West Falls Formation

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

The West Falls Group is a geologic group in New York. It preserves fossils dating back to the Devonian period.

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.

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 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.

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).

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