LATE PALEOZOIC PANGEA TO CENOZOIC APPALACHIANS: ANALOG FOR LATE MESOPROTEROZOIC RODINIA TO CAMBRIAN EASTERN LAURENTIA?
An Appalachian Mountain range (AMR) resulted from the late Paleozoic Alleghanian orogeny and amalgamation of Pangea. The AMR was eroded and sediments were transported westward as far as the western US in the early Permian and early Jurassic. Sediments shed eastward into large Triassic basins and mafic igneous rocks suggest that continental rifting lasted ~ 30 m.y. As the Atlantic Ocean opened, head ward erosion of eastward drainages accelerated. Cretaceous and Tertiary fluvial to marine sediments were unconformably deposited on the roots of the AMR as the passive margin developed during thermal subsidence. Coastal Plain strata span as much as 140 m.y., with sediment as young as 20 m.y. deposited on rocks as old as 1.2 Ga. The New River Plateau in the southern Appalachians still preserves the earlier westward drainage system, while Miocene breaching of the BR captured part of the west-directed drainage system.
The Pangean cycle allows for comparison with the earlier Rodinian cycle. The Late Mesoproterozoic Grenvillian orogeny produced a Grenville Mountain range (GMR) during amalgamation of Rodinia. Eroded sediments dispersed into parts of the orogen and some are buried beneath the Appalachian basin. In the BR, DZ ages of Neoproterozoic paragneisses suggest a local provenance, indicating that the GMR was mostly leveled between ~1.0-0.76 Ga culminating with ~200 m.y. of Late Neoproterozoic extension as recorded by bi-modal igneous and volcanic rocks, and dike swarms. Unconformably above these rocks is a clastic blanket of Cambrian fluvial to marine rocks deposited on the newly formed Laurentian margin. These strata span > 50 m.y., with sediment as young as ~500 Ma deposited on 1.2 Ga rocks. DZ ages of Cambrian rocks support transcontinental rivers draining eastward from the mid-Continent and Canada.