LATE QUATERNARY MOLLUSCS, CENTRAL GREAT LAKES AREA

Study of fossil and modern molluscs has been underway for over a century. Molluscs are the most obvious animal fossils found, occur commonly, require only modest litre-size samples, provide useful paleoecological data, can yield paleoenvironmental interpretation from stable isotope analysis and extended age control beyond radiocarbon from amino acid analysis. F.C. Baker, Pilsbry, Leonard, La Rocque, van der Schalie, A.H. Clarke and other 20th century workers provided essential data on the ecology and distribution of fossil and modern molluscs for the interpretation of fossil assemblages. A few Sangamon interglacial sites have large assemblages of several score taxa. More numerous Wisconsin (sub-till) interstadial sites commonly include molluscs, typically with a dozen or less taxa, usually of shallow, vegetated, freshwater environments; age determination remains a problem. Post-glacial sites are widespread and accessible, with glacial and successor lakes best documented. Colonization during deglaciation was early and rapid into the present (Hudson) interglacial, as shown by groups of sites dated 13,200 BP (Mackinaw: 9 taxa), 12,200 (Iroquois: 26 taxa), 10,500 BP (Algonquin: 57 taxa) and 5,000 BP (Nipissing: 75 taxa). A few marl sites (12,000 - 7,000 BP: ca. 30 freshwater taxa) and a tufa and two alluvial fan sites (10,000 - 5,000 BP: ca. 60 terrestrial taxa) show the evolution of small basin and terrestrial sites of the present interglacial.