The Devonian Harrell Formation is a mapped bedrock unit in Pennsylvania, Maryland, West Virginia, and Virginia.
| Harrell Shale Group | |
|---|---|
| Stratigraphic range: Frasnian | |
| Type | Group |
| Sub-units | Burket Shale[1] |
| Underlies | Brallier Formation, Sonyea Formation, Trimmers Rock Formation |
| Overlies | Mahantango Formation, Millboro Shale, and Tully Limestone |
| Lithology | |
| Primary | shale, sandstone |
| Location | |
| Region | Appalachian Mountains |
| Country | United States |
| Type section | |
| Named by | Charles Butts, 1918[2] |
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."[3]
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°27′N 78°17′W).[2] 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
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