Anyone who has collected fossils from the sedimentary rocks of the Appalachians realizes that many of these strata were deposited in shallow marine environments. These represent strata of both the ancient continental margin that bordered the Paleozoic Proto-Atlantic (Iapetus) ocean, and strata deposited in a variety of basins developed during the three orogenies that affected the Appalachians in the Paleozoic. Paleomagnetic data indicate that throughout this time the mid-Atlantic Appalachian region lay in tropical latitudes which favors carbonate deposition.

The Appalachian stratigraphic succession (Figure 1) contains the historical record of the eastern continental margin and orogenic basins of North America during the Paleozoic. This record includes all the stages in the Wilson Cycle of ocean basins. The Paleozoic Appalachian continental margin located along the edge of the Proto-Atlantic was created during a continental rifting represented by the Catoctin basalt flows (Fichter and Diecchio, 1986a) in the Blue Ridge. Following this rifting, the Appalachian area became part of a divergent (passive) continental margin that is represented by strata from the Lower Cambrian Chilhowee Group probably to the Lower Ordovician Beekmantown Formation (Figure 1). Somewhere between the top of the Beekmantown and the Martinsburg Formation (as will be discussed in this guide) convergence began to affect the Proto-Atlantic coast, and continued sporadically for most of the rest of the Paleozoic (Taconic, Acadian and Alleghenian orogenies). Continental collision culminated this cycle (Alleghenian orogeny: Gondwana collides with North America) and resulted in the final deformation of the mountain belt.

The Appalachian Paleozoic succession also contains the record of many different scales of sea-level fluctuations. The largest of these have resulted in the formation of unconformity-bounded sequences. The unconformities (or discontinuities) represent lowstands of sea-level that exposed much of Appalachian area and caused widespread erosion surfaces. As illustrated in Figure 1, the Sauk, Tippecanoe, and Kaskaskia sequences are well documented in the Appalachian area.