NEOPROTEROZOIC TO ORDOVICIAN RIFT-DRIFT STRATIGRAPHY OF THE PENNSYLVANIA AND QUEBEC SALIENTS AND THE NEW YORK RECESS

Detailed stratigraphic sections, facies mosaics and depositional models have been compiled for Neoproterozoic to Ordovician rift-drift rocks in the Reading Prong and Great Valley sequences of Pennsylvania, New Jersey and New York. Changes in strike-parallel stratigraphic thickness have been documented from the arm-bend of the Pennsylvania salient-New York recess through the juncture of the New York recess and the Quebec salient. Strike-parallel differences, and similarities, in rift-drift facies have also been documented, with respect to deposition in salients vs. recesses.

Interregional correlations, and associated tectonostratigraphic interpretations, were accomplished through deciphering depositional environments preserved in chert. The associated cherts were aligned with discrete formation members in the Great Valley sequence, which led to detailed discrimination of the rift-drift rocks in locations where fossils were sparingly found and detailed stratigraphic correlation was tenuous. Chert horizons are continuous along strike and provide a consistent mapping aid in otherwise monotonous carbonate rocks that extend for tens of kilometers along the Appalachian orocline.

Conversely, the mapped variations in the tectonostratigraphic framework have led to a reconsideration of chert diagenesis in rift-drift rocks. Previous interpretations focusing on a purely organic model of chert diagenesis are being reconsidered in light of how tectonic stresses are controlled by pre-existing boundary conditions. Variations in Paleozoic thrust loading, as controlled by the geometry of the Iapetan rifted margin, are interpreted as being responsible for chertification resulting from pressure solution and layer parallel shortening.