REMNANTS OF A RETREATING ICE FRONT, UPPER SUSQUEHANNA, NY: AN AQUIFER CONNECTION

Laurentide Ice Sheet retreat from the high-relief Appalachian Plateau, east-central NYS, included 10 km valley lobes bound by ice-free slopes in valleys oriented semi-parallel to ice flow. Large-scale stagnation developed in non-through valleys as flow was impeded across upland divides. This lead to general downwasting, limited meltwater sorting and poor lateral continuity. Aquifer potential here is further limited by ineffective recharge and constrained hydrologic transmissivity.

Some km-size remnant ice blocks were also stranded during normal active ice retreat in adjacent through valleys. Here, continuous hydrologic connection with the ice sheet accommodated deposition of laterally continuous sand and gravel that partially buried stranded ice. The resulting well sorted, deposits favor robust aquifer potential. Disconnection from ice sheet meltwater followed retreat from the plateau, thus preserving valley floor mega kettles (dead ice sinks) that formed by eventual ice block decay.

These contrasting retreat conditions produced dissimilar stratigraphy beneath landform assemblages that are diagnostic of aquifer potential. Valleys orientated parallel to the retreating ice front favor landform assemblages similar to non-through valleys, and therefore are also characterized by limited aquifer potential.

Commonly occurring asymmetric north-south valleys contained significant ice-contact inwash from less steep, ice-free, east facing slopes. This accounts for anomalous kame fields resembling moraines that lack an associated valley train. Similar inwash conditions applied to ice-contact lakes, as demonstrated by sub-bottom profiles in Otsego Lake, the site of Glacial Lake Cooperstown. Here, lake sediments inclined gently to the east indicate an abundance of inwash from the west.