The Munising Group or Formation is a thick, white to light grey

Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...

sedimentary unit that crops out in

Michigan Michigan ( ) is a peninsular U.S. state, state in the Great Lakes region, Great Lakes region of the Upper Midwest, Upper Midwestern United States. It shares water and land boundaries with Minnesota to the northwest, Wisconsin to the west, ...

and (to a lesser extent)

Ontario Ontario is the southernmost Provinces and territories of Canada, province of Canada. Located in Central Canada, Ontario is the Population of Canada by province and territory, country's most populous province. As of the 2021 Canadian census, it ...

. 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 An evaporite () is a water- soluble sedimentary mineral deposit that results from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporite deposits: marine, which can also be described as oce ...

deposits are present in places. 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. Its uppermost strata may be

Early Ordovician The Early Ordovician is the first epoch (geology), epoch of the Ordovician period, corresponding to the Lower Ordovician series (stratigraphy), series of the Ordovician system. It began after the Cambrian Stage 10, Age 10 of the Furongian epoch o ...

in age, and contain

conodont Conodonts, are an extinct group of marine jawless vertebrates belonging to the class Conodonta (from Ancient Greek κῶνος (''kōnos''), meaning " cone", and ὀδούς (''odoús''), meaning "tooth"). They are primarily known from their hard ...

trilobite Trilobites (; meaning "three-lobed entities") are extinction, extinct marine arthropods that form the class (biology), class Trilobita. One of the earliest groups of arthropods to appear in the fossil record, trilobites were among the most succ ...

s and phosphatic moulds of

brachiopod Brachiopods (), phylum (biology), phylum Brachiopoda, are a phylum of animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear e ...

s, ostrocoderm fish and

gastropod Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and fro ...

s. The Munising lies

unconformably An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval o ...

above the

Jacobsville Formation Jacobsville Sandstone is a red sandstone formation, marked with light-colored streaks and spots, primarily found in northern Upper Michigan, portions of Ontario, and under much of Lake Superior. Desired for its durability and aesthetics, the sa ...

Stratigraphy

Davis Formation

The Davis Formation or Davis Member is found from

Missouri Missouri (''see #Etymology and pronunciation, pronunciation'') is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. Ranking List of U.S. states and territories by area, 21st in land area, it border ...

through

Illinois Illinois ( ) is a U.S. state, state in the Midwestern United States, Midwestern United States. It borders on Lake Michigan to its northeast, the Mississippi River to its west, and the Wabash River, Wabash and Ohio River, Ohio rivers to its ...

and into

Indiana Indiana ( ) is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders Lake Michigan to the northwest, Michigan to the north and northeast, Ohio to the east, the Ohio River and Kentucky to the s ...

and

. This formation is

Upper Cambrian The Furongian is the fourth and final epoch and series of the Cambrian. It lasted from to million years ago. It succeeds the Miaolingian series of the Cambrian and precedes the Lower Ordovician Tremadocian Stage. It is subdivided into three sta ...

in age. It is named for Davis Creek located in

St. Francois County, Missouri St. Francois County ( ) is a county in the Lead Belt region in the U.S. state of Missouri. At the 2020 census, the population was 66,922. The largest city and county seat is Farmington. The county was officially organized on December 19, 18 ...

by Buehler (1907, p. 231). The formation is composed of

Siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility. Although its permeabil ...

Shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of Clay mineral, clay minerals (hydrous aluminium phyllosilicates, e.g., Kaolinite, kaolin, aluminium, Al2Silicon, Si2Oxygen, O5(hydroxide, OH)4) and tiny f ...

Limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

and Dolomite. The rock of the Davis Formation is a gradual change between the lower Galesville, Ironton and Franconia Formations to the upper Potosi Dolomite. Stratigraphically it is equivalent to the Franconia Formation in Illinois and Missouri. In Illinois it is the lower member of the Franconia. It is a named member of the Franconia in Illinois.

Franconia Formation

The Franconia Formation is a

geologic formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

in the upper mid-western United States, with outcroppings found in

Iowa Iowa ( ) is a U.S. state, state in the upper Midwestern United States, Midwestern region of the United States. It borders the Mississippi River to the east and the Missouri River and Big Sioux River to the west; Wisconsin to the northeast, Ill ...

Minnesota Minnesota ( ) is a U.S. state, state in the Upper Midwestern region of the United States. It is bordered by the Canadian provinces of Manitoba and Ontario to the north and east and by the U.S. states of Wisconsin to the east, Iowa to the so ...

Ohio Ohio ( ) is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders Lake Erie to the north, Pennsylvania to the east, West Virginia to the southeast, Kentucky to the southwest, Indiana to the ...

, and

Wisconsin Wisconsin ( ) is a U.S. state, state in the Great Lakes region, Great Lakes region of the Upper Midwest of the United States. It borders Minnesota to the west, Iowa to the southwest, Illinois to the south, Lake Michigan to the east, Michig ...

. It was named the Franconia Formation due to the first published documentation of exposures in vicinity of

Franconia Franconia ( ; ; ) is a geographical region of Germany, characterised by its culture and East Franconian dialect (). Franconia is made up of the three (governmental districts) of Lower Franconia, Lower, Middle Franconia, Middle and Upper Franco ...

, Minnesota in the 1897 Ph.D. dissertation by Charles P. Berkley at the University of Minnesota titled Geology of the St. Croix Dalles. The Franconian stratigraphic stage was named after this formation. The formation consists of fine-grained glauconitic and dolomitic sandstone with interbedded shaly zones, becoming more dolomitic towards the east and south of its extent. The Franconia has several named members; 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)

Ironton Sandstone

The Ironton Sandstone is located in Indiana, Illinois and Wisconsin. It is stratigraphically equivalent to the Davis Formation to the east and south of an arbitrary cutoff line in northwestern Indiana. In

its equivalent is the Kerbel Formation. The term Ironton Member was first coined by Thwaites, 192:3, p. 550, for exposures of a coarse grained sandstone at the base of the Franconia formation in

Ironton, Wisconsin Ironton is a village in Sauk County, Wisconsin, United States, along the Little Baraboo River. The population was 274 at the 2020 census. The village is located within the Town of Ironton. Like the Town of Ironton, the village was named for de ...

. The Ironton is a medium to coarse grained sandstone with layers of dolomitic sandstone interbedded within the formation.

Galesville Sandstone

The Galesville Sandstone is a geologic unit found in Northwestern

and

. Moving south and west it grades into the Davis Formation. In southern and western Indiana it is a named member of the Davis Formation this continues into Illinois. Named for exposures along Beaver Creek in

Galesville, Wisconsin Galesville is a city in Trempealeau County, Wisconsin, United States. The population was 1,662 at the 2020 census. A dam on Beaver Creek is located at Galesville, forming Lake Marinuka north of the city. The mayor is Vince Howe. History Galesvi ...

. The formation is fine to coarse grained sandstone. Grading upward towards the Ironton Sandstone. The Galesville ranges from about 50' to 100' thick.

Eau Claire Formation

The Eau Claire Formation originally called the Eau Claire Grit or Eau Claire Trilobite Bed (Wooster, 1878). The Eau Claire is found Indiana, Illinois, Wisconsin, Michigan, western Ohio, and western Kentucky. It is also called the Bonneterre Dolomite or Bonneterre Formation in Missouri. The Eau Claire is made up of dolomite, limestone, siltstone and shale. It can be over 1,000' thick in southwest Indiana. The Eau Claire comfortably overlies the

Mount Simon Sandstone The Mount Simon Sandstone is an Upper Cambrian sandstone and is found in many states in the Midwest such as Wisconsin, Minnesota, Iowa, Illinois, and Missouri. The Mount Simon formation is the equivalent of the La Motte Sandstone formation in t ...

everywhere. In northwest Indiana the Eau Claire grades into the Galesville Sandstone. The Eau Claire contains

fossils that date back to the Early to Mid Dresbachian Age (501-497 Ma).

References

{{Chronostratigraphy of Indiana Geologic groups of Michigan Geologic groups of Ontario Cambrian System of North America Cambrian Michigan Cambrian Canada Conglomerate groups Fluvial deposits Deltaic deposits Evaporite deposits Fossiliferous stratigraphic units of North America Paleontology in Michigan Cambrian Indiana Geologic groups of Indiana