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Pinedale glacial history of the upper Arkansas River valley: New moraine chronologies, modeling results, and geologic mapping

By
Avriel D. Schweinsberg
Avriel D. Schweinsberg
Department of Geology, 126 Cooke Hall, University at Buffalo, Buffalo, New York 14260, USA
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Jason P. Briner
Jason P. Briner
Department of Geology, 126 Cooke Hall, University at Buffalo, Buffalo, New York 14260, USA
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Ralph R. Shroba
Ralph R. Shroba
U.S. Geological Survey, MS 980, Box 25046, Denver Federal Center, Denver, Colorado 80225, USA
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Joseph M. Licciardi
Joseph M. Licciardi
Department of Earth Sciences, 56 College Road, University of New Hampshire, Durham, New Hampshire 03824, USA
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Eric M. Leonard
Eric M. Leonard
Department of Geology, 14 East Cache La Poudre Street, Colorado College, Colorado Springs, Colorado 80903, USA
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Keith A. Brugger
Keith A. Brugger
Geology Discipline, Division of Science and Mathematics, 600 E. 4th Street, University of Minnesota-Morris, Morris, Minnesota 56267, USA
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Charles M. Russell
Charles M. Russell
Department of Geology, 14 East Cache La Poudre Street, Colorado College, Colorado Springs, Colorado 80903, USA
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Published:
January 2016

Abstract

This field-trip guide outlines the glacial history of the upper Arkansas River valley, Colorado, and builds on a previous GSA field trip to the area in 2010. The following will be presented: (1) new cosmogenic 10Be exposure ages of moraine boulders from the Pinedale and Bull Lake glaciations (Marine Isotope Stages 2 and 6, respectively) located adjacent to the Twin Lakes Reservoir, (2) numerical modeling of glaciers during the Pinedale glaciation in major tributaries draining into the upper Arkansas River, (3) discharge estimates for glacial-lake outburst floods in the upper Arkansas River valley, and (4) 10Be ages on flood boulders deposited downvalley from the moraine sequences. This research was stimulated by a new geologic map of the Granite 7.5′ quadrangle, in which the mapping of surficial deposits was revised based in part on the interpretation of newly acquired LiDAR data and field investigations. The new 10Be ages of the Pinedale terminal moraine at Twin Lakes average 21.8 ± 0.7 ka (n = 14), which adds to nearby Pinedale terminal moraine ages of 23.6 ± 1.4 ka (n = 5), 20.5 ± 0.2 ka (n = 3), and 16.6 ± 1.0 ka (n = 7), and downvalley outburst flood terraces that date to 20.9 ± 0.9 ka (n = 4) and 19.0 ± 0.6 ka (n = 4). This growing chronology leads to improved understanding of the controls and timing of glaciation in the western United States, the modeling of glacial-lake outburst flooding, and the reconstruction of paleotemperature through glacier modeling.

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Contents

GSA Field Guide

Unfolding the Geology of the West

Edited by
Stephen M. Keller
Stephen M. Keller
Colorado Geological Survey Colorado School of Mines 1801 19th Street Golden, Colorado 80401, USA
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Matthew L. Morgan
Matthew L. Morgan
Colorado Geological Survey Colorado School of Mines 1801 19th Street Golden, Colorado 80401, USA
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Geological Society of America
Volume
44
ISBN electronic:
9780813756448
Publication date:
2016

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