LAURENTIDE RETREAT FROM AN EASTERN SUSQUEHANNA LAKE SYSTEM

Valley floor stratigraphy indicates an extensive system of ice-contact lakes in the eastern Susquehanna Valley from the NY/ PA border to headwaters in Cooperstown, NY (150 km) during Laurentide glacial retreat. Moraine dammed lakes (15-30 km long) occupied the main valley and most tributaries during ice sheet retreat.

Water well driller’s logs show that well-sorted and stratified sand and gravel within deltaic terraces (a.k.a. kame terraces) grade into valley floor lacustrine sediments (50 - 100 m thick) beneath the Holocene floodplain. The deltaic terraces may constitute unconfined aquifers where saturated thickness is sufficient, otherwise, they serve as recharge conduits to widespread confined subaqueous fan sand and gravel aquifers beneath lacustrine sand, silt and clay.

Sub-bottom continuous seismic profiling of Otsego Lake depicts a well stratified sedimentary sequence (88 m thick), including varves, accumulated in Glacial Lake Cooperstown above a basal diamict (<20 m thick) prior to retreat from the basin leading to meltwater divergence down the Mohawk. These same materials, in similar proportions appear in drillers logs as silty sand and clay interstratified with gravel throughout the entire Eastern Susquehanna River basin.

An analog environment at the terminus of Bering Glacier, Alaska indicates rates of sedimentation in ice-contact lakes are on the order of 35-40 cm/day, thus suggesting Susquehanna lacustrine conditions may have existed for as little as 125-250-years, followed by lake drainage and Holocene floodplain development.

These data suggest rapid retreat of the Laurentide Ice Sheet from the Susquehanna and a history of relatively short-live proglacial lakes.