The

Mississippian Mississippian may refer to: * Mississippian (geology), a subperiod of the Carboniferous period in the geologic timescale, roughly 360 to 325 million years ago *Mississippian culture, a culture of Native American mound-builders from 900 to 1500 AD ...

Mauch Chunk Formation is a mapped 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, 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; ...

, 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 ...

. It is named for the township of Mauch Chunk, now known as borough of

Jim Thorpe, Pennsylvania Jim Thorpe is a borough and the county seat of Carbon County in the U.S. state of Pennsylvania. It is part of Northeastern Pennsylvania. It is historically known as the burial site of Native American sports legend Jim Thorpe. Jim Thorpe is ...

and for nearby Mauch Chunk Ridge where the formation crops out.

Description

The Mauch Chunk is defined as a grayish-red

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especia ...

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, ...

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

, and conglomerate. The Loyalhanna Member is a local limestone and sandy limestone at its base, as well as the Greenbrier and Wymps Gap Members. Along the

Allegheny Front The Allegheny Front is the major southeast- or east-facing escarpment in the Allegheny Mountains in southern Pennsylvania, western Maryland, eastern West Virginia, and western Virginia, USA. The Allegheny Front forms the boundary between the Rid ...

, the Loyalhanna is a greenish-gray, calcareous, cross bedded sandstone. A notable exposure of the Loyalhanna Member is

Laurel Caverns Laurel Caverns is the largest cave in the Pennsylvania, Commonwealth of Pennsylvania by volume and area. Located in the community of Farmington, Pennsylvania, Farmington, it sits on the Chestnut Ridge near Uniontown, Pennsylvania, Uniontown, roug ...

in Fayette County.

Depositional environment

The early Mauch Chunk beds were deposited on a large basin receiving most of its sediments from distant highlands. Sea levels fluctuated and allowed some limestone deposition to occur early as well. Since the dominant color of the Mauch Chunk is red, much of the sediment was deposited above sea level in

oxidizing Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...

conditions. The green-colored members indicate a reducing environment characterized by frequent inundation by water in a swamp, delta, or shallow sea. Later beds have frequent conglomerate beds signaling the first wave of the

Alleghenian orogeny The Alleghanian orogeny or Appalachian orogeny is one of the geological mountain-forming events that formed the Appalachian Mountains and Allegheny Mountains. The term and spelling Alleghany orogeny was originally proposed by H.P. Woodward in 19 ...

Fossils

Plants from the division

Pteridospermatophyta The term Pteridospermatophyta (or "seed ferns" or "Pteridospermatopsida") is a polyphyletic group of extinct seed-bearing plants (spermatophytes). The earliest fossil evidence for plants of this type is the genus ''Elkinsia'' of the late Devonian ...

notably Adiantites have been identified. Some fish and worm burrows have also been observed.

Age

Relative age dating of the Mauch Chunk places it in the late Mississippian epoch, with some of the top layers in the early Pennsylvanian epoch, being deposited between 345 and 320(±3) million years ago. It rests conformably atop many formations. Its upper contact is complex. In certain areas, the contact is conformable in others, there is an unconformity. However, the

Pottsville Formation The Pennsylvanian Pottsville Formation is a mapped bedrock unit in Pennsylvania, western Maryland, West Virginia, Ohio, and Alabama. It is a major ridge-former in the Ridge-and-Valley Appalachians of the eastern United States. The Pottsville Fo ...

is always above the Mauch Chunk.Berg, T.M., et al., (1983). Stratagraphic Correlation Chart of Pennsylvania: G75, Pennsylvania Geologic Survey, Harrisburg, Pennsylvania.

Economic uses

In 1953, a small amount of

uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weakly ...

was mined from the Mauch Chunk Formation near Jim Thorpe. (see

Uranium mining in the United States Uranium mining in the United States produced of U3O8 in 2019, 88% lower than the 2018 production of of U3O8 and the lowest US annual production since 1948. The 2019 production represents 0.3% of the anticipated uranium fuel requirements of t ...

)

Description

Depositional environment

Fossils

Age

Economic uses

References

See also