58 Stratigraphy (Posters)

LARGE CHANNEL FEATURE IN WISCOY SANDSTONE: INDICATION OF SEA LEVEL DROP IN THE UPPER DEVONIAN OF WESTERN NEW YORK

Paper number: 58-7
Program: Technical Sessions
Time: 1:30 PM – 5:30 PM

Authors

Abstract

A channel fill 7.5 meters thick and 75 meters wide is developed in the Wiscoy Sandstone Member of the Java Formation, West Falls Group exposed in a road cut near Wayland, New York. The channel is floored by a lag deposit which extends 46 meters across the outcrop and reaches a maximum thickness of 0.9 meters. The lag bed consists of imbricated and aligned pebbles and brachiopods within a matrix of very-fine quartz sand that overlies planar and cross bedded fine sandstones containing vertical and horizontal burrows. Red pebbles up to 5 centimeters in maximum length indicate a terrestrial or near shore source for some of the lag material. Mineralogy of the red clasts as well as surrounding grayish-green sediment and clasts have similar composition. The lag bed also contains cephalopods, conodonts, crinoids, gastropods, ostracodes, and abundant fish fragments. The coarse fossils are layered in several distinct pulses between finer grained sandy intervals.

This stratum is between the Pipe Creek Shale (Frasnian) and the Dunkirk Shale (Famennian), which indicates proximity to the Frasnian-Famennian boundary; conodonts and brachiopods indicate a late Frasnian age. The large channel is developed in offshore shelf strata, as indicated by sedimentary structures and the brachiopod-conodont fauna, suggesting incision by a unidirectional current event. The nearest red-colored strata of this age occur much further to the east, suggesting either transportation of the red clasts, possibly in a submarine canyon-like feature, over 100 km, or progradation of sediment lobes from the Catskill clastic delta as sea level dropped significantly in the upper Devonian. The conglomerate beds represent high energy events, possibly pulses of storm activity.