2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 23-6
Presentation Time: 9:20 AM


RITTENOUR, Tammy, Department of Geology and Luminescence Laboratory, Utah State University, Logan, UT 84322, WOOLDRIDGE, Sayge C., Geology Discipline, University of Minnesota Morris, 600 East 4th Street, Morris, MN 56267, COTTER, James F.P., Geology Discipline, University of Minnesota, Morris, 600 East 4th Street, Morris, MN 56267 and ARENDS, Heather E., Division of Lands and Minerals, MN Department of Natural Resources, 500 Lafayette Road, Box 45, St. Paul, MN, MN 55155-4045, tammy.rittenour@usu.edu

While reconstructions of ice-retreat and drainage reorganization are important for understanding linkages between meltwater discharge and cooling events during deglaciation, age control for ice-margin positions has been largely limited by the scarcity of material for radiocarbon dating in pro-glacial settings. This study investigates the chronology of ice retreat recorded in ice-contact, deltaic and pro-glacial fluvial deposits along the southern margin of the Des Moines lobe in the upper Minnesota River valley, USA. Samples for single-grain optically simulated luminescence (OSL) dating were collected from deposits that mark key ice-margin positions associated with the Big Stone Moraine and lake-level positions associated with glacial Lake Benson, a short-lived pro-glacial lake that formed immediately prior to glacial Lake Agassiz. Geomorphic mapping in the region has identified deltas associated with two lake levels in glacial Lake Benson and several north-south oriented valleys with underfit streams that mark and ice-marginal drainages that formed during ice retreat in relationship to the outer and inner Big Stone Moraine. Single-grain OSL results constrain the timing of ice retreat within the lake basin and suggest the higher delta level was occupied at ~14.8 ka and lake level dropped to the lower, stable phase of glacial Lake Benson at 14.4-14.0 ka. Results are discussed in relationship to the timing of formation and drainage of glacial Lake Agassiz and style and rates of ice retreat in the region.