Silurian - Ordovician Aroostook River Formation (MESOar;0)

State	Maine
Name	Silurian - Ordovician Aroostook River Formation
Geologic age	Silurian - Ordovician
Original map label	SOar
Comments	Aroostook River Formation here named in northeastern ME. Unit is thin-bedded gray to green-gray calcareous slate interlayered with graywacke and siltstone. 600 m thick. Overlies Madawaska Lake Formation; conformably underlies Frenchville Formation. (ME029) Unit description from USGS GEOLEX website (ME078). W - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite Protolith Q - Interbedded pelite and sandstone
Primary rock type	slate
Secondary rock type	graywacke
Other rock types	siltstone
Lithologic constituents	Major Sedimentary > Clastic > Sandstone > ArkoseW - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite Protolith Q - Interbedded pelite and sandstone Sedimentary > Clastic > SiltstoneW - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite Protolith Q - Interbedded pelite and sandstone Metamorphic > Metasedimentary > Metaclastic > Slate (Bed)W - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite 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. Roy, D.C., and Mencher, E., 1976, Ordovician and Silurian stratigraphy of northeastern Aroostook County, Maine: Geol. Soc. Amer., Memoir 148, p. 25-52. USGS Geologic Names Lexicon (GEOLEX) [http://ngmdb.usgs.gov/Geolex/]
Geographic coverage	Aroostook