Triassic-Jurassic stratigraphy of the Culpeper and Barboursville Basins, Virginia and Maryland

Abstract

The presence of Late Triassic and Early Jurassic spores and pollen throughout an exposed stratigraphic section has enabled the systematic palynofloral zonation of the entire Culpeper Group, supported in places by characteristic fish zones. Strata of the Culpeper Group range in age from the Late Triassic to the Early Jurassic. The distribution of strata in the Culpeper Group is explained by accumulation of clastic sediments in a closed basin flanked by fault-block mountains that were episodically uplifted and eroded. Deposition within the basin was controlled by subsidence accompanying extensional tectonics during a dominantly semiarid climate punctuated by periods of abundant precipitation. During the late stages of Jurassic deposition of the Culpeper Group, tholeiitic diabase stocks, sills, and dikes (about 195 Ma) extensively intruded the sedimentary rocks and basalt flows and thermally metamorphosed them. The strata in the Culpeper and Barboursville basins were regionally tilted to the west, particularly along the western border faults, which produced steep dips, drag folds, gravity slumping, and slippage along bedding planes; broad, gently southwest plunging folds, and en echelon and strike-slip faults along the western basin margin; and folds and transverse faults within the basins. -from Authors