Unadilla, Laurens, New Lisbon, and Gilboa Formations

Shale, siltstone, sandstone.
State New York
Name Unadilla, Laurens, New Lisbon, and Gilboa Formations
Geologic age Middle Devonian
Lithologic constituents
Sedimentary > Clastic > Sandstone
Sedimentary > Clastic > Siltstone
Sedimentary > Clastic > Mudstone > Shale
Comments part of Genesee Group 1200-1500 ft. (370-460 m). Secondary unit description from USGS Lexicon website (ref. NY046) and NY021: Gilboa Formation is described at Stevens Mountain Quarry, Grand Gorge, and Hardenburgh Falls. Formation is composed of 2- to 6-m-thick sandstone bodies separated by thinner mudstone-dominated intervals. Unit is divided into four 15- to 20-m-thick sections by three thick mudstones. The fine- to medium-grained sandstone bodies have sharp, erosional bases with tool and flute marks, overlain by intraformational breccia composed of shale clasts, plant fragments, and shelly fossils. Trough cross-strata are most common, but planar cross-strata occur near the tops of the sandstone bodies. The mudstones are dark gray, sparsely fossiliferous, and typically bioturbated. Variations in facies throughout the Gilboa suggest increasing marine influence through the lowest 20 m and decreasing influence through the upper 30 m. Overlies Moscow Formation. Gradationally underlies Oneonta Formation in study area. Grades eastward into Manorkill Formation. Age in this report is Middle Devonian only (Bridge and Willis, 1994).

Fisher, D.W., Isachsen, Y.W., and Rickard, L.V., 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 1:250,000.

Bridge, J.S. and Willis, B.J., 1994, Marine transgressions and regressions recorded in Middle Devonian shore-zone deposits of the Catskill clastic wedge: Geological Society of America Bulletin, v. 106, no. 11, p. 1440-1458.

USGS Geologic Names lexicon found at: http://ngmdb.usgs.gov/Geolex/


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Counties Chenango - Delaware - Greene - Otsego - Schoharie