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Genesee Group

Genesee Group - West River Shale; Genundewa Limestone; Penn Yan and Geneseo Shales; all except Geneseo replaced eastwardly by Ithaca Formation-shale, siltstone and Sherburne Siltstone.
StateNew York
NameGenesee Group
Geologic ageUpper Devonian
Original map labelDg
Comments200-1000 ft. (60-300 m). Secondary unit descriptions from USGS Lexicon website (ref. NY046) and reference NY015: Genesee Formation extended from southwestern NY and western PA into eastern OH and northern WV (de Witt and others, 1993). West of Canandaigua Lake in western NY, the gray shale sequence above the Geneseo Shale Member of the Genesee Formation comprises the Penn Yan Shale Member, the Genundewa Limestone Member, and the West River Shale Member. The Penn Yan, at the base of the sequence, contains the Middle and Upper Devonian boundary. The Genundewa Limestone Member is an irregular- to flaggy-bedded limestone composed largely of the shells of the tiny pteropod STYLIOLINA FISSURELLA. It is only a local unit and does not extend beyond the southern NY border (de Witt and others, 1993). Penn Yan Shale Member of Genesee Formation extended from southwestern NY into western PA. West of Canandaigua Lake in western NY, the boundary between the Middle and the Upper Devonian lies within the lower part of the Penn Yan. Unit consists mainly of dark- to medium-gray shale or mudrock and some beds of black shale, abundant limestone nodules, and a few thin beds of dark-gray siltstone. The Penn Yan is overstepped to the southwest along the Middle Devonian unconformity by the West River Shale Member. To the east of Canandaigua Lake, the Penn Yan and the West River grad laterally into the Sherburne Flagstone and Ithaca Members (de Witt and others, 1993).
Primary rock typeshale
Secondary rock typelimestone
Other rock typessiltstone; black shale
Lithologic constituents
Major
Sedimentary > Clastic > Mudstone > Shale
Minor
Sedimentary > Clastic > Siltstone
Sedimentary > Carbonate > Limestone
Incidental
Sedimentary > Clastic > Mudstone > Shale > Black-shale
Map references
NYS Museum, NYS Geological Survey, NYS Museum Technology Center, 1999, 1:250,000 Bedrock geology of NYS, data is distributed in ARC/INFOr EXPORT format (with ".e00" extension) in 5 seperate files based on printed map sheets, http://www.nysm.nysed.gov/gis.html.
Unit references
D. W. Fisher; Y. W. Isachsen, L. V. Rickard, 1970, Geologic Map of New York State, consisting of 5 sheets: Niagara, Finger Lakes, Hudson-Mohawk, Adirondack, and Lower Hudson, New York State Museum and Science Service, Map and Chart Series No. 15, scale 1:250000.
de Witt, Wallace, Jr., Roen, J.B. and Wallace, L.G., 1993, Stratigraphy of Devonian black shales and associated rocks in the Appalachian basin, IN Roen, J.B., and Kepferle, R.C., eds., Petroleum geology of the Devonian and Mississippian black shale of eastern North America: U.S. Geological Survey Bulletin, 1909-B, p. B1-B57.
USGS Geologic Names Lexicon (GEOLEX)

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