ACADIAN/NEOACADIAN TECTONIC FRAMEWORK OF DEVONIAN-MISSISSIPPIAN SEDIMENTATION IN THE APPALACHIAN FORELAND BASIN

Structural and terrane analyses in the central and southern Appalachians, along with patterns of sediment distribution in the Appalachian basin, now permit more direct correlations between tectonic events along the eastern margin of Laurussia and sedimentary events in the Appalachian foreland basin.

Most of the tectonic events are related to the northwestward convergence of the Carolina terrane with eastern Laurussia. The docking of Carolina began in Early Devonian time near the New York promontory and ended in Late Devonian time with an oblique, transpressive, zippered collision between Carolina and Laurussia. This convergence resulted in the development and merging of black-shale basins, as well as their subsequent southwestward migration during the zippering collision. These black-shale basins and the large, accompanying Catskill clastic wedge developed during three Acadian tectophases with a total duration of about 49 Ma.

In latest Devonian time, the tectonic regime changed as the northern end of Carolina apparently collided with the New York promontory and the Avalon and Meguma terranes, which were being “ejected” southwestwardly along dextral faults in a pincer movement between Gondwana and Laurussia. This event, called the Neoacadian orogeny, created a major metamorphic/deformational complex in southern New England around the New York promontory, and by earliest Mississippian time, had initiated the Price-Pocono clastic wedge and the more eastward Sunbury-Riddlesburg black-shale basin. As terrane ejection continued, dextral shear was transferred to the newly accreted Carolina terrane, causing it to move in a southwestward transpressional regime that generated new deformational loading and clastic sources at the Virginia promontory. The southwestwardly expanding Sunbury basin and overlying Borden-Grainger-Price-Pocono clastic wedge developed during the fourth tectophase, which lasted about 47 Ma until the end of Mississippian time. The long duration of the tectophase may reflect the fact that dextral lateral translation from the central to the southern Appalachians involved the entire 650-km length of Carolina.