FUTURE DEVELOPMENT GUIDED BY ANALYSIS OF THE PAST: FIELD TO LAB STUDY OF RIFT-TO-DRIFT DEPOSITS IN THE NEOPROTEROZOIC TO EARLY CAMBRIAN CHILHOWEE GROUP, SW VA

Rift-to-drift deposits record significant tectonic events, yet the repetitive sequences in these sediments can be difficult to interpret. The Neoproterozoic to early Cambrian breakup of supercontinent Rodinia is recorded in the Chilhowee Group, which is exposed in the Appalachian mountains from Alabama to Vermont. In SW Virginia and N Tennessee, the lower unit marking the final rifting stage is the Unicoi Formation, containing sandstones, conglomerates, and basalts. Overlying units record overall transgression and transition to passive margin, with silty sandstones and shales in the middle Hampton Formation, and quartzites and conglomerates dominating the upper Erwin Formation.

Significant exposures of the Chilhowee Group occur in the Blue Ridge Scout Reservation (BRSR) in SW VA, the focus of our study. The latest detailed mapping of the BRSR was published in 1968 (McDowell). An up-to-date geologic map and structural evaluation will be of great service to the Boy Scouts of America, and aid in a planned clean energy project. It will be a service to the state as well, as we are in coordination with the VA Department of Mines, Minerals, and Energy to contribute to the STATEMAP I-81 Corridor initiative. Finally, this project will enhance ongoing research by Radford University geologists.

Initial questions raised by our evaluation of McDowell’s 1968 map pertain to formational boundaries and structural/fault placement. Of the two fault blocks exposed in the BRSR, rocks in the Hiwassee block were correlated with the known Hampton and Erwin Formations on McDowell’s map. Rocks in the Powhatan block, however, were differentiated simply as lower, middle, or upper Chilhowee. Field exploration allows us to confidently assign formational names to the units in the Powhatan block. Based on the presence of the trace fossil Skolithos in rocks previously labeled “lower Chilhowee” quartzite, we were able to reassign this formation to the Erwin, as Skolithos burrows have not been reported from the Unicoi Formation. This leads us to re-evaluate the structural placement and interpretation of the Powhatan fault. Additionally, we recognize siltstone in proximity to Erwin sandstone as unique from that of the Hampton, suggesting that we can further subdivide the Erwin Fm. as has been done farther south.