BIG LAKE RECORDS PRESERVED IN A LITTLE LAKE’S SEDIMENT: AN EXAMPLE FROM SILVER LAKE, MICHIGAN, USA

Silver Lake is a former embayment of Lake Michigan, separated by a barrier-bar/dune complex. Lake sediment stratigraphy based on vibracores and a GPR transect consists of Lake Michigan Formation (LMF) sand and clay overlain by marl, peat and organic-rich mud, which records lake level fluctuations in both Michigan and Silver Lake. A hardwater corrected date of 11,310 14C BP (Beta169830) at the marl and LMF contact records the beginning of the Greatlakean substage. A 10,460±50 (WW2787) 14C BP age from a buried soil overlain by pebbly sand may be interpreted as a transgression of Lake Algonquin. In other cores, the abrupt transition to marl records a localized perched water table during the Chippewa Low. Peat deposition starting at 8400 yr BP indicates freshening of the water while the abrupt transition to sandy muck at 6600 yr BP is explained by flooding Silver Lake from rising Lake Michigan. Peat-top elevation constrains the lake level curve of the Chippewa transgression. Fine-grained sediment in the western edge of the basin is likely LMF clay overlapping the barrier suggesting that the barrier is Calumet age or older. Eolian sand in the uppermost mud is variable, and occasional bands of sand may relate to when the dunes lost their wooded cover ~400 yr. BP.