A NIPISSING TRANSGRESSION RECORD FROM DUNE DAMMED SILVER LAKE, LITTLE SABLE POINT, LAKE MICHIGAN

Previous determinations of lake levels in the Great Lakes have documented isostatic and climatic signatures based on primarily subaerially exposed geomorphic landforms and their constituent sediment. Peat deposits in coastal areas, and submerged logs and stumps in growth position offer important, but rare, data sets with which to constrain the Nipissing transgression. Two vibracores were recovered from Silver Lake at Little Sable Point along the eastern coastline of Lake Michigan in February 1999. The cores SL1 and SL2 were from 4.2 and 6.4m water depth, respectively, which puts them below the modern level of Lake Michigan. SL1 is a 2m core with a buried spodisol developed in dune sand, capped with lake sand. A wood fragment from the upper soil’s A horizon yielded a 5630±40 (WW2786) 14C, or 6460 cal BP age; while the lower soil’s A horizon yielded a 10,460±50 (WW2787) 14C, or 12,770 cal BP age. SL2 is a 2.5m long core with a 0.75m thick peat with large plant macrofossils and aquatic plant remains, but no gyttja. Above the peat there is 0.75m of sand interbedded with gyttja, and the top of peat is dated at 6140±70 (Beta146718) 14C, or 7000 cal BP, while the base of the peat is dated at 6950±80 (Beta146717) 14C, or 7760 cal BP. Marl with gastropod shells, light gray marl with no shells, and 0.2 m of medium grained sand with rounded pebbles at the base of the core underlie the peat. Considering (1) the location of the soil and peat units, 4.4 and 7.2m below the modern level of Lake Michigan, (2) the mid Holocene ages; and, (3) the capping of lake sediment, the dated samples may be used to constrain the rate of the Nipissing transgression. These initial results from Silver Lake suggest to us that coring coastal dune dammed lakes is an important methodology for collecting detailed information on low lake levels of Lake Michigan, especially at a time when low levels are raising societal concerns.