POSSIBLE FLOODPLAIN INSTABILITY DURING THE YOUNGER DRYAS INDICATED BY TAMARACK LOGS FOUND IN THE LAKE ONTARIO LOWLANDS, NEW YORK STATE

Deposition of gravelly sand and silt plus many logs occurred during the Younger Dryas (YD), ca 12,800-11,750 cal BP, in a small valley within the drumlin fields of the Lake Ontario lowlands in New York State. The characteristics of the logs’ outer surfaces indicate some transport/wear before deposition, but the presence of occasional organic mats in the point bar sediments suggest that deposition was intermittent under variable flow conditions rather than steady high flow conditions.

Log and pollen/macrofossil analyses indicate predominance of tamarack with the occasional presence of spruce. Tamarack is a pioneer species, and can better tolerate and establish in less-than-stable environmental conditions than other boreal species. Minimal abrasion and deterioration of the logs indicate they were transported only short distances and/or minimally scoured when lodged in the stream channel prior to burial within the floodplain. This type of macrobotanical deposition and preservation is known to occur within the floodplain environment and we interpret this to have occurred along a laterally mobile stream with potentially non-cohesive floodplain sediments. Alternatively, substantial flooding could have rapidly eroded portions of the floodplain. Regardless, the predominance of tamarack and the logs’ relatively short lifespans support the intermittent but significant disruption of the floodplain during the YD.

These proxy records help identify the climatic and environmental conditions of the lowlands during the YD, directly following the drainage of proglacial Lake Iroquois. The distribution of the drumlins certainly influenced the routes of stream flow and perhaps the intermittent flooding in the Lake Ontario lowlands.