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West Falls Formation

Fractured concretions in Rhinestreet Shale Member of West Falls Formation

West Falls Formation
Stratigraphic range: Upper Devonian
Type	Geologic formation
Unit of	Elk Group
Sub-units	Angola Shale Member, Rhinestreet Shale Member
Underlies	Java Formation
Overlies	Sonyea Formation
Lithology
Primary	Shale
Other	Black Shale
Location
Region	Mid-Atlantic
Country	United States
Type section
Named for	West Falls, New York

Stratigraphy

The West Falls Formation is part of the Elk Group, which is above the Hamilton Group and below the Bradford 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. don't say depth, say thickness say soemthing about age here

Geographic distribution

The Rhinestreet Shale and Angola Shale Members of the West Falls Formation are both recognized in the subsurface from western New York to eastern Tennessee. The Rhinestreet is the older, underlying member; it lies unconformably atop the shales of the Hamilton Group. It thins westward, and pinches out in Vinton County, Ohio. The Rhinestreet Member is observed further east than the Angola, to central Chemung County, New York. The Angola Member is younger, and conformably overlies the Rhinestreet member. It is not recognized east of the Genesee River. It extends further west than the Rhinestreet Member, into Ohio and eastern Kentucky.

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 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).

Paleoenvironment/Depositional setting

mud in the upper devonian

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- 1,500 feet in depth, reservoir pressure was 225 psi and flow rates ranged from 100-2,000 Mcfd.

References

http://pubs.usgs.gov/imap/i2791/FIG3.pdf http://tin.er.usgs.gov/geology/state/sgmc-unit.php?unit=NYDwf%3B4 http://www.dnr.state.oh.us/Portals/10/pdf/OpenFileReports/OFR_88-3.pdf http://treichlerlawoffice.com/radiation/HillNY.pdf