The Devonian Catskill delta is an exogeosynclinal clastic wedge in the Appalachian basin. Subsidence caused by this load is modeled as flexure of a perfectly elastic crust. Subsidence can be measured accurately in eastern New York and Pennsylvania because of excellent well and outcrop control and the ability to recognize shoreline position.

Calculated flexural response to the load of the Erian Series sediments predicts subsidence smaller than observed values, especially in the eastern portion of the delta. It is necessary to postulate an additional tectonic component of subsidence. Additional subsidence is modeled as a cosine curve decaying exponentially with distance from a point deflection of the crust. This model, plus the flexure caused by sediment load, produces subsidence consistent with observations.

The flexural response of the crust offers an explanation for an unconformity in black shales that developed during the Taghanic age on the west side of the Appalachian basin, with at least 50 m (165 ft) of expected strata missing. This unconformity expands westward and southwestward from the maximum sediment load. The unconformity is unusual because it formed during a sea level rise (Taghanic onlap) which apparently affected all of North America. Flexural modeling predicts upwarp in central and western New York, western Pennsylvania, and eastern Ohio, and offers a plausible explanation for this unconformity.

The tectonic component of the subsidence curve, coupled with the geologic constraints, offers an opportunity to model the location of the Acadian Mountains to the east, which have since been eroded to their roots.

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