14: Pinedale glacial history of the upper Arkansas River valley: New moraine chronologies, modeling results, and geologic mapping
Avriel D. Schweinsberg, Jason P. Briner, Ralph R. Shroba, Joseph M. Licciardi, Eric M. Leonard, Keith A. Brugger, Charles M. Russell, 2016. "Pinedale glacial history of the upper Arkansas River valley: New moraine chronologies, modeling results, and geologic mapping", Unfolding the Geology of the West, Stephen M. Keller, Matthew L. Morgan
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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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Prepared in conjunction with the 2016 GSA Annual Meeting in Denver, Colorado, this volume contains sixteen guides to field trips in this rich geologic region. The four “Great Surveys” of the late 1800s ventured west to explore and document the region’s unknown natural resources and collect valuable geologic information. Many of the field guides in this volume, aptly titled Unfolding the Geology of the West, will cover the same hallowed ground as the early geologic expeditions. Organized into four sections, this volume spans some of the major subdisciplines of geology: (1) stratigraphy, sedimentology, and paleontology; (2) structure and metamorphism; (3) Quaternary landscape evolution; and (4) engineering and environmental geology.