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Role of Sorting on the Composition of Siliciclastic Sediment: Implications for Interpreting Provenance After Limited Transport in an Arid Climate

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Role of Sorting on the Composition of Siliciclastic Sediment: Implications for Interpreting Provenance After Limited Transport in an Arid Climate University of Tennessee, Knoxville TRACE: Tennessee Research and Creative Exchange Masters Theses Graduate School 8-2016 Role of Sorting on the Composition of Siliciclastic Sediment: Implications for Interpreting Provenance after Limited Transport in an Arid Climate Forrest Christopher Driscoll University of Tennessee, Knoxville, [email protected] Follow this and additional works at: https://trace.tennessee.edu/utk_gradthes Part of the Geochemistry Commons, Geology Commons, and the Sedimentology Commons Recommended Citation Driscoll, Forrest Christopher, "Role of Sorting on the Composition of Siliciclastic Sediment: Implications for Interpreting Provenance after Limited Transport in an Arid Climate. " Master's Thesis, University of Tennessee, 2016. https://trace.tennessee.edu/utk_gradthes/4032 This Thesis is brought to you for free and open access by the Graduate School at TRACE: Tennessee Research and Creative Exchange. It has been accepted for inclusion in Masters Theses by an authorized administrator of TRACE: Tennessee Research and Creative Exchange. For more information, please contact [email protected]. To the Graduate Council: I am submitting herewith a thesis written by Forrest Christopher Driscoll entitled "Role of Sorting on the Composition of Siliciclastic Sediment: Implications for Interpreting Provenance after Limited Transport in an Arid Climate." I have examined the final electronic copy of this thesis for form and content and recommend that it be accepted in partial fulfillment of the equirr ements for the degree of Master of Science, with a major in Geology. Christopher M. Fedo, Major Professor We have read this thesis and recommend its acceptance: Annette S. Engel, Robert D. Hatcher Accepted for the Council: Carolyn R. Hodges Vice Provost and Dean of the Graduate School (Original signatures are on file with official studentecor r ds.) Role of Sorting on the Composition of Siliciclastic Sediment: Implications for Interpreting Provenance after Limited Transport in an Arid Climate A Thesis Presented for the Master of Science Degree The University of Tennessee, Knoxville Forrest Christopher Driscoll August 2016 Copyright © 2016 by Forrest Christopher Driscoll All rights reserved. ii ACKNOWLEDGEMENTS Completion of this work was made possible through the assistance of many people. Dr. Chris Fedo provided constant guidance, feedback, and fruitful discussion as an advisor. Committee members Dr. Bob Hatcher and Dr. Annette Engel helped to review my work and progress. Drs. Scott Samson and Mariana Bonich helped during a field season in the Mojave Desert by providing on-site discussion. Dr. Jeff Moersch operated the drone used to obtain high resolution aerial photographs of the field site. Graduate students at the University of Tennessee, friends, and family offered tremendous guidance and support during the completion of my degree. A grant awarded from the Geological Society of America was used to fund the petrography, geochemistry, and travel expenses for this study. iii ABSTRACT This study tested whether transport distances (< 500 m) have the capacity to shape the geochemistry of sediments across multiple grain-size populations due to sorting derived from a single source. In the Stepladder Mountains, Mojave Desert, CA, a < 1 km2 [square kilometers] watershed allows for a controlled study to understand how modern sediments acquire their composition from a single granodioritic source in an arid climate where there is no chemical weathering. Sediments are naturally sorted into distinct grain- size populations, with modes ranging from very fine sand to gravel within a single, alluvial channel. Sediment samples representative of each population were petrographically and geochemically analyzed in order to test the effectiveness of commonly used discrimination diagrams. Sediments became proportionally enriched in plagioclase and biotite and depleted in K-feldspar and quartz with decreasing grain size. * Major elements were plotted in Al2O3 [aluminum oxide]–CaO +Na2O [sodium oxide]– * K2O [potassium oxide] and Al2O3–CaO +Na2O+K2O–FeO+MgO compositional space and indicate that a negligible degree of chemical weathering was involved in sediment production. Trace-element plots normalized to average granodiorite bedrock show strong enrichments in elements thought to be immobile during sedimentary processing (Cr, Co, and Sc) across nearly all sediment samples. Using any of these elements as ratios (Th/Co, La/Sc, Th/Sc, Cr/Th, Zr/Sc) in provenance discriminating plots reveal that sediment was formed source mixing, as sediments in these plots considerably deviate from bedrock composition due to the control grain size has on geochemistry. Sediment rare-earth element (REE) contents also deviate from source composition and show an increase in total REE content, decrease in fractionation of light REEs and heavy REEs, and an iv increase in the magnitude of the negative Eu anomaly with decreasing grain size. Variations in sediment composition and thus geochemical ratios result from mineral sorting during transport, no matter how short. Thus, strong caution must be used when using discrimination diagrams to interpret sediment and sedimentary rock provenance. v TABLE OF CONTENTS 1. INTRODUCTION .......................................................................................................... 1 2. GEOLOGIC SETTING .................................................................................................. 9 3. CHARACTERIZATION OF WATERSHED .............................................................. 11 4. METHODS ................................................................................................................... 13 4.1 Field Work .............................................................................................................. 13 4.2 Textural Analysis and Sample Preparation ............................................................. 13 4.3 Petrography ............................................................................................................. 16 4.4 Geochemical analysis.............................................................................................. 16 5. ANALYSIS OF STEPLADDER BEDROCK AND SAPROLITE .............................. 21 5.1 Stepladder Bedrock ................................................................................................. 21 5.1.1 Petrology .......................................................................................................... 21 5.1.2 Geochemistry ................................................................................................... 23 5.1.2.1 Major Elements ......................................................................................... 23 5.1.2.2 Trace- and rare-earth elements ................................................................ 24 5.2 Stepladder Saprolite ................................................................................................ 27 5.2.1 Petrology .......................................................................................................... 27 5.2.2 Geochemistry ................................................................................................... 30 5.2.2.1 Major elements.......................................................................................... 30 5.2.2.2 Trace- and rare-earth elements ................................................................ 31 5.3 Joint Sets ................................................................................................................. 31 6. ANALYSIS OF STEPLADDER SEDIMENT ............................................................. 33 6.1 Textural analysis ..................................................................................................... 33 6.1.1 CD-1 ................................................................................................................. 33 6.1.2 CD-2 ................................................................................................................. 33 6.1.3 CD-3 ................................................................................................................. 36 6.1.4 CD-4 ................................................................................................................. 36 6.1.5 CD-5 ................................................................................................................. 36 6.1.6 CD-M ............................................................................................................... 37 6.2 Petrography ............................................................................................................. 37 6.2.1 Quartz ............................................................................................................... 39 6.2.2 Plagioclase ....................................................................................................... 39 6.2.3 K-feldspar ........................................................................................................ 40 6.2.4 Biotite ............................................................................................................... 40 6.2.5 Accessory phases ............................................................................................. 41 6.3 Geochemistry .......................................................................................................... 41 6.3.1 Major elements................................................................................................
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