Abstract

Representative samples from 180 bottom sediment stations from Burt Lake, Cheboygan County, Michigan, were analyzed for particle size distribution, carbonate and organic C contents, and color. With a few exceptions the results show a gradation from a medium coarse sand to a gelatinous silt at a water depth of approximately 35 ft, which is an average of 1500 ft from shore. Both the carbonate and the organic C percentages increase with water depth and distance from shore, with the gelatinous silts of the central trough containing an average of 45.5% equivalent calcium carbonate and 27.8% organic C. There are a few striking exceptions, however. The greatest deviation occurs in the deepest part of the lake in what is believed to be the site of an active sinkhole. The 12% sand content, the 67.2% carbonate content, together with only 20.8% organic matter lend support to the theory that springs are presently emanating from that pit in the lake floor. Analysis of these data suggests that the lake originated as a series of sinkholes which later became filled with Valders ice. Stagnation of the ice in these depressions, subsequent deposition of outwash sands and gravels around the blocks, and final melting of the ice eventually resulted in the formation of a sink-hole-kettle lake, Burt Lake.

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