Foreland-basin sequence response to collisional tectonism

As structural salients and recesses evolved from reentrants and promontorie s along the collisional continental margin associated with the Taconic orog eny, cross-strike structural features provided a mechanism for transferring zones of relative subsidence and uplift across the Appalachian foreland ba sin. The regional distribution of Lower Silurian elastic sequences reflects this tectonic influence. Thick, aggradational sequences formed in areas co rresponding to salients in response to high rates of sediment supply and cr eation of sediment accommodation. As the rate of sediment supply exceeded t he rate of accommodation added, shoreline progradation onto the distal fore land ramp produced upward-coarsening sequences. In areas of structural rece sses, accommodation was created by erosion during sea-level fall and lowsta nd, Upward-fining sequences formed as the topographic lows were filled duri ng subsequent sea-level rise. Results from this investigation indicate that predictable variations in for eland-basin deposition and in the resulting stratigraphic pattern occur alo ng regional tectonic strike as well as in the dip direction. The thickness of foreland-ramp sequences is greater in areas of salients than in recesses , whereas the ratio of sandstone to total thickness is greater in the reces ses. Aggradational sequences grading laterally into upward-coarsening progr adational sequences of the distal ramp characterize areas of relative subsi dence, which provides a mechanism for creating sediment accommodation. In c ontrast, deep erosion, common unconformities, and incised valley fills are present in areas corresponding to recesses, where the rate of eustatic fall commonly exceeds the subsidence rate. These along-strike stratigraphic var iations in response to collisional tectonism should be considered in the in terpretation of other foreland-basin successions.