PALEOENVIRONMENT OF GLACIAL LAKE BENSON, WEST CENTRAL MINNESOTA: IDENTIFYING AND INTERPRETING PROXIMAL VARVES

Glacial Lake Benson was first recognized and named by Diedrick and Rust (1975). This pro-glacial lake formed in the present Minnesota River Valley during the late Wisconsinan retreat of the Des Moines lobe. Prior to 1995, studies of Glacial Lake Benson focused on geomorphology and sedimentology to determine lake geometry and history. Since 1995 the documentation of correlatable strand lines (elevation 1075 ft), an outlet channel (elevation 1050 ft), varved lake sediments, and clay rich soils indicates that a single large lake existed while the ice margin retreated from the Antelope Moraine (Leverett, 1932) to a position near the Big Stone Moraine. Glacial Lake Benson drained when a moraine dam in the present Minnesota River Valley was breached.

This study focused on the identification, correlation and paleo-environment interpretation of proximal varves found within Glacial Lake Benson sediments. Pollen of pinus and spores of ambrosia and urticacea were found within the clay and silt layers but were not found in statistically valid concentrations. Samples will be analyzed to determine a “geochemical signature” for the Lake Benson sediments to aid in identification and correlation. Together the information will give a better insight to the history and paleo-environment of Glacial Lake Benson.

Research for this study was funded by a grant from the N.S.F.-R.E.U. Program (NSF-EAR 0353621).