INCIPIENT PANGEAN RIFTING RESPONSIBLE FOR THE INITIATION OF CHINLE-DOCKUM SEDIMENTATION: INSIGHTS FROM THE NEWARK SUPERGROUP AND SHARED LATE TRIASSIC PLATE-SCALE TECTONIC EVENTS AND GEOCHRONOLOGIES

U-Pb ID-TIMS zircon geochronologies from the Late Triassic Chinle-Dockum permit direct correlation of these strata with the Newark Supergroup, supplemented by new and refined litho- and tectono-stratigraphic data and tied to the Newark astrogeochronologic timescale. A consequence of the correlation is the implication of Pangean rift tectonics as the driving mechanism behind major sedimentation events in both the Newark Supergroup and Chinle-Dockum. Newark Supergroup rocks comprise four tectonostratigraphic sequences (TS) that range from Permian to Early Jurassic in age. TS II strata include late Carnian Tuckahoe and Doswell Groups in the Richmond-Taylorsville (R-T) basins of Virginia. TS III consists of early Norian to Rhaetian strata in most Newark Supergroup basins and includes the Chesterfield and King George Groups, which overlie R-T basin TS II.

R-T TS II strata are Carnian age, ~2.5 km of cyclic lacustrine deposits with coals near their base. The TS II/TS III transition is defined by an unconformity in the R-T basins, and approximates the Carnian-Norian boundary (CNB). Coincident is initial development of the Dan River and Bourborsville-Culpeper basins. We hypothesize that sedimentation in these latter basins resulted from accelerated NE-SW extension beginning with coal-bearing lacustrine deposits in the Deep River and Dan River basins dating to 227-Mya.

Initiation of Chinle-Dockum sedimentation at ~228 Mya approximates the CNB, and was promoted by rift extension (Eagle Mills composite basins) and shoulder uplift along the Ouachita-Marathon trend. Thick vertisols, paludal facies and halokinetic deformation of specific stratigraphic intervals indicates prolonged periods of rapid fluctuation of water tables in lower Chinle strata correlative with coal bearing Newark Supergroup TS III strata. There is no compelling evidence for major influence of the Cordilleran arc on Chinle-Dockum sedimentation. In contrast to prevailing tectonic models of southwestern North America, the Late Triassic island arc and associated back arc basin may not have existed at all, and terranes with age equivalent rocks were accreted later during the Mesozoic.