Thesis/Project Report Sheet Surname Or Family Name: .^Rttlf^
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PLEASE TYPE UNIVERSITY OF NEW SOUTH WALES Thesis/Project Report Sheet Surname or Family name: .^rTTlf^... Firstname: Othername/s: Abbreviationfordegree as givenin the University calendar: .^..b:'...^, School: .t , Title: Srrr^. ^a.hrO^ " — A new approach to sediment tracing using natural mineral magnetism has been developed to determine relative sediment contributions at stream junctions. This methc is developed on the basis that well mixed assemblages of magnetic minerals exist in sediment that is delivered to a stream junction, and that relative tributary contributions can be determined at confluences where the magnetic properties of the sediments are distinguishable. The method uses linear relationships between two mineral magnetic parameters to calculate relative tributary contributions to the resultant binary mix in the reach downstream of the confluence. The dominant sediment source catchments may thus be identified by a sequence of confluence measurements along a drainage network The requirements of this technique are that the tributaries and the downstream reach have constant average magnetic parameter relationships (i.e. the sediments are well mixed) over an appropriate period. This is possible because sediment transport mechanisms have an averaging effect as sediment is delivered first to a stream channel, and then transported within the channel. A simple model was developed to explain how random mixing of fluvial sediment can generate linear magnetic parameter relationship and how mixing of linear relationships occurs at confluences. The study empirically examines the spatial and temporal constancy of the magnetic mineral component of fluvial sediments using mineral magnetic parameters. Spatial and temporal constancy important because without it spurious estimates of source contributions can occur • because the magnetic properties of sediment are altered in some way between the sourc and the sediment sink. Also tested in this smdy is how representative the magnetic mineral fraction is of sediment as a whole. The binary combination of sediment at a confluence is the simplest possible mixing situation, requiring a relatively simple calculation to determine proportionate contributions along with statistical uncertainties. The tracing method is not affected by the enrichment or dilution of the magnetic miner; component (i.e. concentration changes), with a noted exception of fine suspended sediment transported over large distances. In such circumstances the method cannot be applied. Homogenization processes that occur during sediment transport ensure that representative sampling along river reaches is not difficult. The method is applicable at any scale where two distinguishable sources of sediment exist, including stream Declaration relating to ju^^^jj^j^^^ ^^ ^^^ location in a drainage basin where sediment is transported. I am fully aware of the policy of the University relating to the retention and use ofhigher degree projectreports and theses, namely that the University retains the copiessubmittedforexamination and is free to aUowthem to beconsultedorborrowed. Subject to the provisionsoftheCopyrig^^ issue aprojectreportor thesis in whole orinpart,inphotostateormicrofilm or othercopyingmedium. lalsoauthorisethepub^ationby University Microfilms ofa350word^bsfract in Dissem^ Llllll§. Signatuii Witness f Date The University recognises that there may be exceptionalcircumstances requiring restrictions on copying or conditions on use. Requests forrestriction for a period of up to2yearsmmtbe made in writlngto the Registrar.Requestsforalongerperiodofrestrictionmay be considered inexceptionalctf^ aletter of support from the Supervisor or Head of School. Such requests mustbe submitted with the thesis/project report FOR OFFICE USE ONLY DateofcompletionofrequirementsforAward: ReristrarandDeputvPrincipal Tins SHEET IS TO BE GLUED TO THE INSIDE FRONT COVER OF THE THESIS THE APPLICATION OF ENVIRONMENTAL MAGNETISM TO SEDIMENT SOURCE TRACING: A NEW APPROACH GARY G CAITCHEON A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy UniversityCollege, School of Geography and Oceanography, The University of New South Wales, Australian Defence Force Academy, Canberra, Australia. April 1998 347; Declaration I hereby declare that this submission is my own work and to the best of my knowledge it contains no material previously published or written by another person,, nor material which to a substantial extent has been accepted for the award of any other degree or diploma at UNSW or any other educational institution, except where due acknowledgement is made in the thesis. Any contribution made to the research by colleagues, with whom I have worked at UNSW or elsewhere, during my candidature, is fully acknowledged. I also declare that the intellectual content of this thesis is the product of my own work, except to the extent that assistance from others in the project's design and conception or in style, presentation and linguistic expression is acknolwedged. Gary Caitcheon ACKNOWLEDGEMENTS This work originated from discussions with Andrew Murray and Bob Wasson about how sediment tracers should be tested, and also from the suggestion by Andrew Murray that differences between lithogenic radionuclide ratios could be used to determine the relative contributions of sediment at stream junctions. This approach to sediment tracing was incorporated into my M Sc (Hons) thesis. I thank Andrew and Bob for their early encouragement to continue with the study of using magnetic minerals to trace sediment. There are several people who have helped me to collect, prepare, and measure samples. These include Graham Chiles, Jacqui Olley, and Mathew Rake. I am particularly gratefril for their help. Also involved with sample collection were Jon Olley, Peter Wallbrink, Laurie Olive, Bob Wasson, Gary Hancock, and Andrew Murray. Jeff Wood improved the Genstat routine developed by Richard Morton that used concurrent linear relationships to determine proportionate contributions to a binary mix. I am particularly grateful to Jeff for his help with, and advice about statistical analysis. David Short generously provided advice on part of the data analysis in Chapter 4, and also reviewed the chapter. I am gratefril to my supervisor, Laurie Olive, for encouragement, advice, and reviewing the work. Special thanks to Jon Olley for acting as a substitute supervisor in the latter stages of the study. His support, encouragement, advice, discussions about ideas, and reviewing this thesis is most appreciated. Finally, I thank my wife Sue, and our family for putting up with this for so long. This work was substantially supported by CSIRO Land and Water. ABSTRACT A new approach to sediment tracing using natural mineral magnetism has been developed to determine relative sediment contributions at stream junctions. This method is developed on the basis that well mixed assemblages of magnetic minerals exist in sediment that is delivered to a stream junction, and that relative tributary contributions can be determined at confluences where the magnetic properties of the sediments are distinguishable. The method uses linear relationships between two mineral magnetic parameters to calculate relative tributary contributions to the resultant binary mix in the reach downstream of the confluence. The dominant sediment source catchments may thus be identified by a sequence of confluence measurements along a drainage network. The requirements of this technique are that the tributaries and the downstream reach have constant average magnetic parameter relationships (i.e. the sediments are well mixed) over an appropriate period. This is possible because sediment transport mechanisms have an averaging effect as sediment is delivered first to a stream channel, and then transported within the channel. A simple model was developed to explain how random mixing of fluvial sediment can generate linear magnetic parameter relationships, and how mixing of linear relationships occurs at confluences. The study empirically examines the spatial and temporal constancy of the magnetic mineral component of fluvial sediments using mineral magnetic parameters. Spatial and temporal constancy is important, because without it spurious estimates of source contributions can occur if the magnetic properties of sediment are altered in some way between the sources and the sediment sink. Also tested in this study is how representative the magnetic mineral fraction is of sediment as a whole. The binary combination of sediment at a confluence is the simplest possible mixing situation, requiring a relatively simple calculation to determine proportionate contributions along with statistical uncertainties. The tracing method is not affected by the enrichment or dilution of the magnetic mineral component (i.e. concentration changes), with a noted exception of fine suspended sediment transported over large distances. In such circumstances the method cannot be applied. Homogenization processes that occur during sediment transport ensure that representative sampling along river reaches is not difficult. The method is applicable at any scale where two distinguishable sources of sediment exist, including stream junctions, or any location in a drainage basin where sediment is transported. CONTENTS Chapter 1 Introduction 10 Chapter 2 Environmental Magnetism and Sediment Source Tracing 13 2.1 Environmental Magnetism 13 2.1.1 Types Of Magnetic Behavior 14 2.1.2 Magnetic Minerals 16 2.1.3 Magnetic Measurements