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Ordovician Shin Brook Formation

Ordovician Shin Brook Formation
StateMaine
NameOrdovician Shin Brook Formation
Geologic ageOrdovician
Original map labelOsb
CommentsNamed 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 typerhyolite
Secondary rock typesiltstone
Other rock typesconglomerate; 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.
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.
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.
USGS Geologic Names Lexicon (GEOLEX)
Geographic coverageAroostook - Penobscot

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