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Menominee Group; Blair Creek Formation

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Dominantly dark-gray, massive, porphyritic tholeiitic basalt. Includes a basal conglomerate and a lean iron-formation in middle of formation
State Wisconsin
Name Menominee Group; Blair Creek Formation
Geologic age Early Proterozoic
Lithologic constituents
Major
Igneous > Volcanic > Mafic-volcanic > Basalt (Flow)Dominantly dark-gray, massive, porphyritic tholeiitic basalt
Minor
Sedimentary > Chemical > Banded-iron-formation (Bed)
Metamorphic > Metasedimentary > Metaclastic > Metaconglomeratebasal metacomglomerate
Comments continental margin assemblage (north of Niagara Fault)
References

Sims, P.K., 1992, Geologic map of Precambrian rocks, southern Lake Superior region, Wisconsin and northern Michigan: U.S. Geological Survey Miscellaneous Investigations Map I-2185, scale 1:500,000.

https://pubs.er.usgs.gov/publication/i2185
NGMDB product
Counties Ashland - Iron - Vilas