PALEOBIOLOGY OF THE SAND BENEATH THE VALDERS DIAMICTON AT VALDERS, WISCONSIN

Previously undescribed pollen, plant macrofossils, molluscs, and ostra codes were recovered from a 2.5-m-thick glaciolacustrine unit of silty sand and clay at Valders, Wisconsin. The interstadial sediment was de posited about 12,200 C-14 yr B.P. after retreat of the Green Bay lobe that deposited diamicton of the Horicon Formation, and before advance of the Lake Michigan lobe that deposited the red-brown diamicton of th e Valders Member of the Kewaunee Formation. Fluctuations of abundance of Candona subtriangulata, Cytherissa lacustris, and three other speci es define four ostracode biozones in the lower 1.7 m, suggesting an op en lake environment that oscillated in depth and proximity to glacial ice. Pollen is dominated by Picea and Artemisia, but the low percentag es of many other types of long-distance origin suggest that the terres trial vegetation was open and far from the forest border. The upper pa rt of the sediment, a massive sand deposited in either a shallow pond or a sluggish stream, contains a local concentration of plant macrofos sils. The interpretation of a cold open environment is supported by th e plant macrofossils of more than 20 species, dominated by those of op en mineral soils (Arenaria rubella, Cerastium alpinum type, Silene aca ulis, Sibbaldia procumbens, Dryas integrifolia, Vaccinium uliginosum v ar. alpinum, Armeria maritima, etc.) that in North America occur large ly in the tundra and open tundra-forest ecotone of northern Canada. Ic e-wedge casts occur in the sand. (C) 1998 University of Washington.