OSL DATING OF A STRANDPLAIN SEQUENCE IN THE PINE RIVER EMBAYMENT OF LAKE SUPERIOR ALONG THE UPPER PENINSULA OF MICHIGAN

Strandplain sequences, sometimes called ridge and swale sequences, that form in embayments along the shores of the Great Lakes have been shown to be meaningful recorders of paleohydrological data over the past 6000 years. In a continuing effort of produce high-resolution lake-level histories for the Great Lakes through the Middle and Late Holocene our team has examined a sequence of ridges northwest of Marquette, Michigan, in the Pine River embayment along the southern coastline of Lake Superior. The strandplain preserves a large dune-capped ridge in the middle of the sequence, which was inferred from geomorphological analysis to have formed during the Nipissing phase of ancestral Lake Superior, as well as 15 pre-Nipissing (landward) and 10 post-Nipissing (lakeward) ridges. To establish a chronology for the ridge sequence and verify the age of the medial ridge, samples for optically stimulated luminescence (OSL) dating were collected from hand-excavated profiles at a frequency of roughly every fifth ridge. A portion of the prominent central ridge had been excavated as a sand borrow pit and afforded an opportunity to collect a vertical OSL sample profile as well. The vertical sampling profile bracketed a paleosol that was identified within the dune sediments and spanned the transition into waterlain foreshore sediments. We present here the OSL dating results for the strandplain sequence as well as the vertical profile. The littoral sediments within the large dune-capped ridge resulted in an age of 4540 +/- 190 yrs., which is consistent with the peak Nipissing phase of the upper Great Lakes. Eolian sediments bracketing the paleosol suggest a hiatus of approximately 900-1000 years with the later period of deposition occurring 3500 +/- 130 years ago; a recognized period of widespread eolian activity through the Great Lakes region.

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