FLUVIAL SYSTEM EVOLUTION AND PALEOENVIRONMENTS UNDER A CHANGING CLIMATE FROM THE YOUNGER DRYAS INTO THE HOLOCENE, LAKE ONTARIO LOWLANDS, NEW YORK

The Younger Dryas (YD) is recognized as a significant cold interval that occurred at the end of the late Wisconsin glacial stade (MIS 2). Although recognized globally, the response of fluvial systems to the changing climate in the Great Lake Region during the YD is largely unknown. Here we document fluvial response to changing paleoclimate conditions and floodplain paleoenvironments based on stratigraphic, sedimentological and paleobotanical analyses in the Bell Creek valley in the Lake Ontario Lowlands, New York State. Our results suggest several phases of floodplain evolution. Basal sediments of excavated trenches represent a moderately high-energy fluvial environment that evolved after 13.0ka when meltwater drainage from Lake Iroquois through the Mohawk River corridor ended. As water levels lowered and streamflow diminished, ~12.5-~12.0ka, the fluvial system gradually converted to a poorly drained low-energy environment, preserving abundant logs and plant macrofossils. Paleoclimate conditions during this interval shifted from cool-dry to cool-moist and back to cool-dry. Deposition of the upper fossil-bearing strata commenced during the Early Holocene (EH), ~ 11.5ka, and reflects floodplain aggradation under an overall warmer, moister climate. The paleoenvironmental record within the transition between the lower organic-rich strata and the upper organic-poor sediments suggests the introduction of temperate tree species into the region after 11.5ka. Above the transition, paleoenvironmental evidence is scarce due to better-drained, oxidized sediments. The YD and EH deposits in the Bell Creek valley infer other river valleys in the Great Lake region may contain important archives of fluvial response to climate, floodplain evolution and paleoenvironments.