GEOTRAVERSE ALONG THE NOTTOWAY RIVER IN SOUTHEASTERN VIRGINIA: NEW COOPERATIVE GEOLOGIC MAPPING ON THE WEST HALF OF THE EMPORIA 30X60-MINUTE QUADRANGLE

A geologic mapping effort that combines FEDMAP, STATEMAP and EDMAP is collecting bedrock, surficial and paleoseismic data in southeast VA, a data-poor region of the southern Appalachian eastern Piedmont. Best available published mapping in this region is the 1:500K-scale 1993 geologic map of Virginia. A 66-km geotraverse was completed along the Nottoway River from Blackstone to Jarratt, VA from July-Sept. 2019, and transects (west to east) the Raleigh(Rt), Spring Hope (SHt) or Triplet (Tt), Roanoke Rapids(RRt) and Petersburg (Pt) terranes.

Rocks of the Rt include foliated megacrystic metagranitoid that contains xenoliths of biotite gneiss and is cut by foliated metagranitoid of the Alberta pluton. An amphibolite-facies high strain zone (Macon or Hollister fault zone?) separates rocks of the Rt from foliated biotite-rich metagranitoid, which may be either basement to the greenschist-facies SHt or the northern extension of the Tt. Biotite-rich metagranitoid also contains xenoliths of biotite gneiss and amphibolite. Phyllonite of the dextral Gaston Dam fault zone (GDFZ) separates biotite-rich metagranitoid from rocks of the RRt. The GDFZ is ~1 km-wide and is sinistrally offset by 0.1 km-thick silicified cataclastite. Amphibolite-facies rocks of the RRt include epidote-bearing greenstone and amphibolite, quartz phenocryst metafelsite, and blue quartz- pebble metaconglomerate; these rocks are cross-cut by metadiorite, hornblendite, and granodiorite locally. East of a newly recognized ~ 1.5 km-wide dextral high strain zone are mica schist and foliated metagranitoid of the Pt.

Along the river are Fe- and Mn-cemented sand and gravel deposits that contain boulders of local bedrock; these terraces are similar to Pleistocene deposits along the James River near Richmond, VA, and may be of the same age. Above the river floodplain are dissected terrace deposits of gravel and mottled sand at basal elevations of 180-feet, 205-feet, 240-feet, and 300-feet above sea level.

Potential paleoliquefaction dikes were discovered at two sites along the traverse. If these features are paleoseismic in origin, the extent of the Central Virginia Seismic Zone paleoliquefaction field is extended 75 km south of the southernmost current paleoliquefaction site on the James river near Goochland, VA.