PRE-LATE WISCONSINAN PLEISTOCENE BIOTA FROM SOUTHEASTERN MICHIGAN, USA

Fossiliferous sediments underlie the Late Wisconsinan Mill Creek and F isher Road tills at the Mill Creek site northwest of Port Huron, Michi gan. Fragmentary remains of 5 fish and 11 mammal taxa occur with 39 ta xa of molluscs, 6 of ostracodes, and a pine-spruce pollen assemblage. While the fish are wide-ranging, the mammals include distinctly northe rn elements such as Dicrostonyx sp., Lemmus sp., Mictomys borealis, an d Microtus xanthognathus. The molluscs include a mixture of cold (Vert igo alpestris oughtoni and V. modesta) and warm (Lioplax sulculosa) ta xa. None of the vertebrates have been found at Michigan sub-till sites before, and Lioplax is new to Michigan, fossil or living. Vertigo han nai is known only as a Pleistocene fossil. At present the age of the b iota is indeterminate. The stratigraphy indicates a Middle Wisconsinan or greater age. A finite C-14 age of 48.3 +/- 0.8 ka (QL-1215) was la ter supplemented by a TL date of 57 +/- 9 ka, but perhaps as old as 30 0 ka. Two clusters of amino acid allo-isoleucine:isoleucine values obt ained from six genera of molluscs are interpreted to represent the co- occurrence of early Sangamonian (AIle/Ile values ranging from approxim ately 0.15 to 0.25) and Illinoian (AIle/Ile values ranging from approx imately 0.25 to 0.35) mollusc fossils at the Mill Creek site. These re sults highlight the need for more reliable Quaternary dating methods. (C) 1997 Elsevier Science B.V.