DETRITAL ZIRCON GEOCHRONOLOGY AND PROVENANCE OF UPPER TRIASSIC SEDIMENTS OF THE DANVILLE BASIN, SOUTHERN VIRGINIA

The ages of Upper Triassic sedimentary rocks of the Danville-Dan River Basin are well constrained by a combination of biostratigraphy (pollen) and magnetostratigraphy. Detrital zircon U-Pb dates do not provide constraints on the timing of sedimentation, but are useful in delineating rift geometries, sediment source pathways and provenance ages of sediment fill in these rift basins.

A sample of arkosic sandstone was collected from an exposure on U.S. 58 near Danville, Virginia from the Dry Fork Formation. The sample was processed and Laser Ablation Inductively Coupled Plasma Mass Spectometry was performed on extracted detrital zircons (n = 115) at the Australian National University. The distribution of ages was unimodal with a strong peak at 400-450 Ma. Two smaller peaks were recorded at 375 Ma and 560 Ma. Four grains exhibited ages older than 900 Ma.

The presence of detrital zircons of mostly Paleozoic age suggests that the sediment was derived from Ordovician through Silurian granite sources within the magmatic tract of the western Piedmont to the southeast of the preserved basin. Thayer and Henika have previously shown this part of the basin was sourced by arc volcanic and subvolcanic granitic rocks adjacent to the Vandola Fault along the southeastern side of the basin. The scarcity of Grenvillian zircons suggests that the basin was isolated from the metaclastic tract of the western Piedmont northwest of the Chatham Fault.