Influence of
Basin Dynamics on Upper Devonian Black Shale Deposition, Western New York State and Northwest
Pennsylvania
Lash, Gary G.1 (1) SUNY
Fredonia, Fredonia, NY
Black shale is ubiquitous to the Upper
Devonian succession of the Appalachian Basin of western New York and northwest Pennsylvania. The spatial
distribution of the organic-rich deposits appears to have been partly
controlled by Acadian basin dynamics. Middle Devonian tectonic quiescence
reflected by the Tully limestone was terminated by development of an Acadian forebulge. The resulting Taghanic
unconformity achieved its maximum hiatal extent in
Chautauqua and Cattaraugus counties, New York, extending south into Pennsylvania. Uplift may have been
controlled by basin structures, including the Clarendon-Linden Fault (CLF),
which lies close to the eastern zero-thickness line of the Tully limestone.
Subsidence of the forebulge is marked by onlap of the Upper Devonian Geneseo
black shale onto the eroded Tully limestone and underlying Middle Devonian
shale. However, the fact that the Geneseo is not
present in extreme western New York and northwest Pennsylvania suggests that the forebulge had migrated to the west. The forebulge
was no longer a positive area in New York when the uniformly
south- and west-thinning Middlesex black shale accumulated. However, the CLF
appears to have accommodated down - to - east offset during deposition of the Rhinestreet black shale resulting in abrupt eastward
thinning of the radioactive facies proximal to the
CLF. Subsidence to the east of the CLF, perhaps a consequence of further
migration of the Acadian thrust complex, ponded the
more clastic facies of the Rhinestreet in this area of the basin; the organic-rich
deposits accumulated in the more elevated region west of the fault. The Upper
Devonian Dunkirk black shale attains a maximum thickness in northwest Pennsylvania reflecting subsidence
of the forebulge perhaps induced by advance of the
Acadian thrust terrane.