|Name||Silurian unnamed mafic volcanic rocks|
Igneous > Volcanic > Mafic-volcanicGS - Greenschist facies; Protolith V - Basaltic volcanic rocks
|Comments||Occurs in Little Bigelow Mountain and Pierce Pond 15-min quads, ME. Divided into unmapped upper member of thickly bedded, slightly calcareous, feldspathic metasandstone and a lower member of thinly bedded calcareous metasandstone, metasiltstone, impure metalimestone, and thin basal metaconglomerate. Includes rocks previously mapped as unnamed calcareous phyllite and related rocks in the Little Bigelow Mountain quad by Boone (1973) and by Moench and Pankiwskyj (1988). Contains shelly fossils in basal layer, but no diagnostic forms identified. Considered to be coeval with Late Silurian(?) Madrid Formation on basis of lithologic similarity and conformable position of both formations below the Carrabassett Formation of the Seboomook Group. The Forks Formation also unconformably overlies pre-Silurian rocks and is probably a shoreline facies of the Madrid. (ME004) Unit description from USGS GEOLEX website (ME078). W - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite; GS - Greenschist facies; E - Epidote-amphibolite facies; Protolith O - Argillaceous limestone and/or dolostone|
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.