Abstract: Revision of the Contact between the Genesee and Sonyea Formations (Upper Devonian) in Western New York

James W. Scatterday, Samuel W. Gowan, Kevin R. Barta

Recent models of the inception of cycles like those that characterize the upper Middle and Upper Devonian rocks of New York predict that the basinal facies of the initial deposits of each of these cycles should rest on an erosional discontinuity. Such a discontinuity, the product of at least two episodes of submarine scour, is found beneath the Middlesex Shale, the basal member of the Sonyea Formation, throughout the Genesee Region of New York. This previously unrecorded discontinuity is evidenced by hiatus concretions and two conodont-rich pyrite lag deposits associated with abundant coalified wood. One lag predates formation of the concretions; the other accumulated following their exhumation. In the study area, the discontinuity lies several meters below the currently ccepted but apparently conformable base of the Middlesex and approximately a half meter above the Beards Creek Concretionary Zone of the West River Member of the Genesee Formation. We suggest that the discontinuity we have recognized marks the beginning of the Sonyea cycle and therefore the strata between it and what is presently regarded as the base of the Sonyea should be included in that formation. The similarity of the strata in question to the Middlesex and the ease of distinguishing them from the West River, both in outcrops and the subsurface, further support our suggestion.

AAPG Search and Discovery Article #90954©1995 AAPG Eastern Section, Schenectady, New York