Franconia Formation
Geologic formation in the upper mid-western United States
From Wikipedia, the free encyclopedia
The Franconia Formation is a geologic formation in the upper mid-western United States, with outcroppings found in Illinois, Indiana, Iowa, Michigan, Minnesota, Missouri, Ohio, and Wisconsin.[1] It preserves fossils dating back to the Cambrian period. It was named the Franconia Formation due to the first published documentation of exposures in vicinity of Franconia, Minnesota[1] in the 1897 Ph.D. dissertation by Charles P. Berkley at the University of Minnesota titled Geology of the St. Croix Dalles.[2] The Franconian stratigraphic stage was named after this formation.
| Franconia Formation | |
|---|---|
| Stratigraphic range: Cambrian | |
| Type | Formation |
| Unit of | Munising Group (IN, MI, WI), Knox Group (IL), Tunnel City Group (IA, MN, WI) |
| Sub-units | Birkmose Member (MO), Davis Member (IL), Derby-Doe Run Member (IL), Ironton Member (IL, WI, MI), Mazomanie Member (WI), Reno Member (MO, MN, WI), Tomah Member (MO) |
| Underlies | Potosi Dolomite and St. Lawrence Formation |
| Overlies | Ironton Sandstone |
| Location | |
| Region | Illinois, Indiana, Iowa, Michigan, Minnesota, Missouri, Ohio, and Wisconsin |
| Country | United States |
The formation consists of fine-grained dolomitic sandstone with interbedded shaly zones, becoming more dolomitic towards the east and south of its extent.[3]
