A REASSESSMENT OF THE ERIE INTERSTADE FROM FIELD WORK IN THE CAYUGA BASIN, CENTRAL NEW YORK

Abstract

The Erie Interstade is generally accepted to have been a relatively warm period associated with retreat of the Laurentian ice sheet (LIS) into the Ontario basin, followed by a readvance to the Valley Heads ice front in central New York. Recent investigations in the Cayuga basin indicate that this ice front retreated only to the Ithaca area during the Erie Interstade. In the Cayuga trough Erie lacustrine strata underlie Valley Heads deposits. Plant assemblages in these strata indicate a sub-arctic environment. Erie deposits also occur in the Fall Creek Valley, where a varved sequence below Valley Heads till and above Nissouri till indicate deposition close to a retreating ice front. Remanent magnetic declination in the varves, best correlated with lower Newport beds of the Middleville fm in the Mohawk Valley, suggest an age of 17.7±0.1 ka cal for the peak of the Erie retreat. Retreat only to the Ithaca area is based on lack of Erie deposits north of Ithaca, oscillation of the ice front around the south end of Cayuga Lake and the lack of a fluvial interval in the Cayuga trough that would have marked retreat into the Ontario basin. Ice core data from Greenland and sea level studies demonstrate that the Erie Interstade was neither a warm period nor a time of significant sea level rise. The Erie Interstade retreat/Valley Heads readvance appears instead to represent a minor reversal in the general, slow ice front retreat from the Last Glacial Maximum ( LGM).