface of the pagodas, suggesting such eroded sand is either quickly removed by wind and rain, or that the breakdown is only proceeding very slowly. Loose white pebbly sand is common on and around the higher, rounded, towers at the Temple of Doom, but less common on the iron-layered towers, suggesting much slower erosion rates on the iron-layered pagodas. If an ironstone capping is removed from the top of a pagoda, generally by undercutting and removal of the friable sandstone below, the remains of the sandstone quickly assumes a rounded, dome-like form (Figure 5.6, Plate 5.14). This freshly exposed sandstone is removed until another near-horizontal iron layer is exposed. Erosion of the pagoda summit then effectively stops, until, in time, this new iron cap is undermined and removed. The towers thus appear to be lowering more than they are wearing back. 150 Plate 5.13. Surveyed pagoda near the Glow-worm Tunnel Road. Note the resistant iron layers, and how they form the flat pagoda summit. This pagoda is about 25m high on the opposite side. Plate 5.14. Surveyed pagoda near the Glow-worm Tunnel Road. This pagoda is beside that in Plate 5.13. Erosion of the resistant iron layer summit quickly results in rounding of the summit and rapid lowering of the tower until another iron layer is exposed. This pagoda is about 25m high on the opposite side. 151 Further insight to the role of variable lithology in shaping the pagodas is given by Schmidt Hammer testing. Table 5.2 summarises results from one small, but representative pagoda along the old Newnes Railway (G.R. 408 165, Cullen Bullen, 1:25 000, 8931-III-N)(Figure 5.6, Plate 5.13). n Hardness Std. Dev. Towers on Newnes Railway. Ironstone layers between towers. 17 34.6 4.2 Sandstone layers between towers. 16 37.7 3.9 Tower 1 Bedrock pediment. 10 30.9 3.6 Jointed pebbly ironstone pediment 10 28.5 5.3 Medium to coarse friable sandstone 10 31.0 3.9 Ironstone 11 35.6 8.0 Coarse pebbly sandstone 10 27.0 3.8 Ironstone 11 36.7 6.1 Ironstone 10 33.6 5.8 Coarse pebbly sandstone 10 25.5 4.0 Ironstone pagoda top 11 25.4 6.5 Sandstone pagoda top 11 31.0 6.4 Temple of Doom White fine to coarse pebbly 15 32.6 2.8 crossbedded sandstone. Table 5.2. Hardness of Newnes Railway and Temple of Doom pagodas from corrected Schmidt Hammer readings. The field observations indicate that, as the ironstones protrude from the tower walls, they are more resistant. Surprisingly, however, the Schmidt Hammer readings give no support to this conclusion; average hardness readings of the ironstones are marginally higher than some of the sandstone layers, but the variability in the ironstones is the greater. Caution is thus warranted in interpreting the Hammer rebound readings. As Young (1988) found in the poorly cemented and friable sandstones of the Bungle Bungle Range, which also exhibit very high readings, the key factor here is not 152 Figure 5.6. Profiles of two small pagodas in flat-bedded sandstone close to the Glow Worm Tunnel Road illustrated in Plates 5.13 and 5.14. The importance of the iron cemented sandstone layers on the morphology of these two pagodas is clearly apparent. The stepped profile of the towers and the flat summits are a result of these more resistant layers. Where an iron layer at the summit is removed, the top rounds off and is quickly eroded until another resistant layer is reached. 153 4-> f-j ai c.S « IB -H - c >y o •*-• 0) 60 O f= .*§ 01 *J o 01 += tn & in £> to •5 S ~ OJ 4-1 ^6 IS x O CTJ M- S B ° •^ • £ X flj C en ta S 3 6.S o i N / 6 cr c E ,B i i &o;Q J O '5 3 o oi g A model for pagoda development can now be proposed (Figure 5.7). Joints only appear to be an important control in focusing initial pagoda isolation. As the pagoda surface is lowered, incision by drainage from the sides of the towers, and the differential resistance of the sandstone and ironstone layers becomes more important and the joints assume a lesser role. This sidewall drainage and erosion is again crossed by perpendicular drainage, finally resulting in the polyhedral shape of the individual towers. 5.4. GRIKES The solutional widening of joints in sandstone has resulted not only in the development of towers, but also of broad platforms dissected by clefts which can be described as "grikes" (see Chapter 2). They are well developed on sandstone pavements in both marine and inland locations within the Sydney Basin. For example, at Monolith Valley they occur in some valley bottoms and appear to be the first stage of tower formation. Many other examples of joint widening are seen in the study area, but the best are at Jervis Bay. At a number of locations around Beecroft Peninsula, the northern headland of Jervis Bay (Figures 5.1, 5.2), laterally extensive marine shore platforms of Snapper Point Formation sandstone dip below sea-level. Many of these platforms are very highly dissected by a network of narrow, deep clefts of 155 Plate 5.15. Grikes on the westward dipping Snapper Point Formation platforms at Honeymoon Bay. Platform surfaces are covered with smaller basins and runnels. Plate 5.16. Grikes at Honeymoon Bay. Lighter coloured sandstone is subject to wave action, whilst the darker rock is above wave influence. Plate 5.17. Parallel grikes at Whale Point. Plate 5.18. Complex grike network at Honeysuckle Point. Person top-right for scale. 157 rectilinear planform (Plates 5.15 to 5.17). These clefts exploit fractures within the bedrock, most commonly, but not always, joints. The surface of the fissured pavements are densely covered with basins and pitting of all sizes, as are the walls and floors of the clefts. For much of this coastline the grikes form a generally simple pattern of very well defined fissures exploiting the joints. Near Honeysuckle Point (G.R. 025 240, Currarong, 1:25 000, 9027-I-N), however, the density of grikes is markedly greater and a more highly developed network of cris-crossing fissures up to 3m deep is found (Plate 5.18). A bedrock fault occurs immediately north of this location, and the greater intensity of fissuring appears to be related to a greater concentration of joints and associated micro-fractures and weaknesses within the rock. The influence of bedrock control in the occurrence of the grikes is obvious. They exhibit a rectilinear planform, the fissures are commonly vertical to near vertical, and they cut across the platforms at a variety of angles, being dependent on the orientation of the shore with the joints. The regularity of form and spacing demonstrates that they are certainly not developing at random. The affinity of the grikes to structural weaknesses within the sandstone is evident from an analysis of the orientation of 412 grikes along the shore from Honeymoon Bay to Dart Point mapped from enlarged air photos (Figure 5.8). Because of the scale of the enlargements, approximately 1:3 800, only the largest grikes were visible. The joint-constrained origin of the grikes is clearly demonstrated by the change in their orientation from Honeymoon Bay southward toward Dart Point (Figure 5.9). These changes in orientation reflect the change in the axis of the Jervis Bay syncline southward along the shore. 158 Figure 5.8. Distribution of grikes along the shore of Jervis Bay from Honeymoon Bay to Dart Point. 159 Figure 5.9. Variability in grike orientation between Honeymoon Bay and Dart Point. For locations see Figure 5.8. Circle radius is 25% of observations. Not all the grikes are opened to the same extent. Some have been widened many metres, often with smaller grikes within, some widened about a metre (Plate 5.19), and some to only a few centimetres. One common feature of individual grikes, however, is a regularity of width along their length. A number of grikes 160 at Honeymoon Bay and Honeysuckle Point are so regular in plan-form that it is hard to envisage a process other than very uniform solutional widening that could account for such a regularity of width along individual joints over lengths of many tens, or even hundreds, of metres. The depth of the Beecroft Peninsula grikes are also variable, being dependant mostly on distance to base level, in this case the ocean, and on variations in local stratigraphic dip. Grikes in both the Honeymoon Bay and Honeysuckle Point areas range from less than 0.5m deep, whereas at Dart Point they attain depths close to 5m. The average depth is approximately 1.6 to 3m. The deepest grikes are generally found where the local dip is steepest, but the width of these grikes does not always increase proportionally with the increase in depth. The length of individual grikes depends largely on their orientation relative to the shoreline. Shore-parallel joint network has resulted in grikes of several hundred metres length being quite common (Figure 5.8). Shore-normal grikes are limited in length by the ocean on one hand and by superficial cover of sediment and vegetation at the back of the platforms on the other, to only a few tens of metres. It is also seen that the length of these sandstone grikes follow a similar rule to those in limestone where grike length is inversely proportional to the density of the major joints (Ford and Williams, 1989) clearly illustrated along the platforms between Honeymoon Bay and Dart Point (Figure 5.8). All grikes here slowly taper downward except where there are local widening at bedding-plane junctions. The general form of the Jervis Bay grikes in cross- section is essentially rectangular, but the base of the grike is often a little 161 Plate 5.19. Interior view of a lm wide Honeymoon Bay grike. The base is solid rock, and the walls are degraded by many smaller weathering forms. 162 narrower than the top of the fissure (Plate 5.19). The walls and floors of the grikes are, however, anything but regular (Plates 5.16 and 5.19), and concentrated secondary solutional attack of the sandstone has resulted in intense small-scale etching and pitting of all exposed sandstone surfaces. Many of these vertical and overhanging surfaces are covered by honeycomb weathering. Bedding-planes, regions of enhanced sandstone porosity or permeability, have been zones of concentrated weathering and erosion, and the grikes are often preferentially widened horizontally along these zones. Selective weathering has proceeded to such an extent that many small arches and windows through sections of solid rock have formed, and even whole grikes drain through small bedding-plane caves. Undercutting and removal of the surrounding platform surfaces has resulted in blocks of once continuous sandstone now being loose, isolated, and sometimes precariously balanced upon the platforms (Plate 5.16). These blocks should thus be considered as clints or even karren tables of Bogli (1980, p.58). In a number of instances the increase in stratigraphic dip has led to inclined joints and therefore grikes exploiting these weaknesses also being similarly inclined. Inclined grikes are also sometimes seen in association with more vertical fissures developed in almost horizontal sandstone. At Dart Point, however, where the sandstone dips quite steeply, some of the deepest grikes, those approaching 5m in depth, are still seen to be near vertical despite the inclined strata. Terminating grikes usually end at a junction with another grike, generally one that runs near-normal to the first. There is rarely any shallowing of the terminating grike before the junction, but a rapid deepening of the terminating grike is seen if the continuing grike is deeper. At the other end of the scale, grikes 163 often begin abruptly upon the pavement surface, reaching average depth within a distance of only a few metres. An open joint may or may not be visible in the sandstone surface just beyond the end of the grike. As previously discussed straight grikes are the norm in the Snapper Point Formation, but are sometimes curvilinear or even practically circular. A comparison of Plates 5.16 to 5.19 with the limestone grikes illustrated in Plate 1 of Williams (1966), Plate 24 of Sweeting (1966), Figure 9.6 of Ford and Williams (1989), or Plate 1 of Goldie (1981), immediately shows the remarkable similarity of the Jervis Bay sandstone grikes with those of several classic limestone regions of northern Great Britain and Ireland. This parallel is all the more stunning when it is remembered that identical grikes are clearly seen occurring in such strikingly dissimilar rocks. These morphological similarities between sandstone and limestone reflect a common, solutional origin. Widening of the Jervis Bay grikes has not resulted from tectonic processes, for there is no vertical displacement between the sides of the grikes, and their bases are in solid rock. Although it is evident that mechanical erosion is concentrated in those fissures experiencing active wave attack, many grikes extend or lie completely above storm regimes. These higher grikes are of identical structure and morphology to their wave-affected neighbours. Furthermore, those at the protected Honeymoon Bay site are identical to, if not more highly developed than those at Honeysuckle Point which are exposed to full coastal wave regime. Concentrated wave energy, and the scouring action of water-borne sand and clasts undoubtedly has had some influence in the enlargement of the intertidal grikes, but in the higher grikes the lack of significant clastic sediments and processes to move them indicates that a process or processes other than purely mechanical exploitation of joints must be 164 responsible for the formation of the grikes and this will be examined in Chapter 11. 5.5. CONCLUSIONS. The widening of joints has resulted in the development of excellent examples in towers and grikes in the sandstone of the Sydney Basin. Moreover, these features are strikingly similar to their counterparts in sandstones of the tropics and in limestone. Two distinctly different sequences of tower development are found in this study area. On the Newnes Plateau the Narrabeen sandstones are matrix supported and poorly cemented, and, although having high compressive strengths, are mechanically quite weak in shear. Joints in this area are seen to influence the boundaries of towers groups, but individual pagodas are controlled more by surface disintegration of the friable sandstones, whilst resistant iron-indurated layers play an important role in the rate of pagoda erosion and impart the characteristic stepped pagoda shape. In contrast, towers on the Nowra Sandstone at the southern end of the study region are strongly controlled by the regional joint network. They display a much higher degree of cementation with abundant quartz overgrowths (Section 11.2), but also a greater degree of fracturing and weathering. Matrix clay is rare. Deep weathering and later excavation of the fractures has been the dominant process, but even so lithologic control is still important, as is shown in the differences in towers between Monolith Valley and Bulee Ridge. The sandstones here are relatively soft, and of low granular cohesiveness, but because of their interlocking fabric they are still capable of standing in sheer faces (cf., Young, 1986). 165 In neither case, however, are the towers the direct result of solution as are their limestone counterparts. They form by granular disintegration of the sandstone. But like their limestone cousins, it is the preferential weathering and erosion of joints and specific beds, pathways for increased groundwater penetration, which is of vital importance, especially in the Nowra Sandstone towers. Thus, the Nowra Sandstone towers should, like those of the Bungle Bungle Range of tropical Australia, be regarded as karstic. Whether the Newnes Plateau pagodas are also karstic is at first sight debatable; they are more controlled by differential lithologic variability and backwearing. However, as petrographic evidence presented in Chapter 11 demonstrates conclusively, intense quartz etching and destruction of matrix material has occurred, and so solutional processes do play an integral role in the development of these towers also. Examination of fissures on sandstone platforms in parts of the region, especially at Jervis Bay, shows them to undoubtedly be widened joints, or grikes. Tectonic or mechanical erosive forces cannot account for the formation of these fissures, although in many instances, notably those at wave level, abrasion and other mechanical forces are undoubtedly in operation. Most have formed well above this wave affected zone. Joints are preferential zones or weakness within the rock, and chemical attack has been highest here, as is demonstrated by innumerable solution pits. Their dominantly solutional origin is further demonstrated by microscopic analysis (Chapter 11). 166 CHAPTER 6. SANDSTONE RUNNELS 6.1. INTRODUCTION In modern karst literature Lapies or Karren are general terms employed to describe the total complex of surficial solution forms, but "the term lapiaz (or lapies, lapiez, rascles, Schratten, or Karren) was used originally by A. Heim, J. Cvijic, and others to describe runnels cut in limestone" (Williams, 1966, p. 155). As discussed in Section 2.6, channels inset into bare rock surfaces, both of limestone and granite, are relatively common, but descriptions of channelised quartz sandstone surfaces are rarer. Nonetheless, runnel forms on quartz sandstones in the Sydney Basin are very common. Runnels occur on all sandstone units, and in all topographic and climatic settings in the Basin. Examples of several types of runnels from several locations (Figure 6.1) will be presented, and various forms and modes of formation examined. The exceptions are rillenkarren, which form by the dissolution action of sheet flow of rainwater that falls directly onto a surface (Bogli, I960, 1980; Ford and Lundberg, 1987). Few unequivocal examples of sandstone rillenkarren have been reported (Section 2.6.1), and no undisputable examples were found in this area. The lack of rillenkarren is probably due to the coarse nature of the host rock not being conducive to the formation of these small rills (Ford and Lundberg, 1987), and in fact, rillenkarren often do not even form on many coarse-grained limestones, marbles or dolomites. 6.2. TYPES OF RUNNELS Rinnenkarren begin where sheet flow of rainwater down a slope breaks into linear streams. Ford and Lundberg (1987) describe them as being much bigger than rillenkarren, generally 12 to 50cm wide, separated by distinct interfluves, 167 Kanangra Walls Grose u /^Bonnum Piq £<& tn Sub-Group IT] t-i H Hawkesbury :':i':-:| Sandstone Nowra C : ra Sandstone EU d- Snapper Point . I Formation TN -• Whale Point Honeymoon Bay •• . 0 10 20 30 40 50 I i i i , r I • • Vincentia 0)1 AfiB? Pointers Gap Figure 6.1. Location of runnel study sites on the Hawkesbury and Nowra Sandstones and the Snapper Point Formation. 168 they have sharp channel rims, rounded bases, and increase in depth and width down slope with increasing catchment area. True rinnenkarren form subaerially throughout their development (Ford and Lundberg, 1987). Rundkarren have both rounded bases and walls, and on limestone generally form beneath a cover of soil or other material (Bogli, 1960, 1980; Jennings, 1985; Ford and Lundberg, 1987). The rounded rims are attributed to more intense solution by lateral soil-base flow roughly normal to the channel orientation beneath a superficial cover of soil or other weathered material. They are similar in size to rinnenkarren, and may deepen down slope (Ford and Lundberg, 1987). Both rinnenkarren and rundkarren commonly display dendritic or meandering plan forms on low angle surfaces, whilst the lengths of both are variable and dependant on the volume of water available, length and gradient of slope, rock texture and amount of cover removed (Ford and Lundberg, 1987). Both sharp rimmed and generally more rounded sandstone runnel forms, which conform to descriptions of both rinnenkarren and rundkarren, are very common in this region, but are frequently sited in positions that pose problems in explaining an often side-by-side development. Here rounded base and wall runnels are found in association with sharp-rimmed runnels on the tops of boulders, on cliff edges, on marine platforms, and in similar locations where it is difficult to envisage the existence of a prior sediment cover in the recent past. In these cases there is rarely any evidence to suggest the rounded runnels are significantly older than the more angular runnels. Also, most individual runnels display characteristics of both rinnenkarren and rundkarren along their length; sections may be well defined with sharp rims and V or 'u' shaped cross-sections, whilst other parts of the same runnel may be much more rounded and less distinct. These changes may occur 169 several times along a single runnel. Many runnels, both rinnenkarren and rundkarren are also flat floored, not rounded as in the classic types, and like the walls and rims, the general form of the base commonly changes from flat to rounded or irregular many times along an individual channel (Figures 6.2 to 6.4). Runnels here may also commonly be seen connecting a series of solution basins down a slope (Plates 4.5, 4.6 and 4.9; Figures 6.3 and 6.4), or conversely, basins may have formed within the runnels. These flat-floored basins give many runnels a stepped profile. Basins may head a runnel, but not act as a water store, and the basins may or may not be inset into the slope for any great depth. Decantation runnels, which develop where water is supplied from an up- slope store rather than from direct precipitation (Ford and Lundberg, 1987), are probably just as common here as those fed by direct precipitation runoff. Water from this store, which is most commonly seepage from a patch of soil, bedding planes, joints, or periodically overflowing solution basins, flows either perennially or intermittently down the bare rock slope, into which it corrodes a channel. It is very common in this region to see a series of basins extending down a gentle rock slope interlinked by decantation runnels, but unlike the chains of basins along other types of runnels, these basins have a persistent long-term water source. Ford and Lundberg (1987, p.132) noted that the diagnostic characteristic of decantation forms is that as they do not "collect extra water down slope, the deepest part of the rill is at or close to the overspill point; it becomes 170 shallower down slope and will eventually extinguish if the available slope is long enough". This shallowing and loss of definable form are often seen here. Just as common, however, are decantation runnels fed by one or a number of sources, and which gradually deepen downslope, attaining their deepest point toward their middle or even lower reaches, before shallowing and finally extinguishing. Downslope shallowing is seen clearly in Figure 6.2 to 6.5, and is most common where the slope is convex-up in profile, steepening down slope. Examples of local decantation rills are shown in Plates 6.4, 6.6, 6.8, 6.10 and 6.11 where patches of vegetation usually act as water stores. It is generally impossible in this study area to tell decantation runnels apart from rinnenkarren, or rundkarren in the field without reference to the runnel head. The water source of decantation rills is of two main types. Where the supply is from a point source, then a single, often meandering rill will develop, and the size and length of the rill is related to the size of the store. Consequently, it might be expected that the larger the volume of water provided by the store, the larger the resulting runnel. This in part appears to be the case; the most well defined runnels originate from sources providing persistent, relatively high-volume seepage. But the rate at which seepage water is provided also appears to be important; high volume flows of short duration may be important in the physical scouring of a runnel, but yet it is the persistent, lower volume flows which are probably the most important for solutional attack. The second type of water source is of diffuse or sheet form. Where this is the case a series of rills, often closely packed, a network of interconnected meandering rills, or a single runnel with a number of headwaters develops. 171 Slope seems to be an important controlling factor in the geometry of the various runnel forms on sandstones as it is on limestone (Sweeting, 1972). Although this apparent relationship has not been quantitatively investigated, it appears that the steeper the slope, the higher the degree of runnel linearity and the lower the probability of intricate meandering runnels. On very steep surfaces wandkarren, sequences of parallel, medium to large, sharp-edged rills that shallow down slope, result from point overspill sources upon steep to near vertical rock faces. If the water is supplied from a diffuse source a series of close-packed rills or 'flutings' will form. 6.3. RUNNEL MORPHOLOGY Long-profiles and cross-sectional characteristics of a number of study area runnels were surveyed, and are presented in Figures 6.2 to 6.4. These surveys clearly show the compound nature of the runnel plan-forms, and the variability in cross-sectional shape. Ford and Lundberg (1987) presented data on the relationships of depth changes downslope from the channel head for limestone rundkarren on Vancouver Island, Canada, which clearly indicated that channel depth continuously increased downslope. It has already been noted that there is difficulty in differentiating between the two classic runnel types on Sydney Basin sandstones, and as Figure 6.5 conclusively demonstrates, runnels in the local area are different to those seen on the Vancouver Island limestones. There is no continual increase in runnel depth with length, rather depth initially increases away from the runnel head, but may then fluctuate dramatically in the central reaches before shallowing, either gradually or abruptly, and extinguishing. Observations of decantation runnels by Ford and Lundberg (1987) indicated a clear decrease in depth away from the runnel 172 Figure 6.2. Plan-forms, long-profiles and cross-sectional shapes of runnels on the quartzose equivalent of the Illawarra Coal Measures at Kanangra Walls. Water supply is from rainfall. The cross-sections have a vertical exaggeration of 1. > 173 Kanangra 3 Kanangra 4 Figure 6.3. Plan-forms, long-profiles and cross-sectional shapes of runnels on the quartzose equivalent of the Illawarra Coal Measures at Kanangra Walls. Water supply is from rainfall. Note the raised channel rims in the upper example. The cross-sections have a vertical exaggeration of 1. 174 Wingecarribee River 1 Wingecarribee River 2 j_ Metres Plan Figure 6.4. Plan-forms, long-profiles and cross-sectional shapes of runnels on the Hawkesbury Sandstone at Wingecarribee River. Water supply is from rainfall. The cross-sections have a vertical exaggeration of 1. 175 head, some at a faster rate than others. However, although none of the runnels shown in Figures 6.2 to 6.4 from the Sydney Basin are decantation type, they all eventually shallow and extinguish on the pavement surface in a similar manner to limestone decantation runnels. Scattergram 100 90 + Kanangra 1 80 - A Kanangra 2 • Kanangra 3 70 m o Kanangra 4 =• 60 - Q. CD +• Q 40 30 - + + A A 20 A A nn A A A 10 -«. 0 aa 0 —r+-1111 ^ i i —i— Scattergram 100 90 - 4 Wingecarribee 1 80 - A Wingecarribee 2 70 "§ 60 o_ £ 50 O- Q 40 30 20 1- A + 4- + 10 + A 0 -r—i-i-i-l+ A — 0.1 1.0 10.0 Distance from Head (m) Figure 6.5. Distance/depth relationships of runnels on some Sydney Basin sandstones. Runnels shown in Figures 6.1 to 6.3 from a quartzose equivalent of the Illawarra Coal Measures at Kanangra Walls and the Hawkesbury Sandstone at Wingecarribee River. 176 There is no published data of similar measurements from other quartz sandstones, so it is not known if similar relationships are found in sandstone runnels elsewhere. 6.4. DISTRIBUTION OF RUNNELS Runnels are very common on most sandstones of the Sydney Basin. The Nowra Sandstone displays many areas where runnel forms of various types are very well developed, and Monolith Valley and the upper Endrick River undoubtedly display some of the best of the runnel forms seen on this sandstone. However, at many other Nowra Sandstone areas on the Sassafras Plateau, for example at 'The Jumps' and around Bhundoo Hill (G.R. 505 058, Tianjara, 1:25 000, 8927-I-S) runnels are very rare. Low-angle sandstone outcrops at Monolith Valley are crossed by many fine examples of runnels with characteristics of each of the three classic types, rinnenkarren, rundkarren and decantation runnels. They occur in a wide range of sizes, from only a few tens of centimetres long and only several centimetres depth, to those which are many tens of metres long and tens of centimetres deep. All these runnels usually meander down slope, and commonly host a series of either flat or hemispherical floored basins. Often several runnels intersect and merge, with the resultant channel assuming a dendritic plan form. The rims of many runnels of all types here, and over the entire study area, are often slightly raised above the surrounding pavement surface. Whitlow and Shakesby (1988) noted that similar features on granites were clearly due to case hardening of the rim by precipitated silica, but there is no visible 177 difference between the upstanding rim and the sandstone further away from the runnels here. Weathered material within all Sydney Basin runnels is generally restricted to pebbles and larger sand granules from the host rock, and indicates a high degree of competence in at least the greatest periodic flows. Excellent examples of linear, 'u' shaped, wandkarren have formed (Plates 6.1 to 6.3) on virtually every cliff-line, tower, and large higher angle rock outcrop at Monolith Valley. These runnels are relatively straight, but may sometimes diverge or converge. The most common sources of water for these flutings are run-off from cliff tops often covered by patches of soil and vegetation, bedding planes and joints, or direct precipitation. The inaccessible location of these flutings has not allowed detailed study. Nowra Sandstone pavements along the upper Endrick River also display excellent runnels of various types, especially amongst the towers near G.R. 485 048, (Endrick, 1:25 000, 8927-IV-S), (Plate 6.4 and 6.5). As at Monolith Valley, it is often difficult to categorise these runnels into the classic types based on gross morphology because they generally exhibit features of supposedly differing modes of formation. It is usually, but not always, easier to differentiate decantation runnels from the other two types based on water source. Several locations on the Tianjara Plateau were also examined where heath, swamp or low woodland vegetation has been stripped from a number of pavements in the geomorphically recent past. These pavements would thus seem ideal places to find true rundkarren. Nonetheless, although some 178 Plate 6.1. Series of linear Wandkarren on the walls of a Nowra Sandstone tower at Monolith Valley. Plate 6.2. Runnels draining over a cliff edge at Monolith Valley. 179 Plate 6.3. A complex group of interconnecting runnels at Monolith Valley resulting in a 'Tray of Loaves'. Similar forms are quite common on the Nowra Sandstone. Photo, R.W. Young. Plate 6.4. A group of runnels beside the upper Endrick River which either drain from vegetation or have a direct rainfall water source. 180 runnels occur here they are relatively few, and the pavements themselves are very degraded with a very irregular surface. Rundkarren are almost never seen being exposed from a covering of soil or other material, and with those very few that are seen to be partly covered, it is normally apparent that they have been buried after formation and colonised by moss, lichen or other small plants. What appear to be classic, albeit shallow, rundkarren at Pointers Gap are shown in Plates 6.6 and 6.8, yet as the water source of these runnels is clearly swampy vegetation at the runnel head they therefore must be classified as decantation runnels. Clearly defined runnels are not common, and the general sandstone surface in this area is very highly pitted and irregular with generally poorly defined basins and drainage channels covering much of the area. Interestingly, however, opaline silica deposits found along the edges of one small group of slightly more clearly defined runnels (Plates 6.6 and 6.7), are generally uncommon in this region, but were reported from Zimbabwean granites by Whitlow and Shakesby (1988). This silica has undoubtedly precipitated from waters trickling down the runnels, and the low pH conditions within the swampy vegetation at the runnel head were probably important in the removal of the silica from the bedrock (Section 9.4.2.). Other partly sedge covered pavements further north on the Tianjara Plateau also displayed only poor to moderate runnel development. It was noted in the analysis of basin formation in Section 4.7.2. that swampy conditions with their low pH and abundant organic acids probably accelerate the lowering of virtually the entire pavement surface, and this has resultant consequences in the poor development of runnels. 181 • Plate 6.5. A complex |runnelled pavement amongst the towers Ibeside the upper Endrick River. Note the sandstone pedestal below the boulder in the centre mid-ground showing the minimum amount of pavement lowering, but the time taken for this is unknown. Plate 6.6. Shallow decantation runnels at Pointers Gap. The source of the water is swampy vegetation at the runnel head. The grey to white opaline rims are not common in the Sydney Basin. 182 Plate 6.7. Detail of the opaline rims of the runnel shown in Plate 6.7. Lens cap is 54mm diameter. Plate 6.8. Decantation runnels on the Nowra Sandstone at Pointers Gap. 183 Runnels are also quite common on the shore platforms around Jervis Bay. For example, on the Snapper Point Formation at Vincentia (G.R. 885 166, Huskisson, 1:25 000, 9027-IV-N) many well defined meandering runnels in excess of 10m long cross the platforms flowing toward the bay. Although numerous joint-controlled fissures or grikes are found in this area (Chapter 5), these runnels are not joint controlled. Where water flows from persistent seepage from the higher ground behind, decantation runnels occur. Virtually identical runnels are found across Jervis Bay on Beecroft Peninsula at Honeymoon Bay, Whale Point and Honeysuckle Point. Runnels are extremely common on the shore platforms above tidal limits, where they usually link chains of solution basins down slope. In these supra-tidal locations the runnels are generally very clearly defined with sharp rims and rounded or flat floors. Where the runnels cross onto sandstone that is intermittently covered by the tide they often acquire a more rounded cross- sectional form more akin to rundkarren than rinnenkarren. This change undoubtedly results from a more general weathering by longer periods of moisture contact and greater volumes of water flowing down the runnel. As was noted for solution basins in these marine locations, the much higher concentration of these features in marine locations is unquestionably the enhanced solubility of silica by dissolved salts. Snapper Point Formation sandstone at Blackall Rocks, on the western edge of the Sydney Basin, also displays a fine range of runnel forms, many linking large solution basins. Kanangra Walls, also on the western margin of the Sydney Basin, can also be noted as a further area of high grade runnel development. The sandstone here is a highly quartzose equivalent of the Illawarra Coal Measures (Herbert and Helby, 1980), and hundreds of runnels of all types are cut into it. One of these is shown in Plate 6.9 and 184 * Plate 6.9. A multi- headwater runnel at Kanangra Walls. Some water is supplied from the vegetation. Plate 6.10. Decantation runnel on the side of a Hawkesbury Sandstone tower at Bonnum Pic. A second similar runnel can be seen at the extreme left. 185 several others in Figures 6.2 and 6.3. It is again clear that possibly the majority of runnels in this study area display characteristics of both classic rundkarren and rinnenkarren. The Hawkesbury Sandstone also displays extensive runnel forms, for example, beside the Wingecarribee River, south of Mittagong, are many fine channelised sandstone pavements. Bonnum Pic also has numerous pavements where many runnels, often several to many tens of metres length, drain the tower sides. The topographic position of these runnels on the tower sides indicates that they must have formed subaerially, but once again they posess both the angular and more rounded characteristics of both rinnenkarren and rundkarren (Plates 6.10 and 6.11). Minor solutional features (pans, small runnels, etc.) are generally absent from the surfaces of the Upper Narrabeen Group sandstone pavements and pagodas, however, larger runnels are an integral factor in the shaping and erosion of the towers themselves. Whilst some major drainage runnels pick out the joint weaknesses, and are commonly deep, very narrow, vertical, often rubble filled clefts often graded to the valley bottom, by far the majority of runnels are not joint controlled. Of those drainage runnels which are not joint influenced (Plate 6.12), many are seen to meander down the sides of the towers. Most are con vex-up, and about 10 to 300cm in width. The floors of the runnels, and the general down-slope profiles are normally relatively smooth, but small steps are found as a result of bedding changes, usually on resistant iron layers. 186 Plate 6.11. Large tower- summit decantation runnel colonised by small trees at Bonnum Pic. Many much larger vegetated runnels are also found here. Plate 6.12. Large 1.5m wide runnel draining the summit of a Black Fellows Hand tower. There is no joint, and the tower is not large. 187 The friability of the pagoda sandstones was noted in Section 5.3.2, but as the catchment of the runnels which drain the ridges is not large, and is often effectively zero, total water input is only from the sides of the towers. The water volumes involved are therefore quite small, and a solutional origin for the runnels can be inferred, perhaps aided by corrasion under extreme rainfall events. 6.5. SANDSTONE HARDNESS AND RUNNEL DEVELOPMENT The variable distribution of runnels across the study region parallels the variability in occurrence of solution basins, with there being a similarity between the occurrence of runnels and that of basins. It is rare that runnels are found in locations where basins are absent, and basins are almost always found where runnels have developed. It seems, therefore, that some controls on the development of basins also influences the formation of runnels. Section 4.7.2 found that climate does not have a great effect in solution basin formation as Basin wide differences in temperature and precipitation are not great, but sandstone hardness or resistance to erosion, and the type of vegetation at a specific site, does appear to be significant in the formation of basins. It also seems just as important in the development of runnels. An identical relationship is seen between sandstone hardness, as tested with a Schmidt Hammer, and the relative degree of runnel development as that found in basin development (Section 4.8, Table 4.18). At the same sites listed in Table 4.18, very clearly defined runnels are seen where 'Excellent' basins are found (for example Wingecarribee River, Monolith Valley, upper Endrick 188 River, and all Snapper Point Formation sites), moderately well developed runnels re found at most Hawkesbury Sandstone sites, but they are generally either very well or very poorly developed on the Nowra Sandstone. The Blue Mountains and Newnes Plateau sandstones display a regionally poor development of smaller runnels, just as they do for basins, but quite large runnels are relatively common on the steeper sides of many of the pagodas. Runnels on low-angle sandstone pavements are generally absent. Sections 4.7.2 and 4.8 concluded that one of the prime factors in the location of solution basins is the local resistance of the sandstone to general surface denudation. The harder, or more specifically more resistant, sandstones require a longer time for erosion than do the softer sandstones before features on the surface are eroded by general lowering of the surface. Thus, runnels which have formed on the more resistant sandstones have a longer period in which to develop before the surface, and the developing runnel with it, is eroded 6.6. CONCLUSIONS The large number of runnels on Sydney Basin sandstones leaves no doubt that channelised flow of water across quartz sandstones produces forms similar to those on limestones. Excellent runnels exist on many of the study areas mechanically weak sandstones, but also on many of the more resistant sandstones. Formation of these features is therefore not just a function of erodability. Indeed, the locations of many of these runnels, and the small catchments they possess, indicate that water flow would be of too low a velocity to achieve much corrasion. Moreover, pitting of the channel floors indicates that chemical attack is the prime process. Concentration of water into discrete flows leads to increased solutional weathering within the 189 runnels, which in turn leads to further growth of the rill channel. This is a reinforcement effect similar to that proposed by Twidale et al. (1974). The classic morphological differences between rinnenkarren and rundkarren as seen on limestones, mostly in the form of either sharp or rounded runnel rims, appears, though, not to hold true for the sandstone runnels seen here. The differences in form between these runnels and their finer-grained limestone analogues, notably the compound variations along individual sandstone runnels, may not necessarily be due to differences in genesis, specifically sub-aerial versus sub-surface, but rather to micro variations in sandstone properties along the length of the runnels. It is possible that more resistant rock may lead to sharper rims, whilst slightly softer rock might erode faster resulting in a more rounded form. These ideas require further investigation, however, specifically by detailed petrographic study. Nonetheless, the use of the individual terms, rinnenkarren or rundkarren, for the sandstone runnels investigated here may be inappropriate. Further, the distinction between the assumed sub-aerial and sub-surface genesis in probably the vast majority of runnels here is obscure, for as already observed many runnels are found in positions for which sub-surface formation was impossible in the geomorphically recent past. Thus, the contention that rounded rimmed runnels only develop at the regolith-fresh rock interface must also be in error for the locations of many near-vertical, 'u' shaped, rills on the sides of cliffs or residual boulders, and atop large outcrops, bears no easily identifiable relationship to prior weathering fronts. Indeed, Watson and Pye (1985) go as far as stating that there is little evidence to support the contention that most runnel forms on crystalline rocks are the result of mechanical erosion or subsurface weathering. It is not argued here 190 that rundkarren and similar rounded features can not, nor have not, developed at the weathering front, for other authors clearly provide evidence that this is so elsewhere, but the reliance on this premise for explaining the majority of runnels found on bare crystalline and quartzose rock surfaces is undoubtedly unjustified. Concentration of waters on bare sandstone surfaces into discrete, confined, flows leads to an increase in the ability of the water to interact with the sandstone. Sub-aerial solutional weathering by concentrated linear flows is a highly significant, if not dominant, process in the formation of channellised forms on bare quartz sandstone surfaces within the Sydney Basin. Further microscopic evidence for this solutional weathering is presented in Chapter 11. 191 CHAPTER 7. SYDNEY BASIN SANDSTONE CAVES 7.1. INTRODUCTION The International Speleological Union defines a cave as a natural underground opening in rock that is large enough for human entry, but this is hardly a genetic definition. Ford and Williams (1989, p.242) give wider scope in their definition of a karst cave as "a solutional opening that is greater than 5 to 15mm in diameter or width. This is the effective minimum aperture for turbulent flow." Earlier chapters of this thesis have been concerned with surface forms, but now subterranean passages will be examined. A number of sandstone caves within the southern Sydney Basin have been discovered, some during this study, and range in size from small karst tubes less than 1 centimetre in diameter, to large active stream passage several metres in width and height. Examples will be drawn from this area beginning with the smallest and proceeding to the larger, enterable examples, and all of these features have parallels with those in limestone. Only true caves excavated through bedrock were examined; large overhangs, collapse, block glides, sea caves, and 'weathering' or 'wind eroded' caves, although extremely common in the area were not studied unless significant solutional weathering was apparent. In all cases carbonate within the bedrock is either absent or of levels not sufficiently significant to be the prime cause for cave formation. 7.2. SUBTERRANEAN CONDUITS Anastomosing or dip-oriented tubes, small conduits within a rock attributed in general to a state of water saturation in which slow laminar motion creates 192 interconnecting patterns of tiny tubes that fork and rejoin, are one of the first signs of concentrated, channelised, groundwater flow in limestone (Jennings, 1985; Dreybrodt, 1988). These conduits are generally only several centimetres in diameter and follow zones of weakness within the bedrock, often bedding planes or joints. A fossil subterranean drainage network of this type occurs in quartz sandstone at Tiger Snake Canyon on the Newnes Plateau (G.R. 442 208, Mt Morgan, 1:25 000, 8931-I-S). Geologically recent cliff collapse of Grose Sub- Group sandstones, that also form part of the external wall of the Tiger Snake Canyon Cave (Section 7.3), has revealed a complex network of interconnected tubes and other voids within the sandstone (Plate 7.1), many of which follow bedding or cross-bedding planes, or cut from one bed to another. This network is not like honeycomb or taffoni weathering, and in fact there is no such weathering of that type in the canyon nearby. Sandstone blocks which have fallen from the cliff also exhibit similar voids on faces that were internal before collapse. Within these voids the sandstone is markedly more friable than the surrounding rock, suggesting a localised removal in solution of cement and matrix. Moreover, a claystone layer exposed by the collapse also displays features very rarely seen on this rock type. Large concave, blister-like hollows in the claystones seem indicative of phreatic formation. The nature of this void network, which follows steeply angled crossbeds, and the general rounded to half-tube cross-sections, allied with the unusually eroded claystone, all point to a formation under phreatic conditions. Later deepening of the canyon would have lowered the local baselevel, draining the system, and subsequent collapse has revealed the network. The age of the collapse is unknown, but large trees have grown on the rubble suggesting it is 193 at least 50 to 100 years old. Modification and weathering is proceeding only slowly, and the cliff and rubble is still quite fresh. Another system of small dip-tubes identical in almost all respects to that just described was also discovered where it also been exposed by rockfall in a similar, inaccessible, position in the cliff wall of Claustral Canyon in the Blue Mountains (G.R. 594 823, Mt Wilson, 1:25 000, 8930-1-N). Other small sub-horizontal to sub-vertical karst tubes a few centimetres in diameter have been discovered during this study, but are different to those just described. These tubes are not laid open by rockfall, but rather the entrances of these tubes are exposed across sandstone outcrops and cliff walls. They are best seen within the Hawkesbury Sandstone at Bonnum Pic, Aherns Lookout ridge, and at Bundanoon (Figure 7.1). Close examination of the sandstone towers, pavements and slick-rock slopes of the crossbedded sandstone at Bonnum Pic (G.R. 47 04, Hilltop, 1:25 000, 8929-II-N) and nearby Aherns Lookout ridge (G.R. 602 017, Hilltop, 1:25 000, 8929-II-N) has revealed many of these small circular tubes. They are 1cm to 10cm in diameter, most extending in excess of 1.5m to 2m sub-horizontally back into the bedrock (the limit of measurement), and often, but not always, close to perpendicular to the rock face (Plate 7.2). The tube mouth is always the lowest point. Some of these tubes follow joints or dominant crossbeds, but in the large majority of cases appears to have no affinity with structural weakness within the rock mass. No water has been seen issuing from these tubes, as examination has always been in dry weather, but silt deposits and staining at the mouth of most indicates recent water outflow. 194 Figure 7.1. Locations of studied caves and speleothems on Sydney Basin quartz sandstones. 195 Plate 7.1. Network of interconnected tubes and other voids within the sandstone above Tiger Snake Canyon Cave. These voids follow bedding or cross-bedding planes, and cut from one bed to another. Plate 7.2. Entrance of a 10cm diameter tube in the Hawkesbury Sandstone at Bonnum Pic. This tube extends in excess of 1.5m back into the rock. Lens cap is 54mm diameter. 196 Identical tubes occur within the same sandstone at Bundanoon (G.R. 521 585, Bundanoon, 1:25 000, 8928-I-S), where a number over 0.5m long can be seen in slick-rock outcrops of white crossbedded sandstone. They again appear to be independent of crossbeding and other structural control. A larger, 15cm diameter, tube over 0.5m long has also been discovered here. Further tube entrances are seen nearby at Mt Carnarvon (G.R. 517 582, Bundanoon, 1:25 000, 8928-I-S), where one excellent example exposed by rockfall is up to 20cm diameter, over 3m long, and closely parallels the contemporary cliff. One can look through the tube from end to end. Another, smaller diameter, tube is found adjacent. These two tubes are both now inactive, but many other small tubes are located around the base of Mt Carnarvon, all of which have been seen to seep water during periods of rain. Many small tubes occur in the Nowra Sandstone of the Budawang Range, especially in the cliffs and towers of Monolith Valley (Section 5.2.1). Long surface stains and drapes originate from dozens of bedding planes, joints, tubes and small solution caves up to 0.5m in diameter (Plate 7.3, 7.4). These undoubtedly attest to a well developed network of subsurface water flow within the Nowra Sandstone. It has not been possible to closely examine many of these small caves due to their inaccessible location in the cliffs, but examination of accessible caves shows them to be similar to, if not larger than, those tubes found in the Hawkesbury Sandstone. The Yadbro Conglomerate below The Castle near Monolith Valley is also riddled with hundreds of tubes many metres in length, some of which are accessible for short distances. An excellent example, which is located beside the walking track to both Monolith Valley, has a large drape of silica cemented sand in its entrance. Long stains issuing from the mouths of tubes on the walls of Nowra Sandstone towers at Monolith Valley. Plate 7.4. Detail of the tubes shown in Plate 7.3. 198 Tubes of this type have not yet been found in the Snapper Point Formation sandstones, but similar, less well developed tubes are found along valley sides in the Narrabeen Banks Wall Sandstone at Butterbox Head near Mount Hay (G.R. 589 757, Katoomba, 1:25 000, 8930-I-S) in the Blue Mountains. Many of the bedrock canyons of the Blue Mountains and Newnes Plateaux, in both the Banks Wall and Burra-Moko Head Sandstones, also have similar tube entrances. Grand Canyon at Blackheath, River Caves Canyon on Budgary Creek, Deep Pass Canyon, Breakfast Creek and Rocky Creek are cases in point. Three excellent and large examples have been found in the walls of Whungee-Wheengee Canyon, Mt Wilson (G.R. 565 918, Wollangambie, 1:25 000, 8931-II-S), two with long water stains draping from their mouths. Further insight into the nature of these tube networks has been gained by the discovery of a dendritic network of branching and meandering tubes (Plate 7.5) exposed by lowering of a Hawkesbury Sandstone pavement at Bonnum Pic. This discovery is particularly significant for it unequivocally illustrates that these tubes form part of a larger integrated karst drainage network within the local sandstones. Remnants of the network, each of a metre or so length, are preserved atop small sandstone pedestals raised up to 10cm above the general sandstone surface level (Plate 7.6). They have been preserved because induration of several centimetres of sandstone by iron and silica has resulted in the tubes being more resistant than the surrounding sandstone. They clearly meander, branch and cut at shallow angles across numerous beds and crossbeds. These fossil tubes can be traced back into the rock slope to entrances of still active parts of the network that carry intermittent flows. Identical iron- indurated tubes are found exposed at Aherns Lookout ridge which can also be traced back into the slope to active tube entrances. 199 m » Mj, - — »» • ^t1 Plate 7.5. Remnants of a subterranean drainage network on pedestals above the Hawkesbury Sandstone slopes of a Bonnum Pic tower. Plate 7.6. Detail of a section of the tube network shown in Plate 7.5. Lens cap is 54mm diameter. 200 The tubes have a roughly circular cross-section, often still with a hole 1cm to 2cm diameter down the centre. This circular cross-sectional shape, associated with the evenly distributed induration, seems to indicate the tubes formed and were wafer filled during a period of phreatic activity below the local water table which is now many tens of metres lower. It has not been possible to date these fossil tubes, but there is no doubt that, as water issues from most other tubes during periods of heavy rain, there still exists at this level an intermittently active, now vadose, karst network within these sandstone masses. There are no previous local descriptions of fossil, or active tubes in sandstones of the Sydney Basin, but there is no reason to assume that these systems are extraordinary. Their discovery in several widespread locations suggests they may in fact be relatively common. The sandstone in which they have been found is typical of much of the Hawkesbury Sandstone, and water movement along joint and bedding planes within the local sandstones is well known (Young and Young, 1988, 1992). These tubes may just be a more developed example of this phenomenon. At a slightly larger scale, although not yet considered to be caves under the International Speleological Union definition, are a number of other local features that also exhibit unequivocal channelised underground water movement. Three types of subterranean flow are recognised: transmission of the entire base-flow of a creek through bedrock under dominantly vadose conditions to re-emerge at a lower point, capture of only a part of a creeks baseflow under dominantly vadose conditions to re-emerge at a lower point, and transmission of the entire base-flow through a bedrock barrier under phreatic conditions. The first two of these are usually associated here with 201 areas of high hydraulic gradient (often a nickpoint), whilst the third is associated with sites of lower hydraulic gradient. Although none of these conditions are overly common, a number of instances can be provided from the study area that are analogous to those on limestones. An example of the first is a small sandstone cave of 3m length on the Bargo River at Mermaids Pool (G.R. 795 085, Picton, 1:25 000, 9029-V-S). Here the base of a pothole intersected a weakness (apparently a bedding plane) along a steep bedrock reach of the river. Subsequent enlargement of the weakness (under conditions of which solution was undoubtedly important as turbulent through-flow would not yet have been attained) and the removal of granular sand has resulted in the capture of the entire base flow through the cave. Similarly, at a small 3m waterfall along Raynon Brook in the Blue Mountains (G.R. 579 838, Mt Wilson, 8930-I-N, 1:25 000) the entire normal flow sinks through the creekbed to pour from a bedding plane about 1.5m below the lip of the falls several tens of metres downstream. Another small cave of this type has been discovered that occurs in the Nowra Sandstone on a tributary of the upper Endrick River near G.R. 485 048, (Endrick, 1:25 000, 8927-1V-S). This creek flows through a shallow bedrock canyon about 5m deep to sink in a small 20cm wide slot in the bed. Water is seen again 3.5m horizontally away flowing at the base of a large 2m diameter, 3m deep pothole, and then disappears underground again for a further 8m until it reappears resurging as a small waterfall 0.5m above a deep bedrock pool (Figure 7.2). The total vertical drop from the sink to resurgence is in the order of 3m. In normal flow, all water goes underground. During flood conditions the old bedrock course across the top of the cave undoubtedly becomes active. 202 Partial underground piracy, or the second type of underground flow, is also found within the region. Below a 15m high waterfall on Lizard Creek, in the Cataract Dam water catchment area (G.R. 032 130, Appin, 1:25 000, 9029-I-S), is a large overhang from which pour a number of small streams of water that have penetrated more than 10m down through the sandstone from the creek above. A similar sequence of events has also occurred in the Blue Mountains at Empress Falls, Valley of the Waters, where a portion of the creek flow, this time at a 30m high waterfall exiting a deep, narrow hanging canyon, resurges from a slightly lower bedrock conduit several tens of metres to the side of the waterfall. In the northern cliff of Bungleboori Creek canyon (G.R. 526 045, Rock Hill, 1:25 000, 8931-II-N), on the Newnes Plateau, a large spring occurs at the intersection of a near horizontal bedding plane and a near vertical joint. Some water from the creek, which is quite steep in this reach, has been diverted along the bedding plane for over 40m and gushes from the wall in a 2+ metre high cascade where it intersects the joint (Plate 7.7). Total subterranean phreatic capture or diversion, the third type of underground flow, has also developed at a number of locations. Along one section of Lizard Creek (G.R. 031 128, Appin, 1:25 000, 9029-I-S), the entire normal creek flow exits a large Hawkesbury Sandstone pool by an unknown underground route, re-emerging 40m downstream. There is no surface flow between the sink and rising. On the Newnes Plateau a similar active cave occurs where Nayook Brook drops 2m over a waterfall into a deep pool in the narrow bedrock Deep Pass Canyon (G.R. 486 072, Rock Hill, 1:25 000, 8931-11- N). This pool also has no exiting surface flow (Figure 7.3), but the water is again seen in another similar sized bedrock pool 5m downstream from which 203 Figure 7.2. Underground flow in the Nowra Sandstone along a tributary of the upper Endrick River. This creek flows through a shallow bedrock canyon to sink in a 20cm wide slot. Water is seen again 3.5m away flowing at the base of a 3m deep pothole, then it reappears as a small waterfall. v l I 1 I I V Plan Metres Figure 7.3. Underground flow in Deep Pass Canyon. Water flows 2m over a waterfall into a deep pool which has no exiting surface flow. The water is again seen in another bedrock pool 5m downstream from which the creek resumes a normal surface course. 204 Plate 7.7. Spring in the wall of Bungleboori Creek canyon on the Newnes Plateau. 205 the creek resumes a normal surface course. An old surface channel is visible, but a conduit has been formed below water level which now carries all base flow. A similar, but much larger example, is found in Arethusia Canyon on Katoomba Creek (G.R. 537 723, Katoomba, 1:25 000, 8930-I-S), in the Blue Mountains. Here flow of a much larger stream than at Deep Pass Canyon leaves a pool by passing under a large, solid sandstone barrier about 3m high to re-emerge about 10m downstream from no obvious point. An almost identical example is found on the Nowra Sandstone on the Endrick River, close by the other small cave mentioned earlier. Water flowing over a 2 to 3m waterfall into a pool passes underground for 20 to 30m to reappear again in a large deep pool. The river here passes beneath several large, 4m diameter, potholes incised in the bedrock the walls and base of which are solid sandstone, but no water flows through them (Figure 7.4). Figure 7.4. Subterrainean flow of the Endrick River through the Nowra Sandstone. Water flowing into a pool passes underground for 20 to 30m to reappear again in a large deep pool. The river passes beneath several large, 4m diameter, potholes incised in the bedrock the walls and base of which are solid sandstone, but no water flows through them. 206 7.3. SANDSTONE CAVES A number of larger cave systems big enough for human entry, also occur within the study area. These caves are of variable origin, most contain active streams, but are usually larger, more developed, examples of the smaller features just described. Undoubtedly the finest example of a sandstone cave within the Sydney Basin is the Natural Tunnel at Hilltop, south of Sydney, (Figure. 7.5) (G.R. 698 977, Hilltop, 1:25 000, 8929-II-N). This is a active stream cave 85m long and 2m to 10m wide in the Hawkesbury Sandstone with entrances at both sink and rising. This cave is comparable in all aspects to sandstone caves reported from the tropics. The cave descends at a gradient of 3 to 5°, with an almost planar sloping roof of dipping sandstone. The stream meanders across a bedrock floor, dropping over a small lm.waterfall about 2/3 through the cave, and over a larger 3m waterfall into a plunge pool below a large sandstone overhang at the downstream entrance. A bedrock canyon which extends for several hundred metres downstream of the cave may mark the former extension of the cave. Pavey (1972a,b) described the cave as forming along a very thin bed of weakness between two sandstone members intersected by the stream. The weakness was slowly enlarged, finally becoming the dominant stream path, leaving the surface streambed dry. Thereafter the stream continued cutting down into the sandstone enlarging the cave. It has been suggested (Pavey, 1975) that this plane of weakness was a shale layer between two sandstone members, but this is not obvious within the cave. 4 tintll HtttrUtI Y-\-m DEVELOPED LONG SECTION n.agneiic 1372 .trvj.n COnttnUiii CROSS SECVIDNS ^•' djnn wndtton* a^oo '.4 ' urni$ion» orortiMng :k lamjt down ctiif t*c9 into ctityon NATURAL TUNNEL HilLlU?. NSW Sutvtyod b, Andrew Pivsy,Rhonda Boldiug.Petet Doivnii, Gsny M«cn on 9-4-72 u(inj tripod mounted ftirflilry compm: Dud libnqitB && • lo CRU 5 0. Cinnouliiicm end rjiawing try Andra* Ftv«y 19-6-72. marrai THE UNIVERSITY OF NEW SOUTH WALES SPELEOLOGICAL SOCIETY R.F.. !;5C0 tikck to Thltl$nyar» Hilltop ro+a Box 17,1 hi Union, UNiW, K«:ulngtcn, 2033 Figure 7.5. The Hilltop Natural Tunnel. Sowrce: Pavey (1972a). 208 Two other caves similar to the Hilltop Natural Tunnel have been reported in Hawkesbury Sandstone, one along Cowan Creek at Ku-ring-gai Chase north of Sydney (Shannon, 1963; Pavey 1974) but the exact location of this cave is unclear and few detailed descriptions exist. The second is Endless Cave at Kincumber, near Gosford, and is 35m long extending back from an overhang 7m wide, 4m deep and 2m high (Pavey, 1975; Jennings, 1983). All three of these caves have formed as the result of concentrated water flow and weathering along a structural weakness in the sandstone, which has then enlarged into the surrounding rock mass. The Narrabeen Group sandstones also have a number of caves, most being on the Blue Mountains and Newnes Plateaux. Fossil networks of large rounded 'tube' shaped caves lined with hard oxides of iron are found within the Banks Wall Sandstone at Leura in the upper Blue Mountains (Osborne and Branagan, 1992) (G.R. 528 668, Katoomba 1:25 000, 8930-I-S). Osborne and Branagan (1992, p.101) noted that "These probable solution structures may be related to the extensive iron concretions which occur in the western Blue Mountains. The concretions, which are the result of iron migration, ("Liesegang patterns"), often take the form of pipe-like bodies up to lm in diameter. A combination of solutioning and direct erosion of poorly cemented sand grains from within such concretions seems to have occurred." These tubes thus appear to be much larger versions of the iron-indurated tube networks found in the Hawkesbury Sandstone at Bonnum Pic. Osborne and Branagan (1992) also state that similar caves occur in this area, but no further details are available. Several other sandstone caves are located on the rugged Newnes Plateau. Deep Pass Cave is located below a large cliff along Nayook Brook, a major 209 tributary of Rocky Creek (G.R. 495 076, Rock Hill, 1:25 000, 8931-II-N), where a small perennial stream emerges from impenetrable holes at the back of the cave, which is in the order of 20m long, and flows out the lower entrance. Extensive cliff collapse is found outside the cave, but it appears that the cave itself has formed along similar lines to the Hilltop Natural Tunnel, through weathering and erosion of a band of weakness within the sandstone, and the enlargement by weathering of the resultant void into the sandstone. Wilson (1991) reported the discovery of a similar sandstone cave nearby in the Rocky Creek area. This cave (Figure. 7.6) (G.R. 459 116, Rock Hill, 1:25 000, 8931-II-N) "consists of a long, medium sized passage ... composed entirely of sandstone. These passages are similar but larger than that of the sandstone cave at Leura, however, not as long. In total there would be 40 to 50m of passage ... Small formations are visible and the cave is partly solid rock and partly in rockpile ... The cave is not formed by an overhanging cliff" (Wilson, 1991, p.6). Extensive search failed to locate this cave. A slightly different type of large cave has been found in Tiger Snake Canyon (Wray, 1994) (G.R. 442 208, Mt Morgan, 1:25 000, 8931-I-S). This cave is 30m long, 5m wide and from 0.5 to 2m high (Figure 7.7), and formed by weathering and erosion of a 1.5m thick claystone bed within the Burra-Moko Head Sandstone, with subsequent weathering and enlargement into the sandstone both above and below the claystone. However, unlike the other caves in the study area, this erosion occurred at the base of the canyon wall forming a deep overhang. Collapse of part of the undermined cliff resulted in the sealing of most of the external opening and the formation of the dark zone. Apart from the external wall of collapse blocks, the cave is formed in solid bedrock. This cave parallels the canyon bottom and a small perennial I Figure 7.6. Sketch of Rocky Creek Cave. Source: After Wilson (1991). Figure 7.7. Tiger Snake Canyon Cave. 211 stream flows through the cave from a narrow slot at the back. Notwithstanding the fact that the cave does not wholly pass through solid rock, extensive secondary deposition of silica speleothems within the cave indicates much movement of silica from the surrounding bedrock, which makes this site highly significant, and is discussed further in Ch 8. Extensive evidence for complex solution voids in the overlying bedrock was presented in Section 7.2. 7.4. FEATURES ADJACENT TO THE STUDY AREA It is necessary here to briefly mention one significant sandstone formation just outside the study area which is at least party solutional in origin. Slaven Cave, near Wallerawang, N.S.W, (G.R. 786-976, Meadow Flat, 1:25 000, 8831-11- S) is a single large natural underground chamber developed within Devonian quartz sandstone and entered from a small doline. The geology and geomorphology of the cave has been described by several authors, and was reviewed by Young and Wray (1994). The cave has two small natural entrances below a small sandstone cliff at the southern end of a medium- sized almost circular doline that measures about 25m N-S with a width of around 20m. The lowest point on the rim is to the NE and is about 4m above the cave entrance. The southern rim is a small 5 to 6m high sandstone cliff, whilst the northern and northeastern walls are degraded with the bedrock covered by surface sediment and regolith. This doline is a locally uncharacteristic feature for this type of bedrock, but nonetheless is of essentially the same form as those developed within limestone. Below the entrance is a single chamber about 35m in diameter and about 10m in height. The walls are solid bedrock, and the floor rockfall. 212 Several processes including subjacent collapse, shrinkage into an ore body, hydrothermal processes, and chemical weathering of a carbonate-rich host rock have been invoked to explain this cave, but none can be fully reconciled with the known geological evidence. Young and Wray (1994) showed, with S.E.M and petrographic evidence that direct chemical solution of the silica has resulted in intense etching and degradation of the quartz-rich bedrock. This work supports the idea first proposed by James (1988). Thus it now seems that removal of silica in solution, similar to that found in many other sandstone caves, was an important process in the formation of Slaven Cave. 15. CONCLUSIONS Interconnected voids found within the quartz sandstones of this study region demonstrate the existence of a well-ordered subterranean hydrologic network, and have parallels to those found in limestones. They are also very much like the cave systems described from quartz sandstones of other temperate regions, and especially those reported from the tropics (Section 2.3). A number of discrete types of void network have formed, under both phreatic and vadose conditions, and most continue to carry perennial, or at least intermittent, water flow. The smallest of these are now abandoned, but bear a great similarity to small, interlinked, lithologically controlled, anastomosing dip- tubes very commonly seen in limestones. Slightly larger drainage systems within the local sandstones are rounded tube like networks, which unlike the dip-tubes, are not constrained by structural or lithologic factors. Entrances of these tubes are seen across sandstone outcrops at a number of locations within the study area, and carry water flow after prolonged rain. These tubes display a meandering and dendritic nature. Whilst complex underground water movement within sandstones, even 213 within this region, was not previously unknown, such concentration of flow into discrete, highly organised, conduits has only rarely been previously reported. Larger, normally structurally controlled, drainage systems are also found within the study region. Three types have been recognised, and water flow through these systems, either phreatic or vadose in nature, is generally controlled by either joints or bedding planes. True sandstone caves are also known in this area, but are of a simpler plan-form to the networks examined earlier. The formation of these caves is more complex than the smaller systems, generally involving enlargement into the surrounding sandstone by both corrosion and corrasion under conditions of turbulent stream flow. The removal of silica in solution from the local quartz sandstones by groundwater is the only way in which the smaller of these subterranean conduits could have developed. But even the larger cave systems, where turbulent flow has been attained and thus where both solution and corrasion have both become significant, must have passed through such a solution- dominated stage in their growth. Study of the development of these caves must, therefore, look at the processes of removal of silica from the sandstone. These processes will be considered in Chapter 11. 214 CHAPTER 8. SPELEOTHEMS OF THE SYDNEY BASIN SANDSTONES 8.1. INTRODUCTION Speleothems are secondary mineral deposits of various composition formed primarily of mineral precipitates from groundwater solutions. They are most prolific in carbonate caves, where a range of forms of widely varying chemical composition has been described (Sweeting, 1972; Hill, 1976; Bogli, 1980; Jennings, 1985; Hill and Forti, 1986). Although silica-based speleothems have been described only comparatively rarely (Section 2.9), a variety of speleothem types were noted in association with quartz sandstones of the Sydney region during the course of this study. These include flowstones, stalactites, stalagmites, and coralline forms. Coralline stalactites are the most widespread, although flowstones are not uncommon, and stalagmites are rare. Speleothems of other non-carbonate minerals, notably iron, are also relatively common. Speleothems occur on all quartz sandstones in the region, but in this study most were observed in the Grose Sub-Group sandstones in the Blue Mountains, the Hawkesbury Sandstone and the Nowra Sandstone (Figure 7.1). Although they are very small they are highly significant because they provide unequivocal evidence of the importance of the solution (and subsequent deposition) of silica in these sandstones. 215 8.2. SILICA FLOWSTONE Chemical reactions in fluids high in dissolved minerals flowing as a thin film over a surface often results in the deposition of solid material from solution. This occurs under both vadose and phreatic conditions and is associated with a shift in the chemical equilibrium of the system. In limestone caves thin films of water high in dissolved calcium carbonate have a high surface area and give off C02, resulting in the crystallisation of calcite as flowstone (Bogli, 1980). As silica concentrations in groundwater are rarely as high as that of calcite, silica is not conducive to thick flowstone accumulations (except near hot springs). Nonetheless thin silica skins are common on some quartz sandstones (Watchman, 1992). They are surface films or layers, generally less than 1mm thick, and form on stable sandstone and quartzite surfaces (Watchman, 1990). They are physically robust, can vary from transparent to opaque, or range in colour from white to almost black, depending on the chemical composition and proportion of included organic matter. It is immediately apparent that although silica skins are widespread, they are not ubiquitous, but are restricted to places where the siliceous substrate can be leached, the silica transported to the rock surface, and then redeposited upon a nearby surface. Microscopic evidence indicates that the silica is deposited onto a sandstone or silica skin surface from rocks higher on a cliff face rather than being derived from the grains and matrix of the sandstone directly underlying the skin (Watchman, 1990). Sites with well-developed flowstones are listed below. Samples from a number of these have been studied in detail, but are also apparently representative of the wide range of other locations. No reaction to dilute HC1 216 was observed with any of the hand specimens, suggesting the flowstones contain little carbonate, and no carbonate was seen in thin-section. Sandstone Unit Location Area Site Location Snapper Point Formation Beecroft Peninsula Mermaids Gulch Nowra Sandstone Wandandian Wandian Road Sassafras Plateau Upper Endrick River Upper Narrabeen Group Blue Mountains Plateau Fortress Creek Canyon Blue Mountains Plateau Mt Hay Canyon Newnes Plateau Deep Pass Cave Newnes Plateau Tiger Snake Canyon Cave Newnes Plateau Hole in the Wall Canyon Hawkesbury Sandstone Bundanoon Mt Carnarvon Hilltop Hilltop Natural Tunnel Table 8.1. Locations of well-developed flowstones. At Mermaids Gulch on the Beecroft Peninsula (Jervis Bay) (G.R. 033 237, Currarong, 1:25 000, 9027-I-N) a thin coating of secondary material was found on a vertical cliff cut in the Snapper Point Formation. This grey flowstone exhibits the same small gour-like structures, 0.5mm to 3mm in diameter, arranged perpendicular to water flow, as is commonly seen on calcite flowstone. Microscopically this flowstone (TS12553) is composed of light grey to dark brown isotropic opal-A of high relief that often shows fine bands 0.01mm to 0.2mm in thickness, but is more commonly non-banded and massive without any particular microscopic structure. A similar white flowstone occurs on the cliffs of Upper Narrabeen Grose Sub- Group sandstones in Tiger Snake Canyon (G.R. 442 208, Mt Morgan, 1:25 000, 8931-I-S). Microscopically (TS12554) this flowstone is almost colourless to dark brown, isotropic, of high relief, and composed of opal-A. It is clearly banded (Plate 8.1), individual layers ranging from 0.01mm to 0.5mm in thickness. The 217 surface of the flowstone is irregular, whilst the banding is seen to parallel the sandstone surface below the flowstone. Successive layers can be seen to cover and smooth out some of the previous surface irregularity, and small gour-like features are seen on the contemporary flowstone surface. Another portion of this flowstone is also seen to be opal-A, dark-brown in colour, massive to slightly banded, and of high relief. However, this section is much thicker (lmm to 12mm), and of much greater porosity. It contains many sand grains of a wide range of sizes. Small gours are also seen upon this flowstone surface. The Wandian Rd flowstone (G.R. 638 127, Sassafras, 1:25 000, 8927-I-N) is white, but in thin-section (TS12555) showed both colourless and dark-brown, isotropic, highly banded layers 0.1mm to 2mm in thickness. The colourless material often appears fibrous, is of low relief, and is identified as chalcedony, whereas the brown material is opal-A (Plate 8.2). There is a much higher proportion of light-coloured chalcedony here than in either of the two other flowstone samples. Numerous tiny, irregular, dark flecks of organic material are scattered throughout the flowstone, as they also are in the Mermaids Gulch and Tiger Snake samples. The rock below all of these flowstones is often very porous, but as the flowstones have sealed the surface it is clear that the source of the flowstone material was not from directly below the skins. The outer flowstone surfaces are hard and presumably have lost some water of hydration from the opal, creating a shell of denser material overlying a more hydrated interior (cf. Hill and Forti, 1986). Plate 8.1. Cross-section photomicrograph of the Tiger Snake Canyon Cave flowstone (TS12554). Note the distinct layering of light grey to dark brown high relief isotropic Opal-A that shows fine bands 0.01mm to 0.5mm in thickness, and the small gour-like structures, 0.5mm to 3mm in diameter, on the surface arranged perpendicular to water flow. Blue dye indicates void. Field of View, 3.95mm. Plate 8.2. Cross-section photomicrograph of the Wandian Rd flowstone (TS12555). The highly banded 0.1mm to 2mm thick, fibrous and colourless, low relief material is chalcedony whilst the brown high-relief material is Opal-A. Blue dye indicates void. Field of View, 3.95mm. 219 Watchman (1992, 1994) found organic material, algal filaments, bacterial and plant fatty acids, and carbonised plant remains encapsulated within opaline silica skins at an aboriginal art site at Gnatalia Creek, near Wandandian south of Nowra, and close to the Wandian Rd site studied here. This carbonaceous material was believed to be of synsedimentary origin, incorporated into the silica skins by later silica layers. Accelerator mass spectrometry (AMS) 14C analysis of this organic material extracted from dark and white portions of a silica skin up to 1mm thick showed a progression of increasing age from near the surface toward the base. The surface and basal layers of the skin were discarded to avoid contamination. The top of a dark layer returned an age of 825 ±55 years (AA7726), whereas the base of this dark layer was 8 265 ±85 years old (AA7728). The bottom of an underlying white silica layer formed 11 235 ±85 years BP (AA7727) (Watchman, 1992). These results were seen to "demonstrate that organic substances on the rock face at Gnatalia Creek were incorporated into silica skins at different times ... Silica skins started to form more than 11,000 years old (sic) and are continuing to form today" (Watchman 1992, p.65). The range of dates is also in agreement with petrological and field evidence from this site which suggests that the silica skins formed continuously over a long time period. Earlier AMS dating of similar silica skins at this site was attempted by McDonald et al (1990), the results suggesting that the start of silica skin formation at Gnatalia Creek was at about 29,795 ±420 years BP (AA5851). This date indicates that silica was being mobilised when temperatures were 5° to 6°C lower than the present (Galloway, 1965; Colhoun, 1991). 220 8.3. SILICA STALACTITES Three distinct types of silica stalactite have been identified forming on quartz sandstones within the Sydney Basin. The first is similar to the typically cylindrical or conical form most frequently associated with stalactites. The second, but even more common type, is similar to the erratic coralline speleothems first described by Swartzlow (1937). The third type, silica 'popcorn', is a sub-group of the second. Again it is impossible to list all observed occurrences of silica stalactites observed during this study, suffice it to say they are locally common across the entire region and detailed reference will therefore only be made to a small number of locations. 8.3.1. Conical or Cylindrical Stalactites Thin, elongate stalactites, similar in many respects to those found in limestone caves have been noted at a number of locations across the Sydney Basin. These stalactites posses a conical form, and generally taper gently from the base to the tip. In all references here, the base is that part attaching to stalactite to the surface from which it hangs; the 'base' is therefore usually the portion furthest vertically from the ground, and the 'tip' is closer to the ground than the 'base'. These stalactites are much smaller than most of their carbonate relatives, typically in the order of 1 to 35mm in length, and from 0.5 to about 3mm in diameter. They are often near circular in section, but more oblate to irregular sections are commonly seen. They tend normally to have a quasi-regular section along their length, although this decreasing in cross- sectional area from base to tip. This type of stalactite is seen to form in protected locations, and are most commonly seen growing from the roofs of sandstone overhangs of all sizes. They are not found under every overhang, one prime requirement being that 221 the roof of the overhang is hot actively eroding. They occur in tight clusters or may be scattered evenly across the roof of the overhang, but do not concentrate along lines of obvious groundwater seepage, along fractures or joints. Conical stalactites appear to be best developed on the Hawkesbury Sandstone, excellent examples being seen in a cave near Mt Carnarvon, Bundanoon, at the Hilltop Natural Tunnel (Section 7.3), in a number of small overhangs in the Lower Blue Mountains. They also occur on the quartz sandstones of the Upper Narrabeen Grose Sub-Group on the Blue Mountains and Newnes Plateaux, with excellent examples being located in Deep Pass Cave, Tiger Snake Canyon Cave (Section 7.3), and in a small overhang above Wallaby Tail Canyon near Newnes (G.R. 465 283, Mt Morgan, 1:25 000, 8931-I-S). They have also been observed in the Nowra Sandstone along the upper Endrick River, and in the Snapper Point Formation at Beecroft Peninsula. Small conical stalactites only several millimetres long from a large overhang cave in the Hawkesbury Sandstone near Mt Carnarvon at Bundanoon were collected for study by Scanning Electron Microscope (S.E.M), optical and thin- section microscopy, X-ray diffraction (X.R.D) and chemical assay. Under S.E.M imaging the surface of the stalactite was seen at low power (65X magnification) (Plate 8.3) to be generally smooth, but at higher magnification (536X) (Plate 8.4) it was obvious that the surface was composed of numerous small overlapping, asymmetric, irregularly spaced 'plates' or 'flecks' of material of various sizes, ranging from about lfim to over 15|im a-axis length. These flecks are much thinner in c-axis than in either a- or b-axis. They layer the surface and overlap significantly to form a scaly skin exhibiting little apparent permeability. Numerous larger lumps composed of near-spherical 222 Plate 8.3. S.E.M image of a stalactite from Bundanoon Cave. The surface is covered by many small flecks of silica and several larger 'blobs', shown in detail in Plate 8.4. Plate 8.4. Enlarged S.E.M image of Plate 8.3 of a stalactite from bundanoon Cave, showing the silica flecks and some desiccation cracking. 223 or irregular accumulations of minute silica plates or flecks identical to that of the rest of the stalactite are scattered across the surface. Some cracking of the surface is also seen which may have resulted during collection or transport, but most probably represents desiccation shrinkage at some stage during the speleothems growth (cf. Hill and Forti, 1986). The elemental composition of these flecks, and that of the general stalactite surface, was determined by S.E.M energy dispersive X-ray analysis spectra (E.D.A.X), which indicated an overwhelming dominance of silica (Figure 8.1), with only a very minor presence of aluminium and possibly a trace of potassium associated with clays. In cross-section the interior of this stalactite was seen with the S.E.M to be similar to the external surface, being composed of tiny, irregular, densely packed flecks, with very little apparent void space, bordering on crypto- crystalline. No layering or banding suggesting alternating phases of stalactite growth was observed. In optical thin-section (TS12552) several stalactites from the same cluster were seen to be composed of isotropic, high relief, dark grey to red-brown amorphous opal-A, with some colourless, fibrous, low relief chalcedony. However, contrary to what was indicated by S.E.M imaging, polarised light shows that most of the central portion of these stalactites are highly banded, and composed of many alternating layers of opal-A, 0.007mm to 0.15mm in thickness, displaying a distinct wavy structure (Plates 8.5 and 8.6). There is no central hole down the axis of the stalactite, through which water could flow 224 Plate 8.5. Long-section photomicrograph of a Bundanoon Cave stalactite (TS12552). It is composed of isotropic, high relief, dark grey to red-brown amorphous opal-A, with some colourless, fibrous, low relief chalcedony. Individual wavy layers are 0.007mm to 0.15mm in thickness. Blue dye indicates void. Field of View, 3.95mm. Plate 8.6. Enlarged long-section photomicrograph of the Bundanoon Cave stalactite of Plate 8.5 showing complex variability in layering of opal-A and chalcedony. Blue dye indicates void. Field of View, 1.11mm. 225 The external 1/5 to 1/4 of the speleothem is composed of a higher proportion of the light-grey opal-A. Banding toward the external surface of the stalactite is less distinct, but is still visible, and banding is more distinct toward the tip. Large pieces of black, organic material are embedded in the stalactite and covered by layered material, as are several quartz sand grains. Full Scale= 1024 Si Bundanoon Cave Stalactite r J.01 20.48 keV Figure 8.1. Bundanoon Cave stalactite S.E.M E.D.A.X. spectrum. The stalactite surface is composed of a high proportion of silica and only a minor amount of aluminium and possibly a trace of potassium associated with clays. Gold peaks result from a conductive coating. Finlayson and Webb (1985) argued for the use of X-ray powder diffraction (X.R.D) in the identification of the phases of silica present in stalactites. The X.R.D spectra of these stalactites, Figure 8.2, shows a broad diffuse hump centred around 25° (2-Theta (20), angle) (approx. 3.6A) that is diagnostic of amorphous opal-A. This peak is here shifted from its normal position an occurrence also observed by Finlayson and Webb (1985, p.4), "the centre of the broad, diffuse peak characteristic of opal-A may vary slightly in wavelength, from a normal position of about 4.1-4.3A to as low as 3.7A". 226 Ifl (1)1010«>IOC\J*TOCOTCQCO*T fcicNirvjcvjcMcococoroTM-TV CM >>nai(DoiDijio)ioNsso r w n ^ o r- c\jr- co U\ i- c 01 D) (O ID IM O f- r- O ID O) to N in c O IX) 03 O CO o tn o) rvj a> rvj ro 'u NOIIDOKINI-IDT-I-NO m"Tcoa)coTrcoc\jc\jocno> rt Q. co co co c\i c\i c\i c\i c\i cvi rvj v-' ^ CD _0J Q. E rt 25 c 0 0 c rt •a c CD % ^ m CN o o o o O CN o o O o O o o o •"3- Uos c~ in m CN 227 Multiple peaks produced by crystalline minerals appear on the trace of Figure 8.2, but identification of these minerals was problematic. Therefore qualitative X-ray fluorescence (X.R.F) was conducted, revealing the presence of a very large amount of silica, a significant fraction of sulphur and aluminium, a little iron and a small amount of calcium. But even with the knowledge of this component chemistry, exact mineral identification from the X.R.D spectra was difficult. The peaks appear to correspond to a mixture of kaolinite and/or muscovite clays, possibly an aluminium sulfate, and/or alunite or anhydrite. More precise identification was not possible, and further study of the composition of these stalactites is hereby warranted. The bulk of the material is, however, amorphous opal-A, and crypto-crystalline chalcedony. 8.3.2. Coralline Silica Stalactites The more common silica speleothems in the Sydney Basin are very delicate and unusually irregular stalactites. They are generally found in patches ranging from less than 0.1m square to several metres square, and in all orientations with respect to the roof, walls or floor of the overhang or cave. The name 'coral' is the only appropriate term for this type of formation (Salzer, 1954). They almost never occur where active granular disintegration of the walls or roof is occurring, but are not restricted to protected cave environments, for they are also found on the walls of sandstone cliffs, and below overhangs, in caves and canyons. All that appears necessary is some modicum of protection from physical damage, and good air circulation. Nonetheless, not all potential locations are host to coral development, and coral does not occur in by far the majority of potential locations. Coralline silica examined in this study bears a remarkable resemblance to calcite cave coral commonly found in limestone caves. The silica speleothems 228 tend, however, to be smaller and more angular. Bogli (1980), stated that calcite coralline forms could be "cauliflower-like, or show small, connected balls of calcite, sometimes arranged like a clump of grapes, single stemmed fungoid formations, or branched stems (coral-like) formations" (p.194), and he justifiably grouped coral with helictites and heligmites as erratic speleothems. Swartzlow (1937) also described branched opaline stalactites resembling small acicular spikes a fraction of a millimetre to about 5mm long. Coralline silica stalactites of the current study area are similar to that described by both Bogli and Swartzlow in that they are dendritic in form (Plates 8.7 and 8.8) and protrude from the walls or roof of the cave or overhang. They are 'cauliflower-like', with short stems and spiky, radiating branches; and they show small connected balls of material, or are of a variety of other irregular shapes. From each stem further, smaller, stems also radiate, and themselves in turn also branch into smaller stems. Along some stems short, acicular spines occur. These stalactites vary in diameter from less than 0.25mm to about 8mm, and, when free-hanging, from less than 1mm to about 70mm in length. The largest measured coral stalactites, which are over 75mm in length, are in Claustral Canyon in the Blue Mountains. Tiger Snake Canyon Cave (Section 7.3) contains the most prolific collection of silica stalactites seen within the study area (Plate 8.9). More than 50% of the roof of this 30m long, 5m wide cave is totally covered with large and small silica coral. As is the case with conical stalactites, joints or other pathways for accelerated groundwater movement do not play an important role in the distributional clustering of coralline speleothems. Patches of coral growth are only rarely seen to be aligned with such pathways, but most commonly are equally distributed over visually homogenous sandstone. This distribution is 229 Plate 8.7. Coralline stalactite from Tiger Snake Canyon Cave. Coin is 23mm diameter. Plate 8.8. A cluster of coralline stalactites from Tiger Snake Canyon Cave. Photo is the same scale as Plate 8.7 230 Plate 8.9. Clusters and individual coralline stalactites on the roof of Tiger Snake Canyon Cave. Photo, Brett Moule. 231 indicative of movement of source water moderately high in dissolved silica through the bulk of the rock mass, and not necessarily along preferential zones of enhanced permeability. The colour range of observed coralline stalactites is variable, from pure white to dark grey to almost black, with grey shades the most prevalent. In a small number of cases it is seen to be a light yellow to yellowish brown, presumably due to the influence of small amounts of dissolved iron compounds. Cleaning of a number of light grey samples with dilute Hydrogen Peroxide indicated some of this surface colouration is due to organic material; oxidation of this surface material resulted in the speleothems displaying a light brown colour. Some colours are therefore due to surface accumulations, not to mineral deposits. Several coralline stalactites representative of their type were examined in detail. These samples were collected from prolific concentrations of such stalactites from Deep Pass Cave (G.R. 495 076, Rock Hill, 1:25 000, 8931-II-N) (Section 7.3), and from the roof of Tiger Snake Canyon Cave (G.R. 442 208, Mt Morgan, 1:25 000, 8931-1-S) (Section 7.3), on the Newnes Plateau, and from an overhang in Fortress Creek Canyon, near Katoomba (G.R. 547 748, Katoomba, 1:25 000, 8930-I-S) in the Blue Mountains. They were all in in-situ growth positions before collection, and there is no reason to suspect that any are in any way significantly different to those others found with them. These caves all lie within the sandstones of the Grose Sub-Group. Plate 8.10 shows that the surface of a coralline stalactite from above the Deep Pass Cave is microscopically irregular with may voids. Higher magnification, 232 Plate 8.11, show this surface to be composed of numerous overlapping, randomly oriented, asymmetrical, and irregularly spaced plates or flecks of material of various sizes, ranging from about lum to over 15|im a-axis length. These flecks are poorly packed, resulting in incomplete filling of space and a consequent high porosity. The surface of a 19mm long stalactite from Tiger Snake Canyon Cave was also seen to be similarly composed of minute randomly oriented and poorly packed plates. E.D.A.X spectra (Figure 8.3) of both stalactite surfaces indicated the bulk of the material to be silicon. A significant amount of aluminium was also identified, along with traces of potassium and chlorine. There is possibly a small amount of iron in the Deep Pass sample, but only silica and aluminium was detected in the Tiger Snake Cave stalactite. These stalactites are thus almost wholly silica. The small amount of aluminium has undoubtedly been derived from the kaolinitic clays within the overlying sandstones, and the potassium was presumably also derived from illite weathering in the sandstone. Unlike the parent rock, which showed well developed clay structures under S.E.M, no identifiable clays were seen in S.E.M images of any of the speleothems. S.E.M imaging shows that the Deep Pass stalactite is composed throughout of tiny overlapping flecks of silica exhibiting a high percentage of void space. The imaging gave no visible indication of concentric zoning or banding attributable to successive stages of stalactite growth, but areas of contrasting density within the speleothem were revealed (Plate 8.12, 191X). Most of the internal region is of similar structure to that of the highly porous surface, but 233 • *• - \ k \ * J* $ ' Plate 8.10. S.E.M image of the irregular surface of a stalactite from Deep Pass Canyon Cave. The surface is composed of many irregularly packed silica flecks and shows much void. 4 :<^V4.''^- \ * -~*L-**;*> 4 * >:$*, \ *'* fc •-*•. S V *"•*• •"• r.^ C^;^JS , * Ifc^A, # EHT=20.00 kV Mag= 1.00 K X Plate 8.11. Higher magnification of Plate 8.10 S.E.M image of the irregular surface of a stalactite from Deep Pass Canyon Cave. The surface is composed of many irregularly packed silica flecks. 234 Full Scale= 4096 Deep Pass Cave Si 1 Au XI Fe V » *nw n»>naii %IM>II.I^- -| | ,,•,, i i n -——A^- .01 10.24 keV Full Scale= 4096 .01 10.24 keV Figure 8.3. S.E.M E.D.A.X traces of the Deep Pass Cave stalactite, they show an overwhelming dominance of silica and only a minor presence of some aluminium, potassium and chlorine probably associated with clays. Gold peaks result from a conductive sample coating. 235 some is of much lower porosity and is composed of much more densely packed flecks. Much of the inside of the stalactite even appears to be crypto- crystalline. S.E.M imaging revealed that the Tiger Snake Cave stalactite is different to the one from Deep Pass. Plate 8.13 (218X) shows that much of the inside of this stalactite is quite massive, similar to that seen for only a portion of the Deep Pass stalactite. Although there is some void space in that from Tiger Snake Cave, there is less than that seen in the Deep Pass Cave sample. There is also much more evidence for secondary infilling of void by deposition of silica. Higher magnification of the Tiger Snake Cave sample revealed the crypto- crystalline nature of the silica, presumably chalcedony. E.D.A.X showed a major silica peak as in previous specimens, but only a tiny aluminium peak (Figure 8.4). Samples from Deep Pass Cave, Tiger Snake Canyon Cave and Fortress Creek were also examined in optical thin-section. A 27mm long stalactite from Deep Pass Cave (TS12548) was seen to be composed of a mixture of fibrous, colourless, low-relief chalcedony, and dark grey-brown, high-relief, isotropic opal-A (Plate 8.14). Some light and dark banding, 0.02mm to 0.25mm thick, is mainly concentrated toward the centre of the stalactite. The stalactite is very porous, but again there is no continuous central hole through which water could move There are numerous inclusions of dark organic material, and colourless quartz grains. 236 Plate 8.12. S.E.M image of a cross-section through a stalactite from Deep Pass Canyon Cave. Note the contrasting density of material of the crypto- crystalline material above-left of centre compared to the rest of the stalactite. Also note the lack of a central drip-water hole, and little indication of layering of material. Plate 8.13. S.E.M image of a cross-section through a stalactite from Tiger Snake Canyon Cave. Note the higher proportion of crypto-crystalline material compared to Plate 8.12. Also note the lack of a central hole, and little indication of layering of material. 237 Plate 8.14. Long-section photomicrograph of the Deep Pass Cave stalactite (TS12548). The highly banded 0.02mm to 0.25mm thick, fibrous and colourless, low relief material is chalcedony whilst the brown material is Opal-A. Blue dye indicates void. Field of View, 3.95mm. 238 In cross-section the stalactites display the same layering, with concentration of the light to colourless chalcedony around the centre, surrounded by the layered dark opal-A. Included dark organic material is common, and there is no indication of a central channel, although some scattered voids are seen. Full Scale= 819 Tiger Snake Cave Stalactite Si iAu A .01 I *-. 20.48 keV Figure 8.4. Tiger Snake Canyon Cave stalactite S.E.M E.D.A.X. spectra. The stalactite is composed of a high proportion of silica but only a minor amount of aluminium. Gold peaks result from a conductive coating. The Tiger Snake Cave stalactites are of much lower porosity than those from Deep Pass Cave, being composed only of isotopic, dark brown to red-brown opal-A (TS12547) (Plate 8.15). The central portions of the stalactites are highly banded, many displaying a distinct wavy or crenulated structure. There is no central hole down the axis of the stalactite (Plate 8.16), but void space, sand grains and dark organic inclusions are commonplace. The outermost layers of the stalactites are composed of a higher proportion of darker material than the centre, and the wavy, crenulated banding is distinct right to the external surface. Banding at the very tip often breaks down into a massive agglomeration of dark-brown material with many inclusions. 239 * >Ph < \ ifr' * Plate 8.15. Long-section photomicrograph of the Tiger Snake Canyon Cave stalactite (TS12547). The highly banded fibrous and colourless, low relief material is chalcedony whilst the brown material is Opal-A. Blue dye indicates void. Field of View, 3.95mm. Plate 8.16. Cross-section photomicrograph of the Tiger Snake Canyon Cave stalactite (TS12547). The concentrically banded fibrous and colourless, low relief material is chalcedony whilst the brown material is Opal-A. Blue dye indicates void. There is no central drip-water hole. Field of View, 3.95mm. 240 The 17mm long stalactite from Fortress Creek (TS12549) lacks the defined layering, and has a significantly higher proportion of void space than that at Tiger Snake Canyon Cave. Organic material is common, as are a few small included sand grains, but in most other respects the two are very similar. Bulk-sample powder X-ray diffraction analysis was also performed upon stalactites from all three locations. The Deep Pass Cave and Fortress Creek stalactite X.R.D traces (Figures 8.5 and 8.6) show a broad, diffuse peak, with a relative intensity of about 950 counts centred around 21° to 24° (20 angle) corresponding to amorphous opal-A (cf. Jones and Segnit, 1971), which has shifted slightly from its normal position. The maximum intensity is here seen near 3.8A (23.4°). Superimposed upon the trace for opal-A are a number of sharper, more intense, peaks produced by crystalline material within the samples. These peaks are unambiguously identified as those produced by quartz and dickite/kaolinite-type clays. The quartz X.R.D pattern has prominent peaks at 3.34A (26.6°) and 4.26A (20.8°) (Finlayson and Webb, 1985), and several smaller peaks at shorter wavelengths. These peaks are all clearly identified on both these X.R.D traces, and are undoubtedly chalcedony. The occurrence of chalcedony is also consistent with the S.E.M observations of areas of higher local density of crypto-crystalline appearance within the stalactite, and the colourless, fibrous material seen in thin-section. Numerous other peaks are also clearly identified upon both traces. Although a number of these have an intensity only just above the opal-A background, especially in the 20° to 35° region of the spectra, they are nonetheless clearly identifiable as belonging to Aluminium-Silicate-Hydroxide, Al2Si205(OH)4, clays. The presence of these dickite/kaolinite clays is consistent with the high kaolinite clay content of the host rock. 241 LoO a s Opal- A rtO) NO(OONN07(BO(00(ONN •S —. COlnTCOcaCDeOOr-CDCQ'r'TOtO O) co -^r in ID cvi in iri to co ai oi co iri f~ .— \_l 1— ".J ^J H) Vkf VM HI Ul Vkl WU Ul *.M identifie d ?=5 [MNNNwwnnwoncoT °»< phou s CM in Cfi *H •^r am o 0) m o in in *r o rovinr~-coTOcocn minera l > m ID CD co r- m o CNCNCNCOCNCNC\IT-T- oa d c (1) g£ QC a; S D c 13 •£ 4-1 o O MJ11DN OlSNONt-NNOON C n oi eo co N lOi-OIOnNr-NOCO 'o 03 W1 C|O -~ N^ j 1-^ 7NlnOIOIMc ^ o f th e trac e on y (Q ) an d K a , D _ tf> >1 CD CN X ^rt in ^ «^ ^ OJ N ftO'& O o O O O o O o o CN Uoa C-M w 242 . o in Z< 0) PH m• i-H O ±j en fO CD CN O COCOCQOOCOCOOO CO CO CO T O CO «T CN CO fl> B =". m«°. m N cn iq co r- oq in co r>- in *r q m r- u> P 3 o i- n ^r ui 4-n< ^ a >-, D c MPS T3 _ m .! oCJ CN X S vO. X"< 3 ooU « £ 3 S •£ o CN o o • o o o o o o 1 en CN O O 3 C*- 10 243 . o in So rf a) 5 cn *— —* 1 U o 5J H N o co co ID co «r >•* £5 oi oi co co cq a oi in N pi, CM"* d *r iri ID cd CN CM N CM CM IM CM P) 1 <3 o 3 6 CM co in o oi m N a c3 o> co r- r- •q- co CN 6 cd QJ *- tr = X O &* OI U ~ C u CO cn CO m T— r^ in . CN m *r CO o r- i— Q. T CO CO CO CO CM CN cn - s j_. QJ CO VH _0J rll «3 Q. ra E OJ n> T5 rj cd in •2 .in™ C cn O p 6 OJ L— tn ra h ai U D § CD ^ r o i cn of / cu u rd QJ r-l -1-1 in a J" CN o O cd T3 x C CO P 01 C cd o •5H n* cd a ^ . o o O o o CN o o o o o o o cn CN a T( 3 O 3 c~ ui 244 The Tiger Snake Cave X.R.D trace (Figure 8.7) was different, however, with the only identifiable mineral present being opal-A. The broad amorphous peak of this opal-A was centred around a low 23° with a relative intensity of about 1050 counts (slightly higher than that for Deep Pass Cave and Fortress Creek, presumably because of the higher proportion of amorphous silica). Diffraction peaks of crypto-crystalline silica and kaolinite clays could only just be identified above the opal-A background on this spectra. This was unexpected in the light of the S.E.M observations of the crypto-crystalline nature of much of a similar stalactite from this location, and illustrates the local variability in speleothem composition. 8.3.3. Silica 'Popcorn' Globular or semi-spherical erratic stalactite forms, 1 to 10mm in diameter and length, are also very common in this area. This globular family contains many varieties, and ranges from single speleothems growing from a wall or other speleothems, to lines or patches one globule deep, and even to great patches many globules deep and resembling bunches of grapes. These clusters may be tightly packed, and many layers deep. There is no typical shape for popcorn-like speleothems found in this area, except that they are globular, cauliflower-like and erratic. Microscopically, they are essentially the same as those coralline stalactites examined. They are composed of poorly packed, irregular, silica flecks, and display a high porosity. They are all apparently composed of opal-A, no evidence was seen for crypto- crystalline chalcedony. 245 8.4. SILICA STALAGMITES Unlike coralline stalactites, silica stalagmites are much rarer, with no previous reports of them from this area having been found. They have only been observed by this author in a small number of localities within the Sydney Basin; both Tiger Snake Canyon Cave (Plate 8.17) and the overhang cave along Fortress Creek Canyon contain the best examples of this type where they are developed upon silica flowstones Other good examples occur in a small overhang above Wallaby Tail Canyon near Newnes. They are physically different from the silica coralline stalactites often found growing above them. They typically take the shape of low hemispherical to irregular mounds, and are more squat and bulbous, and also generally lack the intricate fine branching of the stalactites. The outer skin of some stalagmites are hard, presumably due to the loss of water of hydration within the opal. They look a little like the example shown in Figure 1 of Swartzlow and Keller (1937), and range in size from about 0.2cm to 10cm in diameter and 0.5cm to 5cm in height. There is, however, no direct cause and effect relationship between coralline stalagmites and coralline stalactites above them, as is often seen to be the case with calcite stalactites and stalagmites. If water drips from a stalactite or even plain rock, it does not necessarily form a silica stalagmite below. Indeed it is most common to see stalactites without stalagmites beneath them, and stalagmites are sometimes seen that have no stalactites above them. A 25mm high, 12mm diameter, grey-brown silica stalagmite from an overhang in Fortress Creek Canyon, near Katoomba (G.R. 547 748, Katoomba, 1:25 000, 8930-I-S) was analysed by both X-ray powder diffraction, and optical There is NO p. 246 in original document 247 •*>J^Ax 3&' ' • 1 • It fi lr - • • j > •F r Plate 8.18. Long-section photomicrograph of the Fortress Creek stalagmite (TS12551). Top is to the right. It is composed of banded, 0.1mm to 1mm thick brown to red-brown isotropic opal-A of high relief alternating with fibrous to granular transparent low-relief chalcedony. Blue dye indicates void. Field of view, 3.95mm. Plate 8.19. Enlarged long-section photomicrograph of the Fortress Creek stalagmite (TS12551). This enlargement of Plate 8.18 clearly shows the layers of transparent low-relief chalcedony. Blue dye indicates void. Field of view, 1.11mm. 248 o in en cd < i 'cd QJ OH • 1H <4-i • rH O 4-" en .C rOr-CM^WIDNcOoi^lDSffloidlMlri • i—i SScNCNCNCNCNCMCNCNCNMCOCOMCO^'T'S m en JH CM T O 'cd £ QJ cd TCMinoiOr-cncM •»-cH T3 S CN o o o o o o o o o o o en CN o O O 3 C-«- 1/1 249 thin-section microscopy. The X.R.D trace (Figure 8.8) showed this stalagmite, like the stalactites, to be composed dominantly of opal-A, crypto-crystalline quartz, and dickite/kaolinite clays. The location and intensity of the broad opal-A peak is in an almost identical position to that seen for both the Fortress Creek stalactites and Deep Pass Cave stalactites reported above. It may also be noted that for this stalagmite the quartz peaks are generally more intense, whilst the clay peaks are of similar, or of slightly greater, intensity to those seen in both the Fortress Creek and Deep Pass Cave stalactites. In thin-section (Plates 8.18 and 8.19), this stalagmite is composed of fine to broadly banded, 0.1mm to 1mm thick, light to dark brown to red-brown isotropic opal-A of high relief alternating with fibrous to granular transparent low-relief chalcedony (TS12551). Embedded within the stalagmite are common inclusions, either of dark brown amorphous lumps, up to 0.3mm diameter arranged parallel with the banding and which appear to be organic material, or numerous small to medium sized transparent quartz sand grains. The more intense quartz X.R.D peaks in this stalagmite than the stalactites may be due to this slightly higher proportion of included quartz sand, but the incidence of chalcedony is also visually higher than in any of the stalactites. 8.5. SPELEOTHEM CARBONATE, ORGANIC MATTER AND WATER CONTENT The presence of significant carbonate minerals within these silica stalactites and stalagmites was tested for with dilute 8% w/w HC1, and in no case was a reaction observed. The lack of carbonate was further confirmed by both E.D.A.X, X.R.D spectra, and thin-section study. 250 A local oddity worthy of mention, however, is Palona Cave, a medium sized overhang in the Hawkesbury Sandstone in the Royal National Park (GR 189 207, Otford, 1:25 000, 9129-IV-S). The only real difference between this overhang and the thousands of others like it are the large calcium carbonate stalactites, stalagmites and flowstones (Plate 8.20). Silica speleothems are absent here. The calcite originates within the Hawkesbury Sandstone, but why the calcite levels here are so high is unknown. Calcite deposits of this size are not known elsewhere in this sandstone. Site Initial Weight (g) Final Weight (g) Percent Combustible Fortress Creek 22.29 21.35 4.40 Stalagmite Fortress Creek 21.56 20.77 3.67 Stalagmite Deep Pass Cave 23.23 22.44 3.52 Stalactite Deep Pass Cave 23.52 22.54 4.34 Stalactite Tiger Snake Cave 21.86 21.33 2.48 Stalactite Tiger Snake Cave 21.79 21.29 2.34 Stalactite Fortress Creek 26.25 25.27 3.87 Stalactite Fortress Creek 26.63 24.96 6.69 Stalactite Table 8.2. Loss on ignition of silica speleothems. The proportion of included organic material, water and other combustible matter within the silica speleothems studied here was determined by loss-on- ignition, 1 hour at 700 °C. The proportion of combustible material is variable, but generally is in the range of 2 to 4.5% of the total speleothem weight. In reality these values are probably too low as natural total water content would be higher than indicated here. Samples had been air-dried in storage before combustion, and significant water was also lost in transport after collection as indicated by condensation inside the sample bag. The results do show, 251 Plate 8.20. Large phytokarst carbonate stalactites from Palona Cave, Royal National Park. 252 however, that significant organic material is incorporated within the stalactites, as are significant amounts of water either in liquid form, or incorporated in opal-A. 8.6. FORMATION OF SILICA SPELEOTHEMS Unlike calcite stalactites, stalagmites, and to some extent helictites, which have been well studied (Sweeting, 1972; Ford and Cullingford, 1976; Bogli, 1980; Jennings, 1985; Ford and Williams, 1989; and others), silica stalactites, stalagmites and coralline forms have only been reported in a very few locations and their formation is not well understood (Swartzlow and Keller, 1937; Urbani, 1976; Zawidzki et al, 1976; Jennings, 1979). Successive rings or layers of opaline material deposited around a central speleothem axis were observed by Anderson (1930), Swartzlow (1937) and Urbani (1976), indicating that these silica speleothems, had an increase in size by silica accumulation on the outside. Similar evidence of concentric layering was found in this study of flowstones, stalactites and stalagmites. All specimens studied are constructed of thousands of small, irregularly packed, flecks of opal-A commonly surrounding a central core or discontinuous zones of crypto-crystalline chalcedony. There is no regularity or layering seen under S.E.M imaging, but crenulated, wavy banding of light and dark material is clearly seen in thin-section. Observations by Urbani (1976) showed that there was, more often than not, no fine channel through the length of the stalactites he studied. Identical results were obtained here, and it is immediately obvious that silica laden water does not flow from a central hole as in calcite straw stalactites (Ford and Williams, 253 1989). Furthermore, the small size of many of these coralloid formations precludes formation by the process of drip-water deposition (either via central hole or external flow). Curl (1973a) showed by theoretical calculations, backed by basic experimental results, that the minimum diameter for regular calcite straw stalactites is approximately 5.1mm, and Hill and Forti (1986) cite straw stalactite diameters of 2 to 9mm. The minimum equilibrium diameter of calcite stalagmites is in the order of 3cm (Curl, 1973b; Ford and Cullingford, 1976). The diameters of the smallest parts of most silica coral formations found in this region are much smaller than that possible for growth by drip- water processes, and coralline speleothems must thus form by an alternate mechanism to phreatic deposition. Evaporation of mineral-laden water from the outside of the stalactite is one such process, and evidence of tiny droplets of water upon the outside of local speleothems including branches of coral has been noted by this author on many occasions. Flow of drip-water along these speleothems has never been observed. Carbonate coralline erratics have been explained as "deposits due to the evaporation of water ascending capillarily" (Bogli, 1980, p.194). Evaporation of capillary films of silica laden groundwater as opposed to calcite, is here believed responsible for the formation of coralline stalactites, stalagmites and flowstones. Opaline silica precipitates upon evaporation of water by the following reaction (Hill and Forti, 1986): H4Si04(aq.) -> Si02(amorph.) + 2H20 (1) Amorphous silica (opal-A) is metastable at low temperatures. Under normal conditions amorphous opal precipitates more readily than crystalline silica from supersaturated solutions, but, over time this opal may gradually transform to the more stable chalcedony or even quartz (Urbani, 1976; Hill and Forti, 1986; Morse and Casey, 1988). Quartz and chalcedony may also 254 crystallise directly under high-temperature conditions (Hill and Forti, 1986), or from sea water (Mackenzie and Gees, 1971), but this has not occurred locally. Martini (quoted in Hill and Forti, 1986) has also suggested that direct precipitation of quartz under low-temperature conditions is possible, but notes that it requires a rapid rate of crystallisation from solutions well above the saturation level for quartz (at least several hundred ppm). With an initial condition of high saturation, concentration by evaporation is not required, and the deposition of opal is precluded (Hill and Forti, 1986). Although this may occur in the speleothems studied here, possibly from solutions supersaturated with silica as a result of extreme evaporation concentration, no evidence for such high levels of dissolved silica can be produced (see Chapter 10). Water extruded from micro-fissures or from between grains of the sandstone bedrock migrates by capillary action to the surface of the stalactite or coral and is evaporated slowly from the surface. This process is easily reconciled with the observed evidence of the tiny silica flecks, which are presumably left behind once all water evaporates. This process also accounts for the random packing of the flecks. Concentration of water at the end of a stalactite branch or other surface irregularity by capillary forces leads to deposition of silica at that point, with subsequent lengthening of the branch. Deposition is thus often concentrated at specific locations, rather than extending over much of the surface. It is nonetheless apparent, that there must be reasonable evaporation rates for these speleothem to form. Most locations (cliffs, canyons, and caves) where they are found have reasonably consistent air movements which are conducive to evaporation. Also the rate of water supply must not be too great, 255 that is, on average a greater than or equal to rate of evaporation over water supply. Otherwise sufficient evaporation could not take place, and instead solution of stalactite material would occur. The great dominance of stalactites over stalagmites is easily explained by the more common percolation of water down through the sandstone and the action of gravity in assisting capillary flow down the outside of the stalactite from a source above. In stalagmites, however, capillary forces must draw water against the force of gravity up through the sandstone and then through the stalagmite itself. Flowstones form where silica-laden water flows across or down a surface. A general model summarising these main aspects of silica speleothem growth is outlined in Figure 8.9. Figure 8.9. Simplified model for evaporative silica speleothem development. 256 Here, as in any natural chemical system, both the forward and reverse reaction (solution and precipitation) may both occur at the same time. Nonetheless the possibility that the bulk of these stalactites and stalagmites initially form as crypto-crystalline material, and that later intense re-solution of silica leaves the highly porous opal-A network, seems hard to accept from the observational evidence. No irregular etching pits or other corrosion features are seen on the silica flecks, nor are there any other features diagnostic of intense silica removal. Indeed, within the more massive crypto- crystalline zones numerous points are seen where it appears that voids have been subsequently infilled with silica. Apart from the few silica flowstone ages of Watchman (1994) (Section 8.2), no absolute ages for these local speleothems are available, and thus the rate of accumulation of silica is as yet essentially unknown. The relationship of the banding to speleothem development is thus also not yet clear, neither is the period of time or conditions necessary for the formation of the chalcedony. This work contrasts with the reports of Lassak (1970), who argued that speleothems from the Hawkesbury and Upper Narrabeen sandstones were composed "of laminar limonite" (1970, p. 11), but supports that of Watchman (1990,1992), Young and Young (1992) and Young (1987) who found silica to be the major component of these speleothems. No limonite in the speleothems studied here has been observed, although iron-based speleothems (stalactites, stalagmites and flowstones/tuffs) are found in many places in this region. In conclusion, it must again be emphasised that the character and composition of silica speleothems both demonstrates, and throws much light 257 on the detail of, the movement of silica through the quartz sandstones of the Sydney Basin. 258 CHAPTER 9. THE CHEMICAL WEATHERING OF QUARTZ SANDSTONE 9.1. INTRODUCTION Although karstic phenomena on silicate rocks have been reported for at least 60 years, little attention was given to the detailed study of the solutional processes involved because it was widely believed that most silica-rich rocks (notably quartzite and quartz sandstones) are, unlike limestone, "practically immune to chemical weathering" (Tricart and Cailleux, 1972, p. 152). Goldich's Scale of relative rates of chemical weathering indicates that quartzite and quartz sandstones are about as resistant to weathering as granite, twice as resistant to chemical breakdown as most volcanics and shales, nearly five times more resistant than most metamorphics, and over ten times more resistant to chemical attack than carbonates (Summerfield, 1991). Nonetheless, as documented in Chapter 2, if sandstone solutional landforms are compared in detail with limestone karst, there is very little difference in landform morphology or in the genetic processes involved. Indeed, the recent discovery of large scale solutional features, underground drainage networks, and large cave systems has shattered the classic view of karst formation being unconditionally restricted to 'soluble' rocks (Young and Young, 1992). The significant difference is that in silicates the removal of material by dissolution is restricted to about 10 to 20 percent of rock bulk, compared with the 80 percent or more with most carbonate rocks (Martini, 1979). Thus to explain these large, and often well developed karst terrains found on quartzites and quartz-arenites it is necessary to understand the 259 processes which lead to the removal in solution of that critical 10% to 20% of the bulk rock. 9.2. SILICA SOLUBILITY AND CHEMICAL KINETICS Much investigation into the solubility of silica in water has been based upon thermodynamic principles. It must, however, be noted that, although "thermodynamics is a powerful tool for elucidation (of) geological phenomena where equilibrium is normally attained ... many geological processes are controlled by reaction rates so that they can only be understood in terms of kinetics. Such a situation is illustrated by reactions at low temperatures in the silica-water system" (Rimstidt and Barnes, 1980, p.1683- 4). Thus the kinetics of the reaction or the rate of the solution process may be just as important, or even more important, than the total solubility of the reacting species. Furthermore, reaction rates between silicates and fluids near the Earth's surface are slow enough for fluids to be often out of equilibrium (Brady, 1992), and thus silica-water interactions may not always proceed as would be expected. Martini (1979) also emphasised that as water may flow off a surface without having achieved saturation the kinetics of dissolution, more than the solubility itself, may be important. 9.3. THE SOLUBILITY OF SILICA The solubility of silica under natural conditions is low compared with that of carbonate. The rate of chemical weathering of quartzose rocks is thus much slower than that of many other rocks. Yet compounds of silica are present in all natural waters, either as suspended solids, as colloids, or in solution (Aston, 1983). This silica is released by the weathering of the 260 numerous silicate minerals, only very little originating from direct solution of quartz (Henderson, 1982). In its simplest form, the congruent dissolution of silica can be written (Brady and Walther, 1990) as; 2H20 + Si02(qtz) -» Si(OH)° (1) This Si(OH)4 monomer is the main form of dissolved silica (Iller, 1979), and generally exists as uncharged silicic acid, H4Si04, under near-neutral pH conditions. The silicic acid monomer, Si(OH)4, in natural aqueous solution tends to join or polymerise with other Si(OH)4 units to form hydrophilic acids (Sin02)n_m (OH)2m or hydrophobic amorphous silica Si02.xH20 (Yariv and Cross, 1979). However, the weathering of silicate minerals usually leads not to congruent, but to incongruent dissolution, and the formation or precipitation of various solid phases. The weathering of potassium feldspar, for example, results in the formation of silicic acid in solution and kaolinite clay (Aston, 1983); + 4KAlSi308 + 22H20 -> K + 40H" + Al4Si4O10(OH)8 + 8H4Si04 (2) But concerned as we are here with quartz sandstones and quartzites, only the more pure forms of silica, not the myriad complex silicate minerals, are of immediate interest. 9.4. NATURALLY OCCURRING PURE SILICA Pure silica occurs naturally as eight distinct forms. Five of these show crystalline structure (quartz, tridymite, cristobalite, coesite, and stishovite), 261 and three are amorphous (amorphous silica, opal-A and lechatelierite) (Krauskopf, 1956; Yariv and Cross, 1979). The abundance of the eight allotropes of silica in the geologic environment is not equal. Lechatelierite is a silica glass and very rare, as are coesite and stishovite which are found only in meteorite craters (Yariv, 1979). The other five silica polymorphs are quite common, with quartz probably being the most abundant. It is the geochemistry of these forms of silica that has attracted most attention, but as noted by Siever (1962), in the study of sedimentary rocks the only silica species of real interest are ordinary quartz, opal-A and amorphous silica. 9.4.1. Solubility of Natural Forms In any discussion of the solubility of silica one must clearly distinguish between the different silica polymorphs, for they do not have the same solubility (Siever, 1962), and indeed silica is "unique in the enormous difference in solubility among its polymorphs" (Krauskopf, 1956, p.5). Experimentally determined equilibrium solubilities of amorphous silica and quartz have been often quoted, but as Krauskopf (1956) warned, the often contradictory pre-1956 studies on the low-temperature solubility of silica, were generally limited by the sluggishness of the reaction and the great stability of silica sols. Krauskopf (1956) reported from later research that amorphous silica is soluble to the extent of 60 to 80 parts per million (p.p.m.) (or milligrams per litre, mg/1) at 0°C, 100 to 140 p.p.m. at 25°C, and about 300 to 380 p.p.m. at 90 °C. Siever (1962) also found the equilibrium solubility of amorphous silica at 25 °C to be between 120 to 140 p.p.m., with the solubility in sea water being approximately the same as in distilled water. Yariv (1979) too reported the solubility of amorphous silica to be 60 to 80 mg/1 at 0°C and 100 to 140 mg/1 at 25°C; and he noted that at equilibrium the solubility of quartz is in the range of 6 to 14 mg/1 for Earth surface temperatures. In cold, neutral-pH groundwaters silica concentration usually 262 does not exceed 20 to 30 mg/1, but at higher temperatures silica concentration increases and has been seen, although very rarely, to reach thousands of mg/1 in some hot springs (Serezhinikov, 1989). Limestones are generally regarded as being much more soluble than silica. However, in pure water the most calcite (CaC03) that can go into solution is only about 13 mg/1 at 16°C and 15 mg/1 at 25°C (Jennings, 1985), only slightly higher than quartz. The greater frequency of limestone solution relies on the fact that most natural waters contain acids, notably carbonic acid from dissolved carbon dioxide, and this raises the solubility of calcite drastically, generally into the range of 250 to 350 mg/1 at normal temperatures (Jennings, 1985). The degree to which silica in its various forms is naturally soluble in water is also influenced by a number of factors, including the state of the silica, whether it is in a crystalline or an amorphous form, the pH of solution, the presence of other reactive species, and, as already noted, temperature (Siever, 1962; Yariv, 1979). 9.4.2. The Effects of pH The equilibrium solubility of silica was recognised early as being influenced greatly by the pH of the solute. Correns (1941) found that the solubility of amorphous silica steadily increased above pH 5, but it was the work of Alexander (1954, quoted in Siever, 1962, p.128) "which indicated that the solubility of amorphous silica as monomeric silicic acid, ... was independent of pH from pH values 2 to about 9.5. At higher pH values the solubility does increase, mainly as a result of ionisation of H4Si04". As pH increases, reaction (1) (see above) is no longer the dominant reaction as alkali 263 conditions promote the generation of ions of orthosilicic acid, and the solubility of silica increases due to the increased concentration of negatively charged species in solution, such as SiO(OH)3 and Si02(OH)2". For this reason the silica concentrations in alkali solutions may be many times that in neutral pH (Serezhinikov, 1989). 600- 500- E Q. D. 400- CO O 'in 300- XJ CD > 200- o Amorphous Silica I I ttno a 100 '—«^^ Quartz. ^/ J 0 2 3 4 5 6 7 8 9 10 11 pH Figure 9.1. Relationship of the solubility of silica to pH. After Krauskopf (1956), Iller (1979), and Serezhinikov (1989). Figure 9.1 shows that the solubility of silica is essentially stable from about pH 8 until about pH 3, when the solubility of silica is again seen to rapidly increase. Unfortunately the solubility of silica in this region of low pH has recieved little attention (Serezhinikov, 1989; Brady and Walther, 1990; Bennett, 1991). 264 9.5. EXTERNAL INFLUENCES Divergence from total equilibrium solubility concentrations of silica, and in the rate of solution expected from laboratory modelling, have been observed. Siever (1962) concluded that "the behaviour of natural materials in the geologic environment cannot be precisely judged by comparison with pure materials in the laboratory and that other chemical components may be affecting the equilibria" (p.135). A number of other naturally occurring chemical species have been identified which have marked effects on the dynamics of the silica-water reaction system. 9.5.1. Metal Ions Yariv (1979) suggested that, although the solubility of monosilicic acid is not affected by the presence of monovalent metallic cations, multivalent metallic cations may drastically change the solubility of silicic acid. Reardon (1979) also noted this fact and suggested that iron-silicate complexing, for example the formation of FeH2Si04, may be of significance in the mobilisation of silica in acid waters. Morris and Fletcher (1987) tested the hypothesis that quartz solubility was markedly increased by quartz/ferrous iron reactions, concluding that a rapid release of silica to solution may occur in some ferrous iron solutions under oxidising conditions. The potential solubility of quartz may thus be increased by a factor of ten to that of amorphous silica. Serizihnikov (1989) also found increased solubility of quartz in the presence of iron. Complexing by other multivalent metal ions such as Mn and Al, oxide phases of which are of low solubility at moderate pH but are soluble at low 265 pH, may also be important in complexing and mobilising silica in acid waters (Reardon, 1979). Yet Bennett et al (1988) found no correlation between aluminium in solution and quartz dissolution, while Beckwith and Reeve (1969) and Mullis (1991) reported that low concentrations of Al3+ may strongly inhibit quartz dissolution. Additionally, McFarlane and Twidale (1987) draw the important additional conclusion that the presence of Al3+ ions in solutions of silica will lead to immediate co-precipitation. Other non-metal compounds are also known to assist in the metal- accelerated solution of silica. Waite et al. (1986) report that thiols generated from breakdown of plant matter are known to reduce metals such as Cu2+ and Fe3+, promoting silica dissolution, and also note the ability of thiols to solubilize iron oxides directly. Plant-generated polyphenols can also complex iron oxide (Hingston, 1962). It is, however, the organic acids which have been shown to have the most dramatic effect on the solubility of silica. 9.5.2. The Effects of Organic Acids For over 115 years (Julien, 1879, quoted in Bennett et al, 1988) organic compounds have been suspected of enhancing the mobility of silica. Descriptions of anomalous silica mobility in geologic environments rich in dissolved organic compounds are commonly found, but a model of silica mobility incorporating both the organic and inorganic reaction mechanisms has been slow to appear in the geologic literature (Bennett et al, 1988). Siever (1962) suggested that some organic compounds may lower the solubility of amorphous silica by coating the surface, but that, on the other hand, certain organic compounds may form organic-silica complexes which increase the solubility. Huang and Keller (1970) and Jackson et al. (1978) 266 found that the solubility of many silica minerals was higher in the presence of organic acid anions than in water alone. The solubility of Al, Fe, Ca and Mg were also boosted. A.R.M. Young (1974, 1987) has suggested that caverning in the Hawkesbury Sandstone was due partly to percolating water rich in organic acids which takes the iron-oxide cement into solution. Although the processes associated with the rapid dissolution of alumino- silicate minerals cannot explain rapid weathering of quartz (Bennett et al, 1988), Yariv (1979) found that the solubility of amorphous and crystalline silica increased slightly in the presence of certain organic hydroxy acids. In a study of oil-contaminated shallow groundwater, Bennett et al, (1988) showed that dissolved silica concentrations correlate with concentrations of dissolved organic carbon. Furthermore, they observed that the reactivity of quartz with several organic acids could be defined by the reaction series citrate > oxalate > salicylate > acetate (see also Bennett, 1991). This series parallels the one found by Huang and Keller (1970) for organic acids which form complexes with aluminium and accelerate the dissolution of alumino-silicates at acidic pH's. It seems that only the multi-protic acids (oxalate and citrate) or the multi-functional acids (salicylic acid) accelerate quartz dissolution, whereas acetic acid, a mono-functional mono-protic acid does not accelerate its dissolution (Bennett et al, 1988). In summary, some polar organic anions increase both the rate of quartz dissolution and the apparent equilibrium solubility in aqueous systems by chelating silicic acid in solution, thereby decreasing the activity of the monomeric silicic acid, and resulting in an increase in solubility. Multi functional organic acids accelerate quartz dissolution by decreasing the activation energy. Most of these organic acids are naturally produced during 267 the biodegradation of terrestrial organic matter (Ghosh, 1991). It appears that the greatest increase in quartz solubility occurs in anaerobic environments, and that where dissolved organic carbon is high, temperatures are low, and the pH is buffered to near-neutral conditions, organic-silica interactions may be an important process (Bennett, 1991). 9.5.3. Salts It is evident that many non-metal anions also have significant effects on the weathering of silica-rich rocks. Yariv (1979) proposed that an increase in chloride or sulfate ion concentration, rise of temperature, and and increase in pH, accelerate the dissolution rates of crystalline forms of silica. He also contends that NaCl can act as a catalyst for quartz dissolution. A.R.M. Young (1987) provided a suscinct summary of the complex effects of salt on silica solubility. "It is decreased by increasing concentrations of salts. Marshall and Warakomski (1980) demonstrated an increasing 'salting out' of silica by increasing concentration from 0 to 7 mol for a wide range of salts. Multivalent cations such as Al3+ were the most effective agents (cf. Iller 1979; Okamoto et al. , 1957), and the anion species was of little significance. We may expect, therefore, that the equilibrium solubility of silica in the presence of most salts at high concentrations will be very low, particularly in the absence of appreciable carbonate or phosphate to provide high pH values. However, the presence of sodium chloride has a strong accelerating effect on the rate of dissolution of silica (van Lier et al 1960). Increasing chloride or sulphate ion concentration accelerates the dissolution rate of crystalline silica (Yariv and Cross 1979), whereas increasing pH (between 5 and 11) and increasing sodium chloride concentration accelerate the 268 dissolution rate of amorphous silica (Kastner, 1981)" (A.R.M Young, 1987, p.965). R.W Young (1988) likewise argued that the intense dissolution of silica in the sandstones of the Bungle Bungle Range, Western Australia, may be enhanced by high chloride concentrations, and showed supporting S.E.M images of salt crystals on etched quartz surfaces. Laboratory experimentation has identified many Group 1A salts as having a marked effect on the geochemical properties of silica (Dove and Crerar, 1990; Dove and Elston, 1992), leading Bennett (1991) to state that "experiments using inorganic electrolytes increase the rate of quartz dissolution without decreasing the activation energy, and without increasing solubility" (p.1781). Bennett (1991) further argued that, "the rate of quartz dissolution increases with increasing concentration of alkali metal chlorides in solution ... the effects of sodium and potassium increases with increasing pH from pH 4.5 to 7 ... quartz dissolution rate is enhanced by sodium salts without increasing solubility" (Bennett, 1991, p.1789). von Damm et al. (1991) and Dove (1992) also confirmed that quartz solubility is increased in seawater (about 0.5M NaCl) relative to distilled water, contrary to Siever's earlier (1962) results. 9.5.4. Organic Interactions - Plants and Fungi Henderson and Duff (1963) noted that some fungi and bacteria produce solutions high in organic acids, which may be responsible for breakdown of silicates. Indeed the cumulative effects of such small-scale reactions over long periods of time could contribute significantly to the weathering of minerals. Moses and Smith (1993), Hiebert and Bennett (1992), and Cochran 269 and Berner (1993) also comment on the combined effect of physical and chemical weathering of many silica rocks by bacteria, lichens, fungi and higher plants. Cooks and Pretorious (1987) and Cooks and Otto (1990) used the S.E.M to develop a model of lichen weathering mechanisms involving both biochemical and biophysical processes. In this study area, however, Coates (1989) found that lichens have little effect on the disintegration of Hawkesbury Sandstone. 9.5.5. Temperature The solubility of silica is temperature dependent, with increased solubility at elevated temperatures (Siever, 1962). On a global scale at normal atmospheric temperatures there also appears to be some temperature dependence. This temperature effect was demonstrated by Meybeck (1987) who suggested an average dissolved silica concentration of 13.2 mg/1 in tropical streams, 8.4 mg/1 in temperate streams, but only 3 mg/1 for arctic streams. Meybeck found that within a watershed, dissolved silica loads decreased with altitude, and therefore temperature. Livingstone (1963) also reported a similar broad world wide temperature/dissolved silica relationship. Meybeck (1987) noted that 74% of the silica load delivered by streams to the oceans occurs in the tropical regions, a fact that depends both on the temperature dependent rate of solution, and on discharge. This claim is, however, contended by Douglas (1969, 1978), Davis (1964) and Thomas (1974) who concluded that there is no conclusive evidence for high silica concentrations in tropical rivers, and therefore any suggestion that a high rate of silica removal takes place in the tropics must rest upon evidence of higher stream discharges. Douglas (1969) established a significant 270 relationship between total silica load and runoff, and it would thus appear that high rates of chemical denudation as indexed by silica removal depend largely on runoff (Thomas, 1974). Thus the volume of water, rather that temperature, appears to be the critical factor. 9.5.6. Flushing Rate The bulk removal of silica is dependent not only on its solubility, but also on the rate at which water moves through the rock. Douglas (1978) commented that "the importance for the rate of solution of relatively rapidly moving water has been demonstrated in limestone terrains ... but it is equally significant in silicate areas. ... the rate loss of ions from silicate minerals to waters is controlled by the speed at which dissolved ions are carried away from the surface of the mineral" (p.230). Rimstidt (1980) also emphasised the importance of the flushing rate. Thus, the higher the water throughput in a natural environment, the higher the expected rate of silica removal. It therefore appears that the rate or volume of water movement through the region is the key to the problem. Where water throughput is high, silica remains mobile and may enter streams and be removed from the area, whereas where flushing rates are lower it is not removed as effectively and may by incorporated in the neoformation of clays (Young and Young, 1992). Thiry et al (1988) also emphasised the importance of vadose circulation, or flushing, related to silica solution and the formation of silcrete in their study of quartz sands in the Paris Basin. Above the watertable the sands are corroded, whereas below the watertable silica is deposited. 271 However, constant increase in flushing rate will not result in a constant increase in dissolved silica. As Berner (1978) emphasised, flushing accelerates the dissolution of minerals only up to a limiting rate beyond which additional through flow of water has virtually no effect, and dissolution is controlled by mineral reactivity. 9.6. THE LOCUS OF CHEMICAL ATTACK How, then, is quartzite or quartz sandstone affected by the solution process? White et al (1966) argued that in the hot and extremely wet conditions found on the Venezuelan tepuis (up to 7500mm precipitation p.a.), quartz within the Roraima quartzites was hydrated to much more soluble opal, then removed in solution. Chalcraft and Pye (1984) rejected this mechanism, and showed that direct solution of quartz, without the intermediate hydration to opal, occurs in the Roraima quartzites. They also showed that, while there is preferential solution along joints, beds and lithological contacts, cracks at all scales are foci for water flow and thus are pathways for solution. Moreover, their S.E.M examination of the quartzite showed an intense microscopic pitting of quartz grains and overgrowths, which appeared to be crystallographically controlled. In thin-section, widening of grain to grain contacts was also seen, along with etching and corrosion of both quartz grains and cements, eventually leading to a removal of cement and the freeing of individual detrital grains (Chalcraft and Pye, 1984). Ghosh (1991) who also worked on the Roraima quartzites, found that the unweathered rocks show abundant welding of grains by a pervasive syntaxial quartz cement and by sutured grain-to-grain contacts. In contrast, the weathered samples display an excellent network of lamellar porosity 272 formed by dissolution of quartz cement. This network of silica dissolution has mainly followed the boundaries of adjacent overgrowths. This process is similar to that recently recognised by petroleum geologists in the formation of secondary sandstone porosity by quartz dissolution (Pye and Frinsley, 1985; Shanmugam, 1985; Burley and Kantorowicz, 1986; Hurst and Bjorkum, 1986; Shanmugam and Higgins, 1988), except that it is occurring at near- surface conditions. Wilson (1979) had previously found in a study of the Millstone Grit that minute chemical etch forms which he attributed to slow solution of quartz by solutions of high pH seeping along cleavage and/or fracture planes. Although Wilson could not determine the specific crystallographic faces of the quartz grains on which the etch pits have developed, Wilson noted that, while discrepances in the relevant literature could not be ignored, other workers had reported that V-shaped or triangular pits form on the prism faces, whereas rectangular pits occur on the rhombohedral faces. Burley and Kantorowicz (1986) also described quartz grain surface features including pits, notches and embayments produced by solutional attack, with a tendency for corrosion to be more intense on those surfaces with high free- surface energy (see also Hurst, 1981). They pointed out that free-energy is particularly well developed around grain peripheries, along fractures and between crystal boundaries in rock fragments. Burley and Kantorowicz (1986, p.600) proposed two mechanisms of quartz corrosion; "Dissolution reactions are either controlled by the rate of transport of ions to and away from the reaction surface or by the reaction rate at the solid-solution interface. Transport controlled dissolution is characterised by rapid, non specific corrosion and is typical of strongly 273 concentrated solutions or highly soluble minerals. It gives rise to intense etching and corrosion of all available sites. Surface reaction controlled dissolution, by contrast, is generally slow and more specific, being typical of slow dissolution of relatively insoluble minerals in solutions of low chemical reactivity. Surface reaction controlled dissolution thus tends to produce distinct crystallographically controlled features such as well defined notches". Young (1988), in an S.E.M investigation of the regional extent and intensity of quartz sandstone etching in the east Kimberley, found similar surface- reaction and transport controlled dissolution features. Young (1988) also noted that Hurst and Bjorkum (1986) had challenged the ideas of Burley and Kantorowicz (1986), arguing that quartz dissolution rates are too low for transport-controlled etching. Hurst and Bjorkum emphasise that etching will concentrate at sites with the highest free-energy, and quartz overgrowth lowers the surface free-energy of a detrital grain. According to Hurst and Bjorkum (1986), dissolution will therefore be most rapid at the greatest concentration of detrital grain surfaces and face-corners and edges of overgrowths. Brady and Walther (1990) and Withe and Peterson (1990) support the proposition that silicate dissolution occurs preferentially at high-energy surface sites such as defects, and is controlled by the density of such defects. Young (1988) found the intensity of quartz etching in the Kimberley to be variable, and was more related to the primary porosity of the host rock; the more porous sandstones display a higher potential for the penetration of corrosive solutions. 274 9.7. CONCLUSIONS Although chemical processes are critical to the development of karst in sandstones, the erosion of weathered material are likewise essential to continued development. Martini (1981) notes that karst on quartzite cannot form by solution alone, piping in a vadose environment is needed for mechanical removal or quartz grains. Furthermore Jennings (1983) emphasised that while solution is critical, it actually removes only a small proportion of the rock, and that the loosened grains are removed by physical transport. The slow chemical dissolution of quartz, 'arenisation' in the terms of Martini (1979), usually occurs along crystal boundaries with the freeing of individual grains, although it is often the case that the detrital grains are attacked more than the overgrowths which have lower surface free- energies. This arenisation results in a rock that eventually becomes incoherent, and is thus highly suited to physical erosion. Faster rates of solution promote a general recession of surfaces and joint widening without rock disintegration. A plentiful supply of flowing water is then necessary for the removal of the material produced, preferably under vadose conditions. Unfortunately, the actual mechanisms of this arenisation are still unclear. Even for a single rock unit, the spectacular Roraima orthoquartzite, karst solution has been attributed to the hydration of quartz to amorphous silica under tropical weathering conditions (White et al, 1966), but Chalcraft and Pye (1984) disagree and present S.E.M and X.R.D analyses in support of the 275 claim that this karst formed by the direct solution of quartz grains and silica cement, not involving any intermediate hydration phase. Douglas (1969) demonstrated that the silica load of rivers is dependant on runoff, and thus rainfall. The amount of water moving through a rock will influence solution; for a given solubility regime, the higher the rate of flushing, the higher the silica loss. However, field measurements by Chalcraft and Pye (1984) showed dissolved silica to be very low, indicating that the dissected Roraima landscape must have formed by slow solution over a very long time period. This factor of slow but very prolonged solution is one that has all too often been ignored. The slow rate of solution of the numerous forms of silica, especially quartz, was believed to preclude to formation of karstic landforms on these 'inert' rocks. In the areas where most of the highly developed silicate karst is found, notably South America, Australia and southern Africa, slow rates of solution have been offset by long periods of sub-aerial weathering. In these areas cool temperate, moist temperate or tropical climatic regimes have often been common since at least the Early Tertiary. The actual thermodynamics, and it would seem especially the very complicated reaction kinetics, are critical in the formation of silica karst. Martini (1981) argues that the rate of reaction is just as important as the total solubility, in that the faster the rate the less distance solution can penetrate the rock before saturation. This results in arenisation close to the surface and a general surface lowering, rather than a deep karstification. Slower rates allow joint widening without surface lowering, and slower still is crystal boundary solution with a deep solution of the rock. Voids along 276 crystal boundaries are very thin, and thus water circulation is very sluggish, with saturation being reached after a very short distance unless the kinetics of reaction are very slow. If the rate of silica solution was slower, without changing the total solubility, Martini argues that karst on quartzite would be much more common. But even on one of the most highly karstified quartzites, that of Roraima, limited field measurements indicate the chemical conditions under which this karst is forming are at odds with the laboratory work on silica dissolution. Pouyllau and Seurin (1985, p.51) argued for silica dissolution under very acid conditions, "le millieu ambiant etait tres agressif, avec des pH hyper-acides pour entrainer une dissolution d'une partie de la silice des quartz", not the highly alkaline conditions regarded necesary from laboratory experimentation, but Pouyllau and Seurin (1985) could only provided very limited evidence for slighly acid conditions (pH 4.21 and 4.53). Chalcraft and Pye (1984) similarly found a small number of natural waters at Roraima to be slightly acidic. Thus, even on this one rock type, the problem of a lack of field evidence of silica solubility hampers our understanding, this is unfortunately all the more problematic as there appears to be some disparity with what the laboratory work suggests. Only by the study of the behaviour of silica in many more natural waters will these gaps in our understanding be overcome 277 CHAPTER 10. WATER CHEMISTRY 10.1. INTRODUCTION Laboratory experimentation has repeatedly demonstrated that the solubility of all forms of silica is reasonably low below about pH 8 (Section 9.4.2), but thereafter it rapidly increases with increasing pH (Siever, 1962). Solubility also increases rapidly in acidic waters below about pH 3.5 (Serezhinikov, 1989). Demonstrating the field relevance of these laboratory results is another matter. The fundamental problem is to assess whether the extremes of pH occur in natural streams or pools, and if they do, whether they are associated with high concentrations of silica. An investigation of the pH and silica content of streams and pools on the Sydney Basin sandstones was undertaken to provide comparative data with the published laboratory results. As iron as a multivalent ion has often been considered likely to increase silica solubility (Section 9.5.1), levels of dissolved iron in these waters were thus also recorded. Dissolved oxygen levels were also determined since dissolved silica levels have been found to be higher in anaerobic conditions. In this sense, dissolved oxygen may be used as surrogate for dissolved organic carbon. The effects of numerous organic acids, other metal ions, non-metal anions and various other factors have also been repeatedly demonstrated to influence the solution chemistry and kinetics of silicon, and were briefly reviewed in Section 9.5. The study of these factors in the field is, however much more complex than in the controlled conditions of a laboratory, and an 278 in-depth study of these highly complex interactions was beyond the scope of this research. 10.2. SAMPLING METHODS Natural waters from a large number of solution basins and various streams across the local area were sampled. Some results were also available from previous chemical analysis of local natural streams (Johnson and Johnson, 1972; Johnson, 1982; and others). Measurements were made of pH, dissolved silicon, dissolved iron, dissolved oxygen. pH was measured with a Eutech Cybernetics pHScan 2™ electronic temperature compensating pH meter, regularly calibrated in the laboratory to pH 4, 7 and 9. Si, Fe, and DO was measured with a Lovibond Tintometer Ltd. colorimetric comparator test unit. The Tintometer test equipment provides relative levels of dissolved material rather than levels rigorously comparable with results derived from laboratory analysis. Nonetheless, this equipment has been developed for use in the Streamwatch Program and results obtained with this equipment have been used by the Sydney Water Board in water pollution prosecutions. It is thus deemed adequate for the purposes for which it has been used here. The range and accuracy of the various test equipment used is; • pH by electronic meter in steps of 0.1 pH unit, with an accuracy of ± 0.1 pH unit • Silicon by the Molybdate Blue method from 0.4 to 4.0 mg/1, in steps of 0.4, 0.6,1.0,1.5, 2.0,2.5,3.0,3.5,4.0 mg/1. 279 • Iron by the PPST method from 0.1 to 1.0 mg/1, in steps of 0.1 mg/1 to 0.8 mg/1, then 1.0 mg/1. • Dissolved Oxygen by a modified Winkler Test from 4 to 12 mg/1, in steps of 1 mg/1. Where possible, levels of dissolved Si, Fe and DO were measured in the field. However it was often not practical to conduct these measurements in situ due to time limitations or difficulties in carrying the bulky and fragile test equipment. It was therefore found necessary to collect samples for later measurement of dissolved materials. To ascertain if concentrations of dissolved material varied in the time from collection to analysis, several samples were collected in clean polyethylene sample bottles and analysed as soon as possible after field work. These values were compared with analysis of the same water in the field. The values of dissolved material did not significantly differ, but pH often did vary a little. pH was therefore always measured in the field. These tests confirmed that, provided a full bottle of sample was collected and the analysis was performed within 1 day of collection, the results of later analysis were acceptable. A number of samples were also submitted to the laboratory of Biological and Chemical Analytical Services (BACAS) at the University of Wollongong, for more detailed chemical analysis. Further detailed analysis was also conducted by Dr J. James in the laboratory of the Department of Chemistry at the University of Sydney. 280 O o P o p o p o p p o d d d d d d d d d d d p LQ in o m Tt IN Tt p CN NO in IN in NO CO CO CO 00 i—i i—i \6 a, CN CN CN CN l oo IN CN CN CN CN O O O o CO O o c o O O o o o o d o o o o o o d d d d d d d 0* d d d V V V V V V V V + q p p p p p p ON ON in p CN Tt CN CO CN CN ON NO LO ON CO r-1 r-i CN T—' m NO (—i IN Tt oo oo IN CN in m oq u d d d d d d d d CN + Tt CN "^ ON co CN in t—< Tt CN CO CN NO Tt CN CN NO + O O CN p p CN NO co in NC u co to Tt ON ON d r—i CN NO CN o p p o p ^t p in p in o MS \6 oo d in CN CN CN NO oo. LO lO p IT) o in in in in o d d d d CN d CN CN d V V d V V V V ID in 1 o o c c Tt o in o p d d IN CN oo IN CO CO d Tt 0 CN CN Tt i—1 NO O o O o O o C p c c o O NO CO IN 00 ON CO NO CN in in U CO CN CO IN CN r- 00 es tr> o o o o O O c C p O d d d d d d d d d d d u o o o o c c c p o o p u d d d d d d d CN IN Tt d CO i—' CN in o c in in NO NO w CO CN r-1 X T* IN ON NO 00 ON IN CN NO NO IN a, NO NO NO NO IN in in QJ "SI f tn •4-* > CO "to tn cn "5 U u U U PL, "to "co P (- QJ s U QJ CO C "S •s 13 tn > c OJ re re o QJ u £ £ I 'C 2 ? I- 12 o fc t to C is CO ra S81 CO I 3 CO (0 5- e •a 60 bo E fc 00 u U 3 a- to ^ "QJ o> c o 10.3. RESULTS Results from some previous water chemistry investigations in the region are presented in Tables 10.1 to 10.4, and determinations of dissolved Si, Fe, DO and pH obtained during this study from quartz sandstone solution basins and several creeks are presented in Appendix 3. Site pH Iron Silica (mg/1) (mg/1) A Hillside 5.1 0.1 5.0 B Swamp 5.0 0.9 5.0 F Exits 4.8 0.2 9.0 J 5.1 0.1 <1.0 C Swamp 4.8 0.1 4.0 D to 5.0 0.1 1.0 E Stream 4.6 0.1 4.0 G Swamp 4.5 1.4 <1.0 H to Stream 4.2 0.6 9.0 I Culvert 5.0 56.0 5.0 K 4.9 1.5 9.0 L Molly 5.3 4.2 2.0 M Morgan 5.3 11.7 7.0 N Site 6.2 79.0 8.0 O 5.1 1.4 6.0 Table 10.2. Dissolved silica and iron determinations from the Avon Dam catchment. Source: Young and Sim (1987). 282 Bicarbonate 0 to 413 mg/1 (32 samples, 50% between 50 to 100 mg/1) Chloride 14 to 309 mg/1 (32 samples, 75% < 80 mg/1) Sulphate 0 to 170 mg/1 (32 samples, 66% zero, 1>58 mg/1) Calcium + 2 to 110 mg/1 (32 samples, 75% < 25 mg/1) Magnesium Sodium 5 to 104 mg/1 (75% < 50 mg/1) Silica 1.5 mg/1 Huntley DM5 Bore 80 mg/1 Barrawarra Bore Table 10.3. Water chemistry of Hawkesbury Sandstone waters. Source: Wallis and Johnson (1969). Silica Site mg/1 SSl(a) 11.0 SSl(b) 8.0 SS2 4.5 SS3 3.0 SS4 3.0 SS5(a) 9.0 SS5(b) 10.0 Table 10.4. Surface water dissolved silica concentrations from the Huntley- Robertson district. Source: Johnson and Johnson (1972). 10.3.1. Range of Naturally Occurring pH within this Study Area The range of pH found upon quartz sandstones in this study area varied over 6.4 pH units, that is 6.4 orders of magnitude. The lowest value of 3.2 (Sample #53) was from seepage or creek water below a swamp on the Snapper Point Formation at Little Beecroft Head, Jervis Bay. The highest value of 9.6 was from a basin in Hawkesbury Sandstone at Maldon. The scatter of pH values illustrated in Figure 10.1 is not statistically normal, but skewed slightly towards the alkaline for basins and more toward the acid for creeks. 283 The number of alkaline values obtained is very surprising given the naturally acidic conditions usually associated with quartz sandstones under high runoffs. For example, pH determinations of water within quartz sandstone solution basins at Fontainebleau by Franzle (1971) indicated only mildly acidic conditions (pH 6.3 to 3.6), and not alkaline conditions as found here. Similarly, Alexandrowicz (1989) reported only acid and neutral conditions in a study of solution basins in Poland. The majority of samples studied here were collected from essentially fresh water sources, most basins and creeks being supplied directly from rain water runoff. However, a small number of basins were situated on or close to marine platforms and were thus filled with sea water either directly or by wave splash, or a combination of rain and sea water. The pH of these basins was that of sea water, 8.2. A number of samples had pH levels higher than sea water, but they were generally located at inland locations far from the coast. The presence of localised carbonate within the sandstone was immediately suspected and tested for with dilute hydrochloric acid. In all cases there was no reaction between the rock and acid, indicating significant carbonate was not contributing to the alkaline pH. Study of samples of rock in thin-section and S.E.M X-ray analysis also failed to indicate the presence of any significant carbonate. To further investigate the high alkalinity of these water samples, a number were submitted to the BACAS analytical laboratory for more detailed chemical analysis, and several were analysed by Dr J. James of the Department of Chemistry, University of Sydney. These results of these detailed analysis are presented in Tables 10.5 and 10.6. 284 I-H 03 (m- U rrt ON >N 1—C31 TS o O I-H o o U n o ON 00 ON < crj r-H r-H r-H r-H ,__, IN Q re "^ LO rH CN Tt NO ON NO r-H p H CO ON* CO ON CO CO LN NO w re Fiel d LO NO IN CO ON O r-H CN 00 00 CO 00 CO ON ON ON ° S 2 ON ON ON ON ON ON ON ON I-H «> ^ o r-H r-H I-H I-H r-H r-H r-H U i I 1 I I I I CO CO CO CO ON CO CO CO co ON ON ON ON ON ON ON 'S & *z 00 r-H CN NO CO ON LO 00 LO 3 I_I T* No . CO CO CO CO 2 « oo 00 "o O o p H ON ON CO 00 CO V- Fiel d C « NO "2 ^ C3 Univariate Scattergram of Basin pH. 10 9 .jfc^t. t-1 SD 4 ++* 8 >a + 7 Mean +•*++ .6 +f -1 SD 5 4 - +Ta.* 3 Observations Univariate Scattergram of Stream pH. 8 -f + 7.5 - i-1 SD 7 - 6.5 - 6 ~+ Mean "5.5.5 5 ^«**AAJM^AAAA*A»Afci -1 SD 4.5 4 3.5 3 Observations Figure 10.1. Range of measured pH of basins and streams within this study area. Although some bicarbonate was detected in the high pH samples, the amounts were not large, and in fact were often lower than samples of lower pH. Carbonate levels were also very low. In fact, little was shown from the analyses that could have unequivocally raised the pH of the waters to the observed levels (Dr J. James, pers. com.). The samples were, however, poorly buffered, so that under some conditions low concentrations of bicarbonate 287 could possibly significantly affect pH. Yet the exact cause of these alkaline conditions remains unknown. Nonetheless, the repeated measurement of pH greater than pH 8 demonstrates that the high pH levels thought necessary for silica dissolution in laboratory studies are indeed replicated in some natural waters of this region. 10.3.2. Range of Naturally Occurring Dissolved Silicon in this Area The range of dissolved silica in basins and creeks measured during this study varies from less than 0.4 mg/1 (the lower limit of detection) to 12.0 mg/1, with a mean of 3.4 mg/1 (Figure 10.2). Johnson (1972) found that the dissolved silica concentrations of groundwaters from the Hawkesbury Sandstone in the Robertson district ranged from 3.0 to 12.0 mg/1, with surface waters ranging from 3.0 to 11.0 mg/1. Wallis and Johnson (1969) also reported values of 1.5 mg/1 Si for waters from the same area. These and other previous studies in this region provide comparable figures to those found in this study. It can be seen that although the peak values were obtained from a few basins, the average amounts of dissolved silicon in both streams and basins differs; average levels are 4.9 mg/1 dissolved silica for the streams, and 2.8 mg/1 for basins. This difference is attributable to lithological variations. Whereas stream catchments contain large amounts of silicate minerals and clays which are liable to release large amounts of silica upon weathering, the basins are located within solid quartz sandstone that contain proportionally much less clay. 10.3.3. Relationships of Dissolved Silicon to pH The relationship between the solubility of silica and pH has been well established in the laboratory (Alexander et al, 1954; Krauskopf, 1956; Yariv 288 and Cross, 1979; and others). The laboratory results would suggest that at pH above about 8.5 the concentration of dissolved silica of all forms in solution should increase very rapidly (Figure 9.1). Interestingly, however, it can be seen from Figure 10.3 that in all but one case at pH above about 8.5, the concentrations of dissolved silica did not rise rapidly, but rather the observed scatter of dissolved silica concentrations actually decreased. Univariate Scattergram of Stream Dissolved Silica. 14 12 1 10 8 - en +1 SD £ t- t- c/j 6 " Mean 4 " -1 SD Observations Univariate Scattergram of Basin Dissolved Silica. 14 12 - 10 - 8 - E 6 H +1 SD C/j + + 4 H ±__±fc 4 jj-i fc. __jfc- Mean .0+4 + + .*i- 2 f -H- + H> + f |!^f>W!r*rtri*r^h«il*BinvvWI -1 SD 0 ,™™3^w,™™7&Z. „ 2 Observations Figure 10.2. Range of measured dissolved silicon in basins and streams of this study area. 289 While one sample of pH 9.2 had a concentration of 10 mg/1, the highest measured concentration of 12 mg/1 dissolved silica was found at both pH 3.9 and pH 3.4. This suggests that, in this environment, large amounts of silica are also being moved in solution at acidic pHs. Scattergram of Dissolved Silica and pH for Streams and Basins. 14 12 - 10 A * Basins A A A A ro A Streams £ 6- + + t c/j 4 A 4- 4 4 4-4 4- 4 4 4 2 - •*• -r -r 4 4 4- * + +• * -M- 1-r 1- 4 * + "* 4- f 4-+ 44- 0 • I T I V -—•—r~ T 5 10 PH Figure 10.3. Relationship of dissolved silica to pH in streams and basins. It appears that at least half of the values obtained, those between 1 and 4 mg/1, would be expected to be undersaturated with respect to quartz (solubility -6 to 14 mg/1), although something like 1/10 saturation with respect to amorphous silica. The other half of the samples could be undersaturated to slightly oversaturated with respect to quartz, but still grossly undersaturated with respect to amorphous silica. It thus seems from these results that the laboratory derived relationship between alkaline pH and silica solubility may not hold in this environment. In fact, a striking contrast to the laboratory derived relationships is here seen. 290 Furthermore, the poorly studied acid end of the silica solubility range may be very important here in moving large amounts of silica in solution. 10.3.4. Dissolved Iron The range of dissolved iron in basins and creeks measured during this study varied from less than 0.1 mg/1 (the lower limit of detection) to 2.8 mg/1, with a mean of 0.02 mg/1 for streams and 0.12 mg/1 for basins (if one takes readings of <0.1 mg/1 as equal to zero) (Figure 10.4). The level of dissolved iron in by far the majority of samples, 80%, was below the 0.1 mg/1 limit of detection. Thus iron levels are rarely high enough to be expected to influence silica solubility. Most of these results are comparable to the bulk of Johnson's (1982, 1984) (Table 10.1) results for dissolved iron in local creek waters (0.03 to 2.3 mg/1 Fe) within the region. But even the highest iron concentrations recorded here (2.8,1.4,1.0 mg/1) are tiny compared to the highest recorded by Johnson (1982) for one small stream near Camden (85, 60, 11 mg/1), and for two localised sites by Young and Sim (1987) (56, 79 mg/1), but these high values are site-specific and anomalous regionally (Table 10.2). In a number of locations across the study area the formation of iron-based tufas and speleothems indicates that levels of dissolved iron are locally much higher than the norm, and indeed it was found that iron concentrations at many of these sites was too high to accurately measure with the equipment available. None of these locations are included in the sample set because they are not seen as representative of the area-wide trend of dissolved iron concentrations. Rather, they are sites where iron is precipitation out as groundwater emerges and oxidation occurs. 291 Univariate Scattergram of Dissolved Iron in Streams .35 .3 - .25 - .2 " m E .15- CD .1 + 1 SD .05 i Mean 0 H h—H r- -4~H H H H- H |—+.—1™-|„—K—4-—1-. -.05 Observations Univariate Scattergram of Dissolved Iron in Basins 2.5 2 H - 1.5 ra E 0) "- 1 .5 +1 SD Mean 0 -1 SD -.5 Observations Figure 10.4. Range of measured dissolved iron in streams and basins in this study area. Values of dissolved iron <0.1 mg/1 are shown as 0 mg/1. Note differing scales 10.3.5. Relationships of Dissolved Iron to Dissolved Silicon Figure 10.5 shows that there is no apparent relationship here in the concentrations of dissolved iron and silica in creeks and basins within the study region. These results are at odds with the experimental work of Morris and Fletcher (1987), who showed that iron-silica complexing under oxidising conditions can lead to increased levels of dissolved silicon in solution, and of 292 Reardon (1979), who also suggested a mechanism where silicon was complexed by iron(III) in natural waters, and also possibly other metals such as Al and Mn. But, whereas the reactions recorded by Reardon occurred under very acid conditions, the bulk of waters here were found to be near-neutral to alkaline. Furthermore, the iron concentrations were very low in comparison to the environments studied by Morris and Fletcher. Scattergram of Dissolved Iron and Silica in Streams and Basins 3 2.5 2 • _ 1-5 " + Streams ra E A Basins CD 1 u_ .5 0 + -.5 i i—i—|—r—i—i—|—i—i—i—]—i—i—i—|—i—i—i—J—i—i—•—|—i—r -2 4 6 10 12 14 Si mg/1 Figure 10.5. Relationship of dissolved iron to dissolved silicon in streams and basins in this study area. Values of dissolved iron <0.1 mg/1 are shown as 0 mg/1. It is also interesting to note the ratio of dissolved iron to dissolved silicon is very low, generally between 0.2 and 0.01, and decreasing with increasing silica concentration. Apart from one case, there is no concomitant increase in the amount of dissolved iron in solution as dissolved silicon concentration increases. With the exception of the three samples high in dissolved iron, which are probably influenced by very high levels of dissolved organic matter (in all three samples were large amounts of rotting leaves), the range of 293 dissolved iron (<0.1 to 0.3 mg/1) is remarkably similar for all ranges of dissolved silicon recorded here. 10.3.6. Relationships of Dissolved Oxygen to Dissolved Silicon Bennett et al (1988) found in a study of oil contaminated, shallow groundwater that dissolved silica concentrations correlate with concentrations of dissolved organic carbon, and Bennett (1991) suggested "that the greatest increase in quartz solubility occurs in anaerobic environments ... in environments where dissolved organic carbon is high, temperatures are low, and the pH is buffered to near-neutral conditions, organic-silica interactions may be an important process" (p. 1795). However, the large scatter of levels of dissolved oxygen and dissolved silica observed in the Sydney Basin makes interpretation difficult (Figure 10.6). Scattergram of Silica and Dissolved Oxygen in Streams and Basins 18 16 - 14 12 " A \A A 4 ra 10 - A A + ¥ + Streams 4- IMAAAI A ^ Basins 3 8 A A + 6 - £A A AAA 4 A .AAA 4 ~ A4-* 2 - 0 T T -2 4 6 10 12 14 Si mg/l Figure 10.6. Relationship of dissolved oxygen to dissolved silicon in streams and basins in this study area. 294 From the data presented here it seems that in the streams decreasing levels of dissolved oxygen may correlate with increasing levels of dissolved silicon between 0.1 and 17 mg/1 DO and 0 and 12 mg/1 dissolved silica. Nonetheless, in the solution basins waters were most commonly moderately well aerated, about 5 to 12 mg/1 dissolved oxygen, and held from 0.1 to 6 mg/1 silica in solution. It does appear that the highest levels of dissolved silica were found in poorly aerated basins, as might be expected, but this is countered by the fact that most basins with low dissolved oxygen concentrations, below about 6 mg/1, contained similar amounts of dissolved silica to those more aerated basin waters. 10.4. COMPARISONS WITH DISSOLVED SILICA IN OTHER AREAS The levels of dissolved silicon found here, <0.4 mg/1 to 12.0 mg/1 with a mean of 3.4 mg/1, are much lower than those reported by many previous authors. For example, Davis (1964) showed from a variety of sources (although biased in favour of North American examples) that the median value for silica in groundwater was 17 mg/1, with a range from 12 mg/1 to 23 mg/1, whilst the median value for river water was 14 mg/1. These compare favourably with the figure of 13 mg/1 for river water worldwide found by Livingstone (1963). Aston (1983) also summarised a range of previously reported concentrations of silica in river waters which ranged from 0.3 to 1.3 mg/1 for various Scottish rivers, 6 mg/1 for the Mississippi, 9 mg/1 for the Savannah, U.S.A, and numerous other rivers that range from 10 to 39 mg/1 dissolved silica. Tropical rivers appear to have even higher silica levels. Davis (1964) suggested a higher silica concentration of 24 mg/1, based on African examples, 295 while Douglas (1969) obtained a range of figures from 10 to 25 mg/1 from small streams in north Queensland and Malaysia. Grove (1972) also found that samples from the Niger, Benue, Logone and Senegal Rivers in Africa had a range from 5 to 17 mg/1 with a median value of 10 mg/1 dissolved silicon. On the other hand, Konhauser et al (1992) show no clear-cut climatic trends dissolved silicon for several of the world's major rivers: Upper Amazon 11.1 mg/1, Lower Negro 4.1 mg/1, Rio Grande 30 mg/1, Danube 5 mg/1, Nile 21 mg/1, and Yangtze 5.8 mg/1. Dissolved silicon levels in streams in the Sydney Basin are all much lower than these previously published results. But it must be borne in mind that, whereas the streams studied here drain sandstones those published levels were derived from a wide range of lithologies. That lithological factors are very important in determining the amount of silica in solution is indicated by the fact that determinations from this study area are only slightly less than that found on the quartz Kombolgie Sandstone in Arnhem Land, tropical northern Australia. Of 301 surface water determinations by Noranda Ltd (1978) the average dissolved silicon was found to be 5.33 mg/1. Similar levels of dissolved silica, mean 6.7 mg/1, were also obtained by Dames & Moore (1981) for 111 surface water analysis in the same area. What is more, Mainguet (1972) also cites levels of 5 to 11 mg/1 dissolved silica for natural waters on sandstones in Tchad, and Chalcraft and Pye (1984) note values of the summits of Roraiman tepuis and of 5 to 7 mg/1 dissolved silica at the base of these mesas. Although repeated emphasis has been given to climatic control of silica solution, there is now good reason to doubt it. The Sydney Basin has a temperate climate, Tchad and Arnhem Land have a tropical savanna climate, 296 and Roraima an equatorial climate. Therefore, the striking similarity of the silica concentrations observed in all regions seems linked to this common lithology. 10.5. CONCLUSIONS Much experimental work indicates the vastly increased solubility of silicon in waters of pH above about 8.5, and there is evidence to suggest a similar increase in solubility in acid waters of less than about pH 3.5. Whether these extreme pH conditions occur widely in natural environments has, however, been a moot point. It has been demonstrated here that both in streams and solution basins natural waters do commonly attain conditions at both ends of the pH scale more conducive to higher levels of dissolved silica. Slightly acid conditions discovered here are not surprising in light of the generally acid nature of the bedrock, the cool-temperate climate and the abundant natural vegetation, but the quite acid conditions (< about pH 4) seen in some circumstances were of lower pH than expected, and these showed the highest recorded dissolved silica levels. The highest dissolved silica levels were also associated with low dissolved oxygen conditions, suggesting a link with high organic carbon and organic acids. The highly alkaline conditions within many solution basins were also unexpected. No explanation for these high pH conditions other than poor buffering capacity can be offered. Repeated checking of the calibration of the pH meter used confirmed the reliability of the results, yet the rocks themselves were quartzose and not carbonate-rich. Under these alkaline conditions silica should be expected to be more soluble than at the lower 297 neutral to slightly-acid pH conditions generally encountered for natural waters. Yet the measured silica levels were much lower than predicted by this laboratory-derived relationship. The poorly buffered nature of the high-pH solutions indicate large swings in pH could be expected, but even if the waters only attained these highly alkaline conditions for short periods, repeated shifts into this pH region over long periods of time could have a cumulative effect on dissolution of silica from the basins. The same applies for very low pH. In summary, the field testing, showed that high pH did not correlate with increased silica levels, as would be expected; most of the waters of pH > 9 still had Si levels below 6 mg/1. There is some evidence that waters of very low pH did correlate with increased dissolved silica, or at least a greater range of dissolved silica. Iron levels (because these were low), appeared not to significantly affect the levels of Si determined, nor did DO, except for when it was very low the range of dissolved silica was greater. These results prompt caution against reliance on artificial, laboratory determined values. The levels of dissolved silica recorded in the Sydney Basin are considerably lower than the widely cited levels measured in other parts of the world. Yet the results from the Sydney Basin are closely comparable to those observed from sandstone terrain under tropical regimes. Thus lithology, rather than climate, seems to be the key factor controlling silica yield. Moreover, the development of solutional forms on sandstones depends not only on the rates of weathering, but also on the duration of weathering, and the landsurfaces of the Sydney Basin are of great antiquity. 298 CHAPTER 11. QUARTZ ETCHING AND SILICA SOLUTION IN THE SYDNEY BASIN 11.1. INTRODUCTION A range of quartz sandstone landforms which is of similar morphology to that formed by dissolution of carbonate rocks have been described from this region. Chapter 10 demonstrated that silica is mobile in solution in both basins and streams within the study region, and Chapter 8 showed the presence of widespread accumulations of re-precipitated silica as speleothems, which also attests to the removal and transport of significant amounts of silica from within the Sydney Basin quartz sandstones. It is now necessary to identify the source of the dissolved silica from within these quartz sandstones. A multitude of processes, both chemical and physical, have been invoked in the genesis of the various limestone karst, but the agent common to all of these is a significant component of rock solution. Similarly, the suite of carbonate analogues on Sydney Basin quartz sandstones are formed by a variety of erosive processes, but again the common factor is chemical solution, the process of which is "critical (but not necessarily dominant)" (Jennings, 1983) in the preparation of the sandstone and the development of the specific landforms. Following the theme of Young (1988), several questions are posed here in investigating the chemical weathering of the local quartz sandstones: 299 1. How significant is the etching of quartz grains, and is this etching a regional or local phenomenon? 2. Is there variation in either the type or intensity of etching across the region? 3. What causes the etching? To answer these questions sandstones from the previously described landforms were examined in petrographic thin-section and by S.E.M to determine the extent of solutional weathering. Many previous authors have noted chemical attack and etching of the surface of quartz grains and overgrowths under both field and laboratory conditions (Wilson, 1979; Chalcraft and Pye, 1984; McGreevy, 1985; Burley and Kantorowicz, 1986; Young, 1986, 1987, 1988; A.R.M Young, 1987), and therefore a significant comparative database already exists. Two types of microscopic solutional attack have been noted by others in quartzites and quartz sandstones from tropical regions (Chalcraft and Pye, 1984; Young, 1986, 1987, 1988), and both are identifiable in Sydney Basin sandstones. The first type are small, often V-shaped, pits on grain and overgrowth surfaces which show strong crystallographic control. The second are larger, irregular, embayments or depressions which show no crystallographic control and often penetrate through quartz overgrowths into the grains below. Crook (1968) argued that this type of embayment, and for that matter smoothed surfaces on detrital quartz grains, cannot be explained by physical weathering, but only by solutional attack. It must be noted at the outset, however, that whilst some of the previously reported grain surface textures are believed to have been produced by the 300 dissolution of calcite, dolomite or siderite cement (notably Burley and Kantorowicz, 1986), the proportions of these minerals in the Sydney Basin quartz sandstones are small. Young (1988) also showed that these textures are found on similar carbonate-poor quartz sandstones of the Kimberley. Young, (1988) argued that these two etching types, pits and embayments, are similar to the surface textures produced by the "surface reaction controlled dissolution" (v-pits) and the "transport controlled dissolution" (embayments) of Burley and Kantorowicz (1986) (Section 9.6) where the intensity of etching is dependent of the reactivity of the corrosive solutions. Hurst and Bjorkum (1986), in reply to Burley and Kantorowicz (1986), argued that the rate of quartz dissolution is too low to produce "transport controlled dissolution", but rather maintained that etching is more aggressive at surfaces of highest free-surface energy. Quartz overgrowth lowers surface energy, they note, and dissolution will therefore be most rapid at the greatest concentration of detrital grain surfaces, face corners, and edges of overgrowths (Hurst and Bjorkum, 1986). Similar S.E.M observations of chemical etching was reported from Sydney Basin sandstones by A.R.M Young (1987). Her study found that salts aid in chemically etching the Hawkesbury and Nowra Sandstone by the degradation and dissolution of interstitial clays, and by the accelerated dissolution of detrital grains, overgrowths and contacts at high free-surface energy grain-to- grain and grain-to-overgrowth locations. As voids were widened by solution of both quartz and clay-based silica, grains were loosened and easily removed. 301 11.2. OCCURRENCE OF QUARTZ ETCHING Widespread etching of both quartz grains and overgrowths can be seen in all Sydney Basin Permian and Triassic quartz sandstones. Extensive interlocking quartz overgrowths within the Snapper Point Formation and Nowra Sandstone have resulted in rocks that are generally tightly sutured, but without the total elimination of primary porosity. The porosity, allied with the breakdown of matrix clays, has allowed the penetration of corrosive solutions, with a corresponding very high degree of etching. The Hawkesbury Sandstone is also in places highly etched, but is generally much less altered than for example the Nowra Sandstone at Monolith Valley. Silica loss by corrosion of clay matrix, detrital grains and overgrowths is also commonly seen in the sandstones of the Grose Sub-Group. The high proportion of authigenic clays within these sandstones, however, has been largely responsible for a much lower primary porosity, with a consequently much lower degree of etching, except near the sandstone surface. Extensive etching can thus be seen in all major Sydney Basin quartz sandstones studied here. This areal range of degraded sandstones clearly demonstrates that the chemical etching of quartz grains, whilst of variable intensity, is of regional significance. 11.3. ETCHING TYPE AND INTENSITY The intensity and type of etching within Sydney Basin quartz sandstone is very variable, both across the region and within individual sandstone formations, and is graphically displayed in both S.E.M and thin-section micrographs of the sandstones studied here. Crystallographically controlled v- pits are commonly seen on detrital quartz grains in all the Shoalhaven Group 302 sandstones, especially the Nowra Sandstone at Monolith Valley and the Snapper Point Formation at Jervis Bay, but larger 'transport controlled' embayments are usually much more common. Two samples of Snapper Point Formation sandstone were taken from grikes at Whale Point and Honeysuckle Point, both also being areas of very intense basin and runnel development. Each sandstone sample displayed a closely packed and only poor to moderately sorted fabric; they are extremely well sutured by quartz overgrowths, but display a moderate permeability. Scattered voids of grain size or larger are seen, and many of these are filled by clay matrix, dominantly illite, which near the weathered surface is breaking down. Solutional etching and embayment of the quartz grains and overgrowth surfaces is very common throughout the rock, so that at the sandstone surface grains are now only poorly cemented and very easily detached. Sandstone from grikes at Honeymoon Bay, a location that also displays an extremely fine assortment of basins and runnels, is also moderately to poorly sorted, but very highly sutured by quartz overgrowths and many irregular, welded, grain-to-grain contacts (Plate 11.1). Nonetheless, numerous voids and large clay filled pore spaces are widespread and often lined with black to red- brown opaques. The grains surrounding these voids are very highly etched. Sutures and other grain-to-grain contacts have begun to dissolve leaving narrow voids between grains (Plates 11.2 and 11.3), and these grains are now in parts only poorly cemented. Solutional attack on detrital grains, areas of higher free-surface energy, is generally higher than on overgrowths. Many of the overgrowths are only very slightly corroded (Plate 11.2, 11.3 and 11.4), but they are are by no means immune from attack. Etching is widspread on quartz overgrowth, and most intense on the rhombohedral faces and edges, whilst there is a definite lesser proportion of attack on the overgrowth prism faces. 303 Plate 11.1. Thin-section micrograph of Snapper Point Formation sandstone from a grike wall at Honeymoon Bay (TS 12035). This rock displays a high degree of quartz overgrowth and suturing, but near the surface this cement is being destroyed resulting in widening of inter-granular voids and breakdown of the rock. Field of View, 3.95mm. Plate 11.2. S.E.M image of the Snapper Point Formation within a grike at Honeymoon Bay. The degree of quartz overgrowth within these sandstones is quite high, but without the total elimination of primary porosity. Greatest attack is in areas of higher free-surface energy (detrital grains, overgrowth faces and edges). However, many of the overgrowths, especially prism faces, are only slightly corroded. 388x magnification. 304 Plate 11.3. S.E.M image of Snapper Point Formation from within a grike at Honeymoon Bay showing intense etching of quartz overgrowth. Much of the overgrowth is highly corroded, whilst other areas are only slightly etched. Sutures and other grain-to-grain contacts have begun to dissolve leaving narrow voids between grains that results in a reduction in the rock strength. 955x magnification. Plate 11.4. S.E.M image of the Snapper Point Formation at Honeymoon Bay showing intense etching of detrital grains and quartz overgrowth edges and faces. Note how most of the overgrowth prism faces are only slightly etched. 744x magnification. 305 Salts have repeatedly been identified in the accelerated weathering of sandstone, both physically by crystal growth, and in the acceleration of quartz dissolution rates (Section 9.5.3). Coastal sandstones in this study area, especially those at Jervis Bay, are some of the most highly weathered of almost all Sydney Basin quartz sandstones, and undoubtedly display the finest suite of small solutional weathering features. It must be emphasised, however, that whilst salt crystals were sometimes seen on dried rock surfaces in the field, no sodium chloride (NaCl) or other salt crystals were seen filling voids or disrupting or fracturing grains within Jervis Bay sandstones in either thin section or S.E.M, all the more remarkable when it is remembered that these samples came from highly saline marine platforms. These findings seem to be in direct contrast to the assertions of some authors (e.g. Goudie, 1974) who insist weathering of sandstones in highly saline environments is a product of mechanical breakdown by salt crystal expansion. What is evident, though, are extremely high levels of quartz etching at these locations (see also McGreevy, 1985) and these solutional textures appear to be related to high sodium chloride concentrations in the manner proposed from S.E.M studies by A.R.M. Young (1987), and from laboratory study by Damm et al (1991) who demonstrated that the rate of silica dissolution is raised by sodium chloride in sea-water solutions (Section 9.5.3). The Snapper Point Formation sandstone at Blackall Rocks along the western edge of the Sydney Basin, where large and very well developed basins are found, is finer grained than that at Jervis Bay (Plate 11.5, TS 12032). It is a grain supported, angular to sub-angular, well sorted sandstone, and the voids are filled with degraded kaolin clays, large amounts of opaques, and red-brown iron compounds. Some overgrowths and sutures are seen, but less than the other Snapper Point Formation samples, however the degree of degradation, 306 etching and embayment of these sutures, and also the detrital grains, is quite high (Plate 11.6). S.E.M imaging of the Nowra Sandstone from tower walls and corridor bases at Monolith Valley also shows highly developed system of interlocking quartz overgrowths (Plate 11.7), but chemical etching of both these quartz overgrowths and the detrital grains has been very intense (Plate 11.8). Widening of contacts between grains, even between overgrowths (Plate 11.9), is common, and voids indicated by tracer dye are very widespread, with a resultant high porosity and permeability. Much of the kaolinitic matrix clay material has either been weathered out or is in the process of degrading, with a greater proportion of void space seen toward the sandstone surface (Plate 11.10). The upper Endrick River Nowra Sandstone is much like that at Monolith Valley, and like Monolith Valley a large number of solutional basins, towers, runnels and caves, are found here. The sandstone is moderately to well sorted, rounded to sub-angular, and with extensive optically continuous quartz overgrowths. The rock is grain supported, with little matrix clay, many large voids, and thus very porous. Considerable amounts of opaques and red- brown to orange haematite coat the insides of these voids and flow between grains. Extensive etching and embayment of grains is evident, and like at Monolith Valley the opening of gaps between grains and along sutured grain/overgrowth boundaries is widespread. Toward the weathered surface large numbers of loose, very poorly cemented grains are the result of this cement destruction (Plate 11.11). 307 v*l •$** fm^ • • < * *J» ^ Plate 11.5. Fine grained Snapper Point Formation sandstone at Blackall Rocks (TS 12032). Voids are filled with degraded kaolin clays, large amounts of opaques, and red-brown iron compounds. Surface grains are still well cemented. Field of View, 3.95mm. » ,*&&*** s v ' «v.. 4> .HlK Plate 11.6. Embayed overgrowths and sutures at Blackall Rocks resulting from clay degradation. Field of View, 1.11mm. 308 EHT=15.00 kV UD= 26 mm E.M. Unit Wollongong Plate 11.7. S.E.M micrograph of sutured, interlocking but still highly permeable Nowra Sandstone at Monolith Valley. Intense non-selective etching is seen on high free-surface energy grain and overgrowth faces and edges, but lower energy faces displaying very little attack. 423x magnification. Plate 11.8. Widespread non-selective corrosion on grain surfaces and edges of overgrowths at Monolith Valley alongside uncorroded overgrowth faces. 655x magnification. Plate 11.9. Thin-section micrograph (TS 12037) of the Monolith Valley Nowra Sandstone showing illustrating widening of contacts between grains, even between overgrowths. Voids indicated by blue dye are very widespread, with a resultant high porosity and permeability. Field of View, 3.95mm. Plate 11.10. Thin-section micrograph (TS 12037) of the surface of the Monolith Valley Nowra Sandstone. This shows the high proportion of void near the rock surface and the friable sandstone resulting from degradation of the kaolinitic matrix clay and widening of voids between grains and overgrowths. Field of View, 1.56mm. 310 Quartz overgrowth development within the sandstones of the tower bulges at Bulee Ridge is also well developed, and many grains are well sutured, but the rock nonetheless retains a moderate amount of void space. There are more matrix clays than at Monolith Valley, but again some of these clays are also degraded. Weathering of the clays and etching of quartz grains is highest at the sandstone surface (Plate 11.12). The Triassic Hawkesbury Sandstone from the towers and pavements at Bonnum Pic in the central part of the study area is generally angular to sub- rounded, moderately sorted and dominantly grain supported, but parts are sometimes supported in a kaolinite matrix (Pells, 1977). Some well sutured euhedral quartz overgrowths are seen, but unlike the Snapper Point Formation or Nowra Sandstone, are not developed to to as great an extent. Etching of these grains and overgrowths has been intense in places, but not to the degree seen in the older sandstones. Because of pore-space infill by a higher proportion of matrix clays than the sampled Nowra or Snapper Point Formation sandstones, void within the Hawkesbury Sandstone at Bonnum Pic is less than in the older sandstones. Spaces are mostly filled with clay, long thin streaks of iron compounds, flecks of mica, or numerous black opaques. But even with a lower primary porosity and less pathways for penetration of etching solutions this rock still displays numerous instances of well developed etching phenomena, including many small v-pits and some larger embayments. Rare, scattered, small efflorences of unidentified salt compounds have been noted in a few overhangs or near small cliff-foot springs in both the Nowra and Hawkesbury Sandstone. Yet no microscopic evidence has been found either for significant physical rupture of the sandstone by crystal growth, or 311 Plate 11.11. Thin-section micrograph (TS 12036) of the surface of the upper Endrick River Nowra Sandstone. The high proportion of void near the rock surface and the friable sandstone resulting from degradation of the matrix clay and overgrowths is clearly seen. Many embayed overgrowths are also clearly visible. Field of View, 3.95mm. Plate 11.12. Thin-section micrograph (TS 12040) of the surface of the Nowra Sandstone at Bulee Ridge. The proportion of void near the rock surface is less than at Monolith Valley but it is still seen. The proportion of matrix clay is also slightly higher. Field of View, 3.95mm. 312 for locally increased chemical attack on the rock by the presence of salt compounds. Etching is not confined to the sandstones of the southern and central portion of the study area, as it is also widespread in the Grose Sub-Group sandstones of the Blue Mountains and Newnes Plateau. The friable sandstones across this region, including those at the Old Coach Road, Black Fellows Hand Rocks and the Temple of Doom, are all essentially similar, being composed of poorly sorted angular to sub-rounded quartzose litharenite grains of dominantly small to medium size, but with a few very large quartz grains. Generally, these sandstones are matrix supported, the clays again being dominantly kaolin with some illite (Pells, 1977; Bai et al, 1992), but some areas of grain support are found (Plate 11.13). Matrix clay and quartz overgrowths are believed to have precipitated at the same time (Bai et al, 1992). Optically continuous quartz overgrowths are found, but suturing of grains by quartz is not as common as that seen in the previously described sandstones. Void space is dependent on the degree of clay degradation; several centimetres below the rock surface the clays are often only slightly weathered, but near- surface networks of grain-bordering voids resulting from clay weathering are commonplace (plate 11.15). But this increase in permeability is not just due to clay destruction; some widening of fractures in the quartz grains are also seen, and many grains are also very irregular and etched along high free-energy grain and overgrowth boundaries, and on overgrowth faces (Plate 11.14). This near surface breakdown of the matrix, with increase in the proportion of void space, etching of grains and destruction of overgrowth sutures, leads to the granular incompetence and rapid disintegration of the rock identified with the development of the pagodas (Section 5.3.2). No evidence of salt crystal disruption or growth was found in any pagoda sandstone. 313 Plate 11.13. S.E.M micrograph of unweathered Banks Wall Sandstone from the Clarence Road quarry. Grains are covered by quartz overgrowth showing only some minor v-pitting, with virtually all void filled with unweathered kaolin clays. Plate 11.14. Higher magnification of Plate 11.13. Irregular overgrowth development and localised small, crystallographically controlled etch pits on the overgrowth surfaces. Note also the lack of quartz cement and how the individual grains were not sutured together. 314 Plate 11.15. Thin-section micrograph (TS 12042) of the surface of the Old Coach Road sandstone. Even though quart/, overgrowths cover many of the grains, they are not sutured together but surrounded by kaolin clays. Weathering of these clays at the surface leads to granular disintegration of the rock. Field of View, 3.95mm. Plate 11.16. Thin-section micrograph (TS 12044) within an iron-cemented sandstone layer at Black Fellows Hand. The quartz grains are highly embayed and etched and surrounded by a matrix of opaque iron compounds. Field of View, 1.56mm. 315 The pagoda ironstone layers are of similar fabric to the friable sandstones, but in these zones most matrix clay has been replaced, resulting in grain support in an iron-rich matrix. Etching and embayment of quartz grains and scattered overgrowths has been much more intense in these zones of high iron concentration than elsewhere within these sandstones (Plate 11.16). This higher degree of quartz etching in these zones suggests that the presence of this iron may have increased quartz solubility during diagenesis (Morris and Fletcher, 1987; Serezhinikov, 1989). 11.4. CONCLUSIONS The evidence presented in Chapters 8 and 10 for significant removal and transport of silica in this study area has been confirmed here by microscopic study of the sandstones. These examinations have revealed that large amounts of silica have been chemically removed from the rocks, that quartz grains and overgrowths are highly etched, and that matrix clays and cement are also being destroyed. Thus silica is undoubtedly being removed in solution. Within the sandstones, two main forms of etching are clearly seen, that of small, often v-shaped pits on grain and overgrowth surfaces, and much larger areas of intense, non-specific, etching. These two forms have been previously reported by several authors, and may correspond with the aggressiveness of the etching solutions (Burley and Kantorowicz, 1986). But not all areas within the sandstones are seen to be attacked equally. Detrital quartz grains, grain-to- overgrowth boundaries, overgrowth-to-overgrowth contacts and other similar discontinuity or defects are generally seen to be far more corroded than most overgrowth faces. Yet some overgrowths are etched, usually on the rhombohedral faces and especially in the most weathered sandstones. The 316 apparent crystallographic etching can be explained in terms of variable free- energy, as the overgrowths have a lower free-surface energy than detrital grain or boundary surfaces (Hurst and Bjorkum, 1986). Variability in the intensity and type of quartz etching in this region may be also linked to the degree of primary porosity, both in the amount of interlocking quartz overgrowth, and the proportion of void-filling authigenic clays. As found by Young (1988) for the sandstones of the Kimberley Region, it is the primary porosity which has the most influence on the penetration of corrosive solutions throughout a sandstone, and it is these solutions which are doing the etching; sandstones with little interconnected void provide few pathways for water penetration and are often only mildly weathered, whilst rocks with a high degree of permeability are usually deeply weathered and very highly etched at the microscopic scale. Such an association is seen here also. The Narrabeen sandstones, of high authigenic clay content and low permeability, are only mildly etched, except within the iron-layers or toward the rock surface where breakdown of the clays allows penetration of water and the rock is more intensely corroded. Similar characteristics are seen in the Bonnum Pic Hawkesbury Sandstone. The Snapper Point Formation, on the other hand, although it too has a moderate proportion of matrix clays and highly developed interlocking overgrowths, is more permeable and is therefore much more highly etched. However, at Jervis Bay this is probably also attributable to the chemical effects of sea-water salt solutions. The most highly permeable, and also most highly etched, sandstone studied here is the Nowra Sandstone from Monolith Valley. This rock has a very high proportion of interlinked void, that has allowed the unhampered penetration of water deep into the sandstone, intense and deep etching of the rock-mass, and the production of this interlocking but friable sandstone. 317 In conclusion, the types of etching seen within the Sydney Basin sandstones studied here are of similar type to that reported from quartz sandstones of both tropical and seasonally-arid tropical regions of the world. The specific sites of this etching are similar, as is the relative degree or intensity of the corrosion. Again the evidence points to a striking similarity of silica removal under both tropical and temperate climates. 318 CHAPTER 12. SUMMARY, DISCUSSION AND CONCLUSIONS 12.1. INTRODUCTION The wide ranging existence of solutional features of varying scale on quartzose rocks commonly described as resistant to chemical weathering has in recent years prompted renewed interest into the solubility of silica under diverse conditions. The previous neglect of such features has apparently been due to the long-standing, and it now seems falsely grounded, assumption that quartzose rocks are of very low or practically negligible reactivity. Even though Tricart (1972) asserted that quartzites are practically immune to chemical weathering, researchers during the last two decades have continued to return from the tropical jungles of Roraima and other areas with reports of huge, complex, quartzite landscapes that are in most respects morphologically indistinguishable from many of the worlds classic limestone karsts. As Jennings (1983) emphasised, the clear evidence of solution as the critical, if not dominant process, no longer allows these features to be simply dismissed as pseudo-karst. These solutional phenomena have been most vigorously studied in the worlds wet-tropics, with only little interest so far been shown in cooler regions. Unfortunately, however, the initial recognition and investigation of quartzite and sandstone karst in tropical regions resulted in a climatically- deterministic genetic model being developed that has repeatedly been employed where long-term tropical climates (either contemporary or assumed in the past) are regarded as critical for the genesis of these quartzite 319 or sandstone karst (e.g. White et al, 1966; Chalcraft and Pye, 1984; Pouyllau and Seurin, 1985; Busche and Sponholz, 1992). The aims of this study (Section 1.3) were to investigate the Permo-Triassic quartz sandstones of the humid-temperate Sydney Basin in south-eastern Australia to ascertain, firstly, if solutional landforms are found on the quartz sandstones of this region, and if so, how they compare morphologically to those on more soluble carbonate rocks. The second aim was to investigate if they are also comparable in type, form and scale to solutional forms described from quartzose rocks of the humid tropics. Granting that such dual morphological correspondence could be shown, what then remained to be determined was if a significant component of silica solution in the formation of these landforms could be found, by what processes this silica is liberated from the sandstones, and whether these weathering processes differ markedly to those in the tropical sandstone and quartzite karst. 12.2. SUMMARY OF FINDINGS This study established that the widespread solutional removal of silica has been important in the formation of a wide range of quartz sandstone landforms within the Sydney Basin. Table 2.1 shows the commonly accepted classification of carbonate solutional microforms, and extensive field examination has shown that most of these smaller karren, as well as several larger more complex solutional landforms (towers and caves), are also found on Sydney Basin Permo-Triassic quartz sandstones. These sandstone features are almost identical in variety of type, form, and scale, to the karst karren seen on most limestones. 320 The largest quartz sandstone landforms within the study area in which the process of silica solution can be clearly recognised are large sandstone towers, strikingly similar to limestone Tower Karst. Three main types of towers were identified. The first occurs on the Nowra Sandstone in the Budawang Range toward the southwestern end of the study area (Section 5.2.1), and is best represented around Monolith Valley and Bulee Ridge. In a similar manner to limestone towers (Brook and Ford, 1978; Day, 1978; McDonald, 1979; Zhang, 1980; Jennings, 1985; Drogue and Bidaux, 1992), preferential weathering and erosion of closely-spaced local joint sets, a pattern seen quite clearly on air photographs, has been critical in the development these towers. Structural fissuration is the principal factor of permeability of water in limestone terrain (Jakucs, 1977), and similarly, the localised, closely-spaced and regular fracturing of the Nowra Sandstone has allowed deep penetration of weathering solutions into these quite porous but interlocking sediments. Variations in lithologic factors, notably permeability along beds, and the geotechnical properties of the sandstones themselves (Section 5.3.1), also impart some control on tower morphogenesis. The end result of this deep sub-aerial weathering over a very long time period (at Monolith Valley at least from the Eocene (Young and McDougall, 1985)), is a sandstone of moderate compressive strength, but of low granular cohesiveness because of the destruction of matrix, cement and quartz sutures. The second group of sandstone towers are clearly different to those of the Budawang Range. These 'pagodas' are only found on the Blue Mountains and Newnes Plateaux along the north-western margin of the Sydney Basin (Section 5.2.1), and, individually, display much less reliance on joint-control, not being directly the product of widened joints. Pagodas are formed rather by more widespread granular disintegration and down-wearing of friable, clay- rich, Grose Sub-Group sandstones. Strong lithologic control are exerted by 321 resistant iron-indurated sandstone layers which reduce the rate of pagoda erosion, and impart the characteristic stepped pagoda shape. Towers are also seen on clayey, friable, Hawkesbury Sandstone at a few locations, notably Bonnum Pic. These towers with their slick-rock slopes are more like the pagodas than the first group of towers, but they lack the regularity of iron-layering of the Grose Sub-Group pagoda sandstones and thus the strong lithologic control. Jointing in these Bonnum Pic towers has had a slightly more pronounced role than in the pagodas, but to nowhere near the degree of importance seen in those of the Nowra Sandstone. Unlike limestone towers, none of these sandstone towers are the direct result of solution, but rather form by granular disintegration of friable sandstone. This granular breakdown has led on all these towers, to a greater or lesser degree, to rounded summits and slopes in a similar fashion to that found on the Colorado Plateau by Howard and Kochel (1988) and in the Bungle Bungle Range by Young (1987). Nonetheless, as petrographic evidence in Chapter 11 demonstrated, the variable but often intense solutional weathering of matrix clay, detrital grains and quartz overgrowths has produced rocks more friable and susceptible to erosion than similar but less weathered sandstones elsewhere. Solution has therefore played a direct and integral role in tower morphogenesis in these quartz sandstones. At a smaller scale, preferential weathering and joint widening has also been found, most notably at Jervis Bay (Section 5.4), to lead to the formation of grikes remarkably similar to those seen on limestone (Sweeting, 1966; Williams, 1966; Goldie, 1981; Ford and Williams, 1989). These sandstone grikes, like the larger towers, are covered with numerous solution basins and 322 runnels. Analysis of the rectilinear planform of the grikes on the marine platforms at Jervis Bay (Section 5.4) shows a high degree of correspondence with the local fracture network, also a characteristic feature of limestone grikes. The widths, depths and lengths of these sandstone grikes are also closely comparable to grikes in limestone. In fact, it is morphometrically very difficult to differentiate between these sandstone grikes and those of several classic limestone grike type-locations. Moreover, microscopic evidence (Section 11.3) shows that very intense solutional etching and breakdown of the sandstone along joint partings has lead to localised disintegration and thus grike enlargement. The solutional activity of natural waters in the formation of smaller forms on both carbonates and siliceous rocks, for example rock basins, has long been accepted, but, unlike limestone basins, the direct processes involved in the genesis of quartzites and quartz sandstone basins remain poorly understood (Section 2.7). Basins are extremely common on the major sandstones of this region, but have not been analysed in detail before. The discrete size and form of these basins allowed the morphometry of a large number of these sandstone basins to be examined in detail (Chapter 4), but surprisingly, considering the numerous references to basins in the limestone literature, comparable data from similar studies of limestone basins was not available. In fact, though morphometric data of only a small number of sandstone basins from three other scattered locations around the world had been previously reported (Franzle, 1971; Schipull, 1978; Cooks and Pretorious, 1987), these few studies provided more directly comparable data with local sandstone basins than the entire limestone literature. \ 323 Sandstone basins from widely scattered locations across the study area were found to have a wide range of size, and an essentially random plan-shape. They are, however, of comparable size to those reported from elsewhere in the world. Analysis of basic basin size parameters showed some very significant trends (Section 4.6) both within individual sampling locations and across the region as a whole. These size attributes, basin length, width and depth, are highly correlated (Section 4.6), but analysis of variance indicated some significant differences between sites. These departures were generally explainable, though, in terms of site-specific lithologic, vegetative, or chemical conditions. One of the most obvious of these was a marked lack of basins on the very friable sandstones of the Newnes Plateau, but the very common occurrence of them on the more resistant Hawkesbury and Shoalhaven Group sandstones. Like basins, a very considerable number of channelised water flow runnels are to be seen on most bare sandstone pavements within the Sydney Basin. Some runnels on limestone and granites have been attributed to sub-surface solutional weathering (Section 2.6.2), but the location of many of these runnels on the tops and sides of towers or boulders, and the often small catchment areas they posess, indicates not only that most must have formed sub-aerially by the action of rain or seepage water, but also that the velocity of this flowing water was too low to achieve much corrasion. Moreover the pitting of the channel floors indicates that chemical attack is the prime formative process. Runnels on Sydney Basin sandstones are, with several major exceptions, identical to those on carbonate rocks. Firstly, rillenkarren are not found on Sydney Basin sandstones. However, as rillenkarren are only reported from 324 fine- and medium-grained limestones, and usually absent from coarser- grained dolomites and marbles (Ford and Lundberg, 1987), their absence here is readily attributable to these coarser texture of the quartz sandstones. The other major divergence of sandstone runnels from their limestone cousins is that on Sydney Basin sandstones there does not appear to be the clear-cut difference between angular rimmed, sub-aerially developed rinnenkarren, and the more rounded sub-surface initiated rundkarren as there is on limestones (Ford and Lundberg, 1987). Individual sandstone runnels in this study have been found to exhibit features of both rinnenkarren and rundkarren, and appear also not to follow other trends in depth, for example, derived from limestones (Section 6.3). The exact reasons for this remain unknown, but are possibly related to variations in sandstone resistance. Further research is necessary to resolve this problem. Not only surface forms, but also subterranean caves and other integrated underground drainage networks, which are often taken on limestones to be an indicator of well developed karst, have been located in the study area. Although underground seepage water flow was certainly not unknown in this region prior to this study, probably one of the most significant discoveries of this work is that of numerous small discrete hydrologic networks within many of these sandstones. The smallest of these void systems (Section 7.2) are remarkably like limestone dip-tubes and anastomoses; they no longer carry water flow, are generally only several centimetres in diameter, structurally and lithologically controlled, and have been found in only a few locations when exposed by cliff collapse. Similar features had not previously been described in the sandstone literature. Slightly larger, tube-like networks which are not constrained by structural or lithologic factors, were also discovered 325 during this study at a number of locations across the Basin. Evidence has been found for a meandering, dendritic, nature for these tubes, and many still carry water after rain (Section 7.2). Formation of both these dip-tube anastomoses and dendritic tubes must have occurred under phreatic or epi-phreatic conditions below the water-table, and significant silica must therefore have been removed by the only means possible under these conditions, namely solution. The only other reference to similar tubes has been from sandstones of the Sahara. The largest underground networks, caves accessible to humans, are like many of those reported from other temperate or tropical sandstone regions (Section 2.3), but are not of great length. Only a small number of these caves are known within the Sydney Basin (Section 7.3) and can be seen to have formed generally by a variety of weathering and physically erosive processes. Smaller underground conduits are more common (Section 7.2) and display a wide range of phreatic and vadose characters with most exhibiting some structural control. Speleothems are unarguably most prolific in limestone caves, but are nonetheless not uncommon in caves, overhangs and on cliff walls across wide sections of the Sydney Basin (Chapter 8). Although they are very small, these various silica speleothems are highly significant as they provide definitive evidence of the solution and subsequent re-deposition of silica from within these sandstones. Some previous study had been conducted on both silica and iron-based speleothems in this region (Lassak, 1970; Young 1987; Watchman, 1990, 1992), but none have been as detailed as this current analysis where three generally 326 recognised speleothem types were found; flowstones, erratic stalactites and stalagmites. Microscopic and X-ray analysis of a number of these speleothems showed that all are composed of varying layers of amorphous opal-A and cryptocrystalline chalcedony, with some minor amounts of kaolin clays and other impurities. Levels of carbonate are extremely low. Other speleothems (tuffas, stalactites and stalagmites) of higher iron content are also found in the region, but these were not examined. In all speleothems the silica is deposited from evaporation of groundwater solutions. Stalactites draw water from within the sandstone and concentrate it at the speleothem surface by capillary forces, and likewise with stalagmites water is drawn up from the sandstone by the same process. Flowstones develop by repeated evaporation of small seepage water flows. At the speleothem surface evaporation of the liquid concentrates the dissolved minerals and continued evaporation leaves the dissolved silica behind. There is no continuous central hole down which drip-water migrates as in many carbonate speleothems. Although it is theoretically possible for crystalline silica to precipitate from groundwater solutions (Section 8.6), silica in these speleothems appears to be initially deposited as opal-A. The exact geochemical means by why this metastable amorphous silica later converts to cryptocrystalline chalcedony is still unclear. 327 12.3. DISCUSSION: SIGNIFICANCE OF THE SYDNEY BASIN SANDSTONE SOLUTIONAL LANDFORMS The solutional forms on the sandstones of the Sydney Basin are virtually identical to many of those on limestones. Moreover, as solution has played the critical role in their development, these features must be added to the increasing list of sandstone karst, thereby supporting Jennings (1983) contention that this term could no longer be restricted to carbonate terrain. The climatic determinism which has hitherto constrained the study of sandstone karst has now little to commend it because the sandstone solutional landforms of the humid-temperate Sydney Basin are similar to those in the humid-tropics. The main difference is the absence of poljes and very large cave systems from the Sydney Basin. Although very few direct morphometric data have been published from tropical areas, comparisons with published photographs indicates forms both here in the Sydney Basin and in the tropics are of similar form and dimension. This is all the more important when it is remembered that the studies of quartzite weathering processes have so often stressed the importance of tropical climates. A number of authors have associated microscopic evidence for sandstone and quartzite etching to long periods of sub-aerial weathering under hot, usually wet, tropical climatic conditions (White et al, 1966; Urbani and Szczerban, 1974; Battiau-Queney, 1984; Chalcraft and Pye, 1984; Pouyllau and Seurin, 1985; Busche and Erbe, 1987; Young, 1988; Briceno and Schubert, 1990; Yanes and Ramirez, 1990; Ghosh, 1991; Yanes and Briceno, 1993). But in the cool- temperate Sydney Basin, microscopic study (Chapter 11) revealed evidence for similar etching processes at only marginally lower intensity than that in 328 tropical quartzites. Yet, as seen in Section 3.6, palaeoclimatic indicators from this study area indicate only cool to warm-temperate conditions in southeastern Australia since at least the Early Tertiary, with no evidence of tropical conditions during this time. Quartz etching in the Sydney Basin must, therefore, have occurred under these cooler conditions. It has already been noted in Section 9.5.5 that, although silica solubility is influenced by temperature up to an unspecified reaction-kinetics controlled limiting value, the higher the rate of water throughput or 'flushing rate' in a natural environment the higher the expected rate of silica removal. Rainfall rather than temperature may be the more important factor. Although no where near the high levels received on the summits of the Roraiman tepuis, the rainfall of this region is comparable with that of many other areas of quartzite or sandstone solutional landforms such as those in temperate South Africa (Marker, 1976; Cooks and Pretorious, 1987) or Morocco (Robinson and Williams, 1992). Comparison of dissolved silica levels in this study area with those from sandstone elsewhere, including Roraima, shows that, despite great differences in flushing rates, there is no great difference in total dissolved silica in streams. Average dissolved silica in streams in the Sydney Basin study area is 4.9 mg/1, and in basins 2.8 mg/1 (Section 10.3.2) is not very much different to that of Roraima (1 to 7 mg/1) or Kakadu (5 to 7 mg/1). These Sydney Basin values provide further evidence that it is water throughput, not just high temperatures, which is important in silica solution. The theoretical chemistry of silica dissolution indicates a higher solubility under quite alkaline conditions, but field measurements indicate waters on quartzite or quartz sandstone usually have only a neutral to slightly acid pH. While this is also true for most samples collected in this study, a number of 329 samples were found to have either very low pH (between 3 and 4) usually associated with anoxic highly-organic conditions, or unexplainably high pH's above 8 or even 9 (Section 10.3.1). Under these two extremes of pH, silica is supposedly much more mobile than under near-neutral conditions (Section 9.4.2). But as shown in Section 10.3.3, this was not necessarily always found to be the case in the field. Other factors have been seen to complicate the dissolution of silica, and thus microscopic etching, in the natural environment (Section 9.5). Multivalent iron, for example, has been seen to raise the solubility of quartz, but this effect was not seen in natural waters here (Section 10.3.5). It is the organic acids, though, which are generally believed to have one of the most marked effects on quartz dissolution (Section 9.5.2). The highest recorded levels of dissolved silica in this study came from low pH, low dissolved oxygen conditions, which would seem to indicate organic acids may have been involved. Nevertheless, the results are not conclusive, especially as the identification of specific organic acids was beyond the scope of this study. Chlorides of sodium and potassium, as well as some other salts, have also been indicated in the chemical weathering of silica (Section 9.5.3). It is generally believed, both from laboratory (Dove and Crerar, 1990; Bennett, 1991; Dove and Elston, 1992) and S.E.M studies (A.R.M. Young, 1987; R.W. Young, 1988), that in aqueous solution the presence of these compounds raises the rate of dissolution of silica. Supporting evidence for these assertions was suggested from this study. Whilst no direct observations of salt crystals unequivocally sited at microscopic areas of accentuated etching were found, the study sites with the most intense small-scale solutional landforms (basins and runnels) were on the coastal platforms at Jervis Bay. Microscopically these 330 sandstones were also seen to be quite highly etched, but no salt crystals were seen physically rupturing the rocks. Sodium chloride, in sea water, therefore seems to be important in quartz sandstone weathering. The range of etching environments within this study region can thus be seen to be quite diverse. But a number of these conditions, some of which have been shown to be very important in the dissolution reactions of silica (e.g. pH, flushing rate, organic acids, salinity) are not necessarily a direct function of climate. Furthermore, the amount of dissolved silica in solution, the key factor around which the whole discussion of process revolves, is basically the same in the temperate Sydney Basin as has been found at several other tropical sandstone karst localities and even Roraima, the type-location of tropical quartzite karst. The total number and size of sandstone karst features at places like Roraima is undoubtedly greater than in the Sydney Basin. Yet if the total long-term removal of silica indicated by the size and number of karst features is compared to relative flushing rates, quartz etching in the Sydney Basin sandstones would be closely comparable to, if not in excess of, etching at places like Roraima. 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Solution Basin Morphometric Data by Field Site Snapper Point Formation Blackall Rocks (G.R. 36 13, Bindook, 1:25 000, 8929-IV-S) Ref Length Width Depth W/L Comments 1 120 60 13 0.500 Oval ,flat moss coveredfloor, vertica l walls 2 20 20 7 1.000 Circular,flat mos s coveredfloor, vertica l walls 3 60 40 9 0.667 Oval,flat moss coveredfloor, vertica l walls 4 56 55 18 0.982 Circular,flat moss coveredfloor, vertica l walls 5 135 105 23 0.778 Irregular circle,flat floor, overhun g walls, soil covered floor 6 230 130 28 0.565 Irregular,flat floor, overhun g walls, soil covered base, breached one end 7 150 100 25 0.667 Irregular oval,flat floor, overhun g walls, soil covered base 8 200 63 31 0.315 Highly irregular,flat floor, overhun g walls, soil covered base, 5cm soil 9 140 70 23 0.500 Irregular, flat floor, overhung walls, soil covered base 10 45 33 6 0.733 Within #9, irregular oval, flatfloor, overhun g walls, soil covered base 11 120 60 15 0.500 Irregular oval,flat floor, overhung walls, soil covered base, open one end 12 350 240 65 0.686 Irregular oval,flat floor, overhung walls soil covered base, open two ends 13 430 330 60 0.767 Irregular oval,flat floor, overhun g walls, soil covered base, open one end, Joins #12 14 210 180 40 0.857 Circular, flat floor, overhung walls, soil covered base, open one end, Joins #13 15 215 180 24 0.837 Circular,flat floor, overhung walls, water filled, Joins #14 16 250 160 8 0.640 Irregular oval, flat floor, overhung walls, partly soil covered base 17 210 160 40 0.762 Irregular oval, flatfloor, overhun g walls, soil covered base 18 180 140 21 0.778 Irregular oval, flatfloor, overhun g walls, soil covered base 19 80 55 5 0.688 Irregular, gentle walls,flat bottome d with moss covered floor 20 120 104 5 0.867 Irregular circle, gentle walls,flat bottome d with moss covered floor 21 150 140 35 0.933 Circular, flat bottomed with moss coveredfloor and vertical walls 22 210 200 75 0.952 Circular, flat bottomed with moss coveredfloor and vertical walls 23 240 155 56 0.646 Irregular oval, flat bottomed with moss covered floor and vertical walls 24 60 56 19 0.933 Circular, flat bottomed with moss coveredfloor and vertical walls 25 130 54 32 0.415 Irregular, flat bottomed with moss covered floor and vertical walls 26 75 55 31 0.733 Oval, flat bottomed with moss covered floor and vertical walls 27 68 43 13 0.632 Irregular oval, flat bottomed with moss covered floor and vertical walls 28 44 36 10 0.818 Circular, flat bottomed with moss coveredfloor and vertical walls 29 50 26 5 0.520 Irregular, vertical walls, flatfloor water filled 30 140 120 18 0.857 Circular, vertical walls, flatfloor, wate r filled Honeymoon Bay (G.R. 971 182, Currarong, 1:25 000, 9027-I-N) Ref Length Width Depth W/L Comments 1 14.5 11 4.6 0.759 Oval, hemispherical bottom, overhung walls 2 15.4 14.2 4.2 0.922 Irregular circle, 1/2 steep walls 1/2 overhung,flat floor 3 7 5.8 4.6 0.829 Circular, flat floor, all overhung walls 362 4 52.2 23.4 4.2 0.448 Irregular, gentle to steep sides, pitted flat floor 5 41.2 18.4 3.6 0.447 Irregular, 3/4 gentle walls 1/4 overhung walls, flatfloor with 2 pits. #6 inset in #5 6 13.6 10 4.2 0.735 Inset in #5, Oval shaped, vertical walls, hemispherical floor 7 34.2 20 4.6 0.585 Oval, 1/2 gentle 1/2 vertical walls, hemispherical floor 8 65.2 44 14 0.675 Irregular oval, gentle walls, irregular hemispherical floor 9 10.4 10.4 5 1.000 Circular, vertical walls, hemispherical floor 10 46 20.8 3.6 0.452 Oval, vertical walls,flat floor 11 112 73.4 6.8 0.655 Irregular oval, gentle walls, 1/2 flat 1/2 hemispherical floor 12 35.4 16 2.2 0.452 Oval, gentle walls,flat floor 13 45 29.2 2.8 0.649 Irregular oval, gentle walls,flat floor 14 53.6 34 4.6 0.634 Irregular oval, steep to vertical walls,flat floor 15 15 11.6 7.2 0.773 Oval, vertical walls, hemispherical floor 16 16 15.8 5.6 0.988 Circular, vertical walls,flat floor 17 31.8 29.4 6.2 0.925 Circular, 2/3 vertical 1 /3 gentle walls, hemispherical floor 18 57.2 18.4 5.8 0.322 Irregular oval, 1/2 vertical 1/2 steep walls, irregular pitted floor 19 36.6 20 19.5 0.546 Oval, vertical walls, hemispherical floor 20 25 23.4 17.4 0.936 Square, vertical walls, hemispherical floor 21 34.2 8.6 6.4 0.251 Oval, vertical walls, irregular hemispherical floor 22 103.8 93 9.2 0.896 Irregular circle, gentle to steep walls,flat floor 23 20.8 15.8 5.2 0.760 Oval, vertical walls, hemispherical floor 24 26.2 21 7.4 0.802 Circular, overhung walls, flat floor 25 52 29.2 7.6 0.562 Irregular oval, overhung walls, flat floor 26 184 129 23 0.701 Triangular, vertical to overhung sides, flat floor 27 160 99 26 0.619 Irregular oval, overhung sides,flat floor 28 105 51.6 8.4 0.491 Irregular oval, overhung sides,flat floor 29 79 36 20.8 0.456 Irregular oval, overhung sides,flat floo r 30 65 48 8.4 0.738 Oval, 1/3 overhung 2/3 gentle walls,flat floor Point Perpendicular Lighthouse (G.R. 998 142, Currarong, 1:25 000,9027-I-N) Ref Length Width Depth W/L Comments 1 127 82 24 0.646 Irregular triangle, vertical overhung walls,flat floor wit h outlet 2 119 60 19 0.504 Oval, gentle walls,flat gravel covered floor 3 54 45 3.8 0.833 Circular, gentle walls,flat gravel covered floor 4 60 37 3 0.617 Circular, gentle walls, flat floor 5 67.4 49.5 19.2 0.734 Circular, steep walls, flat floor 6 80 37 4.2 0.463 Irregular oval, gentle walls,flat floo r 7 6 5.8 2.8 0.967 Circular, vertical walls, hemispherical floor 8 5.2 4 3.4 0.769 Circular, vertical walls, hemispherical floor 9 22 14.2 4.4 0.645 Oval, 1/2 vertical walls 1/2 gentle, hemispherical floor 10 20.4 7.8 2.5 0.382 Oval, vertical walls, hemispherical floor 11 17.8 11 4.8 0.618 Rounded triangle, vertical walls, hemispherical gravel covered floor 12 45 13 8.4 0.289 Irregular oval, vertical walls, flat floor 13 121 28.5 23 0.236 Irregular diamond shape, vertical overhung walls, flat floor 14 395 150 24 0.380 Irregular, steep walls # 14 and 15 connected 15 441 333 22 0.755 Circular, vertical walls, flat floor 16 18.6 13 4.8 0.699 Oval, vertical walls, hemispherical floor 17 7.8 4.8 3.8 0.615 Oval, vertical overhung walls, hemispherical floor 18 10.2 9.2 3.2 0.902 Circular, steep walls, hemispherical floor 363 19 36 16.2 5.8 0.450 Oval, steep walls,flat floor 20 7.4 6.4 4 0.865 Circular, vertical walls, hemispherical floor 21 21.4 10.4 5.2 0.486 Oval, vertical walls, flat floor 22 52 40.4 4 0.777 Circular, steep walls,flat floor 23 41.4 24.8 4.4 0.599 Oval, 1/2 steep 1/2 gentle, hemispherical floor 24 179 117 7.8 0.654 Oval, gentle walls,flat floor 25 8.2 6.2 5.8 0.756 Circular, vertical walls, hemispherical floor 26 123.5 103 4.7 0.834 Oval, gentle walls,flat floor 27 106 35 5.2 0.330 Oval, gentle walls,flat floor 28 240 71 37 0.296 Oval, gentle walls,flat floor 29 108 62 10 0.574 Oval, gentle walls,flat floor 30 17.6 12.4 4.4 0.705 Circular, vertical overhung walls, hemispherical floor Whale Point (G.R. 018 244, Currarong, 1:25 000, 9027-I-N) Ref Length Width Depth W/L Comments 1 36 26 17 0.722 Oval, all overhung walls, flat floor 2 33 23 5.5 0.697 Oval, all overhung walls,flat floor 3 50 31 12.5 0.620 Oval, all overhung walls,flat floor 4 56 34 11 0.607 Oval, all overhung walls, flat floor 5 32 32 8 1.000 Oval, all overhung walls,flat floor 6 24 22 4 0.917 Circular, all overhung walls,flat floor 7 64 50 7 0.781 Circular, all overhung walls, flat floor 8 46 40 4.5 0.870 Circular, all overhung walls,flat floor 9 56 30 8 0.536 Oval, 1/2 overhung 1/2 gentle walls,flat floor 10 29 22 3.5 0.759 Circular, all overhung walls, flat floor 11 66 58 4 0.879 Irregular oval, 1/2 overhung 1/2 gentle walls,flat floor 12 46 40 6 0.870 Irregular square, 1/2 overhung 1/2 gentle walls,flat floor 13 30 25 6 0.833 Irregular square, 1/2 overhung 1/2 gentle walls,flat floo r 14 16 10 4.5 0.625 Circular, all overhung walls,flat floo r 15 64 33 5 0.516 Irregular, gentle walls, flat floor 16 19 12 4 0.632 Oval, all overhung walls,flat floor 17 30 29 2.5 0.967 Oval, 1/2 steep 1/2 gentle walls,flat floor 18 60 16 4 0.267 Figure 8, all gentle walls,flat floor 19 30 27 3 0.900 Circular, all gentle walls, flat floor 20 56 35 2.5 0.625 Circular, all gentle walls, flat floor 21 41 24 4 0.585 Circular, all gentle walls, flat floor 22 30 22 4 0.733 Circular, all gentle walls, flat floor 23 45 42 4.5 0.933 Circular, all gentle walls, flat floor 24 41 19 6 0.463 Oval, all gentle walls, flat floor 25 30 25 3 0.833 Circular, 1/2 steep 1/2 gentle walls, flat floor 26 42 23 3 0.548 Oval, steep walls, flat floor 27 22 18 3 0.818 Oval, steep walls, flat floor 28 23 17 4 0.739 Oval, steep walls, flat floor 29 28 20 4 0.714 Oval, steep walls,flat floo r 30 35 15 3 0.429 Oval, gentle walls, flat floor 364 Nowra Sandstone Pigeon House Mountain (G.R. 514 847, Milton, 1:25 000, 8927-II-N) Ref Length Width Depth W/L Comments 1 27 26 10 0.963 Circular, overhung walls, hemispherical floor 2 75 65 10 0.867 Circular, 1/2 vertical 1/2 steep walls, flat floor 3 12 9 3 0.750 Oval, vertical walls, hemispherical floor 4 27 21 4 0.778 Oval, steep walls, hemispherical floor 5 30 30 4.5 1.000 Circular, steep walls, hemispherical floor 6 19 17 3 0.895 Circular, steep indurated walls, hemispherical floor 7 48 37 8 0.771 Oval, steep walls, hemispherical floor 8 29 22 7 0.759 Oval, steep walls, hemispherical floor 9 100 50 10 0.500 Oval, 1/2 overhung 1/2 steep walls, flat floor, sediment filled 10 34 25 5 0.735 Irregular oval, 1/2 steep 1/2 overhung walls,flat floor 11 57 44 10 0.772 Oval, 1/3 vertical 2/3 steep walls, irregular hemispherical floor 12 43 27 10 0.628 Oval, steep to vertical walls, hemispherical floor 13 32 30 9.5 0.938 Circular, steep walls, hemispherical floor 14 18 16 5 0.889 Circular, vertical to steep walls, hemispherical floor, sediment filled, inside #13 15 30 23 7 0.767 Circular, steep walls,flat floor 16 86 40 9 0.465 Figure 8 shape, steep to overhung walls,flat floor 17 165 105 7 0.636 Oval, gentle to steep walls,flat floor 18 32 30 7 0.938 Circular, steep walls, hemispherical sediment filled floor 19 25 21 4 0.840 Oval, gentle walls, flat floor 20 51 44 13 0.863 Regular square shape, steep to overhung walls, hemispherical floor 21 118 50 13 0.424 Irregular oval, gentle walls, hemispherical floor 22 40 37 8 0.925 Circular, gentle walls, hemispherical floor 23 23 19 5 0.826 Oval, steep walls, hemispherical floor 24 36 34 9 0.944 Circular, vertical walls, hemispherical floor 25 65 55 6 0.846 Irregular circle, steep walls,flat floor 26 54 36 14 0.667 Oval, steep to overhung walls, hemispherical floor, moss filled 27 36 36 8 1.000 Circular, steep walls, hemisphericalfloor, moss filled 28 68 50 10 0.735 Irregular oval, steep walls,flat floor 29 45 40 7 0.889 Circular, steep walls, hemispherical floor 30 38 18 5 0.474 Oval, steep walls, flat floor 31 65 25 1 0.385 Oval, gentle walls, flat floor 32 48 40 7 0.833 Irregular triangle, vertical walls, flat floor Monolith 'Valle y (G.R. 443 920, Corang, 1:25 000, 8927-III-N) Ref Length Width Depth W/L Comments 1 54 48 12 0.889 Oval, steep walls, flat floor 2 25 21 8.5 0.840 Oval, steep walls, flat floor 3 29 20 4 0.690 Oval, steep walls, flat floor 4 23 17 5 0.739 Oval, steep walls, flat floor 5 10 10 3 1.000 Circular, steep walls, hemispherical floor 6 76 76 15 1.000 Square, vertical walls, flat floor 7 25 23 11 0.920 Circular, vertical walls,flat floo r 8 51 49 15 0.961 Square, vertical walls, flat floor 9 100 80 7 0.800 Oval, vertical walls, flat floor 10 33 24 11 0.727 Oval, 3/4 vertical walls,flat floor 365 11 30 24 8 0.800 Oval/round, steep walls, sediment filled, hemispherical floor 12 63 5 13 0.079 Oval, steep walls,flat floor 13 20 17 6 0.850 Circular, vertical walls,flat floor 14 7 6 5 0.857 Oval, gentle walls, hemispherical floor 15 150 43 13 0.287 Oval, gentle walls, irregularflat floor 16 9 7 4 0.778 Oval, steep walls, hemispherical floor 17 16 15 9 0.938 Circular, gentle walls, hemispherical floor 18 150 85 15 0.567 Oval, irregular steep walls,flat floor 19 42 36 11 0.857 Circular, 3/4 very steep 1/4 steep walls, flat floor 20 22 19 6 0.864 Circular, 3/4 steep walls,flat floor 21 16 15 6 0.938 Circular, 1/2 vertical 1/2 steep walls, flat floor 22 13 11 4 0.846 Circular, gentle walls,flat floor 23 70 69 12 0.986 Circular, steep walls, flat floor 24 13 12 5 0.923 Circular, 1/2 vertical 1/2 steep walls,flat floor 25 27 25 5.5 0.926 Oval, steep walls,flat floor 26 70 60 7 0.857 Oval, 1/2 steep 1/2 gentle walls, flat floor 27 118 54 11 0.458 Figure '8', 1/2 vertical 1/2 steep walls,flat irregular floor 28 64 59 6.5 0.922 Circular, steep walls, flat floor 29 10 8 4 0.800 Circular, vertical walls, hemispherical floor 30 34 23 7 0.676 Oval, all overhung walls, hemispherical floor 31 137 130 11 0.949 Heart shaped, steep walls, flat floor Tianjara Plateau Ref Length Width Depth W/L Comment 1 180 85 17 0.472 Oval, steep walls, flat floor 2 27 27 9 1.000 Circular, vertical walls, hemispherical floor 3 95 60 31 0.632 Circular, vertical walls, hemispherical floor 4 70 50 8 0.714 Oval, gentle walls,flat floor 5 70 60 21 0.857 Circular, steep walls, hemispherical floor 6 80 65 8 0.813 Circular, steep walls, hemispherical floor 7 34 30 7 0.882 Circular, steep walls, hemispherical floor 8 50 40 10 0.800 Irregular oval, 1/2 gentle 1/2 steep walls, hemispherical floor, water sample #96 9 30 18 8 0.600 Oval, steep walls, hemispherical floor 10 23 22 6 0.957 Circular, steep walls, hemispherical floor 11 23 13 11 0.565 Circular, steep walls, hemispherical floor, water sample #97 12 32 27 7 0.844 Oval, steep walls, flat floor 13 60 60 8 1.000 Triangular, gentle walls, flat floor 14 76 46 12 0.605 Oval, 1/2 vertical 1/2 steep walls, flat floor 15 45 41 8 0.911 Circular, steep walls, flat floor 16 138 70 19 0.507 Oval, vertical walls, flat floor 17 40 40 9 1.000 Circular, 1/2 vertical 1/2 steep walls, flat floor 18 88 47 20 0.534 Oval, all overhung walls, flat floor 19 281 107 29 0.381 Irregular oval, vertical walls, flat floor, moss filled 20 75 63 23 0.840 Oval, vertical to overhung walls, flat floor 21 47 47 3 1.000 Oval, gentle walls, hemispherical floor 22 130 90 19 0.692 Irregular square, vertical walls, flatfloor, mos s filled 23 80 30 9 0.375 Irregular square, vertical walls, flat floor 24 85 54 16 0.635 Irregular oval, 1/2 vertical 1/2 gentle to steep walls, irregular flat floor 25 55 45 10 0.818 Circular, 1/2 overhung 1/2 gentle walls,flat floor 366 26 112 80 15 0.714 Oval, 1/2 vertical 1/2 gentle walls,flat floor, mos s filled 27 93 30 5 0.323 Circular, 1/2 gentle 1/2 steep walls,flat floore d 28 55 50 10 0.909 Circular, steep walls,flat floor 29 110 110 35 1.000 Square, all overhung sides, flat floor, moss filled 30 220 110 30 0.500 Irregular triangle, 1/2 gentle 1/2 steep walls, flat floor 31 85 55 13 0.647 Irregular oval, vertical walls,flat floor Hawkesbury Sandstone DO)c v aie uj.K . bZU 8bz , Mittaj*ong , 1:23 uuu, oyzy-n-b) Ref Length Width Depth W/L Comments 1 37.00 35 13 0.946 Circular, vertical walls, hemispherical floor 2 47.00 22 24 0.468 Oval, vertical to overhung walls, hemispherical floor 3 21.00 14 3 0.667 Irregular oval, gentle walls, hemispherical floor 4 33.00 17 4 0.515 Irregular, gentle walls, flat floor 5 77.00 57 8 0.740 Irregular oval, gentle walls,flat floor 6 21.00 14 3 0.667 Oval, gentle walls,flat floor 7 22.00 13 3 0.591 Irregular oval, gentle walls,flat floor 8 102.00 57 6 0.559 Irregular, gentle walls, flat floor 9 85.00 55 5 0.647 Irregular, gentle walls,flat floor 10 136.00 67 13 0.493 Irregular, gentle walls,flat floor 11 60.00 38 12 0.633 Oval, steep walls,flat floor 12 143.00 45 8 0.315 Irregular, gentle walls,flat floor 13 60.00 50 50 0.833 Circular, vertical walls, hemispherical floor 14 37.00 18 2 0.486 Irregular, gentle walls, flat floor 15 15.00 9 1 0.600 Irregular oval, gentle walls,flat floo r 16 46.00 19 2 0.413 Irregular oval, gentle walls, flat floor 17 27.00 12 2 0.444 Irregular, gentle walls, flat floor 18 43.00 22 4 0.512 Irregular oval, gentle walls,flat floo r 19 22.00 19 5 0.864 Circular, gentle walls,flat floor 20 33.00 19 5 0.576 Irregular rectangle, gentle walls, flat floor 21 46.00 34 3 0.739 Irregular circle, gentle walls,flat floor 22 50.00 46 2 0.920 Circular, gentle walls,flat floo r 23 135.00 70 22 0.519 Irregular rectangle, gentle walls, flat floor 24 28.00 14 7 0.500 Irregular, gentle walls,flat floor 25 41.00 28 26 0.683 Irregular oval, vertical to overhung walls,flat floor 26 69.00 65 105 0.942 Circular, overhung walls, hemispherical floor 27 30.00 16 12 0.533 Oval, vertical walls, hemispherical floor 28 88.00 47 18 0.534 Irregular oval, vertical walls,flat floor 29 59.00 51 25 0.864 Circular, vertical, walls, flat floor 30 50.00 49 100 0.980 Circular, vertical walls, hemispherical floor Maldon Weir (G.R. 815 125, Picton 1:25 000, 9029-IV-S) Ref Length Width Depth W/L Comments 36 12 1.2 0.333 Irregular, gentle walls, flat floor 16 14 0.875 Circular, steep walls, hemispherical floor Oval, steep walls, flat floor 46 37 10 0.804 Irregular, gentle walls, hemispherical floor 23 13 0.565 367 5 34 22 6 0.647 Irregular oval, gentle walls, hemispherical floor 6 23 14 4 0.609 Oval, gentle walls,flat floor 7 30 16 3 0.533 Irregular, gentle walls, hemispherical floor 8 26 25 4 0.962 Circular, gentle walls, hemispherical floor 9 140 102 14 0.729 Irregular oval, steep walled,flat bottomed 10 160 73 9 0.456 Irregular, gentle walls,flat bottome d 11 23 12 4 0.522 Irregular oval, gentle walls, flat bottomed 12 8 5.5 3 0.688 Irregular oval, gentle walls,flat bottomed 13 25 18 9 0.720 Irregular circle, steep walls, flat bottomed 14 55 41 7 0.745 Irregular circle, gentle walls hemispherical floor 15 25 24 10 0.960 Circular, steep walls,flat bottome d 16 48 27 8 0.563 Irregular, gentle walls,flat bottomed 17 20 13 6 0.650 Oval, gentle walls, flat bottomed 18 16 13 6 0.813 Circular, gentle walls, hemispherical bottom 19 50 25 8 0.500 Rounded rectangle, 1/2 gentle 1/2 steep walls, flat floor 20 12 9 .2 0.750 Circular, gentle walls, hemispherical floor Maldon Bridge (G.R. 819 128, Picton 1:25 000,9029-IV-S) Ref Length Width Depth W/L Comments 1 71.00 65.00 7.00 0.915 Circular, gentle walls,flat floor 2 69.00 48.00 2.50 0.696 Irregular oval, gentle walls, flat floor 3 50.00 47.00 26.00 0.940 Circular, vertical walls, hemispherical floor 4 79.00 75.00 26.00 0.949 Circular, vertical walls, flat floor 5 86.00 61.00 33.00 0.709 Irregular circle, vertical to overhung walls, flat floor, #5,6,7 interconnected 6 119.00 43.00 25.00 0.361 Irregular, vertical walls, flat floor 7 8.70 3.80 2.00 0.437 Irregular oval, gentle walls, hemispherical floor 8 30.80 17.40 17.80 0.565 Oval, vertical walls, hemispherical floor 9 25.00 10.00 7.80 0.400 Irregular, 1/2 steep 1/2 gentle walls, hemispherical floor 10 23.00 8.60 6.00 0.374 Highly irregular, vertical walls, hemispherical floor 11 104.00 97.00 9.00 0.933 Circular, gentle walls, flat floor 12 37.00 24.00 3.20 0.649 Oval, gentle walls,flat floo r 13 46.00 31.00 8.50 0.674 Oval, 1/2 gentle 1/2 steep walls, hemispherical floor 14 257.00 90.00 37.00 0.350 Highly irregular, gentle walls,flat floor 15 270.00 210.00 67.00 0.778 Irregular circle, vertical walls 1/4 overhung,flat floor 16 32.00 11.00 7.60 0.344 Irregular, gentle walls, hemispherical floor 17 78.00 36.00 25.00 0.462 Irregular oval, 1/2 steep 1/2 vertical walls, hemispherical floor 18 30.00 27.00 21.00 0.900 Circular, vertical walls, hemispherical floor 19 20.60 17.80 4.80 0.864 Circular, gentle walls,flat floor 20 35.40 27.40 3.50 0.774 Irregular circle, gentle walls, hemispherical floor 21 11.40 7.40 4.40 0.649 Irregular, gentle walls, flat floor 22 256.00 105.00 58.00 0.410 Irregular, vertical walls, flat floor 23 95.00 75.00 18.00 0.789 Irregular oval, vertical to steep walls,flat floor 24 55.00 37.00 27.00 0.673 Oval, steep walls 1 /2 overhung, hemispherical floor 25 120.00 93.00 25.20 0.775 Circular, steep walls, flat floor 26 55.00 45.00 13.80 0.818 Circular, steep walls, hemispherical floor 27 164.00 146.00 31.60 0.890 Circular, gentle walls, flat floor 28 40.00 36.20 23.80 0.905 Circular, steep walls, hemispherical floor 368 Carrington Falls (G.R. 849 660, Kangaroo Valley, 1:25 000, 9028-IV-S) Ref Length Width Depth W/L Comments 1 216 175 13 0.810 Irregular, gentle walls, flat floor 2 106 80 9 0.755 Round rectangle, gentle walls, flat floor 3 119 79 9 0.664 Rounded rectangle, gentle walls, flat floor 4 89 70 14 0.787 Rounded rectangle, vertical walls,flat floor 5 79 63 10 0.797 Rounded rectangle, vertical walls,flat floor 6 44 42 6 0.955 Circular, steep walls,flat floor 7 33 24 10 0.727 Oval, vertical walls, hemispherical floor, along joint 8 222 90 16 0.405 Rounded rectangle, vertical walls, flat floor 9 80 48 12 0.600 Rounded rectangle, vertical walls,flat floor 10 88 63 6 0.716 Rounded rectangle, steep walls,flat floo r 11 60 38 5 0.633 Round rectangle, gentle walls,flat floor 12 58 42 6 0.724 Round rectangle, steep walls, flat floor 13 70 58 8 0.829 Rounded rectangle, vertical walls,flat floor 14 47 42 9 0.894 Rounded rectangle, vertical walls,flat floor 15 65 40 20 0.615 Rounded rectangle, vertical walls, irregular floor 16 30 18 10 0.600 Oval, vertical walls,flat floor 17 19 11 9 0.579 Oval, vertical walls, flat floor 18 28 9 13 0.321 Oval, vertical walls, flat floor 19 29 29 8 1.000 Oval, vertical walls, flat floor 20 108 41 7 0.380 Oval, steep walls,flat floor 21 20 19 3 0.950 Oval, gentle walls, flat floor 22 188 94 11 0.500 Circular, steep walls, hemispherical floor 23 93 37 17 0.398 Oval, steep walls,flat floor 24 123 67 8 0.545 Oval, vertical walls, flat floor 25 111 70 12 0.631 Oval, vertical walls, flat floor 26 82 40 14 0.488 Oval, vertical walls, flat floor 27 31 29 3 0.935 Circular, gentle walls, hemispherical floor 28 34 22 7 0.647 Irregular, gentle walls, irregular floor 29 117 55 6 0.470 Oval, gentle walls, irregular floor 30 200 92 13 0.460 Oval, gentle walls, flat floor, Joint infloor eate n out to 25 cm deep and 15 cm wide Mermaids Pool (G.R. 795 085, Picton 1:25 000, 9029-IV-S) Ref Length Width Depth W/L Comments 1 21 9 2 0.429 Irregular, gentle walls,flat floor 2 11 7 1.5 0.636 Circular, vertical walls,flat floo r 3 13 5 2 0.385 Crescent shaped, gentle walls,flat floo r 4 28 22 4.5 0.786 Circular, gentle walls, hemispherical floor 5 34 19 3 0.559 Circular, gentle walls, hemispherical floor 6 34 21 6 0.618 Circular, gentle walls,flat floor 7 31 24 6 0.774 Circular,l/2 gentle 1/2 steep walls, flat floor 8 24 22 3 0.917 Circular, gentle walls, hemispherical floor 9 136 50 4 0.368 Circular to '8' shaped with #10,11,12 inside, gentle walls, flat floor 10 66 33 32 0.500 Circular, vertical walls, hemispherical floor 11 31 20 25 0.645 Circular, highly undercut walls (L40 W34 at 10cm depth), hemispherical floor, full of sand and gravel 12 26 22 17 0.846 Circular, vertical to overhung walls, hemispherical floor, full of gravel and rocks 13 89 80 12 0.899 Circular, steep to vertical walls, irregular floor 369 14 500 187 29 0.374 Oval, steep walls,flat floor 15 30 19 8 0.633 Circular, gentle walls, hemispherical floor 16 43 20 6 0.465 Circular, gentle walls, hemispherical floor 17 65 45 3 0.692 Circular, gentle walls, hemispherical floor 18 9 5 1 0.556 Oval, gentle walls, hemispherical floor 19 127 107 2 0.843 Irregular circle, gentle walls,flat floo r 20 29 12 3 0.414 circular withflat floor gentle 21 17 12 4 0.706 Circular, gentle to steep walls, hemispherical floor 22 25 12 4 0.480 Circular, gentle walls,flat floor 23 17 10 3 0.588 Circular, gentle walls,flat floo r 24 21 16 4 0.762 Circular, gentle walls, hemispherical floor 25 28 20 9 0.714 Circular, steep walls, hemispherical floor 26 16 10 5 0.625 Circular, gentle walls,flat floor 27 17 10 3 0.588 Circular, gentle walls,flat floor 28 6 5 2 0.833 Circular, gentle walls, hemispherical floor 29 30 27 15 0.900 Circular, steep to vertical walls, hemispherical floor 30 37 28 23 0.757 Circular, vertical walls, hemispherical floor Bargo River (G.R. 798 080, Picton, 1:25 000, 9029-IV-S) Ref Length Width Depth W/L Comments 1 60 41 18 0.683 Irregular, vertical walls, flat floor 2 53 18 8 0.340 Irregular, gentle walls, flat floor 3 103 46 15 0.447 Irregular, gentle walls,flat floo r 4 40 13 21 0.325 Irregular, vertical walls,flat floor 5 56 55 43 0.982 Circular, vertical to overhung walls, hemispherical floor 6 184 79 19 0.429 Rectangle, gentle walls,flat floor 7 43 34 5 0.791 Rounded triangle, gentle walls,flat floor 8 47 23 3 0.489 Oval, gentle walls,flat floor 9 36 15 7 0.417 Oval, gentle walls,flat floor 10 82 38 6 0.463 Oval, gentle walls, flat floor 11 44 17 2 0.386 Oval, gentle walls, flat floor 12 55 37 6 0.673 Oval, gentle walls,flat floor 13 92 41 4 0.446 Oval, gentle walls, flat floor 14 40 26 4 0.650 Oval, gentle walls, flat floor 15 43 23 4 0.535 Oval, gentle walls, flat floor 16 131 52 20 0.397 Oval, 1/2 steep 1/2 gentle walls, flat floor 17 111 80 13 0.721 Oval, 1/2 overhung 1/2 gentle walls, flat floor 18 71 36 7 0.500 Oval, gentle walls, flat floor 19 56 21 4 0.375 Oval, gentle walls, flat floor 20 16 11 8 0.688 Oval, gentle walls, flat floor 21 42 12 9 0.286 Oval, gentle walls, flat floor 22 43 37 46 0.860 Oval, highly undercut, hemisphericalfloor, 1 /2 full gravel 23 149 75 15 0.503 Irregular, steep walls, flat floor 24 77 35 2 0.455 Oval, gentle walls, flat floor 25 62 30 6 0.484 Oval, gentle walls, flat floor 26 77 39 6 0.506 Oval, gentle walls, flat floor 27 770 470 53 0.610 Irregular, gentle walls, irregular floor 28 281 86 15 0.306 Irregular, gentle walls, flatfloor i n crossbed plane 29 136 85 11 0.625 Irregular, gentle walls, irregular floor 370 113 83 17 0.735 Irregular, gentle walls,flat floor 125 61 13 0.488 Irregular, gentle walls, flat floor Weeping Falls (G.E.. 674 862,Mittagong , 1:25 000, 8929-II-S) Re* Length Width Depth W/L Comments 1 50 25 9 0.500 Oval, steep walls, hemisphericalfloor formed on bedding between steeply dipping xbeds 2 23 17 2 0.739 Circular, gentle walls, flat floor 3 50 19 6 0.380 Irregular, gentle walls, generally flat floor 4 80 59 7 0.738 Irregular circle, gentle walls, generallyflat floor 5 81 30 6 0.370 Highly irregular, gentle walls,flat floor on xbed plane 6 200 110 30 0.550 Oval, 1 /2 steep 1/2 overhung walls,flat floor on xbed plane 7 36 34 6 0.944 Circular, gentle walls,flat floo r on xbed plane 8 50 29 10 0.580 Oval, steep walls, flatfloor on xbed plane 9 142 51 16 0.359 Highly irregular, vertical walls, flat floor on xbed plane 10 92 74 14 0.804 Irregular circle, 1/2 gentle 1/2 steep walls,flat floo r on xbed plane 11 60 37 8 0.617 Oval, gentle walls, flat floor on xbed plane 12 89 43 14 0.483 Oval ,steep walls,flat floo r on xbed plane 13 50 24 10 0.480 Irregular, vertical walls,flat floor on xbed plane 14 58 48 9 0.828 Circular, gentle walls,flat floo r on xbed plane 15 24 18 5 0.750 Irregular circle, gentle walls, flat floor on xbed plane 16 114 94 9 0.825 Irregular circle, gentle walls,flat floo r on xbed plane 17 80 46 8 0.575 Irregular, gentle walls,flat floor o n xbed plane 18 28 22 2 0.786 Rounded rectangle, gentle walls,flat floor on xbed plane 19 10 5 3 0.500 Irregular, gentle walls,flat floor on xbed plane 20 37 17 3 0.459 Irregular oval, gentle walls, flatfloor o n xbed plane 21 38 24 7 0.632 Oval, gentle walls,flat floo r on xbed plane 22 51 14 5 0.275 Oval, gentle walls,flat floo r on xbed plane 23 60 42 6 0.700 Irregular circle, gentle walls,flat floor o n xbed plane 24 97 61 8 0.629 Irregular, gentle walls,flat floor o n xbed plane 25 160 57 14 0.356 Elongate oval, vertical walls,flat floor on xbed plane 26 140 65 5 0.464 Irregular, vertical walls,flat floor on xbed plane 27 33 25 4 0.758 Circular, gentle walls, flat floor on xbed plane 28 18 16 4 0.889 Irregular circle, gentle walls, flat floor on xbed plane 29 32 11 6 0.344 Highly irregular, gentle walls,flat floo r on xbed plane 30 56 25 5 0.446 Oval, gentle walls, flat floor on xbed plane Keira (G.R. 015 923, Wollongong, 1:25 000, 9029-II-S) Ref Length Width Depth W/L Comments 1 76 44 10.8 0.579 Oval, gentle walls, flat floored 2 71 36 20.4 0.507 Oval, gentle walls, hemispherical floor 3 80 55 9.2 0.688 Irregular oval, gentle walls,flat floor covered in sediment and moss 4 25 16 9.8 0.640 Irregular oval, gentle walls, hemispherical floor 5 48 40 6.2 0.833 Circular, gentle walls, hemispherical floor 6 41 21 2.2 0.512 Rounded rectangle, gentle walls, flat floor 7 136 55.4 3.4 0.407 Irregular rectangle, gentle walls, flat floor 8 50 32 1.6 0.640 Oval, gentle walls, flat floor 9 57 54 2.8 0.947 Circular, gentle walls, irregular floor 371 10 17 14 5 0.824 Circular, gentle walls, hemispherical floor, sediment filled 11 20 17 2.2 0.850 Circular, gentle walls, flat floor 12 18 14.4 6.8 0.800 Irregular circle, gentle to steep walls, hemispherical floor 13 25.4 23.2 5.8 0.913 Circular, gentle walls, hemispherical floor 14 14 10.8 3.6 0.771 Circular, gentle walls,flat floor 15 10.8 10.8 1 1.000 Circular, gentle walls,flat floor 16 15 11.8 4.4 0.787 Irregular circle, gentle walls, flat floor, sediment and moss filled 17 11.4 10.4 3.8 0.912 Circular, gentle to steep walls, flatfloor, sediment and leaf litter filled 18 26 23.8 14.8 0.915 Circular, overhanging walls,flat floor 19 87 46 16.6 0.529 Irregular oval, steep to overhanging sides,flat floor 20 77 46 11 0.597 Irregular rectangle, gentle to steep walls,flat floor 21 29.2 28.2 20.4 0.966 Circular, gentle walls,flat floor, wet moss covered floor 22 19.6 11.6 4.4 0.592 Irregular oval, gentle walls,flat floor 23 42 33 6 0.786 Circular, gentle walls,flat floo r 24 11 11 3.2 1.000 Circular, gentle walls, hemispherical floor 25 28.2 21.8 9.5 0.773 Irregular circle, gentle to steep walls, hemispherical floor Willow Vale (G.R. 671 870, Mittagong, 1:25 000, 8929-II-S) Ref Length Width Depth W/L Comments 1 113 60 33 0.531 Irregular, steep to vertical walls,flat floor 2 12.2 8 7 0.656 Oval, vertical walls, flat floor 3 99 77 21 0.778 Oval, gentle to steep walls,flat floor 4 35 23 6.4 0.657 Irregular oval, gentle walls,flat floor 5 18 17 2.8 0.944 Circular, gentle walls,flat floo r 6 70 46 8 0.657 Irregular oval, gentle walls, flat floor 7 32 28 4.6 0.875 Circular, gentle walls, flat floor 8 39 26 2.2 0.667 Irregular oval, gentle walls, flat floor 9 16 14 1 0.875 Circular, gentle walls, flat floor 10 11 6 0.5 0.545 Irregular, gentle walls,flat floo r 11 14.5 12 2.5 0.828 Circular, gentle walls,flat floor 12 40.5 25 3.5 0.617 Irregular oval, gentle walls,flat floor 13 48 35 7.5 0.729 Oval, vertical walls, flat floor 14 30 18 5 0.600 Irregular oval, vertical walls,flat floor 15 23 12 3 0.522 Irregular, vertical walls, flat floor 16 24 13 2 0.542 Irregular, 1/2 steep 1/2 vertical walls,flat floor 17 10 9 2 0.900 Circular, vertical walls,flat floor 18 17 12 3 0.706 Irregular circle, 1/2 steep 1/2 gentle walls,flat floor 19 28 17 7 0.607 Oval, vertical walls, flat floor 20 23 19.5 3 0.848 Circular, vertical walls,flat floo r 21 30 17 3.5 0.567 Irregular, gentle walls,flat floo r 372 Appendix 2. Results of the Kruskal-Wallis and Multiple Comparison Tests Kruskal-Wallis Test of Hawkesbury Sandstone basin lengths 1= Box Vale, 2=Carrington Falls, 3=Maldon Bridge, 4= Maldon Weir, 5= Bargo River, 6= Mermaids Pool, 7= Mt Keira, 8= Weeping Falls, 9= Willow Vale. H0 = A*i = M2 = M« a = 0.05 Box Vale Carrington Maldon Maldon Bargo Mermaids Mt Keira Weeping Willow (1) Falls (2) Bridge (3) Weir (4) River (5) Pool (6) (7) Falls (8) Vale (9) n 30 30 28 20 31 30 25 30 21 Ri 3762 4815 3955 1696 5139 2549 2287 4305 1625 Ri 125.40 160.52 141.27 84.80 165.79 84.99 91.48 143.50 77.38 D.F = 8 Cases = 245 Groups = 9 Hc = 52.22 = £0.05,8 15.507 therefore reject H0 Multiple Comparison test of Hawkesbury Sandstone basin lengths. H0 = Ml = A<2 = Vn oc = 0.05 Ranked means 9,4,6,7,3,8,2,5 Comparison Difference Standard Conclusion Q ^<0.05,9 Error 5v9 88.41 20.029 4.414 3.179 Reject HQ 5v4 80.99 20.325 3.984 3.179 Reject H0 5v6 80.80 18.150 4.452 3.179 Reject H0 5v7 74.31 19.050 3.900 3.179 Reject H0 5vl 40.39 18.150 2.225 3.179 Accept H0 2v9 83.13 20.163 4.123 3.179 Reject HQ 2v4 75.71 20.458 3.701 3.179 Reject H0 2v6 75.53 18.298 4.128 3.179 Reject H0 2v7 69.04 19.191 3.597 3.179 Reject H0 2vl 35.12 18.298 1.919 3.179 Accept H0 8v9 66.12 20.163 3.279 3.179 Reject H0 8v4 58.70 20.458 2.869 3.179 Accept H0 3v9 63.89 20.458 3.122 3.179 Accept H0 1 v9 48.02 20.163 2.381 3.179 Accept H0 7v9 14.01 20.977 0.672 3.179 Accept H0 373 Kruskal-Wallis Test of Hawkesbury Sandstone basin widths 1= Box Vale, 2=Carrington Falls, 3=Maldon Bridge, 4= Maldon Weir, 5= Bargo River, 6= Mermaids Pool, 7= Mt Keira, 8= Weeping Falls, 9= Willow Vale. H0 = M> = M2 = M„ <* = 0.05 Box Vale Carrington Maldon Maldon Bargo Mermaids Mt Keira Weeping Willow (D Falls (2) Bridge (3) Weir (4) River (5) Pool (6) (7) Falls (8) Vale (9) n 30 30 28 20 31 30 25 30 21 Ri 3743 4948 4125 1768 4555 2603 2597 4012 1781 Ri 124.76 164.95 147.32 88.42 146.95 86.78 103.90 133.75 84.81 D.F = 8 Cases = 245 Groups = 9 Hc = 38.58 = Zo.05,8 15.507 therefore reject H0 Multiple Comparison test of Hawkesbury Sandstone basin widths H0 = Mi = M2 = M» « = 0-05 Ranked means 9,6,4,7,1,8,5,3,2 Comparison Difference Standard Conclusion Q ^<0.05,9 Error 2v9 80.14 20.164 3.974 3.179 Reject H0 2v6 78.17 18.298 4.271 3.179 Reject H0 2v4 76.52 20.458 3.740 3.179 Reject HQ 2v7 61.05 19.191 3.181 3.179 Reject HQ 2vl 40.18 18.292 2.196 3.179 Accept H0 3v9 62.51 20.458 3.055 3.179 Accept H0 5v9 62.14 20.029 3.102 3.179 Accept H0 8v9 48.94 20.163 2.427 3.179 Accept H0 Kruskal-Wallis Test of Hawkesbury Sandstone basin depths 1= Box Vale, 2=Carrington Falls, 3=Maldon Bridge, 4= Maldon Weir, 5= Bargo River, 6= Mermaids Pool, 7= Mt Keira, 8= Weeping Falls, 9= Willow Vale. HG = Mi = M2 = M* 374 Box Vale Carrington Maldon Maldon Bargo Mermaids Mt Keira Weeping Willow (1) Falls (2) Bridge (3) Weir (4) River (5) Pool (6) (7) Falls (8) Vale (9) n 30 30 28 20 31 30 25 30 21 Ri 3695 4474 4700 2081 4444 2858 2652 3610 1618 123.18 149.15 167.86 104.07 143.35 95.27 106.10 120.35 77.07 R; D.F = 8 Cases = 245 Groups = 9 Hc = 34.25 J£o.o5,8 = 15.507 therefore reject H0 Multiple Comparison test of Hawkesbury Sandstone basin depths HG = Mi = M2 = M„ a = 0.05 Ranked means 9,6,4,7,8,1,5,2,3 Comparison Difference Standard Conclusion Q ^0.05,9 Error 3v9 90.77 20.458 4.437 3.179 Reject H0 3v6 72.59 18.622 3.898 3.179 Reject HQ 3v4 63.78 20.748 3.074 3.179 Accept H0 2v9 72.07 20.164 3.574 3.179 Reject HQ 2v6 53.88 18.298 2.944 3.179 Accept H0 5v9 66.28 20.026 3.310 3.179 Reject H0 5v6 48.09 18.150 2.649 3.179 Accept H0 lv9 46.12 20.164 2.28 3.179 Accept H0 Kruskal-Wallis Test of Nowra Sandstone basin lengths 1= Pigeon House Mt., 2=Monolith Valley, 3=Tianjara Plateau. H0 = M. = M2 = Mn a = 0.05 Pigeon Monolith Tianjara House (1) Valley (2) Plateau (3) n 32 31 31 Ri 1381 1164 1919 R, 43.17 37.65 61.90 D.F = 2 Cases = 94 Groups = 3 Hc = 13.57 5 991 Xl.osa = - therefore reject H0 375 Multiplp Comparison test of Nowra Sandstone basin lengths H0 = Mi = M2 = M„ oc = 0.05 Ranked means 3,1,2 Comparison Difference Standard Conclusion Q Qo.05,3 Error 3v2 24.34 6.85 3.55 3.486 Reject HQ 18.73 3vl 6.80 2.75 3.486 Accept H0 Kruskal-Wallis Test of Nowra Sandstone basin widths 1= Pigeon House Mt., 2=Monolith Valley, 3=Tianjara Plateau. H0 = /i, = JLI2 = jun a = 0.05 Pigeon Monolith Tianjara House (1) Valley (2) Plateau (3) n 32 31 31 R 1365 1168 1931 R. 42.65 37.69 62.30 D.F = 2 Cases = 94 Groups = 3 Hc = 14.16 %lo5,2 = 5-991 therefore reject H0 Multiple Comparison test of Nowra Sandstone basin widths H0 = Mi = M2 = Mn « = 0.05 Ranked means 3,1,2 Comparison Difference Standard Conclusion Q ^0.05,3 Error 3v2 24.61 6.85 3.59 3.486 Reject Ho 3vl 4.96 6.80 0.729 3.486 Accept H0 Kruskal-Wallis Test of Nowra Sandstone basin depths 1= Pigeon House Mt., 2=Monolith Valley, 3=Tianjara Plateau. H0 = Mi = li2= Vn a = 0.05 Pigeon Monolith Tianjara House (1) Valley (2) Plateau (3) n 32 31 31 ^ 1263 1326 1935 ^ 37.59 42.79 62.43 D.F = 2 Cases = 94 Groups = 3 Hc = 14.51 = Zo.o5>2 5-991 therefore reject H0 Multiple Comparison test of Nowra Sandstone basin depths H0 = Mi = M2 = M„ a = 0.05 Ranked means 3,2,1 Comparison Difference Standard Conclusion Q Vo.05,3 Error 3vl 24.84 6.87 3.61 3.486 Reject HQ 3v2 19.64 6.93 2.83 3.486 Accept H0 Kruskal-Wallis Test of Snapper Point Formation basin lengths 1= Honeymoon Bay, 2=Whale Point, 3=Point Perpendicular, 4 = Blackall Rocks. HG = Mi = M2 = M„ a = 0.05 Honeymoon Whale Point Point Blackall Rocks Bay (1) (2) Perpendicular (3) n 30 30 30 30 Ri 1473 1364 1661 2760 R. 49.12 45.48 55.38 92.01 D.F = 3 Cases = 120 Groups = 4 Hc = 34.080 = #0.05.3 7.815 therefore reject H0 377 Multiple Comparison test of Snapper Point Formation basin lengths HG = Mi = M2 = M„ « = 0.05 Ranked means 2,1,3,4 Comparison Difference Standard Condusion Q V0.05,4 Error 4vl 46.58 6.35 7.33 3.314 Reject HQ 4v2 42.90 6.35 6.75 3.314 Reject HQ 4v3 36.63 6.35 5.77 3.314 Reject HQ 3vl 9.90 6.36 1.55 3.314 Accept H0 Kruskal-Wallis Test of Snapper Point Formation basin widths 1= Honeymoon Bay, 2=Whale Point, 3=Point Perpendicular, 4 = Blackall Rocks. HQ = Mi = M2 = M„ a = 0.05 Honeymoon Whale Point Point Blackall Rocks Bay (1) (2) Perpendicular (3) n 30 30 30 30 Ri 1412 1486 1527 2834 R> 47.07 49.55 50.92 94.46 D.F = 3 Cases = 120 Groups = 4 Hc = 38.335 = #0053 7.815 therefore reject H0 Multiple Comparison test of Snapper Point Formation basin widths H0 = fi, = /i2 = p.n a = 0.05 Ranked means 4,3,2,1 Conclusion Comparison Difference Standard Q Qo.05,4 Error 4vl 47.40 6.35 7.46 3.314 Reject H0 4v2 44.92 6.35 7.07 3.314 Reject H0 4v3 43.55 6.35 6.85 3.314 Reject HQ 3vl 3.85 6.35 0.60 3.314 Accept H0 Kruskal-Wallis Test of Snapper Point Formation basin depths 1= Honeymoon Bay, 2=Whale Point, 3=Point Perpendicular, 4 = Blackall Rocks. HG = Mi = M2 = Mn a = 0.05 Honeymoon Whale Point Point Blackall Rocks Bay (1) (2) Perpendicular (3) n 30 30 30 30 R> 1734 1138 1568 2819 R> 57.82 37.95 52.26 93.97 D.F = 3 Cases = 120 Groups =4 Hc = 42.280 = #o.o5,3 7.815 therefore reject H0 Multiple Comparison test of Snapper Point Formation basin depths H0 = Mi = M2 = M„ cc = 0.05 Ranked means 4,1,3,2 Comparison Difference Standard Conclusion Q Vo.05,4 Error 4v2 56.02 6.35 8.82 3.314 Reject HQ 4v3 41.70 6.35 6.56 3.314 Reject HQ 4vl 36.15 6.35 5.69 3.314 Reject HQ lv2 19.87 6.35 3.12 3.314 Accept H0 379 Appendix 3. Dissolved Iron, Silica, Oxygen and pH Determinations from Basins and Steams # Sample Fe Si DO pH Comments Location mg/1 mg/1 mg/1 1 Nepean River, <0.1 2.0 8.5 8.5 Maldon Weir 2 Maldon Weir 0.3 <0.4 8.0 6.9 Medium basin 6cm deep on bench beside river. basin Numerous leaves in pool. 3 Moule's Bore <0.1 6.5 8.0 3.9 Bore water from Narrabeen Group sandstones, Mittagong 100m deep. 5 Maldon Weir <0.1 1.0 10 7.0 10cm deep basin. No visible organic matter. basin 6 Maldon Weir 0.15 2.0 10 6.0 Medium size shallow and irregular basin. Lots basin of organics. 7 Maldon Weir 0.1 0.6 10 6.4 Medium large shallow and irregular basin. basin Some leaves. 8 Maldon Weir <0.1 3.0 - 9.0 Medium basin. Grass growing in water. basin 9 Maldon Weir <0.1 2.0 9.0 9.5 Point where seepage runs out of medium basin rounded flat bottomed basin and into runnel. 10 Maldon Weir <0.1 2.0 4.5 9.2 Shallow irregular basin beside weir. Green- basin grey algal matter in basin. 11 Maldon Weir <0.1 3.0 8.0 9.6 Shallow medium irregular basin. Leaves, twigs basin insects and grey-green algae on base. 12 Maldon Weir 0.3 3.0 6 8.6 Small medium deep basin. Very high organics. basin Water decidedly green 13 Maldon Weir <0.1 0.6 9 7.8 Medium eliptical basin. Leaves, twigs and green basin algae,. 14 Maldon Weir 0.1 2.0 8 6.7 Small overhanging basin. Leaves and insects in basin water. 15 Maldon Weir <0.1 2.5 11 9.2 Deep basin. Leaves and twigs in water. basin 16 Maldon Weir <0.1 3.5 9 7.8 Rain within 3 days and reasonable rain for River several weeks. 17 Maldon Weir - - - 9.0 Same as #12. basin 18 Maldon Weir <0.1 1.25 14 7.1 Same as #14. basin 19 Maldon Weir <0.1 1.5 16 9.0 Same as #12. High pH? HC1 test for carbonate basin showed negative. 20 Maldon Weir <0.1 2.0 6 5.8 Same as #9. basin 21 Maldon Weir <0.1 3.0 9 6.1 Same as #8. basin 22 Maldon Weir <0.1 0.6 8 6.1 Same as #7. basin 23 Maldon Weir 0.1 4.0 6 5.8 Medium irregular basin. Cloudy water with basin leaves and insects. 24 Spring, Bundanoon <0.1 6.5 - 5.8 First spring on track from Fairy Bower Falls to Amphitheatre. 25 Fairy Bower Ck <0.1 7.0 6 5.0 Fairy Bower Creek. Bundanoon 26 Fairy Bower Ck 0.3 1.5 4 5.5 Basin beside #25. Fairy Bower Creek, leaves Bundanoon basin twigs in water. 27 Wishing Well <0.1 0.4 " 5.6 Wishing Well. Bundanoon 28 Wishing Well 0.1 1.0 " 5.6 Basin near car park at Wishing Well. Bundanoon basin 29 Little Capertee Ck, <0.1 8.0 11 6.7 Little Capertee Ck Newnes. Newnes 30 Wolgan River, <0.1 7.0 10 6.9 Wolgan River. Newnes 31 Wallaby Tail <0.1 4.0 10 5.7 Canyon Ck, Newnes 32 Basal pool, Big <0.1 12.0 8 6.2 Hole 33 Maldon Weir <0.1 2.0 10 8.6 Seepage from under blocks N end rock platform. basin 7 days since rain. Full analysis by BACAS. 380 34 Iviaidon Weir <0.i 2.5 11 9.4 Seepage from under blocks. Shallow end. basin 35 Maldon Weir 0.1 1.5 6 8.2 Same as #34. Deeper end. Full analysis by basin BACAS. 36 Maldon Weir - - - 9.2 Same as #34 but 2hrs later. Full analysis by basin BACAS. 37 Maldon Weir 0.1 6.0 8 7.6 Basin. Large amount of leaves and twigs. basin 38 Maldon Weir 0.2 3.0 9 6.1 Basin with leaves and twigs. Full analysis by basin BACAS. 39 Maldon Weir 1.4 2.5 <4 5.6 Dark water and full of organic debris. basin 40 Maldon Weir 1.0 3.5 6 5.9 Irregular triangle basin. Twigs, leaves and basin fallen and stone debris. 41 Maldon Weir <0.1 1.5 9 9.1 Medium crescent shaped basin. A few twigs and basin leaves and insects. Full analysis by BACAS. 42 Maldon Weir 0.1 1.5 8 6.8 Crescent shaped basin. Leaves, twigs and basin blackberry vine growing in water. 43 Maldon Weir 0.1 3.0 9 6.7 Large irregular shallow basin. Green algae on basin bottom with sprinkling of leaves and twigs and insects. 44 Maldon Weir <0.1 1.0 8 6.7 Large irregular pool. Leaves, twigs and insects basin in water. 45 Maldon Weir <0.1 2.5 10 6.8 Medium '8' shaped basin. Some scattered leaves basin and twigs in water. 46 Maldon Weir <0.1 1.5 9 6.5 Oval basin. Some leaves in water. basin 47 Whale Point, <0.1 <0.4 10 8.2 Samll basin on tidal platform. Sea water. Full Beecroft Pen. basin analysis by BACAS. 48 Whale Point, <0.1 2.0 10 8.5 Series of basins on block at edge of vegetation. Beecroft Pen. basin Rainwater with salt spray. Full analysis by BACAS. 49 Honeymoon Bay <0.1 2.5 10 8.9 Basin above tide. Wave splash?. Full analysis basin by BACAS. 50 Point <0.1 0.4 12 6.3 Plate 4.2 Perpendicular basins 51 Point <0.1 <0.4 9 5.6 Two large interconnected '8' Basins. Rainwater. Perpendicular 52 Point <0.1 <0.4 11 6.0 Basin Perpendicular 53 Little Beecroft 0.15 3.5 10 3.2 Small creek draining swmp E side Lobster Bay. Head 54 ------55 ------56 Palona Cave Royal <0.1 2.5 10 4.6 Palona Cave creek water. pH of creek 4.6,5.0 in National Park. puddles below overhang of cave. 57 Deep Pass Cave <0.1 5.0 8.5 5.3 water 58 Claustral Canyon <0.1 5.0 8.5 7,6 Canyon section below falls. 59 Nayook Brook, <0.1 4.0 8.5 6.3 Creek water collected near falls and canyon Deep Pass section. 60 Nayook Brook, 0.1 12.0 9.0 3.4 Solution basin in undercut right of creek below Deep Pass canyon section with falls. Close to claystone band. Beside #59. 61 Wingecarribe <0.1 10.0 6.5 9.2 Overhung basin 2.5m by 2m by 0.5m. Flat floor River basin and a little green algae, 100m east of bridge. 62 Wingecarribe <0.1 5.0 9.0 9.3 Large gently sloping sided flat bottom basin River basin west or #61. 4m by 3rn by 0.4m. Green algae. 63 Wingecarribe <0.1 3.0 7.0 8.2 Medium basin 1.5 by 1.75 by 0.3m gentle to steep River basin sided basin, hemisperical floor. Near #62. Brown algae on floor. 64 Wingecarribe 0.1 0.3 8.0 8 Small 1.0 by 0.6 by 0.2m flat floor basin east of River basin #63. 65 Wingecarribe <0.1 4.5 9.0 8.5 Small 0.5 by 0.3 by 0.2m basin. All overhung River basin sides and flat floor. 66 Wingecarribe <0.1 2.0 9.0 9.1 Small 0.5 by 0.4 by 0.7m basin. Vertical sides River basin and green algae in water. 67 Wingecarribe <0.1 0.6 8.0 7.6 Wingecarribe River western side below bridge. River 68 Wishing Well, 0.5 8.0 <4 6.2 Medium oval basin 20m SE car park. 1.5 by 0.5 Bundanoon by 0.4m. Insects and browm algae on bottom. 381 69 Nayook Brook, 0.1 5.5 6.0 7.2 Waterfall at cave upstream of canyon section. Deep Paas Canvon 70 Breakfast Creek <0.1 7.0 6.0 6.1 Upper Canyon section. 71 Bungleboori Creek <0.1 5.0 9.0 8.3 At Hole in Wall exit track. High pH may be due to storage, samples in aluminium Sigg bottle and transferee! to plastic 1.5 hrs later 72 Tiger Snake <0.1 6.0 8.5 6.4 1 /2 way up cave in pool. Canyon Cave 73 Hole in the Wall <0.1 7.0 10.0 4.8 At first 90 degright-hand tur n in top canyon. Canyon 74 Banks Canyon <0.1 3.5 9.0 6.7 At the base of the 2nd last waterfall. 75 Seepage from <0.1 8.0 9.0 5 From small cave in wall of canyon, true left beading plane, upstream from Hole on the Wall Canyon. Bungleboori Canyon 76 Bungleboori Creek <0.1 7.0 10.0 5.9 77 Tiger Snake <0.1 6.0 8.5 5.8 1/2 way up cave in pool. Canyon Cave 78 Nayook Brook, <0.1 5.5 9.0 6.5 Same spot as #59. Deep Pass Canyon 79 Wallaby Tail <0.1 1.0 10.0 7.1 About 100m upstream of where canyon cut Canyon major cliffs into Wolgan Valley. 80 Wreck Point, Jervis <0.1 3.5 9.0 8.9 Basins in blocks. Basin #7. Bay 81 Wreck Point, Jervis <0.1 <0.4 <4 8.4 Same place as #80. Bayi (3.5) 82 Wreck Point, Jervis <0.1 1.3 6.0 8.5 On pavement in front of blocks. Fresh water. Bay 83 Wreck Point, Jervis <0.1 5.0 9.0 8.6 On pavement in front of blocks. Fresh water. Bay 84 Wreck Point, Jervis <0.1 3.0 8.0 8.6 Basin on blocks. Bay 85 Lobster Point, 0.25 0.6 6.5 7.9 Basin at griked area. Jervis Bay 86 Lobster Point, <0.1 0.4 <4 8.1 Basin at griked area. Jervis Bay 87 Lobster Point, <0.1 1.5 8.0 8 Basin at griked area. Jervis Bay 88 Lobster Point, <0.1 1.5 8.0 8.4 Basin at griked area. Jervis Bay 89 Lobster Point, <0.1 0.4 8.0 8.1 Basin at griked area. Jervis Bay 90 Kanagrara Walls <0.1 1.0 4.0 4.0 Basin on plateau. 91 Kanagrara Walls <0.1 6.0 6.0 4.9 Basin on plateau. 92 Kanagrara Walls 2.8 12 <4 3.9 Basin on plateau, brown organic scum on bottom of basin. 93 Kanagrara Walls <0.1 3.0 5.0 3.8 Basin on plateau. ^ s 60 X C TJ - fxS " s' P J" 60 u X bO+3 s *x B c ^ V- 60 .Sot .2 •" J3 m 0 « S^ ^ U5 > bo "1*- ft •° 01 •S o 'S3 m re O en O (X p CS 0) Irj? Ml*- T3 „r ° 4-1 "M O 6