Huntersville Chert

The Huntersville Chert or Huntersville Formation is a Devonian geologic formation in the Appalachian region of the United States. It is primarily composed of mottled white, yellow, and dark grey chert, and is separated from the underlying Oriskany Sandstone by an unconformity.^[1] The Huntersville Chert is laterally equivalent to the Needmore Shale, which lies north of the New River. It is also laterally equivalent to a sandy limestone unit which is often equated with the Onondaga Limestone. to the west and the Needmore Shale to the east.^[1] These formations are placed in the Onesquethaw Stage of Appalachian chronostratigraphy, roughly equivalent to the Emsian and Eifelian stages of the broader Devonian system.^[2][1]

Huntersville Chert
Stratigraphic range: Emsian to Eifelian
Type	Formation
Sub-units	Bobs Ridge Sandstone Member
Underlies	Marcellus Shale, Onondaga Limestone, Tioga Bentonites
Overlies	Oriskany Formation
Lithology
Primary	chert
Other	siltstone, sandstone, limestone, dolomite
Location
Region	Appalachia and Southeastern United States
Country	United States
Extent	Pennsylvania, Virginia, West Virginia
Type section
Named for	Huntersville, West Virginia
Named by	Price, 1929

Most Huntersville Chert outcrops are located in southeastern West Virginia and southwestern Virginia, though well logs indicate that it was present deep underground in other states in the region. It represents a deep-water environment during a major transgression event. The chert has a mottled appearance due to a heterogenous structure of pure and discolored chert. The darker chert is heavily fractured and contains impurities such as glauconite pellets, silty and argillaceous grains, organic material, or dolomite and calcite crystals. The chert is at least partially biogenic, as some chert facies are primarily composed of hollow sponge spicules filled with hydrocarbons.^[3] Aeolian dust blowing in from hot, dry areas may also be responsible for some of the silica forming the chert.^[4] Compared to equivalent formations, the composition of the Huntersville Chert is at least 50% chert.^[2]

The uppermost layers of the Huntersville Chert are glauconitic sandstones rich in shells of spiriferid brachiopods.^[1] These layers have been named as the Bobs Ridge Sandstone member.^[2] They are directly overlain by a prominent ash bed, the Tioga Bentonite. The Bobs Ridge Sandstone and Tioga Bentonite indicate uplift and volcanic activity in the region, respectively.^[3] The Tioga Bentonite, sometimes called the Tioga Ash Bed or Metabentonite, lies at the base of the Marcellus Shale.^[2]

References

1. Read, J. Fred; Eriksson, Kenneth A. (2012). "Paleozoic Sedimentary Successions of the Virginia Valley & Ridge and Plateau" (PDF). Virginia Tech Scholarly Works, Department of Geosciences.
2. Weed, E.G.A. (1982). "Huntersville Chert (Devonian) extending from southwestern Virginia into southwestern New York, and its Bobs Ridge Sandstone Member" (PDF). Stratigraphic Notes, 1980-1982: Contributions to Stratigraphy, Geological Survey Bulletin. 1529-H: 131–133.
3. Sherrard, S.J.; Heald, M.T. (June 1984). "Petrology of the Huntersville Chert" (PDF). Southeastern Geology. 25 (1): 37–47.
4. Cecil, C. Blaine (2004). "Eolian Dust and the Origin of Sedimentary Chert". USGS Numbered Series. Open-File Report 2004-1098: 1–13. doi:10.3133/ofr20041098.

• Various Contributors to the Paleobiology Database. "Fossilworks: Gateway to the Paleobiology Database". Retrieved 17 December 2021.