The Catskill delta complex and the Acadian Orogeny: A model

The Catskill Delta complex is interpreted to be the aggregate of delta-alluvial wedges and associated facies that developed in the central Appalachians and on adjacent parts of the stable craton from the Early-Middle Devonian transition to the Middle Mississippian during the Acadian orogeny. Recent interpretations of the Acadian orogeny suggest that it probably was related to oblique convergence and transcurrent movement along a major strike-slip fault zone separating the eastern margin of the North American landmass from a linear continental fragment called the Avalon terrane. Distribution of clastic wedges and basinal deposits resulting from this orogeny support a general southwestward progression of orogeny and indicate that the major clastic wedges emanated from areas near promontories on the continental margin during successive phases of Acadian deformation. Three and possibly four such tectophases have been noted. Each tectophase appears to represent increased convergence or possible collision between a specific continental promontory and the Avalon terrane, but some delta development occurred continually along many parts of the orogen in response to each tectophase. The four tectophases are: (1) Collision near the St. Lawrence promontory during the Early-Middle Devonian transition with initiation of the Catskill Delta complex represented by the Needmore and Esopus shales and associated clastics near promontories. (2) Southward migration of deformation and collision near the New York promontory during the Middle Devonian with the development of a large peripheral basin having an east-dipping, western paleoslope. This basin was filled with cyclic delta clastics and carbonates of the Hamilton Group and Tully Limestone. (3) Southward migration of deformation and collision near the Virginia promontory during the Late Devonian to earliest Mississippian accompanied by intense clastic influx of the Geneseethrough- Canadaway groups. As a result, the basin was progressively filled from the east so that basinal environments migrated westward out of the peripheral basin and onto adjacent parts of the stable craton. Eventually the basin was filled and a regional west-dipping paleoslope was established. (4) Migration of deformation southward from the Virginia promontory during the Early to Middle Mississippian as basinal environments in cratonic seas were destroyed and Pocono and equivalent clastic wedges essentially filled the epicontinental sea. Middle Mississippian carbonates mark the end of the Acadian orogeny and Catskill Delta complex.