Pinedale Glacial History of the Upper Arkansas River Valley: New Moraine Chronologies, Modeling Results and Geologic Mapping

This fi eld-trip guide outlines the glacial history of the upper Arkansas River valley, Colorado, and builds on a previous GSA fi eld 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 fl oods in the upper Arkansas River valley, and (4) 10Be ages on fl ood 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 surfi cial deposits was revised *E-mails: avrielsc@buffalo.edu; jbriner@buffalo.edu; rshroba@usgs.gov; joe.licciardi@unh.edu; eleonard@coloradocollege.edu; bruggeka@morris.umn.edu; cmrussell94@gmail.com. Schweinsberg, A.D., Briner, J.P., Shroba, R.R., Licciardi, J.M., Leonard, E.M., Brugger, K.A., and Russell, C.M., 2016, Pinedale glacial history of the upper Arkansas River valley: New moraine chronologies, modeling results, and geologic mapping, in Keller, S.M., and Morgan, M.L., eds., Unfolding the Geology of the West: Geological Society of America Field Guide 44, p. 335–353, doi:10.1130/2016.0044(14). © 2016 The Geological Society of America. All rights reserved. For permission to copy, contact editing@geosociety.org. 336 Schweinsberg et al.

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