Appalachian basin stratigraphic response to convergent-margin structural evolution

From study of Palaeozoic formations in the Appalachian foreland basin, a predictive stratigraphic model is proposed based on facies tract development during convergent-margin structural evolution. Five major facies tracts are recognized: shallow-water carbonates that formed during interorogenic quiescence and initial foreland subsidence; deep-water siliciclastics that accumulated in the proximal foreland basin during early collision; syn-collisional shallow-water siliciclastics; syn-collisional, channellized fluvial sandstones that aggraded in the proximal foreland; and progradational shoreline sandstones that were deposited in response to filling of the proximal foreland. Two other facies tracts that occur are organic-rich siliciclastics ('black shales'), which accumulated in oxygen-deficient areas of low clastic-sediment influx, and incised valley-fill deposits, which formed where subsidence rate was low. Because the origin of each facies tract is dependent upon a unique combination of rate of accommodation change and rate of sediment supply, facies tract distribution is predictable from spatial and temporal patterns of subsidence and uplift associated with plate convergence. Alternating phases of thrust loading and quiescence caused fluctuations between underfilled and overfilled conditions during Palaeozoic evolution of the Appalachian basin. Along-strike variations in stratigraphic thickness, facies tract distribution, and development of unconformities in the Appalachian basin reflect the influence of structural irregularities along the collisional margin. In distal parts of the Appalachian foreland and in areas of structural recesses, eustatic influence on stratigraphic patterns is expressed more clearly than in areas of higher subsidence rate.