Beekmantown Group (VAOb;0)

State	Virginia
Name	Beekmantown Group
Geologic age	Ordovician
Original map label	Ob
Comments	Appalachian Plateaus and Valley and Ridge. From expanded explanation (ref. VA002): Beekmantown Group. Includes the Pinesburg Station Dolomite, the Rockdale Run Formation, and the Stonehenge Limestone (northern Virginia only) or the Beekmantown Formation and Stonehenge Limestone (central and southwestern Virginia). Pinesburg Station Dolomite (Sando, 1956). Dolostone, dark- to light-gray, fine- to medium-grained, medium- to thick bedded with minor nodular white chert. It ranges from 0 to 400 feet in thickness and is equivalent to beds in the upper Beekmantown Formation. Present only in Clarke and Frederick counties and is conformable with the underlying Rockdale Run Formation and unconformable with the overlying New Market or Lincolnshire Limestones. Rockdale Run Formation (Sando, 1958). Dominantly limestone and dolomitic limestone, lesser dolostone with minor chert throughout. Limestone, light- to medium-gray, fine-grained generally, but coarse, bioclastic limestone locally, medium- to thick-bedded. Dolostone, light-gray, fine- to medium- grained, thick-bedded with "butcher block" weathering and minor nodular or bedded chert in both limestone and dolostone. Unconformably overlain by the New Market Limestone where the Pinesburg Station Dolomite is absent. It is laterally equivalent to the Beekmantown Formation and conformably overlies the Stonehenge Limestone. The formation is about 2700 feet thick. Beekmantown Formation (Clarke and Schuchert, 1899). Dominantly dolostone and chert-bearing dolostone with lesser limestone. Dolostone, light- to very-dark-gray, fine- to coarse grained, mottled light- and dark-gray, with crystalline beds locally contains nodular, dark-brown or black chert and thick, hill forming, lenticular chert beds in lower part. Limestone, very-light- to medium-gray, fine-grained, medium- to thick bedded, locally dolomitic and locally fossiliferous. The formation is present from Page and Shenandoah counties southwestward in the easternmost exposures of the Lower Ordovician rocks. It and the underlying Stonehenge Limestone, are equivalent to the Mas cot and Kingsport Dolomites of the upper part of the Knox Group. It is unconformably overlain by Middle Ordovician limestones and conformably overlies the Stonehenge Limestone. Erosion, related to the unconformity at the top of the Beekmantown Group and Knox Group, has produced erosional breccias, local topographic relief, and paleokarst topography as well as significant regional thinning of the rock units. The Beekmantown Group thins from about 3000 feet in Page County to less than 700 feet in Washington County, largely because of post-Beekmantown erosion . Stonehenge Limestone (Sando, 1956). Limestone with interbedded dolostone in north western Virginia. Limestone, dark-gray, fine-grained, laminated to massive, with black nodular chert. Dolostone, light-gray, fine-to very-coarse-grained, as thin- to medium-interbeds or as coarse- grained, massive, reefoidal bodies. Reefoidal bodies are restricted to the middle portion of the formation. The formation conformably overlies the Conococheague Formation and thins northwestward from 400 or 500 feet in the southeasternmost exposures (Page County) to a few tens of feet in the north western exposures (western Rockingham County) and is not recognizable or included in the lower Beekmantown or upper Conococheague in much of southwestern or western Virginia. It is equivalent to the lower part of the Kingsport Dolomite.
Primary rock type	dolostone (dolomite)
Secondary rock type	limestone
Other rock types	chert
Lithologic constituents	Major Sedimentary > Carbonate > Limestone Sedimentary > Carbonate > Dolostone Incidental Sedimentary > Chemical > Chert
Map references	Digital Representation of the 1993 Geologic Map of Virginia", 2003, CD ROM (ISO-9660) contains image file, expanded explanation in pdf, and ESRI shapefiles, viewing software not included. This is a digital version of "Geologic Map of Virginia" published in 1993. Available from: https://www.dmme.virginia.gov/commerce/ [https://www.dmme.virginia.gov/commerce/]
Unit references	Virginia Division of Mineral Resources, 1993, Geologic Map of Virginia: Virginia Division of Mineral Resources, scale 1:500,000 Digital Representation of the 1993 Geologic Map of Virginia - expanded explanation: 2003, Commonwealth of Virginia, Department of Mines, Minerals, and Energy, Divsion of Mineral Resources, Publication 147, 85 pp Digital Representation of the 1993 Geologic Map of Virginia", 2003, CD ROM (ISO-9660) contains image file, expanded explanation in pdf, and ESRI shapefiles, viewing software not included. This is a digital version of "Geologic Map of Virginia" published in 1993. Available from: https://www.dmme.virginia.gov/commerce/ [https://www.dmme.virginia.gov/commerce/]
Geographic coverage	Alleghany - Augusta - Bath - Botetourt - Clarke - Frederick - Highland - Page - Roanoke - Rockbridge - Rockingham - Shenandoah - Smyth - Warren - Washington - Wythe - Bristol - Harrisonburg - Roanoke - Staunton - Winchester