Evolution in a Glaciated Landscape: Contribution of Endemism to Great Lakes Biodiversity
Fisher, Timothy G. .
Glacial Evolution of the Great Lakes Region.
The history of plant colonization and succession in the Great Lakes basins has its beginnings with the events of the last ice age. These basins themselves owe their origins to primarily glacial processes during numerous glaciations during the Quaternary period; extending back in time approximately 2 million years. Recession of glacial lobes within their respective basins was characterized by numerous readvances and still stands, resulting in the formation of moraines and sand and gravel outwash plains. With drainage to lower outlets to the northeast blocked by the receding ice mass, large proglacial lakes developed in each of the modern lake basins, which were at times connected with each other, but ultimately overflowed drainage divides, draining southwards into the Mississippi River system. It is during these times that high elevation beaches formed in the basins, and lake outflow was channelized, forming deep valleys. The time it took for ice to finally recede from the Great Lakes basins is roughly equivalent to the time that they have remained ice free. During the last ~11,000 years lake levels have fluctuated significantly; by nearly 100 m in the Lake Michigan basin alone. These fluctuations are primarily in response to geophysical processes, with past episodes of climate change playing a minor role. In summary, the origin of the landscape and its constituent sediment as plant substrate, everywhere in the Great Lakes basin, can ultimately have its origin traced back to the glacial and deglacial events of the ice ages.
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1 - University of Toledo, Department of Environmental Sciences, 2801 West Bancroft Street, Toledo, OH, 43606, USA
Presentation Type: Symposium or Colloquium Presentation
Location: Boulevard A/Hilton
Date: Tuesday, July 10th, 2007
Time: 8:00 AM