Silurian undifferentiated pelites and sandstones (MESpu;0)

State	Maine
Name	Silurian undifferentiated pelites and sandstones
Geologic age	Silurian
Original map label	Spu
Comments	Most of southeastern half of Stacyville quad. and small part of Shin Pond quad. are underlain by slate, sandstone, and conglomerate included in Allsbury Formation. As defined in Island Falls quad (Ekren and Frischknecht, 1967), the formation consists dominantly of graywacke and black, dark-gray and green slate. Ekren and Friscknecht distinguish 10 bands of black slate across outcrop belt along the parallel that includes Allsbury Road, the type locality of the formation, where they constitute about 10 percent of the formation. The Allsbury in Shin Pond and Stacyville quads is part of same outcrop belt, but here it probably includes somewhat older rocks. About 1/4 of older unit, here classed as sandstone member of Allsbury, consists of coarse-grained sandstone and conglomerate interbedded with gray and green slate. Overlying member of formation consists mostly of gray and greenish-gray slate and some red slate and greenish-gray fine-grained sandstone. These members are not recognized in Island Falls quad where dark carbonaceous slate appears to be more abundant. Sandstone member crops out in faulted anticline north and west of overlying upper member. Base of sandstone member not exposed. At boundary between Stacyville and Shin Pond quads, exposed thickness of sandstone member is probably about 5,000 to 7,000 ft. Sandstone member is probably, at least in part, same age as Frenchville Formation (Early Silurian). (ME042) Unit description from USGS GEOLEX website (ME078). W - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite GS - Greenschist facies Protolith Q - Interbedded pelite and sandstone
Primary rock type	slate
Secondary rock type	sandstone
Other rock types	conglomerate; graywacke
Lithologic constituents	Major Metamorphic > Metasedimentary > Metaclastic > Slate (Bed)W - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite GS - Greenschist facies Protolith Q - Interbedded pelite and sandstone Sedimentary > Clastic > SandstoneW - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite GS - Greenschist facies Protolith Q - Interbedded pelite and sandstone Minor Sedimentary > Clastic > Sandstone > GraywackeW - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite GS - Greenschist facies Protolith Q - Interbedded pelite and sandstone Sedimentary > Clastic > ConglomerateW - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite GS - Greenschist facies Protolith Q - Interbedded pelite and sandstone
Map references	Digital bedrock data downloaded from Maine Office of GIS in September 2005 from http://apollo.ogis.state.me.us/catalog/catalog.asp?state=2&extent=cover#bedrock Bedrock units table (publication date 11/15/2002) downloaded from same site. Permission to redistribute these data granted by Dr. Robert Marvinney, State Geologist of Maine, in September 2006. [http://apollo.ogis.state.me.us/catalog/catalog.asp?state=2&extent=cover#bedrock]
Unit 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. Neuman, R.B., 1967, Bedrock geology of the Shin Pond and Stacyville quadrangles, Penobscot County, Maine, IN Shorter contributions to general geology, 1965: U.S. Geological Survey Professional Paper, 524-I, p. I1-I39. [http://pubs.er.usgs.gov/publication/pp524I] USGS Geologic Names Lexicon (GEOLEX) [http://ngmdb.usgs.gov/Geolex/]
Geographic coverage	Aroostook - Penobscot - Piscataquis