Early Deglaciation of Saginaw Lobe Area



Researchers have identified geological markers across the Saginaw Lobe interfaces with the Michigan, Huron, and Erie lobes, which suggest that the "the Saginaw lobe margin retreated from southern Michigan before the retreat of the Huron-Erie lobe ice by about 15,000 rad. B.P. and never readvanced into the region again."


NEW REGIONAL CORRELATION OF GLACIAL EVENTS AND PROCESSES IN… AND NORTHERN INDIANA AFTER THE LAST GLACIAL MAXIMUM (LGM) 12/23/09 10:43 PM
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North-Central Section–40th Annual Meeting (20–21 April 2006)
Paper No. 25-9
Presentation Time: 11:20 AM-11:40 AM
NEW REGIONAL CORRELATION OF GLACIAL EVENTS AND PROCESSES
IN THE INTERLOBATE AREA OF SOUTHERN MICHIGAN AND NORTHERN
INDIANA AFTER THE LAST GLACIAL MAXIMUM (LGM)
BROWN, Steven E.1, NEWELL, Wayne L.2, STONE, Byron D.2, KINCARE, Kevin A.3, and O'LEARY, Dennis W.4, (1) Indiana
Geological Survey, Indiana University, 3400 Broadway, Gary, IN 46408, steebrow@indiana.edu, (2) U.S. Geological Survey,
926A National Center, Reston, VA 20192, (3) Michigan Geological Survey, PO Box 30256, Lansing, MI 48909-7756, (4) U.S.
Geological Survey, 425 Denver Federal Center, Denver, CO 80225
New geologic mapping by scientists involved in the Central Great Lakes Geologic Mapping Coalition, FEDMAP, STATEMAP,
and EDMAP programs has resulted in a reinterpretation of glacial events since the LGM in northern Indiana and southern
Michigan. This group has established a regional working stratigraphy, identified a multitude of overlapping and cross-cutting
relationships of glacial landforms and landscapes, and developed a relative chronology for ice-margin positions in this
interlobate area. The paradigm for geologic mapping includes concepts of the morphosequence, drawing on examples of
depositional systems and processes observed in modern glacial environments such as the Bering Glacier in Alaska and outlet
glaciers in Iceland. These modern analogs have clear equivalents in the interlobate region where relationships of depositional
and erosional features are all connected through a continuum of proglacial, ice-marginal, subglacial, and stagnant-ice
processes.
Glacial lobes in the Lake Michigan, Saginaw, Huron, and Erie lake basins converged in northern Indiana and southern Michigan
at the LGM. During deglaciation after about 20,000 rad. B.P., the lobes became progressively segregated. The relationships of
landforms and landscapes to the sediment record provide a relative chronology for deglaciation of the glacial lobes. Ice-marginal
landforms of the Lake Michigan, Huron-Erie, and Erie lobes overlap landforms of the Saginaw lobe. Proglacial meltwater
streams that exited margins of the Lake Michigan, Huron-Erie, and Erie lobes crossed a deglaciated terrain previously occupied
by the Saginaw lobe. The resulting cross-cutting relationships of proglacial meltwater stream channels and valleys and the
overlapping ice-marginal landforms indicate that the Saginaw lobe ice margin retreated from southern Michigan while the Lake
Michigan, Huron-Erie, and Erie lobes continued to advance. Proglacial meltwater streams that exited the Erie lobe deposited the
last glacial sediment across the interlobate area. Therefore, the regimen of each lobe was asynchronous. The Saginaw lobe
margin retreated from southern Michigan before the retreat of the Huron-Erie lobe ice by about 15,000 rad. B.P. and never
readvanced into the region again.
North-Central Section–40th Annual Meeting (20–21 April 2006)
General Information for this Meeting
Session No. 25
Glacial Geology: Sediment, Landforms, and Chronology I
Student Center, University of Akron: Ballroom C
8:20 AM-12:00 PM, Friday, 21 April 2006
Geological Society of America Abstracts with Programs, Vol. 38, No. 4, p. 58
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