Cainozoic Landform Evolution on the Shoalhaven Plain N.S.W. With
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University of Wollongong Research Online University of Wollongong Thesis Collection University of Wollongong Thesis Collections 1990 Cainozoic landform evolution on the Shoalhaven plain N.S.W. with special reference to the alluvial and aeolian history over the last 45 million years Jonathan Freeman Nott University of Wollongong Recommended Citation Nott, Jonathan Freeman, Cainozoic landform evolution on the Shoalhaven plain N.S.W. with special reference to the alluvial and aeolian history over the last 45 million years, Doctor of Philosophy thesis, Department of Geography, University of Wollongong, 1990. http://ro.uow.edu.au/theses/1384 Research Online is the open access institutional repository for the University of Wollongong. For further information contact the UOW Library: [email protected] CAINOZOIC LANDFORM EVOLUTION ON THE SHOALHAVEN PLAIN N.S.W. WITH SPECIAL REFERENCE TO THE ALLUVIAL AND AEOLIAN HISTORY OVER THE LAST 45 MILLION YEARS A thesis submitted in fulfilment of the requirements for the award of the degree DOCTOR OF PHILOSOPHY from THE UNIVERSITY OF WOLLONGONG by JONATHAN FREEMAN NOTT B.A(Hons.), M.Sc(Hons.), Dip. Ed. (Wollongong) Geography Department 1990 This work has not been submitted for a higher degree at any other university or institution and, unless acknowledged, is my own work. Jonathan F. Nott i ABSTRACT An alluvial sheet, in places 130m thick and over 2000km2 in area, together with an extensive palaeovalley network and scattered source bordering and terrestrial sand dunes provide a history of drainage and landscape development in the middle and upper Shoalhaven catchment over the last 45 to 60 million years. This record tests the applicability, for this highland catchment, of models of longterm landscape evolution for the passive margin of eastern Australia. It also provides a comparison to lake shore and slope deposits within neighbouring catchments upon which much of our understanding of Late Quaternary climate changes within southeast Australia is based. This study shows that mid Oligocene basalt flows dammed the Shoalhaven River downstream of the eastward bend near Tallong to form a lake approximately 100km in length. In fact, within a relatively brief period of time Lake Tolwong formed twice; the second episode being considerably longer. Into Lake Tolwong were deposited two separate units of well laminated silts and clays, separated by a thin conglomeratic sequence representing a brief return to fluvial conditions. Each of the lacustrine units contains a well preserved spore and pollen assemblage, from cool temperate rainforest taxa, which can be equated with the Early to middle Oligocene lower Proteaceidites tuberculatus Zone of the Gippsland Basin. The second lacustrine unit reached a thickness of 60m before being partially stripped and fluvially reworked following the progradation of approximately 50m of coarse deltaic sediments. Basalt damming of the Endrick River and Limekiln Creek, eastern and western tributary networks within the Shoalhaven catchment, during the Middle Eocene also accounts for the accumulation of lacustrine sedimentary sequences in these valleys. Deposition of these sedimentary sequences has occurred within an extensive palaeovalley network carved into the Shoalhaven Plain. These valleys were excavated into a landsurface which in places was deeply weathered down to at least 150m and, in other areas, capped with a thin sheet of well silicified, generally fine grained sands and shallow valley fills of well ferruginised coarse sands and gravels. The age of the palaeovalley ii network places a minimum age on the deep weathering and deposition of the high level duricrusted sediments throughout the catchment. This age must be at least very Early Tertiary. These Tertiary sedimentary sequences and palaeovalleys provide further evidence of the great antiquity of drainage patterns within the Shoalhaven catchment, as well as the very slow rates of geomorphic change within a tectonically stable landscape that has experienced a stable and humid climate for much of its history. They also show that highland fluvial systems such as the Shoalhaven can evolve independently of external base level controls. The Quaternary alluvial terraces of the upper catchment provide clues to the behaviour of the Shoalhaven River during the Miocene and Pliocene for they show that upstream of the headward advancing Shoalhaven gorge the Shoalhaven River did not re-excavate its Oligocene alluvial fill until probably the Pleistocene. Throughout the Miocene, a period traditionally regarded to have been one dominated by planation to produce the Shoalhaven Plain, the river moved freely across its Oligocene sedimentary base reworking only the upper 10-20m of fill. The Late Pleistocene saw several episodes of valley incision and aggradation. The upper five alluvial terraces at Larbet, near Braidwood are much thicker and contain considerably coarser sediments than the lowest terrace and contemporary floodplain. Thermoluminescence dates from the floodplain and four lowest terraces, spanning a period from 7-460ka, reveal that the Shoalhaven was a much more active stream prior to 57ka. The period 20-35ka, generally regarded as a time in which streams throughout southeastern Australia were active and receiving much sediment as a product of widespread slope instability, is registered as a relatively insignificant period of fluvial activity in the Shoalhaven valley. It is likely that the 14C chronologies of slope and lake shore deposits in neighbouring highland catchments have identified only the dwindling stages of a much wetter period prior to the last glacial maximum which, in the Shoalhaven catchment, culminated in dry, windy conditions and the development of source bordering and terrestrial dunes between 6-19ka. iii ACKNOWLEDGEMENTS In producing this thesis I experienced probably the entire range of emotional states that can affect a person attempting such a task. Only one person shared, or rather endured, each of these states with me; Jeana my wife, who was understanding and strong. Many others also provided invaluable aid, especially the land owners of the several thousand square kilometres over which I traversed. Amongst these were Mr and Mrs Bruce Hush, Duncan Bray, Mr and Mrs Neil Griggs, Murray Griggs and of course the Crisp brothers of Tolwong who, .<**,- tried with very wobbly legs to free the University's hopelessly bogged, winchless, four wheel drive. I would also like to thank the staff of the Geological Division of the Sydney M.W.S & D.B. for providing me with drill logs and cores from the Welcome Reef Dam project; Gerald Nanson, Brian Jones and John Chappell for their accompaniment in the field and critical comment of my ideas on a number of occasions; Lex Metcalfe, Axel Von Krusenstierna and Geoff Black for field support; Murray Wilson for correcting spelling, punctuation and grammatical errors; Ann Young for her comments on Chapter 9; David Price for TL dating; Ian MacDougall for K-Ar dates; Richard Miller for help with cartography; Peter Price for the loan of pollen slides; Lesley Head for her guidance through those first attempts at pollen separation and slide preparation and also for editing Chapter 5; Helene Martin for a brief lesson in Tertiary pollen identification; and Judy Owen, to whom a special thankyou is offered for she really played a supervisory role for my pollen work. Undoubtedly the most helpful person both in the field and with the writing of this dissertation was my supervisor, Bob Young. His continued enthusiasm for the project instilled me with inspiration; his energy in the field I could not match and his intellect was always stimulating. IV TABLE OF CONTENTS ABSTRACT 1 ACKNOWLEDGEMENTS iii TABLE OF CONTENTS iv LIST OF TABLES ix LIST OF FIGURES x LIST OF PLATES xii CHAPTER 1 INTRODUCTION CHAPTER 2 THE CATCHMENT OF THE SHOALHAVEN RTVER: PHYSICAL CHARACTERISTICS 7 2.1 Location 7 2.2 Geology 7 2.3 Topography 9 2.4 Stream System 13 2.5 Climate 14 2.6 Vegetation 15 2.7 Summary and Conclusions 16 CHAPTER 3 A REVIEW OF PREVIOUS WORK IN THE MIDDLE AND UPPER SHOALHAVEN CATCHMENT 18 3.1 Introduction 18 3.2 Tertiary landscape evolution: an historical review 19 3.3 The origins of the Tertiary alluvial sequences: previous research 25 3.4 Quaternary landscape development: a review of previous studies 33 3.5 Summary and Conclusions 40 CHAPTER 4 PALAEOVALLEY NETWORK, AND SEDIMENTOLOGY AND STRATIGRAPHY OF THE TERTIARY SEDIMENTARY FORMATIONS 42 4.1 Introduction 42 4.2 Shoalhaven, Mongarlowe and Nadgigomar palaeovalleys 43 4.2.1 Direction of the Shoalhaven palaeovalley 46 4.2.2 Elevation and gradient of the Shoalhaven palaeovalley 47 4.2.3 Morphology of the Shoalhaven and Mongarlowe palaeovalleys 51 4.3 Tertiary sedimentary units of the middle Shoalhaven catchment 55 4.3.1 Palaeovalley infill sequences (Oligocene) across the Shoalhaven Plain: the broad stratigraphic pattern 56 4.3.2 Weathering within the Nadgigomar Sub-Group of sediments 62 4.3.3 Site descriptions 62 Badgery's Lookdown 63 Bullion and Bonanza Hills 63 Spa Creek 64 Black Springs Creek 69 Old Timberlight 70 OallenFord 71 Nadgigomar Creek 72 Spring Creek and Paul's workings 72 Spring Creek to Charleyong and Bombay Crossing 75 4.3.4 Middle Eocene sedimentary units 82 4.3.5 Pre-Middle Eocene sedimentary units 84 4.4 Summary and Conclusions 86 CHAPTER 5 CHRONOLOGY OF THE TERTIARY SEDIMENTARY FORMATIONS 88 5.1 Introduction 88 5.2 Use of pollen as a chronostratigraphic indicator 89 VI 5.3 Major trends in the Tertiary micro-flora