210 D35. Glacial Geology and Anthropocene Sedimentology

Tuesday, 24 September 2019
1:30 PM - 5:30 PM
Room 221AB, North Building

ANTHROPOGENIC EFFECTS ON THE PROPAGATION OF DETRITAL PROVENANCE SIGNATURES: INSIGHTS FROM THE MISSOURI AND YELLOWSTONE RIVERS

Paper number: 210-2
Program: Technical Sessions
Time: 1:45 PM – 2:00 PM

Authors

  • Kelly Thomson Presenting Author
    Jackson School of Geosciences, The University of Texas at Austin, Austin, TX
  • Daniel F. Stockli
    Jackson School of Geosciences, The University of Texas at Austin, Austin, TX

Abstract

The Missouri River, a major tributary of the Mississippi River, supplied roughly 80-90% of the sediment in the Mississippi making it to the Gulf of Mexico before European settlement of the United States. Currently the Missouri River accounts for only ~ 60% of the modern sediment load reaching the Gulf of Mexico, due to the cumulative effects of anthropogenic activities such as dam construction, agricultural water withdrawal, sand mining, and channel modification through civil engineering project such as levee stabilization. Recent analytical advancements in the rapid acquisition of geochronologic data has allowed detrital zircon U-Pb geochronology to emerge as a tool to quantitatively assess sediment budgets of modern sediment dispersal systems. This study compares detrital zircon U-Pb age spectra collected along down river transects of the Missouri and Yellowstone rivers from their respective headwaters in south western Montana to their confluence in western North Dakota. This stretch of the Missouri river has had significant anthropogenic modification through a series of constructed dams, including the world’s largest earthen dam at Fort Peck. In contrast this stretch of the Yellowstone river is entirely dam-free. Preliminary results indicate that the proportion of U-Pb age components systematically change downstream as a result of sediment mixing and drainage integration with tributaries along the Yellowstone River. Results from the Missouri River, however, indicate significant signal sequestration behind major dams which trap the sand fraction of the river’s sediment load. Samples collected downstream from major dams reveal DZ U-Pb distributions dominated by tributary mixing beneath the dams along with sediment contributed by cutbank and streambed incision. These results are significant to quantify the impact of anthropogenic activities in the headwaters of major river systems and how these artificial perturbations may propagate downstream. The anthropogenically imposed staging of sand in the upstream reaches of river systems has cascading effects for the sediment transport and depositional dynamics downstream. The decrease of sediment discharging at the river’s mouth has the potential to significantly impact communities living along the coast.

Geological Society of America Abstracts with Programs. Vol. 51, No. 5

doi: 10.1130/abs/2019AM-340977

© Copyright 2019 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.