T227 Insights and Challenges for Geomorphic, Geologic, and Paleoseismic Investigations in the Rocky Mountain– Central U.S. Transition Region (New Mexico, Colorado, Wyoming, and Montana)

Tuesday, 27 September 2016
1:30 PM - 5:30 PM
Room 406

USING SURFICIAL DEPOSITS TO CONSTRAIN QUATERNARY FAULT MOVEMENT IN COLORADO: INSIGHTS FROM RELATIVE DATING AND COSMOGENIC RADIONUCLIDE DATING

Paper number: T227-6
Program: Technical Sessions
Time: 2:45 PM – 3:05 PM

Authors

Abstract

In Colorado, the timing of Quaternary fault activity is determined primarily from relative dating methods, such as soils geomorphology and geomorphic relations. Surficial deposits are often assigned an age by correlation with different glacial advances. Fault activity is inferred from the age of the surface that it cuts. Differentiating glacial deposits associated with the Pinedale (MIS-2) or Bull Lake (MIS-6) glaciations, based on their landform morphology, is more straightforward than assigning ages for glacio-fluvial or fluvial deposits. As faults in Colorado cut across both glacio-fluvial fans and fluvial strath terraces, it is difficult to accurately constrain the timing of Quaternary fault activity. The deposition of glacio-fluvial fans is undoubtedly paced by glacial cycles, as great amounts of sediment are released during glaciations. However, the relation between glacial maxima and maximum fan aggradation rates is not clear. It is likely that climatically-driven changes in sediment supply also play a role in the cutting, deposition, and abandonment of Quaternary strath terraces. However, recent measurement of both 26Al and 10Be profiles on strath terraces along the Colorado Front Range reveal long occupation of terrace surfaces, spanning several glacial-interglacial cycles. It is therefore difficult to assign a single age to a terrace surface or to correlate ages with glacial advances, as the “age” at which a terrace was abandoned can be much younger than the “age” at which the bedrock strath was cut. Furthermore, cosmogenic radionuclide dating of terraces demonstrates that river incision differs between basins, which challenges the use of terrace correlation across the region as a dating method. As the chronology of surficial deposits throughout much of the region lacks numeric age constraint, the geohazards associated with Quaternary faulting in the region are also poorly constrained.

Geological Society of America Abstracts with Programs. Vol. 48, No. 7

doi: 10.1130/abs/2016AM-285714

© Copyright 2016 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.