T170 Structural Analysis, Digital Mapping Advances, Tectonics, and Tectonic-Climate Processes from California to Alaska and Elsewhere I: A Celebration of Terry Pavlis’s Diverse Contributions and Career

Tuesday, 24 September 2024
8:00 AM - 10:55 AM
304A

EARLY PLEISTOCENE ARIDITY TRENDS IN DEATH VALLEY, CA: TESTING ANOMALOUS OXYGEN-17 IN SOIL NITRATE AS A NEW PALEO-PRECIPITATION PROXY IN ANCIENT ARID SYSTEMS

Paper number: T170-4
Program: Technical Sessions
Time: 8:40 AM – 8:55 AM

Authors

Abstract

The Neogene sedimentary record of pluvial lakes in the North American southwest is an important archive of terrestrial climate responses to Northern Hemisphere glaciation in regions characterized by an arid background climate. The spatial extents of pluvial lakes in the Pleistocene are thought to have been driven by orbitally controlled glacial-interglacial cycles, though they also reflect the interaction between hemispheric-scale climate cyclicity and more local factors (i.e., local topography, aridity gradients, etc.). In this study, we present a new depositional model for lower Pleistocene playa deposits of the Confidence Hills Formation, Death Valley paired with the first pilot test of the use of anomalous 17O (Δ17O) in soil nitrate as a paleo-precipitation proxy appropriate for ancient hyper-arid depocenters. This geochemical proxy has been developed in modern arid environments, but its application to the geologic record has not been tested.

Our results show that Early Pleistocene aridity cycles in the Confidence Hills spanned a range of ~15-225 mm (2.0-23.2‰ Δ17O) mean annual precipitation (MAP) resulting in the expansion and contraction of a playa system bounded by alluvial fans. These cyclic depositional processes resulted in three lithofacies assemblages: (1) interbedded siltstone and anhydrite deposited along the playa margin; (2) thin-bedded siltstone deposited via sheetfloods in a sandflat environment during the wettest part of the cycle; and (3) massive anhydrite deposited through extended desiccation of the playa following the wettest part of the cycle. Stratigraphic cycles are 10-15 meters thick and most likely coincide with 41 kyr glacial-interglacial cycles based on a temporal calibration using previously published paleomagnetic data and a new Ar-Ar age for an ash bed. The validity of Δ17O as a paleo-precipitation proxy in ancient arid paleo-environments is supported by a clear relationship between lithology and Δ17O values that correlate with MAP. Consistent with our depositional interpretations, siltstone beds yielded low Δ17O values (high MAP), laminated anhydrite beds yielded moderate Δ17O values (moderate MAP), and thick massive anhydrite beds yielded high Δ17O values (low MAP). The apparent relationship between lithology, interpreted depositional processes, and MAP values is promising for future applications of this tool.

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-401552

© Copyright 2024 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.