- Shawangunk Formation
The
Silurian Shawangunk Formation (Ss) is a mapped bedrock unit in easternPennsylvania ,New Jersey , andNew York . It is named for theShawangunk Ridge for which it is the dominant rock type.Description
The Shanwangunk is defined as a light to dark-gray, fine to very coarsed grained
sandstone and conglomerate, containing a fewshale interbeds.Berg, T.M., Edmunds, W.E., Geyer, A.R. and others, compilers, (1980). Geologic Map of Pennsylvania: Pennsylvania Geologic Survey, Map 1, scale 1:250,000.] There are also four members of this formation: Tammany, Lizard Creek, Minsi, and Weiders. The Tammany and Lizard Creek members are equivalent to theClinton Formation and the Minsi and Weiders members are equivalent to theTuscarora Formation in the central and western part of Pennsylvania..]Depositional Environment
The Shawangunk has always been interpreted as
molasse resulting from theTaconic orogeny . The numerous coarse-grained beds, especially in the lower part, suggest a relatively close orogenic source with very high to high energy fluvial systems depositing the sediments. Shale interbeds may indicate a slowing or shifting of these ancient river systems.Fossils
Very few fossils exist in the Shawangunk, however,
Eurypterid s can be found in the middle portions of the formation roughly 420–750 feet from the base in some locations in New York State. [Epstein, J.B., (1993) Stratigraphy of Silurian Rocks in Shawangunk Mountain, Southeastern New York, Including a Historical Review of Nomenclature. United States Geological Survey Publication L14.]Age
Relative age dating of the Shawangunk places it in the Lower
Silurian period, being deposited between 440 to 417 (±10) million years ago. It rests unconformably a top theMartinsburg Formation and conformably below theBloomsburg Formation . [Berg, T.M., et al., (1983). Stratagraphic Correlation Chart of Pennsylvania: G75, Pennsylvania Geologic Survey, Harrisburg, Pennsylvania.]Economic Uses
References
ee also
*
Geology of Pennsylvania
*Geology of New York
*Geology of New Jersey
*Blue Mountain (Pennsylvania)
*Shawangunk Ridge
*Lehigh Gap, Pennsylvania
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