Late Proterozoic Rift Control on the Shape of the Appalachians: The Pennsylvania Reentrant

The Pennsylvania reentrant, the most prominent deviation in the trend of the Appalachians, is the product of Late Proterozoic rifting. The Peters Creek Formation, Pennsylvania-Maryland Piedmont, contains rift-gene rated, deep-water turbidite deposits of Late Proterozoic-Cambrian(?) age. These rocks are an extension of the Westminster terrane and lie well to the northeast of the southern Appalachian Late Proterozoic-Cambrian rift basin (Lynchburg-Chilhowee Group basin). The basin into which the Peters Creek Formation was deposited may have connected the southern rift basin with one to the north. The preservation of the Peters Creek Formation and other age equivalent units within the Pennsylvania reentrant indicates that the New York promontory acted as a buttress to Paleozoic orogenic activity.