SUBAQUEOUS ESKER DELTA DEPOSITION BY EPISODIC ICE TUNNEL FLOW INTO PROGLACIAL LAKE IROQUOIS

High velocity axial jets of glacial meltwater during the retreat of the Laurentide Ice sheet from western New York state deposited a series of prominent ridges of sand and gravel outwash into proglacial Lake Iroquois. Surficial mapping and subsurface data illustrates that stratified deposits overlie diamictons on the Carlton Moraine. Detailed examination of the glaciofluvial environment suggests that the Carlton moraine is a much more diverse environment, representing a complex assemblage of glaciofluvial lithofacies with constructional topography. An esker trend transects the recessional moraine and terminates in a subaqueous fan with a proximal facies deposited on a bench formed by the Carlton Moraine. Several extensive outcrops exist at sand and gravel quarries and eroded bluff escarpments along the Lake Ontario shoreline, allowing measurement of paleocurrent flow and interpretation of bedding structures for assessment and characterization of the vectors and style of ice retreat hydrology. Multiple subglacial discharge events stacked a series of scour and fill cross bedded, clast supported, sandy gravels and matrix supported gravelly sands. The gravel beds are often >1m thick and may represent longitudinal bars formed by torrential channelized flows. The lateral continuity and succession of scour and fill events in the gravel lithofacies indicates migrating gravel waves through a tunnel system that is traceable from ~1km offshore to the proximal fan ~2km from the shoreline. Smaller ridges south of the delta form a distributary network. The gravelly lithofacies consist primarily of locally derived reddish shales and sandstones of the Ordovician Queenston group with a minor fraction of crystalline erratics. Gravel clasts >130 mm diameter indicate flow velocities >1m/s. Distal fan morphology indicates deposition into standing water. This glaciofluvial morphology is incongruent with eskers associated with older recessional moraines nested to the south. No other subaqueous esker delta fans have been identified with the Carlton moraine. Development of this glacial outwash network in western New York was possibly influenced by differential bedrock lithology and fault escarpments, locating the outwash tunnel at a zone of resistance within the underlying substrate.