NEWLY DISCOVERED MESOZOIC BASIN REMNANTS (?) IN THE EASTERN BLUE RIDGE, NORTH-CENTRAL VIRGINIA

Small (<1 km²) exposures of conglomerate and sandstone occur at two localities on the eastern limb of the Blue Ridge anticlinorium, in north-central Virginia. We interpret these as remnant Mesozoic rift basins. Both the Burnley basin and the Beautiful Run basin (new name) occur ~5 km west of the Barboursville and southern Culpeper basins. The deposits unconformably overlie meta-arkoses, phyllites, and graphitic schists of the Neoproterozoic Lynchburg Group. Bedding in these Mesozoic units dips gently to the northeast. The presence of coarse, poorly sorted conglomerates intertongued with sparse, cross-bedded sandstones is consistent with a debris flow dominated, proximal alluvial fan depositional environment. Both the conglomerate and sandstone members of the Burnley and Beautiful Run basins are highly porous and iron-oxide cemented. Conglomerates at both localities display a local provenance with clasts of Lynchburg Group metasedimentary rocks and vein quartz. In contrast, the western border conglomerates of the southern Culpeper and Barboursville basins contain an array of clasts including Catoctin greenstone and Chilhowee Group sedimentary rocks, transported from the western limb of the Blue Ridge anticlinorium, over 25 km to the west. The absence of such clasts in the Burnley and Beautiful Run basins suggests that those basins were not originally connected to the Barboursville and Culpeper basins as predicted by the Birdsboro basin model of Faill (2003). Rather, the Burnley and Beautiful Run basins are more likely small, originally independent half-grabens whose normal faults are, to date, the geologically westernmost expression of the Western Border Fault system associated with Mesozoic rift basins in Virginia. Clast assemblages for the Burnley, Beautiful Run, Barboursville, and southern Culpeper basins suggest that the Mesozoic geography of the Blue Ridge province differed markedly from the modern.