Foreknobs Formation

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Foreknobs Formation
Stratigraphic range: Late Devonian
Conglomerate Foreknobs Fm.jpg
Conglomerate from Foreknobs Formation, Rt. 994, near western side of bridge going over Raystown Lake, Huntingdon County, Pennsylvania
Type sedimentary
Unit of Greenland Gap Group
Sub-units Mallow Member, Briery Gap Sandstone Member, Blizzard Member, Pound Sandstone Member, and Red Lick Member
Underlies Catskill Formation, or Hampshire Formation in VA
Overlies Scherr Formation, or Brallier Formation in VA
Thickness 1321 ft at type section
Lithology
Primary siltstone, sandstone, conglomerate
Location
Region Appalachian Mountains
Extent Pennsylvania, Maryland, Virginia, West Virginia
Type section
Named for Fore Knobs of Allegheny Front
Named by J. M. Dennison, 1970

The Devonian Foreknobs Formation is a mapped bedrock unit in Pennsylvania, Maryland, Virginia, and West Virginia.

Description[edit]

The Foreknobs Formation contains massive sandstones; siltstone; "redbeds" of brownish-gray sandstone, siltstone, and shale containing scattered marine fossils; and occasional quartz-pebble conglomerate or conglomeratic sandstone beds.[1]

Stratigraphy[edit]

Dennison (1970) renamed the old Chemung Formation the Greenland Gap Group and divided it into the lower Scherr Formation and the upper Foreknobs Formation. De Witt (1974) extended the Scherr and Foreknobs into Pennsylvania, but did not use the term Greenland Gap Group.[2]

Boswell, et al. (1987), does not recognize the Scherr and Foreknobs Formations in the subsurface of West Virginia and thus these formations are reduced from "group" to "formation" as the Greenland Gap Formation.[3]

Rossbach and Dennison (1994) extended the Foreknobs into the Catawba syncline of southwestern Virginia.[4]

The Foreknobs is divided into the following Members, in ascending order: Mallow Member, Briery Gap Sandstone Member, Blizzard Member, Pound Sandstone Member, and Red Lick Member

Fossils[edit]

Foreknobs Formation containing abundant Mucrospirifer brachiopods, from near upper reservoir of Bath County Pumped Storage Station

Red beds within the Foreknobs contain scattered marine fossils, such as brachiopods.

Notable Exposures[edit]

Type section: along WV Highway 42, 0.48 km northwest of Scherr, Grant County, West Virginia

Age[edit]

Relative age dating places the Foreknobs in the late Devonian.

References[edit]

  1. ^ Dennison, J.M., 1970, Stratigraphic divisions of Upper Devonian Greenland Gap Group ("Chemung Formation") along Allegheny Front in West Virginia, Maryland, and Highland County, Virginia: Southeastern Geology, v. 12, no. 1, p. 53-82.
  2. ^ de Witt, Wallace, Jr., 1974, Geologic map of the Beans Cove and Hyndman quadrangles and part of the Fairhope quadrangle, Bedford County, Pennsylvania: U.S. Geological Survey Miscellaneous Investigations Series Map, I-801, 6 p., 1 sheet, scale 1:24,000
  3. ^ Boswell, R.M., Donaldson, A.C., and Lewis, J.S., 1987, Subsurface stratigraphy of the Upper Devonian and Lower Mississippian of northern West Virginia: Southeastern Geology, v. 28, no. 2, p. 105-131.
  4. ^ Rossbach, T.J., and Dennison, J.M., 1994, Devonian strata of Catawba syncline, near Salem, Virginia, IN Schultz, Art, and Henika, Bill, Fieldguides to Southern Appalachian structure, stratigraphy, and engineering geology: Virginia Polytechnic Institute and State University, Department of Geological Sciences Guidebook, Geological Society of America, Southeastern Section, Annual Meeting, Blacksburg, VA, April 7–9, 1994, no. 10, p. 95-126.