STRATIGRAPHIC SIGNIFICANCE OF MOLLUSCA FROM GLACIAL LAKE TONAWANDA, WESTERN NEW YORK

Recent coring of eastern Glacial Lake Tonawanda indicates possible isolation from the Tonawanda basin-center after detachment from the Glacial Lake Warren basin, and a regional drop in water level. An assemblage of mollusk species have been recovered from gouge cores taken from the northeastern margin of Glacial Lake Tonawanda, western New York. Core depths extend from 2 to 8 meters, and grade upward from a basal till and diamicton to several meters of lacustrine clays, overlain by 2 meters of peat. Cores were sampled at 10 centimeter intervals from strategic locations of the Holley Embayment of Glacial Lake Tonawanda. A weighed fraction was taken from undisturbed cores, yielding a rich shelly fauna from the clay and sandy-silt horizons within each core. Textural analyses and percent organic matter indicate a transition at the 140-150 cm depth interval, coinciding with an environmental transition from lacustrine to muckland.

Gastropod species identified are members of the Families Valvatidae, Planorbidae, Lymnaeidae, Physidae, Zonitidae and Endontidae, with bivalves represented by the Family Sphaeriidae. Most Families are represented by a single species. The Valvatidae Family is represented by Valvata tricarinata simplex east of the Batavia Moraine in the Holley Embayment, and V. tricarinata to the west, suggesting that the waters of the Holley Embayment were environmentally isolated from the west by the Batavia Moraine.

Species counts of individuals were plotted against depth to show changes in numbers of individuals during lake evolution. Comparison of species-count data with the textural analysis indicate those species that remained following eutrophication of the lake basin, coincide with increases in sand and organic matter concentrations. The data suggest that V. tricarinata simplex was absent following eutrophication of the Holley Embayment of Glacial Lake Tonawanda.