Using Biogenic Structures to Interpret Sharp Lithologic Boundaries: An Example from the Lower Devonian of New York

Abstract

ABSTRACT Trace fossils are abundant at the interface between the Lower Devonian Esopus Shale and Carlisle Center Formation at Cherry Valley. They give new evidence concerning the magnitude of the depositional break represented by the sharp contact, which previously was interpreted as an unconformity. Traces include Cruziana, Fustiglyphus, horizontal and vertically oriented traces of various sizes, and knobs and scratch markings, many of which are well-preserved sole markings on the lowermost Carlisle Center bed. Although the Cruziana and scratch marks could have been produced in the underlying semi-consolidated Esopus muds and later preserved by infilling of Carlisle Center sands, it is unlikely they would have survived an extended period of erosion or nondeposition. Cr ziana and scratch markings are cut by burrows which presumably were made by soft-bodied animals and apparently extend through both Esopus and Carlisle Center rocks, implying that the Esopus sediments were unconsolidated during deposition of the lowermost Carlisle Center sands. Clearly the sharp contact represents at most a short depositional hiatus. Recognition and interpretation of trace fossils at other sharp lithologic boundaries may clarify the stratigraphic relationships.