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Ordovician Munsungun Lake Formation

Ordovician Munsungun Lake Formation
StateMaine
NameOrdovician Munsungun Lake Formation
Geologic ageOrdovician
Original map labelOml
CommentsMunsungun Lake Formation is part of the late Middle Ordovician to early Late Ordovician volcanogenic tract in northern Maine. Rocks are largely felsic volcanic tuffs, agglomerates and flows. Subsidiary lithologies include sandstone, siliceous shale, and chert. Extensively intruded by diabase sills in the study area. Regionally extensive, cropping out in a belt over 60 km in length and 5 km in width. Total thickness is estimated to be 1500 m in the westernmost portion of the outcrop belt. Unconformably overlies the Lower Ordovician Chase Brook Formation and conformably overlies the Bluffer Pond Formation in the Munsungun Lake area where chert was extensively quarried by early humans for tool making. Elsewhere conformably underlies the Blind Brook Formation. The Middle Ordovician Munsungun Lake was deformed during the Devonian Acadian Orogeny. (ME067) Unit description from USGS GEOLEX website (ME078). W - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite Protolith T - Rhyolitic volcanic rocks
Primary rock typefelsic volcanic rock
Secondary rock typesandstone
Other rock typesshale; chert; basalt
Lithologic constituents
Major
Igneous > Volcanic > Felsic-volcanic (Pyroclastic, tuff)W - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite Protolith T - Rhyolitic volcanic rocks
Minor
Igneous > Volcanic > Mafic-volcanic > Basalt (Dike or sill)W - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite Protolith T - Rhyolitic volcanic rocks
Incidental
Sedimentary > Clastic > Mudstone > ShaleW - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite Protolith T - Rhyolitic volcanic rocks
Sedimentary > Chemical > ChertW - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite Protolith T - Rhyolitic volcanic rocks
Sedimentary > Clastic > SandstoneW - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite Protolith T - 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.
Hall, B.A., 1970, Stratigraphy of the southern end of the Munsungun anticlinorium, Maine: Maine Geol. Surv., Bull. 22, 63 p.
Pollock, S.G., Hamilton, N.D. and Doyle, R.A., 1994, Geology and archaeology of chert in the Munsungun Lake Formation; B6, 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. 159-181.
Geographic coverageAroostook - Piscataquis

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