Ordovician sandstone and pelite of the Depot Mountain sequence (MEOdmp;0)

State	Maine
Name	Ordovician sandstone and pelite of the Depot Mountain sequence
Geologic age	Ordovician
Original map label	Odmp
Comments	Depot Mountain Formation recently divided into unnamed lower and upper members in the belt between Seven Islands and Riviere Bleue. The conglomerate subunit of Boudette et al (1976) is not mappable. Rocks similar to those of the type locality are here assigned to the lower member, which consists of thick-bedded, dark gray, fine-to-coarse grained, feldspathic graywacke interbedded with dark gray and black slate or phyllite. Sequences of lithic and crystal tuff and roundstone conglomerate occur locally within lower member. Upper member consists of dark gray, foliated, lithic graywacke interbedded with laminated gray slate. Thickness of the lower member is unknown; upper member may exceed 1000 m. Graptolites from lower member yield Late Ordovician (Caradocian) age. Upper member younger than overlying Fivemile Brook Formation. Therefore, rocks assigned to Depot Mountain appear to extend in age from at least Caradocian to the middle of the Llandoverian (Early Silurian). Along Dead Brook fault, unit overlies St. Daniel Formation, extended from CAN to replace the name Estcourt Road Formation of earlier reports. (ME064) 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	graywacke
Secondary rock type	slate
Other rock types	conglomerate
Lithologic constituents	Major Sedimentary > Clastic > Sandstone > Graywacke (Bed)W - 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 Incidental Igneous > Volcanic > Felsic-volcanic (Pyroclastic, tuff)W - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite Protolith Q - Interbedded pelite and sandstone Sedimentary > Clastic > Conglomerate (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. Boudette, E.L., Hatch, N.L., Jr., and Harwood, D.S., 1976, Reconnaissance geology of the Upper St. John and Allagash river basins, Maine: U.S. Geol. Surv., Bull. 1406, 37 p. Neuman, R. B., pers. communication, 1983. Roy, D.C., 1989, The Depot Mountain Formation; Transition from syn- to post-Taconian basin along the Baie Verte-Brompton line in northwestern Maine, IN Tucker, R.D., and Marvinney, T.G., eds., Studies in Maine geology; structure and stratigraphy; Volume 2: Maine Geological Survey, p. 85-99. USGS Geologic Names Lexicon (GEOLEX) [http://ngmdb.usgs.gov/Geolex/]
Geographic coverage	Aroostook