Ordovician unnamed volcanic rocks

Ordovician unnamed volcanic rocks
State Maine
Name Ordovician unnamed volcanic rocks
Geologic age Ordovician
Lithologic constituents
Major
Igneous > Volcanic > Felsic-volcanicW - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite; GS - Greenschist facies; Protolith W - Mafic to felsic volcanic rocks
Igneous > Volcanic > Mafic-volcanicW - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite; GS - Greenschist facies; Protolith W - Mafic to felsic volcanic rocks
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.
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.

NGMDB product
Counties Aroostook - Penobscot - Piscataquis