ABSTRACT SHINPAUGH, JOSHUA ERIK. Geochemical Signatures of Potential Sediment Sources to Lake Quinault, Washington. (Under the direction of Dr. Elana Leithold). Over centennial to millennial time scales, sediment production in mountainous areas of the world is typically dominated by episodic events such as earthquakes and storms, which commonly trigger widespread mass wasting. As streams carry these sediments out of the affected catchments, downstream sites of sediment accumulation, such as lakes and continental margins, have the potential to record these erosional processes. Widespread deep- seated landsliding should produce sediments with geochemical properties similar to those of bedrock while shallow landslides should produce sediment with geochemistry reflecting larger components of soil and vegetation. Lake Quinault, on the western side of the Olympic Peninsula, sits in a landslide-prone region atop the Cascadia Subduction Zone (CSZ). Evidence for great subduction earthquakes along the CSZ with a typical recurrence interval of 300-500 years has been documented. The lake, formed behind a glacial moraine between 20,000 and 29,000 years ago, has the potential to record the geomorphic response to these events. The goal of this study was to examine recent sources of sediment in the lake’s catchment and to establish geochemical criteria by which this response might be reconstructed. Sources, including bedrock, soils, river terrace, and paleo-lacustrine sediments were sampled and their inorganic and organic geochemical signatures characterized. Stream samples were also gathered and analyzed to test applicability of source geochemistry in the determination of stream sediment derivation. Chemical Index of Alteration (CIA) and Weathering Index of Parker (WIP) values were calculated from inorganic geochemical data. Total organic carbon (TOC) concentrations, δ13C isotopic ratios and atomic carbon to nitrogen (C/N) ratios were also analyzed. Additionally, Rock Eval pyrolysis was utilized to differentiate organic geochemical signatures of recent carbon from soils and vegetation from that of bedrock-derived fossil carbon. CIA and WIP weathering indices showed that sediment produced within the catchment has not been extensively weathered and closely resembles bedrock. WIP values prove to be the most useful criteria for discriminating between soils and bedrock based on inorganic geochemistry, and for delineating their relative contributions to sedimentary deposits in the catchment. Measurements of TOC, δ13C and C/N, indicate mixing of young carbon from recent vegetation and fossil carbon from bedrock in stream sediment and other deposits in the catchment, but cannot be used to quantify the relative contributions from those two carbon pools. Deconvolution of S2 curves obtained from Rock Eval pyrolysis permits delineation of recent and fossil carbon contributions to sedimentary deposits, elucidating the geomorphic mechanisms (deep or shallow) most responsible for sediment production. The methods utilized in this study should be useful for future investigations of the sedimentary history preserved in Lake Quinault and the region’s upland response to great subduction earthquakes. © Copyright 2013 by Joshua Erik Shinpaugh All Rights Reserved Geochemical Signatures of Potential Sediment Sources to Lake Quinault, Washington by Joshua Erik Shinpaugh A thesis submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the degree of Master of Science Marine, Earth, and Atmospheric Sciences Raleigh, North Carolina 2013 APPROVED BY: _______________________________ ______________________________ Dr. DelWayne Bohnenstiehl Dr. Karl Wegmann ________________________________ Dr. Elana Leithold Chair of Advisory Committee DEDICATION For my wife, Liz. You have remained graceful and solid throughout this endeavor, providing untiring love, support, and patience for which I am forever grateful. ii BIOGRAPHY I was born on November 15, 1983, to Clyde and Tammie Shinpaugh of Copperhill, Tennessee. Nestled in the Appalachian Mountains of southeast Tennessee, the Copper Basin area was a small community conducive to exploring the outdoors via hiking, biking, four- wheeling, or simply driving along the back roads and enjoying the scenery. It also came with a rich history of mining; a community founded because of its geologic setting. I didn’t realize it at the time, but my interest in the natural aspects of my childhood home would be the foundation for my career path. Though the opportunity to play football took me to the University of Tennessee at Chattanooga in 2002, an interest in geology got me to graduation in 2007. I left UTC with a B.S. in Geology, a future wife, and a job offer for a Geologist position with the U.S. Army Corps of Engineers in Savannah, GA. While with the USACE, I had the privilege of working with a group of incredible people on projects from New Orleans, LA, to Fargo, ND. I was able to learn valuable lessons as a professional, meet a number of great colleagues and friends, and cement my interest in a career as a Geologist which, in turn, led me to NCSU in 2011 to begin my graduate studies. iii ACKNOWLEDGMENTS Many thanks go first to my committee. To my advisor, Dr. Elana Leithold, thank you for allowing me the opportunity to work with you on such an exciting and interesting project and, most importantly, thank you for your support and encouragement. Dr. Karl Wegmann, thank you for helping to get a recovering professional back into student mode and providing ArcGIS crash courses that put ESRI courses to shame. Dr. Del Bohnenstiehl, thank you for your essential help with data analysis and for your help with a better understanding of the foreign language of MatLab. Thanks also go to Dr. Chris Osbourne for your advice regarding organic data and to Daniel Rojas-Jimenez for offering your time and assistance with EA-MS analyses. Thank you, Bruce Riddell, not only for providing assistance with sample preparation, but also for providing some great humor on the especially tough days. Thanks also go to my friends and colleagues in MEAS that have made this experience at NCSU such a memorable, rewarding one. A very special thank you goes to Dr. Ann Holmes, Dr. Jon Mies, and Dr. Habte Churnet at the University of Tennessee - Chattanooga. This research was made possible by a grant from The Geological Society of America. iv TABLE OF CONTENTS LIST OF TABLES ................................................................................................................ vii LIST OF FIGURES ............................................................................................................. viii 1.0 INTRODUCTION..............................................................................................................1 1.1 Geologic Setting ...............................................................................................................4 1.2 Seismic History ................................................................................................................7 1.3 Quinault Watershed ..........................................................................................................8 1.4 Sediment Origin Proxies ................................................................................................12 1.4.1 Inorganic Geochemistry ..........................................................................................12 1.4.2 Organic Geochemistry .............................................................................................14 2.0 METHODS .......................................................................................................................18 2.1 Sampling .........................................................................................................................18 2.2 Inorganic Geochemical Analysis....................................................................................24 2.2.1 Preparation Inorganic Geochemistry .......................................................................24 2.2.2 Inorganic Geochemical Analyses ............................................................................24 2.2.3 Carbonate Content ...................................................................................................25 2.3 Preparation for Organic Geochemical Analysis .............................................................26 2.3.1 Size Fractionation ....................................................................................................26 2.3.2 Organic Carbon Analyses ........................................................................................27 2.3.2.1 Organic Carbon, Total Nitrogen, and δ13C Isotope Analysis ..........................27 2.3.2.2 Rock Eval Analysis ..........................................................................................28 2.4 Principal Component Analysis .......................................................................................33 3.0 RESULTS .........................................................................................................................35 3.1 Inorganic Geochemistry .................................................................................................35 3.1.1 Inorganic Principal Component Analysis Size Fractionation .................................35 v 3.1.2 Weathering Indices ..................................................................................................45 3.2 Organic