http://researchcommons.waikato.ac.nz/ Research Commons at the University of Waikato Copyright Statement: The digital copy of this thesis is protected by the Copyright Act 1994 (New Zealand). The thesis may be consulted by you, provided you comply with the provisions of the Act and the following conditions of use: Any use you make of these documents or images must be for research or private study purposes only, and you may not make them available to any other person. Authors control the copyright of their thesis. You will recognise the author’s right to be identified as the author of the thesis, and due acknowledgement will be made to the author where appropriate. You will obtain the author’s permission before publishing any material from the thesis. LATE HOLOCENE MUD SEDIMENTATION AND DIAGENESIS IN THE FIRTH OF THAMES: BENTONITES IN THE MAKING A thesis submitted in partial fulfilment of the requirements for the Degree of Master of Science in Earth Sciences at the University of Waikato by Timothy R. Naish UNIVERSITY OF WAIKATO 1990 ABSTRACT Late Holocene mud sedimentation in the southern Firth of Thames has been described from analysis of a number of shallow marine sediment cores. Three distinct lithofacies are distinguished on the basis of sediment texture and mineralogy. A laterally extensive greenish grey mud, typically bioturbated and massive, with sporadic uncorrelatable interbedded shell layers is termed the Firth of Thames mud facies. Nearer shore sediments are usually coarser and are subdivided into two facies: a siliciclastic sand facies (river mouth sand facies) comprising more prominent interbeds of sand in mud and associated with sedimentation at the mouth of the Waihou River; and a mixed terrigenous-carbonate gravel facies (delta fan gravel facies) associated with deposition on small delta fans adjacent to streams draining the Coromandel Range. The areal distribution of all three facies over the late Holocene has been controlled largely by northward progradation of the coastal Hauraki Lowland associated with the rapid sediment infilling of the Firth of Thames since sea level reached its present height 6500 y B.P. From seismic evidence the Holocene muds are up to 10m thick. The cores in this study penetrated only to 5.5m sub-bottom depth and yielded an oldest radiocarbon age of 5000 y B.P. The age data indicate an average rate of offshore vertical sediment accumulation of 1.5 mmly. Up to 15 km of progradation of the southern shoreline of the coastal Hauraki Lowland has occurred over the late Holocene at an average rate of up to 2.5 m/y, notably from 3500 y B.P to 1200 y B.P. Progradation is evidenced by the occurrence of coarsening-upward sequences in nearer shore cores of the Firth of Thames, as well as their changing faunal composition, particularly the upward increase in abundance of the foraminifer Ammonia beccarri, a good indicator of brackish water conditions, which suggests a gradual seaward encroachment of the freshwater influence of the Waihou River over the late Holocene. Basal muds which are similar in composition to marine sediments of the Firth of Thames are overlain by peat dated at 6025 y B.P in a peat core from Kopouatai Peat Bog, and suggest that marine conditions existed in this inland region of the Hauraki Depression prior to 6025 y B.P. Muds range from silty clays to clayey silts and consist principally of volcanic glass, smectite and halloysite, with smaller amounts of other volcanic-derived siliciclasts and allophane and illite, as well as skeletal carbonate (mainly aragonite) and organic matter. A contemporaneous decrease in the abundance of volcanic glass (55-15 wt°/o down-core) and an increase in smectite concentration (8-45 wt % down-core) occurs with sub-bottom depth. Specific mineralogical analyses (XRD and IR) and evidence from scanning electron microscopy suggest the smectite is montmorillonitic in composition and authigenic in nature. Moreover, the absence of smectite in the bottom sediments of rivers draining the Hauraki Lowland precludes a detrital origin. ii The diagenetic transformation of volcanic glass to smectite in sediments of the Firth of Thames is described by a sequential kinetic model which involves a parabolic dissolution coupled with a first order precipitation of smectite via the formation of an intermediate hydrated glass phase. The rate constant calculated from the sequential kinetic model is 3.35 x 10-4y-1. The half-life of the glass is 1475 y, implying rapid early diagenetic alteration of volcanic glass to smectite to form late Holocene bentonitic deposits. Thermodynamic stability considerations imply that the first order precipitaion of smectite may be favoured by conditions of pH and Na+ activity typical of interstitial fluids having sea water salinity under mildly anoxic conditions. iii ACKNOWLEDGEMENTS First and foremost I thank my supervisors Cam Nelson and Terry Healy for their continued interest and enthusiasm in the topic, in particular Terry for setting up the project and for entrusting me with his P .C., and Cam for the patient and skillful editing of an often tortuous manuscript. Peter Hodder is also thanked for his guidance with "kinetic-related text" and editing of Chapter 7. Advice, help and interest from other staff members has been greatly appreciated. In particular, Chris Hendy, Mike Dravitzki, Steve Bergin, Dudley Bell and Steve Stokes are thanked for assistance with field and laboratory work. Sydney Wright and Elaine Norton (Earth Sciences secretaries) are warmly thanked for help with preparation of the final manuscript. Peter de Lange is thanked for his comments and for "lending me" one of his peat cores. Dr Alan Hogg of the University of Waikato Radiocarbon Dating Laboratory is thanked for dating and advice on samples. Alf Harris and David Wild (MIRINZ, Ruakura - Hamitton) are thanked for assistance with SEM work and David Stringer (School of Engineering, University of Auckland) is also thanked for allowing me access to the School of Engineering SEM. Terry Hume ( DSIR Water Quality Centre - Hamilton) is thanked for his interest and comments on the project and Hamish Spencer ( University of Waikato) is thanked for help with identification of molluscs. Drs G. Gibson (University of Auckland) and N. Hornibrook (retired) are thanked for assistance with the identification of ostracods and forams and Dr L. Carter (DSIR, New Zealand Oceanographic Institute - Wellington) is thanked for making .available seismic charts of the Firth of Thames. Ken Palmer (Analytical Facility - Victoria University) is acknowledged for X-ray fluorescence spectroscopy. Thanks to Tim Bamford (University of Waikato photographer) for superb production of photographic plates. To my fellow "third years" - Glen B., Rob, Wayne, Glenn W., Grant, Hobbs, Frances, Gary, Kay, Vance and Barry thanks for the comradeship during those long months and late nights of thesis writing. Helen, thanks for everything and Abby just think, no more Firth of Thames mud stinking your room outL And last but certainly not least I'd like to thank my family for their support and encouragement, and in particular Karen for her love, support and endless encouragement during my Masters resarch. iv TABLE OF CONTENTS Page Abstract Acknowledgements iii Table of contents iv CHAPTER ONE - INTRODUCTION 1.1 Introduction 1 1 .2 Objectives of study 3 1.3 Approach to study 3 CHAPTER TWO - REGIONAL SETTING 2.1 Introduction 5 2.2 Coastal geomorphology 5 2.3 Drainage 6 2.4 Regional geology 7 2.5 Tectonic setting 8 2.6 Holocene sea level fluctuations 9 2.7 Bathymetry 9 2.8 Hydrodynamic setting 10 Tidal currents 10 Wave-generated currents 10 CHAPTER THREE - CORE STRATIGRAPHY 3.1 Introduction 12 3.2 Site selection 12 3.3 Core recovery 14 3.4 Core stratigraphy 16 Firth of Thames mud facies 18 River mouth sand facies 18 Delta fan gravel facies 19 3.5 Storm bed shell layers 19 3.6 14C Chronology 22 3.7 Discussion 24 v CHAPTER FOUR - SEDIMENT TEXTURE 4.1 Introduction 25 4.2 Ternary texture plots 25 4.3 Lateral variations in sediment texture 27 4.4 Vertical variations in sediment texture 29 CHAPTER FIVE - SEDIMENT MINERALOGY 5.1 Introduction 32 5.2 Clay mineralogy 32 X-ray diffraction analysis 32 Differential thermal analysis 34 Infrared absorption analysis 35 5.3 Silt fraction mineralogy 38 X-ray diffraction analysis 38 Differential thermal analysis 40 Infrared absorption analysis 40 5.4 Sand mineralogy 40 5.5 Quantitative estimation of sediment composition 41 Smectite, halloysite and illite 42 Allophane 43 Calcium carbonate 44 Volcanic glass 45 Organic matter 46 5.6 Discussion 47 Lateral variations in sediment mineralogy 47 Vertical variations in sediment mineralogy 50 Sediment geochemistry 51 CHAPTER SIX - SEDIMENT FAUNA 6.1 Introduction 52 6.2 Microfossil components 52 Foraminifera 52 Ostracods 56 Diatoms 59 vi 6.3 Macrofossil components 60 Bivalves 60 Gastropods 62 CHAPTER SEVEN .. SEDIMENT DIAGENESIS 7.1 Introduction 63 7.2 Part A - Evidence supporting a diagenetic origin for smectite 64 X-ray diffraction analysis 64 Infrared absorption analysis 67 Scanning electron microscopy 68 7.3 Discussion 68 7.4 Part B - A proposed kinetic weathering model for the transformation of glass to smectite 72 Stability and thermodynamic considerations 72 Summary of previous glass studies 75 Assumptions 76 Kinetics of volcanic glass dissolution and smectite precipitation 77 7.5 Discussion: Implications of the sequential kinetic model 83 CHAPTER EIGHT· THE LATE HOLOCENE SEDIMENTATION HISTORY OF THE SOUTHERN FIRTH OF THAMES 8.1 Introduction