GREAT GULLY: THE NEED FOR DETAILED STRATIGRAPHY, SEDIMENTOLOGY, AND STRUCTURAL ANALYSIS TO SUPPORT GLACIAL CHRONOLOGY

Near the village of Union Springs in Cayuga County, New York is an east-west trending gully that preserves glacial sediment. Draining into Cayuga Lake, Great Gully is approximately 6.5 km long, 350 meters wide at is widest, and at its deepest 45 meters . There are 8 tributaries branching off this main gully, all to the south. The east-west nature of the gully allows for the area to be a natural trap for glacial sediments as the Laurentide Ice Sheet advanced across the Finger Lakes Region of New York. The gully is rimmed with a moraine along the northern edge and is also associated with glaciolacustrine and glaciofluvial features. The steep nature of the terrain provides numerous exposures of rock and glacial sediments. Exposures include Marcellus bedrock, diamictons (inferred to be glacial till) and glaciofluvial and glaciolacustrine sediments.

A detailed survey of the exposures was conducted to document and connect the nature of the sediments, the stratigraphy, and the structural elements of the sediments. This level of detail is used to confirm the origin of diamictons and lateral continuity of the units. Generally the stratigraphy displays alternating tills and glaciofluvial or glaciolacustrine sediments. Four distinct tills are noted. An analysis of the tills was conducted using clast fabric, faults, folds and joints. The glaciofluvial and glaciolacustrine sediments were analyzed, as these sediments also contained structures including faults, folds, and climbing ripples. A Brunton compass was used to measure the structures, and were plotted and analyzed with Stereonet 7.2.0 by Richard W. Allmendinger.

Structural analysis indicates patterns consistent with an advance of ice across the gully. The attitudes of the folds and faults, as well as clast fabrics are consistent with stress as ice encountered preexisting topography. Supporting evidence to the preexistence of the gully are climbing ripples that indicate flow direction parallel to the gully. Multiple dating methods on the glaciofluvial sediment associated with the ripples confirm the gully was an open flow system prior to the late Wisconsinan. Careful examination of stratigraphy, sedimentology and structural deformation is fundamental in making hypothesis regarding complex glacial settings.