Late Wisconsinan and Holocene coastal evolution of the southern shore of Lake Michigan
Late Wisconsinan and Holocene coastal evolution of the southern shore of Lake Michigan (in Quaternary coasts of the United States; marine and lacustrine systems, Charles H. Fletcher (editor) and John F. Wehmiller (editor))
Special Publication - Society of Economic Paleontologists and Mineralogists (December 1992) 48: 397-413
The late Wisconsinan and Holocene coastal evolution of southern Lake Michigan contrasts with the coeval history of ocean-coast settings. Multiple transgressive and regressive events occurred, and rates of lake-level change were often greater than the most rapid eustatic sea-level changes. A succession of lower high-lake maxima is recorded in mainland beaches, spits, and beach-ridge/dune complexes across the Chicago/Calumet lacustrine plain. The plain, which extends approximately 120 km from north of Chicago to the Indiana-Michigan border, was the sink for net-southerly littoral transport. During the high-lake phases between 14.5 ka and about 3.5 ka, littoral transport from the eastern and western lake shores terminated in separate spits on opposite ends of the lacustrine plain. Since about 3.5 ka, littoral transport converged along the southern shore. Gradual changes in coastal geomorphology, brought about by littoral processes acting within an overall trend of lake-level decline over the past 2,500 years, formed the modern coastal geography. The Chicago River was transformed from a westward- to an eastward-flowing drainage; littoral-sediment accretion resulted in an extensive beach-ridge/dune complex and a 35-km stream-mouth deflection forming the Grand Calumet River. A model for the coastal sedimentary evolution during the transgressive phases indicates minimal-sediment supply until rate of lake-level change declined and a peak lake level was reached. Wave erosion along the glacial-bluff lake margins could then supply the littoral-transport system. The overall depositional history of the south Lake Michigan coast is that of a regressive and progradational system.