Geomorphic and sedimentologic evidence for the separation of Lake Superior from Lake Michigan and Huron |
| |
| Authors: | John W Johnston Todd A Thompson Douglas A Wilcox Steve J Baedke |
| |
| Institution: | (1) Department of Geological Sciences, Indiana University, 1005 East Tenth Street, Bloomington, IN 47405, USA;(2) Present address: Department of Earth Sciences, University of Waterloo, 200 University Ave., W. Waterloo, Ontario, N2L 3G1, Canada;(3) Indiana Geological Survey, Indiana University, 611 North Walnut Grove, Bloomington, IN 47405, USA;(4) U.S. Geological Survey Great Lakes Science Center, 1451 Green Road, Ann Arbor, MI 48105, USA;(5) Department of Geology and Environmental Science, James Madison University, MSC 6903, Harrisonburg, VA 22807, USA |
| |
| Abstract: | A common break was recognized in four Lake Superior strandplain sequences using geomorphic and sedimentologic characteristics.
Strandplains were divided into lakeward and landward sets of beach ridges using aerial photographs and topographic surveys
to identify similar surficial features and core data to identify similar subsurface features. Cross-strandplain, elevation-trend
changes from a lowering towards the lake in the landward set of beach ridges to a rise or reduction of slope towards the lake
in the lakeward set of beach ridges indicates that the break is associated with an outlet change for Lake Superior. Correlation
of this break between study sites and age model results for the strandplain sequences suggest that the outlet change occurred
sometime after about 2,400 calendar years ago (after the Algoma phase). Age model results from one site (Grand Traverse Bay)
suggest an alternate age closer to about 1,200 calendar years ago but age models need to be investigated further. The landward
part of the strandplain was deposited when water levels were common in all three upper Great Lakes basins (Superior, Huron,
and Michigan) and drained through the Port Huron/Sarnia outlet. The lakeward part was deposited after the Sault outlet started
to help regulate water levels in the Lake Superior basin. The landward beach ridges are commonly better defined and continuous
across the embayments, more numerous, larger in relief, wider, have greater vegetation density, and intervening swales contain
more standing water and peat than the lakeward set. Changes in drainage patterns, foreshore sediment thickness and grain size
help in identifying the break between sets in the strandplain sequences. Investigation of these breaks may help identify possible
gaps in the record or missing ridges in strandplain sequences that may not be apparent when viewing age distributions and
may justify the need for multiple age and glacial isostatic adjustment models.
This is the third in a series of ten papers published in this special issue of Journal of Paleolimnology. These papers were
presented at the 47th Annual Meeting of the International Association for Great Lakes Research (2004), held at the University
of Waterloo, Waterloo, Ontario, Canada. P.F. Karrow and C.F.M. Lewis were guest editors of this special issue.
The U.S. Government's right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged. |
| |
| Keywords: | Great Lakes Lake Superior Beach ridge Lake level Sault outlet Holocene |
| 本文献已被 SpringerLink 等数据库收录！ |
|
