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West Falls Formation
Stratigraphic range: Frasnian
Fractured concretions in Rhinestreet Shale Member of West Falls Formation
Type	Geologic Group
Sub-units	Angola Shale (NY) Nunda Sandstone (NY,PA) West Hill Formation (NY) Gardeau Formation (NY,PA) Grimes Siltstone (NY) Rhinestreet Formation (NY,PA) Walton Formation (NY) Moreland Shale (NY) Millport Shale (NY) Beers Hill Formation (NY) Slide Mountain Formation (NY) Honesdale Formation (NY)
Underlies	Java Formation
Overlies	Sonyea Group
Lithology
Primary	Shale
Other	Black shale
Location
Region	Appalachian Basin
Country	United States
Extent	Kentucky  New York  Ohio  Pennsylvania  Tennessee  Virginia  West Virginia
Type section
Named for	West Falls, New York

The West Falls Group is a geologic group in the Appalachian Basin. It dates back to the Devonian period. Also stratigraphically equivalent to the Portage Group.

Description

Stratigraphy

The West Falls Group is a geologic group in New York. It dates back to the Devonian period. Also stratigraphically equivalent to the Portage Group.

The West Falls formation is bounded above by the Java Formation and below by the Sonyea Formation. It comprises the Angola Shale and Rhinestreet Shale Members. It was deposited during the Acadian Orogeny and is part of the Salina thrust sheet.

Also known as the West Falls Formation in New York.

Geographic distribution

The West Falls is recognized in the subsurface from western New York to eastern Tennessee.

Lithology

The predominant lithology of the West Falls Group is shale. The Rhinestreet Member can be further subdivided into two shale types: a thick, fissile black shale underlies a gray to greenish-gray shale that likely indicates a transitional environment. The Angola member is a gray to greenish-gray shale, easily distinguished by its consistent low gamma ray signature, which is typical of this shale type.

Paleontology

The West Falls Formation was deposited during the Frasnian stage of the Upper Devonian. Two distinct community types are observed in the group: "a shallower water spiriferacean-rhynchonellide-bivalve species ensemble, and a deeper water assemblage of unattached epibenthic and sessile semi-infaunal brachiopods" (Sutton, McGee).

Economic significance

Both members of the West Falls Formation have been assessed for oil and gas exploration. The USGS has determined that the average total organic carbon (TOC) in the Rhinestreet Shale is 0.89%; the TOC in the Angola Shale is 1.47%.

The Rathbone shale field in Rathbone, Steuben County, New York was discovered in 1931. 31 wells were drilled in this field, targeting the Angola and Rhinestreet members. Of these, 24 produced natural gas, 4 were dry holes, 2 were plugged and abandoned, and one produced oil. The wells were typically 900 to 1,500 feet (270 to 460 m) in depth, reservoir pressure was 225 pounds per square inch (1,550 kilopascals) and flow rates ranged from 100 to 2,000 thousand cubic feet (2,800 to 56,600 m) per day.

References

1. "Figure 3" (PDF). pubs.usgs.gov.
2. "Angola and Rhinestreet Shales (NYDwf;4)". tin.er.usgs.gov. Retrieved 2017-07-12.
3. "Open File Reports" (PDF). dnr.state.oh.us.
4. "Late Devonian marine ecosystems of the lower West Falls Group in New York | The Catskill Delta | GeoScienceWorld Books | GeoScienceWorld". specialpapers.gsapubs.org. Retrieved 2017-07-12.
5. "NY Hill Radiation" (PDF). treichlerlawoffice.com.
6. "Radiation" (PDF). treichlerlawoffice.com.

External links

• Rickard, L.V.; Isachsen, Y.W.; Fisher, D.W. (1970). "Geologic map of New York: Finger Lakes sheet". New York State Museum. Retrieved 2015-09-17.
• A Map
• State Geology
• OFR 88-3

• Earth sciences
• Devonian
• Paleontology

• Geologic groups of New York (state)
• Devonian Pennsylvania