The Late Silurian Tonoloway Formation is a mapped

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

bedrock unit in

Pennsylvania Pennsylvania (; ( Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, ...

Maryland Maryland ( ) is a state in the Mid-Atlantic region of the United States. It shares borders with Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware and the Atlantic Ocean to ...

Virginia Virginia, officially the Commonwealth of Virginia, is a state in the Mid-Atlantic and Southeastern regions of the United States, between the Atlantic Coast and the Appalachian Mountains. The geography and climate of the Commonwealth ar ...

and

West Virginia West Virginia is a state in the Appalachian, Mid-Atlantic and Southeastern regions of the United States.The Census Bureau and the Association of American Geographers classify West Virginia as part of the Southern United States while the B ...

. The Tonoloway is roughly equivalent to the Salina group that is found to the north and west.

Description

The basal 50 m consists of medium-dark-gray laminated to thin-bedded

calcisiltite Calcisiltite is a type of limestone that is composed predominantly, more than 50 percent, of detrital (transported) silt-size carbonate grains. These grains consist either of the silt-size particles of ooids, fragments of fossil shells, fragments of ...

with shale partings and interbeds. Overlying 5 m are light-yellowish-gray to olive-gray mudstone and shale. Above this interval are 75 m of laminated calcisiltite with interbeds of thick to very thick bedded calcisiltite. The remainder of the formation is cyclic, consisting of three or four resistant ledges of laminated limestone and shale. Uppermost 20 m contains a variety of limestones. Lower contact with the Wills Creek is probably conformable. Upper contact is conformable and undulatory, occurring at the base of the "calico" limestone of the

Keyser Formation The Late Silurian to Early Devonian Keyser Formation is a mapped limestone bedrock unit in Pennsylvania, Maryland, Virginia, and West Virginia. Description The Keyser is a nodular limestone overlain by thick- and thin-bedded limestone and lam ...

.Faill, R.T., Glover, A.D., and Way, J.H., 1989, Geology and mineral resources of the Blandburg, Tipton, Altoona, and Bellwood quadrangles, Blair, Cambria, Clearfield and Centre Counties, Pennsylvania: Pennsylvania Geological Survey Topographic and Geologic Atlas, 4th series, 86, 209 p., scale 1:24,000 and 1:48,000

Depositional environment

The

depositional environment In geology, depositional environment or sedimentary environment describes the combination of physical, chemical, and biological processes associated with the deposition of a particular type of sediment and, therefore, the rock types that will be ...

of the Tonoloway is interpreted as shallow marine.

Notable exposures

* Tonoloway Ridge (type section), in Pennsylvania, Maryland, and West Virginia. * Along

Little Juniata River The Little Juniata River, sometimes called the "Little J," is a U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map, accessed August 8, 2011 tributary of the Juniata River in the Susquehanna River wa ...

, 2 km northeast of

Bellwood, Pennsylvania Bellwood is a borough in Blair County, Pennsylvania, United States. It is part of the Altoona, PA Metropolitan Statistical Area. The population was at 1,829 as of the 2020 census. Geography Bellwood is located at (40.601566, -78.333616). Acco ...

* Blue Rock, and other large outcroppings, in the

Smoke Hole Canyon Smoke Hole Canyon — traditionally called The Smoke Holes and later simply Smoke Hole — is a rugged long gorge carved by the South Branch Potomac River in the Allegheny Mountains of eastern West Virginia, United States. The area is rather iso ...

of eastern West Virginia *

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, in

Hardy County, West Virginia Hardy County is a county in the U.S. state of West Virginia. As of the 2020 census, the population was 14,299. Its county seat is Moorefield. The county was created from Hampshire County in 1786 and named for Samuel Hardy, a distinguished V ...

Age

Relative age dating places the Tonoloway in the late Silurian.

References

Geologic formations of Pennsylvania Silurian Maryland Silurian geology of Virginia Silurian West Virginia Pridoli geology Limestone formations of the United States Silurian south paleopolar deposits Silurian southern paleotemperate deposits {{Maryland-geologic-formation-stub