GEOTRAVERSE ALONG THE MEHERRIN RIVER IN SOUTHEASTERN VIRGINIA: AN UPDATE OF USGS GEOLOGIC MAPPING ON THE WESTERN HALF OF THE EMPORIA 30X60-MINUTE QUADRANGLE, VIRGINIA AND NORTH CAROLINA

New bedrock and surficial geologic mapping and paleoseismic research, funded by USGS FEDMAP, EDMAP, and Earth MRI in the southern Appalachian Piedmont of SE VA, yields valuable geologic information in an area with little previous data. A 72-km traverse along the Meherrin River from near South Hill to Emporia, VA, completed in Aug. 2022, complements a Nottoway River traverse to the north completed in 2019. High-resolution magnetic and radiometric data collected in 2021 through Earth MRI greatly aided mapping of lithologies and major structures.

The Meherrin River crosses, from west to east, the Neoproterozoic to Early Devonian Raleigh (Rt), Spring Hope (SHt), Triplet (Tt), and Roanoke Rapids (RRt) terranes. The Macon, Hollister, and Gaston Dam fault zones of the Eastern Piedmont fault system separate these infrastructural and suprastructural terranes. Rt and Tt rocks include amphibolite-facies, polydeformed and migmatitic biotite gneiss and biotite granitoid gneiss. Discrete zones of magnetite mineralization in these rocks coincide with linear N-S magnetic anomalies that likely represent zones of high-strain within the Rt. Interlayered pegmatitic granite and biotite gneiss display an elevated-K anomaly in a structural dome west of the late Paleozoic Lawrenceville pluton, which is associated with high K, Th, and magnetic anomalies. East of the Macon fault zone, greenschist-facies metasandstone, schist and felsic metavolcanic rocks comprise the SHt and are distinct from Rt and Tt rocks that flank the SHt across the Macon and Hollister fault zones, respectively. The Gaston Dam fault, which separates the Tt from the RRt, is marked by a linear magnetitic anomaly that corresponds to a magnetite-bearing quartzite in the RRt. Metamudstone, mafic and felsic metavolcanic rocks, diorite and granodiorite intrusions, and lava flows of amphibole-rich basalt of the greenschist-facies RRt correspond to linear magnetic anomalies aligned with the regional NW-SE trend of the terrane.

Surficial mapping identified a 2-3 m-thick alluvial sequence locally preserving polygonal fractures, as well as soft-sediment deformation structures (SSDS) at a site near Emporia. A conventional radiocarbon age of 150 ± 30 BP dates the SSDS to a liquefaction field that may have resulted from an M4.5+ event near Petersburg, VA, in 1774.