The Late

Silurian The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago (Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozoi ...

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 wh ...

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 be ...

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, Ma ...

Maryland Maryland ( ) is a U.S. state, state in the Mid-Atlantic (United States), 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; ...

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

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 ...

. 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 o ...

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.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 b ...

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 w ...

, 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 of eastern West Virginia *

Trout Pond Trout Pond — formerly called Old Pond — located near Wardensville in Hardy County, West Virginia, USA, is the state's only natural lake. The small "lake" is situated in the Trout Pond Recreation Area (TPRA) of the George Washington Nation ...

, 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 Vi ...

Age

Relative age dating places the Tonoloway in the late

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