Paper No. 10
Presentation Time: 11:15 AM
CHRONOLOGY OF LATE WISCONSIN GLACIAL LAKES IN FOND DU LAC COUNTY, EAST-CENTRAL WISCONSIN
SANDERFOOT, Benjamin, Department of Geology, University of Wisconsin Oshkosh, 645 Dempsey Trail, Oshkosh, WI 54901-8649, MODE, William N., Department of Geology, University of Wisconsin - Oshkosh, Oshkosh, WI 54901 and HOOYER, Thomas S., Department of Geosciences, University of Wisconsin Milwaukee, P.O. Box 413, Lapham Hall 366, Milwaukee, WI 54201, sandeb88@uwosh.edu
As the Green Bay Lobe (GBL) of the Laurentide Ice Sheet receded from east-central Wisconsin near the end of the Wisconsin Glaciation, a series of ice-marginal lakes was impounded by the ice margin. The largest of these was glacial Lake Oshkosh. In Fond du Lac County, a smaller lake called glacial lake Fond du Lac was impounded when the GBL readvanced (during overall recession) into Fond du Lac County. This advance, part of the Middle Athelstane Phase, terminated at the Eureka moraine and deposited till of the Kirby Lake Member of the Kewaunee Formation. Drainage of glacial Lake Fond du Lac was northward along the western edge of the GBL through an outlet at 860 feet a.s.l. and into glacial Lake Oshkosh. A new AMS 14C date on plant macrofossils from the base of glacial Lake Fond du Lac sediment places the formation of the lake and first occupation of the Eureka moraine by the GBL at 15,485 +/- 175 cal. yr B.P. (13,110 +/- 60 14C yr B.P.). There are only two other dates that provide direct age control on ice advance of the Middle Athelstane Phase in this area. All three dates are on macrofossils and they range from 15,310 to 16,730 cal. yr B.P.
The dated organic material was taken from a hollow-stem auger core in the basin of glacial Lake Fond du Lac. The stratigraphy of that core is representative of the sequence of events during the last part of the Wisconsin Glaciation in Fond du Lac County. At the base of the core is till of the Horicon Member of the Holy Hill Formation. This till was deposited by the GBL during the last glacial maximum and during ice recession from the maximum. Lake sediment on top of the till was deposited in an early phase of glacial Lake Fond du Lac. This lake formed during ice recession. The organic-rich lake sediment that yielded the 14C date represents the initial formation of glacial Lake Fond du Lac in front of the Eureka moraine. The organic-rich lake sediment was buried by minerogenic lake sediment deposited as the lake deepened, and this sediment ceased being deposited when the Lake Fond du Lac drained because the GBL receded a few miles into the Lake Winnebago lowland. During ice recession, glacial Lake Oshkosh formed with an outlet of ca. 800 feet a.s.l.
