Silurian - Ordovician Frontenac Formation (MESOf;0)

State	Maine
Name	Silurian - Ordovician Frontenac Formation
Geologic age	Silurian - Ordovician
Original map label	SOf
Comments	The Frontenac, since its naming, has been a subject of disagreement concerning its lithologic components, stratigraphic position, and structural presentation. The author and his colleagues (Bothner, Pollock, and Moench) consider the Frontenac to be Silurian and to lie beneath the Seboomook Group. Canadian geologists reverse the stratigraphic order and place the Frontenac in the Devonian and above units correlated with the Seboomook. The formation is informally divided into lower and upper portions. In most exposures the lower portion consists of thickly bedded, light bluish-gray to greenish gray, fine- to medium-grained, quartzofeldspathic, variably calcareous wacke. Wacke beds are typically interbedded with thinly bedded, dark gray mudstone slate. The upper portion, similar in bedding and composition to the lower portion, is generally non-calcareous and lacks, for the most part, the volcanic and hypabyssal intrusive rocks. Underlies Late Silurian and Early Devonian Ironbound Mountain Formation. (ME058) Unit description from USGS GEOLEX website (ME078). W - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite GS - Greenschist facies Protolith Q - Interbedded pelite and sandstone
Primary rock type	graywacke
Secondary rock type	slate
Other rock types
Lithologic constituents	Major Sedimentary > Clastic > Sandstone > GraywackeW - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite GS - Greenschist facies Protolith Q - Interbedded pelite and sandstone Metamorphic > Metasedimentary > Metaclastic > Slate (Bed)W - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite GS - Greenschist facies 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. Marvinney, R.G., 1994, Sedimentological aspects of the Frontenac, Ironbound Mountain, and Northeast Carry Formations near Seboomook Lake, Maine; B2, IN Hanson, L.S., ed., Guidebook to field trips in north-central Maine: New England Intercollegiate Geological Conference Guidebook, [86th] Annual Meeting, Millinocket, ME, September 23-25, 1994, p. 67-89. USGS Geologic Names Lexicon (GEOLEX) [http://ngmdb.usgs.gov/Geolex/]
Geographic coverage	Oxford - Piscataquis - Somerset