Ordovician Shin Brook Formation (MEOsb;0)

State	Maine
Name	Ordovician Shin Brook Formation
Geologic age	Ordovician
Original map label	Osb
Comments	Named for Shin Brook, Penobscot Co., northeastern ME. Crops out along Shin Brook. Consists of bedded waterlaid volcanic sandstone and conglomerate, massive porphyritic rocks that are probably crystal tuffs, and volcanic breccia. Bedded rocks range from fine-grained siltstone to coarse-grained conglomerate. Full thickness not known. 904 ft thick at type section, of which 304 ft is exposed; type section is probably only a fraction of entire section. Northwest of segment of Grand Pitch Formation brought up by faulting, Shin Brook crops out for 1500 ft along the brook and on adjacent bluffs. Overlies Cambrian(?) Grand Pitch Formation; underlies metadiabase. Contains fossils. (ME068) Unit description from USGS GEOLEX website (ME078). W - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite Protolith U - Rhyolitic volcanic rocks
Primary rock type	rhyolite
Secondary rock type	siltstone
Other rock types	conglomerate; breccia
Lithologic constituents	Major Igneous > Volcanic > Felsic-volcanic > RhyoliteW - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite Protolith U - Rhyolitic volcanic rocks Minor Sedimentary > Clastic > ConglomerateW - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite Protolith U - Rhyolitic volcanic rocks Sedimentary > Clastic > SiltstoneW - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite Protolith U - Rhyolitic volcanic rocks Incidental Igneous > Volcanic (Volcaniclastic, volcanic breccia)W - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite Protolith U - Rhyolitic volcanic rocks
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] Neuman, R.B., 1964, Fossils in Ordovician tuffs, northeastern Maine, with a section on Trilobita by H.B. Whittington, IN Contributions to general geology, 1963: U.S. Geological Survey Bulletin, 1181-E, p. E1-E38. [http://pubs.er.usgs.gov/publication/b1181E] USGS Geologic Names Lexicon (GEOLEX) [http://ngmdb.usgs.gov/Geolex/]
Geographic coverage	Aroostook - Penobscot