Munising Formation

Munising Formation
Stratigraphic range: Cambrian-?Early Ordovician
Light-colored Musining Formation overlying the red Jacobsville Formation in Pictured Rocks National Lakeshore
Type	Formation
Sub-units	Miner's Castle Member, Chapel Rock Member, Basal Conglomerate, Eau Claire Formation
Underlies	Au Train Formation
Overlies	Jacobsville Sandstone
Thickness	1,700 ft (520 m)
Lithology
Primary	Conglomerate
Other	Anhydrite
Location
Region	Michigan  Ontario
Country	United States  Canada

The Munising Group or Formation is a 1,700 feet (520 m) thick, white to light grey^[1] Cambrian sedimentary unit that crops out in Michigan and (to a lesser extent) Ontario. At one end of its extent, it comprises a basal conglomerate overlain by the Chapel Rock Member and the Miners Castle Member; elsewhere, it comprises the Eau Claire, Galesville (=Dresbach), and Franconia Members. Anhydritic evaporite deposits are present in places.^[2] The conglomerate was deposited by rivers in flood, with the Chapel Rock member, which contains deltaic deposits, representing transgression as the conglomerate cones became submerged; the Miners Castle member was deposited further from the shoreline, representing shelf deposits.^[3] Its uppermost strata may be Early Ordovician in age, and contain conodonts, trilobites and phosphatic moulds of brachiopods, ostrocoderm fish and gastropods.^[4]

The Munising lies unconformably above the Jacobsville Formation.^[1]

References

1. "Pictured Rocks: Geologic Formations". US National Park Service. Retrieved August 5, 2011.
2. Paul A. Catacosinos (1973). "Cambrian Lithostratigraphy of Michigan Basin". The American Association of Petroleum Geologists Bulletin. 57 (12): 2404–2418. doi:10.1306/83d9132b-16c7-11d7-8645000102c1865d.
3. Charles a. Haddox, R. H. D. (1990). "Cambrian Shoreline Deposits in Northern Michigan". SEPM Journal of Sedimentary Research. doi:10.1306/212F9250-2B24-11D7-8648000102C1865D.
4. Miller, J. F.; Ethington, R. L.; Rose, R. (2006). "Stratigraphic Implications of Lower Ordovician Conodonts from the Munising and Au Train Formations at Pictured Rocks National Lakeshore, Upper Peninsula of Michigan". PALAIOS. 21 (3): 227–237. doi:10.2110/palo.2004.p04-50.