GEOLOGY BEYOND ROADCUTS: GEOLOGIC MAPPING OF THE SALTVILLE AND BROADFORD QUADRANGLES, SOUTHWEST VIRGINIA

USGS STATEMAP support through the Virginia Division of Geology and Mineral Resources provided the opportunity for 7.5' scale mapping of the Saltville and Broadford quadrangles over the past three years. The geology of these two quadrangles highlights aspects of stratigraphic variation between the Saltville Block and the Pulaski Block to the south (studied locally) and the Saltville Block and Copper Creek - Narrows Block to the north. For example, paleotopographic relief, evident in the Saltville Block is less significant on the Copper Creek—Narrows Block and offshore mudrocks of the Middle Ordovician Rich Valley Formation are represented on the Copper Creek—Narrows Block by more proximal limestone-rich sections. In addition, we have been able to compare and contrast the intrablock structures of the Saltville and Copper Creek—Narrows Blocks. The latter lacks significant internal faulting and is characterized by several major folds, whereas the former contains both folds and significant, but narrow, intrablock deformation zones (IDZs) containing both folds and faults.

Geologic mapping once again shows that roadside geology cannot reveal all there is to discover in any given area. Although some IDZs are present in roadside exposures, the traditional mode of detailed mapping resulted in discovery at more remote sites of significant fossil localities, an Ordovician paleoseismite zone in the Bowen Formation of the Copper Creek-Narrows Block, and major Quaternary deposit complexes reflecting varying conditions of erosion and deposition along mountain flanks and in isolated gullies.