Upper Precambrian-Lower Paleozoic Clastic Sequences, Blue Ridge and Adjacent Areas, Virginia and North Carolina

Abstract

Abstract Late Proterozoic to Early Paleozoic stratified assemblages of the central and southern Appalachian Blue Ridge, Piedmont, and Valley and Ridge provinces document the initial origin and early evolution of the eastern margin of ancient North America. A series of thick, late Proterozoic (post-Grenville, 950 to 1100 Ma) clastic sequences record an initial episode of continental distension and rifting with the development of localized, interior, Triassic-like grabens adjacent to a major, scarp-bounded continental edge that bordered either a Proto-Atlantic (Iapetus) Ocean or a smaller, marginal back-arc basin. Overlying, younger stratified sequences document the gradual development of a passive, Atlantic-type continental margin with shallow water shelf sediments of a continental terrace deposited subjacent to deeper water continental rise deposits. The purpose of this field excursion is to familiarize participants with the regional setting, overall lithology and characteristics, and tectonic setting of selected units within the Blue Ridge and adjacent regions that document the evolutionary history briefly described above. All stops will be within the Blue Ridge province itself or along its immediate boundaries with the Piedmont and Valley and Ridge provinces. Stratigraphic units to be seen include: (1) Grandfather Mountain Formation: late Proterozoic fanglomerate and associated alluvium of a rift-related, Newark-like interior basin; (2) Mount Rogers Formation (or Volcanic Group): glacio-fluvial deposits (including tillite and dropstone-bearing laminated pebbly mudstone) and interbedded peralkaline pyroclastics and flows; (3) earliest Cambrian Chilhowee Group: initial shallow water shelf deposits of a developing passive, Atlantic-type continental margin terrace; and (4) Early Paleozoic Alligator Back Formation: metasedimentary and meta-volcanic rocks believed to be altered from deeper water continental rise deposits believed to have been deposited subjacent to the developing continental shelf.