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Helderberg Group

Helderberg Group - Alsen, Becraft, New Scotland, Kalkberg, Coeymans, and Manlius Limestones.
StateNew York
NameHelderberg Group
Geologic ageLower Devonian
Original map labelDhg
Comments400-500 ft. (120-150 m). Secondary unit descriptions from USGS Lexicon website (ref. NY046) and NY043: Throughout most of the Hudson River Valley region, Becraft Formation conformably and gradationally overlies the Lower Devonian New Scotland Formation. In western part of outcrop belt, unit conformably and gradationally overlies the Lower Devonian Kalkberg. Conformably and gradationally underlies the Alsen Formation, or unconformably underlies the Oriskany Sandstone or other Deerparkian units. Becraft crops out as part of a narrow, tightly folded and faulted belt of rocks from Kingston, in Ulster Co., to Ravena, in Albany Co. Westward into Schoharie Co., faulting and folding die out. Becraft crops out in only two places on the east side of the Hudson River--at Becraft Mountain and at Mount Ida. Though several workers have tried to extend Becraft correlations to other regions of the Eastern U.S., these extensions have not been accepted by all. Present study indicates that Becraft was strongly affected by deep-burial diagenesis (3.2 to 6.5 km) following subaerial exposure. Texture varies widely. Locally hand specimens have gneissic texture and in thin section resemble marble (Simonsen and Friedman, 1991).
Primary rock typelimestone
Secondary rock type
Other rock types
Lithologic constituents
Major
Sedimentary > Carbonate > Limestone
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.
Simonsen, Jeff and Friedman, G.M., 1991, Deep-burial limestone diagenesis of the Lower Devonian Becraft Formation (Helderberg Group) of the Hudson River Valley area: Northeastern Geology, v. 13, no. 1, p. 39-63.
USGS Geologic Names Lexicon (GEOLEX)

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