Basement structure of the Appalachian Basin in Pennsylvania

Basement structure beneath the Pennsylvanian portion of the Appalachian basin, where some of the deepest basement in the basin is found, is investigated by constructing a map of the Precambrian unconformity using 3939 new point estimates of basement depth determined from seismic reflection profiles and P-wave receiver functions, combined with geophysical and well log data used in other published basement maps. The map shows a gradual and uniform deepening of the basement from depths of ~1500 m in the northwest to ~6000 m in the southeast, consistent with a foreland basin plate flexure model. However, basement depths in two regions, when compared to depths predicted by a plate flexure model, show basin over-deepening. One to two km of over-deepening coincides with the Neoproterozoic-early Paleozoic Rome Trough in southwestern Pennsylvania, and the Northumberland Deep Basement Zone (NDBZ) in east-central Pennsylvania shows two to two and a half km of over-deepening. Basin over-deepening in the Rome Trough does not extend into northern Pennsylvania, pointing to a termination of the trough within central Pennsylvania. The origin of basin over-deepening in the NDBZ is less certain but overlaps spatially with the southern portion of the Neoproterozoic Scranton Rift. The preservation of one or more failed Neoproterozoic-early Paleozoic rifts within the basement structure of the Appalachian Basin suggests crystalline basement was not significantly deformed by the Paleozoic orogenic events associated with basin formation. It also supports models placing the locus of Laurentian rifting from Rodinia well to the east of the Appalachian Basin.