FORMATION OF THE BIG STONE MORAINE, MINNESOTA: CHANNEL GEOMETRY ANALYSIS AND PALEO-TERRACES OF THE ICE MARGINAL, GLACIAL MUSTINKA RIVER

The Big Stone Moraine, west central Minnesota, was created by the Des Moines Lobe prior to the formation of Lake Agassiz. This was the last major constructional feature by the Des Moines Lobe. The objective of this study is to reconstruct the history of the formation of the Big Stone Moraine using ice marginal channel geometry and paleo-terraces. Previous studies have attributed the glacial Pomme-de-terre River and the glacial Chippewa River to formation during the deposition of the inner and outer Big Stone Moraine respectively. This research attempted to establish if the glacial Mustinka River is a third ice marginal channel, thus delineating a third ice marginal position in the Big Stone Moraine.

To determine the origin, geometry and paleo-flow characteristics of the glacial Mustinka River, cross sectional areas and gradients were determined from topographic maps and field mapping of glacial terraces. Sedimentology of the paleo-terraces was studied to determine depositional environment, flow regime, and to determine the “head of outwash” and outlet of the glacial Mustinka River. Finally, sediment of the Mustinka River will be dated using optically stimulated luminescence (OSL) dating.

Initial results show cross sectional areas and gradients of the glacial Mustinka River are indicative of an ice marginal stream. Cross bedding within the sediments of the Mustinka River terraces show high flow rates and and incorporated re-mobilized diamictite indicates that the ice was close to the river. At its outlet, the elevation of the Mustinka River is 1070 ft., suggesting it may have drained from Lake Agassiz.

Research for this study was funded by a grant from the NSF-REU Program (NSF-EAR 0640575).