The
Devonian
The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...
Harrell Formation is a mapped
bedrock
In geology, bedrock is solid rock that lies under loose material ( regolith) within the crust of Earth or another terrestrial planet.
Definition
Bedrock is the solid rock that underlies looser surface material. An exposed portion of bed ...
unit in
Pennsylvania
Pennsylvania, officially the Commonwealth of Pennsylvania, is a U.S. state, state spanning the Mid-Atlantic (United States), Mid-Atlantic, Northeastern United States, Northeastern, Appalachian, and Great Lakes region, Great Lakes regions o ...
,
Maryland
Maryland ( ) is a U.S. state, state in the Mid-Atlantic (United States), Mid-Atlantic region of the United States. It borders the states of Virginia to its south, West Virginia to its west, Pennsylvania to its north, and Delaware to its east ...
,
West Virginia
West Virginia is a mountainous U.S. state, state in the Southern United States, Southern and Mid-Atlantic (United States), Mid-Atlantic regions of the United States.The United States Census Bureau, Census Bureau and the Association of American ...
, and
Virginia
Virginia, officially the Commonwealth of Virginia, is a U.S. state, state in the Southeastern United States, Southeastern and Mid-Atlantic (United States), Mid-Atlantic regions of the United States between the East Coast of the United States ...
.
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:[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 197]
/ref>
*Bivalvia
Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class (biology), class of aquatic animal, aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed b ...
: ''Buchiola livonae'' (?), ''B. retrostriata'', ''Paracardium doris'', ''Pterochaenia fragilis'', ''Lunlulicardium'' (?)
*Cephalopod
A cephalopod is any member of the molluscan Taxonomic rank, class Cephalopoda (Greek language, Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral symm ...
a: ''Bactrites aciculum'', ''Probeloceras lutheri''
*Cricoconarida (class of Mollusca
Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...
): ''Styliolina fissurella''
Notable Exposures
Type locality is at Horrell Station, Blair County, Pennsylvania
Blair County is a county in the Commonwealth of Pennsylvania. As of the 2020 census, the population was 122,822. Its county seat is Hollidaysburg, and its largest city is Altoona. The county was created on February 26, 1846, from parts of Hu ...
().[ In 1918, when Butts described and named the type section, the USGS topo map spelled the location "Harrell", but the local spelling was "Horrell".]
Age
Relative age dating places the Harrell in the late Devonian
The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...
.
References
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Devonian System of North America
Shale groups of the United States
Devonian Maryland
Devonian geology of Pennsylvania
Devonian Pennsylvania
Devonian geology of Virginia
Devonian West Virginia
Devonian southern paleotemperate deposits
Sandstone groups of the United States
Geologic groups of Maryland
Geologic groups of Pennsylvania
Geologic groups of Virginia
Geologic formations of West Virginia