Silurian The Forks Formation

Silurian The Forks Formation
State Maine
Name Silurian The Forks Formation
Geologic age Silurian
Lithologic constituents
Major
Metamorphic > Metasedimentary > Metaclastic > Metasiltstone (Zeolitic (prehnite-pumpellyite), Greenschist, Amphibolite epidote-amphibolite)W - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite; GS - Greenschist facies; E - Epidote-amphibolite facies; Protolith O - Argillaceous limestone and/or dolostone
Minor
Metamorphic > Metasedimentary > Metacarbonate > Marble (Zeolitic (prehnite-pumpellyite), Greenschist, Amphibolite epidote-amphibolite)W - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite; GS - Greenschist facies; E - Epidote-amphibolite facies; Protolith O - Argillaceous limestone and/or dolostone
Metamorphic > Metasedimentary > Metaclastic > Metasandstone (Zeolitic (prehnite-pumpellyite), Greenschist, Amphibolite epidote-amphibolite)W - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite; GS - Greenschist facies; E - Epidote-amphibolite facies; Protolith O - Argillaceous limestone and/or dolostone
Metamorphic > Metasedimentary > Metaclastic > Metaconglomerate (Zeolitic (prehnite-pumpellyite), Greenschist, Amphibolite epidote-amphibolite)W - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite; GS - Greenschist facies; E - Epidote-amphibolite facies; Protolith O - Argillaceous limestone and/or dolostone
Comments In central Maine trough, Sangerville Formation is mapped as principal sandstone and shale facies, and subdivided into (ascending) Patch Mountain Limestone Member (name revised from Patch Mountain Member to emphasize lithology), consisting of thinly interbedded impure marble, coarsely crystallized calc-silicate rocks, granofels, and pelitic schist (high metamorphic grade), or thinly interbedded, gray micritic metalimestone, limy metasandstone, metasiltstone, and slate or pelitic schist (low metamorphic grade); a conglomerate member; euxinic shale lenses; Taylor Pond Member of Hussey (1983), consisting of feldspathic biotite- and hornblende-biotite granofels, thinly bedded calc-silicate rocks, and sparse garnet-rich laminations (coticule); an unnamed limestone member similar to Patch Mountain Limestone Member but at a higher stratigraphic level; and Thorncrag Hill Member of Hussey (1983), consisting of migmatitic pelitic gneiss and some calc-silicate rocks. Anasagunticook Member of Pankiwskyj and others (1976) and Moench and Pankiwskyj (1988) is tentatively reassigned to Waterville Formation, following usage of Osberg (1988). (ME004) Unit description from USGS GEOLEX website (ME078). GS - Greenschist facies; E - Epidote-amphibolite facies; AA - Low rank amphibolite facies; AB - Medium rank amphibolite facies; AC - High rank amphibolite facies; Protolith N - Limestone and/or dolostone
References

Osberg, P.H., Hussey, A.M., and Boone, G.M., 1985, Bedrock geologic map of Maine: Maine Geological Survey, Dept. of Conserv., scale 1:500,000.

Moench, R.H., Boone, G.M., Bothner, W.A., Boudette, E.L., Hatch, N.L., Jr., Hussey, A.M., III, Marvinney, R.G. and Aleinikoff, J.N., 1995, Geologic map of the Sherbrooke-Lewiston area, Maine, New Hampshire, and Vermont, United States, and Quebec, Canada: U.S. Geological Survey Miscellaneous Investigations Series Map, I-1898-D, 56 p., 2 sheets, scale 1:250,000, Prepared in cooperation with the Maine Geological Survey and the New Hampshire Geological Survey.

https://pubs.er.usgs.gov/publication/i1898D

Post, E.V., pers. communication, in Espenshade, G.H., and Boudette, E.L., 1967.

US Geological Survey, 2005, National Geologic Map Database, Geologic Names Lexicon "GEOLEX", http://ngmdb.usgs.gov/Geolex/.

NGMDB product
Counties Piscataquis - Somerset