Stratigraphy, Sedimentology and Tectonic Significance of the Talaterang and Shoalhaven Groups in the Southern Sydney Basin
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1995 Stratigraphy, sedimentology and tectonic significance of the Talaterang and Shoalhaven groups in the Southern Sydney Basin Stuart Clifford Tye University of Wollongong
Recommended Citation Tye, Stuart Clifford, Stratigraphy, sedimentology and tectonic significance of the Talaterang and Shoalhaven groups in the Southern Sydney Basin, Doctor of Philosophy thesis, School of Geosciences, University of Wollongong, 1995. http://ro.uow.edu.au/theses/ 1983
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STRATIGRAPHY, SEDIMENTOLOGY AND TECTONIC SIGNIFICANCE OF THE TALATERANG AND SHOALHAVEN GROUPS IN THE SOUTHERN SYDNEY BASIN
A thesis submitted in fulfilment of the requirements for the award of the degree of
DOCTOR OF PHILOSOPHY
THE UNIVERSITY OF WOLLONGONG NEW SOUTH WALES, AUSTRALIA
by
STUART CLIFFORD TYE BSc (Hons), James Cook University of North Queensland
SCHOOL OF GEOSCIENCES 1995 ABSTRACT
The Permian (Sakmarian-Artinskian) Talaterang and Shoalhaven Groups form the basal part of the Sydney Basin succession at its southernmost onshore extremity. A new stratigraphic model is proposed for the southern Sydney Basin and, although the previous group division is retained, considerable rearrangement of formations within and between the groups has been necessary as a result of recent field work. The Talaterang Group now includes the Clyde Coal Measures (incorporating the previous Pigeon House Creek Siltstone) and the Wasp Head Formation. The lower units in the overlying Shoalhaven Group are the Yadboro and Tallong Conglomerates, Pebbley Beach Formation, Yarrunga Coal Measures and Snapper Point Formation. The Yarrunga Coal Measures is now considered to be a completely separate unit from the Clyde Coal Measures and overlies the Tallong and Yadboro Conglomerates. Five distinct depositional systems are recognised. Within the Talaterang Group, north-directed sediment dispersal in the mud-rich alluvial Clyde Coal Measures sequence and high energy east-directed debris flows in the Wasp Head Formation (system 1) suggest axial and transverse drainage related to possible north-trending extensional (rift) sub-basins similar to units in the Gunnedah and Bo wen Basins. A succeeding phase of passive thermal subsidence initiated deposition of the Shoalhaven Group comprising a high energy west-directed alluvial braidplain to coastal succession (Yadboro and Tallong Conglomerates, Yarrunga Coal Measures and Pebbley Beach Formation; system 2), a broadly transgressive fluvial to marine sandstone and siltstone succession (Snapper Point Formation and Wandrawandian Siltstone; system 3), a progradational (regressive) shoreface succession (the lower Nowra Sandstone; system 4) and a transgressive marine succession (upper Nowra Sandstone and Berry Siltstone; system 5). Two tectonic phases correspond with the lithostratigraphic group divisions. The Talaterang Group was deposited within fault-bounded sub-basins (grabens or half grabens) as a result of an extensional phase which is widely documented at this stratigraphic level elsewhere in the Sydney-Bowen Basin. The Shoalhaven Group was deposited during a second phase represented by thermal sag and embryonic foreland development. Major flooding events which culminated in maximum flooding surfaces within the Wandrawandian Siltstone and the Berry Siltstone resulted from foreland accretion events during early basin development. This is indicated by a change from wave-dominated to longshore tidal facies within shoreface sediments near the top of Snapper Point Formation, and the presence of a tuffaceous unit in the Wandrawandian Siltstone, indicating that the foreland may have become emergent at this time. This inferred tectonic activity may represent the onset of the Hunter-Bowen Orogeny which came to a climax much later during the Late Permian. The Nowra sandstone represents a progradational shoreface system which was derived from the cratonic western margin of the basin. This progradation may have resulted from uplift and subsequent erosion of the foreswell or forebulge of the basin, related to the tectonic loading event at the onset of deposition of the Wandrawandian Siltstone. Three orders of sea level change are recognised within the succession. Third order change is the result of dominantly tectonic processes related to thermal subsidence and foreland accretion events. Fourth and fifth order sea level changes resulted in facies changes and parasequence development within the Yadboro and Tallong Conglomerates, Pebbley Beach Formation and Snapper Point Formation. There is good evidence within the Pebbley Beach Formation that these fourth and fifth order sea level changes were accompanied by climatic changes. On this basis fourth and fifth order sea level changes are attributed to Milankovitch Orbital forcing mechanisms. Fourth and fifth order •cyclicity is superimposed on the larger third order tectonic trend. The Talaterang and Shoalhaven groups provides insight into sedimentation at the cratonic margin of a foreland basin during embryonic stages of development. The succession reveals the complex interaction between tectonic affects (subsidence and uplift) and eustatic sea-level changes. ACKNOWLEDGEMENTS
Firstly, I would like to thank in general, the academic and technical staff of the Department/Discipline of Geology at the University of Wollongong for their assistance during the three and bit years that it took to complete this PhD. Thankyou to the Tasmanides Research Program which provided financial support for the scholarship.
In particular I would like to thank my supervisor; Brian (Indiana) Jones, for his constructive criticism and general support. I would also like to thank Colin Murray-Wallace and Adrian Hutton; the former for reading early drafts of chapters and the latter for long hours lifting core boxes at the Londonderry Core Library. Thanks to Dave Carrie and Max Perkins who provided essential technical support in sample preparation and computery things. Thanks also to Chris Fergusson whom provided me with employment within the department for the last six months, so that I could finish the thesis in house. I would also like to thank all my fellow postgraduate students who provided light relief, especially Tim Green for the long technical discussions over lunch at the bar.
In addition to the folk at the University of Wollongong I would also give special thanks to Chris Fielding from the University of Queensland who put me on the right track during the latter half of 1993.
I am grateful for the access and the help provided by the Londonderry Core Library of the Department of mineral resources during the long hours of core logging. Thankyou to John and Jackie Bamberry who provided much needed core data.
I am grateful to my parents who have provided unerring support during my entire career as a student.
Last of all I thank my family; Kerrie, Euan, Bailey and the one in utero who never failed to be there when I needed them. TABLE OF CONTENTS
1.0 INTRODUCTION 1 1.1 Tectonic Development of the Sydney Basin 1 1.2 Overview of Permian to Triassic sedimentation within the Sydney Basin . . 2 1.3 Aims 2 1.4 Database 4 1.5 Basement and Intrusive Geology 4 1.6 Structure 4 1.7 Previous work in the southern Sydney Basin 4 1.8 Permian Sea-level Change 5 1.9 Geographic and climatic setting 6
2.0 STRATIGRAPHY 7 2.1 Talaterang Group 7 2.1.1 Clyde Coal Measures 8 2.1.2 Pigeon House Creek Siltstone 9 2.1.3 Wasp Head Formation 10 2.1.4 Related Units 11 2.2 Shoalhaven Group 11 2.2.1 Yadboro and Tallong Conglomerates and equivalents 12 2.2.2 Yarrunga Coal Measures 13 2.2.3 Pebbley Beach Formation 14 2.2.4 Snapper Point Formation 15 2.2.5 Wandrawandian Siltstone and Nowra Sandstone 15 3.0 SEDIMENTOLOGY OF THE TALATERANG GROUP 17 3.1 Clyde Coal Measures 17 3.1.1 Facies Analysis 17 3.1.2 Pigeon House Creek Siltstone 24 3.1.3 Depositional Systems 26 3.1.4 Discussion and implications for basin development 29 3.2 Wasp Head Formation 30 3.2.1 Facies analysis 30 3.2.2 Depositional systems and sea-level history 39 3.3 Depositional setting of the Talaterang Group 42
4.0 SEDIMENTOLOGY OF THE SHOALHAVEN GROUP 43 4.1 Yadboro, Tallong Conglomerate and Equivalents 43 4.1.1 Lithofacies 43 4.1.2 Badgery's Breccia 47 4.1.3 Fluvial style 48 4.1.4 Vertical facies changes 51 4.1.5 Isopachs and Palaeocurrents 52 4.1.6 Depositional model 54 4.2 Yarrunga Coal Measures 55 4.2.1 Facies analysis 56 4.2.2 Depositional system 58 4.3 Pebbley Beach Formation 59 4.3.1 Facies analysis 59 4.3.2 Climatic change and possible Milankovitch orbital forcing 67 4.3.3 Depositional model 68 4.4 Snapper Point Formation 72 4.4.1 Facies analysis Il 4.4.2 Palaeocurrents and palaeoshoreline oz 4.4.3 Isopachs 83 4.4.4 Vertical and lateral facies relationships °^ 4.4.5 Lateral facies changes and depositional model 91 4.5 Wandrawandian Siltstone 94 4.5.1 Facies description "4 4.5.2 Warden Head 95 4.5.3 Isopachs 96 4.5.4 Depositional model 96 4.6 Nowra Sandstone • 96 4.6.1 Lithofacies 97 4.6.2 Palaeocurrents 101 4.6.3 Isopachs 101 4.6.4 Depositional model 102
5.0 PETROLOGY 105 5.1 Sandstone Petrography 105 5.1.1 Texture 105 5.1.2 Detrital Minerals 105 5.1.3 Authigenic Minerals 107 5.1.4 Classification 107 5.2 Provenance 108 5.3 Implications for basin development 109
6.0 DEPOSITIONAL SYSTEMS AND TECTONIC SETTING Ill 6.1 Depositional Systems Ill 6.1.1 Clyde Coal Measures - Wasp Head Formation alluvial/marine shelf system Ill 6.1.2 System 2 - Yadboro/Tallong - Pebbley Beach - Yarrunga bedload fluvial to marine system 113 6.1.3 System 3 - Snapper Point - Wandrawandian marine shelf 115 6.1.4 System 4 - Wandrawandian - Nowra progradational wedge 119 6.1.5 System 5 - Upper Nowra - Berry transgressive shelf 121 6.2 Hierarchy of sea-level change 122 6.2.1 Third order cyclcity 122 6.2.2 Fourth and Fifth order cycles 123 6.3 Global Implications 124
7.0 CONCLUSIONS 127 7.1 Stratigraphic conclusions 127 7.2 Sedimentological conclusions 127 7.3 Petrographic Conclusions 129 7.4 Tectonic Conclusions 129
REFERENCES 131
FIGURES - CHAPTER 1 FIGURES - CHAPTER 2 FIGURES - CHAPTER 3 FIGURES - CHAPTER 4 FIGURES - CHAPTER 5 FIGURES - CHAPTER 6 TABLES APPENDIX 1 - LOCATIONS OF MEASURED SECTIONS APPENDIX 2 - MEASURED SECTIONS APPENDDC 3 - PALAEOCURRENT DATA APPENDIX 4 - LIST OF SAMPLES AND POINT COUNT DATA 1.0 INTRODUCTION
The study area is located within the southernmost Sydney Basin which forms part of the larger Permian to Triassic Sydney-Bowen Basin (Fig 1.1). The area includes all Permian strata that lie between Nowra and South Durras along the coast and Tallong to the west (Fig. 1.1). This includes much of the plateau and gorge country of Morton National Park. The inaccessibility of this region may help to explain the paucity of geological studies carried out in a region which lies within 300 km of Sydney and less than 2 hours drive from Wollongong. The Early Permian (Sakmarian-Artinskian) Talaterang and Shoalhaven Groups are the focus of this study (Fig. 1.1), which comprehensively examines the stratigraphy and sedimentology of the Early Permian formations in order to explain both the tectonic and palaeogeographic development of the basin during its embryonic stages.
1.1 Tectonic Development of the Sydney Basin The Sydney basin is part of me larger Sydney-Gunnedah-Bowen Basin (Fig. 1.2), which is related to the major Permian to Triassic Pangean basins along me Panthalassan margin of Gondwana. This major system is found in eastern Australia, Antarctica, India, South Africa and South America. Before the Early Permian, Eastern Australia had a complex tectonic history. During the Late Carboniferous (Pennsylvanian) the convergent plate margin within eastern Australia changed to a dextral transform margin as a result of a collision between a mid-ocean ridge and a trench system (Murray et al. 1987; Fergusson & Leitch 1993) similar to me San Andreas fault system in western United States. This change formed me Texas Coffs Harbour Megafold and caused cessation of convergent tectonics along the eastern Australian margin. The Early Permian (approximately 280 Ma; Murray et al. 1987) marks a major reorganisation of the plates and the resumption of a convergent tectonic regime. The mechanism by which subsidence of the Sydney-Bowen Basin was initiated in me Early Permian is still controversial (Schiebner 1993). Veevers et al. (1994a) related me development of the basin to transtension associated with me rotation and heat release within Pangaea during me Late Carboniferous. This period is marked by me intrusion of Carboniferous granitic complexes. Veevers et al (1994b) described the Permian to Triassic history of the basin by dividing it into 7 stages. The Permian stages are in agreement with those outlined by Baker et al. (1993; Fig. 1.3). These stages are outlined below. Stage A: Initial extension and volcanism began in me Early Permian and extended from 290-268 Ma. Sedimentation within this stage is generally restricted to sub-basins which developed as a result of rifting. Stage B: Extension was followed by a general sag over me entire platform, giving rise to marine conditions and the initiation of an embryonic magmatic arc and foreland basin during the period 268-258 Ma. The magmatic arc is
1 represented by the present position of the New England Fold Belt in eastern Australia. Jones et al. (1984) postulated that a hypothetical magmatic arc (me Currarong Orogen) lay offshore to the southeast of the basin. Post- Triassicrifting associated with the opening of the Tasman Sea has removed all remnants of this arc. Stages C-F: After 258 Ma (the approximate age of the Hunter Bowen Orogeny) the Sydney-Bowen Basin had developed into a mature foreland basin. Stage G: The foreland stage continued untilrifting of the orogen during stage G in the Late Triassic.
1.2 Overview of Permian to Triassic sedimentation within the Sydney Basin Deposition within me Sydney-Bowen Basin (Fig. 1.4) began during me Early Permian with me onset ofrifting an d thermal sag (see above). Deposition of the Talaterang and Shoalhaven Groups occurred during this phase of tectonism (Tye et al. 1995). The onset of tectonism is marked by widespread volcanism in many parts of the basin, but it is absent in me southern Sydney Basin succession. Units deposited during this phase are the Rylstone Volcanics in me northern Sydney Basin, me Werrie Basalt and me Boggabri Volcanics in me Gunnedah Basin and me Lizzie Creek and Comet Volcanics in me Bowen Basin. The onset of widespread thermal subsidence in conjunction with a eustatic sea level rise, caused a major transgression which led to me deposition of the shallow marine sequences of the lower Shoalhaven Group. Uplift and volcanism during the Late Permian marked me onset of the foreland basin stage (stage C), referred to as me Hunter-Bowen Orogeny (Schiebner 1974). The Gerringong Volcanics in me southern Sydney Basin, which were formed during this interval, were probably associated with a developing magmatic arc to the east of the present exposed basin. Widespread regression over the basin led to the deposition of Late Permian coal measure sequences in me southern and northern Sydney Basin. Sedimentary environments were dominated by alluvial fan, alluvial plain and deltaic complexes (Bamberry 1991). The Late Permian coal measures were succeeded by conglomerate, sandstone and shale of a dominantly fluvial environment (Denghani 1994). This succession is represented by me Late Permian to Triassic Narrabeen Group within me Sydney Basin. The top of me Bald Hill Claystone marks a small marine transgression near me top of me Narrabeen Group. Uplift and erosion of the Lachlan Fold Belt resulted in a rejuvenation and reorganisation of me drainage system and the deposition of me Triassic Hawkesbury Sandstone which achieves a maximum thickness of 300 m (Conaghan & Jones 1975). The last stage of sedimentation within me Sydney Basin is represented by me paralic shale dominated Wianamatta Group.
1.3 Aims To date there have been no comprehensive studies of me Early Permian succession of me
2 southern Sydney Basin. The tectonic context and the controlling mechanisms of sedimentation have not been adequately assessed. This study will attempt to redress these inadequacies through detailed sedimentological analysis. The relationship between tectonics and eustatic sea level change will be examined. The central focus of this study will be me sedimentology of me various formations (chapters 3 and 4) which comprise the Shoalhaven and Talaterang Groups. Before considering the sedimentology, however, me stratigraphy of the southern Sydney Basin has been reassessed, as detailed mapping has revealed existing models to be flawed. A new lithostratigraphic model (outlined in chapter 2) forms me basis of a new tectonic framework for me southern Sydney Basin which is consistent with models proposed elsewhere in me Sydney-Bowen Basin (e.g. Baker et al. 1993; Veevers et al. 1994b). Sedimentary provenance will be considered briefly in a petrology chapter (chapter 5) and builds upon me comprehensive petrological study undertaken by Gostin (1968). The final chapter (chapter 6) provides a detailed sedimentological and tectonic interpretation of the Talaterang and Shoalhaven Groups and attempts to relate these units to me rest of me Sydney Bowen Basin and the other Permo-Triassic pangean basins along the panthalassan margin of Gondwana. The Sydney Basin is interpreted as a retro-arc or embryonic foreland basin during me Early Permian. This study provides me opportunity to study in detail, a sedimentary succession that was deposited at the cratonic margin of the basin during this early stage of foreland basin development and, in this sense, me study will build upon me work of Devlin et al. (1993) and Cant and Stockmal (1993) on other foreland basins. The specific questions which form me focus of this study are: a) Are existing stratigraphic models adequate for the southern Sydney Basin? b) What sedimentary environments were responsible for me deposition of me southern Sydney Basin succession? c) What was the palaeogeographic development of me southern Sydney Basin during me Early Permian? d) What affect have tectonics, eustasy and climate had upon sedimentation within me basin? e) What can me sedimentary succession of me southern Sydney Basin reveal about me tectonic development of the Sydney Basin during me Early Permian? f) How does the succession conform with existing tectonic models of me Sydney-Bowen Basin and correlative successions in other Permian-Triassic Pangean Basins along me Panthalassan margin of Gondwanaland? Are mere any implications for these successions? This work will compliment the work of Carr (1984), Bamberry (1991) and Denghani (1994) who studied me Late Permian volcanics, Illawarra Coal Measures and Narrabeen Group of me southern Sydney Basin, respectively.
3 1.4 Database A total of 108 detailed sedimentary sections were measured in the study area (Fig. 1.5; Appendix 1). Lateral correlations between sections in the gorges could be determined by air photo interpretation. In addition, data from 41 drill holes (Fig. 1.5, Appendix 2) were incorporated into me study. Of these, ten of the fully cored Elecom Clyde River cores drilled by the Electricity Commission in 1981 and DM Callala DDH 1 were logged in detail. Data from a further 30 drill holes were incorporated into me study. Topographic maps were used to provide an approximation of unit thickness between measured sections for the purpose of isopach map construction. This method has been found useful by Le Roux and Jones (1994) who tested its reliability for me Nowra Sandstone within me same area. Measured sections have been annotated using symbols shown in Figure 1.6. Palaeocurrent data from all formations is presented as Appendix 3. Petrographic data is presented in Appendix 4.
1.5 Basement and Intrusive Geology The basement consists of highly deformed Ordovician to Devonian units of the Lachlan Fold Belt. A number of igneous intrusions are found within me area (Fig. 1.1). The most notable of these are me Milton Monzonite, Termeil Monzogabbro and, in me subsurface, the Coonemia Monzogabbro. K-Ar dating by Facer and Carr (1979) showed the age of these intrusions to be Late Permian and as such they were probably intruded contemporaneously with the deposition of the Gerringong Volcanics at me top of the Shoalhaven Group. Basalt and diorite of Tertiary age can be found overlying Permian Formations as cappings on mountains.
1.6 Structure In me southern Sydney Basin me exposed basal part of the Permian sedimentary succession is situated close to the western cratonic margin of the basin and, more to me point, was distant from the eastern margin which bore the brunt of the Permo-Triassic Hunter-Bowen contractional event. As a consequence, the Talaterang and Shoalhaven Groups have remained relatively undeformed with gentle easterly and northeasterly dips of 2°- 6° being typical. Thrust faulting, which affected Permian successions at some eastern localities, such as Jervis Bay and Warden Head, are interpreted as resulting from me Late Permian Hunter-Bowen Orogeny (Wiles 1995).
1.7 Previous work in the southern Sydney Basin The earliest work in this region was carried out by David and Stonier (1891) and Harper (1915). These workers named some of me basic stratigraphic units in me area and published the first account of me Clyde Coal Measures. The first comprehensive study of me area was me reconnaissance mapping undertaken by McElroy and Rose (1962). They proposed a stratigraphic model for me southern Sydney Basin which was later modified by Gostin and Herbert (1973) and Herbert (1980a). Subsequent attempts to modify the stratigraphy were carried out by Evans
4 et al. (1983) and Evans (1991). Gostin (1968) undertook a detailed study of the coastal exposures of the southern Sydney Basin which was later built upon by me work of Carey (1978), Ramli and Crook (1978), Runnegar (1980a), Stutchbury (1989), Bann (1990), Mifsud (1990) and Straub (1993). In me inland parts of me southern basin work has been less intense. Herbert (1972) proposed an interpretation for me basal Yadboro and Tallong Conglomerates and Seggie (1978) and Walker (1980) carried out detailed mapping studies within the Budawang Ranges in me southwestern part of me basin. Le Roux and Jones (1994) published a detailed sedimentological study of the Nowra Sandstone. Bembrick and Holmes (1976) and Elecom (1986) published regional studies based on drillcore analysis. These reports provided important subsurface information. Paleontological studies based on coastal exposures were published by Runnegar (1969, 1980a) and Dickins et al. (1969). Runnegar (1979) also provided a detailed account of me occurrence of Eurydesma fauna within me Pebbley Beach Formation. Palynological studies relevant to the area are those of Helby and Herbert (1971), concerning me age of the Pigeon House Creek Siltstone, and those of Evans et al. (1983) and Evans (1991). To date mere has been no detailed and comprehensive stratigraphic and sedimentological studies of the southern Sydney Basin. In the light of recent developments in me understanding of the tectonic development of the Sydney-Bowen Basin (e.g. Baker et al 1993; Tadros 1993b; Veevers et al. 1994b) it is important to examine the context of me sediments at the southernmost extremity of me basin. Preliminary results which reassess me stratigraphy of the study area have already been published (Fielding and Tye 1994; Tye and Fielding 1994; Tye et al. 1995; Tye et al. in press).
1.8 Permian Sea-level Change There have been few sequence stratigraphic studies undertaken within me Sydney Basin (see section 1.7). Arditto (1991) recognised six eustatic cycles within me Late Permian Illawarra Coal Measures and proposed an approximate duration of 4-6 Ma for each cycle which is in me range of third order cyclicity (see Vail et al. 1977 for definition of cycle periodicity). In contrast Herbert (1994) interpreted cycles within the Newcastle Coal Measures as having fourth order cyclicity (500 000 to 200 000 yr). The Early Permian corresponds with a period of general sea levelrise i n response to the melting of a major ice sheet which was prevalent during me Late Carboniferous (Veevers & Powell 1987). This sea-level change is interpreted by Veevers and Powell (1987) as a eustatic 3rd order sea level change. Fourth and fifth order cyclothem sequences with approximate periodicities of 400 000 to 10 000 years have been widely identified within Late Carboniferous successions (e.g. Klein & Kupperman 1992; Maynard & Leeder 1992; Calder & Gibling 1994) and are interpreted as being glacial-eustatic in origin, related to Milankovitch (1941) orbital
5 forcing mechanisms. In me Early Permian, cycles with similar periodicities have been recognised (e.g. Berger et al 1989; Borer & Harris 1991; Miller & West 1993; Yang & Baumfalk 1994) and are similarly interpreted as Milankovitch (1941) orbitally forced cycles.
1.9 Geographic and climatic setting During the Early Permian Australia was part of the large Gondawana land mass. Gondwana comprised the amalgamation of Australia, Antarctica, India, Africa and South America. Eastern Australia was located at me margin of me continent, connected to Antarctica and adjacent to the palaeo-Pacific Ocean (Fig. 1.7). The South Pole was located towards the eastern edge of Antarctica (Crowell & Frakes 1973), near to eastern Australia, suggesting that the latitude of the southern Sydney Basin was similar to mat of the present day Ross Ice Shelf. Previous climatic studies (Gostin 1968; Dickins 1984) have concluded that eastern Australia and in particular me southern Sydney Basin was in a cold climate phase. Gostin (1968) sited glacial dropstones and petrographic evidence of ice influence within the basin. The cold period is associated with a widespread Gondwana glaciation mat began in the Late Carboniferous and persisted until the Early Permian (Sakmarian; Dickins 1984; Veevers & Powell 1987). The transgression during the Sakmarian mat marks the end of this glaciation is characterised by a distinctive cold water Eurydesma fauna (Runnegar 1979; Dickins 1984) mat is found throughout the Permian to Triassic Pangean basins. It is within this cold climatic setting mat the formations that form me focus of this study were deposited.
6 2.0 STRATIGRAPHY
The earliest stratigraphic study within this area was undertaken by David and Stonier (1891). They divided me sequence in me southern Sydney Basin into four units; the Clyde Coal Measures, Conjola beds, Wandrawandian Siltstone and Nowra Grits. Detailed mapping by McElroy and Rose (1962) enabled them to update and modify the stratigraphic scheme (Fig. 2.1), including new units such as me Pigeon House Creek Siltstone. They also redefined the marine sequence above the Yadboro Conglomerate as the Conjola Formation. Gostin (1968) studied me coastal outcrops between Durras and Ulladulla and elevated the Conjola Formation to Sub-group status. The Conjola Sub-Group was subdivided into three distinct units; the Wasp Head Formation, Pebbley Beach Formation and the Snapper Point Formation. Gostin and Herbert (1973) presented a new stratigraphic framework (Fig. 2.1).
Considerable rearrangement of formations took place, the most important being me repositioning of me Clyde Coal Measures above the Yadboro and Tallong Conglomerates.
The only study since Gostin and Herbert (1973) which has proposed an alternative stratigraphic model is mat of Evans et al (1983; Fig. 2.1) based on me mapping of bom Seggie
(1978) and Walker (1980).
Most of these studies have been based on mapping in limited areas (McElroy and Rose,
1962; Gostin, 1968; Evans et al, 1983) or on drillcore data and limited fieldwork (Gostin and
Herbert, 1973). No studies have undertaken a detailed sedimentary facies analysis of all units within me southern Sydney Basin. Detailed facies analysis accompanied by careful description of stratigraphic relationships in me field has enabled a clear and coherent stratigraphic model to be proposed (Fig. 2.2).
2.1 Talaterang Group
Gostin and Herbert (1973) used the name Talaterang Group to include all "dominantly terrestrial sediments beneath me marine Shoalhaven Group and the Clyde Coal Measures (or me Yarrunga
Coal Measures)" (Fig.2.1). In me original definition, therefore, me Talaterang Group comprised the Yadboro/Tallong Conglomerates (and equivalents) and the Pigeon House Creek Siltstone.
Work undertaken herein suggests that the Yadboro and Tallong Conglomerates are
7 laterally equivalent to me Pebbley Beach and Snapper Point Formations and, as such, should be included in me overlying Shoalhaven Group. In addition to this the Clyde Coal Measures and
Wasp Head Formation, previously incorporated into the Shoalhaven Group by Gostin and Herbert
(1973), should be included in me Talaterang Group. The reasons for this rearrangement will be discussed below.
2.1.1 Clyde Coal Measures
The name Clyde Coal Measures was applied by David and Stonier (1891) to a basal Permian succession consisting of coal seams, siltstone and sandstone in me Clyde River valley and the adjacent coastal areas. McElroy and Rose (1962) documented five localities where the Clyde
Coal Measures are to be found. They contended that the Clyde Coal Measures underlies the
Yadboro Conglomerate, siting evidence from Longfella Ridge (GR: 8927-509027, Section C from
McElroy and Rose, 1962).
Gostin and Herbert (1973) correlated the Clyde Coal Measures with me Yarrunga Coal
Measures to the north. The Yarrunga Coal Measures crop out in me Kangaroo River and are present in a number of drillholes (e.g. Callala No.l, Coonemia No.l). At these localities the
Yarrunga Coal Measures overlie the Tallong Conglomerate. Gostin and Herbert (1973) suggested that me Clyde Coal Measures overlies the Yadboro Conglomerate in me Clyde Valley area and mat the earlier interpretation of McElroy and Rose (1962) was incorrect.
All known localities of the Clyde Coal Measures were examined in detail as a part of this study, notably in Budawang Creek (GR: 8927-462992), Bunnair Creek (GR:8927-629972) and me type section in me upper Clyde River Gorge (GR: 8927-509027). The Clyde Coal
Measures comprises a succession of clastic sedimentary rocks with interbedded coal seams up to 2m in thickness. In all cases me coal measures directly overlie either Devonian or
Ordovician basement. The coal measures are overlain by me marine Snapper Point Formation where the Yadboro Conglomerate is absent. On Longfella Ridge (GR: 8927-509027) the
Yadboro Conglomerate is present and clearly overlies the coal measures. The assertion of
Gostin and Herbert (1973) that me Clyde Coal Measures overlies me Yadboro Conglomerate is clearly incorrect.
8 The type section (Section F) of McElroy and Rose (1962) includes an interpreted angular unconformity. This angular unconformity is reinterpreted from recorded field observations to be an erosional surface at the top of lateral accretion surfaces in small channel sandstone bodies
(see section 4.1). The type section for the Clyde Coal Measures can therefore be extended to include the overlying sandstone body which forms a small waterfall on me Clyde River (see Fig.
2.3).
McElroy and Rose (1962) identified Gangamopteris (?), Noeggerathiopsis and
Glossopteris cf. gangamopteroides within the coal measures indicating a Permian age for the unit. Helby (1968a) identified microflora which indicate a lower Evans' Stage 3 Permian age
(Evans et al. 1983).
2.1.2 Pigeon House Creek Siltstone
The Pigeon House Creek Siltstone was a name which McElroy and Rose (1962) introduced for a sequence of carbonaceous siltstone and sandstone underlying me Yadboro Conglomerate and unconformably overlying Ordovician strata within the vicinity of Pigeon House Creek. They assigned the unit to the Shoalhaven Group which infers mat it overlies the Clyde Coal Measures stratigraphically. Gostin and Herbert (1973) argued mat the Pigeon House Creek Siltstone is stratigraphically distinct from me Clyde Coal Measures based on palynological evidence presented by Helby and Herbert (1971) which concluded that me Pigeon House Creek Siltstone is of Late Carboniferous age, considerably older man me Early Permian age derived for me
Clyde Coal Measures. This places me Pigeon House Creek Siltstone as the oldest unit in me southern Sydney Basin, underlying me Tallong and Yadboro Conglomerates. However, Evans
.et al. (1983) re-interpreted me microflora identified by Helby and Herbert (1971) as a lower stage 3a (Sakmarian-Artinskian) microflora which correlates with me Clyde Coal Measures.
The type section on me lower slopes of Cambage Head (GR: 8927-501887; McElroy and
Rose 1962) was visited. The unit consists of a succession of carbonaceous siltstone and rippled cross-laminated and trough cross-bedded sandstone (see section 3.1). The unit definitely underlies the Yadboro Conglomerate, which forms a high cliffline above the lower slopes, and it overlies Ordovician basement. The sequence is lithologically similar in all respects to the
9 Clyde Coal Measures and the facies sequence is identical, both being mud-rich alluvial deposits
(see section 3.1). The only difference between the Clyde Coal Measures and the Pigeon House
Creek Siltstone is the absence of coal in me latter.
The most striking similarity between me units is the palaeocurrent direction which is towards the north. North-directed sediment dispersal within both the Clyde Coal Measures and the Pigeon House Creek Siltstone is contrary to what would be expected if the basin was undergoing passive thermal sag. It implies mat dispersal was confined by north-trending structures, herein interpreted as grabens or half grabens related to an early phase of rifting. On the basis of the similarity of sedimentary facies and palaeocurrent direction, the Clyde Coal
Measures and me Pigeon House Creek Siltstone are reinterpreted as facies equivalents, deposited during me same phase of sedimentation.
Given mat the Pigeon House Creek Siltstone and the Clyde Coal Measures are here interpreted as being equivalent, it is suggested that the term Pigeon House Creek Siltstone should be discarded in favour of Clyde Coal Measures. The term Clyde Coal Measures should be used for all sandstone-siltstone sections containing abundant carbonaceous matter and few or no burrows at this basal stratigraphic level.
2.1.3 Wasp Head Formation
The Wasp Head Formation was defined by Gostin and Herbert (1973) as being me basal unit of me Conjola Sub-group which is part of me larger Shoalhaven Group (Fig. 2.1). The type section was defined as the coastal cliffs extending from Myrtle Beach to Wasp Head near South
Durras.
The sequence for me most part consists of interbedded siltstone and sandstone of interpreted shallow marine origin. The formation unconformably overlies highly cleaved and folded Ordovician Wagonga Beds. The basal parts of me formation contain large breccia units, which are interpreted as debris flow deposits locally derived from a north-trending tectonic slope
(see section 3.2). The north trending structure is interpreted as being a graben or half graben margin and, as such, me formation was deposited during me same rifting phase as me Clyde
Coal Measures. The Wasp Head Formation differs from me Clyde Coal Measures in mat it was
10 a subaqueous rather man a subaerial environment.
The localised nature of outcrop for me Wasp Head Formation and the presence of debris flow deposits suggest mat me formation should be included in me Talaterang Group rather man me Shoalhaven Group, as asserted by Gostin and Herbert (1973). The Wasp Head Formation should be redefined to include all sandstone-siltstone successions with common bioturbation and associated conglomerate, diamictite and breccia beds at this basal stratigraphic level.
Marine fossils are present within me formation and were described by Runnegar (1969).
Faunas consist of bivalves, brachiopods and bryozoans. Dickins et al. (1969) suggested mat me
Wasp Head Formation is of Sakmarian age and correlated it with me Allandale Formation
(Dalwood Group) within me northern Sydney Basin.
2.1.4 Related Units
Several units appear to occur at me same stratigraphic level as the Clyde Coal Measures and
Wasp Head Formation but cannot be confidently correlated. Immature clastic units have been encountered in some drillcore, most notable being Elecom Clyde River 12 (59.82-62.41m) and
DM Callala 1 (533.6-570.0m). In all cases these units directly overlie basement. The sequences consist of silty matrix-rich conglomerates and breccias. These deposits are correlated with me
Talaterang Group on me basis of their lithological similarity and equivalent stratigraphic position above the Ordovician basement and below the Shoalhaven Group.
2.2 Shoalhaven Group
The Shoalhaven Group disconformably or possibly conformably overlies the Talaterang Group and consists of stratigraphic units herein interpreted as being of marine shelf to coastal plain origin grading into me coarse clastic high energy alluvial facies of me Tallong and Yadboro
Conglomerates. The Yadboro and Tallong Conglomerates were previously assigned by Gostin and Herbert (1973) to the Talaterang Group. We argue mat the setting and lateral facies relationships of these coarse units with me Snapper Point Formation are such mat they should be considered as part of the Shoalhaven Group. The Yarrunga Coal Measures, previously correlated with the Clyde Coal Measures, is herein reinterpreted as a distinct unit overlying and
11 fringing me Tallong and Yadboro Conglomerates which is stratigraphically equivalent to the
Pebbley Beach Formation (Fig 2.2).
2.2.1 Yadboro and Tallong Conglomerates and equivalents
The Yadboro Conglomerate was defined by McElroy and Rose (1962) and the Tallong
Conglomerate by Herbert (1972). Both units are dominated by clast supported cobble conglomerate and unconformably overlie Ordovician basement where the Talaterang Group is absent. The claim by Herbert (1972) mat these deposits represent a late Carboniferous fluvio- glacial or fluvial drainage pattern is demonstrably incorrect since the units are clearly interstratified with and, in places such as Pigeon House Creek, overlie rocks of Permian age.
The Yagers and Burrawang Creek Conglomerates were defined by Herbert (1972) as tributary channels of me main Tallong Conglomerate, outcropping in me Shoalhaven Gorge and Kangaroo
River respectively.
The Yadboro Conglomerate is me major lower cliff forming unit which occurs in the
Clyde Valley region. It forms me lower clifflines of The Castle and Byangee Walls; the major landforms of the Yadboro area. The Tallong Conglomerate outcrops in me Marulan area and within me Shoalhaven Gorge.
As discussed previously me Pigeon House Creek Siltstone and me Clyde Coal Measures have been interpreted as facies equivalents and definitely underlie the Yadboro and Tallong
Conglomerates. The Yadboro and Tallong Conglomerates are overlain by me Snapper Point
Formation or me Yarrunga Coal Measures (where present; Fig.2.2).
The lateral extent of the conglomeratic units is far greater man portrayed by Herbert
(1972; see section 4.1). Conglomerate outcrop has been found between me two conglomerate lobes within Touga Creek (GR:8928-365251). The conglomerate units form part of me same semi-continuous alluvial sheet, which was initiated after me early extensional phase and deposition of the Talaterang Group. The Tallong and Yadboro Conglomerates may be stratigraphically equivalent to the Megalong Conglomerate farther north.
The Badgery's Breccia was interpreted by Herbert (1972) as a sedimentary breccia of morainic origin, adjacent to the main Tallong Conglomerate channel. The Badgery's Breccia
12 is here reinterpreted (section 4.1) as a immature basal facies of the Tallong Conglomerate. The
Badgery's Breccia should not be considered as a separate stratigraphic unit.
2.2.2 Yarrunga Coal Measures
Woolnough (1909) was the first to document the occurrence of coal in me Shoalhaven River area. Since then a number of new discoveries have been made in me Kangaroo River (Gray
1969), Coonemia No.l (Condon 1969) and DM Callala DDH 1 (Bembrick and Holmes 1971,
1976). Gostin and Herbert (1973) correlate me Yarrunga Coal Measures with me Clyde Coal
Measures based on palynological work by Helby (1968b).
Herbert (1980a) described an outcrop of Yarrunga Coal Measures at the junction of
Kangaroo River and Yarrunga Creek prior to me construction of Tallowa Dam. At this locality the Yarrunga Coal Measures is definitely described as overlying me Tallong Conglomerate.
DDH Callala 1 (520.5-483.4m) and Coonemia No.l also show me coal measures definitely overlying me Tallong Conglomerate. In all cases me Yarrunga Coal Measures are overlain by me Snapper Point Formation.
Seggie (1978) reported a coal seam occurring above me Yadboro Conglomerate in Pigeon
House Creek. Field reconnaissance has failed to find this locality. A sequence consisting of highly carbonaceous siltstone and fine sandstones has been found in Elecom Clyde River 8
(325.27-320.41m) occurring above a 36m conglomerate unit, which correlates with me Yadboro
Conglomerate. Similarly, a carbonaceous silty unit at Badgery's Lookout and a 5.5 m sequence consisting of interbedded conglomerate, very fine-grained sandstone and highly carbonaceous shale in Tallowa Gorge both overlie the Tallong Conglomerate in me north of me study area.
It is probable that these successions are equivalent to the Yarrunga Coal Measures.
The sedimentary facies within me Yarrunga Coal Measures are distinct from those found in me Clyde Coal Measures and are interpreted as coastal plain facies (see section 3.1). The difference of facies and stratigraphic relationships between me Yarrunga and Clyde Coal
Measures suggests that they cannot be correlated and must be considered as separate stratigraphic units. The Yarrunga Coal Measures are here reinterpreted as being part of a coastal plain succession overlying and laterally adjacent to me Tallong and Yadboro Conglomerates (Fig. 2.2).
13 2.2.3 Pebbley Beach Formation
The Pebbley Beach Formation was defined by Gostin and Herbert (1973). The type section extends along me coast from Wasp Island in the south to the base of Clear Point. The disconformable contact between me Pebbley Beach Formation and the underlying Wasp Head
Formation is clearly visible on Wasp Island. The formation is dominated by silty shallow marine facies (see section 4.2). The Snapper Point Formation conformably overlies the Pebbley
Beach Formation at Clear Point where the boundary is defined below a prominent conglomerate bed (Gostin & Herbert 1973).
The sandy marine facies found near the base of me Sydney Basin sequence in all the
Elecom Clyde River drillcores show no evidence of me silt-dominated facies which typify coastal exposures of me Pebbley Beach Formation. Any subdivision into Pebbley Beach and
Snapper Point Formation would be completely arbitrary. South of Island Beach (GR:8926-
603595) the contact between me Pebbley Beach and Snapper Point Formation is exposed and is clearly gradational and indistinct. This contrasts with the sharp, distinct contact of silt- dominated facies of me Pebbley Beach Formation and coarse sandy facies of the Snapper Point
Formation to the south at Clear Point.
It is herein suggested mat me term Pebbley Beach Formation should be restricted to me silt-dominated marine sequences in the southernmost parts of me basin where the formation can be clearly delineated. This restricts me extent of me formation, at me present, to the coastal exposures south of Termeil. The Pebbley Beach Formation is interpreted as a coastal to shallow marine equivalent to me Tallong Yadboro Conglomerate which fringed me alluvial braidplain system (section 4.3). Equivalent coastal facies of the Pebbley Beach Formation and me laterally equivalent Yarrunga Coal Measures may be found in me subsurface farther to me northeast, fringing me Yadboro and Tallong Conglomerates. The coastal localities are the only localities which can be definitively classified as Pebbley Beach Formation, given current information.
The Pebbley Beach Formation contains rare marine fossils which include bivalves, brachiopods, bryozoans, gastropods, foraminifer and crinoids (Runnegar 1969). One conulariid specimen has also been found (Runnegar 1969). On me basis of me faunal assemblage correlation has been made with me Farley Formation in me Hunter Valley.
14 2.2.4 Snapper Point Formation
The type section for me Snapper Point Formation was defined by Gostin and Herbert (1973) at me coast between Clear Point and Crampton Island where it conformably overlies the Pebbley
Beach Formation. Elsewhere, the Snapper Point Formation conformably overlies the Tallong and Yadboro Conglomerates and the Yarrunga Coal Measures. Where these units are absent, the formation unconformably overlies basement.
The Snapper Point Formation is dominated by shallow marine facies (see section 4.4).
Where it overlies me Yadboro and Tallong Conglomerates mere are intervals of fluvial strata which were termed me Jindilara facies by Evans et al (1983). These fluvial intervals are however, interbedded with nearshore marine facies. Thus, the term Jindilara facies should be abandoned and this interval should be retained within the Snapper Point Formation,
Fossils are common throughout me formation and consist of bivalves, brachiopods, gastropods, bryozoans, conulariids (Bann 1990 in prep) and rare crinoid stems (Runnegar 1969).
The Snapper Point Formation probably correlates with me lowest part of me Branxton Formation in me Hunter Valley (Dickins et al. 1969; Runnegar 1980a).
2.2.5 Wandrawandian Siltstone and Nowra Sandstone
The units above the Snapper Point Formation within me Shoalhaven Group display a sheet like architecture. The stratigraphic position of bom the Wandrawandian Siltstone and Nowra
Sandstone is not contentious and is in agreement with all previously published material (McElroy and Rose 1962; Gostin and Herbert 1973; Figs. 2.1, 2.2).
The term Wandrawandian pebbly sandstone was first used by David and Stonier (1891) to describe a silt dominated unit in the vicinity of Wandrawandian Creek (now Wandandian).
The name was later changed to Wandrawandian Siltstone by Joplin et al. (1952). Gostin and
Herbert (1973) named me silt dominated interval at me coast the Ulladulla Mudstone. Since these units can be correlated and consist of me same lithologies me term Ulladulla Mudstone should be abandoned in favour of me pre-existing term Wandrawandian Siltstone.
The Wandrawandian Siltstone is highly fossiliferous, containing abundant bivalves,
15 brachiopods, bryozoans and crinoids (Runnegar 1969). On me basis of the faunal assemblage correlation has been made with me lower Branxton Formation and me Fenestella zone in the northern Sydney Basin (Dickins et al. 1969).
The Nowra Sandstone was first used by Joplin et al (1952), modifying me pre-existing term "Nowra Grits" used by David and Stonier (1891). On me basis of me faunal assemblage
(dominated by bivalves and brachiopods) the Nowra Sandstone has been correlated with the
Muree Sandstone in the Hunter Valley (Dickins et al. 1969).
16 3.0 SEDIMENTOLOGY OF THE TALATERANG GROUP
3.1 Clyde Coal Measures
Early work on me Clyde Coal Measures was undertaken by David and Stonier (1891) and
Harper (1915). McElroy and Rose (1962) sectioned all the known outcrops of Clyde Coal
Measures. They visited five localities, the most important of these being me 40m section in me upper Clyde River (Fig. 2.3). A total of 11 sections were taken through me Clyde Coal
Measures by McElroy and Rose (Fig. 2.3). More recent work on me upper Clyde River section was carried out by Walker (1980).
The environment of deposition for me Clyde Coal Measures was not well understood.
McElroy and Rose (1962) interpreted me coal measures as freshwater deposits and Walker
(1980) as swamp deposits which developed north of an alluvial fan represented by me Yadboro
Conglomerate. Similarly me palaeogeographic setting of me coal measures was also poorly understood. McElroy and Rose (1962) identified a basement low, referred to as the "Talaterang
Low". This low was later interpreted as a depocentre for Early Permian deposition and in particular me Clyde Coal Measures and Pigeon House Creek Siltstone (Herbert 1980a; Evans et al. 1983; Evans 1991). The stratigraphic position of me Clyde Coal Measures relative to me
Yadboro Conglomerate was also poorly defined.
Exposure of the Clyde Coal Measures occurs in isolated pockets, scattered over me southern part of me study area (Fig. 1.1). The isolated and patchy nature of me coal measures has been confirmed by an Elecom drilling program which encountered no Clyde Coal Measures in a total of 12 fully cored drillholes (Elecom 1986). All me known outcrops of me Clyde Coal
Measures were visited in mis study, which includes the type section in me upper Clyde River
Gorge (McElroy & Rose 1962). Access to outcrops of the coal measures was difficult and may explain me paucity of detailed sedimentological analysis.
3.1.1 Facies Analysis
A total of 6 sections (Figs 3.1 & 3.2) were measured at three of me five localities visited. The outcrop at me remaining two localities was deemed too poor to measure. On me basis of these
17 sections, 6 sedimentary facies have been identified (Table 3.1). The coal measures are interpreted as alluvial deposits with overbank facies being volumetrically dominant.
Facies A: Channel sandstone
Description: This facies is relatively minor in the Clyde Coal Measures. Only three outcrops of this facies were observed. They were found at the base of both the Upper Clyde River and
Kilpatrick Creek sections (Figs 3.1 & 3.2).
The facies consists of pebble and granule conglomerate and medium to coarse sandstone,
The thickness of this unit could not be ascertained as the base was not exposed. The poorly sorted conglomerate consists of angular granule to pebble sized clasts within a medium sandstone matrix. Clast lithologies are dominated by quartz and quartzite, typical of the Ordovician basement sequence. This facies is overlain by floodplain sediments (facies B and C) in both the Upper Clyde River section and the Kilpatrick Creek section. Sandstone contains trough cross-bedding and ripple cross-lamination. Sets are typically in me order of 15 to 20 cm.
Some units grade upwards from pebble conglomerate and medium sandstone to fine and very fine sandstone at me top. No geometric information is available for facies A due to the poor lateral extent of me exposure at all localities.
Palaeocurrent data (Fig 3.3) from this facies shows a large variation with a vector mean of 328° and a vector magnitude of 66%.
Interpretation: The presence of trough cross-bedding and ripple cross-lamination suggests deposition from a unidirectional current under low flow regime conditions. The composite nature and coarseness of me sandstone units relative to me sandstone in me rest of me sequence suggests that they are channel deposits rather man coarse overbank deposits. Conglomeratic units at me base of the section, overlying basement are interpreted as lag deposits, laid down following initial incision via fluvial processes.
Distinguishing between channel facies (facies A) and thick overbank sandstone in facies
B is difficult. The composite nature of the lower sandstone unit was used as a distinguishing factor. Overbank sandstone also consist of individual units that are underlain and overlain by
18 finer grained facies.
Facies B: proximal floodplain
Description: This facies consists of interbedded medium to very fine sandstone, carbonaceous siltstone and coal seams. The facies sequence consists of approximately 50% sandstone.
Sandstone unit thickness ranges up to a maximum of 1.5m but most are in me order of
0.2 to 1.0m. Sandstone units have sharp, planar bases and tops. They contain small scale trough cross-bedding, ripple cross-lamination and some flat lamination. Symmetrical ripples were identified on me top of one unit. Small channel structures are common within these units (Fig.
3.4a). Dimensions of these channels are typically 1 to 2 metres wide and up to 1 m deep.
Thicker units of sandstone contained thin siltstone partings suggesting superimposed sandstone beds. There is evidence of abundant soft sediment deformation and me development of flame structures within some units.
Siltstone is highly carbonaceous, containing abundant plant debris. Units are often sandy and laminated.
The thickness of coal seams within the sequence varies, with a maximum thickness of
60 cm. Coal seams are thinly banded and show a metallic lustre. Where the seam overlies a sandstone unit (Fig. 3.4b) me contact is sharp and undisturbed and there is no evidence of rooting or seat-earth development. Coal seams are found in intermittent association with bom sandstone and siltstone beds. One unit in section 1 of me Upper Clyde River locality has numerous coal seams of no greater thickness man 10 cm interbedded with fine to coarse, graded, silty sandstone.
Limited lateral exposure does not permit me geometry of units within this facies assemblage to be fully ascertained. Sandstone units at the base of me Kilpatrick Creek sections are markedly lensoidal and could be seen pinching out over a distance of approximately 100m.
Facies B is overlain by facies C in me Upper Clyde River sections and is erosionally overlain by facies F or A, in me Kilpatrick and Bunnair Creek sections, respectively.
Interpretation: This facies is interpreted as an overbank floodplain deposit. Sediment laden
19 flood waters overtopped or breached levee banks to deposit coarse splay sand units on the floodplain. Fining upward units with sharp upper contacts suggest deposition under waning flow conditions followed by an abrupt cessation in current activity. Siltstone units were deposited from suspension on vegetated floodplains during quiet periods.
The lensoidal geometry of some sandstone beds suggests that they may be splay deposits which typically have a lobate or rarer "tongue" shape (Elliot 1974) extending from a small breach in a levee bank. Splay size may vary considerably within me same alluvial system and there does not appear to be a reliable method of determining the distance from the source channel (Mjos et al. 1993). The sandstone units probably represent me stage one splays of
Smith et al. (1989) which are deposited as sheet-like and lensoidal bodies close to the main channel. The presence of channel structures within some sand sheets indicates that flow was laterally confined to feeder or splay channels. The abundance of splay sandstone units within this facies, relative to facies C, suggests mat it was deposited in close proximity to the main tributary channel.
The pervasive presence of coal and carbonaceous siltstone within this facies sequence suggests mat me depositional environment was predominantly backswamp, on low lying, poorly drained areas of a floodplain. Periodic flood events caused deposition of coarse sandstone units, interpreted as sheet flood or splay deposits. Wave ripples at me upper contact of one unit suggest reworking in standing water by wind-generated waves following deposition. The discontinuous nature of me coal seams suggests deposition near or adjacent to active channels
(Allen 1965; Smith 1983; Fielding 1984). Periodic influxes of sediment from overbank flows resulted in an unfavourable environment for the thick accumulation of peat. Alluvial coal- forming environments are typically limited in lateral extent due to me generally narrower extent of alluvial plains (Fielding 1984). Small lateral movements of me alluvial system could cause coal formation to cease.
Facies C: distal floodplain
Description: This facies (Fig 3.4c) consists of interbedded carbonaceous siltstone, coal seams and minor sandstone. It differs from facies B in mat it is dominated by fine-grained sediment.
20 Siltstone and sandstone units are similar to those described for facies B. Sandstone beds are very thin, having a maximum thickness of 65cm, and contain ripple cross-lamination. Siltstone beds are laminated and some have irregular structures which may be caused by rooting.
Deformed bedding is common within me siltstone units.
Coal seams are intimately related to siltstone and may show complex interbedded sequences. One such succession was observed in me Upper Clyde River section 2 (Fig. 3.4d)
Several coal seams occur in this unit and are highly lensoidal, pinching out into siltstone. This facies contains me thickest coal seam developed within me coal measures; 96 cm in section 6.
Torbanite and cannel coal is associated with me carbonaceous sequences. Facies C gradationally overlies Facies B in me Upper Clyde River sections. In me Bunnair Creek section facies C is erosionally overlain by facies A.
Combined palaeocurrent data from facies B and C show north-directed sediment dispersal with a vector mean of 2° and a vector magnitude of 62%.
Interpretation: The interpretation, as for facies B, is a backswamp environment on an alluvial floodplain. The thickest accumulations of peat will typically be found at me greatest distance from me channel deposits (Flores 1983). It is here where coal forming conditions will be most favourable and uniform. The paucity of sandstone within this facies also suggests mat it is more distal from me main channel than facies B.
The green alga Botryococcus found in torbanite is a floating organism which inhabits freshwater environments (Guy-Ohlson 1992) and is commonly found in lacustrine environments.
The presence of torbanite within this facies suggests there was some subaqueous deposition and ponding on me floodplain.
Facies C probably represents the most distal deposits from me fluvial channel on a poorly drained floodplain. Wetland environments consisted of peat bogs and in lower lying areas, small lakes or lagoons. Carbonaceous wetland sedimentation was interrupted by deposition of thin beds of fine sandstone and silty siltstone which represent distal splay and flood sedimentation.
21 Facies D: Bay-Head Delta (tidal channels)
Description: This facies occurs in me Upper Clyde River (Figs 3.1) below the main cliff forming sandstone unit which forms the top of both sections. The facies is marked by a thick heterolithic unit with well developed lateral accretion surfaces (Fig. 3.4e). The unit is pervasively ripple cross-laminated along the low angle dipping surfaces. The interval containing these low angle surfaces is a composite unit which is 2 m thick. Individual beds within the interval range up to 70 cm. The heterolithic units consist of fine sandstone and siltstone couplets. There does not appear to a fining upward trend through me units.
Successive beds have lateral accretion surfaces dipping in opposing directions. The dip direction changes from 045° in me lowest bed to 166° in a bed directly overlying it. The base of this upper unit seems to have a channelised, erosional base but due to incomplete exposure this interpretation cannot be definite.
Palaeocurrent measurements taken from small scale trough cross-beds associated with this facies suggest palaeoflow was towards both me north and south (Fig. 3.3). Caution should be taken when reading and interpreting this data as mere are only a small number of measurements.
This facies has a sharp underlying contact with me floodplain alluvial sediments of facies
C and is overlain by finer grained sediments of facies E in both of the Upper Clyde River sections (Fig. 3.1).
Interpretation: This facies contains inclined heterolithic stratification (IHS) as defined by Thomas et al (1987). This type of stratification has been recorded in a variety of environments including delta plains, submarine fans, meandering fluvial systems and intertidal deposits. The reversal of palaeoflow from north to south within this facies suggests that this system is tidally influenced. Similar facies have been reported at the landward end of estuaries (Allen 1991).
The facies represents me initial incursion of marine processes into a previously alluvial environment. The environment is interpreted as a bay-head delta, at the landward end of an estuary. This represents the zone C fluvial/tidal sediments of Nichol (1991). The low angle
(IHS) surfaces represent lateral accretion at point bars within a tidally influenced meandering fluvial system. Mud layers are probably deposited from me suspended load during periods of
22 tide dominated flow when me river level is at a low stage (Nichols et al. 1991; Jones et al.
1993).
Facies E: Estuarine Lagoon
Description: The sequence is dominated by siltstone, sandy siltstone and medium sandstone.
Pyrite staining and bioturbation are pervasive throughout the sequence.
One bed of medium sandstone was recorded within this facies in section 2 of the Upper
Clyde River. The unit was 40 cm thick and contained flat lamination, strong bioturbation and pyrite staining. Finer grained units are highly carbonaceous, contain large coalified wisps and are very thinly laminated (Fig. 3.4f). Flaser and lenticular bedding is evident in thinly laminated siltstone beds.
Facies E overlies facies D and is erosionally overlain by facies F in bom of me Upper
Clyde River sections.
Interpretation: The interpreted environment of deposition is an estuarine basin or lagoon, situated in me central portion of a estuary. This interpretation is justified, based on me associated facies and the context of these facies within me sequence. Facies E is underlain by interpreted tidally influenced fluvial facies at me landward end of an estuary and is erosionally overlain by estuarine inlet/barrier facies. In a transgressive sequence the intervening sediments are likely to be lagoonal fine-grained facies (see section 3.1.2). The structures within me facies support this interpretation. The strong bioturbation, and pyrite staining within this facies suggest that deposition was marine influenced. A relative quiescent environment is indicated by the
.predominance of silt lithologies within me facies. The lenticular bedding within me fine sequences suggest that deposition may have been influenced by tides.
The thin medium sandstone unit which crops out within this facies in section 2 of the
Upper Clyde River represents a washover deposit, sourced from an adjacent sand barrier.
The central portions of estuaries typically contain an energy minimum because it is a zone of convergence between fluvial and tidal energy (Dalyrimple et al. 1992). Due to this energy minimum me estuarine lagoon or basin is characterised by silt-mud dominated sediments
23 (Allen 1991; Nichol 1991; Nichols et al 1991; Dalyrimple et al. 1992).
Facies F: Estuarine Inlet\Barriers
Description: This facies occurs at the top of all sections (Figs 2.3, 3.1 & 3.2). It is dominated by a composite unit of fine to coarse, pebbly sandstone. The bases of units are commonly erosional and may be capped by a pebbly lag. Broad channel-shaped erosionally based units were found in sections 3 and 5. The unit is trough cross-bedded throughout with minor ripple cross-lamination. Bioturbation was found at me base of this sequence in section 5 and one log cast occurred at the base of this unit in section 6. This unit is laterally persistent over the entire length of exposure, approximately 1.5km.
Palaeocurrent measurements from this facies show a dominantly north-directed distribution
(Fig. 3.3). This facies is overlain by shoreface facies of me Snapper Point Formation.
Interpretation: This facies is interpreted as estuarine inlets at me mouth of an estuarine system.
Bioturbation suggests a marine influence. The context of this facies, lying between the fine grained estuarine facies (facies E) and the marine facies of me Snapper Point formation suggests a barrier/inlet environment. The northerly palaeocurrent distribution (Fig. 3.3) indicated by cross-bedding, suggests dominance of flood currents over ebb currents. Trough cross-bedding resulted from bedform migration of 3-D megaripples under lower flow regime conditions. The laterally persistent nature and me paucity of fine-grained lithologies within me facies suggests a major increase in energy regime throughout the entire depositional system. Tidal sand bar facies are well documented at the marine end of modern estuaries (Harris 1988; Dalyrimple et al. 1990; Nichol 1991).
3.1.2 Pigeon House Creek Siltstone
The Pigeon House Creek Siltstone was identified by McElroy and Rose (1962), who distinguished this unit from me Clyde Coal Measures on me basis mat coal and carbonaceous sediments are absent from me sequence. Gostin and Herbert (1973) interpreted me unit as an alluvial succession but considered it as separate from me Clyde Coal Measures. As has been
24 already discussed in section 2.0, the Pigeon House Creek Siltstone is herein reinterpreted as equivalent stratigraphically to the Clyde Coal Measures and as such me term has been abandoned. It is discussed separately here to highlight me similarities of the facies within me two successions.
The type section (section B) of McElroy and Rose (1962) was visited (Fig. 3.5) and crops out in a creek bed which flows down me eastern side of me Clyde River gorge. The nature of the outcrop does not provide lateral exposure which could yield important architectural information. The sedimentary sequence consists of 44 m of interbedded fine lithic sandstone and sandy light to dark grey siltstone. The sequence is disconformably, and erosionally overlain by me coarse braidplain facies of the Yadboro Conglomerate.
Sandstone thickness ranges up to 4 m. Small scale trough cross-stratification, ripple cross-lamination and flat lamination are common structures identified in the units. The basal contacts of sandstone beds are commonly sharp and occasionally loaded. Upper contacts are irregular and symmetrical wave ripples were identified at the top of three units. Interference ripples were found on me top of one sandstone unit, approximately 15 m up me sequence.
Siltstone units are laminated to thin bedded and in some cases contain very thin sandy horizons which are flat laminated or ripple cross-laminated.
The palaeocurrent distribution for me Pigeon House Creek Siltstone is shown in Figure
3.3. The vector magnitude is high (98%) varying only a small amount from me vector mean.
The palaeoflow was directed towards me north as for the Clyde Coal Measures (Fig. 3.3).
The environment of deposition is interpreted as a low energy alluvial system. The facies are identical to facies A and B outlined above for me Clyde Coal Measures. The majority of the sequence contains interbedded siltstone and sandstone, interpreted as overbank facies B. The distinction between facies A and B sandstone is difficult due to the quality of exposure. The thicker sandstone units may be channel deposits. Thinner sandstone bodies, interbedded with siltstone, are interpreted as splay deposits, formed by the breaching or overtopping of levee banks along me main channel. Thinly interbedded sandstone and siltstone is interpreted as overbank deposits.
The entire succession represented by the Pigeon House Creek Siltstone suggests
25 deposition was more proximal to me main channel than most of the Clyde Coal Measures exposures. The absence of coal within me section simply reflects the lack of significant backswamp development. The absence of facies C from the succession does not prohibit correlation of me Clyde Coal Measures with me Pigeon House Creek Siltstone. The differences between me two units should be interpreted as localised variations within the same depositional system. The northerly palaeocurrent direction, and an almost identical vector mean (Fig. 3.3), within both units would seem to substantiate this interpretation. The distinctive "buff to olive green siltstones" reported by McElroy and Rose (1962) are herein interpreted as local weathering features of the siltstone within me creek bed.
3.1.3 Depositional Systems
Two distinct depositional systems can be observed within me Clyde Coal Measures (including me previously named Pigeon House Creek Siltstone). These are best observed in me Upper
Clyde River sections (Fig. 2.3). The Clyde Coal Measures is interpreted as a transgressive sequence. The two depositional systems identified within me sequence are described below.
Depositional system A: mud-rich alluvial
The sparse exposure and limited lateral extent of me Clyde Coal Measures do not permit the style of me fluvial system to be accurately delineated or classified. Several characteristics of the sequence, however, do suggest a probable fluvial style. a) The fluvial sequence is dominated by overbank facies, comprising greater man 90% of me available exposure. b) Overbank facies (B and C) pervasively contain lithologies such as coal, torbanite and highly carbonaceous siltstone which are indicative of wetland environment deposition. c) The sequence contains abundant sheet sandstone, interpreted as splay deposits, suggesting channel avulsion events were commonplace in interchannel areas. d) Palaeocurrent data (Fig. 3.3) show a large variation indicative of a highly sinuous fluvial system.
These features are typical of those reported from anastomosing fluvial systems. Anastomosing
26 fluvial sequences are not well documented in sedimentological literature (Smith and Smith 1980;
Smith 1983; Eberth and Miall 1991). Such systems consist of multiple channels and are characterised by extremely stable channel positions and abundant avulsive events in interchannel areas (Smith 1983). Thick sequences of overbank sediments in the Clyde Coal Measures suggests long, continuous periods of floodplain deposition, indicative of a stable channel belt
(Eberth and Miall 1991). The presence of wetland sediments suggests that the environment was poorly drained with a very low gradient, typical of modern anastomosing systems (Smith and
Smith 1980; Rust 1981; Smith 1983).
The predominance of channel facies within me Pigeon House Creek Siltstone sequence and it's relative absence from me other exposures suggests mat me channel belt may have been laterally confined on me alluvial plain. No narrow, vertically stacked channel fill deposits were identified, indicative of anastomosing deposits (Smith 1983; Eberth and Miall 1991).
A striking characteristic of me coal seams within me Clyde Coal Measures is the absence of bioturbation in me floor rock (Fig. 3.4b). Seat earths are well developed at me base of
Carboniferous coal seams which were deposited in warm, tropical climates (Diessel, 1992).
Most Gondwana coals, however, have less developed seat earths as they were deposited in cool, temperate climates which were less favourable for me development of extensive palaeosols.
There is ample evidence for a cold, ice affected climate in eastern Australia during me Early
Permian (Gostin 1968; Dickins 1984; Veevers & Powell 1987 and see sections 3.2 and 4.0).
Martini and Glooschenko (1985) suggested that the environment of deposition for Early Permian
Coals was probably fen-like or bog-like. Modern cold climate Canadian peats within this type of environment show little rooting at their base. Sedges and trees have shallow root systems which could be entirely contained within me peat layer (Martini & Glooschenko 1985). Any minor rooting mat was present may not have been evident due to the relatively poor exposure.
A low energy, mud dominated gently sloping, water logged alluvial system was responsible for me deposition of me Clyde Coal Measures. Although it is not possible to say definitively mat the fluvial style was anastomosing, me facies sequence is very similar to mat outlined by Smith (1983) for modern anastomosing systems.
27 Depositional System B: Estuary
Facies D to F at me top of the Clyde Coal Measures succession have features which suggest a transgressive estuarine sequence deposited under a regime of rising relative sea-level.
Ideally, estuarine systems can be divided into a tripartite zonation (Roy et al. 1980;
Nichol 1991; Dalyrimple et al 1992; Fig 3.6). The model consists of (a) an outer zone which is dominated by wave processes; (b) a central dissipative low energy zone; and (c) a tidally
influenced fluvial zone. This zonation within estuaries is marked by distinct lithological changes;
commonly a transition from sand to mud to sand in response to the changing energy regime.
This zonation shows up clearly in many modern estuaries (e.g. Allen 1991; Nichol 1991; Nichols
et al. 1991). The facies zonations are more obvious in wave-dominated estuaries rather man
tide dominated estuaries due to higher tidal current speeds farther up the estuary within me latter
(Dalyrimple et al. 1992).
The sequence in me upper part of me Clyde Coal Measures shows three distinct facies
which are interpreted as representing me three estuarine zonations described above. The base
of facies D in me Upper Clyde River sections (Fig. 3.1) marks the flooding surface, recording
me first incursion of marine influences into me system. Facies D represents deposition within
laterally accreting fluvial channels with significant tidal influence. Flooding continued and facies
D gave way to low energy sedimentation (facies E) within me central portion of the developing
estuary. The final phase of sedimentation is represented by me estuarine inlet facies F. The
estuarine inlet channels may have removed a significant amount of underlying lagoonal facies.
The deposition of this unit marks a significant increase in tidal current energy within me inlets.
With continued relative rise in sea-level and continued coastal retreat, estuarine sedimentation
was replaced with wave-dominated shoreface sedimentation, represented by me Snapper Point
Formation which conformably overlies me Clyde Coal Measures.
Two important characteristics of me estuarine sequence suggest mat deposition probably
occurred within a wave-dominated estuary. They are:
a) the stark contrast between facies showing tripartite zonation is typical of wave-
dominated estuaries (Nichol 1991; Dalyrimple et al. 1992); and
b) me sequence is overlain by shoreface sediments of me Snapper Point Formation,
28 which contain amalgamated hummocky cross-stratification indicative of wave action
(see section 3.2.1).
3.1.4 Discussion and implications for basin development
The interpretation presented above for me Clyde Coal Measures and the Pigeon House Creek
Siltstone has implications for me understanding of the early development of the southern Sydney
Basin. The major palaeocurrent direction for me Clyde Coal Measures is towards me north (Fig.
3.3). This is contrary to what would be expected if me basin was undergoing passive thermal sag. Under these conditions an east-directed current would be expected, due to the north-south orientation of the basin. A north-directed current suggests mat me fluvial system may have been laterally restricted by north-trending structures. These structures are herein interpreted as normal faults which bound north-south trending extensional sub-basins. This extensional phase has been identified at me same stratigraphic level elsewhere in me Sydney-Bowen Basin complex (Baker et al. 1993; Tadros 1993b; Bamberry et al. 1995). The Clyde Coal Measures are also sedimentologically similar to me Reids Dome Beds in me northern Bowen Basin (Draper and
Beeston 1985).
It is, therefore, postulated that early subsidence in me southern Sydney Basin was accommodated by me formation of north trending extensional sub-basins. Subsidence in me sub- basins allowed low energy fluvial systems, with associated wetlands, to develop and peat to accumulate. Peat generally only accumulates in alluvial environments in rapidly subsiding basins
(Fielding 1985). Sediment aggradation was unable to keep pace with me rapid subsidence, lowering base level to me point where marine incursion occurred. The narrow and elongate nature of me sub-basins was such that they developed into estuaries. Eventually, with continued flooding me estuaries gave way to open marine sedimentation of me Snapper Point Formation as the intervening highs were overstepped. The Clyde Coal Measures and Wasp Head
Formation (see below) represent me earliest record in me southern Sydney Basin of me transgression which resulted in the deposition of me Snapper Point Formation and
Wandrawandian Siltstone.
29 3.2 Wasp Head Formation
The Wasp Head Formation was first defined by Gostin (1968), forming the basal unit of the
Shoalhaven Group. Runnegar (1969) identified macrofossils from me formation and Dickins et al (1969) attempted age correlations. McCarthy (1979) studied the ichnology of the formation and interpreted depositional environments. The general environment of deposition for the formation was correctly interpreted as shallow marine by all previous workers.
3.2.1 Facies analysis
Detailed sections were measured through three headlands of the Wasp Head Formation (Fig. 3.7), namely, northern end of Myrtle Beach, southern end of Emily Miller Beach and the exposures at Wasp Head. Most of the sequence has excellent exposure allowing detailed investigation of sedimentary structures. On me basis of the field observations seven sedimentary facies have been recognised (Table 3.2).
Facies A: debris flows
Description: Four units of sedimentary breccia were found in me lower 20m of the formation, at me southern end of Dark Beach and me northern end of Myrtle Beach. The breccia units are poorly sorted and consist of large angular blocks of argillite and phyllite (derived from basement Ordovician Wagonga Beds) with a maximum clast size of approximately 3.5 m. The units are ungraded, typically clast supported, with a poorly sorted matrix of sand, silt and clay.
Oasts are distinctly unweathered. The upper and lower contact of these units is typically sharp and planar (Fig. 3.8a) except at one location on the southern side of Dark Beach where me
. lower contact is irregular. A gradation to overlying flat laminated sandstone was evident at the upper contact of one breccia unit. The maximum breccia unit thickness is approximately 4 m.
All of the breccia beds thin towards me east. The uppermost unit contains a sandstone parting which thickens towards this same direction.
Interpretation: The random fabric and me smooth upper and lower contacts are consistent with these units being deposited as cohesive debris flows (Lowe 1982; Surlyk 1984; Pickering et al
30 1986; Lomas 1992). The features of these units conform to facies Al.l as described by
Pickering et al. (1986). Deposition resulted from a high concentration debris flow which subsequently underwent rapid sedimentation via frictional freezing. The fact that the breccias are interbedded with plane bedded, trough cross-bedded and hummocky cross-stratified fine sandstone would suggest mat deposition occurred in a sub-aqueous, shallow marine environment
(see facies B). The grade and texture of me breccia units suggests that they are locally derived
- also indicated by me unweathered nature of the clasts. The gradational upper boundary of some breccia units and numerous rounded chert pebbles indicates reworking by traction currents following emplacement.
The lateral thinning of me breccia beds towards me east indicates that me palaeoflow of me debris flows was towards the east.
facies B: littoral shoreface
Description: This facies forms me lower part of me formation (0-16m) and is interbedded with me thick sedimentary breccia units (facies A). It consists of a sequence of fine- to medium- grained pebbly lithic sandstone beds (Figs 3.7, 3.8b). Sedimentary structures contained in the facies include flat lamination, trough cross-bedding and hummocky cross-stratification.
Sigmoidal cross-bedding was identified within two units of this facies. Maximum recorded thickness of a sandstone unit within this facies was 92 cm but most beds ranged from 20-
40cm.
Plane bedded sandstone units, although predominantly plane bedded, do contain medium to coarse phases which contain ripple lamination and low-angle cross-stratification. Small (20 cm wide, 8 cm deep) granule to pebble lined scours filled with granule-rich flat-bedded sandstone was evident in some of these units.
Hummocky cross-stratified sandstone (HCS) units are common in this facies comprising approximately 20% of the total succession. Bed thickness ranges from 30-70 cm. HCS becomes more dominant upwards through me sequence forming an amalgamated succession near the top. HCS beds may contain erosional, coarse, pebbly basal contacts and grade upwards to fine sandstone. HCS was also identified which graded upwards to parallel stratification within
31 individual units (as also recorded by Walker et al. 1983). The HCS is generally very low angle
(<10°) and strongly anisotropic.
Some beds within me sequence contain sparse to moderate bioturbation which is difficult to identify due to an absence of silt linings on the burrows. The traces can only be identified where pebbly horizons are disturbed. Runnegar (1969) identified molluscs, gastropods and stenoporoid bryozoans in this facies.
Palaeocurrent data (Fig. 3.9) obtained from trough cross-bedding indicates sediment dispersal towards me northwest.
Interpretation: This facies is interpreted as a foreshore facies. Flat laminations were worked by wave action in a beach environment. Longshore and onshore currents reworked pebbly sand towards the northwest. Sigmoidal cross-bedding in some of these units indicates the possible presence of tidal currents (Kreisa & Moiola 1986; Uhlir et al. 1988; Dalyrimple 1992).
Hummocky cross-stratification (HCS) was first defined by Harms et al. (1975) and is well documented in ancient sequences (e.g. Cant 1980; Dott & Bourgeois; 1982; Leckie and
Walker 1982; Brenchley et al. 1993). The consensus of opinion is mat HCS is a structure formed by storm action (Harms et al. 1975; Duke 1985; Klein & Marsaglia 1987; Duke et al.
1991). However, me interpreted mechanism forming HCS has caused substantial debate in sedimentological literature. Allen and Underbill (1989) favour a dominantly unidirectional current for its formation, in direct contrast to the interpretation of Southard et al. (1990) which favours purely oscillatory flow. The probable mechanism is one of combined flow (Duke 1985;
N0ttveldt & Kreisa 1987; Duke et al. 1991; DeCelles & Cavazza 1992) which is also supported by grain fabric studies of HCS units by Cheel (1991). HCS is not diagnostic of water depth or environment as it has been described as occurring in tidal environments (Bartsch-Winkler &
Schmoll 1984; Fielding & McLoughlin 1992), shoreface environments (Leckie and Walker 1982;
Craft & Bridge 1987; Brenchley et al 1993) and in turbidite sequences (Prave & Duke 1990).
The common occurrence of HCS in shoreface environments between fairweather and storm wave base probably reflects a more favourable environment for preservation (Dott and Bourgeois
1982).
32 Storm action is interpreted as me depositional mechanism for the HCS in facies B. HCS units in this facies are interbedded with planar bedded sandstone and trough cross-bedded pebbly sandstone, interpreted as upper shoreface deposits in me littoral nearshore zone. This suggests deposition of HCS has occurred above fairweather wave base. This is also supported by the absence of finer-grained facies reflecting background quiet water fairweather sedimentation, common in deposits between fairweather and storm wave base. The anisotropic nature of the
HCS may reflect a larger unidirectional component within me combined flow man mat of deeper water HCS. The gradation to parallel stratification at me top of some HCS beds suggests a return to a dominant unidirectional flow as me storm wanes. Preservation of HCS within me foreshore sediments may reflect a high sedimentation rate. The increase in proportion of HCS sandstone upwards within this facies may indicate an increase in relative sea-level.
facies C: upper shoreface A
Description: The facies comprises interbedded massive and parallel bedded lithic fine sandstone and thin pebble conglomerate (Fig. 3.7). Sandstone contains abundant pebbles especially near me tops of units, where overlain by a pebble layer. In these cases pebbles appear to have
"sunk" into the underlying sandstone and are often orientated with me a-axis vertical (Fig. 3.8c).
Pebble conglomerate layers are no more man 30 cm thick and may grade upwards to sandstone.
Bioturbation is clearly evident at the tops of some units. Silt tube lining of burrows is completely absent but burrowing can be identified in some units where pebbly layers have been disturbed (Fig. 3.8d).
Interpretation: The interpretation of this facies is problematic. Massive sandstone beds in a shallow marine context are normally associated with rapidly deposited sand, as a result of storm action. The sequence contains parallel lamination and is stratified, with beds clearly defined.
In this aspect, the facies is similar to that of me underlying facies B. Pebble conglomerates are probably graded storm deposits.
The absence of silt lined trace fossil burrows makes identification of me degree of bioturbation within units difficult to ascertain. The disturbed pebble layers (Fig. 3.8c) at me tops
33 of some sandstone units were tentatively interpreted by Gostin (1968) as cryoturbation structures.
However, many of these disturbed layers are clearly a result of bioturbation. Figure 3.8d is a plan view of a sand bed with pebble filled Rosselia tubes. The massive bedding within this part of the sequence may be entirely due to bioturbation which is not well preserved. Another alternative is that wave fluidisation or wave pumping could have liquified the sediment, destroying primary structures.
Bioturbation within me surface mixed layer (up to 3-15cm below the sediment-water interface) are typically not well preserved (Savrda & Ozalas 1993). In this zone, sediments are typically soupy and have low shear strengths (Savrda & Ozalas 1993) and, as a result, homogenise me sediment without any clearly identifiable trace fossils. Rapid burial of the substrate and me surface mixed layer will essentially isolate the sediment from any further bioturbation (Savrda & Ozalas 1993). In this facies of the Wasp Head Formation me sedimentation rate may have been high enough to have buried the sediment beyond the limit of burrowing organisms.
The facies is interpreted as being deposited on me upper shoreface, probably deeper than facies B. Pebble conglomerate and sandstone units probably reflect deposition from storms.
Bioturbation subsequent to deposition has overprinted original bedforms.
facies D: upper shoreface B
Description: This facies consists entirely of an amalgamated succession of swaley cross-stratified
(SCS) sandstone (Figs 3.7, 3.8e). SCS sandstone occurs in me middle of me Wasp Head
Formation, between 7 and 13 m in me Wasp Head section. Individual beds related to single
. depositional events are difficult to discern but boundaries interpreted from laterally extensive lag layers suggest that bed thicknesses are in me order of 1-2.5 m. The facies consists entirely of broad (up to 2-3 m), concave-up swales with gently undulating laminae, and low angle (<10°) truncation surfaces. The unit comprises well sorted, quartzose medium sandstone with abundant iron staining. Pebble lenses are common, concentrated at me base of scours (Fig. 3.8e). Within me sequence there are rare, laterally persistent, shelly pebble lags with rounded to well rounded clasts. Minor soft sediment deformation structures indicative of dewatering were found within
34 one bed.
Fossils within me iron-rich lag layers have been described by Runnegar (1969) and consist of bivalves, gastropods and rare brachiopods. The fossil assemblage includes the bivalve
Eurydesma typical of high energy nearshore environments (Runnegar 1979).
Interpretation: Swaley cross-stratification was first defined by Leckie and Walker (1982) and has since been described in other shallow marine sequences (McCrory and Walker 1986; Rosenthal and Walker 1987; Yagishita et al. 1992). The association of SCS and its similarity to HCS suggests that it was formed by storms (Leckie and Walker 1982; McCrory and Walker 1986).
SCS probably reflects a highly energetic, storm-dominated environment where HCS units have amalgamated together. Reworking of sand units by storms occurred to such a degree that siltstone or lithofacies indicative of fairweather deposition are completely absent. In addition, me concave-up swales are preferentially preserved over hummocks, also suggesting abundant reworking.
The interpreted depositional environment for this facies is upper shoreface. Highly energetic storm generated combined flow currents reworked sand into characteristic SCS. Other structures, typical of the nearshore zone, such as those described above for facies B may have been completely overprinted by storm wave activity.
facies E: lower shoreface
Description: This facies consists of amalgamated HCS lithic fine sandstone (Figs 3.7, 3.8f).
Unit boundaries (first order boundaries of Dott and Bourgeois, 1982) are difficult to discern.
Where present these boundaries are undulating, eroding into underlying sediments and are often capped by a thin pebbly lag. The facies contains numerous pebbly lenses concentrated at the base of swales. These pebbles are typically sub-rounded to well rounded. Large isolated clasts also occur in this part of me sequence. Bioturbated siltstone units or intraclasts (typical of fairweather deposition below fairweather wave base) are completely absent from this facies.
Interpretation: Amalgamated hummocky cross-stratification (HCS) sequences are common in
35 storm-dominated shelf environments (Dott and Bourgeois 1982; Surlyk and Noe-Nygaard 1986;
Brenchley et al. 1993). The interpretation of this facies is similar to that of facies B and C.
Sand deposits from frequent storm events have been superimposed, forming a thick sequence.
The absence of bioturbated fine-grained units within the facies indicates deposition was probably above fairweather wave base. Hummocks preserved within me sequence suggest that it may have been deposited in a deeper environment than mat of facies B and C, i.e. on the lower shoreface.
Facies F: transition offshore A
Description: This facies succession occurs at the base of the section at Wasp Head (Figs 3.7,
3.10a). It consists of three basic lithofacies: (a) fine-grained HCS sandstone; (b) bioturbated siltstone - silty sandstone; and (c) pebble conglomerate which may contain large scale wave ripples.
HCS sandstone units attain a maximum thickness of 40 cm. Most beds grade upwards to overlying bioturbated silty sandstone. The upper contacts are gradational due to pervasive bioturbation. Thinner HCS sandstone beds are laterally discontinuous due to complete biogenic homogenisation with underlying and overlying bioturbated beds.
Towards the top of facies F HCS beds become thinner (5-10 cm) and small scale. This part of the sequence is also abundantly bioturbated and has truncated burrows indicating numerous erosion and deposition events within a small interval.
Pebble conglomerate beds are clast supported, poorly sorted and have sharp bases.
Bioturbation has partly reworked these units into underlying units, destroying original bedforms.
Large scale symmetrical wave ripples are evident in some beds (Fig. 3.10a) with wave lengths in me range 1.5-3.8 m and amplitudes 15-20 cm. Due to extensive bioturbation within this sequence the relationship between pebble conglomerate and HCS beds is difficult to discern.
It is clear mat some rippled conglomerate beds do cap HCS beds. A mean strike direction of
028° was obtained from ripple crests. This direction indicates oscillatory current flow was towards 118° or 298°.
Large clasts are scattered through me sequence, typically associated with me fine-grained
36 bioturbated facies (Fig. 3.10b).
McCarthy (1979) identified a diverse range of trace fossils within this facies. Dominant ichnospecies were identified as Rosselia and Cylindrichnus. No body fossils were identified.
Interpretation: This facies is interpreted to have been deposited below fairweather wave base.
Fairweather deposition is characterised by fine-grained sandstone and siltstone. Periodic storm events emplaced sharp based HCS units into this normally quiescent environment. The relatively small thickness of the storm beds suggests deposition occurred at me seaward toe of HCS formation in a transitional environment between nearshore and offshore environments, probably close to storm wave base. Bioturbation, subsequent to deposition, has reworked and homogenised much of me sediment, destroying most of me original bedforms and some of me original unit architecture. Only me thicker storm sandstone units remain relatively undisturbed within me sequence.
Large scale coarse-grained ripples (CGR) within this facies are commonly found associated with sequences containing HCS (Leckie & Walker 1982; Leckie 1988; Fielding 1989;
Cheel & Leckie 1992). Leckie (1988) concluded, after examining bom modern and ancient examples, mat CGR are not diagnostic of water depth and may form in depths ranging from 3-
160 m. The CGR within this facies are closely associated with HCS sandstone beds. CGR were interpreted by Cheel and Leckie (1992) to form in two stages:
1) deposition from offshore directed storm currents under primarily unidirectional combined flow; and
2) reworking of conglomerate by asymmetrical oscillatory flow by onshore propagating storm waves.
Large coarse-grained wave ripples are interpreted as forming under dominantly oscillatory combined flow, identical to HCS (Leckie 1988; Jennette and Pryor 1993). Large Coarse grained wave ripples are, therefore, interpreted as a coarse-grained equivalent of HCS.
Hummocky cross-stratification is formed preferentially where the grain size of me sediment is less than medium sand (Cheel & Leckie 1992). Winnowing of fine material following HCS sand deposition under waning storm conditions may cause a coarsening of the sediment and
37 subsequent CGR formation. Wave-ripple crests form roughly parallel to palaeobathymetry and are, therefore, a good approximator for determining orientation of palaeoshoreline (Leckie 1988).
The palaeocurrent data obtained from wave-ripple crests would indicate a palaeoshoreline for the
Early Permian in the southern part of the basin orientated in a north-northeasterly direction, approximately parallel to 030°.
Large boulder-sized clasts within the fine-grained facies are interpreted as dropstones, deposited as a result of ice rafting.
McCarthy (1979) interpreted this facies as a protected shoreface environment. The pervasive presence of HCS throughout this sequence indicates that storm activity was a dominant depositional process and the environment is more likely to represent an unprotected transitional offshore environment.
Facies G: transition offshore B
Description: This facies is similar to mat described above for facies F. Lithofacies consist of thick intensively bioturbated silty fine sandstone, quartzose sandstone and coarse pebbly sandstone/pebble conglomerate (Figs 3.7, 3.10c).
Thick sandstone beds in me lower part of this facies contain HCS. Towards the top of the sequence beds become thinner and are dominated by parallel lamination (< 20 cm). Lower contacts of units are sharp and erosional and upper contacts tend to be gradational due to extensive bioturbation. In me lower parts of me sequence thick units (< 50 cm) appear to be an amalgamation of several thinner beds. Bioturbation is sparse within sandstone beds and where present, consists of escape traces and Skolithos type assemblages. Thin pebble conglomerate layers are found in association with HCS and plane bedded sandstone units and may contain large scale symmetrical wave rippled horizons. Large clasts (1-2 m), shelly fossils and coalified logs are associated with these conglomerate lags.
Palaeocurrent data from large scale wave ripples suggests current direction towards the northwest-southeast with a vector mean crest trend of 034° (Fig. 3.9).
Brachiopods (dominated by Spirifer species), bivalves (Eurydesma; Fig. 3.10d) and bryozoans were identified by Runnegar (1969) within me conglomerate beds. One conglomerate
38 layer near me top of the formation was particularly fossiliferous, comprising approximately 50% carbonate material.
The silty sandstone units of this facies are much thicker man those of facies F. Unit thickness ranges up to 3 m. The units are intensely bioturbated and are dominated by
Diplocraterion, Large Diplocraterion, Skolithos, Cylindrichnus and Rhizocorallium, which is typical of environments below wave base (McCarthy, 1979).
Interpretation: The environment of deposition is interpreted as being similar to mat for facies
F. Deposition occurred, below fairweather wave base near me seaward extent of HCS sand deposition. Combined flow currents during major storms deposited and reworked sand into HCS units and coarser material into large scale symmetrical wave ripples. The close association of
CGRs at me top of HCS units suggests they formed during waning storm periods. The presence of dominantly parallel lamination within sandstone beds may indicate a dominantly unidirectional component to the combined flow (Brenchley et al. 1993).
The greater thickness of sandy siltstone beds (indicative of fairweather deposition) in facies G compared with facies F may reflect a more abundant sediment supply. Alternatively, storms may have been less frequent and/or less intense due to increased water depth.
3.2.2 Depositional systems and sea-level history
A depositional history for me Wasp Head Formation is presented in Figure 3.11. The sequence consists of two parasequences, labelled A and B in Figure 3.11. Van Wagoner et al. (1988) defined a parasequence as a "relatively conformable succession of genetically related beds or
. bedsets bounded by marine flooding surfaces or their correlative unconformities". Parasequences typically, are composed of a lower transgressive phase and an upper regressive or progradational phase. Usually, me transgressive interval is thin and may only consist of a thin pebbly lag (see flooding surface in Pebbley Beach Formation; section 4.3) and as such parasequences normally consist of upward-shoaling successions. As pointed out by Arnott 1995) the original definition of parasequence by Van Wagoner et al (1988) makes no provision for successions where me transgressive deposits are thick. As will be discussed below, me Wasp Head Formation is a
39 deposit where the transgressive component of the parasequence is volumetrically dominant over the regressive component.
Deposition of parasequence A began with initial flooding at surface A which coincides with me unconformity. Upper shoreface sedimentation of facies B, C and E were deposited above me unconformity. Sediment dispersal was directed towards the northwest via longshore currents. Interbedded with me foreshore facies are thick breccia beds (facies A) comprising large angular, unweathered, locally derived clasts. There is no evidence that the debris flows at the base of the Wasp Head Formation are glacially related. The grade, texture and fabric of the breccia beds suggests that they are more likely to be derived from a steep, north trending tectonic slope.
The lower part of the parasequence is broadly transgressive and culminates in me deposition of transitional offshore facies (Facies F). This interval contains a maximum flooding interval (Fig. 3.11). Above this maximum flooding surface B mere is a change to a regressive or progradational sedimentation regime which comprises an upward-shoaling shoreface sandstone body (Fig. 3.10e). One distinctive aspect of tins parasequence is the relatively thick transgressive phase of me parasequence compared with me regressive phase. The facies at the top of me regressive phase are upper shoreface facies, dominated by swaley cross-stratification.
At the top of this shoreface sand body is a thin pebbly layer which is interpreted as a flooding surface (surface B; Fig. 3.11) which marks the top of parasequence A and the base of parasequence B. This surface is chosen as me stratigraphic bounding surface for me parasequence because it marks me base of me overlying transgressive sequence which, as described by Arnott (1995), is me least subjective surface.
The lower part of parasequence B consists of a transgressive succession of lower shoreface to transitional offshore deposits of facies G (Fig. 3.11). HCS sandstone units become volumetrically less important upward within me section. The upper part of this parasequence is not exposed at these localities.
The relative importance of me transgressive component of bom parasequences A and B may be the result of an accommodation dominated depositional regime (Swift et al. 1991a).
Similar sequences are described from the Argentine shelf (Parker et al. 1982) and the Middle
40 Ordovician Rockcliffe Formation of Ontario (Arnort 1995). An accommodation dominated regime results from me inability of sediment supply to keep pace with me rate of relative sea level rise. A relative fall in sea level is represented by the shoreface sandstone body in me middle of me section. The small thickness of me upward shoaling succession at the base of this shoreface sandstone suggests a relatively rapid fall of sea level (Rosenthal & Walker 1987;
Hadley & Elliot 1991). Erosion at the base of the shoreface sandstone body may have truncated the underlying regressive component of parasequence A.
The Wasp Head Formation is interpreted as a nearshore shelf sequence deposited under conditions of rising relative sea level. This generated an accommodation-dominated deposition regime which led to higher preservation of transgressive deposits (Swift et al. 1991a).
Superimposed on this general sea level rise is a relative sea level fall which resulted in me progradation of a shoreface sandstone body which defines the top of parasequence A. This may have resulted from: (a) a 4m order eustatic sea level change similar to those identified in me
Pebbley Beach and Snapper Point Formations (see section 4.0) (b) a decrease in me rate of subsidence; or (c) from a local variation in sediment supply. The upward-shoaling succession is 3-5m thick which seems too small to be accounted for by a simple increase in sediment supply, therefore, an explanation using (a) or (b) is favoured.
The flooding surface B at me base of the second deepening upward sequence marks a change from dominantly lithic sandstone to quartzose sandstone (see section 5.0). Sediment reworked into me progradational facies D were derived from me underlying transgressive sequence. This infers that sediment within this facies has undergone two stages of reworking:
(1) during initial transgression; and (2) reworked during progradation. This increase in
. reworking across the flooding surface B could explain me more mature, quartzose nature of me sediment.
The breccia beds within me basal portions of me sequence are critical for me interpretation of me depositional setting of the Wasp Head Formation. As discussed above, me units are interpreted as locally derived debris flows. Palaeocurrent indicators suggest palaeoflow was directed towards the east (Fig. 3.9). The source for these flows was probably a north- trending, steep slope. This structure is herein interpreted as a fault bounding a graben or half
41 graben related to the same early phase of extensional sub-basin formation responsible for the deposition of the Clyde Coal Measures. The palaeoflow indicated by the debris flows suggests dispersal transverse or perpendicular to the fault.
3.3 Depositional setting of the Talaterang Group
Bom the Clyde Coal Measures (including me Pigeon House Creek Siltstone) and the Wasp Head
Formation are tentatively interpreted as being formed in sub-basins related to an early phase of basin extension. Despite the different depositional environments for the Clyde Coal Measures and the Wasp Head Formation they show many similarities.
(a) Both formations are found at the base of the Sydney Basin sequence.
(b) Bom formations are highly localised. The Wasp Head Formation is only found in coastal outcrop at the coast near Durras and the Clyde Coal Measures occurs in isolated pockets within me gorges of me southern Budawang range.
(c) Sediment dispersal data within both formations suggests deposition was controlled by north-trending structures.
Low energy fluvial deposition of the Clyde Coal Measures represents axial drainage in the extensional sub-basins and me high energy debris flows represent transverse or perpendicular drainage. The fundamental difference between me two formations is that deposition occurred under marine conditions within me Wasp Head Formation.
The Clyde Coal Measures and Wasp Head Formation represent transgressive sequences.
Deposition in me upper part of the Clyde Coal Measures culminated in me deposition of estuarine facies and me entire Wasp Head Formation (although it does contain a small
.progradational episode) is a broadly transgressive sequence. The rise in relative sea-level observed in both formations is probably me initial transgressive phase of a major third order sea level change which is represented by me overlying Snapper Point Formation and Wandrawandian
Siltstone.
42 4.0 SEDIMENTOLOGY OF THE SHOALHAVEN GROUP
4.1 Yadboro, Tallong Conglomerate and Equivalents
Previous work on me basal coarse successions of me Shoalhaven Group has been carried out by Herbert (1972, 1980a,b). Gostin and Herbert (1973) assigned the Tallong and Yadboro
Conglomerates to me underlying Talaterang Group; interpreting these units as the oldest in me
Sydney Basin sequence. However, these units have been reassigned herein (section 2.0) to the
Shoalhaven Group (Fig. 2.2) based on field observations. The coarse basal units crop out in two separate localities (Fig. 1.1). The Tallong Conglomerate crops out as outliers northwest of
Marulan, in me Shoalhaven Gorge and has also been identified in drillcore (Coonemia No.l, DM
Callala DDH 1). The Yadboro Conglomerate forms a lower cliffline in me southern part of the
Budawang range in me vicinity of Yadboro Homestead. It crops out at the base of well known landforms such as The Castle and Byangee Walls.
Herbert (1972) interpreted the conglomerate successions as pre-Permian drainage systems
(Fig 4.1). Two major drainage networks with east-directed dispersal were identified, corresponding with me present position of me Tallong and Yadboro Conglomerates. The coarse detritus filling me palaeo-valleys is now interpreted as being of high energy fluvial origin with little evidence for glacially related deposition. Herbert (1980b) identified a diamictite unit in
Callala DDH1 (Bembrick and Holmes 1976) with pebbles mat "show distinct striations and more rarely facets". Herbert (1980b) sited this as evidence for Late Carboniferous glaciation.
4.1.1 Lithofacies
The Yadboro and Tallong Conglomerates consist of essentially me same lithofacies and hence have identical environmental interpretations. Hence, the following lithofacies descriptions are intended to encompass bom me Tallong and Yadboro Conglomerates and their equivalent units.
Miall (1978) devised a lithofacies scheme which is commonly used to describe alluvial environments. Since me scheme is widely used and understood it is used herein to describe these sequences (Table 4.1).
43 Gravelly facies
Gm: massive to horizontally stratified conglomerate
Description: This is the dominant lithofacies within the Tallong and Yadboro Conglomerates.
It consists of large, laterally continuous sheets of pebble conglomerate. Maximum unit thickness is approximately 5 m but stacked successions of this facies can reach much greater thicknesses.
The basal contact is typically erosional where it overlies finer grained facies but boundaries between units in stacked successions of the same facies are often very difficult to distinguish.
Clasts are sub-rounded to rounded and typically pebble to cobble sized with a poorly sorted matrix of fine to coarse sand. Maximum observed clast size was 23 cm. Internal stratification is poorly developed and beds appear massive to crudely horizontally stratified. Units often contain alternations between pebbly and sandy horizons. Some larger pebbles are preferentially horizontally aligned along me a-b plane which defines the flat stratification. Imbrication is well developed within some horizons.
Interpretation: The general consensus in me sedimentological literature suggests that this facies developed as lag deposits or low amplitude migrating bed forms in both alluvial and marine environments. Hein and Walker (1977) observed crude horizontal stratification developed in me
Kicking Horse River, British Colombia. They concluded that me facies developed from deposition of diffuse gravel sheets during high-water discharges. Continued growth and accretion creates longitudinal or diagonal bars. Miall (1977) and Steel and Thompson (1983) suggested me same genesis for this facies in ancient deposits. Alternations in grain size within units may be due to fluctuations in stream velocity (Nemec and Steel 1984).
Gt: trough cross-bedded conglomerate
Description: Trough cross-bedded conglomerate facies are found within bom me Tallong and
Yadboro Conglomerates. The facies is difficult to distinguish from Gm facies due to me large clast-size and lack of internal stratification. Troughs are seen best in plan view where orientation of clasts delineates the bedform. Limbs of troughs are of a low-angle, typically 5-
10°. Troughs can reach a maximum of approximately 3-4m wide and 50cm deep and are
44 sometimesfilled wit h sandy or silty facies (Ss; Fig. 4.2a). Troughs appear as solitary sets with internal stratification (where visible) parallel to me basal erosion surface.
Interpretation: The process which forms cross-stratification within gravels is not well understood due to a lack of experimental data (Allen, 1993). Miall (1977) and Steel and Thompson (1983) suggest that low-angle trough cross-stratification forms through a process of cutting and filling of minor channels under upper or lower flow regime, plane bed conditions.
The presence of solitary sets of trough cross-beds with stratification parallel to me basal erosion surface and presence of Ss facies overlying and filling remnant troughs suggests that they probably formed via a cut and fill process as described by Miall (1977) and Steel and
Thompson (1983).
Gp: Planar cross-bedded conglomerate
Description: This facies is rare within me Yadboro and Tallong Conglomerates and only two clear exposures of this facies were observed. The maximum recorded thickness of Gp units is approximately 3m but most beds fall in me range of 0.5-lm. The dip of foresets can be as high as 25°. Clasts range from cobble to fine pebble size. Individual foresets show well developed grading with me coarsest material at me base. Units are laterally persistent for tens of metres, often erosionally truncated by overlying units.
Interpretation: The process which forms planar cross-beds in gravelly sediment is not fully understood. Hein and Walker (1977) suggested the cross-bedding developed within downstream accreting transverse bars in alluvial systems. Rust (1984) postulated that Gp facies result from deposition during falling stage when longitudinal bars emerge. This emergence causes flow to divert from me bar axes to adjacent channels. The cyclic grading of individual foresets within
Gp units is attributed to the periodic avalanching of gravel bedforms (Rust 1984).
Sandy facies
Sh: Plane bedded sandstone
45 Description: This lithofacies consists of plane bedded medium to coarse sandstone. The units are usually pebbly and may contain distinct pebbly horizons. Thickness varies but is typically no greater man lm. Units of Sh are quite laterally extensive but may change gradationally into
Gm or St facies. Where units are not erosionally truncated by overlying units the beds commonly grade upwards to St facies and Fl facies.
Interpretation: This lithofacies is interpreted as upper flow regime deposits. The grading upwards, present in some beds suggests that the lithofacies were deposited under waning flow conditions, possibly following a major flood event.
St: Trough cross-bedded sandstone
Description: This facies consists of medium to coarse, pebbly sandstone. Foresets are usually low angle with 10°-15° being typical. Thickness of trough cross-bedded lithofacies varies from
15-90cm. As mentioned above this facies shows lateral transitions into plane bedded facies.
These beds generally have me same geometry as facies Sh.
Interpretation: This lithofacies is interpreted as a low flow regime deposit, formed by the migration of low amplitude three-dimensional dunes (Collinson and Thompson, 1989). The lateral transition of this facies into plane bedded units and the low amplitude of me foresets suggest mat deposition may have occurred close to transitional regime where bedforms are washed out (Smith 1990).
Ss: sandstone scour fills
Description: This lithofacies is a common sandstone lithofacies which occurs throughout the
Tallong and Yadboro Conglomerates (Fig. 4.2a). It consists of trough shaped scours and scour fillings. Scours range in width from 1-15 m and depth from 8-60 cm. Scour-fill lithology consists of fine- to coarse-grained pebbly sandstone. Internal sedimentary structures consist of ripple cross-lamination, trough cross-bedding and flat lamination. In most cases internal bedding is parallel to me scour base. A two stage scour-fill was evident in one scour which consisted
46 of two units of ripple laminated sandstone, separated by an erosional surface. The sandstone within me scour-fills is often capped by a thin layer of laminated siltstone.
Interpretation: This lithofacies is common in alluvial conglomeratic sequences (Cant and Walker
1976; Miall 1977; Bryant 1983). The sandstone fills probably represent deposition during low water periods of reduced flow whereby transport and bedform migration of gravel sheets within the alluvial system had ceased following a flood, and flow was confined to lateral channels adjacent to gravel bars, which subsequently filled with sand. Waning flow conditions following a flood may also explain me presence of fine-grained sandstone to siltstone at the top of many of these scours. The scours mat were present on me tops of bars following cessation of high water deposition may also have been filled with sandstone resulting in me observed unit geometry for facies Ss.
Fl: laminated siltstone
Description: This is the rarest lithofacies within me alluvial conglomeratic sequences (Fig. 4.2b).
Thickness is restricted to less than 50 cm and it only occurs between major cycles of conglomerate deposition (see 4.1.3) or as lensoidal deposits (up to approximately 100m wide).
The siltstone is typically laminated and is carbonaceous in places.
Interpretation: This lithofacies is interpreted as a low energy deposit on an abandoned channel or alluvial plain. The lateral extent of these units suggests that they may represent major floods.
Rare lensoidal siltstone beds within me Tallong Conglomerate probably represent suspended sediment deposited on an abandoned part of the alluvial plain, laid down following a flood event.
4.1.2 Badgery's Breccia
The Badgery's Breccia crops out on the western margin of me basin at Badgery's Lookout (GR:
8928-345482). The breccia is approximately 18m thick and forms me basal part of the section
(Figs 4.2c & 4.3). It consists of moderately to poorly sorted, angular to sub-rounded clasts with
47 a maximum clast size in me range of 7 - 12 cm. Rare clasts are as large as 1.25 m.
Composition is dominated by phyllite and quartzite, typical of the underlying Ordovician turbidite lithologies. The fabric of the breccia is dominantly clast supported and the matrix comprises medium- to coarse-grained sand. Most clasts are randomly oriented but some large clasts show definite imbrication. Minor medium-grained sandstone lenses, typically < 1 m wide, are associated with the breccia and it passes upward into more stratified facies, consisting of interbedded sandstone and pebble conglomerate, more typical of the Yadboro and Tallong
Conglomerates at other localities.
Another 80 cm unit of breccia was found at the base of a section in Tallowa Gorge
(GR: 8928-462517). Maximum clast size ranged between 30 and 90 cm. The texture and fabric of the breccia is identical to that of the Badgery's Breccia. Clast lithologies are dominated by phyllite, identical to mat of the underlying Devonian basement.
Interpretation: Packham (1962) interpreted me Badgery's Breccia as a glacial tillite. Herbert
(1972) argued against a glacial origin for the unit, suggesting mat there was no clear evidence that it was glacially related. Herbert (1972) interpreted the breccia as a talus or alluvial fan deposit, adjacent to a major river, indicated by me position of the Tallong Conglomerate.
The moderately sorted, clast supported fabric and sandy matrix of me Badgery's
Breccia suggest mat it is a stream flow deposit rather man a tallus deposit as proposed by
Herbert (1972). Imbrication data (Fig. 4.4) from large clasts within me Badgery's Breccia suggest a east-directed palaeoflow, which is the same as me Tallong Conglomerate. These breccias are herein, re-interpreted as basal and localised streamflow facies of the Tallong
Conglomerate.
4.1.3 Fluvial style
Architectural-element analysis in fluvial sequences was outlined by Miall (1985) to escape from fixed "end member" facies models which rely mainly on vertical profile analysis and not on three dimensional geometry. The method divides fluvial sequences into eight major elements which are defined on me basis of me following characteristics:
48 a) nature of lower and upper bounding surfaces; b) external geometry; c) scale; and d) internal geometry.
Ramos and Sopeiia (1983) devised a similar architectural element scheme specifically for gravelly braided river sequences. They identified five elements: sheets of massive conglomerate, tabular cross-stratified conglomerate, lateral accretion conglomerate, channel-fill conglomerate, coarse- to medium-grained sandstone and fine-grained sediments.
Three of Miall's (1985) architectural elements are present within me Tallong and
Yadboro Conglomerates (Table 4.2). The most volumetrically important elements are GB
(gravelly bars and bedforms) and SB (sandy bedforms). Overbank fines (OF) are a very minor component and only crop out at sixth order surfaces.
Lateral profiles are a commonly used technique to describe sandy fluvial sequences (e.g.
Allen 1983; Miall 1988; Miall and Turner-Peterson 1989) but its use in conglomeratic alluvial sequences is less common (Ramos and Sopeiia 1983; Smith 1990). Lateral profiles have proved very important for describing fluvial environments. Two photo mosaics (Figs 4.5 & 4.6) have been constructed in an attempt to describe me alluvial environment represented by me Tallong and Yadboro Conglomerates. The outcrops chosen for these profiles are typical examples of facies assemblages observed in the Tallong and Yadboro Conglomerates at all localities. Bom profiles were taken from outcrops at "Johnny Fields" property (GR: 8928-263642).
Profile 1: This profile (Fig. 4.5) shows a stacked succession of 7 GB elements comprising 7 depositional units, and is perpendicular to me interpreted palaeoflow. The units are dominated by Gm lithofacies with minor Ss and Gt. The sequence is interpreted as a stacked succession of longitudinal bar deposits. These gravel sheets do not represent a single depositional event but rather a series of events, as evident from me numerous thin sandstone lenses dispersed through me units. Cross-bedding within me conglomerate units near me top of the mosaic, and also in me bottom right, are probably me result of lateral accretion on me flanks of longitudinal bars, corresponding to me lateral accretion conglomerate of Ramos and
Sopeiia (1983). The unit containing cross-beds at me bottom right of the mosaic has been
49 erosionally truncated by the overlying gravel unit.
Trough cross-bedded conglomerate (Gt) with sandstone scour fills (Ss) are extensively developed at the centre right of the profile. These may correspond to channel fill facies (Ramos and Sopeiia 1983) adjacent to a longitudinal bar. During high water periods gravel was probably deposited on and adjacent to bars whereas during low water, bars became emergent and flow was restricted to lower lying channels which subsequently filled with sandy bedforms.
Unit boundaries are difficult to discern within this profile but a probable bedding hierarchy can be defined. Bedding hierarchy in fluvial sequences was first devised by Allen
(1983) who defined three types of contacts. This system was modified by Miall (1988) into a six stage hierarchy (Table 4.3) which is me system used here. Clearly defined unit boundaries on Figure 4.5 probably reflect 3rd and 4th order surfaces, reflecting downstream accretion of macroforms such as longitudinal bars. Within units, minor bedding surfaces, which are draped by thin sandstone lenses, probably represent second order surfaces. These boundaries should be considered reactivation surfaces whereby sand is deposited over gravel bars during low water stages.
Profile 2: This profile (Fig. 4.6) is slightly different, with sandstone elements more volumetrically important man in profile 1. This profile contains both GB and SB architectural elements. Seven distinct units were identified with gravel beds separated by sandstone facies.
Unlike the Ss lithofacies present in profile 1, many of the sandstone lithofacies are laterally persistent and contain flat lamination, low angle lamination and trough cross-bedding. The environment of deposition is probably one where there is less energy man mat of profile 1, reflected in me dominance of sandy lithofacies within me succession.
Several aspects of me Tallong and Yadboro Conglomerates suggests deposition occurred on a high energy proximal braided system. These are: a) abundance of Gm, Gt and Sh lithofacies; b) predominance of GB architectural elements; c) paucity of overbank facies; d) rare evidence of lateral accretion; e) absence of channel structures and sheet-like geometry of coarse units; and
50 f) absence of rapid downstream facies changes and debris flow facies indicate a braidplain rather man a alluvial fan.
In general the fluvial style represented by the Tallong and Yadboro Conglomerates is typical of a proximal braided fluvial system, similar to me Scott model of Miall (1977), facies association G„ of Rust (1978) and model 2 of Miall (1985). This type of fluvial style is characterised by the predominance of gravelly facies (GB architectural elements) and in vertical profile comprises superimposed bar deposits. The alluvial plain probably contained numerous shallow channels which branched and rejoined frequently. A modern analogue for this type of sequence are proximal braided outwash braidplains such as the Kicking Horse River (Smith
1974; Hein and Walker 1977) which were deposited in a similar cold climate setting,
4.1.4 Vertical facies changes
The Tallong and Yadboro Conglomerate sequences are cyclical in nature, consisting of crude fining upward sequences. The cycles are obvious within me Yadboro Conglomerate within me vicinity of Byangee Walls and The Castle where the unit is at its thickest. These cycles stand out as prominent benches on me cliffline (Fig. 4.2d) and appear to be continuous across the entire width of cliff exposure (Fig. 4.2e). A section through the Yadboro Conglomerate at The
Castle is presented in Figure 4.7.
The bases of the cycles are erosional and typified by a well rounded cobble conglomerate, dominated by GB elements and a fluvial style such as that shown in profile 1
(Fig. 4.5). Upwards through me cycle SB lithofacies become more common and the style changes to that shown in profile 2 (Fig. 4.6). The cycles are usually capped by a thin siltstone.
These fine-grained facies at me tops of the cycles are laterally continuous over large distances.
The siltstone facies could be traced over a distance of 7 km within me vicinity of Yadboro, parallel to palaeoflow, and appears to extend across the entire palaeovalley. The conglomeratic bases of these cycles are interpreted as major sixth-order bounding surfaces (Miall 1988) and indicate boundaries between major pulses of fluvial sedimentation. The lateral extent of the siltstone units suggests that they represent a major event in me depositional history of the braidplain. There was no evidence of marine influence found within me siltstone facies and thus
51 the facies may represent a major lacustrine flooding surface, similar to that outlined by Plint &
Browne (1994). Another alternative is that these deposits reflect a lateral shift of the alluvial system to another part of the palaeovalley, allowing deposition of fine-grained sediment during fluvially inactive periods. However, the lateral continuity of the cycles across the exposed part of the palaeovalley suggests that the cycles may be related to basin-wide relative sea-level changes rather man allocyclic geomorphological controls. The cyclical nature of the alluvial sequence suggests that episodic basin subsidence or eustatic sea-level changes (see chapter 6) were responsible. Major facies changes within braidplain environments have been widely documented (Hazeldine & Anderton 1980; Nemec 1990; Plint & Browne 1994). Hazeldine &
Anderton (1980) and Plint & Browne (1994) attributed these facies changes to episodic tectonic activity which rapidly decreased base level. In bom cases major changes in palaeocurrent direction were recorded due to tectonic tilting.
Major faults have not been identified as a important tectonic influence in me southern
Sydney Basin during me period of deposition of me Shoalhaven Group. Therefore it would be unlikely that rapid and episodic changes in subsidence could explain me interpreted flooding events. Glacio-eustatic sea level changes corresponding with Milankovitch (1941) cyclicity have been documented for me Permian (Borer & Harris 1991; Miller & West 1993). Sea level changes within me Pebbley Beach Formation (see section 4.3) are interpreted as orbitally forced cycles and show good evidence of climatic change. The observed cycles within me Yadboro
Conglomerate may be related to this Milankovitch cyclicity. Flooding surfaces within me sequence are interpreted as representing periods of relative sea level rise associated with interglacial periods. During glacial periods mere is a decrease in relative sea level, causing a progradation of another alluvial sheet. The strong seasonality in flow conditions generated by spring maw periods associated with me cold climate would promote the transport of gravel and sand (Plint & Browne 1994).
4.1.5 Isopachs and Palaeocurrents
The lateral distribution of me conglomerate units (Fig. 4.8) shows mat deposition was restricted to two main palaeo-distributary systems. The northern system is referred to as the Tallong
52 Conglomerate and me southern system is the Yadboro Conglomerate. There are, however, outcrops of conglomerate scattered between these two exposures. For example, conglomerate consisting of the same lithofacies of me Tallong and Yadboro Conglomerates was found in
Touga Creek (GR: 8928-371246).
The Tallong Conglomerate is an elongate body (Fig. 4.8) which trends in a southeasterly direction in me vicinity of Marulan and Wingello in me western portion of me study area. An incomplete thickness of 206m was recorded in me Long Swamp Bore for me Tallong
Conglomerate near Tallong (Department of Mines 1883). A deeply incised channel-fill termed me Yagers Conglomerate by Herbert (1972) is exposed within me Shoalhaven Gorge. This was interpreted by Herbert (1972) as a tributary of me main channel represented by me Tallong
Conglomerate. The thickness of this fill is approximately 120 m and extends 1 to 1.5 km along me Shoalhaven Gorge in me vicinity of Yagers Lookout (GR: 8928-418434). Another outcrop of Tallong Conglomerate is also visible at Hoddles Cliff (GR:8928-493471; 4.2f). To me east of this locality me lateral exposure of me Tallong Conglomerate becomes discontinuous and patchy (Fig. 4.8) with approximately 50 m of conglomerate encountered in me Shoalhaven
Gorge downstream of Tallowa Dam at Three Mates Bluff (GR:8928-566445), 60 m in Yarrunga
Creek DDH1 near me junction of the Kangaroo River and Yarrunga Creek and 138.7 m was encountered in Coonemia No.l.
The Yadboro Conglomerate forms an east-facing lobe (Fig. 4.8) and has a maximum thickness of 180 m at me eastern end of Byangee Walls (GR: 8927-490880). The conglomerate extends 8 km east-west and 20 km north-south. The conglomerate exposure rapidly attenuates towards the north where it can be clearly seen lensing out at me contact between basement and the overlying Snapper Point Formation (Fig. 4.9a). It is important to note mat me southwestern edge of this conglomerate body in me vicinity of Corang Peak (GR:8927-363912) has been has been removed due to erosion and mat the Yadboro Conglomerate may have continued south for some distance. A 36 m interval of conglomerate was encountered within Elecom Clyde River
8 but this interval appears to be isolated and unconnected with me main conglomerate body.
The locations of the Tallong and Yadboro Conglomerates clearly correspond to basement depressions (Fig. 4.10). There is no evidence that these depressions were created by glacial
53 processes. These topographic lows were depocentres for high energy alluvial sedimentation during me Early Permian. Herbert's (1972) assertion that the Tallong and Yadboro
Conglomerates are of Late Carboniferous age is demonstrably incorrect since they clearly overlie
Permian strata (see section 2.2). The Tallong and Yadboro Conglomerates are herein interpreted as a part of the same single semi-continuous alluvial apron. The present position of the main conglomerate bodies simply reflects the position of valleys which resulted from alluvial incision during the Early Permian.
The isolated patches of Conglomerate within the eastern part of the study area may represent localised basement depressions which contained thicker accumulations of conglomerate fill. Subsequent erosion during the Early Permian transgression failed to remove the sediment from these depressions. This would seem to be supported by the basement contour map (Fig.
4.10) which shows a clear depression at the location of Coonemia No.l.
Palaeocurrent data is presented in Figures 4.4 and 4.11. It is clear mat all the alluvial sediment was derived from eastward flowing streams.
4.1.6 Depositional model
The Tallong and Yadboro Conglomerates form part of a semi-continuous alluvial braidplain succession. Incision and subsequent deposition was initiated in me Early Permian, probably caused by the onset of passive thermal subsidence, which affected the entire basin (Phase 2 of
Baker et al. 1993; Phase B of Veevers et al. 1994b). The high energy braidplain systems were derived from me west and were concentrated within two major incised valleys which correspond with the current position of me Yadboro and Tallong Conglomerates. The Braidplain system was subsequently subjected to four major base level rises, possibly caused by Milankovitch
(1941) orbital forcing which caused flooding and deposition of siltstone facies possibly within coastal and/or lacustrine environments. Base level falls initiated high energy braidplain progradations influenced by strongly seasonal climatic conditions. In this sense four me cycles within me Yadboro Conglomerate represent braidplain delta successions as ouflined by
McPherson et al. (1987) and Orton (1988). The progradation substantially eroded underlying sediments and in some cases completely removed me underlying fine-grained facies. High
54 energy braidplain deposition was eventually succeeded by the coastal facies of the Yarrunga Coal
Measures (see section 4.2) or me sandy-fluvial and marine facies of the Snapper Point
Formation.
The recognition of me Tallong and Yadboro Conglomerates as Permian units and not
Late Carboniferous as proposed by Herbert (1972) is important. The Tallong and Yadboro
Conglomerates represent a semi-continuous alluvial apron which was derived from me western margin of me basin. This phase represents me second period of basin development, following me initial extensional phase represented by the Talaterang Group. This same alluvial apron can probably be correlated with basal conglomeratic units to the north, namely the Megalong
Conglomerate and the conglomerate unit in me vicinity of Rhylstone. This corresponds to Phase
2 of Baker et al. (1993) or Phase B of Veevers et al. (1994b) and represents a period of passive thermal sag over me entire Sydney Basin.
4.2 Yarrunga Coal Measures
The Yarrunga Coal Measures were correlated with me Clyde Coal Measures by Gostin and
Herbert (1973) and Herbert (1980a). The stratigraphic position of me Yarrunga Coal Measures, situated above the Tallong Conglomerate suggests mat they are a completely separate unit from the Clyde Coal Measures. The only previously identified exposure of me Yarrunga Coal
Measures is located at me junction of Kangaroo River and Yarrunga Creek (Gray, 1969). The construction of Tallowa Dam has since submerged this locality. The only available information can be derived from drillcore. Of these drillcores, three were fully cored, namely DM Callala
DDH1, Elecom Clyde River 8 and Elecom Clyde River 1. Coonemia No.l and Wandandian
Bore were not fully cored but contain significant intervals of coal bearing strata.
Silt dominated intervals lying between me Tallong Conglomerate and Snapper Point
Formation located within Tallowa Gorge (GR:8928-460517) and at Badgery's Lookout may also correlate with the Yarrunga Coal Measures.
In all cases, except for the Wandandian Bore interval, me Yarrunga Coal Measures overlie the Tallong Conglomerate. It is interpreted herein mat these sediments belong to a sandy fluvial to coastal plain succession which developed between the high energy braidplain and
55 laterally adjacent marine sedimentation. It ensued as a consequence of the transgression responsible for me deposition of the Snapper Point Formation and Wandrawandian Siltstone.
4.2.1 Facies analysis
Given the relatively small areal and stratigraphic interval which the Yarrunga Coal Measures occupies, and me sparsity of outcrop, each of the known successions will be described and interpreted individually. The sequence is probably more extensive but does not outcrop.
a) DM Callala DDH1
The sequence identified as Yarrunga Coal Measures (Fig. 4.12) within this drillcore is located between 520.5 and 483.4 m and overlies the Tallong Conglomerate (interpreted as a proximal braidplain facies, see section 4.1). The interval is overlain by bioturbated sandy strata of the
Snapper Point Formation.
The coal measure sequence consists of interbedded siltstone and fine- to medium-grained sandstone (Fig. 4.12). The sandstone is flat laminated, ripple cross-laminated and cross-bedded with many beds fining upwards to siltstone. The siltstone is highly carbonaceous, with abundant plant debris, flat laminated and typically contains pyrite. Both the siltstone and sandstone are sparsely bioturbated.
The predominance of fine-grained and carbonaceous sediment suggests a relatively quiet environment. The presence of bioturbation and pyrite suggest possible marine influences. The context of me facies between alluvial facies (Tallong Conglomerate) and shallow marine facies
(Snapper Point Formation), and me afore mentioned sedimentological features, would suggest mat the Yarrunga Coal Measures facies may be a coastal plain succession, located behind a protective barrier. The thick sandstone bodies within me succession may represent distributary channels or tidal inlets. Siltstone units probably represent back barrier lagoon and swamp facies.
b) Badgery's Lookout and Yagers Lookout
Between me Tallong Conglomerate and me Snapper Point Formation at bom Badgery's Lookout and Yagers Lookout there is a 2 m thick laminated siltstone with plant debris (Fig. 4.9b) and
56 pyrite. This unit is underlain by high energy alluvial facies and overlain by shallow marine facies. The context of this unit would therefore imply mat it is probably of coastal origin and, therefore, correlates with me Yarrunga Coal Measures.
c) Elecom Clyde River 8
An interval of 18 m (329.1 - 311.5 m) contains sediments which could be classified as equivalent to the Yarrunga Coal Measures. The interval overlies 36 m of Yadboro
Conglomerate and is overlain by marine sediments of the Snapper Point Formation.
The sequence consists of interbedded coarse- to fine-grained sandstone and siltstone. The sandstone is cross-bedded or plane-bedded. Many sandstone units fine upwards to siltstone.
Siltstone units are highly carbonaceous, pyritic and may contain plant debris. The presence of pyrite and bioturbation suggests marine influences. The context of me facies suggests again mat these sediments were deposited on a coastal plain within a low energy fluvial system.
d) Elecom Clyde River 1
Between me Tallong Conglomerate and me Snapper Point Formation within Elecom Clyde River
1 mere is a 10 m (243.36 - 254.96 m) interval mat probably correlates with me Yarrunga Coal
Measures. The sediments consist of interbedded conglomerate, very coarse- to very fine-grained sandstone and siltstone. Conglomerate units are clast supported and contain rounded clasts within a sandy matrix. Sandstone beds are typically plane bedded, more rarely cross-bedded and may contain carbonaceous lenticles and silty bands. Sandstone unit thickness ranges up to 80 cm. Rare bioturbation was found in two sandstone beds. Siltstone beds are highly carbonaceous
. and are wavy bedded in places. Silty phases have a maximum thickness of 30 cm recorded for this interval. Upper contacts of these siltstone units are sharp and could be erosive.
As for me three previous localities inferences concerning me environment of deposition for this interval depend largely upon the context of facies. The interval clearly overlies high energy alluvial strata of the Tallong Conglomerate and is overlain by probable sandy shallow marine strata of the Snapper Point Formation. The presence of bioturbation and pyrite suggests probable marine influences. The environment of deposition is probably a sandy coastal plain.
57 Sandstone and conglomerate beds probably represent tributary channels (possibly estuarine).
Sandstone beds towards me top of the succession, mat abruptly overlie and are overlain by siltstone units, may represent overbank splay sedimentation or alternatively, washover sand deposits in a lagoonal or distributary bay setting. Silty units may represent overbank or lagoonal sedimentation.
e) Coonemia No.l
Condon (1969) interpreted a 65 m interval (512.1 - 576.7 m) in Coonemia No.l as the Clyde
Coal Measures and described the lithologies as consisting of approximately 15% sandstone, 70% siltstone and shale and 15% coal. The interval overlies 140.1 m of Tallong Conglomerate.
Bembrick and Holmes (1976) reinterpreted the unit as the Yarrunga Coal Measures. They interpreted me sequence from geophysical and lithological logs as a meandering fluvial sequence consisting of channels (sandstone beds) and fine-grained organic-rich overbank facies.
As for the previous localities this locality probably represents a coastal plain environment with meandering channels and overbank and/or lagoonal sedimentation.
4.2.2 Depositional system
In all cases me Yarrunga Coal Measures overlies me Tallong Conglomerate and is overlain by shallow marine sediments of me Snapper Point Formation. The Yarrunga Coal Measures is interpreted as a coastal plain complex which developed on and adjacent to the fluvial drainage system represented by me Tallong Conglomerate. Deposition of me Yarrunga Coal Measures represents a significant decrease in energy along me drainage system. High energy braidplain sedimentation gave way to a more meandering fluvial style consisting of dominantly sandy and silty sediment. The sedimentary successions described above suggest a coastal environment with sand lithologies showing characteristics of fluvial channel facies and silty facies representing floodplain, lagoonal or interdistributary bay conditions. The transgression responsible for deposition of me overlying Snapper Point Formation probably reworked fluvial sediments into strandlines, behind which, organic-rich floodplain and lagoonal sediments could accumulate.
58 4.3 Pebbley Beach Formation
The Pebbley Beach Formation crops out in me southern part of the study area along me coast between Wasp Island and Clear Point (Fig. 4.13). Sections were measured in me upper portions of the formation. The Pebbley Beach Formation consists of nearshore and coastal successions associated with me early stages of me major marine transgression represented by me Snapper
Point Formation and the Wandrawandian Siltstone.
The Pebbley Beach Formation has been studied previously by Gostin (1968), Stutchbury
(1985, 1989) and Mifsud (1990). Runnegar (1969, 1980a) analysed the invertebrate fauna from me formation.
4.3.1 Facies analysis
A number of sections were measured through me Pebbley Beach Formation (Fig. 4.14a). On this basis five sedimentary facies were delineated (table 4.4).
A: Intertidal channel and channel abandonment facies
Description: This facies is evident at Point Upright, Mill Point and Clear Point (Figs 4.14a,
4.9c,d) and is marked by steep-sided channels, up to approximately 6m deep. The width of me channels is difficult to determine because of me difficulty of finding a cross-section which is not oblique or laterally erosional. Oblique sections can be traced laterally for hundreds of metres. One channel which cropped out in plan view on me northern side of Mill Point (Fig.
4.9e) showed a width of approximately 15 m.
Most channels have no lag deposits developed at me base with only occasional pebble and granule sized clasts marking me erosional boundary. However, some channels on me northern side of Mill Point and Point Upright contain a thick heterolithic inclined basal unit consisting of interbedded medium-grained sandstone and dark carbonaceous siltstone (Fig. 4.9f).
The sandstone contains pervasive ripple cross-lamination and in places trough cross-bedding.
This unit is abruptly overlain by a mud-rich unit which comprises me major proportion of me channel fill, as described below.
The fill of all channel bodies within me Pebbley Beach Formation is dominated by
59 inclined heterolithic strata (Fig. 4.9d,e). Lithologically the unit consists of interlaminated fine- to very fine-grained sandstone and siltstone. Internally the heterolithic strata consist of flaser and lenticular bedding (Fig 4.15a). Ripple laminations show symmetrical ripple tops and interference patterns in plan view and undulatory lamination, chevron lamination and bidirectional lamination in sectional views.
One channel fill on Mill Point contains a relatively thin (maximium 20 cm) ripple laminated unit of fine-grained sandstone (Fig. 4.9c). The ripple laminated unit is overlain by a dark, carbonaceous, lenticular bedded siltstone. These units have a lensoidal geometry and pinch out towards channel margins. The thickness of the carbonaceous siltstone unit varies but reaches a maximum of approximately 50 cm. This facies occurs in an intensively channelled sequence, containing numerous cross-cutting channels. Channels have evidentiy eroded to approximately me same base level.
Palaeocurrent data taken from structures within facies A show a scattered trend (Fig.
4.16) but there does seem to be a dominant east-directed flow. Lateral accretion surfaces generally dip towards me north (Fig. 4.16).
Interpretation: The inclined strata mat dominate me channel fill are interpreted as epsilon cross- bedding (Allen 1963) or inclined heterolithic strata (IHS; Thomas et al. 1987). This type of cross-bedding is attributed to me lateral migration of point bars within a meandering channel system. The type of lamination found in this facies is typical of structures formed under combined wave and current flow (De Raaf et al. 1977). The interlamination of sand and silt throughout this facies suggests frequent alternations in me energy regime. The bidirectional palaeocurrent distribution, ripple structures and me interlaminated nature of me sediments suggests that me sediments were of tidal origin. This is supported by me context of me interval, overlain and underlain, in many cases by bioturbated intertidal sediments (see below).
The absence of bioturbation in me channel facies suggests that deposition was rapid enough to prevent extensive colonisation by burrowing organisms.
The fact mat these sediments are confined to channels and show evidence of tidal activity suggests they represent meandering tidal channels. The channels are very similar to those found
60 on intertidal mud flats in modern environments (Clifton & Phillips 1980; Clifton 1983). The base of the channelised unit probably marks me intertidal-subtidal boundary (Clifton 1988).
The tidal channels on me northern side of Mill Point show a three stage evolution: a) incisement of channel and deposition of basal coarse facies under relatively high energy conditions; b) deposition of inclined strata consisting of interlaminated fine-sand and silt under moderate energy conditions on channel banks during me phase of channel migration; and c) abandonment of channel and cessation of current activity leading to ponding within channel and deposition of dark, carbonaceous silt.
Lensoidal sand units within me channel-fills probably represent fluvial transported flood sediment or, alternatively, storm deposits which have been washed into me tidal channels.
Given mat me shoreline was orientated approximately north-northeast (see facies F and section 4.4), me predominant direction of palaeoflow was seaward, consistent with a significant fluvial influence. Analysis of lateral accretion surfaces shows that channels migrated dominantly in a northerly direction which may coincide with me direction of longshore currents.
B: Tidal flats
Description: This facies consists of laterally continuous units of sandy siltstone and interlaminated fine- to very fine-grained sandstone and siltstone (Fig. 4.15b). Internally, structures vary from massive to lenticular and flaser bedding (Fig. 4.15c,d; cf. Reineck &
Wunderlich 1968). Interlamination structures are similar to those described above for facies A.
The percentage of silt and the degree of bioturbation varies between beds. Most beds contain pyrite and some soft sediment deformation structures. Coalified and silicified logs are present and are well exposed in plan view along the rock platforms (Fig. 4.15e).
Trace fossils are dominated by Phycosiphon, Diplocraterion, Skolithos and Rosselia (Bann in prep).
Palaeocurrent data (Fig. 4.16) show bimodal sediment dispersal mat was dominantly northwest and southeast with vector mean directions of 345° and 165°.
61 Interpretation: The predominantly fine-grained nature of this facies suggests a standing water environment. The abundance and type of interlamination structures indicate that there were alternating periods of high and low energy under combined flow conditions. In the context of this coastal sequence, the facies probably represents a back barrier, tidally influenced environment. The abundant bioturbation present in some units of this facies suggests that deposition was slow enough to allow colonisation by burrowing organisms. Clifton (1988) suggested mat intense bioturbation in back-barrier environments is most likely to occur on intertidal flats (Fig. 4.14b). Changes in me grade of bioturbation and the proportion of sand within successive units reflect changes in position and energy regime within me back-barrier setting. Small changes in relative sea-level could result in a change from an intertidal environment to a subtidal environment. Such changes could be caused by changes in the position of feeder channels, thus altering me rate of sediment supply to parts of the back- barrier lagoon in combination with compaction and subsidence. Palaeocurrent data indicate that palaeoflow within me back-barrier environment was parallel to the inferred shoreline which may indicate influence of tidal flow behind a barrier. The symmetrical nature of the ripples suggests reworking by bom flood and ebb currents or alternatively reworking by waves in shallow standing water.
C: Lagoon
Description: This facies consists of relatively thin (up to approximately lm) units of dark, pyritic siltstone. The units are highly carbonaceous and laterally extensive.
Interpretation: The fine-grained carbonaceous nature of these units suggests a very low energy, probably standing water environment. The facies is typically associated with facies B. This facies probably represents the deeper, quieter parts of a back-barrier lagoon where mere is little or no tidal influence on me bottom sediment (Fig. 4.14b). The carbonaceous nature of the unit probably results from a relatively low sedimentation rate in me central portions of me lagoon.
62 D: Washover/Flood tidal delta
Description: This facies consists of laterally extensive successions of interbedded medium- grained sandstone, fine-grained sandstone, siltstone and minor coarse pebbly beds (Fig. 4.15b).
Much of the facies is intensely bioturbated. Sandstone units have sharp lower contacts with underlying fine-grained sediments but many contacts have undergone subsequent bioturbation.
Interpretation: The interpretation of this facies is largely based on me facies association. The facies is found within thick intervals of facies B (tidal flat deposits;Fig. 4.14a). The sediments are distinctly coarser man surrounding sediments and thus probably represent higher energy sedimentation. The facies is interpreted as either washover storm deposits or possibly flood tidal delta deposits in a back-barrier environment (Fig. 4.14b). Units closely associated with tidal inlet deposits, such as those in me Clear Point section (Fig. 4.14a), are more likely to be flood tidal delta deposits. The association of a sequence of several depositional units within this facies interval suggests a series of depositional events in rapid succession. This is probably indicative of a flood tidal delta rather than a washover event which would probably consist of only one bed.
Tidal deltas typically form on me landward side of barriers (termed flood tidal deltas), adjacent to a tidal inlet. In wave-dominated systems me flood tidal delta typically forms large lobate sand bodies which interfmger with lagoonal sediments (Moslow and Tye 1985). A wave- dominated regime is postulated for me depositional environment of the Pebbley Beach Formation due to me predominance of wave structures (i.e. hummocky cross-stratification) within me sandy shoreface facies (see facies E). The presence of wave generated shallow marine facies in me overlying Snapper Point Formation and the underlying Wasp Head Formation also indicates that me shoreline was wave-dominated (see section 4.4). The pervasive bioturbation and lithology of the deposit is typical of flood tidal deltas described elsewhere (e.g. Israel et al 1987; Boyd
& Honig 1992).
E: Tidal Inlet
63 Description: This facies consists of laterally extensive successions of interbedded medium- grained sandstone (Fig.l5f). Sandstone beds have sharp lower contacts with underlying fine grained sediments. The maximum thickness of sandstone recorded was 97 cm. Units devoid of bioturbation are typically quartzose and well sorted. Internal structures within the sandstone beds consist of small and medium scale trough cross-bedding and combined flow lamination.
In places the bedforms are sigmoidal in shape and appear to be arranged in bundles which are bounded by thin fine-grained drapes (Fig. 4.15f). These structures are similar to those described as sigmoidal tidal bundles by Kreisa and Moiola (1986). Some beds are fossiliferous and contain molluscs and brachiopods. Siltstone units interbedded with sandstone units are similar to those described above for lagoonal facies. They are typically intensively bioturbated and contain similar ripple structures.
Palaeocurrent measurements from me trough cross-bedding within me facies shows a northwesterly trend (Fig. 4.16) with a vector mean of 317°.
Interpretation: Sigmoidal bundles containing silt drapes within me large cross-bedded sandstone units indicate possible neap/spring tide cyclicity (Visser 1980). The mud drapes represent slack water periods corresponding to me neap tide. Since a relatively high energy regime under tidal influence was responsible for depositing these units, a tidal inlet environment is postulated.
Kumar and Sanders (1974) showed mat tidal inlets could migrate laterally for 8 km, depositing a sand body over me entire distance. This could explain me absence of channelisation at me base of me facies, since me deposit appears to be a large, laterally extensive sand sheet.
Palaeocurrent data show that palaeoflow was directed primarily onshore. This indicates mat flood currents were more dominant within me tidal inlets man were ebb currents. This dominance would promote me formation of flood tidal deltas (facies D).
F: Shoreface
Description: This facies consists of interbedded units of clean, well sorted fine-grained sandstone, sandy siltstone and coarse pebbly sandstone. The sandstone units contain excellent examples of hummocky cross-stratification (HCS; Figs. 4.14a; 4.17a,b). Many of these units are composed
64 of amalgamated HCS beds. Hummocky cross-stratified beds are sometimes capped by a dark carbonaceous siltstone layer. Bioturbation within HCS units is moderate to rare. Sandy siltstone beds are pervasively bioturbated, pyritic and contain thin lensoidal sandy micro-HCS phases.
Coarse pebbly phases are typically thin (maximum of approximately 10 cm) and capped by large coarse-grained ripples (Fig. 4.17c).
Palaeocurrent measurements (Fig. 4.16) were taken from wave ripples and trough cross- bedding within me facies. Trough cross-beds show a northwesterly trend with a vector mean direction of 320°. Wave ripples show a east-southeast to west-northwesterly trend with vector mean flow directions of 140° and 320°.
Interpretation: This unit is interpreted as a shoreface deposit. The processes which form HCS have been described previously (section 3.2.1). Similar shoreface deposits have been described in numerous places elsewhere (e.g. Dott & Bourgeois 1982; Leckie & Walker 1982) Although
HCS sandstone beds have been described in lagoonal facies (Fielding & McLoughlin 1992), the large thickness of me interval containing HCS suggests a shoreface environment is more probable.
The palaeocurrent data indicates the major direction of storm waves. The strike of large coarse-grained wave ripple crests has been used to provide an approximate orientation of the palaeoshoreline (Leckie 1988). This suggests a paleoshoreline orientated approximately northeast,
050°.
G: Offshore
. Description: This facies consists of sandy siltstone with minor, thin sandstone lenses. The unit is pervasively bioturbated and contains numerous silicified logs. Sandstone beds reach a maximum thickness of 2-3 cm and contain wave ripple lamination.
Interpretation: The fine-grained nature of this facies suggests a quiescent environment of deposition. This facies grades up into shoreface facies (facies F) and as such me environment of deposition probably represents an offshore environment, probably just above storm wave base.
65 The presence of wave laminated sandstone beds within the facies suggests that the environment
of deposition lies at the extreme seaward limit affected by storms.
H: Diamictite
Description: Diamictite beds range up to 35 cm thick and contain boulders up to 1.5 m (Fig.
4.17d). Pebbles and cobbles are typically patchy or clustered in distribution and range from
angular to well rounded. The matrix of the diamictite is dominated by silty sandstone. Most
beds are strongly bioturbated and burrows of Diplocraterion extend from the lower bed boundary
into the underlying otherwise unburrowed siltstone. Large boulder sized clasts are loaded into
underlying fine-grained units. A diamictite unit at the top of the Clear Point section is capped
by a 10 cm bed of pebbly coarse sandstone. The diamictite beds are interbedded with facies I
which is dominated by laminated siltstone.
Interpretation: The intercalation of diamictite facies with other facies of interpreted marine origin
suggests that the diamictite beds were deposited subaqueously in a marine environment. This
is also supported by me presence of Cruziana-style bioturbation within me units. The diamictite
beds are interpreted as resulting from me settling of suspended sediment and ice-rafted debris.
Ice-rafted deposits have been documented on modern Arctic and Antarctic shelves (Alley et al.
1989; Powell & Molnia 1989). Ice dumped from floating ice may often occur as clusters of
clasts and boulders (Powell 1981). The absence of striated pebbles and the roundness of many
clasts within me diamictite units suggests deposition by shore or river ice and not glacial ice
(Gostin 1968). Following deposition me diamictite unit was bioturbated.
I: Ice affected shelf
Description: This facies consists of massive medium gray siltstone (Fig. 4.17e). It has a
massive bioturbated texture but has no discrete traces preserved except for phycosiphon. One
unit was distinctly sandy and contained a very thin foram-rich sandstone bed with wood
fragments.
66 Interpretation: This facies is interpreted as being deposited on a shelf with complete ice cover.
The silty nature of the facies suggests a very low energy environment of deposition. The absence of sandy interbeds suggests the environment was completely unaffected by storms for long time periods and was protected from wave reworking. The facies is interpreted as being deposited from suspended sediment plumes below an ice cover. A Pleistocene analogue for this facies was described by Vorren et al. (1989) in the sediments of the Barents Sea.
4.3.2 Climatic change and possible Milankovitch orbital forcing
The succession at South Pebbly Beach shown in Figure 4.18 shows good evidence for climatic changes. There are two intervals consisting of interbedded diamictite (facies H) and massive siltstone (facies I) separated by a thick interval interpreted as offshore facies (G). These two intervals are interpreted as representing major periods of glaciation. Within these sequences there are smaller scale changes resulting in an interbedded facies H and I succession (Fig. 4.17f).
The smaller scale facies changes are interpreted as resulting from alternations between periods of perennial ice cover and seasonal ice cover. During glacial periods when the shelf had perennial ice cover, wave action could not affect the sea floor, allowing only fine-grained low energy deposition from suspension (facies I). During periods of seasonal ice cover, periods of ice breakup and thaw resulted in the deposition of rainout diamictite facies (facies H). Aerobic water allowed habitation of the sea floor by organisms which caused bioturbation of the sediment following deposition.
The thickness of one complete cyclothem, comprising the ice affected sequence and the offshore siltstone is 7.5 m (Fig. 4.19). The thickness of the small scale facies sequences within the cold periods typically range between 50 cm and 100 cm. There is a high probability that climatic changes at this scale were caused by Milankovitch orbital forcing. Sequences interpreted as resulting from orbital forcing mechanisms have been previously identified in the
Permian by Frakes (1979), Anderson (1982), Borer & Harris (1991), Miller & West (1993) and
Yang & Baumfalk (1994). The lack of any datable material within the cyclothem sequences in the succession at South Pebbles does not allow the periodicity of climatic fluctuations to be ascertained. Anderson (1982) estimated the periodicity of climatic variations of Permian
67 sequences within me Delaware Basin at 100 ka years. Borer & Harris (1991) identified cycles of both 100 ka year and 400 ka year duration within Late Permian sequences within me same basin. Berger et al (1989) and Yang & Baumfalk (1994) identified Permian cycles corresponding to periodicities of 100, 67, 44.3, 35.1, 30, 21 and 17.6 ka. Algeo & Wilkinson
(1988) estimated that cycles of 1-20 m thickness generally have a period of 21 ka to 413 ka years which falls within Milankovitch (1941) periodicity. Two periodicities are evident within the "South Pebbles" section. The larger periodicity corresponds with the broader climatic change responsible for me deposition of the two interstratified diamictite - massive siltstone intervals and offshore siltstone facies (Fig 4.19). The time scale resulting in the deposition of this sequence probably represents the longer periodicities identified for the Permian, lying within me range 100 to 400 ka. The smaller scale climatic changes probably represent high frequency precessional cycles with lower periodicities of approximately 21 ka using the work of Berger et al. (1989) and Yang & Baumfalk (1994) as an analogue.
Another indicator of possible climatic change is the presence of glendonites on Clear
Point (Fig. 4.20a). Glendonites are pseudomorphs after me mineral ikaite (CaC03.6H20; Kaplan
1979). Ikaite has been recorded in several places including Antarctica (Suess et al 1982), Zaire deep sea fan (Jansen et al. 1987) and at Barrow, Alaska (Kennedy et al. 1987). Ikaite is unstable at temperatures above 5°C at which point it decomposes to calcium carbonate
(Shearman & Smith 1985; Jansen et al. 1987). Glendonites have been recorded at numerous localities within me Sydney Basin and are attributed to cold climatic conditions (Carr et al.
1989).
The thick shelled mollusc Eurydesma is found within me Pebbley Beach Formation. It is a cold climate fauna which has been found in numerous localities within eastern Australia and other parts of Gondwana (Runnegar 1979; Dickins 1984; Veevers & Powell 1987). The occurrence of Eurydesma within this formation is further confirmation of cold climate during deposition.
4.3.3 Depositional model
The exposed section of the Pebbley Beach Formation is interpreted as four parasequences (Fig.
68 4.19), using me term parasequence as defined by Van Wagoner et al (1988; see description in section 3.2.2). Parasequences within me Pebbley Beach Formation are interpreted as resulting from climatic change and associated sea level changes caused by Milankovitch (1941) cyclicity
(see section 4.3.2). The depositional history of me formation will be described with specific reference to each parasequence defined in Figure 4.19.
The basal parasequence A crops out at the base of the South Pebbles section and consists of an upward-shoaling shoreface succession. The shoreface sandstone is capped by a sequence of interbedded facies I and H which indicates a period of ice influence (see section 4.3.2) in a shallow water setting. The fact that this cold period coincides with me top of the shoaling upward cycle indicates that the relative fall in sea level is probably climate driven and is associated with a glacial period. This first diamictite sequence is abruptly overlain by offshore facies (facies G). This abrupt facies change probably marks the next transgression and a return to warmer conditions (unaffected by ice) and higher relative sea level. This abrupt facies change also marks me base of me next parasequence (parasequence B).
The second parasequence crops out at me top of me South Pebbley Beach section and consists of offshore facies overlain by a second diamictite succession. Thin sandstone beds become more prevalent towards me top of me offshore facies suggesting shallowing. Small sand lenses within me diamictite sequence suggest traction movement of sand, indicative of shallow water conditions. A shallowing trend is also inferred from a) extrapolation from underlying offshore facies and b) ice affected conditions probably correspond with a glacial period and thus a lower relative sea level. At me top of the diamictite succession, me massive siltstone (facies
I) interbeds are distinctly sandy and contain thin phases of sandstone with abundant wood
. fragments and forams. The thickness of facies I beds also decreases towards me top of this interval. This suggests a possible period of warming as me megacycle comes to an end. The top of this interval is marked by a unit which shows evidence of wave reworking suggesting shallow water conditions, probably on a shoreface. The abrupt facies change overlying this second diamictite sequence is interpreted as a transgressive interval marking a rapid deepening of facies and the base of the overlying parasequence (parasequence C; Fig. 4.19).
Parasequence C is well exposed at Mill Point (Fig. 4.19). The basal part of the sequence
69 consists of offshore facies which coarsen upwards into shoreface sandstone facies (facies F) which is interpreted as being deposited above or close to fairweather wave base. The thickness of the sequence from the top of the offshore facies to the top of the shoreface sandstone body is 7.5 m. If it is assumed that sea level did not change appreciably during deposition of this succession, the difference in water depth between me environments of deposition represented by offshore facies (facies G) and shoreface facies (facies F) was only approximately 7 m. Since facies F is interpreted as deposited close to or above fairweather wave base and facies G is interpreted as being deposited close to storm wave base, a difference of only 7 m between fairweather and storm wave base is inferred from this section. This difference is probably too low for an open shallow marine setting. Therefore, a eustatic sea level fall must be invoked to explain the low thickness of this upward-shoaling succession. The top of the shoreface facies marks a change to predominantly silt-dominated facies of a back-barrier environment.
The back-barrier environment represented by the Pebbley Beach Formation is interpreted as a wave-dominated estuary (Figs. 3.6; 4.14b). The style of estuary is very similar to that represented by the facies at the top of the Clyde Coal Measures (section 3.1). This is supported by three main points of evidence outlined below.
(l)the pervasive presence of high energy wave generated structures (i.e. HCS) in shoreface facies within me formation;
(2) me general lack of sand within the back-barrier facies suggests that the barrier was effective, typical of wave-dominated estuaries (Dalyrimple et al. 1992); and
(3) the presence of a well developed tripartite facies regime (described below), similar to modern analogues of wave-dominated estuaries (e.g. Nichol 1991; Allen 1991;
Nichols et al. 1991). Zones include a fluvially influenced bay-head delta, a low- energy central basin and a sandy marine plug, consisting of barrier and/or inlet facies.
The transition to back-barrier sedimentation in parasequence C at Mill Point is followed almost immediately by me onset of low energy facies indicative of the central basin of an estuary (facies C). Facies B which is associated with facies C and is interpreted as tidal flat deposits formed at me margins of me lagoon. On south Mill Point and Clear Point me central basin facies are incised by large channels (facies A) which are interpreted as me bay-head delta
70 facies at the upper end of an estuary. The palaeocurrent data (Fig. 4.16) for this facies shows a dominantly east-directed palaeoflow which suggests possible fluvial influence. The presence of facies D sediments within the back-barrier facies probably represent distal flood tidal deltas or washover deposits. The position of tidal inlet facies (facies E) and flood tidal delta facies within the back-barrier facies probably reflects lateral changes in me position of inlets.
The channel system represented by facies A crops out stratigraphically lower in me section adjacent to Pebbley Beach which is located west of me Mill Point sections (Fig. 4.14a).
This suggests mat the channel system has prograded towards me east, consistent with me basinward progradation of facies upward through me parasequence.
At the top of the south and north Mill Point sections and halfway up the Clear Point section mere is a sandy interval which is capped by a thin lag deposit which consists predominantly of disarticulated valves of me thick shelled mollusc Eurydesma (Fig. 4.20b).
Eurydesma is a opportunistic species which colonised hard, current swept substrates (Runnegar
1979). The surface at me base of this sandy interval is interpreted as an omission surface
(Barm, in prep) and is interpreted as a transgressive surface, marking a rapid rise in sea level from back-barrier conditions to offshore marine deposition. This surface marks me base of me final parasequence (parasequence D) within the Pebbley Beach Formation. The facies sequence within this parasequence is similar to mat of me underlying parasequence C. The maximum flooding interval is probably contained within me transgressive unit or near me base of the unit containing me offshore siltstone facies which, in mm, coarsens upward to an HCS sandstone body. Above this the facies changes to a typical back-barrier environment. The thickness of me shoaling upward succession in this upper parasequence is only about 3m. The low thickness of this facies suggests that progradation alone was not responsible for me change from offshore sedimentation to shoreface sedimentation. A fall in relative sea level must be inferred to account for me dramatic change in facies over only 3 m. Glendonites (Fig. 4.20a) were found within me back-barrier facies of me upper part of this sequence and are interpreted as a cold climate phenomenon (see section 4.3.3). The presence of glendonites within me upper part of the parasequence where relative sea level is interpreted as being low is consistent with me sea level changes being driven by glacio-eustatic processes.
71 The presence of intensely deformed beds within me sequence (Fig. 4.20c) suggests that the area was tectonically active, contemporaneous with deposition. These beds show large, excellent examples of ball and pillow structures, flame structures and sand volcanoes which are interpreted as resulting from earthquakes.
The top of the Pebbley Beach Formation is marked by the basal erosional foreshore facies of the Snapper Point Formation (Fig. 4.15b). This is interpreted as a transgressive surface as relative sea level rose again.
4.4 Snapper Point Formation
The Snapper Point Formation is laterally extensive and sand dominated. It has a sheet-like architecture and is found across me entire study area (Fig. 1.1). Because of the lateral extent of the formation me facies sequences are diverse. The first part of this section will describe the range of sedimentary facies within me formation as a whole. Section 4.4.2 describes regional sequences typical of particular parts of die southern Sydney Basin.
4.4.1 Facies analysis
The Snapper Point Formation has been divided into 14 facies based on physical and biogenic sedimentary structures, grain size and lithology. This section provides initial interpretations of the individual units. Integrated interpretations are provided in later sections, (sections 4.4.4 and
4.4.5). The Snapper Point Formation was predominantly deposited within a shallow marine environment, above storm wave base. Sedimentary facies are summarised in Table 4.5.
Non-marine facies
A: Braided Fluvial
Description: This facies consists of interbedded medium- to coarse-grained sandstone and conglomerate units. This facies shows abundant evidence of channelisation. Internally, sandstone structures consist of plane beds, planar cross-stratification, trough cross-stratification and some epsilon cross-stratification. All units within me facies contain abundant scattered pebbles.
72 Interpretation: The structures within me sandstone suggests deposition under lower to upper flow regime conditions. The coarse nature of me facies suggests deposition occurred under high energy conditions. This facies is interpreted as a high energy sandy braided river environment and is similar to model 4 of Miall (1985).
Nearshore facies
B: Breccia/ chaotic conglomerate
Description: This facies consists of angular breccia and disordered, matrix supported conglomerate. Two thick intervals of breccia were found within the central part of me study area at me base of me formation. Commonly, the facies occurs as a 0-50 cm thick laterally persistent layer. The maximum clast size is approximately 20 cm. The matrix is typically poorly sorted, consisting of silty sandstone. This facies always overlies basement which, in mm, comprises almost 100% of me clast lithologies.
Interpretation: This facies is interpreted as a high energy transgressive deposit, indicating mat a flooding event has taken place. In some cases me facies may overlie a ravinement surface, indicating sea level rise following a regressive event. Transgressive lags are produced by me winnowing action of shoaling waves as me surf zone propagates landward (Swift 1968). The size of clasts within me facies is such mat landward transportation is minimal.
C: Coastal
Description: This facies consists of fine-grained sandstone and siltstone. The only exposure of this facies is found on me Princes Highway, north of Milton (Fig. 4.20d). The facies contains thinly interbedded units of sandstone and siltstone. These units are flaser and lenticular bedded and contain ripple lamination structures indicative of combined wave and current activity as described by De Raaf et al (1977). Clean well-sorted sandstone beds contain hummocky cross- stratification (HCS) and reach a maximum thickness of 50 cm. Some HCS beds have lenticular architecture and are laterally discontinuous over a distance of 10 - 20 m. This facies also
73 contains units of intensely bioturbated sandy siltstone.
Interpretation: This facies is very similar to facies B, described above for the Pebbley Beach
Formation. Combined wave and current lamination structures within me thinly bedded sandstone
and siltstone units suggest tidal influence. Sandstone beds containing HCS (indicative of wave
reworking) probably represent storm deposits. The sandstone dominated intervals may have been
deposited in a back-barrier environment, possibly at a flood tidal delta. The quality of the
exposure does not allow an accurate interpretation to be made but all the available evidence
suggests a protected coastal environment, as for me Pebbley Beach Formation.
D: Beach / Foreshore
Description: This facies consists of interbedded medium- to coarse-grained pebbly sandstone and
conglomerate (Fig. 4.15b). The internal structure of me beds is dominated by parallel and/or
low-angle lamination. Low-angle lamination surfaces truncate each other at low angles (<10°).
Shell fragments are common within me facies. Clasts and shell fragments are typically aligned
with bedding. At me base of Clear Point this facies contains me thick shelled mollusc
Eurydesma.
Interpretation: This facies is interpreted as a beach or foreshore environment. Parallel and low-
angle lamination is typical of sediments within me surf zone (Clifton 1969; Elliot 1986).
Parallel lamination is generated in me high energy swash zone. The presence of Eurydesma,
an opportunistic species mat colonised current swept, sublittoral substrates (Runnegar 1979),
supports this interpretation.
Shoreface facies
E: Longshore sand bars
Description: This facies consists of thick composite units of medium- to coarse-grained well sorted sandstone (Fig. 4.20e) that are laterally extensive over large distances (several kilometres).
Internally, the structure of me sandstone comprises plane lamination, planar cross-bedding, trough
74 cross-bedding, low-angle cross-bedding and rare swaley cross-stratification. Individual sets of planar cross-bedded sandstone are as thick as 1.1 m. Planar cross-bedding has in some cases, tangential basal contacts and may be associated with mud drapes (Fig. 4.21a). The dip and thickness along foresets changes laterally within some beds (Fig. 4.20f). At one locality at
Beecroft Peninsula, low angle reactivation surfaces, dipping in me direction of longshore current palaeoflow were found associated with subordinate small scale trough cross-bedding, indicating palaeoflow oblique to me dip direction of me large foresets. Individual planar cross-bedded units are separated by a planar surface, often marked by a thin pebbly lag. Most trough cross- beds are typically 20 - 30 cm thick. One bed within this facies was capped by large coarse grained wave ripples. The facies contains some units with significant bioturbation which typically consists of Macronichnus and Skolithos species.
Interpretation: Planar cross-bedding results from me migration of straight crested bedforms under unidirectional currents. The style of cross-bedding is similar to mat found in tidal sand bank environments (Bridges 1982; Allen & Homewood 1984; Dalyrimple 1984). Mud drapes and thickening of foresets is probably caused by variations in tidal velocity due to neap-spring tidal cyclicity (Allen and Homewood 1984). During spring periods, strong currents produce thick foresets with a low-angle on me dipping plane due to enhanced reworking. During neap periods, currents are weaker and steeper dipping and thinner foresets are deposited, often accompanied by mud drapes. Large shallow dipping bedding planes with subordinate trough cross-bedding probably represent me lateral migration surfaces of sand bars. Stride et al. (1982) stated a value of 0.1 m/s as me maximum current velocity responsible for me deposition of sand sheets in European seas.
Large dunes migrated via tidally influenced longshore currents generating laterally extensive planar cross-bedded units. This facies is very similar to me tidal shelf facies described by Richards (1986) and to facies of the overlying Nowra Sandstone (see section 4.6). The predominance of facies indicative of unidirectional currents with tidal influences suggests that deposition occurred on a tide-dominated shelf. The lateral extent of me facies suggests it is a sheet-like sand body. Bioturbated units associated with the facies may represent a marginally
75 deeper environment, adjacent to the sand ridges or banks.
F: Upper shoreface
Description: This facies is dominated by fine- to medium-grained well sorted sandstone units up to several metres thick. The internal structure of this facies is dominated by hummocky cross-stratification with gently curved intersecting laminae. The laminations are dominated by swales (concave up forms) with only rare hummocks preserved (Fig. 4.21b). Bioturbation is typically absent to rare, and no fossils were found within me facies. Pebbles are commonly found along bedform laminae and at the bases of swales.
Interpretation: This facies is interpreted as an upper shoreface deposit. The presence of HCS suggests deposition under combined wave and current flow (as discussed previously in section
3.2), The facies is identical to the swaley cross-stratification of Leckie and Walker (1982). The coarseness of me sandstone and scale of the stratification suggest deposition in a high energy environment. The absence of fine-grained interbeds, intraclasts and bioturbation, indicative of fairweather sedimentation, suggests deposition occurred above fairweather wave base.
G: Middle shoreface
Description: This facies is very similar to facies F (described above) and consists of amalgamated hummocky cross-stratification. Unlike facies F this facies has thin interbeds of truncated bioturbated silty sandstone and abundant silty intraclasts at me bases of units.
Interpretation: This facies represents me mudstone-cutout type of amalgamated hummocky cross- stratification as described by Dott and Bourgeois (1982). The bioturbated silty sandstone, interbedded with me HCS units represents relatively quiescent fairweather sedimentation. The depositional environment for this facies must, therefore, lie below fairweather wave base, free from constant wave-reworking. The thinness and paucity of bioturbated intervals within me sequence suggests mat me environment is still relatively high energy with frequent storm activity, probably lying in me middle shoreface.
76 H: Pebblv middle to upper shoreface
Description: This facies is very similar to those described above. The facies is dominated by interbedded fine- to medium-grained pebbly sandstone and conglomerate (Fig. 4.21c). The internal structure of the conglomerate is dominated by plane bedding and hummocky cross- stratification. The conglomerate beds are plane bedded, matrix to clast supported and consist of sub-angular to rounded clasts. The matrix of the conglomerate consists of poorly sorted sandstone. The conglomerate beds reach a maximum thickness of approximately 80 cm and are laterally continuous. Similar to facies G, there are thin lensoidal beds of bioturbated siltstone and sandy siltstone interbedded within this facies.
Interpretation: This facies is very similar to the amalgamated hummocky cross-stratified facies
G. The difference is the coarseness of this facies which suggests very high energy conditions and a close proximity to sediment supply. The coarse sediment was probably supplied to the nearshore zone via flooding rivers. Similar shoreface facies have been described by Leithold
& Bourgeois (1984) and Decelles (1987). The conglomerates within this facies are identical to
Leithold & Bourgeois" (1984) laterally extensive tabular conglomerates.
Transition offshore/shoreface and offshore facies
I: Embavment
Description: This facies consists of a succession of bioturbated silty fine-grained sandstone beds and minor coarse phases (Fig. 4.21d). The sandstone units are pervasively bioturbated which has destroyed any pre-existing sedimentary structures. There are small lenses of clean, well sorted laminated sandstone within these bioturbated units which have escaped biogenic disturbance. Coarse layers are thin (<15 cm) comprising medium- to coarse-grained pebbly sandstone. They are sharp based and usually contain large symmetrical straight crested wave ripples that have wave lengths ranging from 0.6 to 1.1 m and heights of 10 - 20 cm.
Interpretation: The pervasive bioturbation and fine grain size of the silty sandstone beds suggests
77 that deposition occurred below fairweather wave base. Laminated sandstone beds and the wave- rippled coarse beds are interpreted as storm deposits. Large coarse-grained wave ripples (CGR) are not a good indicator of water depth. Forbes and Boyd (1987) found gravel ripples formed between depths of 15 and 65 m and up to 5 km from shore. Large coarse-grained wave ripples are formed by long period storm waves (Leckie 1988) and probably formed during the waning phase of a storm (Gillie 1979). Leckie (1988) interpreted CGRs as the coarse-grained equivalent to HCS. Bioturbation subsequent to deposition has destroyed much of the sedimentary structure within me sandstone. Lenses of undisturbed sandstone have survived within some beds and appear to be remnants of thick storm beds which have escaped significant bioturbation. The facies probably represents a bioturbated type of amalgamated sequence as described by Dott and
Bourgeois (1982). The number of storm event beds is significantly less than other inner shelf facies within me formation. The frequency and intensity of storm events appears to have been much reduced. This suggests mat me environment may have been semi-protected. For this reason me environment of deposition is interpreted as an embayment
J: Shell bank
Description: This facies consists of fossiliferous graded units of coarse- to medium-grained sandstone (Fig. 4.21e). The bases of individual units are erosional and typically consist of coarse-grained, well sorted sandstone. This part of the unit is dominated by fossil death assemblages with abundant disarticulated shells. The shells within me death beds are very rarely broken and fragmented. Death beds with abundant juvenile species were found. This lower part grades upward into intensely bioturbated silty sandstone which may contain molluscs in life position. Bioturbation within this facies comprises Astersoma, Rosselia, Rhizocorallium (Normal and large), Phycosiphon and Catenichnus (Bann inprep).
Interpretation: The degree of bioturbation, abundance of molluscs and me relative fineness of the facies in me upper part of me graded beds suggests mat deposition mainly occurred under quiescent conditions. The coarse-grained and highly erosional base suggest mat they are event beds, probably resulting from storms. The absence of shell fragmentation indicates deposition
78 from a current of short duration (Fursich & Oschmann 1993). At the peak of a storm, powerful combined flow storm currents disarticulated me molluscs, depositing a well sorted coarse grained, fossiliferous lag. Following me storm, conditions returned to normal and intense colonisation by fauna and fine-grained deposition ensued. The facies represents a shell bank deposit which was periodically eroded and reworked by storm waves. The environment of deposition probably lay seaward of me shoreface, below fairweather wave base.
K: Transition shoreface/offshore
Description: This facies consists of interbedded well sorted fine-grained sandstone, sandy siltstone and coarse sandstone. The sandstone beds have a lenticular architecture, lensing out within metres (Fig. 4.22). The basal contacts of me sandstone beds are sharp and erosional.
Individual sandstone bed thickness ranges up to approximately 20 cm but amalgamated units may be as thick as 80 cm. Amalgamation of sandstone beds is common (Fig. 4.22). Evidence for amalgamation is the presence of silty lenses and bioturbated horizons within sandstone beds, bom indicative of a break in sedimentation. Internally the structure of me sandstone beds is dominated by HCS. Large Coarse-grained wave ripples occur within thin coarse sandstone phases associated with me HCS beds (Fig. 4.23a).
Between sandstone beds there are intensely bioturbated fine-grained beds. Silty beds are often lensoidal due to truncation by sandstone beds. Bioturbation consists of diplocraterion,
Large Diplocraterion, Rosselia, Astersoma, Phycosiphon and palaeophycus.
Interpretation: The interpreted depositional environment for this facies was one dominated by quiet muddy sedimentation and bioturbation. Sandstone beds are interpreted as rapidly emplaced storm deposits. Storm generated combined flow currents worked sand into HCS-type bedforms.
The presence of HCS suggests deposition must have occurred above storm wave base. This type of facies is widely documented below fairweather wave base in storm dominated environments (eg. Dott and Bourgeois 1982; Leckie and Walker 1982; Rosenthal and Walker
1987; Brenchley et al. 1993). The lenticular architecture of me sandstone beds may represent a dominant oscillatory current within combined flow (Brenchley et al. 1993). The lenticular
79 nature of the sandstone bodies suggests that they accumulated in discontinuous patches, probably dish or swale shaped which had dimensions up to tens of metres in diameter and approximately
20 cm deep. The presence of mud partings within sandstone bodies suggests that some sandstone beds do not represent single events but are the result of the amalgamation of several depositional episodes. The environment of deposition is interpreted as a transitional environment between shoreface and offshore whereby normal deposition was relatively quiescent and mud dominated. Periodic storm events deposited large volumes of sand which were worked by combined flow storm waves. The environment lies at the seaward toe of the sand dominated shoreface.
L: Pebbly upper offshore
Description: This facies consists of interbedded coarse-grained pebbly sandstone and bioturbated pebbly fine-grained sandstone (Fig. 4.23b). Coarse-grained sandstone beds have sharp, erosional bases and are typically 10 to 15 cm thick but where amalgamated can achieve a thickness as large as 1 m. The coarse-grained beds contain pervasive wave ripple lamination with numerous low angle truncation surfaces and me appearance of swaley cross-stratification, as described previously. In places me coarse-grained beds appear to contain small scale trough cross- stratification. The fine-grained beds contain abundant pebbles and are pervasively bioturbated.
Bioturbation consists of Phycosiphon, Large Diplocraterion, Rosselia, Astersoma, Diplocraterion and Skolithos.
Interpretation: The presence of fine-grained bioturbated units within me facies suggests mat the normal environment of deposition was relatively quiescent, below fairweather wave reworking.
The sharp based beds with wave ripple lamination are interpreted as being deposited by storm events. The coarse-grained nature of the storm deposits suggests that this sediment was derived from a pebbly and coarse sand shoreface. In this sense this facies probably represents more seaward equivalents of shoreface facies H.
Facies M: Upper offshore
80 Description: This facies consists of interbedded poorly sorted silty fine- to medium-grained sandstone and coarse-grained pebbly sandstone to pebble conglomerate (Fig. 4.23c). Most individual beds show grading and are in me range from 0.5 to 1 m thick. The coarse-grained pebbly phases are never thicker man 20 cm and contained pebbles ranging up to approximately
10 cm, with most being 0.5-5 cm. Many coarse-grained pebbly beds contain large coarse grained symmetrical wave ripples. Ripples vary in wavelength with values between 0.13 and
1.00 m. Ripple heights vary between 2 cm and 11 cm. Abundant mollusc shells are associated with me coarse grained beds. The most striking aspect about this facies is the intensity of me bioturbation. The biogenic reworking of these sediments has masked almost all sedimentary structures and many unit boundaries. In some of me thicker sandstone beds some HCS and plane lamination is visible. Bioturbation consists of Large Diplocraterion, Phycosiphon,
Rosselia, Astersoma, Diplocraterion, and Macronichnus.
Interpretation: The fine grain size and me pervasiveness of me bioturbation within this facies suggest deposition occurred between fairweather and storm wave base and mat biogenic reworking has generally overwhelmed the physical processes. Coarse-Grained beds containing large coarse-grained wave ripples are interpreted as high intensity storm deposits produced by oscillatory currents under waning storm conditions (Gillie 1979; Leckie 1988). Storm emplaced
HCS sandstone beds were probably deposited by storms of lower intensity. The pervasiveness of bioturbation within this facies suggests mat me average sedimentation rate was low. In between storm events, sediments were completely reworked by organisms, which destroyed most sedimentary structures. De Decker (1988) found that storm waves were able to transport cobbles
10 cm in diameter at water depths of 15 m and 1 cm pebbles at depths of 30 m in megaripple fields in an open shelf setting. This would suggest that deposition for this facies was in me approximate range of 15 to 30 m, located seaward of me shoreface, in an upper offshore environment.
N: Lower offshore
Description: This facies consists of thinly interbedded siltstone and fine- to very fine-grained
81 sandstone (Fig. 4.22). Laminated sandstone interbeds reach a maximum thickness of 10 cm with most beds approximately 2 - 3 cm thick. Sandstone interbeds have sharp contacts with underlying siltstone. The facies contains minor bioturbation.
Interpretation: The grain size of this facies suggests a low energy environment. The sharp based nature of the sandstone interbeds suggest that they were emplaced by storms in a distal environment. Evidence of wave action is completely absent from the facies, it is, therefore, interpreted that this facies was deposited below storm wave base, probably in a lower offshore environment.
Facies 0: Shelf
Description: The facies consists of intensely bioturbated, pyritic siltstone (Fig. 4.23d). The interval is highly fossiliferous, containing brachiopods, bryozoans and crinoid fragments.
Coalified logs and numerous large clasts are scattered throughout the unit. Large clasts are angular and range up to approximately 30 cm. The facies does contain thin (approximately 2 -
3 cm thick) sandy phases but these are intensely bioturbated.
Interpretation: This facies is interpreted as an offshore deposit, formed below storm wave base.
The large clasts within me facies are interpreted as dropstones, resulting from ice rafting.
Bioturbated coarse phases within me facies are probably distal storm deposits, similar to the sandstone interbeds within facies N.
4.4.2 Palaeocurrents and palaeoshoreline
Palaeocurrent data from the Snapper Point Formation is shown in figure 4.24. Data from non- marine facies in me southwestern part of the study area show a easterly trend with a vector mean direction of 111°. The direction is very similar to mat in me underlying conglomeratic facies of the Yadboro Conglomerate and probably represents more distal extension of me same depositional system.
Data collected from large coarse-grained wave ripples within me marine facies of me
82 formation, shows mat waves propagated in a northwesterly or southeasterly direction with a vector mean of 295° or 115°. Cross-bedded facies at me top of the sequence show a northerly trend (Fig. 4.24) which corresponds to me direction of longshore currents. The vector mean obtained from 64 readings within this upper sequence was 359°.
Based on me orientation of wave ripple crests an approximation can be made of the orientation of the palaeoshoreline (Forbes & Boyd 1987; Leckie 1988). This suggests a shoreline trending approximately 025°.
4.4.3 Isopachs
The Snapper Point Formation forms an eastward thickening wedge (Fig. 4.25). The formation rapidly thickens from less man 50-100 m in me west to more man 300 m near me present coast.
This area of increased thickness corresponds with an increase in gradient on me basement contour map (Fig 4.10) suggesting possible control by regional sag. The isopach map (Fig 4.25) shows two general depocentres which broadly correspond to the positions of me underlying
Yadboro and Tallong Conglomerates. The seemingly anomalous high thickness values recorded to the northwest of Jervis Bay are problematic and will be discussed further (see section 6.3).
The central part of me region shows distinctly lower thickness values and corresponds to a basement high (Fig. 4.25 & 4.11).
4.4.4 Vertical and lateral facies relationships
The Snapper Point Formation varies greatly across the basin and as such it is difficult to describe. The formation has been divided into regions which show similar facies patterns in order to describe me formation more effectively.
Southwestern region
The southwestern region includes the area within me vicinity of me underlying Yadboro
Conglomerate (Fig. 4.26). The basic facies within these sequences are shown in Figure 4.27.
The Snapper Point Formation in this area overlies the Yadboro Conglomerate and where this is absent, it overlies basement. There is a lateral facies change towards me west. The Yarrunga
83 Coal Measures appear to be absent from this region.
Near Corang Peak (GR: 8927-344912) the sequence consists of a thick succession of
facies A, interpreted as a sand-dominated braidplain deposit. Palaeocurrent data at this locality
shows a definite east-directed trend with a vector mean of 103° and a vector magnitude of 90%
(Fig. 4.24).
To the east, in me upper reaches of Pigeon House Creek (GR: 8927-526942) me
sequence changes to a succession of intercalated facies A and facies F (Fig. 4.27 & 4.23e). The
contacts between the facies units appear to be sharp and transitional facies are absent. The
palaeocurrent trend from trough and planar cross-bedding within the braided river facies (facies
A) shows a consistent east-directed trend, as for me facies at Corang Peak (Fig. 4.24). The
intervening facies F comprises a monotonous succession of clean and well sorted sandstone
which contains pervasive HCS. At localities such as upper Pigeon House Creek and Landslide
Creek (directly below Pigeon House Mountain me facies A intervals stand out as a series of
sandstone benches which can be traced laterally for several kilometres (Fig. 4.23e).
The section at Conjola Creek (GR:8927-609988) differs from me other sections in mat
it does not overlie me Yadboro Conglomerate (Fig. 4.27). The sequence is very similar to mat
of upper Pigeon House Creek and consists of interbedded facies A and facies F. Within this
section me facies A sandstone showed clear channelisation features and complex barform
development. Palaeocurrent data from facies A showed a clear east-directed trend (Fig. 4.24).
The sequence at Jindilara Creek (GR: 568858-556864; Fig. 4.27) overlies me Yadboro
Conglomerate. The basal part of me section represents a transgressive sequence with facies A,
directly overlying me Yadboro Conglomerate, passing up into me marine sediments of facies F
and eventually facies G. Regression resulted in the deposition of a coarsening upward
succession, culminating in me deposition of trough cross-bedded facies A sandstone at me top of me section. This section contains only one of me cycles which have been described above and the section has been truncated by subsequent erosion.
The Snapper Point Formation in me southwestern part of me basin is interpreted as a series of braidplain delta progradations represented by the sandy braidplain facies (facies A).
The bases of intervening shoreface sandstone intervals (facies F) reflect marine flooding events.
84 Flooding events (Fig. 4.27) reflect changes from a supply to accommodation dominated regime as a result of relative sea-level rise. Braid deltas were first described by McPherson et al.
(1987) as a purely braided alluvial plain system which progrades into a standing body of water.
Orton (1988) further defined braid deltas as systems whereby a solitary river progrades into a standing body of water. Orton (1988) defined the term braidplain delta to describe deltas consisting of laterally extensive braidplain systems. The lateral extent of the facies A sandstone bodies of at least 15 km, from Pigeon House Mountain in me south to Conjola Creek in the north, suggests mat these sequences are braidplain systems. The extent of me braidplain progradation during this period was far greater man me lateral distribution of me underlying
Yadboro Conglomerate. For example, me section in Conjola Creek has sand-dominated braidplain facies directly overlying basement. The intervening facies F sandstone intervals within the sequence probably represent wave-dominated distributary mouth bar deposits. The well sorted nature of these deposits and the pervasive presence of HCS suggests nearshore high wave energy. The Jindilara Creek section is a more distal equivalent of the Pigeon House Creek succession. In this case, me marine interval between me subaerial braidplain facies shows silty interbeds and bioturbation which probably represents an upper shoreface environment near the mouth of the alluvial system.
Northwestern region
This region (Fig. 4.26) encompasses the Shoalhaven and Tallowa Gorges in the northwestern part of me study area. Five sections from this region are shown in Figure 4.28. The localities are in close proximity to the position of me underlying Tallong Conglomerate at the base of me
Badgery's lookout, Hoddles Cliff (Fig. 4.2f) and Yagers Lookout sections. The conglomerate passes upward into stratified sandy facies indicative of a sandy braided fluvial environment. In the Badgery's Lookout and Yagers Lookout sections, me conglomerate is overlain by carbonaceous silty facies, herein interpreted as coastal facies equivalent to me Yarrunga Coal
Measures. The Yarrunga Coal Measures were probably deposited behind strandlines of me advancing Snapper Point Formation, which is represented by nearshore marine facies F. In me
Tallowa Gorge and Hoddles Cliff sections the Yarrunga Coal Measures are absent and me
85 Tallong Conglomerate passes directly upwards into the sandy nearshore marine facies of the
Snapper Point Formation (Fig. 4.28). Where the Tallong Conglomerate is absent on the adjacent palaeohighs, the Snapper Point Formation directly overlies basement. This is the case within the
Tallowa Dam section where Ordovician strata is directly overlain by facies F sandstone of the
Snapper Point Formation. The transition from the Tallong Conglomerate to the Snapper Point
Formation thus represents a transgressive sequence from high energy braided fluvial through transitional coastal facies to high energy shallow marine facies.
The Snapper Point Formation is monotonous in this region and is dominated by high energy shoreface sedimentation (Fig. 4.33a; facies F, G and H). The presence of facies H to the west of this region (Fig. 4.28) reflects the relative proximity of a fluvial source. The fluvial system represented by me underlying Tallong Conglomerate retreated cratonward in response to me transgression and thus was probably still providing sediment to the northwestern part of the basin. These deposits are very similar to those described by Leithold and Bourgeois (1984).
Small changes in relative sea-level are evident within me sequence. Conglomerate- based intervals containing trough cross-bedding is present within me lower part of the Hoddles
Cliff and Tallowa Gorge sections (Fig. 4.28). This interval has an east-directed palaeocurrent distribution (Fig. 4.24) and facies indicative of braided fluvial environment (Miall 1977). This interval is interpreted as resulting from a small relative fall in sea-level and may be explained by allocyclic events. Such an event could follow a shift in position of me fluvial source providing sediment to me nearshore zone, such a shift would increase the sedimentation rate thus causing progradation of the fluvial system.
A silt-dominated interval within me upper part of me Hoddles Cliff section (Fig. 4.28) is interpreted as a major flooding event. The base of me interval is marked by coarse sandstone and pebble conglomerate containing wave ripple lamination, interpreted as a flooding or transgressive surface. Above this, me interval is dominated by micro-HCS and bioturbated sandy siltstone. The flooding surface could be traced laterally across me cliffline for several kilometres.
In general me facies sequence within this part of me study area reflects me proximity of a major fluvial source, interpreted as me high energy river system represented by me Tallong
86 Conglomerate. This fluvial system retreated cratonward in response to the transgression responsible for me deposition of the Snapper Point Formation.
Central region
This part of me study area is characterised by a relative basement high (Figs 4.11, 4.26). The isopach map for me Snapper Point Formation also shows a lower relative thickness in this region (Fig. 4.25).
Sections measured through me Snapper Point Formation at Yalwal and Wandandian are shown in Figure 4.29. The sequence is typified by a coarse breccia facies at me base which passes upward into high energy nearshore marine facies. Farther to me east, a road cutting on me Princes Highway exposes coastal facies (Fig. 4.20d) that are very similar to those of me
Pebbley Beach Formation.
The central region corresponds with a topographic high and lies between me two palaeovalleys. In this region sections through me Snapper Point Formation are relatively thin
(Fig. 4.25). This probably reflects sediment bypassing via the fluvial systems and consequently a lower sedimentation rate. Since this area was topographically higher me transgression probably occurred later man in lower lying areas of me adjacent palaeovalleys.
Eastern region
The eastern area encompasses all coastal exposures from Clear Point in the south to Jervis Bay in me north (Figs. 4.13 & 4.26). Facies indicate mat me environment during deposition of me
Snapper Point Formation in this region was a shoreface to offshore environment. The complete sequence is only exposed in drillcore while me coastal exposures represent only me lowermost
(Fig. 4.30 & Fig. 4.31) and uppermost (Fig. 4.32) parts of me Snapper Point Formation.
Elecom Clyde River 10 (Fig. 4.32) is located near Jervis Bay and, as such can be easily correlated with outcrop sections. It shows a sequence consisting of five parasequences, labelled
A to E (Fig. 4.32). These parasequences are marked by a lower transgressive phase, which shows a fining upward trend, and an upper regressive coarsening upward phase. Coarse conglomeratic units at the top of the coarsening upward half of each parasequence are interpreted
87 as flooding surfaces. Deeper facies of the parasequence are dominated by intensely bioturbated sandy siltstone, interpreted as the maximum flooding interval. Coarse facies within shallow phases of parasequence deposition are dominated by pervasively bioturbated, fossiliferous sandstone, which may show evidence of plane bedding or low-angle stratification.
Sections from the southern part of the coast are presented in Figures 4.30 and 4.31.
These outcrops have been me focus of many studies (Gostin 1968; Carey 1978; Bann 1990).
The southern region encompasses all the coastal sections from Clear Point in the south to North
Termiel Point in me north (Figs 4.13, 4.30). Gostin & Herbert (1973) presented an interpretation of the stratigraphy of me coastal sections of this region which is basically in agreement with me interpretation presented herein. The base of the Snapper Point Formation is exposed at Point Upright, Clear Point and Dawsons Island (Figs. 4.15b & 4.21d). The sequence comprises four low order cyclical successions (Figs. 4.30 & 4.31) which probably correspond with parasequences A and B in ECR10 (Fig. 4.32). Although these cyclical successions are also technically parasequences they will be described in terms of cycles to avoid confusion with me fourth order parasequences as defined in ECR10 for me entire Snapper Point
Formation (Fig. 4.32). The cycles in the southern coastal exposures probably represent superimposition of fourth order and fifth order eustatic sea level changes or, alternatively, autochthonous processes such as changes in sediment supply. The regressive phase of each cycle is dominated by foreshore and shoreface sandstone bodies representing periods of low relative sea level and shoreline progradation. Periods of relative high sea-level are typified by offshore facies, close to storm wave base.
The base of me Snapper Point Formation is marked at Clear Point by a foreshore succession dominated by facies D (Figs 4.15b, 4.30) which represents a transgressive barrier deposit. Farther along the coast at South Island Beach me basal contact between me two formations is again exposed but here it is only marked by a thin pebbley lag layer. The absence of barrier facies at South Island Beach (Fig. 4.30) suggests mat me mechanism of barrier retreat may have been episodic and discontinuous (Swift et al 1991b). Directly overlying me foreshore facies is an embayment facies which contains coarse phases with large coarse-grained wave ripples. Wave rippled coarse-grained sandstone units become less prevalent
88 upwards within this section. The embayment facies contains the maximum flooding event of the lowest cycle. The embayment facies is overlain by a sharp based shoreface sand body
(facies F) which crops out at south Pretty Beach, south Snapper Point and south Termeil.
Sharp-based shoreface sandstone bodies have been previously described by Rosenthal & Walker
(1987) and Plint (1988). Rosenthal & Walker (1987) interpreted them as resulting from rapid progradation of the shoreface associated with a rapid sea-level fall. This interpretation would fit me data from me Snapper Point Formation. The shoreface sandstone body (facies F) is overlain by a wave rippled coarse-grained sandstone which is interpreted as a transgressive surface. This surface marks the change from a supply-dominated to accommodation-dominated regime and a cratonward facies shift. It also marks me base of me next cycle.
The lower half of the second cycle (Figs. 4.30) crops out at south Snapper Point and consists of a transgressive sequence which culminated in me deposition of me lower offshore facies N (Fig. 4.22), i.e. a shoreface to lower offshore facies succession. The silty shelfal facies interval contains me maximum flooding event which marks the change from transgressive to regressive depositional regimes; the latter forms me upper half of me cycle. Above me maximum flooding interval (Fig. 4.30) in the south Snapper Point section me coarsening upward part of me cycle (facies M) probably represents a minor shoaling event. The shallowest facies of this shoal is interpreted as a shell bank environment (facies J; Fig. 4.2 le; Fig. 4.31). The abundance of organisms may represent favourable wave or climate conditions at me time of deposition.
The top of me shell bank interval on Snapper Point must define a flooding surface although it is difficult to discern due to me pervasiveness of storm lag deposits. It marks me base of me next cycle which is very similar to me previous cycles in mat it contains bom a transgressive and regressive phase. The lower part of me sequence is transgressive, comprising facies M, which fines upward into a silt-dominated interval (at approximately 25 m in me north
Snapper Point section; Fig. 4.31). This interval probably marks a minor deepening and me maximum flooding surface of the third cycle. The regressive phase consists of a coarsening upward succession comprising facies M which grades up to the shoreface deposit of facies F.
This second shoreface sand body is found at me top of the north Snapper Point section and
89 the base of the Nuggans Point section. Nuggans Point probably represents the stratigraphically uppermost section based on correlation with the upper part of the north Snapper Point section.
The lower transgressive half of the fourth cycle (Figs 4.31) is exposed within the southern part of Nuggans Point.
The occurrence of a diamictite interval within me South Island Beach section (Fig. 4.30) suggests there has been a change to an ice-affected sedimentation regime. This may reflect the onset of a glacial period, similar to those exposed in the Pebbley Beach Formation (see section
4.3). The cause of me fall in relative sea-level higher in me sequence is difficult to determine.
The basal conglomerate units within the second shoreface sandstone body do contain large boulder sized clasts which may have resulted from ice rafting. If these units are interpreted as being glacially influenced men mere may be justification in suggesting that the sea-level falls were associated with periods of glaciation.
Carey (1978) interpreted the gross environment of deposition for the Snapper Point
Formation in me vicinity of Snapper Point as a prograding barrier beach system under dominantly regressive conditions. The environmental interpretation presented above is in stark contrast with mat presented by Carey (1978) who interpreted all facies above me lower shoreface sand body (facies F; Fig. 4.22) as backbarrier deposits, laid down under a regressive depositional regime. The fining upward sequence (interpreted as a transgressive sequence herein) above the lower shoreface sandstone bodies contains facies typical of a storm-dominated shelfal environment as described in numerous places elsewhere (e.g. Leckie & Walker 1982; Decelles
1987; Brenchley et al. 1993). The facies in me Snapper Point Formation also contain pervasive hummocky cross-stratification which would support an open shelf interpretation as outlined above.
Large ball and pillow structures at north Snapper Point suggest mat tectonic movement
(earthquakes) may have occurred contemporaneously with deposition.
The upper part of me formation is exposed at me coast (Figs. 4.32 & 4.33b) in me Jervis
Bay area and comprises me two uppermost parasequences (parasequences D and E). The lower part of me first parasequence is dominated by facies L, interpreted as a pebbly inner shelf deposit (Figs. 4.23b & 4.32) and is equivalent to an interval which is approximately 100m above
90 a thick siltstone unit in ECR10. Possiblefifth orde r sea level changes during me deposition of this succession are indicated by amalgamated coarse sandstone intervals and the presence of conglomeratic layers, interpreted as ravinement surfaces. This thick interval of facies L is abruptly overlain by a thick interval of siltstone (facies O; Figs. 4.23d, 4.33c & 4.32) indicating a major flooding event. The base of this siltstone unit marks a transgressive surface which forms the base of me uppermost parasequence. This siltstone unit is evident in all sections and is an excellent marker bed. The thickness of this unit varies across the basin with a maximum thickness of 5.7 m in me Banisters Head section. The top of the siltstone unit marks me base of a coarsening upwards regressive sequence (Figs. 4.32 & 4.33c), dominated by facies E, which is interpreted as an offshore tidal sand deposit. Cross-bedding from this part of me sequence shows a north-directed palaeoflow (Fig. 4.24 & 4.34), indicating me dominant direction of longshore currents. The interval consists of units of planar and trough cross-bedded sandstone with thicknesses of 2-4 m. Units are usually bounded by pebble conglomerate lag deposits.
The thickness of the entire interval is approximately 20 m. This part of me sequence is interpreted as representing longitudinal sand bodies, consistently reworked by longshore tidal currents. Similar facies have been reported from modern shallow tidal-dominated shelf environments by Chang-shu & Jai-song (1988) and Stride et al. (1982). Similar upward coarsening sequences have been described by Bridges (1982). This change to cross-bedded dominated shoreface facies marks a change to a tide-dominated shelf which appears to continue through me deposition of me Nowra Sandstone (see section 4.6). The cross-bedded interval marking me top of me uppermost parasequence is overlain by a transgressive sequence which fines rapidly upward to the Wandrawandian Siltstone (see section 4.5).
4.4.5 Lateral facies changes and depositional model
Deposition of me Snapper Point Formation was controlled by fluctuations in sea level. Up to five cycles of sea level change have been identified within me Snapper Point Formation. These sea level fluctuations resulted in facies changes and me development of parasequences in me eastern area and may have been caused by several factors:
(a) eustatic sea level change;
91 (b) changes in me rate of tectonic subsidence;
(c)fluctuations in sediment supply.
All of the mechanisms ouflined above would produce changes in the accommodation- supply ratio which results in either transgression or regression. Numerous changes in the rate of tectonic subsidence over such a relatively short time period (approximately 3 Ma) would seem an unlikely explanation, especially in an embryonic foreland basin which is probably undergoing passive thermal sag. Climate generated changes in sediment supply are possible but cannot be adequately tested within these successions. Climate changes could be generated by Milankovitch orbitally forced cyclicity, which would infer probable eustatic sea level changes. Similar cyclicity has been identified in me underlying Yadboro Conglomerate and Pebbley Beach
Formations and has been interpreted as fourth order cycles with a periodicity in me order of 105 years. The fluctuations in previous formations are interpreted as being generated by orbitally forced eustatic sea level changes on the basis of the widespread nature of flooding surfaces within me Yadboro Conglomerate and me evidence for climate and sea level change within me
Pebbley Beach Formation (see sections 4.1 and 4.3). Eustatic sea level changes, with a similar periodicity to those of the Yadboro Conglomerate and Pebbley Beach Formation, is the preferred explanation for me cause of cyclicity within me Snapper Point Formation.
Cross-sections showing cross-basin correlation for me Snapper Point Formation are presented in Figures 4.35 and 4.36. The sea level fluctuations are represented by distinct facies changes in me southwestern part of me basin and by parasequences in me eastern part of me study area. In me southwestern part of me basin deposition is characterised by alternating nearshore marine and braidplain delta deposition (Fig. 4.35). The surfaces separating me braidplain delta and overlying nearshore marine facies are interpreted as flooding surfaces which probably correlate with flooding surfaces in the parasequences farther east. Correlative surfaces in the northwestern area are more difficult to define. A silt-dominated interval within me
Hoddles Cliff section probably correlates with me thick siltstone interval of parasequence C in
ECRU and ECR10 (Fig, 4.36).
The sedimentary packages, bounded by flooding surfaces (as defined by parasequences in me eastern part of me area) show a marked increase in thickness to me east. This is
92 particularly evident between me Pigeon House Creek and ECR8 sections in figure 4.35 which shows an increase in individual cycle thickness from approximately 10m to >50 m. This increase in thickness is also evident on me isopach map (Fig. 4.25) which shows a substantial increase in formation thickness along a linear zone which runs approximately parallel to me coastline in me south but cuts inland to me west of Nowra and continues northwards. This zone also corresponds with a large increase in gradient on me basement topography map (Fig.
4.10). This zone is interpreted as a major basin hinge zone and will be discussed later in section 6.3. This zone appears to have had a marked affect on facies distributions and fourth order cycle thickness.
Transgressive phases resulted in shoreline retreat and me deposition of nearshore and shoreface sediments to me west of me hinge zone (Fig. 4.37). The increasing depth eastward of this zone was such mat a transgressive, fining-upwards sequence was deposited, which culminated in a silt-dominated unit typical of offshore sedimentation. This siltstone defines me interval of maximum flooding within each of me parasequences in me eastern area (Fig. 4.37).
During phases of fourth order regression the facies to me west of the hinge zone were dominated by nearshore marine and non-marine facies. In the southwest this phase is characterised by braidplain delta progradation whereas in me northwest it is represented by high energy nearshore marine deposition, although one braidplain delta facies interval has been noted
(Fig. 4.27). During regressive phases it is probable that this hinge zone marked me position of maximum progradation of the shoreline in me southwestern area. The central area is characterised by sediment bypassing and, consequently had a relatively low rate of sedimentation.
Concurrently to me east and seaward of the hinge zone, sedimentation was characterised by regressive sequences which usually culminated in shoreface sedimentation. Subsequent transgression caused shoreline retreat, flooding of me braidplain deltas to me west and deposition of a transgressive half sequence, the base of which defines me start of me next parasequence.
Most parasequences exposed in the eastern area have bom transgressive and regressive half sequences preserved, i.e. a transgressive phase overlain by a regressive phase. This suggests that preservation potential was high in me shelfal environment (Swift et al. 1991a). In this sense me shelf deposits are similar to me Miocene marine deposits of Maryland presented by
93 Swift et al (1991a) and me deposits of the Wasp Head Formation discussed herein (section 3.2).
In addition, these deeper areas acted as a depocentre for sediment derived from fluvial networks which were located west of the study area. For this reason me formation and component cycle thickness dramatically increases across the hinge zone.
Deposition of the Snapper Point Formation was broadly aggradational as there is no net landward or basinward facies shift upward through me formation. This indicates that sediment supply was approximately balanced by me rate of increase in accommodation space. In the eastern area the formation forms an aggradational parasequence set (Van Wagoner et al. 1988;
Mitchum & Van Wagoner 1991).
4.5 Wandrawandian Siltstone
The Wandrawandian Siltstone is a fine-grained unit within me Shoalhaven Group. Where exposed me unit consists of intensely bioturbated fossiliferous, sandy siltstone. The fine-grained nature of me formation renders exposure in most cases poor. The unit can be delineated by a vegetated bench between the quartz sandstone dominated Snapper Point Formation and Nowra
Sandstone.
4.5.1 Facies description
Sedimentologically, me Wandrawandian Siltstone is identical to facies O of the Snapper point
Formation and as such is interpreted as a lower offshore to shelfal siltstone, deposited below storm wave base (Fig. 4.33d). Sandy phases evident within core probably represent distal storm deposits which have subsequently been bioturbated.
An excellent section is exposed at Lagoon Head (GR: 8927-677782). The basal part of this section (Fig. 4.38) consists of interbedded very-fine sandstone and bioturbated siltstone.
Sandstone beds are lensoidal, typically 5-20 cm thick and are bioturbated. Siltstone units are thoroughly bioturbated, pyritic and highly fossiliferous. Fossils comprise brachiopods, corals, crinoids and bryozoans (see Runnegar 1969). This sequence is interpreted as a distal storm deposit and may represent transitional facies between the Wandrawandian Siltstone and the
Snapper Point Formation. Towards me top of me section me facies change abruptly (Fig. 4.38).
94 The interval is composed of two lithofacies comprising conglomerate and sandstone. A basal coarse-grained lithofacies consists of intensely convoluted fossiliferous cobble conglomerate which contains large intraclasts of the underlying siltstone (Fig. 4.33e). Clasts within me conglomerate are angular to rounded, poorly sorted and reach a maximum size of 30-40 cm.
The matrix of the conglomerate is silt-dominated. The conglomerate rapidly attenuates laterally within 20 m and becomes a thin (20 cm) lag deposit underlying me sandstone. The overlying medium-grained sandstone lithofacies consists of two amalgamated beds (Fig. 4.39a) which each consist of a basal plane bedding facies and an overlying convoluted facies. The base of me second bed being marked by a 20 cm thick conglomeratic lag deposit. The sandstone units have a combined maximum thickness of 1.9 m. The lithofacies thins laterally, giving it a distinct lensoidal shape. The facies are interpreted as mass flow deposits. The deposit probably resulted from high energy turbidity currents (Lowe 1982). The fabric of the basal conglomeratic layer suggests mat this material may have been transported as a cohesive debris flow (Pickering et al 1986). The sandstone interval above represents high density suspended sediment deposition.
The geometry of me interval suggests mat me mass flow deposit has a lobate morphology.
A medium quartz sandstone interval with a 50 cm basal conglomerate unit at approximately 130 m in ECR3 occurs within the Wandrawandrian Siltstone. A mass flow interpretation is also invoked for this interval.
Outcrops and drillcore show abundant large clasts in me siltstone which are interpreted as dropstones. Ice was clearly still prevalent during deposition of the Wandrawandian Siltstone.
Glendonites at Warden Head (Fig. 4.39b) also support a cold climate hypothesis.
4.5.2 Warden Head
One coastal exposure of me Wandrawandian Siltstone has generated considerable interest (Gostin
1968; Gostin & Herbert 1973; Scott 1984; Wiles 1993, 1995) . This interest is centred on a chaotic interval within me section (Fig. 4.33d). Deformation occurred prior to lithification when water content was high (Wiles 1995). The interval consists of a west dipping duplex structure with west over east thrust faults confined by roof and floor thrusts. Later deformation resulted in back-thrusting and minor strike-slip faulting (Wiles 1995). Dewatering structures such as sand
95 dykes are associated with the deformation. The deformation at Warden Head had previously been interpreted as a slump related structure (Scott 1984). Wiles (1995), however, interpreted the structure as the leading edge of the deformation associated with the Hunter Bowen Orogeny within me southern Sydney Basin. Age constraints derived from similar structures within the northern Sydney Basin suggest an age of 265 - 255 Ma (Gulson et al. 1990; Wiles 1995).
4.5.3 Isopachs
The isopach map (Fig. 4.40) of the Wandrawandian Siltstone shows that the thickness of the unit varies between 0 and 196m. The formation forms a eastward thickening wedge with the largest thickness recorded near to the present coast. To the west, in me Shoalhaven Gorge, me formation can be clearly seen pinching out between the Snapper Point Formation and the Nowra
Sandstone. The same is not true to the southwest where me formation forms Corang Peak. The transgression represented by me Wandrawandian Siltstone obviously extended much farther inland within this region than it did to the north.
4.5.4 Depositional model
The Wandrawandian Siltstone is interpreted as a middle to outer shelf deposit representing me distal facies resulting from the transgression which began with the Snapper Point Formation.
Ice periodically deposited large dropstones within the otherwise fine-grained, intensely bioturbated, fossiliferous siltstone. Earthquakes may have caused rare high density turbidity currents which were deposited on me shelf as lobate sand bodies.
Deformation related to me Hunter-Bowen orogeny during me Late Permian was probably responsible for me chaotic structures evident at Warden Head (Wiles 1993).
4.6 Nowra Sandstone
The Nowra Sandstone varies in thickness from zero up to approximately 120 m. The sandstone caps most of me cliff lines in me southernmost Sydney Basin. The Nowra Sandstone overlies the Wandrawandian Siltstone at every locality except in me northwestern part of me Shoalhaven
Gorge where the Wandrawandian Siltstone is non-existent. In this case the Nowra Sandstone
96 directly overlies me Snapper Point Formation. The contact between me Nowra Sandstone and the Wandrawandian Siltstone is only visible at a small number of localities such as Boyd
Lookout, Pointers Gap Lookout and Tianjara Falls. The contact is typically sharp in me northwestern area where the Wandrawandian Siltstone is absent but gradational in all other areas.
The contact with me overlying Berry Siltstone is seldom seen except in core (Elecom Clyde
River 1) and appears to be gradational.
The unit is dominated by quartzose pebbley medium-grained sandstone. In many sections a matrix to clast supported conglomerate is present which Fisher (1972) defined as me Purnoo
Conglomerate Member.
Earlier work on me Nowra Sandstone dates back to David and Stonier (1891). More recent previous work on me Nowra Sandstone was carried out by McElroy and Rose (1962),
Fisher (1972), Herbert (1980a) and Le Roux and Jones (1994). The environment of deposition for me sedimentary sequence is interpreted in all previous work as shallow marine. The most recent work carried out by Le Roux and Jones (1994) interpreted me formation as a deposit which occurred in response to a regressive-transgressive episode. The Purnoo Conglomerate
Member (Fig. 4.39c) is interpreted as a ravinement surface marking a change from a regressive to transgressive regime.
4.6.1 Lithofacies
Le Roux and Jones (1994) gave a comprehensive facies analysis. The work carried out herein identified and classified me same seven lithofacies which are outlined below (Table 4.6).
Hummocky cross-stratified sandstone was identified by Le Roux and Jones (1994) in a measured section at Wogamia (station 7). No other hummocky cross-stratified sandstone was found at me outcrops visited.
Facies A: Conglomerate
Description: This facies is found in most sections. The thickness of me facies varies from <5 cm to 80 cm, although Le Roux and Jones (1994) recorded a maximum of 1.8 m. This facies commonly forms a lag at the base of sandstone beds. In such cases me conglomerate is normally
97 thin, commonly only one pebble thick. More rarely, the facies is found as a thicker bed which has been termed the Purnoo Conglomerate Member (Fig. 4.39c; Fisher 1972).
The Purnoo Conglomerate Member typically consists of pebble to boulder, clast to matrix supported conglomerate. The clasts are sub-angular to well-rounded within a quartzose medium- grained sandstone matrix. Clast lithologies are dominated by chert, quartz, quartzite and sandstone with minor volcanic clasts. There appears to be no significant direction of pebble imbrication within me conglomerate beds.
Interpretation: Thin conglomerate beds at me base of sandstone beds probably represent lag deposits, resulting from the winnowing of finer grained material by storms. Since sandstone beds within me formation are pebble-rich it would require little erosion to concentrate pebbles into a lag deposit (Le Roux & Jones 1994).
The thicker conglomerate bed is more significant. Gravels similar to these are common in transgressive sand sheets (Swift et al. 1991b) and are me result of the erosional retreat of me shoreface. In most cases transgressive lags are discontinuous and may occur as ridged sheets parallel to the shoreline (Swift et al 1986) marking successive phases of shoreface retreat (Swift et al. 1991b). This may explain me absence of me conglomerate within many of the measured sections of me Nowra Sandstone.
Facies B: Plane bedded and low angle cross-stratified sandstone
Description: This is a common facies within me Nowra Sandstone (Fig. 4.39e). Individual unit thickness is generally in me range of 0.2 to 1 m but amalgamated units of facies B can be up to approximately 20 m thick. Lithologically the sandstone is dominated by well sorted quartzose medium-grained sandstone. Pebbly lags are common at the base of individual beds. Pebbles are common throughout me beds and may occur as patches and lenses. The structure of me sandstone is dominated by plane beds and low angle cross-beds (0-10°) which may truncate each other at low angles.
Bioturbation is difficult to discern within the units but where present it appears to be vertical sand tubes of Skolithos. Disarticulated brachiopods and bivalve fossils are found rarely
98 within the facies.
Interpretation: This type of facies is typical of foreshore environments (Elliot 1986). Low angle lamination is produced by swash action (Clifton 1969; Le Roux & Jones 1994).
Facies C: Planar cross-bedded sandstone
Description: cosets classified as facies C (Fig. 4.41a) range up to a thickness of approximately
2-3 m, individual sets are typically 0.2 - 0.8 m. The inclination on foresets is quite high varying, between 11° and 26°. The facies is dominated by medium- and coarse-grained quartzose sandstone. As for facies B, unit boundaries are often marked by pebbly lag deposits.
Le Roux and Jones (1994) documented cosets splitting and pinching out laterally along dip over distances of tens of metres. One coset at Boyd's Lookout showed sigmoidal geometry.
Palaeocurrent data show a consistent northeasterly direction (Fig. 4.42).
Rare Skolithos bioturbation within me units is evident. Rare fossils are present and are dominantly brachiopods and bivalves.
Interpretation: The planar cross-bedding was generated by me migration of straight crested dunes, which migrated under me influence of northeasterly directed longshore currents. The presence of sigmoidal geometry within one bed would suggest possible a possible tidal influence
(Kreisa & Moiola 1986). This facies is found in association with foreshore facies which suggests a nearshore origin. Similar facies are documented in shoreface environments (Driese et al. 1991) and result from me migration of sand banks or sheets (Stride 1988).
Facies D: Trough cross-bedded sandstone
Description: Units are not as thick as those of facies C. Thickness ranges up to approximately
3.7 m but individual sets are typically 10-40 cm. Cosets of trough cross-bedded sandstone are associated with plane bedded and low-angle cross-stratified sandstone. Lithologically me facies is dominated by medium-grained sandstone. Beds contain pebbles and often have a pebbly base.
Bioturbation is usually Skolithos type ichnospecies.
99 Interpretation: Trough cross-bedding results from the migration of sinuous crested dunes. The association of this facies with plane-bedded and low-angle cross-stratified sandstone suggests deposition was shallow, probably upper shoreface, similar to that of facies C. Facies D may represent a slightly deeper environment as postulated by Le Roux and Jones (1994), adjacent to the main sand bank represented by facies C.
Facies E: Massive/Bioturbated Sandstone
Description: This facies encompasses all units in which no discernible primary sedimentary structures could be determined. In many cases it is clear mat the massive appearance of this facies is caused by bioturbation which is dominated by Skolithos. The thickness of beds is variable but is generally not greater man 1-2 m. As for me preceding facies, this facies contains abundant pebbles and often has a pebbly lag at the base.
Interpretation: The lack of sedimentary structures within the facies means that the environment of deposition is difficult to determine. The presence of bioturbation suggests periods of lower energy. The association of the facies with all of the preceding facies suggests that it also represents a shoreface environment. The massive structure within some beds may be due to wave fluidisation within me high energy surf zone.
Facies F: Interbedded sandstone and bioturbated silty sandstone
Description: This facies only occurs at the base of the formation (Fig. 4.41b) and in me sections at me present coast (Crookhaven Heads and Penguin Head; Fig. 4.41c) which represent the most easterly exposure of me Nowra Sandstone. Where me facies crops out at me base of the main sandstone succession it represents a transitional facies between me Wandrawandian Siltstone and the Nowra Sandstone. Lithologically me facies consists of interbedded fine-grained sandstone and bioturbated silty sandstone. The sandstone beds are usually bioturbated and may have a lenticular geometry, thickening and thinning over a distance of several metres. Sandstone thickness ranges up to approximately 80 cm but most beds are in me order of 20-40 cm.
100 Siltstone beds are carbonaceous, pyritic and intensely bioturbated.
Interpretation: The facies resembles lower shoreface to transitional offshore facies similar to those documented elsewhere (e.g. Dott and Bourgeois 1982; Rosenthal and Walker 1987). This interpretation is likely considering me context of me facies between me offshore deposited
Wandrawandian Siltstone and me interpreted shoreface facies of the Nowra Sandstone. The lenticular geometry of the sandstone beds may be due to the action of orbital waves (Brenchley et al. 1993).
4.6.2 Palaeocurrents
Palaeocurrent measurements were taken from cross-bedding within me formation. The rose diagram shows a northeasterly trend with a vector mean of 021° (Fig. 4.42). Figure 4.42 also shows the consistent northeasterly trend of palaeocurrents for me Nowra Sandstone. This consistent palaeocurrent direction is attributed to prevailing longshore currents.
4.6.3 Isopachs
An isopach map for me Nowra Sandstone has been constructed in Figure 4.43. The method used to obtain thicknesses was from measured sections and from 1:25 000 scale topographic maps. The resultant isopach diagram is very similar to mat of Le Roux and Jones (1994).
The Nowra Sandstone varies in thickness from 0 - 126 m but most thickness vary between 40 and 80 m. The formation forms a westward thickening wedge. The sandstone is concentrated into two major depocentres located in me north and south of me study area both of which have thicknesses of more than 120 m (Fig. 4.43). The depocentres correspond with the position of the Tallong and Yadboro Conglomerates. The high values in me northern part of me area (Fig. 4.43) represent a combined thickness of bom me Snapper Point Formation and the Nowra Sandstone and are therefore deceptively high. Values taken to the east of this area where the Snapper Point and Nowra Sandstone are distinct units show mat me thickness of me sandstone is still greater man 90m. This northern area may represent a separate depocentre.
101 4.6.4 Depositional model
Le Roux and Jones (1994) identified a sand shoal or sand ridge complex on the basis of grain size, percentage of conglomerate and me prevalence of high energy sandstone lithofacies (Fig.
4.44). This would seem to be a valid interpretation based on the facies succession. Sediment was supplied to the nearshore zone via river systems which correspond with the position of pre existing fluvial systems (i.e. the Tallong and Yadboro Conglomerates). The greater thickness of the formation at these localities (Fig. 4.43) is simply related to the proximity of the fluvial source.
One of the most striking aspects of the Nowra Sandstone is the almost complete absence of wave generated sedimentary structures such as hummocky cross-stratification, swaley cross- stratification and large coarse grained wave ripples (Fig. 4.45) which are pervasive in shallow marine strata lower in me Shoalhaven Group. This suggests that prevailing north-northeast directed longshore currents were capable of overprinting all wave generated structures. A modern analogue for this situation may be the shallow seas surrounding me British Isles (Stride et al 1982) where deposits were formed by transgressive tide-dominated seas. Stride et al.
(1982) stated mat currents greater man 100 cm/s are required to generate sand ridge complexes.
These are probably me type of current conditions responsible for me deposition of the Nowra
Sandstone. Storm deposits are only preserved in distal, less tidally influenced depositional settings within this type of environment. This is me setting represented by the sections at the extreme eastern edge of me sandstone wedge (e.g. Crookhaven Heads and Penguin Head; Fig.
4.41b, 4.45).
The Purnoo Conglomerate Member is interpreted as a transgressive deposit overlying a ravinement surface (Le Roux and Jones 1994; Fig. 4.45). Figure 5 from Le Roux and Jones
(1994) clearly shows that me conglomerate is found progressively stratigraphically lower within the sandstone towards the west. The interpreted easternmost extent of the conglomerate should be a good approximation for me maximum regression of me shoreline. This is located in the vicinity of Nowra (Le Roux and Jones 1994). The Nowra Sandstone basically consists of two stacked or amalgamated shoreface sand bodies (Fig. 4.45). In this sense it is similar to the
Kakwa Member of me Cardium Formation (Hart & Plint 1994). The eastward thickening sand
102 wedge below me ravinement surface was deposited under a regressive regime, (i.e. sea-level fall) and me westward thickening sandstone wedge above the ravinement surface was deposited during transgressive conditions, (i.e. during a sea-level rise). The apparent absence of the conglomerate member within many of me measured sections may indicate mat the transgression proceeded as a series of discrete phases in each case generating a erosional surface of local importance
(Plint & Walker 1987; Hart & Plint 1994).
Le Roux and Jones (1994) sited the prevalence of cross-bedded facies above me Purnoo
Conglomerate Member as evidence mat it represents a transgressive deposit. Under transgressive conditions shoreface profiles are translated landward and upward (Bruun 1962). This causes erosion on me upper and landward parts of me shoreface as me shoreline recedes. As a result of marine transgression, facies seaward of me erosion point would preferentially be preserved
(Dominguez and Wanless 1991). This means mat deeper facies are theoretically more likely to be preserved above me ravinement surface. In the measured sections presented bom herein (Fig.
4.45) and in Le Roux and Jones' (1994; Fig. 5), there does not seem to be a significant facies change across this boundary. This may be a function of the shelf profile. In a situation where the shelf is broad and shallow me facies distinction across this erosion point will be less distinct.
Drawing on analogues of similar modern deposits around me British Isles (Stride et al. 1982) the assumption of a shallow shelf would seem to be valid.
The Nowra Sandstone is very similar to me facies succession of the upper Snapper Point
Formation (see section 4.4) in mat it is dominated by cross-bedded facies. The change to dominantly cross-bedded strata within me upper Snapper Point Formation and Nowra Sandstone indicates a change from dominantly wave-dominated to tide-dominated shelf conditions. This probably indicates a change from an open to a constricted seaway. The Nowra sandstone also shows a continuation of sediment dispersal towards the north which began in me upper Snapper
Point Formation. This change in sediment dispersal within me shoreface sandstone bodies of the upper Snapper Point Formation and me Nowra Sandstone probably represents a major restructuring of the dispersal pattern associated with me development of me Sydney Basin into a foreland basin during me Late Permian.
The Nowra Sandstone is very similar to me Staircase Sandstone Member (Fielding 1989)
103 and the Catherine Sandstone (John and Fielding 1993) in me Bowen Basin, which both represent similar prograding sand bodies. Both of these sandstone bodies show considerably more influence of waves.
104 5.0 PETROLOGY
Thin sections of 125 sandstone samples were analysed and point counted (Appendix 4).
Samples were collected from all the major units within the region. Most of the samples were collected from me Elecom Clyde River drillcores, as these were unweathered and provided a good areal distribution of data over me basin. In addition to these samples, data from 49 samples analysed by Gostin (1968) were incorporated into me analysis. Thin sections were analysed using 300 point counts and classified into me major framework parameters. The aim of this chapter is to relate me petrology of me rock units to a tectonic model for me Sydney-
Bowen Basin.
5.1 Sandstone Petrography
5.1.1 Texture
Samples vary from poorly to well sorted and from fine- to coarse-grained. The volume of framework grains within me sandstone samples varies. The matrix component is volumetrically more important in bioturbated samples compared with unbioturbated samples due to me biogenic mixing of sandstone and siltstone lithologies. In unbioturbated sandstone samples me non- framework component is typically < 15% of total rock volume.
5.1.2 Detrital Minerals
Quartz
Quartz is me most abundant detrital fragment within me Shoalhaven Group and most samples of me Talaterang Group. In all samples, except for some which are low in me Wasp Head
Formation, the quartz content varied between 60 and 95% of me framework components with most samples containing more mat 80%. Most quartz fragments are monocrystalline and show undulose extinction. Polycrystalline quartz is also common.
Feldspar
Feldspar is generally rare within me samples, with a range of 0 to 12% within all formations
105 except for me Wasp Head Formation which contained 0 to 34% feldspar. K-feldspar is typically more abundant than plagioclase. K-feldspar consists of orthoclase and cross-hatched microcline grains. Feldspar grains are typically altered, with dissolution and replacement by calcite as common phenomena.
The areal distribution of feldspar is controlled by proximity to granite source terrains.
For example, high feldspar contents were recorded for sandstone units within ECR2 which is
close to me Yalwal Granite.
Rock Fragments
A variety of rock fragments is found within the samples. Except for the lower part of the Wasp
Head Formation me volume varied between 4 and 41%. In the lower part of the Wasp Head
Formation, me lithic content ranged up to 95% of framework grains. Unmetamorphosed
sedimentary rock fragments were rare to absent within all samples of me Talaterang and
Shoalhaven Groups. Metamorphic fragments consist of argillite and quartz-mica schist and other low grade meta-sedimentary fragments. Volcanic grains consist of fine-grained fragments. In thin section me latter grains often have me appearance of chert fragments but can be distinguished on the basis of rare phenocrysts or because of partial alteration to clay minerals.
Chert fragments are dominantly black chert and are, in some cases, cross-cut by polycrystalline quartz veins.
Accessory minerals and material
Muscovite is a common accessory mineral within me samples, even within coarse-grained sandstone, but never has an abundance of more man approximately 4%. Grains of muscovite are usually bent and fractured as a result of compaction. Biotite is completely absent from all samples. Many samples contained a high content of organic material with 5% recorded in some samples. The high organic matter content is always associated with bioturbated samples. Heavy minerals that were observed include tourmaline, zircon and various opaque grains, interpreted as ilmenite.
106 5.1.3 Authigenic Minerals
Quartz, carbonate and clay cementation were observed within me sandstone units. Quartz overgrowths are common throughout all samples. Identification was made easy in some cases by the presence of dust rims around detrital grains. Rare chert cement was also observed.
Quartz overgrowths are less developed in samples with a high percentage of matrix. This applies to most of the bioturbated sandstone samples. Carbonate cementation is common within me samples and consists of calcite and/or siderite. Calcite cementation is common in coarse grained matrix poor samples whereas siderite is associated with organic matter and occurs as small earthy masses. In fossiliferous samples, calcite is a dominant volumetric component.
Calcite is commonly observed replacing feldspar and volcanic fragments. X-ray diffraction and thin section analyses of selected samples showed mat me dominant clay minerals within me samples are kaolinite, illite and chlorite, with mixed-layer illite/smectite a minor component.
Rare glauconitic grains were found in a few samples from me Snapper Point Formation.
5.1.4 Classification
Samples from me Talaterang and Shoalhaven Groups are generally feldspar poor (Fig. 5.1). The percentage of quartz and lithic components, however, is variable. The lithic component is dominated by metamorphic, metasedimentary and volcanic detrital components (Fig. 5.2).
Talaterang Group
The distribution of samples taken from me Talaterang Group is shown in Figure 5.3. Samples from me Wasp Head Formation show a large spread of data within me litharenite, felspathic litharenite, sublitharenite and subarkose fields. The samples with high lithic content were taken from the lower part of the Wasp Head Formation where the lithic component was almost 100% argillite and metasedimentary chert. The two samples from me Clyde Coal Measures show compositions which are classified as sublitharenite and Feldspathic litharenite.
Shoalhaven Group
Most samples from the Shoalhaven Group are classified as sublitharenite (Fig. 5.1) using me
107 classification scheme of Folk et al. (1970). A small number of samples can be classified as litharenite, feldspathic litharenite, lithic arkose, arkose and subarkose. The breakdown of composition by formation is shown in figure 5.4. This shows that the Nowra Sandstone and me Tallong/Yadboro Conglomerate contain almost no feldspar. The relative quartzose nature of the Nowra Sandstone has been attributed to increasingly deeper levels of erosional unshipping related to the erosion of the Lachlan Fold Belt (Conaghan et al in Veevers et al. 1994a).
Another more probable explanation is that the sediments of the Nowra Sandstone were extensively reworked in the interpreted shoreface environment (see section 4.6) thus eliminating the less stable (chemically and physically) detritus. In general, the compositions of the formations are very similar and it is difficult to distinguish the formations on the basis of mineralogical composition.
5.2 Provenance
All of the rock types identified during me thin section analyses are found within southeastern
New South Wales (Fig. 5.5). Gostin (1968) identified two major source rock groups for
Permian strata on the south coast. The first group contained argillite, chert, black chert and composite quartz grains (quartz-mica schist) and were interpreted as derived from Ordovician argillite and metaquartzite. The second group comprised unstrained quartz grains, volcanic rock fragments and feldspar and was derived from mixed volcanic and granitic terrains.
Talaterang Group
There is a major change in composition of sandstone within me Wasp Head Formation.
Approximately half-way up me coastal section (near me base of me swaley cross-stratified shoreface sandstone body) me sandstone composition changes from dominantly lithic to quartzose. The lithic fragments within the lower part of me formation are comprised of argillite, black chert and metaquartzite. The lithologies within the sandstone beds are identical to those in me underlying Ordovician Wagonga Beds, which is a deformed and metamorphosed turbidite sequence. This suggests that the grains within me lower part of me formation are locally derived. The upper part of the formation is quartz dominated and contains feldspar and volcanic
108 rock fragments in addition to detritus from the Wagonga Beds. Thus, the sediment provenance has increased in area to encompass granitic and volcanic terrains which are present to the west of the coastal outcrop (Fig. 5.5).
The Clyde Coal Measures show a similar composition to the upper part of me Wasp
Head Formation. This suggests a similar sediment provenance, derived from me surrounding pre-Permian hinterland.
Shoalhaven Group
Sediment dispersal directions within me Tallong and Yadboro Conglomerates indicate mat sediment was shed from me west. All the samples from me Shoalhaven Group were quartz- dominated and basically contain a similar mixture of rock fragments. The fragments comprise meta-sediment, metaquartzite, fine-grained silicic volcanic fragments and feldspar. There is virtually no variation in composition across me study area (Fig. 5.6). Small variations in feldspar content are probably caused by proximity to granite. For example, ECR2 is located near the Yalwal Granite which results in a slighfly higher feldspar content. The detrital material for me Shoalhaven Group is derived from me local, pre-Permian basement rocks located within and to me west of the study area (Fig. 5.6).
5.3 Implications for basin development
The samples from me Talaterang and Shoalhaven Groups have been plotted on QFL and QmFLt diagrams showing me tectonic fields of Dickinson and Suczek (1979) and Dickinson et al.
(1983; Fig. 5.7). Most of the samples plot within the recycled orogenic field (RO). As
.described above, sediment was shed from the west, derived from meta-sedimentary and granitic- volcanic terrains of the Lachlan Fold Belt.
Baker et al. (1993) presented a 3-phase model for me development of me Bowen Basin
(Fig. 1.3). Phase 1 is characterised by basement faulting and me formation of grabens and half- grabens. Samples from phase 1 were classified as recycled orogen (RO) and undissected arc
(UA) terrains. Phase 2 marks the onset of passive thermal subsidence and sediments were derived from the western cratonic margin and classified as recycled orogen (RO). The final
109 flexural loading phase (phase 3) began with me formation or rejuvenation of a volcanic arc to me east which shed sediment to the basin. Samples from this phase are rich in volcanogenic sediment and are classified as magmatic arc (MA) and lithic recycled (LR) provenance. The sediments from me southern Sydney Basin are similar to those of phase 2. This is consistent with the interpreted tectonic setting for the deposition of the Shoalhaven Group.
The Talaterang Group has been tentatively interpreted herein, as a rift fill and as such is equivalent to Baker et a/.'s (1993) extensional phase 1. The petrography does not reflect a volcanic source terrain as may be expected from some rift basins. This was also found to be me case by Baker et al (1993) for units such as the Reids Dome Beds. Volcanism does not necessarily have to accompany rifting. A good modern example is the Malawi end of the East
African Rift system where volcanism is limited (Reading 1986). The southern Sydney Basin was situated at me southern extremity of me rift system and as such volcanism was probably absent. For this reason volcanic units were absent from me base of the section and as such no volcanic signature is found in me overlying detrital sediments which comprise the sub-basin fills.
The sedimentary signature simply reflects me petrology of units of the pre-existing Lachlan Fold
Belt.
Sediments comprising me Shoalhaven and Talaterang Groups were derived from the
Lachlan Fold Belt to me west during an extensional (Talaterang Group) and a passive thermal subsidence phase (Shoalhaven Group) which are equivalent to phases 1 and 2 of Baker et al.
(1993) and stages A and B of Veevers et al. (1994a),
110 6.0 DEPOSITIONAL SYSTEMS AND TECTONIC SETTING
6.1 Depositional Systems
Five depositional systems have been defined within me Talaterang and lower Shoalhaven Groups to distinguish intervals of genetically related strata. These systems correlate with major episodes of transgression and regression within me basin which, in turn, relate to me tectonic development of the basin.
6.1.1 Clyde Coal Measures - Wasp Head Formation alluvial/marine shelf system
The onset of sedimentation within me southern Sydney Basin is marked by the accumulation of mud-rich alluvial and shallow marine sediments within small extensional sub-basins (Fig.
6.1a). Low energy alluvial systems (Clyde Coal Measures) drained me inland sub-basins axially, dominantiy towards the north. Coastal facies at the top of the upper Clyde Valley section suggest that the grabens came under marine influences in me late stages of Clyde Coal Measures accumulation.
This change in facies indicates me northwestern margin of the marine incursion into grabens in me southeastern part of me basin. The same transgression resulted in me deposition of me upper nearshore high-energy marine facies of me Wasp Head Formation (Fig. 6.1a). High energy transverse (eastward) sediment dispersal in me latter is indicated by me coarse breccia units towards the base of the formation and probably represents mass movement off me uplifted rift margin. Shallow marine sedimentation in me Wasp Head Formation consists of two transgressive sequences, each marked at the base by high energy shoreface sand bodies. The upper transgressive sequence probably correlates with me transgressive succession at me top of the Clyde Coal Measures section. The occurrence of me Talaterang Group in extensional sub- basins accounts for its restricted distribution (see section 3).
The base of this depositional system is marked by a major unconformity (Fig. 6.2-6.4) between strata of the pre-Permian highly deformed Lachlan Fold Belt and units of me Sydney
Basin. The upper boundary is defined by the contact with either depositional system 2, or, where this is absent, the shallow marine sediments of system 3.
Ill The Clyde Coal Measures and the Wasp Head Formation have a palynological age of stage 3a (Evans 1991). This conforms to an Early Permian (Sakmarian) age. Veevers et al.
(1994b) suggested that the age of this early extensional phase is between 290-268 Ma throughout me Sydney-Bowen Basin.
Initial extension during me Early Permian has been documented from many parts of the
Sydney-Bowen Basin (e.g. Roberts & Engel 1987; Fielding et al 1990; Johnson & Henderson
1991; Schiebner 1993; Bamberry et al 1995) and conforms with phase A of Veevers et al
(1994b) and stage 1 of Baker et al (1993; Fig. 1.3). This extensional regime had not been recognised previously from me southern Sydney Basin but is the interpreted depositional environment for System 1 (Talaterang Group; see section 3.0) on the basis of sedimentological and stratigraphic relationships. The Clyde Coal Measures are very similar to the Reids Dome
Beds in me Bowen Basin (Draper & Beeston 1985) and the Goonbri and Maules Creek
Formations in me Gunnedah Basin (Tadros 1993b). The rift interpretation of the Clyde Coal
Measures and me Wasp Head Formations is made tentatively as there is no seismic or field
evidence to show definitely that normal faults exist in basement. The basement contour map
(Fig. 4.10) contains an interesting anomaly in the vicinity of Connemia No.l, north of Jervis
Bay, where mere is a dramatic change in me depth to basement over a small distance
(approximately 5 - 10 km). These changes could be me result of a fault bounded sub-basin
within basement. It is also interesting to note mat the proposed Clyde Coal Measures graben
lies at me southern extremity of the Meandarra Gravity Ridge which may be the subsurface
expression of the volcanic rift (Fig. 6.5; Murray 1990; Schiebner 1993).
Deposition of the Clyde Coal Measures and me Wasp Head Formation took place during
a widespread phase of extension of me east Australian platform which began approximately 290
Ma ago (Veevers et al. 1994b). In more easterly parts of the Sydney-Bowen Basin complex
the onset of this phase is marked by extensive volcanism. In me Bowen Basin me Comet and
me Lizzie Creek Volcanics were deposited. In the Gunnedah Basin me Boggabri Volcanics and
the Werrie Basalt were extruded (McMinn 1993; Tadros 1993b). In me northern Sydney Basin
me Rylstone Volcanics were deposited. Extension resulted in me formation of grabens and half
grabens. Detrital sedimentation within extensional sub-basins is represented by the Reids Dome
112 Beds in the Denison Trough of me Bowen Basin (Fielding et al 1990; Baker et al. 1993), the Goonbri and Leard Formations in the Gunnedah Basin (Tadros 1993b) and by the Dalwood
Group in the northern Sydney Basin (Veevers et al. 1994b). The absence of volcanism within me southern Sydney Basin, which marks the onset of this extensional phase in other parts of me Sydney-Bowen Basin is probably due to it being at me southern extremity of the rift zone represented by the Meandarra Gravity Ridge (Fig. 6.5). A good modern analogue for me rifting stage is the East African Rift System. Volcanism is extensive in me northern parts of the rift system (e.g. Ethiopian and Kenyan Rifts) but is limited at me southern extremity (Malawi Rift;
Reading 1986; Tiercelin 1990). The localities at me southern extremity of me East African Rift system are probably similar to me tectonic setting of the southern Sydney Basin. Volcanic units are also completely absent from me basal sections of the Denison trough of the Permian Bowen
Basin. Sedimentation within me sub-basins of this trough are characterised by sandy river systems and locally fed alluvial fans (Draper & Beeston 1985), similar to the Clyde Coal
Measures. The Denison Trough was located a large distance from me embryonic magmatic arc and is at me northern extremity of me rift zone (Meandara Gravity Ridge). It is probably a sensible analogue within me Sydney-Bowen system for the relative position of the exposed southern Sydney Basin during the same period.
6.1.2 System 2 - Yadboro/Tallong - Pebbley Beach - Yarrunga bedload fluvial to marine system
System 2 includes the Yadboro and Tallong Conglomerates, me Pebbley Beach Formation and the Yarrunga Coal Measures (Fig. 6.3). Passive thermal subsidence initiated incision and
, progradation of a coarse alluvial apron from me western margin of the Sydney Basin (Fig. 6.1b).
High energy braidplains (Tallong and Yadboro Conglomerates) developed with sediment dispersal to the east. Fine-grained carbonaceous facies (Yarrunga Coal Measures) and silt-dominated facies (Pebbley Beach Formation) were deposited on a gently subsiding sediment starved coastal plain and shallow marine shelf which fringed the high energy braidplains in the southern part of me basin (Fig. 6. lb). Fourth order eustatic sea level changes resulted in periodic flooding of me high energy braidplain and the deposition of silty facies. Four of these flooding intervals
113 have been noted. These same eustatic sea levelfluctuations cause d rapid shoreline retreat and coastal progradation. Climatic changes accompanied these sea level changes and the inner shelf is likely to have been periodically completely covered by ice during glacial periods (see section
4.3). The presence of abundant dropstones throughout the Pebbley Beach Formation suggests mat sea ice was important during deposition of the entire succession (Gostin 1968; section 4.3).
The Yadboro and Tallong Conglomerates form thick conglomeratic wedges which were derived from me western cratonic margin of the basin. The units are restricted to two main palaeovalleys (Fig. 6.1b).
Only the upper part of the correlative Pebbley Beach Formation is exposed and comprises four parasequences which form a parasequence set. The regressive phase of each parasequence shows a progressive basinward facies shift. The top of parasequence A contains shoreface facies whereas me top of the parasequences C and D comprise tidally influenced back-barrier facies
(Fig. 4.19). The Yarrunga Coal Measures is interpreted as a transitional facies, between me
Yadboro/Tallong Conglomerate and the Pebbley Beach Formation. Base level changes responsible for me flooding surfaces within the Yadboro Conglomerate and marine flooding surfaces within me Pebbley Beach Formation probably correlate. Exact correlation of specific surfaces is not possible due to the absence of a complete section through me Pebbley Beach
Formation. Parasequences and flooding surfaces within bom the Pebbley Beach Formation and the Yadboro Conglomerate resulted from fourth order Milankovitch (1941) cycles (sections 4.1
& 4.3).
A major rise in relative sea-level towards the end of the deposition of this system caused a rapid cratonward facies migration. The upper Yarrunga Coal Measures forms a thin transgressive systems tract that was deposited behind strandlines of the advancing shoreline, as it covered me Yadboro Conglomerate.
The sedimentary successions within this system represent an aggradational to progradational parasequence set, mat formed during a sediment-dominated depositional regime (Fig. 6.3). The upper part of the succession is a thin retrogradational transgressive unit which reflects a major flooding event at me end of me deposition of this system.
This system has an erosional contact with me underlying strata of system 1 where the
114 latter is present (Figs. 6.2-6.4). The western boundary of the alluvial units is an incised palaeovalley which can be seen clearly in the field (Fig. 6.6a). The nature of me boundary in the eastern part of me area is difficult to define due to a lack of subsurface information.
System 2 is overlain by a major flooding surface defined by me base of system 3 (Fig. 4.14a).
The base of the Pebbley Beach Formation has a palynological age of stage 3a (Evans
1991). The remaining parts of me depositional system have a stage 3b-4 palynological age
(Evans 1991). These deposits formed at me onset of the second tectonic phase which began at approximately 270 Ma (Late Sakmarian).
Between me initial extensional phase (represented by system 1) and the compressional foreland phase there is interpreted to be a period of passive thermal decay or sag (Fielding et al. 1990; Baker et al. 1993; Veevers et al. 1994b). Deposition of system 2 was initiated by me onset of this thermal sag phase along me length of me Sydney-Bowen Basin. This phase corresponds to phase B of Veevers et al (1994b) and stage 2 of Baker et al (1993).
Contemporaneous deposits in other parts of me Sydney Bowen Basin are me Rutherford and
Fairley Formations in me Hunter Valley, me Maules Creek Formation in me Gunnedah Basin and me lower Cattle Creek Formation in the Bowen Basin.
6.1.3 System 3 - Snapper Point - Wandrawandian marine shelf
Deposition of me Snapper Point Formation began following me major flooding and shoreline retreat represented by me Yarrunga Coal Measures. Shortly after me onset of this stage, the marine transgression represented by the Snapper Point Formation had drowned all me previous terrestrial environments in me southern Sydney Basin (Fig. 6.1c). This system was laterally extensive and was not restricted to palaeovalleys or sub-basins as for me previous two depositional systems. The Snapper Point Formation forms an eastward thickening lens. Fourth order eustatic sea level changes resulted in facies changes in me south-western part of me study area and parasequence development in the east. The central part of me study area represents a topographic basement high between two palaeovalleys incised by me previous depositional system. This area remained emergent for longer man other areas and as such was probably transgressed later by the shoreline. During sea level highstand deposition was characterised by
115 nearshore and shoreface sedimentation across the western parts of the basin and middle to outer shelf fine-grained sedimentation in me east. During periods of sea level fall braidplain deltas prograded eastward in me southwest with nearshore marine deposition ensuing in all other parts of the southern Sydney Basin. Five parasequences have been identified in the eastern area which combine to form an aggradational parasequence set (Fig. 6.3). Deposition of the shallow marine Snapper Point Formation was curtailed by a major flooding event which resulted in a cratonward facies shift and me deposition of the fine-grained offshore facies of me
Wandrawandian Siltstone (Fig. 6. Id). The Wandrawandian Siltstone contains the maximum flooding surface of the third order transgression that began at the base of system 2.
The Snapper Point - Wandrawandian marine shelf system abruptly overlies underlying systems where they are present (Figs. 6.2 - 6.4, 6.6b,c). Where underlying systems are absent this system overlies basement. The upper contact of this system is defined by the maximum flooding surface within me Wandrawandian Siltstone.
The Snapper Point Formation has a stage 3b-4 palynological age. The Thermal sag phase of Sydney Basin development is interpreted as occurring over the period 268 - 258 Ma
(Artinskian; Veevers et al. (1994b). The Snapper Point Formation was deposited during me early part of this phase. The Wandrawandian Siltstone has a stage 5 palynological age (Evans
1991).
The Sydney Basin is interpreted as compressional foreland basin during me Late Permian
(e.g. Battersby 1981; Schiebner 1993; Veevers et al. 1994b). The thermal sag phase therefore represents a transitional phase between early rifting during the Early Permian and compressional foreland loading during the Late Permian. Embryonic foreland basin sedimentation is normally comprised of deep water facies (Flemings & Jordan 1990; Allen et al. 1991; Cant & Stockmal
1993) reflecting the rapid flexure induced subsidence during the early stages of basin development. This type of sedimentation is common near me zone of maximum subsidence, adjacent to me active fold-thrust belt (Leckie and Smith 1992; Fig. 6.7). The absence of deep water facies, indicative of this phase within me southern Sydney Basin is probably due to the sequences being situated close to the cratonic margin or hinge zone of me basin (Fig. 6.7) where subsidence was not as great. Chronostratigraphically equivalent deep water facies were probably
116 located to the east and northeast and may be represented by the Manning Group in me New
England Fold Belt which is of Early Permian age and approximately 9 km thick, containing turbidite sequences (Jenkins 1990, 1992). Flexural loading may have actually begun during this early transitional phase. During me early stages of orogenesis the developing foreland is likely to lack topographical expression and may not be emergent above sea level. It is only when me foreland is significantly exposed above sea level mat the orogen may supply a significant amount of sediment to the basin (Cant & Stockmal 1993) and a signature of orogenesis will be recorded in me sedimentary succession. This makes it difficult to determine me time of transition from me passive thermal sag phase to the foreland compressional phase in me southern
Sydney Basin.
There are two major flooding events associated with me deposition of this system:
Flooding Event A: which bounds systems 2 and 3 and;
Flooding Event B: which forms me contact between the Snapper Point Formation and me
Wandrawandian Siltstone within system 3.
These flooding events represent two major cratonward facies shifts in an otherwise basically aggradational sedimentation regime. This is shown by the aggradational parasequence sets of system 2 and the Snapper Point Formation within system 3. This suggests mat for me most part sediment supply from me western cratonic margin was able to keep pace with me increase in accommodation space.
Whether me cause of flooding event A is tectonic related or eustatic related is difficult to determine. The event may have occurred too early in me development of me basin and may also be too rapid to invoke loading induced subsidence. Rapid flooding could have resulted from eustatic sea level change but a similar effect could be provided by a marked reduction in sediment supply which would accompany regional subsidence. There is good evidence mat me second flooding event (flooding event B) was me result of rapid subsidence associated with foreland loading. This is indicated by a distinct facies change which occurs within me Snapper
Point Formation. In lower parts of me formation, shoreface sedimentation is dominated by wave-generated structures such as hummocky cross-stratification (see section 4.4). Within me last parasequence, wave generated structures are absent and me shoreface is dominated by tidal
117 or longshore sand ridge facies. This implies a change from an open shelf setting to a tide- dominated constricted seaway, similar to the North Sea and English Channel (Johnson et al.
1982) respectively, during the last stages of Snapper Point deposition. It also marks a major shift in sediment dispersal direction from dominantly eastward (transverse to basin axis) to northward (parallel with basin axis) which is typical of mature foreland basins (Cant & Stockmal
1993). This constriction was probably caused by the emergence above sea level of the developing orogen to the east. Structural highs within me Gunnedah Basin were probably also transgressed by this time, allowing an open seaway between the southern Sydney Basin and me
Bowen Basin. The transgression which marked the onset of Snapper Point deposition is evident throughout me Sydney-Bowen Basin and is characterised by the Eurydesma fauna (Runnegar
1979). In me northern Sydney, Gunnedah and Bowen Basins, the marine facies of me Branxton,
Porcupine and Cattle Creek Formations respectively, were deposited. By me end of this stage, there was an open seaway along me length of me Sydney-Bowen Basin. In addition to this facies change, the Wandrawandian Siltstone contains a tuffaceous unit (see Runnegar 1980b) which is me first record of volcanism within me southern Sydney Basin. This confirms mat by
Wandrawandian time me orogen was emergent. The basin loading caused by this emergence correspond with me onset of me Hunter-Bowen Orogeny, which came to a climax much later
(255Ma; Fergusson & Leitch 1993).
Devlin et al. (1990) proposed a model for me sedimentary response to a loading event within a foreland basin (Fig. 6.8). The model suggests that mere is a time lag between me onset of flexural subsidence and me arrival of sediment from me newly uplifted and eroded orogen. Initial rapid flooding is associated with the onset of foreland loading and thus a transgressive system tract is produced. Subsequent erosion of me uplifted orogen during a later period of tectonic quiescence results in a highstand progradational system. This characteristic transgressive - regressive stratigraphic pattern is common on me active orogenic side of foreland basins (Flemings & Jordan 1990; Allen et al 1991; Cant & Stockmal 1993; Devlin et al 1993).
The orogen to me east of me southern Sydney Basin was probably not emergent until the deposition of me upper Snapper Point Formation and, as such, was not shedding any sediment to me cratonic side of me basin until me Late Permian. Initial sedimentation from an uplifted
118 foreland would be deposited close to me active orogenic margin. For this reason me foreland loading event which is interpreted to have caused flooding event B is not followed directly by a progradational clastic wedge derived from me orogen.
The thickness of the Snapper Point Formation is controlled by a north trending hinge zone (section 4.4) which is shown in Figure 4.25. Tectonic subsidence seems to have been much greater eastward of this zone. The hinge zone is located to on me eastern fault margin of the interpreted grabens and half grabens which acted as sub-basins for me Clyde Coal
Measures and Wasp Head Formation of system 1.
6.1.4 System 4 - Wandrawandian - Nowra progradational wedge
The transgressive sedimentation regime which characterised the previous depositional system ended with me maximum flooding surface within me Wandrawandian Siltstone. The onset of deposition of system 4 is marked by a change to a regressive or progradational depositional regime which culminated in me deposition of the shoreface sediments of the Nowra Sandstone
(Fig. 6.1e). Deposition during the early stages is characterised by fossiliferous, bioturbated siltstone (Wandrawandian Siltstone) which is interpreted as a shelf deposit. Mass flows derived from me west periodically deposited thick lobes of sand. Large dropstones and glendonites within me unit indicate mat cold climatic conditions prevailed and seasonal sea ice was present over me shelf.
As progradation proceeded and the shoreline advanced into me basin, a regressive sequence (Fig. 6. If) was deposited which consists of a coarsening upward shoreface succession
(lower half of Nowra Sandstone). The shoreface facies consists entirely of cross-bedded tide- dominated facies indicative of dispersal by longshore tidal currents. Sediment dispersal is dominantly towards me north-northeast, approximately parallel to me axis of me foreland basin.
The presence of this type of facies within me Nowra Sandstone indicates a continued constricted seaway, open to the north, which became evident in me upper Snapper Point Formation. The preserved sandstone body thickens towards me east from me cratonic margin in me western part of the study area. The maximum progradation of this clastic wedge into the basin is probably represented by the approximate position of the present coastline in me vicinity of Nowra where
119 the formation rapidly attenuates towards the east. At Crookhaven Heads and Penguin Head the
Nowra Sandstone facies is thin and typical of the lower shoreface.
The lower boundary for this system is the maximum flooding surface contained within me Wandrawandian Siltstone (Fig. 6.3). In me northwestern part of the area the Wandrawandian
Siltstone is non-existent and the boundary is marked by an erosion surface between the Nowra
Sandstone and Snapper Point Formation (Fig. 6.6c). The upper boundary is marked by a ravinement surface (Purnoo Conglomerate Member) which is interpreted as the start of the next major transgressive sequence.
The Wandrawandian Siltstone, Nowra Sandstone and Berry Siltstone all have a palynological age of stage 5 (Evans 1991). A tuffaceous layer near me top of me
Wandrawandian Siltstone has an age of 260 Ma (Veevers et al. 1994b). This age conflicts with the 260 Ma date obtained from the Bumbo Latite Member (Carr 1984) within me lower
Broughton Formation. An age of 260 Ma for the lower Broughton Formation seems to be more consistent with me other ages obtained from me Gerringong Volcanics. This suggests that me
Berry Siltstone has a minimum age of 260 Ma.
The Nowra Sandstone represents a progradational clastic wedge derived from me cratonic margin of me basin. Veevers et al. (1994a) interpreted this progradation from me cratonic margin as me result of uplift within the Lachlan Fold Belt. The uplift of the fold belt was probably caused by me rise of a forebulge or foreswell at the cratonic margin associated with loading at me orogen. In me Alberta Basin, Plint et al. (1993) found mat the rise of the forebulge resulted in an extensive erosion surface which extended into me basin and was overlain by a progradational shoreface sandstone body. The Nowra Sandstone has a gradational contact with me underlying Wandrawandian siltstone at most locations. If this basal erosional surface did exist, it was probably located at the base of correlative units to the west of the present exposure within basin and has been subsequently removed by post-Permian erosion.
Progradation probably resulted from erosion of the forebulge during a period of tectonic quiescence which followed me foreland loading represented by flooding event B. It is interesting to note mat a progradational system does follow me interpreted foreland loading event. In this sense the succession above flooding event B does conform to me Devlin et al.
120 (1990) model for sedimentary response to a foreland accretion event. In me case of me Nowra
Sandstone however, me progradational clastic wedge is derived from the cratonic margin and not me uplifted orogen.
The same progradational episode is represented in me northern Sydney Basin by me
Muree Sandstone. The Nowra Sandstone has probably correlates with the Porcupine Formation in me Gunnedah Basin and me upper Cattle Creek Formation or me Aldebaran Formation in me
Bowen Basin. In all cases me Nowra Sandstone correlates with marine formations suggesting that an open seaway existed along me length of me Sydney-Bowen Basin.
6.1.5 System 5 - Upper Nowra - Berry transgressive shelf
Following me progradation of the lower Nowra Sandstone me upper part of me formation was deposited under a transgressive depositional regime. Following shoreline retreat, sedimentation returned to middle to outer shelf sedimentation represented by the Berry Siltstone (Fig 6.If).
The upper part of the Nowra Sandstone represents a west-thickening clastic wedge.
The lower boundary of this depositional system is defined by a ravinement surface which is represented by me Purnoo Conglomerate Member (Fig. 6.3). This ravinement surface represents a type 2 sequence boundary (Van Wagoner et al. 1988) using sequence stratigraphic terminology. The upper boundary is the maximum flooding surface within me Berry Siltstone.
The flooding event C and the resultant transgression which marks me onset of this stage of deposition probably represents a rapid increase in subsidence caused by foreland accretion.
The volcanic units represented by the Gerringong Volcanics of me Broughton Formation probably herald the beginning of me foreland compressional stage (Phase C of Veevers et al.
1994b; stage 3 of Baker et al 1993; Fig. 1.3).
The transgressive event, which culminated in me Berry Siltstone, has correlative units within the northern Sydney Basin and the Gunnedah Basin. These units are the Mulbring
Siltstone in me northern Sydney Basin and me lower Watermark Formation (Tadros 1993b) in the Gunnedah Basin.
121 6.2 Hierarchy of sea-level change
Three scales of sea-level change are recognised within me southern Sydney Basin succession.
These changes are interpreted asfifth, fourth and third order cycles (Vail et al. 1977). The periodicity of the cycles is difficult to determine due to a lack of definite age control,
Biostratigraphically (Dickins et al 1969) suggests an age range from approximately the middle of the Sakmarian to the base of Kungurian (approximately 275 to 260 Ma) for the deposition of me sequence from me base of the Wasp Head Formation to the top of the Nowra Sandstone.
The earliest date obtained from me igneous units of the Gerringong Volcanics at the top of me
Shoalhaven Group is also 260 Ma (Carr 1984). This places a minimum age constraint on the lower part of the Shoalhaven Group. In most cases the order of the cycles is recognised on me basis of relative cycle thickness.
6.2.1 Third order cyclcity
Third order cycles have durations of 1 - 10 Ma which corresponds with the longest period of cycle identified within the Talaterang and Shoalhaven Groups. The third order trend is shown in Figure 6.9. Two cycles are recognised. The first started at the base of me Shoalhaven
Group. The lower half of thisfirst cycle was broadly transgressive until a maximum flooding surface within the Wandrawandian Siltstone. The upper half of me cycle was regressive and culminated in me deposition of the progradational wedge of me Nowra Sandstone. The ravinement surface that caps me Nowra Sandstone formed the boundary between me lower and upper cycles. Only the lower half of me second cycle is included within this study. It comprises a transgressive sequence which ended with a maximum flooding surface within me
Berry Siltstone.
The relative effects of eustatic and tectonic components must be determined. The Early
Permian coincided with a eustatic transgression associated with me melting of a major ice sheet which existed during me Late Carboniferous and Early Permian (Veevers & Powell 1987) and is recorded in me sedimentary record across equivalent Early Permian basins of South Africa,
South America and Antarctica. Ross and Ross (1988) identified approximately 6 transgressive and regressive sequences on me worlds stable cratonic shelves during me period 280 - 260 Ma
122 (Sakmarian-Artinskian). In addition to these eustatic effects this period of deposition in me
Sydney Basin coincided with phases of rifting, thermal sag and incipient foreland flexure. It would be extremely difficult, if not impossible to determine accurately the relative contribution of tectonic and eustatic effects to 3rd order cyclicity. Basin subsidence is likely to have been active throughout deposition of the Talaterang and Shoalhaven Groups and was probably acting in concert with a general eustatic sea level rise. There is evidence that at least one of me major flooding events resulted from foreland loading. In general, tectonic affects seem to have had a dominant influence on deposition in me southern Sydney Basin.
Large intervals of me Sydney Basin sequence are characterised by an aggradational sedimentation pattern, as is the situation with systems 2 and 3. This indicates mat sediment supply kept pace with me rate of relative sea level rise. This sea level rise was probably related primarily to basin subsidence. Flooding event A, which formed the contact between systems
2 and 3, was probably related to a sharp decrease in sediment supply related to regional subsidence. The two following flooding events are interpreted to have been caused by foreland accretion events. The sedimentation pattern which followed these events is consistent with this interpretation. Flooding event A results in a rapid increase in subsidence and a major cratonward facies shift. A period of tectonic quiescence followed which allowed sediment supply to outpace me rate of increase in accommodation space. This resulted in me progradation of a clastic wedge (me Nowra Sandstone) from me cratonic margin. Renewed foreland accretion caused a third flooding event (flooding event C) and another cratonward facies shift.
In conclusion it seems likely that me observed third order cyclicity is dominated by tectonic effects. Flooding events B and C are sedimentary signatures of tectonic activity in me embryonic foreland basin.
6.2.2 Fourth and Fifth order cycles
Fourth order cyclicity has been identified within me Wasp Head Formation, me Yadboro and
Tallong Conglomerates, the Pebbley Beach Formation and me Snapper Point Formation. These cycles are manifested as facies changes within vertical sections and by parasequence deposition
123 in marine systems. Parasequences combine to form parasequence sets which comprise genetically related parasequences with distinctive stacking patterns (Mitchum & Van Wagoner
1991). Evidence from the Pebbley Beach Formation (section 4.3) suggests that these cycles were generated by Milankovitch orbital forcing mechanisms. The periodicity of fourth order cycles is difficult to determine due to a complete lack of adequate time constraints. This problem deems it virtually impossible to determine the difference between fourth and fifth order cycles within me succession. Fifth order cycles have only been definitively located within me
Pebbley Beach Formation. The cycles are manifested as alternations between massive siltstone
(representing periods of total ice cover) and diamictite (periods of seasonal ice cover, characterised by dropstone facies). This sequence has already been discussed (section 4.3) and is interpreted as a low periodicity orbitally forced sequence with a duration in me order of 0.01 to 0.1 Ma. It is inferred that the climate changes associated with these facies occur contemporaneously with small scale sea-level changes. Small scale cyclical facies changes within me Snapper Point Formation may also be fifth order cycles. Figure 4.33b shows me sequence at Mermaids Inlet, Jervis Bay. Within this succession mere is a clear change from amalgamated sandstone beds at me bottom of the photograph to a more silt dominated interval within me same general facies. This change is probably due to a small rise in relative sea level which could be attributed to fifth order cyclicity. Recognition of these low order cycles is difficult because of the nature of the sedimentary environment which is dominated by storm event beds. It is clear mat high frequency cycles are present within me succession but they are difficult to define. Numerous cycles of various periodicities have been identified in other
Permian sequences (Borer & Harris 1991; Yang & Baumfalk 1994). For example, Yang and
Baumfalk (1994) identified Milankovitch (1941) periodicities of 100, 67, 44.3, 35.1, 30 and 21 ka for cycles within me Early Permian Upper Rotliegend Group of Greenland.
This fourth and fifth order cyclicity is a eustatic effect which overprints me third order cyclcity (Fig. 6.9) previously interpreted as a dominantly tectonic affected cycle.
6.3 Global Implications
The tectonic stages recognised by Veevers et al (1994a) and Baker et al (1993) are evident
124 throughout the Permian - Triassic Pangean basins which are exposed in Antarctica, South Africa and South America (Veevers et al. 1994b). In me South African Carboniferous to Triassic
Karoo Basin me extensional and thermal sag stages are represented by the Dwyka Formation and the Ecca Groups, respectively. The Dwyka Formation was deposited during me Late
Carboniferous to Early Permian and consists of glacial pavements and diamictite facies (Visser
& Loock 1988; Visser 1990). These deposits correspond with the Late Palaeozoic glaciation which affected much of Gondwana (Veevers & Powell 1987) and are also evident in Antarctica and South America (Eyles et al. 1993; Collinson et al 1994; L6pez-Gamundi et al. 1994).
During the Early Permian, following me collapse of the Late Carboniferous ice sheet (Visser
1991), a major marine transgression occurred, probably caused by combined basin subsidence and eustatic sea level rise. As a result of this transgression me shallow marine sands of me
Ecca Group were deposited. Coal measure sequences associated with a deltaic progradation (me
Vryheid Formation) have a palynological stage 3b age (Milsteed 1994) which correlates in age
(Evans 1991) with me Pebbley Beach to Snapper Point Formations in the southern Sydney
Basin. This period is marked by probable climatic and sea level changes associated with fourth order Milankovitch (1941) cyclicity (see section 4.1, 4.3, 4.5, 6.1) within these two formations in me Shoalhaven Group. This Milankovitch (1941) cyclicity may be an important control in me development of contemporaneous successions throughout Gondwana. In particular it may
control the development of coal seams within carbonaceous sequences such as those described by Cairncross and Cadle (1988) from the Early Permian Vryheid Formation, as has been
demonstrated in me Late Permian Coal bearing sequences in me southern Sydney Basin (Arditto
1991). The transgression represented by the Shoalhaven Group in the southern Sydney Basin
correlates with a major diachronous transgression which affected most of the Pangean Permian
basin (Veevers et al. 1994c). The transgression is marked by the presence of the cold water
Eurydesma fauna throughout Gondwana (Runnegar 1979; Dickins 1984). Cold climate in eastern
Australia seems to have remained well into the Permian as indicated by ice rafted debris and
glendonites within me Wandrawandian Siltstone and niawarra Coal Measures. The reason for
this is related to the palaeolatitude of eastern Australia during the Early Permian. The polar
125 wander path on figure 1.7 (from Crowell and Frakes 1973) shows the pole migrated from southern Africa in the Early Carboniferous to eastern Antarctica, in close proximity to Australia, during the Early Permian. The migration of the pole explains the presence of the extensive glacial deposits of me Dwyka Formation in South Africa during me Early Carboniferous and their absence during me Early Permian in me same area. The presence of Eurydesma fauna may also reflect the movement of me polar region during me Late Carboniferous to Early
Permian as it is associated with cold water conditions. It also explains why cold climate persisted far into me Permian within eastern Australia.
126 7.0 CONCLUSIONS
The Talaterang and Shoalhaven Groups of me southern Sydney Basin are an Early Permian
(Sakmarian to Kungurian) succession which was deposited close to the cratonic margin of a retro-arc to foreland basin.
7.1 Stratigraphic conclusions a) The Permian Talaterang and Shoalhaven Groups form me basal part of me Sydney Basin succession at its southernmost extremity. Although me Group names of pre-existing stratigraphic models have been retained, recent detailed field mapping has necessitated me rearrangement of formations within these groups. This new stratigraphic model forms the framework for a new tectonic model for me southern Sydney Basin, which conforms with recent tectonic models constructed for other parts of me Sydney-Bowen Basin.
b) Based on stratigraphic and sedimentological evidence me Clyde Coal Measures and Wasp
Head Formation have been assigned to the Talaterang Group. The term Pigeon House Creek
Siltstone has been abandoned and this unit should be incorporated into me Clyde Coal Measures.
Sandstone - siltstone successions with abundant carbonaceous matter and few burrows at this basal stratigraphic level should be considered as part of me Clyde Coal Measures. Similarly, sandstone - siltstone successions with associated diamictite and breccia beds and abundant bioturbation should be considered part of me Wasp Head Formation.
c) The Yadboro and Tallong Conglomerates (and equivalents) have been assigned to me
Shoalhaven Group which also includes the Yarrunga Coal Measures, me Pebbley Beach
Formation, me Snapper Point Formation, me Wandrawandian Siltstone and me Nowra Sandstone.
7.2 Sedimentological conclusions a) Five depositional systems have been recognised within the Talaterang and Shoalhaven Groups.
127 b) Depositional system 1 comprises the units of the Talaterang Group. The Clyde Coal
Measures is interpreted as being deposited within a mud-rich alluvial environment, possibly characterised by an anastomosing fluvial style. Sediment dispersal within me formation was directed towards the north. A transgression is represented by estuarine facies at the top of the succession. The Wasp Head Formation was deposited within a shallow marine environment.
Thick Breccia units near me base of me formation are interpreted as being derived from a north- trending tectonically active slope.
c) Depositional system 2 comprises the Tallong and Yadboro Conglomerates, the Pebbley Beach
Formation and the Yarrunga Coal Measures. The Tallong and Yadboro Conglomerates are interpreted as high energy braidplain successions, forming a part of a semi-continuous west- derived sheet, concentrated within palaeovalleys. The Yarrunga Coal Measures and Pebbley
Beach Formation are interpreted as fluvial to coastal deposits which fringed the high energy braidplains represented by me Tallong and Yadboro Conglomerates. The Yarrunga Coal
Measures retreated over these braidplains in response to a major transgression, depositing a thin, fine-grained, carbonaceous interval. The Pebbley Beach Formation is a shallow marine to coastal formation. Coastal deposits are dominated by backbarrier and tidal channel facies but also include some deepwater facies. The presence of diamictite units and glendonites within interpreted glacial phases suggests that eustatic sea level changes accompanied me climatic changes responsible for me 4m and 5th order cycles. This system forms a aggradational to slightly progradational parasequence set. The Yarrunga Coal Measures was deposited during a major flooding event which resulted in me deposition of the Snapper Point Formation over the entire southern basin.
d) Depositional system 3 comprises me Snapper Point Formation and the lower part of the
Wandrawandian Siltstone. The Snapper Point Formation is dominated by shallow marine facies.
Fourth order eustatic sea level fluctuations resulted in distinct facies changes in me south west and parasequence development in me east. The presence of a north trending basinal hinge zone resulted in a rapid increase in thickness of me Snapper Point Formation to me east of me study
128 area. This hinge zone also controlled facies distribution. The top of the Snapper Point
Formation is marked by a second major flooding event which resulted in me deposition of the offshore to shelfal Wandrawandian Siltstone.
e) Depositional system 4 represents a progradational or regressive sequence which culminated in me deposition of a shoreface sandbody of the lower Nowra Sandstone which was influenced by longshore tidal activity. The top of this system is defined by a transgressive ravinement surface (me Purnoo Conglomerate).
f) Depositional system 5 is a transgressive sequence which resulted in me deposition of me
Berry Siltstone. The flooding event which culminated in me maximum flooding surface within the Berry Siltstone was the final flooding event within me lower Shoalhaven Group.
7.3 Petrographic Conclusions a) Most samples plot on QFL diagrams as sublitharenite using me classification scheme of Folk et al. (1970). The petrology of me Talaterang and Shoalhaven reflects derivation from a recycled orogen provenance field (Dickinson et al. 1983) which in this case coincides with me
Early Palaeozoic Lachlan Fold Belt. The petrology reflects deposition during early extensional and thermal sag tectonic phases as defined by Baker et al. (1993).
7.4 Tectonic Conclusions a) Two distinct tectonic phases are recognised within me southern Sydney Basin succession.
These phases conform to phases A and B as outlined by Veevers et al (1994b) and coincide with me stratigraphic group divisions as redefined herein. An initial extensional phase is represented by me sediments of the Talaterang Group which were deposited within fault bounded sub-basins. The second period of tectonic development represented by me Shoalhaven Group was deposited during a thermal sag or embryonic foreland basin phase.
b) The Clyde Coal Measures and the Wasp Head Formation are interpreted as being deposited
129 within grabens or half grabens related to an Early phase of extension which has been widely documented elsewhere in the Sydney-Bowen Basin. This interpretation is based on sedimentological and stratigraphic evidence and, in addition, the formations compare favourably with other deposits of the same origin elsewhere in me basin.
c) Three distinct flooding events are recognised. There is good evidence that the second and third flooding events (B and C) were the result of an increased subsidence rate due to foreland accretion at me orogen. This loading may indicate the onset of the Hunter-Bowen Orogeny which climaxed much later during me Late Permian.
d) A change to longshore tidal facies near the top of the Snapper Point Formation and the presence of a tuffaceous layer within me Wandrawandian Siltstone suggest mat the orogen became emergent at this time. It also represented a change from transverse to longitudinal sediment dispersal within me basin.
e) The progradational sequence which resulted in the deposition of me Nowra Sandstone probably represents a period of tectonic quiescence and a possible increase in sediment supply provided by uplift of me forebulge in me cratonic margin of the foreland basin.
f) Three orders of sea level change are recognised within the Talaterang and Shoalhaven Groups.
Third order change is interpreted as dominantly tectonically controlled. Fourth and fifth order changes are interpreted as eustatic sea level changes which were driven by Milankovitch orbital forcing mechanisms. Fourth and fifth order sea level changes are superimposed on me larger and longer third order changes.
130 REFERENCES
ALGEO T.J. & WILKINSON B.H. 1988. Periodicity of mesoscale Phanerozoic sedimentary cycles and me role of Milankovitch orbital modulation. Journal of Geology 96, 313-322.
ALLEN G.P. 1991. Sedimentary processes and facies in the Gironde estuary: a recent model for macrotidal estuarine systems. In Smith D.G., Zaitlin B.A. and Rahmani R.A. eds. Clastic Tidal environments. Canadian Society of Petroleum Geologists. Memoir 16. 29-40.
ALLEN J.R.L. 1963. The classification of cross-stratified units, with notes on their origin. Sedimentology 2, 93-114.
ALLEN J.R.L 1965. A review of me origin and characteristics of recent alluvial sediments. Sedimentology 5, 89-191.
ALLEN J.R.L. 1983. Studies in fluviatile sedimentation: bars, bar complexes and sandstone sheets (low sinuosity braided streams) in me Brownstones (L. Devonian), Welsh Borders. Sedimentary Geology 33, 237-293.
ALLEN J.R.L. 1993. Sedimentary Structures: Sorby and me last decade. Journal of the Geological Society, London 150, 417-425.
ALLEN P.A. & HOMEWOOD P. 1984. Evolution and mechanics of a Miocene tidal sandwave. Sedimentology 31, 63-81.
ALLEN P.A. & UNDERHILL J.R. 1989. Swaley cross-stratification produced by unidirectional flows, Bencliff Grit (Upper Jurassic), Dorset, UK. Journal of the Geological Society of London 146. 241-252.
ALLEN P.A., CRAMPTON S.L. & SINCLAIR H.D. 1991. The inception and early evolution of me North Alpine Foreland Basin, Switzerland. Basin Research 3, 143-163.
ALLEY R.B., BLANKENSHIP D.D., ROONEY ST. & BENTLEY C.R. 1989. Sedimentation beneath ice shelves - the view from ice stream B. Marine Geology 85, 101-120.
ANDERSON R.Y. 1982. A long geoclimatic record for me Permian. Journal of Geophysical Research 87, 7285-7294.
ARDITTO P.A. 1991. A sequence stratigraphic analysis of the Late Permian succession in me Southern Coalfield, Sydney Basin, New South Wales. Australian Journal of Earth Sciences 38, 125-137.
ARNOTT R.W.C. 1995. The parasequence definition-are transgressive deposits inadequately addressed? Journal of sedimentary research B65, 1-6.
BAKER J.C., FIELDING C.R., DE CARITAT P. & WILKINSON M.M. 1993. Permian evolution of sandstone composition in a complex back-arc extensional to foreland basin: me Bowen Basin, eastern Australia. Journal of Sedimentary Petrology 63. 881-893.
BAMBERRY W.J. 1991. Stratigraphy and sedimentology of me Late Permian Illawarra Coal Measures, Southern Sydney Basin, New South Wales. PhD thesis, University of Wollongong, Wollongong (unpubl.).
BAMBERRY W.J., CLARK N.R. & SINELNIKOV A.V. 1995. Basement morphology and structure - Surat Basin in New South Wales. In: Proceedings of the 29th Symposium on advances in the study of the Sydney Basin, pp.253-260. University of Newcastle, Newcastle.
131 BANN K.L. 1990. Sedimentology and diagenesis of the Early Permian Snapper Point Formation, southern Sydney Basin, New South Wales. BSc(Hons) thesis, University of Wollongong, Wollongong (Unpubl.).
BANN K.L. in prep. Ichnology and sedimentology of the Pebbley Beach and Snapper Point Formations, southern Sydney Basin, New South Wales. PhD thesis, University of Wollongong, Wollongong (unpubl.).
BARTSCH-WINKLER S. & SCHMOLL H.R. 1984. Bedding types in Holocene tidal channel sequences, Knick arm, upper Cook Inlet, Alaska. Journal of Sedimentary Petrology 84, 1239- 1250.
BATTERSBY D.G. 1981. New discoveries in me Surat/Bowen Basin. APEA Journal 21, 39- 44.
BEMBRICK C.S. & HOLMES G.G. 1971. Preliminary report on DM Callala DDH 1. Quarterly Notes Geological Survey of New South Wales 4, 1-3.
BEMBRICK C.S. & HOLMES G.G. 1976. An interpretation of the subsurface geology of the Nowra-Jervis Bay area. Records of the Geological Survey of NSW 18.
BERGER A., LOUTRE M.F. & DEHANT V. 1989. Astronomical frequencies for pre- Quaternary paleoclimate studies. Terra Nova 1, 474-479.
BORER J.M. & HARRIS P.M. 1991. Lithofacies and cyclicity of the Yates Formation, Permian Basin: Implications for reservoir heterogeneity. American Association of Petroleum Geologists Bulletin 75, 726-779.
BOYD R. & HONIG C. 1992. Estuarine sedimentation on me Eastern Shore of Nova Scotia. Journal of Sedimentary Petrology 62, 569-583.
BRENCHLEY P.J., PICKERJLL R.K. & STROMBERG S.G. 1993. The role of wave reworking on me architecture of storm sandstone facies, Bell Island Group (Lower Ordovician), eastern Newfoundland. Sedimentology 40. 359-382.
BRIDGES P.H. 1982. Ancient offshore tidal deposits. In: Stride A.H. ed. Offshore Tidal Sands. Chapman and Hall, pp. 172-192.
BRUUN P. 1962. Sea level rise as a cause of shore erosion. American Society of Civil Engineers, Proceedings of Water Harbours Division 88, 117-130.
BRYANT I.D. 1983. Facies sequences associated with some braided river deposits of Late Pleistocene age from Southern Britain. In Collinson J.D. & Lewin J. eds. Modern and ancient fluvial systems. International Association of Sedimentologists Special Publication 6, 267- 275.
CAIRNCROSS B & CADLE A.B. 1988. Depositional environments of me coal bearing Permian Vryheid Formation in me east Witbank Coalfield, South Africa. South African Journal of Geology 91, 1-17.
CALDER J.H. & GIBLING M.R. 1994. The Euramerican Coal Province: controls on Late Paleozoic peat accumulation. Palaeogeography, Palaeoclimatology, Palaeoecology 106, 1- 21.
CANT D.J. 1980. Storm-dominated shallow marine sediments of the Arsaig Group (Silurian- Devonian) Nova Scotia. Canadian Journal of Earth Sciences 17. 120-131.
132 CANT D.J. & WALKER R.G. 1976. Development of a braided river facies model for the Devonian Battery Point Sandstone, Quebec. Canadian Journal of Earth Sciences 13, 102- 119.
CANT D.J. & STOCKMAL G.S. 1993. Some controls on sedimentary sequences in foreland basins: examples from the Alberta Basin. In: Frostick L.E. & Steel R.J. Tectonic controls and signatures in sedimentary successions. International Association of Sedimentologists Special Publication 20., 49-65.
CAREY J. 1978. Sedimentary environments and trace fossils of me Permian Snapper Point Formation, southern Sydney Basin. Journal of the Geological Society of Australia 25, 433- 458.
CARR P.F. 1984. The Late Permian Shoshonitic Province of the southern Sydney Basin. PhD thesis, University of Wollongong, Wollongong (unpubl.).
CARR P.F., JONES B.G. & MIDDLETON R.G. 1989. Precursor and formation of Glendonites in die Sydney Basin. Australian Mineralogist 4, 3-12.
CHANG-SHU Y. & JAI-SONG S. 1988. Tidal sand ridges on me east China Sea shelf. In: de Boer P.L., van Gelder A. & Nio S.D. Tide influenced sedimentary environments and facies. pp. 23-38. D.Reidel Publishing Company.
CHEEL R.J. 1991. Grain Fabric in hummocky cross-stratified storm beds: genetic implications. Journal of Sedimentary Petrology 61, 102-110.
CHEEL R.J. & LECKJE D.A. 1992. Coarse grained storm beds of me Upper Cretaceous Chungo Member (Wapiabi Formation), Southern Alberta, Canada. Journal of Sedimentary Petrology 62, 933-945.
CLIFTON H.E. 1969. Beach lamination-nature and origin. Marine Geology 7, 553-559.
CLIFTON H.E. 1983. Discrimination of subtidal and intertidal facies in Pleistocene deposits, Willapa Bay, Washington. Journal of Sedimentary Petrology 53, 353-369.
CLIFTON H.E. 1988. Sedimentologic approaches to palaeobathymetry, with applications to me Merced Formation of central California. Palaios 3, 507-522.
CLIFTON H.E. & PHILLIPS R.L. 1980. Lateral trends and vertical sequences in estuarine sediments, Willapa Bay, Washington. In: Field M.W., Bouma A.H., Colburn LP., Douglas R.G. & Ingle J.C. eds. Quaternary depositional environments of the Pacific Coast. Pacific section of Society of Economic Paleontologists and Mineralogists, Pacific Coast Palaeography Symposium No.4, 55-77.
COLLINSON J.D. & THOMPSON D.B. 1989. Sedimentary Structures. Unwin Hyman Ltd.
COLLINSON J.W., ISBELL J.L., ELLIOT D.H., MILLER M.F. & MILLER J.M.G. 1994. In Veevers J.J. & Powell C.McA. Permian-Trias sic Pangean Basins and foldbelts along the Panthalassan Margin of Gondwanaland. Geological Society of America Memoir 184. 173- 222.
CONAGHAN P.J. & JONES J.G. 1975. The Hawkesbury Sandstone and me Brahmaputra: A depositional model for the continental sheet sandstones: Journal of the Geological Society of Australia 22, 275-283.
CONDON M.A. 1969. Coonemia No.l well completion report. Genoa Oil NL. (Unpubl.).
133 CRADDOCK C. 1970. Geologic maps of Antarctica. In Bushnell V.C. & Craddock C eds. Antarctic Map Folio Series, Folio 12. American Geological Society, New York.
CRAFT J.H. & BRIDGE J.S. 1987. Shallow-marine sedimentary processes in me Late Devonian Catskill Sea, New York State. Geological Society of America Bulletin 98, 338-355.
CROWELL J.C. & FRAKES L.A. 1975. The Late Palaeozoic Glaciation. In Campbell K.S.W. ed. Gondwana Geology. Australian National University Press, Canberra, pp. 313-331.
DALYRIMPLE R.W. 1984. Morphology and internal structure of sandwaves in the Bay of Fundy. Sedimentology 31, 365-382.
DALYRIMPLE R.W. 1992. Tidal Depositional Systems. In Walker R.G. & James N.P. eds. Facies Models: Response to sea level change (2nd edition). Geological Association of Canada.
DALYRIMPLE R.W., KNIGHT R.J., ZAITLIN B.A. & MIDDLETON G.V. 1990. Dynamics and facies model of a macrotidal sand-bar complex, Cobequid Bay - Salmon River Estuary (Bay of Fundy). Sedimentology 37, 577-612.
DALYRIMPLE R.W., ZAITLIN B.A. & BOYD R. 1992. Estuarine facies models: conceptual basis and stratigraphic implications. Journal of Sedimentary Petrology 62. 1130-1146.
DAVID T.W.E. & STONIER G.R. 1891. Report on coal-measures of Shoalhaven District and on bore near Nowra. Annual Report Department of Mines NSW for 1890, 244-255.
DECELLES P.G. 1987. Variable preservation of Middle Tertiary, coarse-grained, nearshore to outer-shelf storm deposits in southern California. Journal of Sedimentary Petrology 57, 250- 264.
DECELLES P.G. & CAVAZZA W. 1992. Constraints on me formation of Pliocene hummocky cross-stratification in Calabria (southern Italy) from consideration of hydraulic and dispersive equivalence, grain-flow theory, and suspended-load fallout rate. Journal of Sedimentary Petrology 62. 555-568.
DE DECKER R.H. 1988. The wave regime on me inner shelf south of me Orange River and its implications for sediment transport. South African Journal of Geology 91, 358-372.
DEHGHANI M.H. 1994. Sedimentology, genetic stratigraphy and depositional environment of the Permo-Triassic succession in me southern Sydney Basin, Australia. PhD thesis, University of Wollongong, Wollongong (unpubl.).
DE RAAF J.F.M., BOERSMA J.R. & VAN GELDER A. 1977. Wave-generated structures and sequences from a shallow marine succession, Lower Carboniferous, County Cork, Ireland. Sedimentology 24, 451-483.
DEVLIN W.J., RUDOLPH K.W., EHMAN KD. & SHAW C.A. 1990. The effect of tectonic and eustatic cycles on accommodation and sequence stratigraphic framework in me southwestern Wyoming foreland basin (abstr.) 13th International Sedimentological Congress, Nottingham, England, p. 131.
DEVLIN W.J., RUDOLPH K.W., SHAW C.A. & EHMAN KD. 1993. The effect of tectonic and eustatic cycles on accommodation and sequence-stratigraphic framework in me Upper Cretaceous foreland basin of southwestern Wyoming. In Posamentier H.W., Summerhayes C.P., Haq B.U. & Allen. Sequence stratigraphy and facies associations. Special Publication International Association of Sedimentologists 18. 501-520.
134 DICKINS J.M. 1984. Evolution and climate in the Upper Palaeozoic. In: Brenchley P. Fossils and Climate. John Wiley & Sons Ltd, pp.317-327.
DICKINS J.M., GOSTIN V.A. & RUNNEGAR B. 1969. The age of me Permian sequence in the southern part of the Sydney Basin. In: Campbell K.S.W. (ed.) Stratigraphy and Palaeontology. Essays in honour of Dorothy Hill, pp. 211-255. Australian University Press, Canberra.
DICKINSON W.R. & SUCZEK C.A. 1979. Plate Tectonics and sandstone compositions. American Association of Petroleum Geologists Bulletin 63, 2164-2182.
DICKINSON W.R., BEARD L.S., BRAKENRIDGE G.R., ERJAVEC J.L., FERGUSON R.C., INMAN K.F., KNEPP R.A., LINDBERG FA. & RYBERG P.T. 1983. Provenance of North American Phanerozoic sandstones in relation to tectonic setting. Geological Society of America Bulletin 94, 222-235.
DIESSEL C.F.K. 1992. Coal bearing depositional systems. Springer-Velag. Berlin, New York.
DOMINGUEZ J.M.L. & WANLESS H.R. 1991. Facies architecture of a falling sea-level strandplain, Doce River coast, Brazil. In: Swift D.J.P. & Oertel G.F. eds. Shelf sand and sandstone bodies. Special Publication International Association of Sedimentologists 14. 259- 282.
DOTT R.H. & BOURGEOIS J. 1982. Hummocky stratification: Significance of its variable bedding sequences. Geological society of America Bulletin 93, 663-680.
DRAPER J.J. & BEESTON JW. 1985. Depositional aspects of the Reids Dome Beds, Denison Trough. Queensland Government Mining Journal 86. 200-210.
DRIESE S.G., FISCHER M.W., EASTHOUSE K.A., MARKS GT, GOGOLA A.R. & SCHONER A.E. 1991. Model for genesis of shoreface and shelf sandstone sequences, southern Appalachians: palaeoenvironmental reconstruction of an Early Silurian shelf system. In: Swift D.J.P. & Oertel G.F. eds. Shelf sand and sandstone bodies. Special Publication International Association of Sedimentologists 14. 309-338.
DUKE W.L. 1985. Hummocky cross-stratification, tropical hurricanes and intense winter storms. Sedimentology 32, 167-194.
DUKE W.L., ARNOTT R.W.C. & CHEEL R.J. 1991. Shelf sandstones and hummocky cross- stratification: New insights on a stormy debate. Geology 19, 625-628.
EBERTH D.A. & MIALL A.D. 1991. Stratigraphy, sedimentology and evolution of a vertebrate- bearing, braided to anastomosedfluvial system, Cutler Formation (Permian-Pennsylvanian), north-central New Mexico. Sedimentary Geology 72. 225-252.
ELECTRICITY COMMISSION. 1986. Geological report southern part of the Sydney Basin and author Authorisation No. 234 (Clyde River - Nowra Area). Development Division Report No. DE 272.
ELLIOT. 1974. Interdistributary bay sequences and their genesis. Sedimentology, 21, 611-622.
ELLIOT T. 1986. Siliclastic Shorelines. In: Reading H.G. ed. Sedimentary environments and facies. Blackwell Scientific Publications, pp. 155-188.
EVANS P.R. 1991. Early Permian palaeogeography of me southern Sydney Basin. In: Proceedings of the 25th Symposium on advances in me study of me Sydney Basin, pp.202- 206. University of Newcastle, Newcastie.
135 EVANS P.R., SEGGIE R.J. & WALKER M.J. 1983. Early Permian stratigraphy and palaeogeography, southern Sydney Basin. In: Proceedings of the 17th Symposium on Advances in the Study of me Sydney Basin, additional programme information. University of Newcastle, Newcastle.
EXON N.F. 1974. The geological evolution of the southern Taroom trough and the overlying Surat Basin. The APEA Journal 14, 50-58.
EYLES C.H., EYLES N. & FRANCA A.B. 1993. Glaciation and tectonics in an active intracratonic basin: me Late Palaeozoic Harare" Group, Parana" Basin, Brazil. Sedimentology 40, 1-26.
FACER R.A. & CARR P.F. 1979. K-Ar dating of Permian and Tertiary igneous activity in the southeastern Sydney Basin, New South Wales. Journal of the Geological Society of Australia 26, 73-79.
FERGUSSON C.L. & LEITCH E.C. 1993. Late Carboniferous to Early Triassic Tectonics of the New England Fold Belt, eastern Australia. New England Orogen '93 Conference Proceedings, 53-57.
FIELDING C.R. 1984. Upper Delta Plain lacustrine and fluviolacustrine facies from me Westphalian of the Durham coalfield, NE England. Sedimentology 31, 547-567.
FIELDING C.R. 1985. Coal depositional models and the distinction between alluvial and delta plain environments. Sedimentary Geology 42. 41-48.
FIELDING C.R. 1989. A tide- and wave- moulded shelf sequence from the Permian of the southwest Bowen Basin, Queensland, Australia. Australian Journal of Earth Sciences 36, 29- 40.
FIELDING C.R., FALKNER A.J., KASSAN J. & DRAPER J.J. 1990. Permian and Triassic depositional systems in me Bowen Basin. In: Bowen Basin Symposium Proceedings, pp. 21- 25. Geological Society of Australia, Brisbane.
FIELDING C.R. & McLOUGHLIN S. 1992. Sedimentology and palynostratigraphy of Permian rocks exposed at Fairbairn Dam, central Queensland. Australian Journal of Earth Sciences 39, 631-649.
FIELDING C.R. & TYE S.C. 1994. Stratigraphy of the Talaterang and Shoalhaven Groups in me southernmost Sydney Basin. In 28m Symposium on Advances in me Study of me study of me Sydney Basin, pp. 212-219.
FISHER R.W. 1972. Stratigraphy and sedimentology of the Permian sequence in the Shoalhaven River: Tallong area, Sydney Basin, NSW. BSc(Hons) thesis, University of New England, Armidale (unpubl.).
FLEMINGS P.B. & JORDAN T.E. 1990. Stratigraphic modelling of foreland basins Interpreting thrust deformation and lithosphere rheology. Geology 18, 430-434.
FLORES R.M. 1983. Basin facies of coal-rich Tertiary fluvial deposits, northern Powder River Basin, Montana and Wyoming. In J.D. Collinson and J. Lewin Eds. International Association of Sedimentologists Special Publication 6. 501-515.
FOLK R.L., ANDREWS P.B. & LEWIS DW. 1970. Detrital sedimentary rock classification and nomenclature for use in New Zealand. New Zealand Journal of Geology and Geophysics 13, 937-968.
136 FORBES D.L. & BOYD R. 1987. Gravel ripples on me inner Scotian Shelf. Journal of Sedimentary Petrology 57, 46-54.
FRAKES L.A. 1979. Climates throughout geologic Time. Amsterdam, Elsevier, 310p.
FURSICH FT. & OSCHMANN W. 1993. Shell beds as tools in basin analysis: the Jurassic of Kachchh, western India. Journal of the Geological Society, London 150, 169-185.
GILLIE R.D. 1979. Sand and Gravel deposits of the coast and inner shelf: east coast, Northland Peninsula, New Zealand. PhD thesis, University of Canterbury, Christchurch, New Zealand.
GOSTIN V.A. 1968. Stratigraphy and sedimentology of the Lower Permian sequence in me Durras-Ulladulla area, Sydney Basin, New South Wales. PhD thesis, Australian National University, Canberra (unpubl.).
GOSTIN V.A. & HERBERT C. 1973. Stratigraphy of the Upper Carboniferous and Lower Permian sequence, southern Sydney Basin. Journal of the Geological Society of Australia 20, 49-70.
GRAY N.H. 1969. Some thoughts on me Lower Permian rocks in me lower Shoalhaven River. In 3rd Symposium on Advances in the Study of the study of the Sydney Basin.
GULSON R.L., DIESSEL C.F.K., MASON D.R. & KROGH T.E. 1990. High precision radiometric ages from me northern Sydney Basin and their implication for the Permian time interval and sedimentation rates. Australian Journal of Earth Sciences 37, 459-469.
GUY-OHLSON D. 1992. Botryococcus as an aid in me interpretation of palaeoenvironment and depositional processes. Review of Palaeobotany and Palynology 71, 1-15.
HADLEY D.F. & ELLIOT T. 1993. The sequence-stratigraphic significance of erosive-based shoreface sequences in me Cretaceous Mesaverde Group of northwestern Colorado. In Posamentier H.W., Summerhayes C.P., Haq B.U. & Allen. Sequence stratigraphy and facies associations. Special Publication International Association of Sedimentologists 18. 521-536.
HARMS J.C., SOUTHARD J.B., SPEARING D.R. & WALKER R.G. 1975. Depositional environments as interpreted from primary sedimentary structures and stratification sequences. Society of Economic Paleontologists and Mineralogists Short Course Notes No.2, 161p.
HARPER L.F. 1915. Geology and Mineral Resources of the southern coalfield. Memoir of the geological survey of NSW 7.
HARRIS P.T. 1988. Large-scale bedforms as indicators of mutually evasive sand transport and me sequential infilling of wide-mouthed estuaries. Sedimentary Geology 57. 273-298.
' HART B.S. & PLINT A.G. 1994. Origin of an erosion surface in shoreface sandstones of me Kakwa Member (Upper Cretaceous Cardium Formation, Canada): importance for reconstruction of stratal geometry and depositional history. In Posamentier H.W., Summerhayes C.P., Haq B.U. & Allen. Sequence stratigraphy and facies associations. Special Publication International Association of Sedimentologists 18. 451-468.
HAZELDINE R.S. & ANDERTON R. 1980. A braidplain facies model for me Westphalian B Coal Measures of north-east England. Nature 264, 51-53.
HEIN F.J. & WALKER R.G. 1977. Bar evolution and development of stratification in me gravelly, braided, Kicking Horse River, British Columbia. Canadian Journal of Earth Sciences 14, 562-570.
137 HELBY R.J. 1968a. A Lower Permian microflora from the three foot seam, Clyde River Coal Measures. Report of the Geological Survey of NSW, Palynology (unpubl).
HELBY R.J. 1968b. Palynological report on Yarrunga Creek DDH No. 4. Report of the Geological Survey of NSW, Palynology (unpubl.).
HELBY R.J. & HERBERT C. 1971. Relationship of the Clyde Coal Measures to the Pigeon House Creek Siltstone, southern Sydney Basin. Quarterly notes of Geological Survey of NSW 8.
HERBERT C. 1972. Palaeodrainage patterns in me southern Sydney Basin. Geological survey of New South Wales Record 14, 5-18.
HERBERT C. 1980a. Southwestern Sydney Basin. Geological survey of New South Wales Bulletin 26, 10-52.
HERBERT C. 1980b. Evidence for glaciation in the Sydney Basin and Tamworth Synclinorial zone. Geological of Survey of New South Wales Bulletin 26, 274-293.
HERBERT C. 1994. Cyclical sedimentation in me lower Newcastle Coal Measures. In 28th Symposium on Advances in me Study of the study of the Sydney Basin, pp. 134-141.
ISRAEL A.M., ETHRIDGE F.G. & ESTES E.L. 1987. A sedimentologic description of a microtidal, flood-tidal delta, San Luis Pass, Texas. Journal of Sedimentary Petrology 57, 288- 300.
JANSEN J.H.F., WOENSDREGT C.F., KOOIESTRA M.J. & VAN DER GAAST S.J. 1987. Ikaite pseudomorphs in Zaire deep Sea fan: an intermediate between calcite and porous calcite. Geology 15, 245-248.
JENKINS R.B. 1990. Aspects of the Lower Permian sequences in me Manning River area and their tectonic significance./n Proceedings of me 24m Symposium on advances in me study of me Sydney Basin, pp.49-56. University of Newcastle, Newcastle.
JENKINS R.B. 1992. A geologic and thermal history of the Manning Group. In Proceedings of the 26th Symposium on advances in me study of me Sydney Basin, pp.39-46. University of Newcastle, Newcastle.
JENNETTE D.C. & PRYOR W.A. 1993. Cyclic alternation of proximal and distal storm Facies: Kope and Fairview (Upper Ordovician), Ohio and Kentucky. Journal of Sedimentary Petrology 63, 183-203.
JOHN B.H. & FIELDING C.R. 1993. Reservoir potential of the Catherine Sandstone, Denison Trough, East-Central Queensland. APEA Journal 1993, 176-187.
JOHNSON M.A., KENYON N.H., BELDERSON R.H. & STRIDE A.H. Sand Transport. 1982. In Stride A.H. ed. Offshore Tidal Sands. Chapman and Hall, pp. 58-94.
JOHNSON S.E. & HENDERSON R.A. 1991. Tectonic development of me Drummond Basin, eastern Australia: backarc extension and inversion in a Late Palaeozoic active margin setting. Basin Research 3, 197-213.
JONES B.G., MARTIN G.R. & SENAPARTI N. 1993. Riverine-tidal interactions in the monsoonal Gilbert River fandelta, northern Australia. Sedimentary Geology 83, 319-338.
JONES J.G., CONAGHAN P.J., McDONNELL K.L., FLOOD R.H. & SHAW S.E. 1984. Papuan
138 Basin analogue and a foreland basin model for the Bowen-Sydney Basin In: Veevers J.J. ed., Phanerozoic Earth history of Australia. Clarendon Press, Oxford, England, pp. 243-262.
JOPLIN G.A., HANLON F.N. & NOAKES L.C. 1952. Explanatory Notes to Wollongong 4- mile Sheet. Geological Survey of NSW, Sydney.
KAPLAN M.E. 1979. Calcite pseudomorphs (pseudogaylussite, jarowite, thinolite, glendonite, gennoishi, White Sea Hornlets) in sedimentary rocks: origins of the pseudomorphs. Lithology and Mineral Resources 14, 623-636.
KENNEDY G.L., HOPKINS D.M. & PICKTHORN W.J. 1987. Ikaite, the glendonite precursor, in estuarine sediments at Barrow, Arctic Alaska. Geological Society of America, Abstracts with programs 19, 725.
KLEIN G.V. & KUPPERMAN J.B. 1992. Pennsylvanian cyclothems: Methods of distinguishing tectonically induced changes in sea level from climatically induced changes. Geological Society of America Bulletin 104, 166-175.
KLEIN G.V. & MARSAGLIA KM. 1987. Hummocky cross-stratification, tropical hurricanes, and intense winter storms. Sedimentology 34. 33-359.
KREISA R.D. & MOIOLA R.J. 1986. Sigmoidal tidal bundles and other tide-generated sedimentary structures of me Curtis Formation, Utah. Geological Society of America Bulletin 97. 381-387.
KUMAR N. & SANDERS J.E. 1974. Inlet sequence: a vertical succession of sedimentary structures and textures by lateral migration oftidal inlets . Sedimentology 21, 491-532.
LECKIE D. 1988. Wave-formed, coarse-grained ripples and their relationship tp hummocky cross-stratification. Journal of Sedimentary Petrology 58, 607-622.
LECKIE D.A. & WALKER R.G. 1982. Storm and Tide-dominated shorelines in Cretaceous Moosebar-Lower Gates Interval-outcrop equivalents of deep basin gas trap in western Canada. American Association of Petroleum Geologists Bulletin 66, 138-157.
LECKIE D.A. & SMITH D.G. 1992. Regional setting, evolution and depositional cycles of me western Canada Foreland Basin. In Macqueen R.W. & Leckie D.A. Foreland Basins and Fold Belts. American Association of Petroleum Geologists Memoir 55.
LEITHOLD E.L. & BOURGEOIS J. 1984. Characteristics of coarse-grained sequences deposited in nearshore, wave-dominated environments-examples from me Miocene of southwest Oregon. Sedimentology 31, 749-775.
LE ROUX J.P. & JONES B.G. 1994. Lithostratigraphy and depositional environment of the Permian Nowra Sandstone in the southwestern Sydney Basin, Australia. Australian Journal of Earth Sciences 41, 191-204.
LOMAS S. 1992. Submarine mass-flow conglomerates of me Tarentaise Zone, Western Alps: sedimentation processes and depositional setting. Sedimentary Geology 81, 269-287.
LOPEZ-GAMUNDI OR., ESPEJO I.S., CONAGHAN P.J. & POWELL C. McA. 1994. Southern South America. In: Veevers J.J. & Powell C.McA. Permian-Trias sic Pangean Basins and foldbelts along the Panthalassan Margin of Gondwanaland. Geological Society of America Memoir 184. 281-330.
LOWE D.R. 1982. Sediment Gravity Flows: 2. Depositional models with special reference to the deposits of high-density turbidity currents. Journal of Sedimentary Petrology 52(1), 279-
139 297.
MARTINI LP. & GLOOSCHENKO W.A. 1985. Cold climate peat formation in Canada, and its relevance to Lower Permian Coal Measures of Australia. Earth Science Reviews 22, 107- 140.
MAYNARD J.R. & LEEDER M.R. 1992. On the periodicity and magnitude of Late Carboniferous glacio-eustatic sea-level changes. Journal of the Geological Society of London 149, 303-311.
MCCARTHY B. 1979. Trace fossils from a Permian shoreface-foreshore environment, Eastern Australia. Journal of Paleontology 53(2), 345-366.
McCRORY V.L.C & WALKER R.G. 1986. A storm and tidally influenced prograding shoreline- Upper Cretaceous Milk River Formation of Southern Alberta, Canada. Sedimentology 33, 47- 60.
McELHINNY M.W. 1973. Palaeomagnetism and Plate Tectonics. Cambridge University Press, Cambridge.
McELROY C.T. & ROSE G. 1962. Reconnaissance Geological Survey: Ulladulla 1-mile Military Sheet and southern part of Tianjara 1-mile Military Sheet. Bulletin of the Geological Survey of NSW 17.
McMINN A. 1993. Palynostratigraphy. Geological Survey of New South Wales, MemoirGeology 12, 135-143.
McPHERSON Le, SHANMUGAM G. & MOIOLA R.J. 1987. Fan-deltas and braid deltas: varieties of coarse-grained deltas. Geological Society of America Bulletin 99, 331-340.
MIALL A.D. 1977. A review of me braided river depositional environment. Earth Science Reviews 13, 1-62.
MIALL A.D. 1978. Lithofacies types and vertical profile models in braided river deposits: a summary. In Miall A.D. ed. Fluvial Sedimentology. Canadian Society of Petroleum Geologists Memoir 5, 597-604.
MIALL A.D. 1985. Architectural-element analysis: a new method of facies analysis applied to fluvial deposits. Earth Science Reviews 22, 261-308.
MIALL A.D. 1988. Architectural elements and bounding surfaces in fluvial deposits: anatomy of the Kayenta Formation (Lower Jurassic), southwest Colorado. Sedimentary Geology 55, 233-262.
MIALL A.D. & TURNER-PETERSON C.E. 1989. Variations in fluvial style in me Westwater Canyon Member, Morrisson Formation (Jurassic), San Juan Basin, Colorado Plateau. Sedimentary Geology 63, 21-60.
MIFSUD J. 1990. The sedimentology and diagenesis of me Upper Pebbley Beach Formation, southern Sydney Basin. BSc(Hons) thesis, University of Wollongong, Wollongong (unpubl.).
MILANKOVITCH M. 1941. Cannon of isolation and ice age problems (in german). Academy Roy ale Serbe, Belgrade Special Publication 133, 633p.
MILLER K.B. & WEST R.R. 1993. Reevaluation of Wolfcampian cyclothems in northeastern Kansas: significance of subaerial exposure and flooding surfaces. Current Research on Kansas Geology, Summer 1993, Bulletin 235, Kansas Geological Survey, Lawrence, pp.l-
140 26.
MILLSTEED B.D. 1994. Palynological evidence for the age of me Permian Karoo coal deposits near Vereeniging, northern Orange Free State, South Africa. South African Journal of Geology 97, 15-20.
MITCHUM R.M. & VAN WAGONER J.C. 1991. High frequency sequences and their stacking patterns: sequence stratigraphic evidence of highfrequency eustatic cycles. Sedimentary Geology 70, 131-160.
MJOS R., WALDERHAUG O. & PRESTHOLM. 1993. Crevasse splay sandstone geometries in me Middle Jurassic Ravenscar Group of Yorkshire, UK. Special Publication International Association of Sedimentologists 17, 167-184.
MOSLOW T.F. & TYE R.S. 1985. Recognition and characterisation of Holocene tidal inlet sequences. Marine Geology 63, 129-151.
MURRAY C.G. 1990. Tectonic evolution and metallogeny of me Bowen Basin. In Bowen Basin Symposium, Geological Society of Australia, Queensland Division, Proceedings, 201-212.
MURRAY C.G, FERGUSSON C.L., FLOOD P.G, WHITAKER W.G. & KORSCH R.J. 1987. Plate tectonic model for me Carboniferous evolution of the New England Fold Belt. Australian Journal of Earth Sciences 34, 213-236.
MURRAY C.G., SCHIEBNER E. & WALKER R.N. 1989. Regional geological interpretation of a digital coloured residual Bouguer gravity image of eastern Australia with a wavelength cut-off of 250 km. Australian Journal of Earth Sciences 36, 423-449.
NEMEC W. 1990. Depositional controls on plant growth and peat accumulation in a braidplain delta environment: Helvetiafjellet Formation (Barremian-Aptian), Svalbard. In McCabe P.J. & Parrish J.T. Controls on the distribution and quality of Cretaceous Coals. Geological Society of America Special Paper 267.
NEMEC W. & STEEL R.J. 1984. Alluvial and coastal conglomerates: their significant features and some comments on gravelly mass-flow deposits. In Koster E.H. & Steel R.J. Sedimentology of gravels and conglomerates. Canadian Society of Petroleum Geologists, Memoir 10, 1-31.
NICHOL S.L. 1991. Zonation and sedimentology of estuarine facies in an incised valley, wave- dominated, microtidal setting. In Smith D.G., Reinson G.E., Zaitlin B.A. & Rahmani R.A. eds. Clastic Tidal Sedimentology. Canadian Society of Petroleum Geologists Memoir 16. 41- 58.
NICHOLS M.M., JOHNSON G.H. & PEEBLES P.C. 1991. Modern sediments and facies model for a microtidal coastal plain estuary, the James estuary, Virginia. Journal of sedimentary Petrology 61. 883-899.
NOTTVEDT A. & KREISA R.D. 1987. Model for me combined-flow origin of hummocky cross-stratification. Geology 15, 357-361.
ORTON G.J. 1988. Pliocene-Holocene fan-delta and braid-deltas in me Crati Basin, southern Italy: a consequence of varying tectonic conditions. In Nemec W. & Steel R.J. eds. Fan Deltas: Sedimentology and Tectonic Settings, pp. 23-49. Blackie and son, Glasgow.
PACKHAM G.H. 1962. An outline of the Geology of New South Wales. In A Goodly Heritage, p.33. Australia and New Zealand Association for the Advancement of Science, Sydney.
141 PARKER G, LANFREDI N.W. & SWIFT D.J.P. 1982. Substrate response to flow in a southern hemisphere ridgefield. Sedimentary Geology 33, 195-216.
PICKERING, K.T., STOW, D.A.V., WATSON, M.P. & HISCOTT, R.N. 1986. Deep Water Facies, Processes and models: A Review and Classification Scheme for Modern and Ancient Sediments. Earth Science Reviews 23, 75-174.
PLINT A.G. 1988. Sharp-based shoreface sequences and "offshore bars" in me Cardium Formation: their relationship to relative sea-level changes. In Wilgus C.K., Hastings B.S., Kendall C.G.St.C, Posamentier H.W., Ross C.A. & Van Wagoner J.C. eds. Sea-level Changes: an Integrated Approach. Society of Economic Paleontologists and Mineralogists Special Publication 42. 357-370.
PLINT A.G. & WALKER R.G. 1987. Cardium Formation 8. Facies and environments of the Cardium shoreline and coastal plain in the Kakwa Field and adjacent areas, northwestern Alberta. Bulletin Canadian Petroleum Geologists 34, 48-64.
PLINT A.G., HART B.S. & DONALDSON W.S. 1993. Lithospheric flexure as a control on stratal geometry and facies distribution in Upper Cretaceous rocks of the Alberta Basin. Basin Research 5, 69-77.
PLINT A.G. & BROWNE G.H. 1994. Tectonic event stratigraphy in a fluvio-lacustrine, strike- slip setting: me Boss Point Formation (Westphalian A), Cumberland Basin, Maritime Canada. Journal of Sedimentary Research B64, 341-364.
POWELL R.D. 1981. A model for sedimentation by tidewater glaciers. Annual Glaciology 2, 120-134.
POWELL R.D. & MOLNIA B.F. 1989. Glaciomarine sedimentary processes, facies and morphology of the south-southeast Alaska shelf and fjords. Marine Geology 85, 359-390.
PRAVE A.R. & DUKE W.L. 1990. Small-scale hummocky cross-stratification in turbidites: a form of antidune stratification. Sedimentology 37, 531-539.
RAMLI N. & CROOK K.A.W. 1978. Early Permian depositional environments, southern Sydney Basin. The APEA Journal 70-76.
RAMOS A. & SOPENA. 1983. Gravel bars in low-sinuosity streams (Permian and Triassic, central Spain). In Collinson J.D. & Lewin J. eds. Modern and ancient fluvial systems. International Association of Sedimentologists Special Publication 6, 301-312.
READING H.G. 1986. African Rift tectonics and sedimentation within the African Rift Systems. In Frostick L.E., Renaut R.W., Reid I. & Tiercelin J.J. eds. 1986. Sedimentation in the African Rifts. Geological Society Special Publication No. 25. pp. 3-8.
REINECK H.E. & WUNDERLICH F. 1968. Classification and origin of flaser and lenticular bedding. Sedimentology 11, 99-104.
RICHARDS M.T. 1986. Tidal bedform migration in shallow marine environments: evidence from me lower Triassic, Western Alps, France. In: Knight R.J. & McLean J.R. Shelf Sands and Sandstones. Canadian Society of Petroleum Geologists Memoir 11, 257-276.
ROBERTS J. & ENGLE B.A. 1987. Depositional and tectonic history of me southern New England Orogen. Australian Journal of Earth Sciences 34, 1-20.
ROSENTHAL L.R.P. & WALKER R.G. 1987. Lateral and Vertical facies sequences in the Upper Cretaceous Chungo Member, Wapiabi Formation, southern Alberta. Canadian Journal
142 of Earth Science 24, 771-783.
ROSS C.A. & ROSS J.R.P. 1988. Late Paleozoic transgressive-regressive deposition. In Wilgus C.K., Hastings B.S., Kendall C.G.St.C, Posamentier H.W., Ross C.A. & Van Wagoner J.C. eds. Sea-level Changes: an Integrated Approach. Society of Economic Paleontologists and Mineralogists Special Publication 42. 227-248.
ROY P.S., THOM B.G. & WRIGHT L.D. 1980. Holocene sequences on an embayed high energy coast: an evolutionary model. Sedimentary Geology 26. 1-19.
RUNNEGAR B. 1969. Permian fossils from the southern Sydney Basin. In: Campbell K.S.W. (ed.) Stratigraphy and Palaeontology. Essays in honour of Dorothy Hill, pp. 276-298. Australian University Press, Canberra.
RUNNEGAR B. 1979. Ecology of Eurydesma and me Eurydesma fauna, Permian of eastern Australia. Alcheringa 3, 261-286.
RUNNEGAR B. 1980a. Biostratigraphy of me Shoalhaven Group. Geological Survey of New South Wales Bulletin 26, 376-382.
RUNNEGAR B. 1980b. Excursion guide, Day 7, stop 3, Montague Roadstead, Jervis Bay (Early Permian Shoalhaven Group): Sydney New South Wales. New South Wales Geological Survey Bulletin, 26, 523-530.
RUST B.R. 1978. Depositional models for braided alluvium. In Miall A.D. ed. Fluvial Sedimentology. Canadian Society of Petroleum Geologists Memoir 5, 605-625.
RUST B.R. 1981. Sedimentation in an arid-zone anastomosing fluvial system: Cooper's Creek, central Australia. Journal of Sedimentary Petrology 51. 745-755.
RUST B.R. 1984. Proximal braidplain deposits in me Middle Devonian Malbaie Formation of Eastern Gaspe\ Quebec, Canada. Sedimentology 31, 675-695,
SARVDA C. & OZALAS K. 1993. Preservation of mixed-layer ichnofabrics in oxygenation event beds. Palaios 8, 609-613.
SCHIEBNER E. 1974. A plate tectonic model of the Palaeozoic tectonic history of New South Wales. Journal of the Geological Society of Australia 20, 405-426.
SCHIEBNER E. 1993. Tectonic Setting. Geological Survey of New South Wales Memoir Geology 12, 33-46.
SCOTT A. 1984. The depositional/structural environment of the Ulladulla Mudstone. BSc(Hons) Thesis, Macquarie University, Sydney (unpubl.).
SEGGIE R.J. 1978. Geology of me Sydney Basin to the west of Ulladulla. BSc(Hons) thesis, University of New South Wales, Sydney (unpubl.).
SHEARMAN D.J. & SMITH A.M. 1985. Ikaite, the parent mineral of jarrowite-type pseudomorphs. Proceedings of the Geologists Association 96, 304-314.
SMITH D.G. 1983. Anastomosed fluvial deposits: modern examples from Western Canada. Special Publication International Association Sedimentologists 6, 155-168.
SMITH D.G & SMITH N.D. 1980. Sedimentation in anastomosed river systems: examples from alluvial valleys near Banff, Alberta. Journal of Sedimentary Petrology 50.157-164.
143 SMITH N.D. 1974. Sedimentology and bar formation in me upper Kicking Horse River, a braided outwash stream. Journal of Geology 82, 205-223.
SMITH N.D., CROSS T.A., DUFFICY LP. & CLOUGH S.R. 1989. Anatomy of an avulsion. Sedimentology 36, 1-23.
SMITH S.A. 1990. The sedimentology and accretionary styles of an ancient gravel-bed stream: Budleigh Salterton Pebble Beds (Lowe Triassic), southwest England. Sedimentary Geology 67, 199-219.
SOUTHARD J.B., LAMBIE J.M., FEDERICO D.C., PILE H.T. & WEIDMAN C.R. 1990. Experiments on bed configurations infine sands under bidirectional purely oscillatory flow, and the origin of hummocky cross-stratification. Journal of sedimentary Petrology 60. 1- 17.
STEEL R.J. & THOMPSON D.B. 1983. Structures and textures in Triassic braided stream conglomerates ("Bunter" Pebble Beds) in me Sherwood Sandstone Group, North Staffordshire, England. Sedimentology 30, 341-367.
STRAUB K. 1993. Sedimentology of the Snapper Point Formation in me Jervis Bay area. BSc(Hons) thesis, University of Wollongong (unpubl.).
STRIDE A.H. 1988. Preservation of marine and sand wave structures. In De Boer, Van Gelder A. & Nio S.D. Tide-influenced sedimentary environments and facies. Reidel Publishing Company, pp. 4-13.
STRIDE A.H., BELDERSON R.H., KENYON N.H. & JOHNSON M.A. 1982. Offshore tidal deposits: sand sheet and sand bank facies. In: Stride A.H. ed. Offshore Tidal Sands. Chapman and Hall, pp. 95-125.
STUTCHBURY R.J. 1985. The depositional environment of me Permian Pebbley Beach Formation, southern Sydney Basin, New South Wales. BSc(Hons) thesis, Macquarie University, Sydney (unpubl.).
STUTCHBURY R.J. 1989. The Early Permian Pebbley Beach Formation: Deposition in a cold climate. In: 23rd Symposium on advances in me study of me Sydney Basin, pp. 102-108.
SUESS E., BALZER W., HESSE K.F., MULLER P.J., UNGERER C.A., & WEFER G. 1982. Calcium Carbonate hexahydrate from organic-rich sediments of the Antarctic shelf: Precursors of glendonites. Science 216, 1128-1130.
SURLYK F. 1984. Fan-delta to submarine fan conglomerates of me Volgian-Valanginian Wollaston Forlan Group, East Greenland. In Koster E.H. and Steel R.J. eds. Sedimentology of Gravels and Conglomerates, pp. 359-382. Canadian Society of Petroleum Geologists, Memoir 10 (1984).
SURLYK F. & NOE-NYGAARD N. 1986. Hummocky cross-stratification from me Lower Jurassic Hasle formation of Bornholm, Denmark. Sedimentary Geology 46, 259-273.
SWIFT D.J.P. 1968. Coastal erosion and transgressive stratigraphy. Journal of Geology 76, 444- 456.
SWIFT D.J.P., THORNE LA. & OERTEL G.F. 1986. Fluid process and sea floor response on a storm dominated shelf: middle Aflantic Shelf of North America. Part II: response of the shelffloor. In: Knight R.J. & McLean J.R. Shelf Sands and Sandstones. Canadian Society of Petroleum Geologists Memoir 11, 191-211.
144 SWIFT D.J.P., PHILLIPS S. & THORNE LA. 1991a. Sedimentation on continental margins, V: parasequences. In: Swift D.J.P. & Oertel G.F. eds. Shelf sand and sandstone bodies. Special Publication International Association of Sedimentologists 14. 153-187.
SWIFT D.J.P., PHILLIPS S. & THORNE LA. 1991b. Sedimentation on continental margins, IV: lithofacies and depositional systems. In: Swift D.J.P. & Oertel G.F. eds. Shelf sand and sandstone bodies. Special Publication International Association of Sedimentologists 14. 89- 152.
TADROS N.Z. 1993a. Introductory notes. Geological survey of New South Wales, Memoir Geology 12, 3-12.
TADROS N.Z. 1993b. Tectonic Evolution. Geological Survey of New South Wales, Memoir Geology 12. 47-54.
THOMAS R.G., SMITH D.G, WOOD LM., VISSER L, CAVERLY-RANGE E.A. & KOSTER E.H. 1987. Inclined heterolithic stratification-terminology, description, interpretation and significance. Sedimentary Geology 53. 123-179.
TIERCELIN J.J. 1990. Rift-basin sedimentation: responses to climate, tectonism and volcanism. Examples of me East Africa Rift. Journal of African Earth Sciences 10, 283-305.
TYE S.C. & FIELDING C.R. 1994. Sedimentology of me Talaterang and Shoalhaven Groups in me southernmost Sydney Basin. In: 28th Symposium on advances in me study of me Sydney Basin, pp.220-227.
TYE S.C, JONES B.G. & FIELDING C.R. Early Permian Palaeoenvironments in me southern Sydney Basin, New South Wales, Australia. In: Centennial Geocongress, Geological Society of South Africa, pp. 804-807
TYE S.C, FIELDING C.R. & JONES B.G. in press. Stratigraphy and sedimentology of me Talaterang and Shoalhaven Groups of me southernmost Sydney Basin. Australian Journal of Earth Sciences.
UHLIR D.M., AKERS A. & VONDRA CF. 1988. Tidal inlet sequence, Sundance Formation (Upper Jurassic), north-central Wyoming. Sedimentology 35.739-752.
VAIL P.R., MITCHUM R.M., TODD R.G, WIDMIER J.M., THOMPSON S., SANGREE LB., BUBB J.N. & HATLELID W.G. 1977. Seismic stratigraphy and global changes of sea level. In Payton CE. ed. Seismic stratigraphy-applications to hydrocarbon exploration: American Association of Petroleum Geologists, Memoir 26, pp 49-212.
VAN WAGONER J.C., MITCHUM R.M. Jr., POSAMENTIER H.W., VAIL P.R., SARG J.F., LOUTIT T.S. & HARDENBOL J. 1988. An overview of the fundamentals of sequence stratigraphy and key definitions of sequence stratigraphy. In Wilgus C.K., Hastings B.S., Kendall C.G.StG, Posamentier H.W., Ross C.A. & Van Wagoner J.C. eds. Sea-level Changes: an Integrated Approach. Society of Economic Paleontologists and Mineralogists Special Publication 42. 39-47.
VEEVERS J.J. & POWELL C.McA. 1987. Late glacial episodes in Gondwanaland reflected in transgressive-regressive depositional sequences in Euramerica. Geological Society of America Bulletin 98, 475-487.
VEEVERS J.J., CLARE A. & WOPFNER H. 1994a. Neocratonic magmatic-sedimentary basins of post-Variscan Europe and post-Kanimblan eastern Australia generated by right-lateral transtension of Permo-Carboniferous Pangaea. Basin Research 6, 141-157.
145 VEEVERS J.J., CONAGHAN P.J. & POWELL CMcA. 1994b. Eastern Australia. In Veevers J.L & Powell CMcA. Permian-Triassic Pangean Basins andfoldbelts along the Panthalassan Margin of Gondwanaland. Geological Society of America Memoir 184. 11-172.
VEEVERS J.J., POWELL CMcA., COLLINSON LW. & LOPEZ-GAMUNDI OR. 1994c. Synthesis. In: Veevers J.L & Powell CMcA. Permian-Triassic Pangean Basins andfoldbelts along the Panthalassan Margin of Gondwanaland. Geological Society of America Memoir 184. 331-353.
VISSER LN.J. 1990. The age of the late Palaeozoic glacigene deposits in southern Africa. South African Journal of Geology 93, 366-375.
VISSER J.N.J. 1991. Self-destructive collapse of the Permo-Carboniferous marine ice sheet in me Karoo Basin: evidence from the southern Karoo. South African Journal of Geology 94, 255-262.
VISSER LN.J. & LOOCK J.C. 1988. Sedimentary facies of the Dywka Formation associated with me Nooitgedacht glacial pavements, Barkly West District. South African Journal of Geology 91, 38-48.
VISSER M.J. 1980. Neap-spring cycles reflected in Holocene subtidal large-scale bedform deposits: a preliminary note. Geology 8, 543-546.
VORREN T.O., LEBESBYE E., ANDREASSEN K. & LARSEN KB. 1989. Glacigenic sediments on a passive continental margin as exemplified by the Barents Sea. Marine Geology 85, 251-272.
WALKER M.J. 1980. The Geology of the upper Clyde River District, NSW. BSc(Hons) thesis, University of New South Wales, Sydney (unpubl.).
WALKER R.J., DUKE W.L. & LECKIE D.A. 1983. Hummocky stratification: Significance of its variable bedding sequences: Discussion and reply. Geological Society of America Bulletin 94. 125-1251.
WILES L.A. 1993. Structural Complexity of the southern Sydney Basin, slumping or tectonic deformation? BSc(Hons) thesis, University of Newcastle, Newcastle (unpubl.).
WILES L.A. 1995. Tectonic deformation in the southern Sydney Basin. In: Proceedings of the 29th Symposium on Advances in me Study of the Sydney Basin, additional programme information. University of Newcastle, Newcastle, pp. 261-268.
WOOLNOUGH W.G. 1909. The general geology of Marulan and Tallong, NSW. Proceedings of the Linnian Society of NSW 34.
YAGISHITA K, ARAKAWA S. & TAIRA A. 1992. Grain Fabric of hummocky and swaley cross-stratification. Sedimentary Geology 58, 181-189.
YANG C.S. & BAUMFALK Y.A. 1994. Milankovitch cyclicity in me Upper Rofliegend Group of the Netherlands offshore. In: de Boer P.L. & Smith D.G. Orbital forcing and cyclic sequences. International Association of Sedimentologists Special Publication 19, 47-62.
146 FIGURES TC^
MARULAN 4TALL0NG ".yBadgery's lookout G* ,xN» ta.W' °
• NOWRA
.35° 00' Callala DDH1 (Or si O JERVIS BAY
L 35° 15' N
10km •'ULLADULLA
n Is
'.•.'• Snapper Pt — Broughton Fm -- Pebbley Beach Fm '•"• Yadboro/Tallong Congl /// Wasp Head Fm • Clyde Coal Measures + 1" Igneous Intrusion
Myrtle beach 150° 00' 150° 30' I
Figure 1.1: Location diagram for the southern Sydney Basin. 138°E 150"
-12°S OLIVE RIVER BASIN
12°S -
16° -
- 20" QUEENSLAND i CALEN BASIN
Mackay 20° -
24° -
0 Moreton Is. Brisbane ^Qstradbroke Is.
28°
0£
Newcastle ^ 32° Sydney Wollongong -36
36° _
QKing Is. 250 500 km -40° I SCALE
TASMANIA BASIN 40° - Hobart 138°E 144" 150° 156° I 19681
Figure 1.2: Location of Sydney-Gunnedah-Bowen Basin and other Permian coal-bearing basins of eastern Australia (from Tadros 1993a). 5 Figure 13: Conceptual model for the Permian evolution of me Sydney-Bowen Basin. Phase 1 (extension; Veevers* stage A): formation of grabens and half grabens. Phase 2 (thermal sag or embryonic foreland; Veevers' stage B): passive thermal sag across basin. Phase 3 (compressional or mature foreland; Veevers' stages C to F): uplifted and active orogen. (modified from Baker et al. 1993). -o -o r i tn > Pm re re p> , P g v o P vT 3 PI
D. D. ore s H oo Z O n p_ 3- p P p p o p =i 3 o ft EL -1 P P -i p a" c 3- P P 3 B n O -a o TO < o o o re p c 3 CO a 3 p -i •a c » o a •a -1 1-1 c B9 •a o c CO Q in a. •a o c 3 CS CO CO CO o 3 c c I O" a- ?= CO G cr co c TO TO o O a- 3 -1 o 3 c C TO c >-i o •a c 13 •a 3= c 03 DO 00 n •ma 2 "a m o a. B O •a o rS ra m o re TO_ rt 3" s tr TO D. i-j > n O P n CO a- re 3 00 H to o P =1 P c 3" ni n p rt CO P_ & a. -i Q 5 CO •n P n re" •—• o re Z P S, P o' 3 E2 H5 a- r*i cr •a co M D C c c -i c P 5" »" < < <• 2 B 3" < p n. =• £L 1 re O p" a. SI Q. 5 CO -i rt D. 3 o" ft c ft c 3 P < ° 3 c O p < 2 2 5"=5 =s o '"' O O o o 2 > o o o a. a. p H r TJ_ •a p 5' Figure 1.5: Locations of measured sections and drillcores. See table 1.1 for grid references. LITHOLOGIES
O o. %*°o%'0 Conglomerate 4-4- 4- 4- 4- 4- Igneous intrusion F Coal BED CONTACTS Gradational Sharp/undulating Sharp/erosive or irregular Sharp/planar SEDIMENTARY STRUCTURES erosion surface load structures flat lamination \r o extraforrnational clasts low Angle lamination • intraformational clasts hummocky cross-srraification ® dropstones SSSL cross-bedding (T=trough, 0(7 clast imbrication P=planar) (3 pyrite staining small symmetrical wave ripples £T plant folage large coarse grained wave / fragmented ripples logs current ripple cross-lamination £> / coaly traces current lenticular bedding ^ root traces interference ripples yy burrows tidal bundles/sigmoidal cross- G» pyrite stain bedding *J pD® marine macrofossils convolute bedding jft. OD Eurydesma ure 1.6: Symbol Key for measured sections. Figure 1.7: Reconstruction of Gondwana continents during the Late Paleozoic showing migration path of the south magnetic pole. Note the position of the pole during me Early Permian in Eastern Antarctica, close to Sydney Basin of Eastern Australia. (Modified from Crowell & Frakes 1973). Figure 2.1: Previous stratigraphic models for me southern Sydney Basin. W LITHOSTRATIGRAPHY E DEPOSITIONAL ENVIRONMENT Figure 2.2: Revised lithostratigraphy for me southern Sydney Basin. See text for details of revisions. YCM= Yarrunga Coal Measures. Figure 2 J: Clyde Coal Measures in the upper Clyde Valley (type section of McElroy and Rose (1962). Shows lower alluvial succession containing coal seams (labelled a) and the estuarine succession (labelled b). The prominent sandstone unit at the top of the section is that of facies F (estuarine inlet/barriers). Clyde Coal Measures Upper Clyde River Section 1 Section 2 Snapper Point Fm. m Snapper Point Fm. 35- Estuarine Inlet V-VA ' F Estuarine Inlet 35 t 30- ^vw „j 33; coi Estuarine Lagoon Estuarine Lagoon Tidal Channels 30 5==g I C<» 25 — / Tidal Channels Estuarine Lagoon Tidal Channels Col 20 V. - & K 20 15 IS- Co! 10- ^\" \ 1 10 S .S. B / 5- clay silt sand gravel 0- Basement Aclay silt sand gravel Figure 3.1: Measured sections from the Upper Clyde River. These sections correspond with the type section of McElroy and Rose (1962). See figure 1.6 for Key to symbols used on sections. *1 O era* f c a ' 01 CO re -S CD • CD C u> V O Si ** 1 r-t- w o" 01 I re 3 3 en a. O U3" C •n 1-1 01 TO < Facies (B J o Tl a Palaeocurrent TO o c. c B 5V) 23 5 o *• CO c c BS 5= 65 3 (JO n "a TO TO CS3T o o X| c 0) 0 >< « a /" / O E. * ° o ^ / ° / s ^-" o "-t SG. ° S / O / n V) CO 01. / TO 3 1 » TO a in C/3 -0»1 -• ^^ n=72 n=12 Facies B and C Facies D M|r: n=27 n=7 Facies E Pigeon House Creek Siltstone N n=27 r n=14 Figure 3.3: Palaeocurrent frequency distributions for the Clyde Coal measures. Figure 3.4a: Small channel structure within crevasse splay unit. Figure 3.4b: Coal seam with sharp base. Measuring tape = lm. Upper Clyde River section, Clyde Coal Measures. Clyde Upper Clyde River, Clyde Coal Measures. Figure 3.4c: Distal floodplain facies (facies C). Upper Clyde River Figure 3.4d: Interbedded coal seams and Siltstone units within distal Section, Clyde Coal Measures. floodplain facies (facies C). Upper Clyde River section, Clyde Coal Measures. Figure 3.4e: Lateral Accretion surfaces Gabelled a) within facies D. Figure 3.4f: Estuarine lagoon facies (facies E), Upper Clyde River Upper Clyde River section, Clyde Coal Measures. Section, Clyde Coal Measures. Pigeon House Creek-Siltstone — Clyde River palaeocurrent m Yadboro Conglomerate 1 / 40-- AU J oO • a. x 0) c CD eu M 0) c c a sz on >- + •5 CO (0 O J) c u E a u. 3 w 01 o a •a c (Q C a a •o o o u. Basement clay sand gravel Figure 3.5: Measured section of the Pigeon House Creek Siltstone at Cambage Head. Corresponds with me type section for me Pigeon House Creek Siltstone of McElroy and Rose (1962). Figure 3.6: Schematic representation of an idealised wave-dominated estuary from Dalyrimple et al (1992) showing energy distribution (A), morphological components (B) and longitudinal facies distribution (C). Note me distinct tripartite facies distribution. Myrtle Beach Sth Emily Miller Beach Wasp Head m ", • "*, •:'-J \ \ J " ' 0 , JT • . A A* *A*<« | • 1 ..... -1 •• • • .-x . - . . o 0 • 1 ' . * -JS>— r • ' =£i= • ° • " —**— '„ ' •' r«= .' — -i .1 • —**— ". in •1 ^-=. '•. — '. — . t| . '. . • . • -^— '. • . -''*-. • • 1 . • . — -— — •__- =r*T .. * L y * « • * 4 A 4 1 <-\ \ r ** . J . • , ° " ' o .^"n^ ' ,"/"i" "JT :A debris flow . —— —i—n • • • i • • i • i clay silt sand gravel | clay silt ^^ grave| Figure 3.7: Measured sections from the Wasp Head Formation. See Figure 1.6 for Symbol Key. Figure 3.8a: Thick Breccia unit at the north end of Myrtle Beach, Figure 3.8b: Lithic pebbly sandstone of facies B. Wasp Head Wasp Head Formation. Note the distinct planar base. Measuring stick Formation, north end of Myrtle Beach. = 2 m. Figure 3.8c: Disturbed pebble layer within facies C sandstone unit. Figure 3.8d: Disturbed pebble layer in plan view showing distinctive Wasp Head Formation, north end of Myrtle Beach. Rosselia trace. Wasp Head Formation, north end of Myrtle Beach. Figure 3.8e: Swaley cross-stratification within facies D. Note Figure 3.8f: Hummocky cross-stratification within facies E. Note the agglomeration of pebbles at the base of some swales. Wasp Head hummock in the centre of the photograph Gabelled a). Wasp Head Formation, south of Wasp Head. Formation, South Emily Miller Beach. Cross-bed data - Facies B n=27 Wave ripple data N n=20 Figure 3.9: Palaeocurrent frequency distributions from the Wasp Head Formation, ••»>, , Figure 3.10a: Facies F succession. Note the large coarse grained Figure 3.10b: Dropstones within facies G; Wasp Head Formation, rippled horizon, upon which the hammer is resting. Wasp Head Wasp Head. Formation, south of Wasp Head. Figure 3.10c: The offshore succession of facies G, dominated by Figure 3.10d: Eurydesma specimen within a coarse horizon near the pervasively bioturbated units of silty sandstone. Measuring stick = 2 top of the exposed section at Wasp Head Formation, Wasp Head. m. Wasp Head Formation, Wasp Head. a o 8 Figure 3.10e: Upward shoaling shoreface sand body comprising facies F at the base (labelled a) and quartzose facies D (labelled b) at the top of the succession. Measuring stick = 2 m. Wasp Head Formation, south of Wasp Head. Top not exposed 80- •tf-a^-a- flooding surface B 70- o a a —! ^-frl 60- maximum flooding interval z o h- 50- < 5 rx O Li. 40- D < UJ X 0. 30- CO < 20- A £. A A A A A _ o ° -| AAAAAAAA 10 /AV/y A A A A A A A Al >>»"• flooding surface A Z >} I rr ° I I T™I 5 H- M Lti m J A* m g Figure 3.11: Composite section of the Wasp Head Formation showing interpreted parasequences and sea-level change. See text for discussion. Figure 4.1: A Late Carboniferous fluvial network as proposed by Herbert (1972; 1980a). From Herbert 1980a Figure 4.2a: Sand filled scour (facies Ss) within trough cross- Figure 4.2b: Siltstone unit within Tallong Conglomerate. Measuring bedded (Gt) and plane-bedded conglomerate facies. Measuring stick stick = 2 m. "Gibraltar Rocks". = 2m. Tallong Conglomerate, "Johnny Fields". Figure 4.2c: Badgery's Breccia, at the base of the Badgery's Figure 4.2d: View of eastern side of Byangee walls from Cambage Lookout section (Fig. 4.3). Head. The photograph shows four prominent clifflines which correspond to the four uppermost cycles within the Yadboro Conglomerate. Vegetated benches correspond to thin siltstone intervals which define cycle boundaries. Figure 4.2es View of south side of Byangee Walls showing benches Figure 4.2f: outcrop of conglomerate in the Shoalhaven Gorge at (highlighted by arrows) which define cycle boundaries. Length of Hoddles Cliff. Conglomerate is overlain by Snapper Point Formation. exposure is approximately 2 km. Nowra Sandstone forms the uppermost cliffline in the top right of the photograph. 40 - Q-Q .0 . Q. t 13 .nl E u. e •5 5 • u . a a 2-i33 Q. V • c~>-.o. co o a> O i_ RJ to c ta i_ CD 01 >- 20 og • °. o' Figure 43: Measured section from Badgery's Lookout. The Badgery's Breccia forms the basal conglomeratic interval of the section. See Figure 1.6 for key to symbols. Tallong Conglomerate Badgery's Breccia Yadboro Conglomerate n=223 Figure 4.4: Summary of palaeocurrent data for the Yadboro and Tallong Conglomerates and Badgery's Breccia. Rose petals indicate frequency. Note the east-directed dispersal pattern for me Badgery's Breccia. (^ GRGm^^-- /~~— J-- G0 Gm ^-^JBSh^^^V / GB Gm >Vv*- ___——=~-\. / K GB Gm \ / ' """— ^^Sfi^ L \ / GB Gm ~~" Z==:f^J_^3^L_^l - ' ^\ r / == '.\'.'.'.'•: SB Sh '. *.•• ^~T~~~y ' ^ — ?\ ~GnT / GB Gm \ - 1 m 0 —-^_ GB GB Gm ~~ \ Figure 4.6: Lateral profile 2: photomosaic and interpretative line drawing of a Tallong Conglomerate succession at "Johnny Fields". Architectural elements of Miall (1985) are indicated by bold abbreviations and lithofacies of Miall (1978) in normal type abbreviations. See tables 4.1 and 4.2 for definition of abbreviations. yf\ «- flooding If) / c CO , "<5 o / n. > / T3 o / CO u. J3 •71 «- flooding / c / ••" *t CO CD / Q. <•> / T3 > / CO O / n -7\ *- flooding co / c CD / CO o / Q. > / •o o / CO L. .D A\ «- flooding CM . c CD / CO O / Q. > / "D CO o / lm S3 *- flooding CD c CO O Q. > 73 o CO mm J2 Figure 4.7: Measured section of the Yadboro Conglomerate at the Casfle showing me five sedimentary cycles and interpreted flooding intervals which bound mem. See Figure 1.6 for symbol key. GELLO MILTON 'ULLADULLA —so— Isopachs (m) • Data points contour interval - 50m Figure 4.8: Isopach map for me Yadboro and Tallong Conglomerates. Figure 4.9b: Carbonaceous siltstone of the Yarrunga Coal Measures at Yagers Lookout section. Measuring tape = 1 m. Figure 4.9c: Intertidal channel of facies A at Mill Point. Channel Figure 4.9d: Inclined heterolithic stratification within intertidal fill consists of heterolithic strata (a), ripple laminated sandstone (b) channel facies A at Mill Point. Pebbley Beach Formation. and carbonaceous siltstone (c). Pebbley Beach Formation. I Figure 4.9e: Intertidal channel of facies A in plan view, showing Figure 4.9f: Basal unit of intertidal channel facies (facies A). The lateral accretion surfaces. Pebbley Beach Formation, North side of unit contains interbedded medium-grained sandstone and siltstone Mill point. indicating alternating energy conditions. Measuring tape = 1 m. Pebbley Beach Formation, Mill Point. $ contours in metres above present sea level datapoint inferred position of grabens Figure 4.10: Basement contour map showing positions of inferred graben structures related an extensional phase in the Early Permian. 0 5 rokm i i i MILTON ULLADULLA «r Data Point Figure 4.11: Palaeocurrent map for the Yadboro and Tallong Conglomerates. z O ////// /r* #~-i/—* (0) IS. * 490- <9fT-. Co) ////// yrty ///// 500- ////// J»>r~ '(o) If ? Sill J'^rM.r=^-L — ^ r (0) 510- EJ">(<>) 0.(0) (0) 520 _ si o o Figure 4.12: Measured section of the Yarrunga Coal Measures in DM Callala DDH1. See Figure 1.6 for symbol key. FornTations3' ^^ maP ** S0Uth&m C°aStal SeCti°nS 0f ** PebbIey Bea<* ** Snapper Point m aj Ui Ofl aj 4J c o •a aes o £L aj a. c- co c 00 60 c o •a a. •c u CO CD CO O CJ a) aj OJ cr C *o3 «J O u. •C CJ CO 4J ffl >, > aj OH Ad CD ,_, O s £ CM E n CO C/sS^ C o u. •O3 aj a CO vn T3 (1) u. ?-t-> •pf-p 3 3 CO Oil 3 CO iCD_ O -IZ v. Bay-head delta Central Basin Barrier/Inlet Figure 4.14b: Depositional model for backbarrier facies of the Pebbley Beach Formation. Figure shows distinct tripartite facies zonation, typical of wave-dominated estuaries (see figure 3.6). See text for facies descriptions. Figure 4.15a: Ripple lamination structures within facies A. Structures Figure 4.15b: The top part of the Clear Point Section at Clear Point. are typical of combined wave and current flow. Pebbley Beach Section is dominated by heterolithic tidal flat facies B (labelled B) Formation, Mill Point. and also contains lagoonal facies C (labelled C), washover facies D (labelled D), and tidal inlet facies (labelled E). Tape measure at bottom of photo = 1 m. Pebbley Beach Formation. Figure 4.15c: Ripple lamination showing combined flow structures Figure 4.15d: Ripple lamination in plan view. Tape measure = 1 m. within facies B. Pebbley Beach Formation, Mill Point. Pebbley Beach Formation, Mill Point. Figure 4.15e: Silicified log with root base intact. Pebbley Beach Figure 4.15f: Tidal inlet facies in the centre of the photograph Formation, North side of Mill Point. (labelled E) with tidal bundle (labelled tb). Bounding drapes of the bundle are indicated by arrows. Tape measure = 1 m. Pebbley Beach Formation, Clear Point. Total - Pebbley Beach Formation Facies A n=151 n=12 Facies B ^ Facies E n=16 n=34 Facies F - Wave ripples Facies F - Total n=16 n=44 Figure 4.16: Summary of palaeocurrent data for different facies of the Pebbley Beach Formation. Rose petals indicate frequency of occurrencex. Figure 4.17a: Hummocky cross-stratification within shoreface facies Figure 4.17b: Block of sandstone from shoreface facies F showing F. Tape measure = 1 m. Pebbley Beach Formation, Clear Point. low angle truncation of internal laminations within hummocky cross- stratification. Tape measure = 1 m. Pebbley Beach Formation, Clear Point. Figure 4.17c: Large coarse-grained wave ripples within shoreface Figure 4.17d: Diamictite unit (facies H) with large dropstones. Note facies F. Tape measure = 1 m. Pebbley Beach Formation, Clear the patch of pebbles upon which the hammer is resting. Pebbley Point. Beach Formation, north of Depot Beach. Figure 4.17e: Massive siltstone unit (facies I) capped by diamictite Figure 4.17f: Interbedded facies I and H, south of Pebbley Beach. unit (facies H). Tape measure = 1 m. Pebbley Beach Formation, Note the bioturbated contact between the units. Pebbley Beach South of Pebbley Beach. Formation. ICE COVER CLIMATE INTERGLACIAL 9Q&& >. o o >> o x: o > o .*CD: •ca GLACIAL WO^^q'Ol CO ^~ a) CO CO o a. 0O'fi£>dm0 * INTERGLACIAL .**. S = Seasonal ice cover p = Perennial ice cover *• ^ 11 •'' i'''' i mud silt sand gravel m Figure 4.18- Measured section at South Pebbles showing interpreted depositional environments and prevailing climatic conditions. See text for detailed discussion. See Figure 1.6 for symbol key. PARASEQUENCES CLIMATE H L 0 SPF 40- Glacial S \\\ Vuf o Interglacial 30- Glacial ^ tt ( k^-* 20- * 4 Interglacial ^ If r* \ % Glacial i ' • * I ' • '"' • " " '"O ^ / B Interglacial / \ \ / = o Glacial 1—T^ 111 I • I •' • ' 1 m mud silt sand gravel Figure 4.19: Composite section of me exposed Pebbley Beach Formation showing interpreted parasequences. The channelised interval within me section corresponds to the channelised interval exposed at Mill Point (see Fig. 4.14). See Figure 1.6 for symbol key. c Figure 4.20a: Glendonite. Pebbley Beach Formation, Clear Point K- shells Figure 4.20c: Ball and Pillow structures indicating soft sediment Figure 4.20b: Transgressive interval (labelled T) capped by deformation, possibly caused by earthquake. Measuring tape = 1 m. disarticulated and articulated Eurydesma shells. Pebbley Beach Pebbley Beach Formation, north Mill Point. formation, Clear Point. Figure 4.20d: Coastal facies in road cutting on Princes Highway, Figure 4.20e: Longshore sand bar facies (facies E). Note the change north of Milton. Note reflector post at the bottom of the photograph in dip angle of foreset lamina above the head of the person in the for scale. Snapper Point Formation. photograph. Snapper Point Formation, near Wilsons Beach, Currarong. V •^r.--*•-•«•.-*sp*r> Figure 4.21a: Mud drapes in longshore bar facies (facies E). Snapper Figure 4.21b: Swaley cross-stratification within upper shoreface Point Formation, near Abrahams Bosom Beach. facies (facies F). Tape measure = 1 m. Snapper Point Formation, Hoddles Cliff. Figure 4.21d: Embayment facies (facies I; labelled I) overlying a flaser bedded unit of the Pebbley beach Formation (labelled PBF). Note backpack at base of cliff for scale. Snapper Point Formation, South Pretty Beach. Figure 4.21c: Facies H succession, note the pebbly units within Figure 4.21e: Coquinite unit of facies J comprising Vacunella, section. Bar is approximately 1 m. Snapper Point Formation, Megadesmus and Astartilla valves. Shoalhaven Gorge, near Badgery's Lookout. <•- aouanbas aArssajgsirejj rt en -•8J trt <*-< SO. CO o 1.9 v-x 3 a 8 s 8o rt "O r3 .2 2 o ^ ft rt tz\ 4> •s ? & 00 O ffl "2 ° ~ S^§ 5 «-> c/i c e/ iQ 3M G '»-i '73 rt •!=! rt 2n rt o ^3 ~- rt rt 4> o o fi 3 o £ azg .52 . E rt -3 T3 rt8. jD3 cj rt rt • l—< O CO rt o eg o •w rt00 rt ™-t ^3 «> .fi «3 a o 2 3 rt O rt .a 9 «5 •• rt y <^ o <3 cj .2 . E ~-^ "S Figure 4.23a: Large coarse-grained wave ripples. Snapper Point Figure 4.23b: Succession of facies L (pebbly inner shelf). Snapper Formation, South side of Snapper Point. point Formation, St Georges Head, Jervis Bay. Figure 4.23d: Offshore siltstone (facies O). Note the numerous large clasts, interpreted as dropstones within the unit. Hammer for scale is left of centre of photograph. Snapper point Formation, Bannisters Head. ...^•^•^•_.-3SS^i Figure 4.23c: Cliff section on north Snapper Point showing facies Figure 4.23e: Succession within Pigeon House Creek. Sandstone M (inner shelf). Snapper Point Formation. cliffs represent fluvial facies (facies A). Intervening vegetated benches represent marine facies F (upper shoreface). Snapper point Formation. Braidplain facies Wave ripples n=43 n=156 Longshore Tidal facies Corang Peak n=64 n=14 Braidplain facies - Braidplain facies Pigeon House Creek Conjola Creek N n=20 n=13 Figure 4.24: Summary of Palaeocurrent data for the Snapper Point Formation. Length of rose petals indicates frequency of occurrence. • 35 • 170 combined SPF and NS isopachs in metres Ulladulla . datapoint /h 0 5 10 i 1 1 km Figure 4.25: Isopach Map for the Snapper Point Formation. Note the increase in thickness over a small distance between the 100 m and 300 m isopachs. This zone probably corresponds with a basin hinge zone. 1 Tallong Bore 2 Badgery's Lookout 3 Yagers Lookout 4 Tallowa Gorge 5 Hoddles Cliff 6 Tallowa Dam 7 Junction Yalwal/Shoalhaven 8 Yalwal 9 ECR2 10 Ben's Walk 11 ECR 11 13 Penguin Head 14 ECR 10 15 Little Beecroft Head 16 Bulee Gap 17 Tianjara Falls 18 Perch Hole Road 19 Stoney Creek 20 ECR 4 21 ECR 5 - 22 Kilpatrick Creek 23 Clyde River 24 ECR 3 25 Conjola Creek 26 Corang Creek 27 The Castle 28 Upper Pigeon House Creek 29 Landslide Creek 30 Pigeon House Mountain 31 Pointers Gap Lookout 32 Jindilara Creek 33 ECR 12 34 ECR 8 35 Bannisters Head Figure 4.26: Locality map for sections shown in Figures 4.27, 4.28, 4.29, 4.32, 4.35, 4.36 and 6.2. to CD O I o c w (0 O o n o n 3 C c S C*> VC E •a o c m a 0) VI TJ 3 TJ O O X rt O C CN •<*' tU I— o S3 o ttJJ E CD CO CD >- wm w c c •a r '5b " Q CO co lU9JjnD03G|Dd CO o c c CO **?:• WU«WiM s Cfl c o o CO Cfl T3 CO u 3 Cfl rt •uy iu|Od jaddeus sajnseevM 9)ejaujo|6uoo 6uo||Bi cu |BOO B6unueA u 3 SB Perch Hole Rd. Yalwa 30 20 Shoreface Shoreface 10 O o o v basement W//\ -t i i i i i i basement mud silt sand gravel mud silt sand gravel Figure 4.29: Measured sections from the central area. See Figure 4.26 for locations and Figure 1.6 for symbol key. Sth Snapper Pt. Nth Termeil Pt. mid-outer shell maximum flooding interval CYCLE 2 S Sth Termeil Pt. Sth_Pretty Beach transgressive ,L surface Shoreface Sth Island Beach Clear Pt. CYCLE 1 Embayment •.'••A ° foreshore Figure 4.30: Measured sections from the south coast showing interpreted sedimentary cycles (see text for detailed discussion). See Figure 4.13 for section locations and Figure 1.6 for symbol key. Meroo Pt. Nuggans Pt. Nth Snapper Point Willinga Pt. mid-outer shelf maximum flooding interval mid-outer shelf CYCLE 3 Shell Bank CYCLE 2 mid-outer shelf Figure 431- Measured sections from the south coast showing interpreted sedimentary cycles. The base of the North Snapper Point section correlates with the top of the South Snapper Point section in Figure 4.30. See Figure 4.13 for locations and Figure 1.6 for symbol key. ECR10 Bannisters Hd. Figure 4.32: Measured sections from the upper part of the Snapper Point Formation showing interpreted parasequences in ECR10. Note the scale change from the ECR10 section to the Little Beecroft Head section. See figure 4.26 for locations and Figure 1.6 for symbol key. " iJgf*- m&f£ W ---. Figure 4.33a: The Snapper Point Formation within the Shoalhaven Figure 4.33b: Section at Mermaids Inlet, Beecroft Peninsula. Gorge comprising monotonous succession of nearshore marine Siltstone interval (labelled A) marks the lower part of the uppermost sandstone. Hoddles Cliff. parasequence within the Snapper point Formation. The underlying succession belongs to that of the underlying parasequence. Changes in grainsize such as in the silty interval in the centre of the photograph may represent higher order cycles. Snapper point Formation. Figure 4.33c: Uppermost parasequence in the Snapper Point Figure 4.33d: Intensely deformed interval at Warden Head. Formation showing regressive sequence from offshore siltstone facies Wandrawandian Siltstone. at the base to foreshore and longshore sand bar facies at the top. Near Mermaids Inlet, Beecroft Peninsula. Figure 4.33e: Intensely convoluted and deformed conglomeratic unit underlying lobate sandstone body. Note the siltstone intraclasts at the top right of the conglomeratic unit and the irregular basal contact. Wandrawandian Siltstone, Lagoon Head. Figure 4.34: Palaeocurrent map for longshore sand bar facies (Snapper Point Formation) at the top of parasequence E. Figure 435: Measured sections from the Snapper Point Formation showing correlation between the western and eastern areas. Note the scale change between the Pigeon House Creek and ECR8 sections and also the ECR10 and southern area section. This diagram shows the vast thickening of cycle thickness from west to east (see text for detailed discussion). ECR10 and the composite southern section have been included to show correlation between coastal sections. See Figure 4.26 for locations and Figure 1.6 for symbol key. w ECH11 Hoddles Cliff Badgery's Lookout ECR10 Parasequence B IVU f Figure 4.36: Measured sections from the Snapper Point Formation showing correlation between northwestern and eastern areas Note the scale change between the Hoddles Cliff and ECRU section. As for Figure 4.35, this diagram shows the vast cycle thickening from the west to east (see text for detailed discussion). See Figure 4.26 for locations and Figure 1.6 for symbol key Transgression NW MFI1^ transgression FS Sea level curve B NW Progradation sw regression transgression Sea level curve Figure 4.37: Schematic representation of the southern Sydney Basin during Snapper Point period showing depositional response to transgression (A) and regression (B). Sea-level rise results in transgression and consequent nearshore marine deposition in the west and an upward fining sequence (transgressive half sequence) in the east. Subsequent sea-level fall results in braidplain progradation in the west and an upward coarsening sequence (regressive half sequence) in the east culminating in nearshore (shoreface) marine sedimentation. 15 - & shelf (9 v7 0 10- % tr F IT W mass flow oMo0 0 < c> "^r "CO 5 -. £_A A* W^" 60 6 shelf ^ %. W Id's 35\&z 0 ^?ff i \ 11111 m mud silt sand grave Figure 438: Measured section of the Wandrawandian Siltstone at Lagoon head. See Figure 1.6 for symbol key. Figure 4.39a: Lagoon Head section showing amalgamated plane Figure 4.39b: Glendonite at Warden Head. Wandrawandian Siltstone. bedded sand units lensing out towards the north. Blue backpack (arrowed) for scale. Wandrawandian Siltstone, Lagoon Head. Figure 4.39c: Conglomeratic facies of Purnoo Conglomerate Member Figure 4.39d: Nowra Sandstone at Tianjara Falls. (hammer resting on unit). Nowra Sandstone, Yawal Mountain. Figure 4.39e: Low angle cross-bedding. Measuring stick = 2 m. Nowra Sandstone, Deans Gap Road. f* j? isopachs in metres datapoint Figure 4.40: Isopach map of the Wandrawandian Siltstone. VV I \*t. r i«' -*4 vJ Figure 4.41a: Planar cross-bedded facies (facies C). Measuring stick Figure 4.41b: Interbeddechsandstone and bioturbated sandy siltstone = 2 m. Nowra Sandstone, Tianjara Falls. facies (facies F) at base of Tianjara Falls section. Increments on measuring stick = 10 cm. Nowra Sandstone. Figure 4.41c: Interbedded sandstone and bioturbated sandy siltstone facies (facies F) at Penguin Head, Culburra. Measuring tape = 1 m. Nowra Sandstone. t Figure 4.42: Summary of palaeocurrent data and palaeocurrent map for the Nowra Sandstone. Rose petal length indicates frequency of occurrence. <§> isopachs in metres datapoint Figure 4.43: Isopach map for the Nowra Sandstone. Figure 4.44: Palaeoenvironmental map from Le Roux and Jones (1994) showing position of interpreted sand shoal, coarse lithofacies, the ratio between low angle (Sh) and high angle (Sx) stratification and depocentres. Note the correlation between the position of depocentres and the position of the Yadboro and Tallong Conglomerates (Figure 4.8). o cro rjc "r S C P rt re b ^ a 0 CO CO TO TO <=" g TOo "~ £TO *• ena CO TO TO O TO P. TO* O o 5^ °> 3 TO e TO E.cfo P- TO z TO _ o - £"aa P ^ 5' o » co c- ps co O p o' P Q. >^ H-, O CTO CO CD TO gg_ TO ^g £ o cro i— oB cro °^crotro TO Q> O TO « P "i ^ P P3 v> TO — 3 fi ^ P TO TO CT Co o p " pr 3 c TO •" _ ^^ — TO • o e: I | » E S a tr TO TO TO o 2 = 5 m Q QUARTZARENITE SUBARKOSE °S8S$& SUBLITHARENITE o SG *• TG Figure 5.1: QFL plot for sandstone samples from the Talaterang and Shoalhaven Groups. Classification scheme is that of Folk et al. (1970) Q=total quartz, F=total feldspar, L=total lithics, TG=Talaterang Group, SG=Shoalhaven Group. Lm SG TG / / / / Lv Ls Figure 5.2: LmLvLs plot for sandstone samples from the Talaterang and Shoalhaven Groups. Lm=metamorphic lithics, Lv=volcanic lithics, Ls=sedimentary lithics, TG=Talaterang Group, SG=Shoalhaven Group. Figure 53: QFL plot of sandstone samples from formations of the* Talaterang Group. Classification as per Folk et al (1970). WHF=Wasp Head Formation, CCM=Clyde Coal Measures. • ° / / / 1 \\ / / \ / V \ \ \ = ws F \ \ \ \ /' / / / — \ \ Figure 5.4: QFL plots of sandstone samples from formations of the Shoalhaven Group. Classification scheme is that of Folk et al. (1970). TALLC=Tallong Conglomerate, PBF=Pebbley Beach Formation, SPF=Snapper Point Formation, WS=Wandrawandian Siltstone, NS=Nowra Sandstone. PRE-PERMIAN SOURCE ROCKS IN SOUTH EASTERN N.S.W. 20ml 20 K / v • V V ' V 90- • V • • V • V • V V V V • V - V ' • V ' • V ' V . V 80- V V V . V r . V . • V . 70- 60- 0 <0. X X O 0 X Figure 5.5: Distribution of Pre Permian rocks from Gostin (1968). Bar graphs show proportions of different rock types within each annulus at radial distances of 0, 25, 50, 75 and 100 miles. Figure 5.6: QFL plot showing variation of Snapper Point Formation sandstone composition with core locality. Locations of cores is given in Figure 4.26. Plot shows that there is no significant variation in composition across the study area. Q ° SG • TG Lt Figure 5.7: QFL and QmFLt plots for sandstone samples from the Talaterang and Shoalhaven Groups, showing inferred provenancefields of Dickinson et al. (1983) and Dickinson and Suczek (1979). Qm=monocrystalhne quartz, F=total feldspar, Lt=total lithics + polycrystalline quartz. Key to provenance fields. CI=craton interior, BU=basement uplift, DA=dissected arc, LR=lithic recycled, M=mixed, QR=quartzose recycled, RO=recycled orogenic TA=transitional arc TC=transitional continental, TR=transitional recycled, UA=undisSd ic Figure 6.1: Early Permian palaeogeographic development of the southern Sydney Basin during deposition of (a) Clyde Coal Measures and Wasp Head Formation, (b) Tallong/Yadboro Conglomerate, Yarrunga Coal Measures and Pebbley Beach Formation, (c) Snapper Point Formation, (d) Wandrawandian Siltstone, (e) Nowra Sandstone and (f) Berry Siltstone. STAGE 3 - 268 Ma (Evans stage 3b-4) units: Snapper Point iFormation comments: • tectonic phase B • flooding event A at onset of stage STAGE 4 - 265 Ma (Evans stage 5) units: Wandrawandian Siltstone /v comments: • tectonic phase B • flooding event B • foreland loading at orogen y\ •A- • emergent orogen • subaerial volcanism -s\ y\. y\ Figure 6.1 (cont.) STAGE 5 - 262 Ma (Evans stage 5) units: Nowra Sandstone comments: • tectonic stage B • tectonic quiescence • Progradation of clastic wedge STAGE 6 - 260 Ma (Evans stage 5) units: Berry Siltstone comments: • tectonic stage B - C • flooding event C • renewed foreland loading Figure 6.1 (cont.) gf S» w * 0 en NJ •Sl^o^f-. ??! P P 1-1 .. TO co TO CO O 1-1 C CO CO I CO ."> •I' 0" TO 1 y, 01 Cfl O o 3- 3 01 cs 01 c =r o -i -i n i o o o1-1 o cTOo c*-*o O c 8 -a c TO co C C C. TO co TO TO cro c •-I TO k> co TO O c. c TO c; C. c n m C5 cro w E ECR4 Kilpatrick Ck. Figure 6.2b: East-West cross-section across the central area of the southern Sydney Basin See Figure 4.26 for section locations. CCM=CIyde Coal Measures, YC=Yadboro Conglomerate SPF=Snapper Point Formation, WS=Wandrawandian Siltstone, NS=Nowra Sandstone* W c Landslide Ck. ECR12 ECR8 The Castle Corang non-marine SPF :o0\ • 0 „ °n o Figure 62c: East-West cross-section across the southern part of the southern Sydney Basin. See Figure 4.26 for section locations. Abbreviations as for 6.2b. (a) SYSTEM 5 SYSTEM 4 SYSTEM 3 SYSTEM 2 SYSTEM 1 (b) w SYSTEM 5 _ flooding event C — progradation _ — _ _ SYSTEM 4 - ~ maximum Hooding surface _. _-outer marine shelf — flooding event B fluvial/nearshore marine -—_ nearshore marine/shelf 01 SYSTEM 3 < flooding event A SYSTEM 2 SYSTEM 1 Figure 6.3: Schematic cross-section (a) and Time-space (Wheeler) diagram (b) for southern Sydney Basin. CCM=Clyde Coal Measures, WHF=Wasp Head Formation, T/YC=Tailong/Yadboro Conglomerate, YCM=Yarrunga Coal Measures, PBF=Pebbley Beach Formation, SPF=Snapper Point Formation, WS=Wandrawandian Siltstone, NS=Nowra Sandstone, BS=Berry Siltstone. Tallo g Bore Cora ^ Nowra Sandstone _Y Wandrawandian Siltstone Snapper Point Formation y\r Pebbley Beach Formation ~'a Tallong/Yadboro Conglomerate A Wasp Head Formation f Clyde Coal Measures Figure 6.4: Fence diagram for units of the southern Sydney Basin. C.R.= Clyde River, L.C.=Landslide Creek. Townsvilie TN \ "* ( '•• \& Qr. X GOGANGO GALILEE o OVERFOLDED ^ BASIN i-V ZONE 200 km 1 ID \ f" V) Q: : * • \ r- f :,:.'::..::- Rockhampton Q4 % 0% o 0 IP 3 Bnsbane THOMSON AND O LACHLAN iFOLD BELTS 0 r° ^ CD m J0-- r- —i \ V.WERRIE / REFERENCE * WW^BASAL T / Geological boundary «•- Fault Axis of Taroom Trough and 7 >::. :;|;S|/Newcastie depocentres of Gunnedah Basin : (after Exon 1974 and Tadros 1988c) LACHLAN \«':i Meandarra Gravity Ridge FOLD (from Murray. Scheibner & Walker 1989) BELT fef-7 :«)Sydney /OT|- / w- Permian - Triassic basins /42' M4' 146" US' «o- «2- «<• /«• 19683 Figure 6£: Structural map of the Sydney-Bowen basin showing the position of the Meandarra Gravity Ridge, (from Tadros 1994b modified from Murray 1990). Figure 6.6a: View looking south from Mount Bushwalker. Basal cliffliue (labelled YC) is the Yadboro Conglomerate and can be clearly seen pinching out to the north. The Snapper Point formation is difficult forms the uppermost part of the lower cliffline and can be seen to the far right of the photograph (labelled SPF). The Wandrawandian Siltstone (labelled WS) is denoted by the vegetated bench between the two major clifflines. The uppermost cliffline is formed by the Nowra Sandstone (labelled NS). Figure 6.6b: View looking north from Pigeon House Mountain. Lower cliffline within the gorge is Yadboro Conglomerate (labelled YC) and is overlain by Snapper Point Formation (SPF), Wandrawandian Siltstone (labelled WS) and Nowra Sandstone (labelled NS). Note the characteristic sandstone cliffs of the Snapper Point Formation in the southwestern part of the area, defining interbedded fluvial and marine facies. Figure 6.6c: The Snapper Point Formation (labelled SPF) and Nowra Sandstone (labelled NS) in the Shoalhaven Gorge, near Yagers Lookout. Note the sharp contact between the two formations. EAST WEST SU8DUCT1ON-IN0UCED SUBSIDENCE Figure 6.7: Idealised structural and stratigraphic cross-section from the western Canada foreland basin. The arrows indicate direction, relative uplift, subsidence and thrusting. The sediments of the southern Sydney Basin were deposited close to the cratonic margin of the basin in zone 4 (Hinge zone). From Leckie and Smith 1992. Figure 6.8: A typical clastic wedge resulting from a foreland accretion event. Foreland loading leads to a high subsidence rate and the deposition of transgressive depositional systems. Subsequent erosion of the foreland causes sedimentation to overwhelm subsidence and thus a highstand progradational tract is produced, derived from the orogen. (From Cant and Stockmal 1993 based on concepts in Devlin et al 1993). 5th Order 4th Order 3rd Order comments — _ — LU C/3 CO CD < X 0- renewed foreland loading o z ravinement surface <— flooding event C C/3 ^~ o r- o LU tectonic quiescence 5 _— ~ maximum flooding surface <— flooding event B - onset of foreland loading - orogen becomes emergent LL Q. i - ? J^-_ — <— flooding event A o >• 8) — LL _ m ° \- passive thermal sag/embryonic foreland Q. o ° s o ( — >- 0 S 1 1- a* A c LL * \ I O o O \ LU rifting i < I o 0- o sea-level fall sea-level rise "^ Figure 6.9: Interpreted relative sea-level curves for the Talaterang and Shoalhaven Groups. Diagram shows the three orders of cyclicity. Tectonic effects on third order change are indicated in the last column. TABLES Facies Lithology Sedimentary Structures interpretation pebble conglomerates and trough cross-bedding and deposition from lower flow A: Channel composite units of fine to ripple cross-lamination regime within fluvial channel medium-grained sandstone interbedded fine-grained ripple cross-lamination, splay deposition near B: Proximal sandstone sheets, minor channelisation, soft channel, waterlogged floodplain carbonaceous siltstone and sediment deformation floodplain and peat bogs thin coal seams interbedded carbonaceous waterlogged floodplain, peat C: Distal siitstone, oil shale, coal ripple cross-lamination, soft bogs with distal splay floodplain seams and minor sheet sediment deformation deposits sandstone beds tidally influenced fluvial D: Bay-head heterolithic unit consisting of ripple cross-lamination and deposition at the landward Delta siltstone and sandstone lateral accretion surfaces end of estuary central basin of estuary with E: Estuarine carbonaceous siltstone and thin lamination, bioturbation minor washover sand Lagoon minor sandstone deposits thick composite units of erosional contacts, deposition at marine end of F: Estuarine medium- to coarse-grained channelisation, trough estuary within a barrier-inlet inlets/barriers sandstone and minor pebble cross-bedding and bimodal system conglomerate palaeocurrent distribution Table 3.1: Facies summary for the Clyde Coal Measures. Sedimentary Facies Lithologies Fossils Interpretation Structures A: debris cohesive debris flow breccia, siit-rich matrix chaotic fabric absent flows deposits flat lamination, upper shoreface fine- to medium-grained B: littoral hummocky cross- molluscs, gastropods under influence of sandstone, pebble shoreface stratification, trough and bryozoans longshore tidal conglomerate cross-bedding currents fine-grained sandstone massive to plane wave fluidisation C:upper Traces: Rosselia, and minor pebble bedding, minor and bioturbation on shoreface A Skolithos conglomerate bioturbation upper shoreface molluscs (including wave-reworked D:upper medium-grained swaley cross- Eurydesma), upper shoreface shoreface B sandstone stratification gastropods, rare deposition brachiopods amalgamated wave-reworked E: lower fine-grained sandstone hummock cross- Traces: Skolithos lower shoreface shoreface stratification depostion hummocky cross- Traces: deposition between stratification, large fine-grained sandstone, Diplocraterion, fairweather and F: transition coarse-grained wave siltstone and pebble Rhizocorallium, storm wave base in offshore A ripples, pervasive conglomerate Rosselia, transition offshore bioturbation in siltstone Psammichnites environment beds Brachipods, molluscs hummocky cross- thick units of fine and bryozoans. stratification, plane as for facies F but G: transition grained silty sandstone, Traces: bedding, pervasive probably in deeper offshore B fine sandstone and Diplocraterion, bioturbation in fine water environment siltstone Rhizocorallium, grained unit Rosselia Table 3.2: Facies summary for the Wasp Head Formation. Facies Facies Sedimentary Structures Interpretation code Gms massive, matrix supported gravel grading debris flow deposits Gm massive or crudely bedded gravel horizontal bedding, imbrication longitudinal bars, lag deposits, sieve deposits Gl gravel, stratisfied trough cross beds minor channel fills Gp gravel, stratisfied planer cross beds longitudinal bars, deltaic growths from older bar remnants St sand, medium to very coarse, solitary or grouped trough cross beds dunes (lower flow regime) may be pebbly Sp sand, medium to very coarse, solitary or grouped planer cross beds linguoid. transverse bars, sand may be pebbly waves (lower flow regime) Sr sand, very fine to coarse rippje cross lamination ripples (lower flow regime) Sh sand, very fine to very coarse horizontal lamination planer bed flow (upper flow may be pebbly parting or streaming lineation regime) SI sand, very fine to very coarse low angle (<10°) cross beds scour fills, washed-out dunes, may be pebbly antidunes Se erosional scours with intraclasts crude cross bedding scour fills Ss sand, fine to very coarse, may be pebbly broad, shallow scours scour fills Fl sand, silt, mud deposits fine lamination, vey small ripples overbank or waning flood Fsc silt, mud laminated to massive backswamp deposit Fcf mud massive, with freshwater molluscs backswamp pond deposits Fm mud, silt massive, desiccation cracks overbank or drape deposits c coal, carbonaceous mud plant, mud films swamp deposits P carbonate pedogenic features paleosol Table 4.1: Lithofacies scheme devised by Miall (1977, 1978) for fluvial environments. Facies Architectural element Geometry Interpretation Miall (1978) tabular or sheet-like, laterally gravel bar deposits, includes Gm, Gt, Gp, extensive units, forms GB both longitudinal and Sh, St, Ss multistorey sheets, interbedded transverse bar types with SB elements tabular or sheet-like, laterally Sh, St minor SB extensive units, closely sand bar deposits Gm associated with element GB overbank deposition on or Fl thin, laterally extensive units abandoned braidplain Table 4.2: Summary of Architectural elements for the Tallong and Yadboro Conglomerates. First order Set-Bounding surfaces Second order Coset-bounding surfaces, associated with a change of lithofacies type Cross-cutting erosion surfaces which dip at a low Third order angle and run from the top to the bottom of a macroform. They record increments of macroform accretion Flat to convex-up surfaces representing the upper Fourth order bounding surfaces of macroforms. Facies assemblages above and below the surface may be quite different. Fifth order Laterally extensive surfaces bounding channel-fill complexes. Sixth order Surfaces defining mappable subdivisions Table 4.3: Bounding surface hierarchy for fluvial systems as outlined by Miall (1988). Facies Lithology Characteristics Trace fossil types Interpretation large channelised heterolithic base heterolithic-interbedded very Inclined heterolithic stratification, fine to fine sandstone and Phycosiphon, A combinedflow ripple structures, intertidal channels siltstone, rare lensoidal fine Diplocraterion may be capped by lensoidal sandstone carbonaceous mud unit Rosselia, Psammichnites, heterolithic-interbedded very laterally continuous units, Planolites, Phycosiphon, tidal flats - margins of B fine tofine sandstone and combinedflow ripple structures , Conostichus, back-barrier lagoon siltstone, sandy siltstone bioturbation, logs Diplocraterion, Rhizocorallium laterally continuous, pervasive central basin of back- c dark carbonaceous siltstone Phycosiphon, Rosselia bioturbation, pyrite staining barrier lagoon laterally continuous units, Diplocraterion, Skolithos, washover or flood tidal D silty fine to medium sandstone pervasive bioturbation, associated Phycosiphon, delta deposits with facies B and C Palaeophycus laterally continuous, trough cross- bedding, sigmoidal tidal bundles, Diplocraterion, Rosselia, E medium sandstone mud drapes, ripple cross- tidal inlet deposits Skolithos lamination, rare bioturbation, sharp base laterally continuous, hummocky Diplocraterion, Rosselia, cross-stratification within clean Asterosoma. Taenidium interbedded clean, well sorted sandstone units, pervasive barretti, Phycosiphon, F fine sandstone and silty shoreface bioturbation in silty sandstone, Teichichnus, sandstone some amalgamation of HCS Rhizocorallium, sandstone beds Palaeophycus, Skolithos pervasive bioturbation, micro- Phycosiphon, Rosselia, sandy siltstone with minor fine G hummocky cross-stratification, Diplocraterion, offshore sandstone phases logs Chrondrites silty diamictite with clasts up Diplocraterion, offshore ice rainout H to approximately 1.5m in pervasive bioturbation, logs Rhizocorallium deposits diameter 1 massive siltstone biogenically homogenised Phycosyphon ice covered shelf Table 4.4: Facies summary for the Pebbley Beach Formation. Facies lithologies Characteristics Trace fossil types Interpretation medium to coarse trough cross-bedded, grained sandstone, A plane bedded, pebble absent braided river pebbly sandstone and imbrication, channelised conglomerate predominantly thinnly interbedded siltstone and combined flow ripple back-barrier tidally Rosselia B fine sandstone with some lamination, HCS within influenced environment lenticular fine sandstone sand bodies, bioturbation beds poorly sorted angular to transgressive shoreline often contains chaotic rare Polykladichnus, rounded pebble to deposit, ravinement c fabric Arencolites boulder conglomerate surface plane bedded, low angle Interbedded medium to cross-bedded.abundant Palaeophycus, beach or foreshore coarse sandstone and D thick shelled molluscs Arencolites deposit conglomerate (Eurydesma) planar cross-bedded, trough cross-bedded Gyrolithes, thick units of medium to plane bedded, mud Macaronichnus, tidally influenced coarse sandstone and E drapes, thickening Monocraterion, very longshore sand deposits pebbly sandstone foresets, moderate large Rosselia, Skolithos bioturbation amalgamated HCS rare Large Diplocraterion,Wav e dominated upper thick monotonous units of (swaley cross- F Phycosiphon, Skolithos, shoreface, above medium sandstone stratification), siltstone Arencolites fairweather wave base and bioturbation absent thick units of fine to wave dominated middle amalgamated HCS, Diplocraterion, medium sandstone with shoreface, close to but G siltstone units are Phycosiphon, Rosselia, thin lensoidal siltstone below fairweather wave bioturbated Astersoma beds base sandstone contains interbedded fine to amalgamated HCS, fluvially influenced wave medium sandstone, Rosselia, Astersoma, H Conglomerate is plane dominated shoreface pebble conglomerate and Diplocraterion bedded, siltstone is deposit minor siltstone bioturbated pervasive bioturbation, Dipocraterion, Rosselia, minor lenses of thick sequences of fine Rhizocorallium, semi-protected undisturbed HCS 1 silty sandstone, minor Astersoma, embayment, sediment sandstone, dropstones, conglomerate Teichnichnus, was emplaced via storms large coarse grained Phycosiphon wave ripples, logs Table 4.5: Facies summary for the Snapper Point Formation. Facies lithologies Characteristics Tracefossil type s Interpretation pervasive bioturbation, Astersoma, Rosselia, storm lag deposits, abundant disartiulated coarse shelly sandstone Rhizocorallium, large probably above storm molluscs in coarse J grading up to bioturbated Rhizocorallium, wave base on the interval, molluscs in life fine silty sandstone Phycosiphon, Large shoreface, sediment position in upper silty Diplocraterion starved sandstone Wave lamination, minor trough cross-bedded, Phycosiphon, Large Storm influenced upper Interbedded, pebbly swaley and hummocky Diplocraterion, Rosselia,offshor e deposit, source coarse sandstone, and L cross-stratif icatjon, Astersoma, area probably a fluvially silty fine sandstone peravsive bioturbation in Diplocraterion, Skolithos influenced shoreface fine silty sandstone interbedded silty fine Large Diplocraterion, sediment starved, storm sandstone and thin pervasive bioturbation, Phycosiphon, Rosselia, dominated, upper coarse pebbly sandstone, large coarse-grained M Astersoma, offshore, deposition coarse grained lithologies wave ripples, minor HCS Diplocraterion, probably occurred close are minor in comparison and plane bedding Macaronichnus to storm wave base with facies L thinnly interbedded flat lamination, minor Phycosiphon, Rosselia, distal storm deposit, N siltstone and fine to very HCS Astersoma, Planolifes lower offshore fine sandstone pervasive bioturbation, siltstone, sandy siltstone pervasive-indistinct lower offshore 0 dropstones, logs Table 4.5 (cont.) Facies Lithology Structures Interpretation conglomerate, pebbly storm and transgressive lag A plane bedded sandstone deposits plane bedding and low angle B medium-grained sandstone foreshore bedding, minor bioturbation medium- and coarse planar cross-bedding, minor C longshore tidal sand bars grained sandstone bioturbation deeper facies associated with D medium-grained sandstone trough cross-bedding facies C massive, pervasive difficult to ascertain, probably E medium-grained sandstone bioturbation shoreface interbedded fine-grained pervasive bioturbation, F sandstone and bioturbated sandstones have distinct lower shoreface siltstone lenticular geometry Table 4.6: Facies summary for the Nowra Sandstone. APPENDIX 1 Locations of sections Section Grid reference Badgery's Lookout 8928-346481 Bannisters Point 8927-712880 Beecroft Peninsula 9027-017235 Bens Walk 8927-795381 Boyd Lookout 8927-603044 Bulee Gap 8927-385129 Bunnair Creek 8927-630973 Burrier - Road cutting 8928-707357 Cambage Head 8927-501887 Clear Point 8926-593566 Conjola Bridge 8927-664998 Conjola Creek 8927-608988 Corang 8927-360905 Crampton Island 8927-650743 Crookhaven Heads 9028-962360 Deans Gap Road 8928-658264 Gibralter Rocks 8828-742650 Govenors Head 9027-962108 Hoddles Cliff 8928-493471 Jindelara Creek A 8927-568858 Jindelara Creek B 8927-556858 Johnny Fields 8928-265643 Kilpatrick Ck 8927-461992 Lagoon Head 8927-679782 Landslide Creek 8927-520869 Leahaven 9028-772376 Little Beecroft Head 9027-030240 Little Oakey Creek 8928-381303 Longfella Ridge 8927-494845 Meroo Point 8927-634705 Mill Point 8926-584559 Mount Bushwalker 8927-533955 Myrtle Beach 8926-558476 Narrawallee Inlet 8927-701901 North Dawsons Island 8926-601590 North Granite Rock 8926-597584 North Oakey Creek 8928-395337 North Snapper Point 8926-623607 North Steamers Beach 9027-932050 Nowra Golf Club 9028-804394 Nuggans Point 8927-634690 Old Burrier Fire Trail 8928-631352 Penguin Head 9028-976322 Perch Hole Road 8927-674086 Pigeon House Mountain 8927-514847 Point Upright 8926-576527 Section Grid Reference Pointers Gap Lookout 8927-593944 Shoalhaven Gorge A 8928-364460 Shoalhaven Gorge B 8928-372455 South Conjola 8927-658946 South Emily Miller Beach 8926-558485 South Island Beach 8926-607597 South Pebbles 8926-574544 South Pretty Beach 8926-610602 South Snapper Point 8926-615603 South Termeil 8927-635725 St-Georges Head 9027-900021 Stoney Creek 9027-953057 Tallong 8928-341541 Tallowa Dam 8928-547491 Tallowa Gorge 8928-465515 The Castle 8927-451903 Three Mates Bluff 8928-563452 Tianjara Falls 8927-566112 Touga Creek 8928-373244 Tullyangela Clearing 8928-411313 Upper Clyde River 8927-510032 Upper Pigeon House Creek 8927-525943 Wandean Gap 8927-640127 Warden Head 8927-720832 Wasp Head 8926-560492 Willinga Point 8926-634580 Yagers Lookout 8928-416435 Yalwal 8928-618337 Yalwal Gap 8928-631330 Yalwal Mountain 8928-608305 Yalwal Road 8928-703350 Yalwal/Shoalhaven Junction 8928-606427 Yarramunmun Fire Trail A 8928-596255 Yarramunmun Fire Trail B 8927-590224 Yarramunmun Fire Trail C 8927-550139 Yarrunga Creek 8928-597518 DRILLCORE Grid Reference Elecom Clyde River 1 8928-433546 Elecom Clyde River 2 8928-700282 Elecom Clyde River 3 8927-536045 Elecom Clyde River 4 9027-760015 Elecom Clyde River 5 8927-402991 Elecom Clyde River 6 8927-615742 Elecom Clyde River 8 8927-688933 Elecom Clyde River 10 9028-936270 DRILLCORE Grid Reference Elecom Clyde River 11 9028-793244 Elecom Clyde River 12 8927-614954 DM Callala DDH1 9028-892268 Armco Shoalhaven DDH1 8928-685362 Bellambi Shoalhaven DDH1 8928-613524 Wandrawandian Bore 8927-710194 Genoa Oil Coonemia 1 9028-909284 Huskisson DDH1 9027-872197 BMR Wollongong No. 1 9028-807285 BMR Wollongong No. 2A 9028-855286 Tallong Bore 8928-330542 Long Swamp DDH 8928-327579 APPENDIX 2 Measured sections Key to abbreviations: CCM = Clyde Coal Measures, WHF = Wasp Head Formation, TC = Tallong Conglomerate, YC = Yadboro Conglomerate, YCM = Yarrunga Coal Measures, PBF = Pebbley Beach Formation, SPF = Snapper Point Formation, WS = Wandrawandian Siltstone, NS = Nowra Sandstone. 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