STRATIGRAPHIC, STRUCTURAL & CHRONOLOGIC EVIDENCE FOR A COMPLEX ICE MARGINAL POSITION IN THE EASTERN CATSKILLS

A stream cut exposure along a prominent ridge transverse to the Beaver Kill Valley near Willow, NY in the Eastern Catskill Mountains documents a complex sequence of glacial sedimentation at an ice margin. Previous studies recognize constructional landforms as the product of independent ice masses. Despite being constrained by rugged bedrock valley walls within an upland setting, data suggests this ice margin resulted from a 10 km long valley glacier originating from the Hudson Lobe of the Laurentide Ice Sheet.

Detailed stratigraphic, sedimentologic and structural analysis reveals an uncharacteristic sequence inclusive of eight discrete diamicton units, interpreted as deformation tills interlaced with glaciofluvial and glaciolacustrine deposits. Diamictons are generally matrix supported, clast rich, overconsolidated and range in thickness from 0.24m- 7.0m. Diamictons exhibit pervasive deformation including folds, shearing, boudins and measurable fabrics.

In mid section of the exposure is a 4m thick sequence of varves composed of laminated silty-fine sand and clay, presumably affiliated with a proglacial lake in the Esopus Creek valley. The majority of varves within the exposure do not display the deformation observed within the diamictons that occur above and below the varve section. Oversized clasts as large as 0.3m occur within the varve units and some couplets contain sandy horizons that contain gravel sized material. Diamictons below the varves display recumbent folds, clast plowing and boudins. The lower most diamictons contain a higher percentage of crystalline lithologies whereas diamictons in the upper section display a higher percentage of local Devonian sedimentary rocks.

The valley morphology upstream from the Willow Moraine displays a flat low relief plain 0.75km in width composed of sand, downstream from the moraine the valley develops a narrow 0.15 km wide sinuous expression, armored with cobbles and boulders. The upstream valley is interpreted as a proglacial lake basin that developed with ice retreat. The Willow Moraine is consistent with a model of active dynamic ice behavior. Varve chronology within the exposure, combined with organic material recovered within the Willow basin may provide a means to constrain the age of moraine emplacement.