The Glacial History of the Upper Mersey Valley
Total Page：16
File Type：pdf, Size：1020Kb
THE GLACIAL HISTORY OF THE UPPER MERSEY VALLEY by A a" D. G. Hannan, B.Sc., B. Ed., M. Ed. (Hons.) • Submitted in fulfilment of the requirements for the degree of Master of Science UNIVERSITY OF TASMANIA HOBART February, 1989 CONTENTS Summary of Figures and Tables Acknowledgements ix Declaration ix Abstract 1 Chapter 1 The upper Mersey Valley and adjacent areas: geographical 3 background Location and topography 3 Lithology and geological structure of the upper Mersey region 4 Access to the region 9 Climate 10 Vegetation 10 Fauna 13 Land use 14 Chapter 2 Literature review, aims and methodology 16 Review of previous studies of glaciation in the upper Mersey 16 region Problems arising from the literature 21 Aims of the study and methodology 23 Chapter $ Landforms produced by glacial and periglacial processes 28 Landforms of glacial erosion 28 Landforms of glacial deposition 37 Periglacial landforms and deposits 43 Chapter 4 Stratigraphic relationships between the Rowallan, Arm and Croesus glaciations 51 Regional stratigraphy 51 Weathering characteristics of the glacial, glacifluvial and solifluction deposits 58 Geographic extent and location of glacial sediments 75 Chapter 5 The Rowallan Glaciation 77 The extent of Rowallan Glaciation ice 77 Sediments associated with Rowallan Glaciation ice 94 Directions of ice movement 106 Deglaciation of Rowallan Glaciation ice 109 The age of the Rowallan Glaciation 113 Climate during the Rowallan Glaciation 116 Chapter The Arm, Croesus and older glaciations 119 The Arm Glaciation 119 The Croesus Glaciation 132 Tertiary Glaciation 135 Late Palaeozoic Glaciation 136 Chapter 7 Conclusions 139 , Possible correlations of other glaciations with the upper Mersey region 139 Concluding remarks 146 References 153 Appendix A INDEX OF FIGURES AND TABLES FIGURES Follows page Figure 1: Location of the study area. 3 Figure 2: Solid geology of the upper Mersey Valley. 4 Figure 3: Rainfall map of part of western Tasmania showing isohyets which intersect the study area. Values are in mm. (Bureau of Meteorology, 1980) 10 Figure 4: Aerial view of the irregularly-shaped Chalice Lake showing the glacially abraded surface and the centripetal drainage pattern. The steep-sided valley which bounds the eastern edge of the Cathedral Plateau runs from lower right to top left and Chapter Lake is visible in the upper centre part of the photograph. 30 Figure 5: The U-shaped Mersey Valley viewed from Cathedral Mountain with the flat-floored Lees Paddocks and the river meandering across them. The narrow plateau below Mount Pelion East is visible on the top left of the photograph. Mount Pillinger is in the background showing a 'reverse slope'. 30 Figure 6: A small hanging valley at Grail Falls where the stream from Chalice Lake flows into the overdeepened valley which contains 'Chapter Lake. Ice moulded valley edges are also visible. 34 Figure 7: Glacial striations on mudstone lying beneath Rowallan Till. The smoothed surface of the mudstone is clearly visible and the blocky, fissile nature of the mudstone can be seen by the way it has broken on the left of the photograph. 34 Figure 8: Miniature crag and tail in mudstone, lying underneath soliflucted Croesus Till. The smooth nature of the surface is apparent where it has been washed. Ice movement was generally in the same direction as the photograph was taken. 35 Figure 9: Pressure release gully at the top of the Mersey Valley above Steers Plain. The width of the gully is approximately 5 m and boulders on the floor result from minor toppling. 49 Figure 10: Rowallan Till is superimposed on Arm Till. The matrix of the Rowallan Till is unweathered and is a greyish colour. The matrix of the Arm Till shows manganese staining and is weathered a reddish brown colour. 49 Figure 11: Stratigraphic column of the February Creek section showing Rowallan Till superimposed on Arm Till. 52 Figure 12: The section in the overspill channel of Rowallan Dam. 53 Figure 13: The sedimentary complex resting on the quartzite and schist rock bar below the Rowallan Dam. The unconformity between Arm and Rowallan age sediments is shown by the arrow. The two sticks are 5 m apart. The boulders at the top of the complex are fill. 53 Figure 14: The Rowallan Dam section showing Arm age soliflucted till underneath Rowallan age till and glacifluvial sand and gravel. The iron pan appearance of the unconformity is clearly visible. 53 Figure 15: The quarry and logging road section in the upper Arm Valley which demonstrates the relationship between Arm Till and Croesus Till. 55 Figure 16: A summary of the statistically significant results obtained using the Scheffe Test. 71 Figure 17: Extent of the three glaciations in the upper Mersey Valley. 77 Figure 18: The Jacksons Creek valley just before its steep descent from the Central Pateau. At this point the stream flows at a depth well below the surface. The thick scree deposits are mainly the result of toppling. 81 Figure 19: The Central Plateau viewed from Mount Jerusalem showing results of ice scour. The lack of soil and vegetation can be seen, as can numerous rock basin lakes. 81 Figure 20: Part of the Walls of Jerusalem area which were unaffected by the Rowallan Glaciation. Note the thick scree at the base of the West Wall and the abundant vegetation compared with Figure 19. 85 Figure 21: Pi!linger Bog Section. 89 vi Figure 22: Dublin Bog Section (from Hill Colhoun and van de Geer, 1988). 93 Figure 23: The marshy near-horizontal surface of Dublin Bog stands out from the surrounding sclerophyll forest. Behind the largest eucalypt wet area can be seen with sphagnum moss visible. 93 Figure 24: Section in the river bank at the confluence of Wurragara Creek and Reedy Creek, showing deformation till overlying Permian sediment. 96 Figure 25: Deformation till at Horeb Falls. The hammer is resting on the outcrop of Permian mudstone, which can be seen to be blocky as it is jointed at right angles. The block at the end of the stick has only moved a few millimetres. 96 Figure 26: Thick lodgement till in the Fish River valley with a veneer of ablation till at the top. A sub-horizontal lineation is visible withinin the till. 96 Figure 27: Stratigraphic column adjacent to Steers Plain at 319678 (Rowallan). 100 Figure 28: Stratigraphic section at 288682 (Cathedral) showing sand and gravel overlying lodgement till and underlying meltout till. 100 Figure 29: Comparison of fabric analyses of lodgement till and flow till at a section adjacent to Steers Plain at 319678 (Rowallan) 102 Figure 30: Small faults in sandstone in a thick section in the Fish River valley. The faults are near vertical and are overlain by gravel and till. 104 Figure 31: Rhythmite in the section in the Fish River valley. The rhythmites are folded by the overburden pressure. Compare with the sandstones in Figure 30. 104 Figure 32: Striations in dolerite on a moulded surface where the ice overtopped the edge of the Mersey Valley near Cathedral Mountain. The striations have been protected from erosion by water. Normally this feature would be under water but an exceptionally long dry spell of weather lowered the level of the lake by approximately 2 m. 107 Figure 33: Ice flow directions for the Rowallan Glaciation. 109 vii Figure 34: The organic deposit below Cathedral Mountain in the upper Mersey Valley. The rhythmic layering and the presence of abundant charcoal are clearly visible. 126 Figure 35: The section above Parangana Dam showing a complex of tills with flow till at the top of the sequence. 127 Figure 36: Rhythmites underlying Croesus Till at the Lemonthyme Power station. 134 Figure Al: General locations in western and west-central Tasmania. A5 Figure A2: Locations in the study area. A6 Figure A3: Locations in the Cathedral Mountain area. A7 Figure A4: Locations in the Lake Myrtle area. A8 Figure A5: Locations in the Walls of Jerusalem area. A9 Figure A6: Locations in the Lake Rowallan area. Al 0 Figure A7: Locations in the Lake Mackenzie area. Al 1 TABLES Page Number Table 1: Stratigraphic summary of the February Creek section. 52 Table 2: Stratigraphic summary of the the sections in the upper Arm Valley. 56 Table 3: Summary of weathering rind data analyses. 69 Table 4: Results of the Fisher LSD test showing statistically significant breaks in the weathering data. 72 Table 5: Summary of recent glacial studies in Tasmania. 140 viii Acknowledgements Throughout the six years part time work and excess of 150 field days that this thesis took to complete many people have been of assistance and are gratefully acknowledged. My family encouraged, assisted with many tasks and were understanding throughout. It would have been impossible to complete the task without the support of my wife Marie, my children, Louise and David, and my mother and father. A number of colleagues, but mainly Mike Dunphy, Brian East, Darrell Fisher and Neville Grady, were very helpful either as assistants and company in the field or as proof readers for the manuscript. The Hydro Electric Commission provided rainfall data, allowed the use of their map library and willingly copied maps for field use. The TSIT in particular the AV Centre, School of Architecture and School of Education lent facilities for the production of the manuscript. Figures 1, 3 and A2 were adapted from maps drawn by Dr G. van de Geer as part of the paper, Hannan and Colhoun (1987). I also wish to express sincere appreciation for the help, careful supervision and friendship of my supervisor Prof E. H. Colhoun. Declaration Except as stated herein this thesis contains no material which has been accepted for the award of any other degree or diploma in any university, and that, to the best of my knowledge and belief, the thesis contains no copy or paraphrase of material previously published or written by another person, except when due reference is made in the text of the thesis.