SIGNIFICANCE AND AGES OF MID-WISCONSINAN ORGANIC DEPOSITS IN SOUTHERN MICHIGAN

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Abstract
Four recently drilled, closely spaced wells near Kalkaska, Michigan encountered a thick zone of organic-rich sediments at a depth of about 130 m; all are interpreted as part of the same unit. Two radiocarbon dates and botanical data derived from the carbonaceous material along with associated sediments indicate that about 35,000 B.P. the site was ice-free, poorly drained, and supported first an open and later a closed boreal forest. These two and eight additional radiocarbon determinations (four finite and four “infinite”) from wood recovered during other research are compared with all other previously published dates for Middle Wisconsinan material from southern Michigan. This array of ages suggests that at least parts of the state were not glaciated during much if not all of the Middle Wisconsinan, including the Cherrytree Stadial. Botanical evidence also indicates that about 35,000 B.P. the climate in the northwest part of the Southern Peninsula was considerably cooler than at present, possibly being influenced by a glacier with a margin in Ontario.