Christopher M. Bailey | USGS Science

USGS2017

Geology of the Petersburg batholith, eastern Piedmont, Virginia

The 295-300 Ma Petersburg batholith in east-central Virginia forms one of the largest and northernmost of the Alleghanian plutonic complexes in the southern Appalachian Piedmont. The batholith is primarily composed of granite including massive and foliated (both magmatic and solid-state fabrics) varieties. The plutonic complex intruded medium-grade metamorphosed volcanic/plutonic rocks of the Roanoke Rapids terrane. The western edge of the batholith experienced right lateral transpressional deformation associated with movement on the Hylas fault zone during the Alleghanian orogeny; this was followed by normal faulting and exhumation during the development of the Triassic Richmond basin. Much of the batholith was buried by a thin veneer of primarily Cenozoic siliciclastic sediments at the western edge of the Atlantic Coastal Plain. Granite rocks of the Petersburg batholith have long been quarried for both dimension and crushed stone. The purpose of this trip is to discuss the age, origin, and tectonic significance of the Petersburg batholith.

Virginia↗

USGS2012

Preliminary geologic map of the Stanardsville 7.5' quadrangle, Greene and Madison Counties, Virginia

The Stanardsville 7.5-minute quadrangle is located about 30 kilometers north of Charlottesville, Virginia, in the eastern foothills of the Blue Ridge and within the Blue Ridge physiographic province. The quadrangle contains a small part of the eastern margin of Shenandoah National Park along Saddleback Mountain just north of Swift Run Gap and stretches of Swift Run and the South, Conway, and Rapidan Rivers. The broad valleys occupied by these southeast-draining streams alternate with ridges as much as 1,700 feet high to produce a varied topography, with the 3,000- to 4,000-foot-high Blue Ridge defining the western horizon. The bedrock geology of the quadrangle was mapped at a scale of 1:24,000 as part of the Geology of Shenandoah National Park Project (which was conducted from 1995 to 2008) of the U.S. Geological Survey National Cooperative Geologic Mapping Program. The results of the mapping were incorporated in the Geologic Map of the Shenandoah National Park Region, Virginia ( USGS Open-File Report 2009-1153 ).

Virginia↗

USGS2009

Geologic Map of the Shenandoah National Park Region, Virginia

The geology of the Shenandoah National Park region of Virginia was studied from 1995 to 2008. The focus of the study was the park and surrounding areas to provide the National Park Service with modern geologic data for resource management. Additional geologic data of the adjacent areas are included to provide regional context. The geologic map can be used to support activities such as ecosystem delineation, land-use planning, soil mapping, groundwater availability and quality studies, aggregate resources assessment, and engineering and environmental studies. The study area is centered on the Shenandoah National Park, which is mostly situated in the western part of the Blue Ridge province. The map covers the central section and western limb of the Blue Ridge-South Mountain anticlinorium. The Skyline Drive and Appalachian National Scenic Trail straddle the drainage divide of the Blue Ridge highlands. Water drains northwestward to the South Fork of the Shenandoah River and southeastward to the James and Rappahannock Rivers. East of the park, the Blue Ridge is an area of low relief similar to the physiography of the Piedmont province. The Great Valley section of the Valley and Ridge province is west of Blue Ridge and consists of Page Valley and Massanutten Mountain. The distribution and types of surficial deposits and landforms closely correspond to the different physiographic provinces and their respective bedrock. The Shenandoah National Park is underlain by three general groups of rock units: (1) Mesoproterozoic granitic gneisses and granitoids, (2) Neoproterozoic metasedimentary rocks of the Swift Run Formation and metabasalt of the Catoctin Formation, and (3) siliciclastic rocks of the Lower Cambrian Chilhowee Group. The gneisses and granitoids mostly underlie the lowlands east of Blue Ridge but also rugged peaks like Old Rag Mountain (996 meter). Metabasalt underlies much of the highlands, like Stony Man (1,200 meters). The siliciclastic rocks underlie linear ridges from 800 to 400 meters in altitude. The Page Valley is underlain by Cambrian and Ordovician carbonate rocks. Siliciclastic rocks are mostly west of the South Fork of the Shenandoah River and underlie Massanutten Mountain. Surficial deposits in the highlands include colluvium and debris fans. The lowlands have broad alluvial fans, alluvial plains, and fluvial terraces. Ridges underlain by siliciclastic rocks have abundant boulder fields. Numerous sinkholes and caves are due to the dissolution of the carbonate bedrock.

Open-File Report↗