THE EXTENT AND TIMING OF A PRE-LATE WISCONSINAN ICE MARGIN IN CENTRAL INDIANA: A NEW VIEW FROM GLACIAL-LACUSTRINE SEDIMENTS FROM PORTER CAVE

Evidence for proglacial lakes in central Indiana has been well document for over 100 years. These laminated sediments intercalated with glacial tills, loess and paleosols and record the advance and retreat of the Illinoian and Wisconsinian ice sheets. Karst and associated caves found within the mapped margins for the late Quaternary ice sheets have been previously suggested as high-stand outlets for these lakes. Glacial Lake Quincy, the oldest stratigraphically of the lakes in the Mill Creek area in central Indiana partially overlies karst terrain. Some caves in this area contain an abundance of glacial-lacustrine sediments and are associated with many mid-drainage waterfalls and under fit valleys reflecting a complex glacial history. A critical discovery is the ubiquitous presence of well-preserved proglacial lake sediments within Porter Cave that contain organic material ideal for radiocarbon dating and sediments amenable for optically stimulated luminescence (OSL) dating. Previously reported borehole records indicate that lake sediments were over run by the advancing ice margin subsequently depositing a glacial diamicton. We report the first quantitative chronologic control derived from 14C and OSL ages on Glacial Lake Quincy sediments within Porter Cave. This data indicate the formation of Glacial Lake Quincy ca. 30 to 45 ka in the paleo-Mill Creek coincident with the Roxana Loess deposition in the Midwest. Mapped ice sheet margin associated with common waterfalls and distribution of lake sediments indicates that the ice sheet margin during marine oxygen isotope stage-3 was similar in extent as the last glacial maximum.