Reconstructing the age of coastal sand dunes along the northwestern shore of Lake Huron in Lower Michigan: Paleoenvironmental implications and regional comparisons

摘要

Coastal sand dunes are very common in Lower Michigan, especially along Lake Michigan due to prevailing westerlies and high sand supply. These western dunes have been the focus of numerous geomorphic investigations that demonstrate a history for the past 5000 years. Coastal dunes on Lower Michigan's shore with Lake Huron are far less common and have yet to be examined. They have the potential to yield important information about regional wind patterns and their response to lake-level fluctuations. This study is the first to investigate such dunes and focuses on Manitou Beach in northeastern Lower Michi-gan. The chronology was reconstructed through optical dating of eolian sands.Three dune groups were examined. The Algonquin group contains low-relief dunes on the Algonquin lake plain that apparently formed about 6 ka, perhaps due to a warmer/drier climate. The extensive Man-itou group contains prominent ridges between the shore and a bluff eroded during the Nipissing high lake stand about 5.5 ka. Most ridges apparently formed shortly after the lake regressed and about 4 ka. A large, easterly oriented parabolic dune developed about 2.8 ka on the eastern side of the dune field. The Ham-mond group consists of a dunes perched on the Nipissing bluff on the west side of the study area. These dunes also formed between about 5 and 4 ka. This study demonstrates that (1) dunes here are generally older than those on the west coast of Lower Michigan, and (2) unusually strong easterly winds apparently occurred around 2.8 ka.