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 Group 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 in depth, reservoir pressure was and flow rates ranged from per day. ==References==