DISTRIBUTION, THICKNESS, AND AGE OF LOESS DEPOSITS IN WEST CENTRAL MINNESOTA: IMPLICATIONS FOR THE AGE AND ORIGIN OF THE BIG STONE MORAINE

Loess is an accumulation of windblown massive, fine sand and silt. Previous studies of loess in Minnesota have focused on thick (greater than 3m) loess deposits outside of the glacial border. In west central Minnesota, a relatively thin (less than 1.3m) loess deposit of limited areal extent is exposed in portions of Stevens, Pope, Big Stone, Traverse, Grant, and Swift Counties. This loess deposit appears to have formed in association with the inner or outer phase of the Big Stone Moraine, the last significant moraine deposited by the late glacial Des Moines Lobe. The goal of this research is to: determine if loess deposition occurred during a specific phase of the formation of the Big Stone Moraine; and if loess deposition was the result of a climatically significant even. Additionally, Optically Stimulated Luminescent (OSL) dating will be used to determine the absolute age of the loess unit.

Loess deposits were mapped on a 1:100,000 scale topographic maps and exposures were described, loess thickness was measured, and samples were taken for grain size and OSL analysis. Distributions of thickness were plotted on a base map of ice marginal positions associated with the Big Stone Moraine to determine loess source area. OSL samples were taken from two locations including multiple samples from one location to determine the age of the loess and loess accumulation rates. Initial results indicate loess deposition occurred during, or immediately after, the deposition of the inner Big Stone Moraine.

Research for this study was funded by a grant from the N.S.F.-R.E.U Program (NSF-EAR 1262945).