CHANGING FLOODPLAIN ENVIRONMENTS SINCE THE YOUNGER DRYAS IN THE LAKE ONTARIO LOWLANDS, NEW YORK

The stratigraphy of floodplain deposits along Bell Creek records changing paleoenvironmental conditions since the Younger Dryas (YD) in the Lake Ontario Lowlands of New York. Floodplain stratigraphy was documented using forty-five 1.5 x 2 meter trenches excavated by backhoe to a depth of 2 to 3.5 meters below the ground surface. Wood samples were collected from exposed subfossil logs found in the streambed and within the floodplain stratigraphy. Sedimentological, stratigraphic and paleoecological analyses of the valley fill are supported by 36 radiocarbon dates, 33 of which span the YD interval.

Valley fill dating to the middle and late YD reveal a riverine landscape consisting of a low-lying floodplain that supported a boreal-like, riparian open forest community dominated by tamarack (Larix laricina) and spruce (Picea spp.). As regional climate began to warm in the very late YD, the floodplain began to aggrade slowly and wetlands and ponds developed on a still poorly drained floodplain. The poorly drained conditions persisted into the early Holocene as regional climate continued to warm, thus allowing more temperate tree species, including hemlock and elm, to colonize the floodplain. Floodplain wetlands and ponds remained within at least this portion of the Bell Creek valley well into the Holocene, possibly ending as regional climate transitioned to warm/dry in the Middle Holocene. Bell Creek appears to have been in a generally aggradational mode since that time. Middle and late Holocene floodplain aggradation is identified in the Bell Creek valley and other eastern North American fluvial systems as a geomorphic response to climate.