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Copyright is owned by the Author of the thesis. Pennission is given for a copy to be downloaded by an individual for the purpose of research and private study only. The thesis may not be reproduced elsewhere without the pennission of the Author. PALEOENVIRONMENTAL ANALYSIS OF QUATERNARY STRATA IN THE LEVIN AREA A thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Quaternary Science at Massey University ALAN HENRY SEWELL 1991 ·-~-. - - ,.-.··,_·.:·.-· Frontispiece: Pencil sketch looking north from the Tararua foothills, south-east of Potts Hill, across the Tokomaru Marine Terrace and Manawatu River flood plain beyond. ABSTRACT Marine transgression during the Last Interglacial resulted in widespread inundation of the southern Manawa tu area. The Otaki Formation constitutes the relatively thick blanket of predominantly marine sand deposited at the height of the transgression and is now exposed in a partially dissected marine terrace abutting the Tararua Range. Sedimentation was controlled by basement block faulting related to a regional strike-slip tectonic regime on the south­ eastern margin of the South Wanganui Basin. Wave-induced longshore currents from the north-west supplied abundant sediment to the coast. North-east of Levin the Kairanga Trough, occupying a north-east-trending structural depression between uplifted basement blocks, formed the centre of an embayment during the transgression. Tide-dominated depositional processes predominated around the margins of the embayment. In the Forest Lakes area, the absence of seaward barriers resulted in an open wave-dominated coastline. Between Ohau and Shannon mixed wave/tide processes predominated. Stabilisation of sea level resulted in shoreline progradation which was especially marked south of Levin where a dune belt formed, mantling the coastal cliff and later migrating inland. Retreat of the sea was followed by differential uplift and dissection of the newly exposed marine terrace. Two later marine transgressions cut treads in the earlier marine terrace, their strandlines being controlled by the previously established drainage pattern. ·Ameliorating climate associated with the major sea level regression of the Last Glacial was accompanied by several phases of loess and minor dune sand accumulation on the exposed marine terraces. At the same time large areas of the terrace coverbeds were removed due to river aggradation. Final truncation of the Last Interglacial marine terraces occurred during the Holocene transgression. Tectonic warping of the marine terraces is continuing along pre-existing basement faults. iv ACKNOWLEDGEMENTS I would like to thank my joint supervisors; Mrs Julie Palmer, Dr Vince Neall, and Dr Bob Stewart for their guidance, assistance and valued discussion throughout the course of this study. I also thank Dr Alan Palmer who contributed much, in the same way. I am indebted to the DSIR Geology and Geophysics, for the provision of aerial photographs, maps and numerous other data. In particular, I would like to thank Mr Len Brown for his helpful advice and encouragement and Dr D.C. Mildenhall for the pollen analysis. I am also indebted to the Manawatu Wanganui Regional Council, in particular, Gabor Bekesi for the provision of borelog data and helpful advice. Special thanks to Zac, Margaret Waters, and members of my extended family for their constant encouragement and support throughout the course of this study. V TABLE OF CONTENTS TITLE PAGE i FRONTISPIECE ii ABSTRACT iii ACKNOWLEDGEMENTS iv TABLE OF CONTENTS V LIST OF FIGURES vii LIST OF TABLES ix CHAPTER 1 INTRODUCTION 1.1 Purpose and Scope of Study 1 1.2 Location of Study Area 1 1.3 Methods 3 1.3.1 Field Work 3 1.3.2 Sampling Methodology 3 1.4 Regional Setting 5 1.4.1 Physiography 5 1.4.2 Geology 6 1.5 Previous Work 11 1.6 Terminology 15 CHAPTER 2 GEOMORPHOLOGY 17 2.1 Introduction 17 2.2 Forest Lakes 17 2.3 Ohau 23 2.4 Levin-Potts Hill 24 2.5 Tokomaru-Makerua 27 CHAPTER 3 STRATIGRAPHY AND FACIES ANALYSIS 31 3.1 Introduction 31 3.2 Older Pleistocene Sediments 31 3.2.1 Pukehou formation 34 3.3 Otaki Formation 35 3.3.1 Introduction 35 3.3.2 Forest Lakes 37 A. Lithology and Sedimentology 37 B. Contacts and Thickness 43 C. Paleoenvironmental Inferences 45 3.3.3 Ohau 46 A. Lithology and Sedimentology 46 B. Contacts and Thickness 47 C. Paleoenvironmental Inferences 50 3.3.4 Levin-Potts Hill 52 A. Lithology and Sedimentology 52 B. Contacts and Thickness 57 C. Paleoenvironmental Inferences 59 3.3.5 Tokomaru-Makerua 62 A. Lithology and Sedimentology 62 B. Contacts and Thickness 80 C. Paleoenvironmental Inferences 81 vi 3.3.6 Summary 83 CHAPTER 4 PALEOCURRENT ANALYSIS 85 4.1 Introduction 85 4.2 Data Collection and Processing 86 4.3 Discussion 86 CHAPTER 5 GRAIN SIZE PARAMETERS AND MINERALOGY 90 5.1 Grain Size Parameters 90 5.1.1 Methodology 90 5.1.2 Discussion 93 5.2. Mineralogy 95 5.2.1 Introduction 95 5.2.2 Texture 97 5.2.3 Composition 97 5.2.4 Discussion 98 CHAPTER 6 PALEONTOLOGY AND PALYNOLOGY 101 6.1 Paleontology 101 6.2 Palynology 103 CHAPTER 7 STRUCTURE 105 7.1 Introduction 105 7.2 Forest Lakes 107 7.3 Ohau 109 7.4 Levin-Potts Hill 110 7.5 Tokomaru-Makerua 115 7.6 Summary 118 CHAPTER 8 PALEOENVIRONMENTAL SYNTHESIS AND GEOLOGICAL 119 HISTORY OF THE OTAKI FORMATION 8.1 Concluding Comments 125 REFERENCES 126 APPENDIX A Summary of borelog data Al APPENDIX B Measured section descriptions Bl APPENDIX C Paleocurrent data Cl APPENDIX D Grain size analysis raw data Dl APPENDIX E Palynological report El MAP 1 Geology, Forest Lakes. MAP 2 Geology, Ohau. MAP 3 Geology, Levin-Potts Hill. MAP 4 Geology, Tokomaru-Makerua. vii LIST OF FIGURES Figure 1.1 Location map of study area. 1.2 Physiography of southern Manawatu district. 1.3 A flat topped interfluve typical of the partially dissected marine terraces in the Horowhenua district. 1.4 Map of the South Wanganui Basin showing basin boundaries and present distribution of early Pliocene, late Pliocene - early Pleistocene and mid - late Pleistocene sediments. 1.5 Marine terrace nomenclature. Figure 2.1 Simplified map showing the boundaries of the four areal subdivisions designated in the study area. 2.2 Aeolian Otaki Formation abutting the Last Interglacial sea cliff north of Waitohu Stream near Otaki. 2.3 A flight of three marine terraces on the eastern shore of Lake Waitawa, Forest Lakes. 2.4 The Tokomaru Marine Terrace in fault contact with the greywacke foothills at Laws Hill. 2.5 Two marine terraces on the north flank of the Shannon Anticline. 2.6 An inferred fault scarp along the inner margin of the TMT north of Shannon. 2.7 Two marine terraces north of Shannon. Figure 3.1 Oxygen isotope stages. 3.2 Bore hole correlation columns across the TMT at Ohau. 3.3 Bore hole correlation columns across Pukehou Anticline and South Manakau Stream. 3.4 Measured section description for the type section of the Otaki Formation. 3.5 Silty bed in homogeneous, well sorted sandstone. 3.6 Large scale cross-bedding and intraformational slumping in Otaki dune sand. 3.7 Bore hole correlation columns north-west from Pukehou Hill. 3.8 Measured section correlation columns at Ohau illustrating the nature of the local coverbed stratigraphy. 3.9 Ohakean loess overlying Koputaroa dune-sands. 3.10 A paleosol separating two units of Otaki beach sand within the Otaki Formation. 3.11 Scoured surfaces in Otaki beach sand. 3.12 Gently dipping, parallel laminated sandstone bounded by horizontal, parallel laminated sandstone. 3.13 Bore hole correlation columns across part of the Shannon and Levin anticlines. 3.14 Measured section description of L98. viii Figure 3.15 Part of the well exposed outcrop at (Ll) S24/156716. 3.16 Measured section description of Ll. 3.17 Convolute lamination. 3.18 Measured section description of L118. 3.19 Probable intertidal channel with large rip-up clasts of silt along its base. 3.20 Measured section description of Ll20. 3.21 Diagram illustrating a fan-delta association. Figure 4.1 Current rose diagrams. Figure 5. 1. Scatter plots of skewness versus standard deviation and standard deviation versus mean. Figure 7.1 Major fault trends along the south-east margin of the South Wanganui Basin. 7.2 Main structural features in the Manawatu district west of the axial ranges. 7.3 Structural contour map of the Tokomaru wave cut platform across the Levin Anticline. 7.4 Topographic contour map across the Levin and Shannon anticlines. 7.5 Simplified cross-section across the Shannon Anticline, Levin Anticline and Poroutawhao High. 7.6 Small scale faulting in the Otaki Formation south of Tokomaru. Figure 8.1 Sequence of diagrams illustrating the inferred paleoenvironmental changes that accompanied deposition of the Otaki Formation. ix LIST OF TABLES Table 1.1 Summary of Late Quaternary stratigraphy, south­ west North Island. Table 5.1 Location and description of samples selected for grain size analysis. Table 5.2 Grain size statistical parameters. Table 5.3 Sample locations, field descriptions and rough mineral analyses of thin sectioned samples of indurated sandstone of the Otaki Formation. l CHAPTER 1 INTRODUCTION 1.1 PURPOSE AND SCOPE OF STUDY In recent years there have been major advances in the understanding of the evolution of the South Wanganui Basin including a well documented chronology of Quaternary sea level fluctuations. Much of this information has arisen from studies carried out both onshore and offshore in the Wanganui and south Taranaki areas. Little stratigraphic and sedimentological investigation of late Quaternary strata in the southern Manawatu area has been undertaken since Oliver mapped the Otaki Formation in 1948.

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