HR: 1340h
AN: U13B-1164    [Abstracts]
TI: Large floods and rapid deglaciation of the Lake Michigan Lobe and environs, ca. 19 to 18 ka
AU: * Curry, B
EM: curry@isgs.uiuc.edu
AF: Illinois State Geological Survey, 615 E. Peabody Dr., Champaign, IL 61820, United States
AU: Brown, S
EM: brown@isgs.uiuc.edu
AF: Illinois State Geological Survey, 615 E. Peabody Dr., Champaign, IL 61820, United States
AU: Hajic, E
EM: e.hajic@comcast.net
AF: Illinois State Museum, 1011 East Ash Street, Springfield, IL 62703, United States
AU: Konen, M
EM: mkonen@niu.edu
AF: Northern Illinois University, Davis Hall, De Kalb, IL 60115, United States
AB: Our collective research indicates that features attributed to large floods are associated with events separated in time by about 900 years. The oldest event is interpreted from a long and narrow morainal gap floored by coarse sand and gravel outwash that likely formed by a plungepool and migration of this nickpoint via overflow of Glacial Lake Wauponsee across the Marseilles Moraine near Oswego, Illinois. The weighted mean of four AMS C-14 ages of tundra plant stems and leaves identified from the base of the overlying lake fill is 18,900 ± 35 cal yr BP (15,710 ± 35 yr BP). The age of another overflow channel across the Marseilles Moraine is not yet known, but similar channel floor elevations relative to the Oswego channel suggest that they were contemporaneous. Landforms attributed to a younger large flood are located downstream of where the Fox River breaches the Woodstock Moraine in Algonquin, Illinois. Radiocarbon ages of tundra plant fossils preserved in sediment of ice-walled and slackwater lakes associated with the Woodstock and West Chicago Moraines indicate the younger floods likely predate 18,080 cal yr BP (14,860 ± 40 yr BP; UCIAMS-26265). A statistically similar age of 18,000 cal yr BP (14,830 ± 50 yr BP; B-207031) was obtained from organics preserved in a slackwater lake deposit in the Illinois River valley near Havana. The slackwater lake basin is floored by coarse gravelly sand attributed to the latest stage of flooding. At this time, the similar C-14 ages are the only evidence that link the proglacial and distal sites (more than 150 km apart) to the same flood. Based on continuity of morainic ridges, we believe that the large floods that eroded scarps into the southern margin of the Valparaiso Moraine north and parallel to the Kankakee River in NW Indiana and NE Illinois are contemporaneous with the younger large floods discussed above. The scarp was eroded by meltwater from interlobate areas of the Lake Michigan and Huron-Erie Lobes. The rate of deglaciation of the Lake Michigan Lobe (LML) is estimated from the youngest ages obtained from ice- walled lake plains and the age of the southern maximum Wisconsin Episode LML (23,960 cal yr BP (20,000 yr BP)). Overall, the rate of retreat from the Shelbyville Moraine to the Lake Border Moraines is about 60 m/yr, but the initial meltback/meltdown rate (from the Shelbyville to the Marseilles Moraine) was about double that, 135 m/yr. The initial faster meltback rate is attributed to more effective drainage away from the glacier margin.
DE: 0718 Tundra (9315)
DE: 0746 Lakes (9345)
DE: 1105 Quaternary geochronology
DE: 1130 Geomorphological geochronology
DE: 1637 Regional climate change
SC: Union [U]
MN: 2007 Fall Meeting