Simplified tectonic history of eastern North America. The Carboniferous-Permian period witnessed the collision of North America and Africa (top), marking the final stage in the assembly of Pangea. This resulted in the formation of gently dipping thrust faults and moderately to steeply dipping thrust and strike-slip faults. The Triassic period (bottom) witnessed the first stage in the breakup of Pangea, as North America and Africa started to rift apart. This resulted in the formation of moderately to steeply dipping normal and oblique-slip faults--many of which were reactivated Paleozoic faults--that formed the border faults of the rift basins (blue). Click on the image to see a larger version. Modified from Withjack et al. (1998).