Outlet Channels for the Post-Duluth Lakes in the Upper Peninsula of Michigan.
Drexler, Christopher William
1981
Abstract
The glacial history of the Upper Peninsula of Michigan has received little study since the publication of Leverett's (1929) classic work. Leverett's interpretation of the geologic history of the Upper Peninsula was based primarily upon his recognition and interpretation of moraines and shorelines. For a variety of reasons these l and forms are very difficult to use for historical reconstructions in the Upper Peninsula. It has become increasingly clear since Leverett's publication that a number of his interpretations were erroneous. A different way of approaching the problem of deciphering at least a portion of the glacial history of the Upper Peninsula is to study the outlet channels of the Post-Duluth lakes. The importance of these features is that they connect the western end of the Lake Superior basin with both the eastern end of that basin and with the basin of Lake Michigan at a time when the central part of the Lake Superior basin was still occupied by the ice sheet. This permits lake stages in these different basins to be correlated by physical tracing. Furthermore, in many instances segments of the outlet channels were ice marginal so that both the position of the ice margin relative to the existence of specific glacial lakes and the rate and manner of ice retreat can be studied. Finally, many of the channels contain small lakes in which organic material has accumulated since the channels were ab and oned. Coring of these lakes and obtaining ('14)C dates on the basal organic material lead to an estimation of the duration of the Post-Duluth interval, as well as the dates of its inception and termination. Important results pertaining to the geologic history of the Post-Duluth interval discovered during this study are: (1)the Post-Duluth interval began about 10,000 B.P. and ended about 9,600 B.P., (2)at the time Lake Sub-Duluth came into existence the Chippewa, Stanley and Hough lakes were already in existence in the Lake Michigan and Lake Huron basins. Lake Minong was, at that time, a small pro-glacial lake confined to the southeastern end of the Lake Superior basin, (3)several lakes doubtfully included by Farr and (1960) in the Post-Duluth interval, and having shorelines developed at elevations below that of the Beaver Bay shoreline, are now known to be Post-Duluth lakes. Two of these have been named for their outlet sills: Glacial Lake Huron Mountain and Glacial Lake Shelter Bay. Furthermore, some paleohydrologic characteristics of the Post-Duluth outlet channels have been determined. Approximate water depth and peak discharge could be calculated for one of the channels. In addition, a large variety of l and forms produced by fluvial erosion and deposition have been identified. Some of the l and forms were produced by very large flood events and are analogous, but of smaller scale, to l and forms produced by the catastrophic floods that eroded the scabl and s of eastern Washington.Types
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