Harrell Shale Explained

Harrell Shale Group
Type:	Group
Age:	Frasnian
Period:	Middle Devonian-Late Devonian
Prilithology:	shale, sandstone
Namedby:	Charles Butts, 1918^[1]
Region:	Appalachian Mountains
Country:	United States
Subunits:	Burket Shale^[2]
Underlies:	Brallier Formation, Sonyea Formation, Trimmers Rock Formation
Overlies:	Mahantango Formation, Millboro Shale, and Tully Limestone

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

Description

The Harrell Formation was first described by Charles Butts in 1918. Hasson and Dennison (1978) state "The Harrell Shale consists of very dark gray, thinly laminated, platy- to sheety-weathering shale underlain in certain areas by the grayish black shale of the Burket Member."

Fossils

Hasson and Dennison reported the following fossils from several outcrops of the Harrell:^[3]

• Bivalvia

Buchiola livonae (?), B. retrostriata, Paracardium doris, Pterochaenia fragilis, Lunlulicardium (?)

• Cephalopoda: Bactrites aciculum, Probeloceras lutheri
• Cricoconarida (class of Mollusca): Styliolina fissurella

Notable Exposures

Type locality is at Horrell Station, Blair County, Pennsylvania (40.45°N -95°W).^[1] In 1918, when Butts described and named the type section, the USGS topo map spelled the location "Harrell", ^[4] but the local spelling was "Horrell".^{[5] [6]}

Age

Relative age dating places the Harrell in the late Devonian.

References

Notes and References

1. Butts, Charles, 1918, Geologic section of Blair and Huntingdon Counties, central Pennsylvania: American Journal of Science, 4th series, v. 46, p. 523-537.
2. de Witt, Wallace, Jr., Roen, J.B., and Wallace, L.G., 1993, Stratigraphy of Devonian black shales and associated rocks in the Appalachian basin, IN Roen, J.B., and Kepferle, R.C., eds., Petroleum geology of the Devonian and Mississippian black shale of eastern North America: U.S. Geological Survey Bulletin, 1909-B, p. B1-B57.
3. Hasson, Kenneth O., and Dennison, John M., 1978, STRATIGRAPHY OF THE DEVONIAN HARRELL AND MILLBORO SHALES IN PARTS OF PENNSYLVANIA, MARYLAND, WEST VIRGINIA, AND VIRGINIA, Project Final Report for Energy Research and Development Administration Contract #EY-77-C-21-8153, May 1978 https://edx.netl.doe.gov/dataset/stratigraphy-of-the-devonian-harrell-and-millboro-shales-in-parts-of-pennsylvania-maryland-west-v
4. Web site: "Topography: Hollidaysburg Quadrangle" . Department of the Interior. 1920.
5. News: Another McAbee plant explosion . The Pittsburgh Post . 18 August 1904 . 5 .
6. Web site: Blair County Pennsylvania Railroad Stations .