The DeKalb mounds of northeastern Illinois as archives of deglacial history and postglacial environments

Quaternary Research - Tập 74 - Trang 82-90 - 2010
B. Brandon Curry1, Michael E. Konen2, Timothy H. Larson1, Catherine H. Yansa3, Keith C. Hackley1, Helena Alexanderson4, Thomas V. Lowell5
1Illinois State Geological Survey, Institute of Natural Resource Sustainability, University of Illinois at Urbana-Champaign, 615 E. Peabody Dr., Champaign, IL 61820, USA
2Department of Geography, Northern Illinois University, De Kalb, IL 60115, USA
3Department of Geography, Michigan State University, 227 Geography Building, East Lansing, MI 48824-1117, USA
4Dept. of Physical Geography and Quaternary Geology, Stockholm University, SE-106 91 Stockholm, Sweden
5Department of Geology, University of Cincinnati, Cincinnati, OH 45221-0013, USA

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AbstractThe “type” DeKalb mounds of northeastern Illinois, USA (42.0°N, −88.7°W), are formed of basal sand and gravel overlain by rhythmically bedded fines, and weathered sand and gravel. Generally from 2 to 7 m thick, the fines include abundant fossils of ostracodes and uncommon leaves and stems of tundra plants. Rare chironomid head capsules, pillclam shells, and aquatic plant macrofossils also have been observed.Radiocarbon ages on the tundra plant fossils from the “type” region range from 20,420 to 18,560 cal yr BP. Comparison of radiocarbon ages of terrestrial plants from type area ice-walled lake plains and adjacent kettle basins indicate that the topographic inversion to ice-free conditions occurred from 18,560 and 16,650 cal yr BP. Outside the “type” area, the oldest reliable age of tundra plant fossils in DeKalb mound sediment is 21,680 cal yr BP; the mound occurs on the northern arm of the Ransom Moraine (−88.5436°W, 41.5028°N). The youngest age, 16,250 cal yr BP, is associated with a mound on the Deerfield Moraine (−87.9102°W, 42.4260°N) located about 9 km east of Lake Michigan. The chronology of individual successions indicates the lakes persisted on the periglacial landscape for about 300 to 1500 yr.

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Quaternary Research

Tập 74

82-90

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