Geologic units in Michigan (state in United States)

Paint River Group; Upper part - Dominantly Fortune Lakes Slate, but includes other rocks in poorly exposed areas. Correlated with upper part of Baraga Group.

Lithology: slate

Bois Blanc Formation (Early Devonian) at surface, covers 0.1 % of this area

Bois Blanc Formation

Lithology: limestone; dolostone (dolomite)

Bedford Shale (Late Devonian) at surface, covers 0.5 % of this area

Bedford Shale

Lithology: shale; sandstone

Marshall Sandstone (Mississippian) at surface, covers 5 % of this area

Marshall Sandstone

Lithology: sandstone; siltstone

Tymochtee and Greenfield Formations, Undivided (Silurian) at surface, covers < 0.1 % of this area

Tymochtee and Greenfield Formations, Undivided - Dolomite, olive-gray to yellowish- brown, thin to massive bedded, upper two-thirds commonly contains brownish-black to gray shale laminae; locally developed brecciated zones in lower one third.

Lithology: dolostone (dolomite); shale

Black River Limestone (Late Ordovician) at surface, covers 1.0 % of this area

Black River Limestone

Lithology: limestone

Traverse Group (Middle Devonian) at surface, covers 2 % of this area

Traverse Group

Lithology: limestone; shale

Oronto Group; Nonesuch Shale (Middle Proterozoic) at surface, covers < 0.1 % of this area

Oronto Group; Nonesuch Shale - Gray, green, and brown lithic siltstone, shale, and sandstone. Copper sulfides and native copper occur locally near base

Lithology: siltstone; shale; sandstone

Baraga Group; Volcanic-sedimentary unit (Early Proterozoic) at surface, covers < 0.1 % of this area

Baraga Group; Volcanic-sedimentary unit - Interlayered fine- to medium-grained metasedimentary rocks and metavolcanic rocks in poorly exposed areas in southern Baraga County, Mich.

Lithology: metasedimentary rock; metavolcanic rock

Sunbury Shale (Mississippian-Devonian) at surface, covers 0.2 % of this area

Sunbury Shale

Lithology: black shale

Jacobsville Sandstone (Middle Proterozoic) at surface, covers < 0.1 % of this area

Jacobsville Sandstone - Red, brown, and white quartzose sandstone, and minor siltstone, shale and conglomerate

Lithology: sandstone; siltstone; shale; conglomerate

Jacobsville Sandstone (Middle Proterozoic) at surface, covers 3 % of this area

Jacobsville Sandstone - Red, brown, and white quartzose sandstone, and minor siltstone, shale and conglomerate

Lithology: sandstone; siltstone; conglomerate; shale

Michigan Formation (Mississippian) at surface, covers 5 % of this area

Michigan Formation

Lithology: shale; black shale; sandstone; dolostone (dolomite); limestone; evaporite

Menominee Group, undivided (Early Proterozoic) at surface, covers < 0.1 % of this area

Menominee Group, undivided - Includes Negaunee Iron-formation, Siamo Slate, and Ajibik Quartzite in areas where units are too thin to map individually.

Lithology: slate; quartzite; iron formation

Copper Harbor Conglomerate; Volcanic member (Early Proterozoic) at surface, covers < 0.1 % of this area

Copper Harbor Conglomerate; Volcanic member - Basaltic to andesitic volcanic flows interbedded within the conglomerate and sandstone

Lithology: andesite

Engadine Dolomite (Early Silurian) at surface, covers 0.7 % of this area

Engadine Dolomite

Lithology: dolostone (dolomite)

Powder Mill Group; Kallander Creek Volcanics (Middle Proterozoic) at surface, covers < 0.1 % of this area

Powder Mill Group; Kallander Creek Volcanics- Basalt, andesite and lesser rhyolite flows. Basalt flows near base of the formation contain plagioclase phenocrysts, some in radiating clusters

Lithology: basalt; andesite; rhyolite

Manistique Formation (Early Silurian) at surface, covers 0.5 % of this area

Manistique Formation

Lithology: dolostone (dolomite); limestone

Ellsworth Shale (Late Devonian) at surface, covers 2 % of this area

Ellsworth Shale

Lithology: shale; siltstone; sandstone

Gneiss and amphibolite (Late Archean, 2.640-2.750 Ma) (Late Archean) at surface, covers 0.6 % of this area

Gneiss and amphibolite (Late Archean, 2.640-2.750 Ma) - Interlayered quartzofeldspathic gneiss and amphibolite in Marenisco, Mich., area and northwestern Wisconsin. Protoliths are bimodal intermediate and mafic volcanic rocks (Sims and others, 1984).

Lithology: gneiss; amphibolite

Porcupine Volcanics (Middle Proterozoic) at surface, covers 0.2 % of this area

Porcupine Volcanics - Generally dark-gray basalt, andesite, and felsite flows and subordinate interflow sedimentary rocks

Lithology: basalt; andesite; rhyolite; medium-grained mixed clastic

Saginaw Formation (Pennsylvanian) at surface, covers 8 % of this area

Saginaw Formation

Lithology: sandstone; shale; coal; limestone

Mafic metavolcanic rocks (Early Proterozoic) at surface, covers < 0.1 % of this area

Mafic metavolcanic rocks - Dominantly tholeiitic basalt and basaltic andesite flows and tuffs; associated with sheet dikes, massive and layered metagabbro, and ultramafic rocks. In northeastern Wisconsin, rocks have been named the Quinnesec Formation.

Lithology: basalt; andesite; gabbro; ultramafic intrusive rock

Baraga Group; Michigamme Formation, undivided (Early Proterozoic) at surface, covers 2 % of this area

Baraga Group; Michigamme Formation, undivided - Thick and stratigraphically varied formation of sedimentary and less abundant volcanic rocks. Metamorphosed graywacke is predominant rock of Michigamme Formation. Calcareous concretions common. Metamorphosed from cholorite to sillimanite grade (Cannon, 1986). Mapped undivided in poorly exposed areas

Lithology: graywacke; metasedimentary rock

Munising Formation (Late Cambrian) at surface, covers 0.6 % of this area

Munising Formation

Lithology: sandstone; shale; conglomerate

Mafic metavolcanic rocks (Early Proterozoic) at surface, covers < 0.1 % of this area

Lithology: basalt; andesite; gabbro; ultramafic intrusive rock

Point Aux Chenes Shale (Late Silurian) at surface, covers 0.1 % of this area

Point Aux Chenes Shale

Lithology: shale

Metabasalt (Late Archean) (Late Archean) at surface, covers 0.1 % of this area

Metabasalt (Late Archean) - Derived from mafic to intermediate pyroclastic rocks and massive to pillowed lava flows. Unit mapped as Ramsey Formation by Prinz (1981) south of Gogebic Range; mapped as Mona Schist and Kitchi Schist in northern complex of Marquette District.

Lithology: meta-basalt; tuff; schist

Menominee Group; Emperor Volcanic Complex (Early Proterozoic) at surface, covers < 0.1 % of this area

Menominee Group; Emperor Volcanic Complex - Metamorphosed intermediate to mafic pyroclastic and flow rocks in easternmost part of Gogebic Range

Lithology: meta-basalt; metavolcanic rock

Baraga Group; Michigamme Formation, undivided (Early Proterozoic) at surface, covers < 0.1 % of this area

Lithology: graywacke

Baraga Group; Michigamme Formation; Gray to black slate (Early Proterozoic) at surface, covers 0.3 % of this area

Baraga Group; Michigamme Formation; Gray to black slate - Strongly cleaved. Represents lower stratigraphic part of formation

Lithology: slate

Powder Mill Group; Siemens Creek Volcanics (Middle Proterozoic) at surface, covers < 0.1 % of this area

Powder Mill Group; Siemens Creek Volcanics - Dark-gray basalt and minor porphyritic andesite. Generally strongly magnetic with reversed remanent magnetism. Underlain by a thin unit of quartzose sandstone (Bessemer Quartzite).

Lithology: basalt; andesite

Peavy Pond complex (Early Proterozoic) at surface, covers < 0.1 % of this area

Peavy Pond complex - Chiefly hornblende metagabbro, but includes metanorite, metatonalite, granodiorite, and granite (Bayley, 1959).

Lithology: metamorphic rock; granodiorite; granite

Berea Sandstone (Late Devonian) at surface, covers 0.2 % of this area

Berea Sandstone

Lithology: sandstone; siltstone

Trempealeau Formation (Late Cambrian) at surface, covers 0.8 % of this area

Trempealeau Formation

Lithology: sandstone; shale; dolostone (dolomite)

Portage Lake Volcanics (Middle Proterozoic) at surface, covers 0.8 % of this area

Portage Lake Volcanics - Lava flows, mostly basalt, andesite and felsite flows and subordinate interflow sedimentary rocks.

Lithology: basalt; andesite; rhyolite; mudstone

Coldwater Shale (Mississippian) at surface, covers < 0.1 % of this area

Coldwater Shale - Shale; gray; clayey thin bedded; siderite nodules common; as much as 150 feet thick.

Lithology: shale

Porcupine Volcanics (Middle Proterozoic) at surface, covers < 0.1 % of this area

Porcupine Volcanics - Generally dark-gray basalt, andesite, and felsite flows and subordinate interflow sedimentary rocks

Lithology: rhyolite; basalt; andesite; mixed clastic/volcanic

Big Hill Dolomite (Late Ordovician) at surface, covers 0.3 % of this area

Big Hill Dolomite

Lithology: dolostone (dolomite); limestone

Menominee Group; Negaunee Iron-formation (Early Proterozoic) at surface, covers < 0.1 % of this area

Menominee Group; Negaunee Iron-formation - Highly metamorphosed banded iron-formation. Principal iron-formation in Marquette trough and nearby areas. Includes abundant metadiabase sills.

Lithology: iron formation; diabase

Baraga Group; Copps Formation (Early Proterozoic) at surface, covers < 0.1 % of this area

Baraga Group; Copps Formation - Fine- to medium-grained graywacke and less abundant gray to black slate. Thin basal conglomerate west of Lake Gogebic contains clasts of underlying Archean rocks in a quartzitic and argillaceous matrix.

Lithology: graywacke; slate; meta-conglomerate

Baraga Group; Tyler Formation (Early Proterozoic) at surface, covers < 0.1 % of this area

Baraga Group; Tyler Formation - Light- to dark-gray, feldspathic, fine-grained sandstone, argillaceous siltstone, and argillite. Near base, ferruginous argillite contains beds of cherty sideritic and pyritic iron-formation

Lithology: sandstone; argillite; iron formation

Metadiabase (Early Proterozoic) at surface, covers < 0.1 % of this area

Metadiabase - Variably metamorphosed dikes, sills and subconcordant sheets of diabasic rocks. Probably coeval (in part) with volcanic rocks of Hemlock Formation (unit Xh)

Lithology: mafic metavolcanic rock

Migmatitic gneiss and amphibolite (Late to Early Archean) (Archean) at surface, covers 0.9 % of this area

Migmatitic gneiss and amphibolite (Late to Early Archean) - Varied gneisses of mostly unknown age in cores of gneiss domes and fault-bounded uplifts (Archean gneiss terranes). Except for the Watersmeet dome (Late to Early Archean), all dated rocks are Late Archean. Includes granite of Late Archean age that transgresses gneisses and amphibolite.

Lithology: gneiss; migmatite; amphibolite

Detroit River Group (Devonian) at surface, covers < 0.1 % of this area

Detroit River Group - Dolomite; brown to gray; medium to thick bedded; laminated; nodules or interbeds of anhydrite and/or gypsum; basal part becomes sandy dolomite or fine-grained sandstone; as much as 170 feet thick.

Lithology: dolostone (dolomite); evaporite; sandstone

Queenston Shale (Late Ordovician) at surface, covers 0.3 % of this area

Queenston Shale

Lithology: shale

Antrim Shale (Devonian) at surface, covers < 0.1 % of this area

Antrim Shale - Shale; dark brown to black; carbonaceous, thinly laminated; 0 to 230 feet thick.

Lithology: shale; black shale

Bass Island Dolomite (Late Silurian) at surface, covers 0.1 % of this area

Bass Island Dolomite

Lithology: dolostone (dolomite); shale; limestone; sandstone

Menominee and Chocolay Groups, undivided (Early Proterozoic) at surface, covers < 0.1 % of this area

Menominee and Chocolay Groups, undivided - Mapped where units are too thin to show separately on map

Lithology: metasedimentary rock; metavolcanic rock

Burnt Bluff Formation (Early Silurian) at surface, covers 0.6 % of this area

Burnt Bluff Formation

Lithology: limestone

Cataract Formation (Early Silurian) at surface, covers 0.3 % of this area

Cataract Formation

Lithology: shale; limestone; dolostone (dolomite); sandstone

Trenton Limestone (Late Ordovician) at surface, covers 1 % of this area

Trenton Limestone

Lithology: limestone; dolostone (dolomite); shale

Utica Shale (Late Ordovician) at surface, covers 0.5 % of this area

Utica Shale

Lithology: black shale

Collingwood Limestone (Late Ordovician) at surface, covers 0.1 % of this area

Collingwood Limestone

Lithology: limestone; black shale

Copper Harbor Conglomerate (Middle Proterozoic) at surface, covers 0.3 % of this area

Copper Harbor Conglomerate - Red lithic conglomerate and sandstone; mafic to felsic volcanic flows similar to those of the unnamed formation (unit Yu) are interlayered with the sedimentary rocks.

Lithology: conglomerate; sandstone; lava flow

Dickinson Group, undivided (Late Archean) (Late Archean) at surface, covers < 0.1 % of this area

Dickinson Group, undivided (Late Archean) - Metavolcanic and metasedimentary rocks in Dickinson County, Mich. From youngest to oldest, consists of Six-Mile Lake Amphibolite, Solberg Schist, and East Branch Arkose.

Lithology: amphibolite; schist; metasedimentary rock; gneiss

Detroit River Group (Middle Devonian) at surface, covers 0.8 % of this area

Detroit River Group

Lithology: dolostone (dolomite); limestone; sandstone

Baraga Group; Michigamme Formation; Mafic to intermediate flows and pyroclastic rocks, including Clarksburg Volcanics member (Early Proterozoic) at surface, covers < 0.1 % of this area

Baraga Group; Michigamme Formation; Mafic to intermediate flows and pyroclastic rocks, including Clarksburg Volcanics member - Poorly exposed. Includes Clarksburg Volcanics member which is mostly mafic to intermediate pyroclastic rocks in Marquette trough, between Marquette Bay and Champion

Lithology: metavolcanic rock

Menominee and Chocolay Groups, undivided (Early Proterozoic) at surface, covers < 0.1 % of this area

Menominee and Chocolay Groups, undivided - Mapped where units are too thin to show separately on map

Lithology: metasedimentary rock; metavolcanic rock

Bell Shale (Middle Devonian) at surface, covers < 0.1 % of this area

Bell Shale

Lithology: black shale; limestone

Oronto Group; Freda Sandstone (Middle Proterozoic) at surface, covers 0.6 % of this area

Oronto Group; Freda Sandstone - Mainly reddish-brown, medium- to fine-grained lithic arkosic sandstone, siltstone, and micaceous silty shale.

Lithology: arkose; siltstone; shale

Paint River Group; Lower part (Early Proterozoic) at surface, covers < 0.1 % of this area

Paint River Group; Lower part- Includes Stambaugh Formation, Hiawatha Graywacke, Riverton Iron-formation, and Dunn Creek Slate (James and others, 1968). Correlated with lower part of Baraga Group

Lithology: graywacke; iron formation; slate

Coldwater Shale (Mississippian) at surface, covers < 0.1 % of this area

Coldwater Shale - Mostly gray shale

Lithology: shale

Sylvania Sandstone (Early Devonian) at surface, covers < 0.1 % of this area

Sylvania Sandstone

Lithology: sandstone; dolostone (dolomite)

Prairie du Chien Group (Ordovician) at surface, covers < 0.1 % of this area

Prairie du Chien Group - Dolomite with some sandstone and shale; includes Shakopee and Oneota Formations

Lithology: dolostone (dolomite); sandstone; shale

Menominee Group; unexposed magnetic unit (Early Proterozoic) at surface, covers < 0.1 % of this area

Menominee Group; unexposed magnetic unit- Surrounds gneiss domes in Gogebic County, Mich. and Vilas County, Wisc., and occurs in north-central Dickinson County. Probably correlative with part of Blair Creek Formation (unit Xbc). Previously correlated with uppermost unit of Blair Creek Formation (Sims and others, 1984).

Lithology: iron formation; slate

Menominee Group; unexposed magnetic unit (Early Proterozoic) at surface, covers < 0.1 % of this area

Menominee Group; unexposed magnetic unit - Surrounds gneiss domes in Gogebic County, Mich. and Vilas County, Wisc., and occurs in north-central Dickinson County. Probably correlative with part of Blair Creek Formation (unit Xbc). Previously correlated with uppermost unit of Blair Creek Formation (Sims and others, 1984).

Lithology: iron formation; slate

Dacite and volcanogenic graywacke (Early Proterozoic) at surface, covers < 0.1 % of this area

Dacite and volcanogenic graywacke - Includes andesite tuff. Occurs in northeastern Wisconsin. Dacite has age of 1866 +/- 39 Ma.

Lithology: dacite; graywacke; andesite

Powder Mill Group; Siemens Creek Volcanics (Middle Proterozoic) at surface, covers < 0.1 % of this area

Powder Mill Group; Siemens Creek Volcanics- Dark-gray basalt and minor porphyritic andesite. Generally strongly magnetic with reversed remanent magnetism. Underlain by a thin unit of quartzose sandstone (Bessemer Quartzite).

Lithology: basalt; andesite

Mackinac Breccia (Early Devonian) at surface, covers < 0.1 % of this area

Mackinac Breccia

Lithology: limestone; sedimentary breccia

Portage Lake Volcanics; Rhyolite at Bergland (Middle Proterozoic) at surface, covers < 0.1 % of this area

Portage Lake Volcanics; Rhyolite at Bergland

Lithology: rhyolite

Sainte Ignace Dolomite (Late Silurian) at surface, covers < 0.1 % of this area

Sainte Ignace Dolomite

Lithology: dolostone (dolomite)

Oronto Group; Freda Sandstone; Conglomerate member (Middle Proterozoic) at surface, covers < 0.1 % of this area

Oronto Group; Freda Sandstone; Conglomerate member

Lithology: conglomerate

Grand River Formation (Pennsylvanian) at surface, covers 0.3 % of this area

Grand River Formation

Lithology: sandstone; shale

Oronto Group; Freda Sandstone (Middle Proterozoic) at surface, covers < 0.1 % of this area

Oronto Group; Freda Sandstone - Mainly reddish-brown, medium- to fine-grained lithic arkosic sandstone, siltstone, and micaceous silty shale.

Lithology: arkose; siltstone; shale

Prairie du Chien Group (Early Ordovician) at surface, covers 0.9 % of this area

Prairie du Chien Group

Lithology: dolostone (dolomite); sandstone; shale

Paint River Group; Upper part (Early Proterozoic) at surface, covers < 0.1 % of this area

Paint River Group; Upper part - Dominantly Fortune Lakes Slate, but includes other rocks in poorly exposed areas. Correlated with upper part of Baraga Group.

Lithology: slate

Menominee Group; Composite unit of Siamo Slate and Ajibik Quartzite (Early Proterozoic) at surface, covers < 0.1 % of this area

Menominee Group; Composite unit of Siamo Slate and Ajibik Quartzite - Siamo Slate is laminated green siltstone and argillite. Ajibik Quartzite is white, buff, and pink orthoquartzite and less abundant sericite quartzite.

Lithology: quartzite; argillite; siltstone; slate

Stonington Formation (Late Ordovician) at surface, covers 0.5 % of this area

Stonington Formation

Lithology: limestone; shale

Menominee Group; Ironwood Iron-formation (Early Proterozoic) at surface, covers < 0.1 % of this area

Menominee Group; Ironwood Iron-formation- Interbedded cherty and slaty iron-formation. Locally, secondary enrichment has formed "soft ore" bodies. In eastern part of Gogebic Range, Ironwood Iron-formation is intercalated with pyroclastic rocks of Emperor Volcanic Complex, and in eastern half of T. 47 N., R. 43 W. (where mapped within unit Xip) consists entirely of black slate

Lithology: iron formation; slate

Rhyolite to dacite (Early Proterozoic) at surface, covers < 0.1 % of this area

Rhyolite to dacite - Massive to flow-banded rocks of greenschist metamorphic grade in northeastern Wisconsin; virtually undeformed.

Lithology: felsic metavolcanic rock

Basaltic and andesitic breccia (Early Proterozoic) at surface, covers < 0.1 % of this area

Basaltic and andesitic breccia - Exposed in northeastern Wisconsin

Lithology: volcanic breccia (agglomerate)

Granitic rocks (Early Proterozoic) at surface, covers < 0.1 % of this area

Granitic rocks - Gray to pinkish-gray, mottled, medium-grained syenite, granite, and granodiorite. Moderately strong propylitic alteration and weak cataclasis. Forms small bodies south of Crystal Falls, MI (James and others, 1968). A body near Tobin Location has a U-Pb concordia intercept age of 1840 +/-5 Ma (Z.E. Peterman, written communication, 1988). Includes porphyritic red granite that intrudes Lake Archean Dickinson Group - Red mylonitic gneissic granite (about 1970 Ma).

Lithology: syenite; granite; granodiorite

Chocolay Group, undivided (Early Proterozoic) at surface, covers < 0.1 % of this area

Chocolay Group, undivided - In Dickinson County, Mich., includes Randville Dolomite, Sturgeon Quartzite, and Fern Creek Formation. In Marquette range, between Marquette Bay and Champion, includes Wewe Slate, Kona Dolomite, Mesnard Quartzite, and Enchantment Lake Formation

Lithology: quartzite; dolostone (dolomite); slate

Badwater Greenstone (Early Proterozoic) at surface, covers < 0.1 % of this area

Badwater Greenstone - Dark-greenish-gray, pillowed to massive tholeiitic basalt and pyroclastic rocks. Correlated with the Hemlock Formation on basis of geology and similarity in chemical composition.

Lithology: basalt; pyroclastic

Metagabbro (Early Proterozoic) at surface, covers < 0.1 % of this area

Metagabbro - Mafic to ultramafic bodies defined and delineated principally by positive magnetic and gravity anomalies; includes diorite bodies. Comagmatic with unit Xmi

Lithology: gabbro; ultramafic intrusive rock; diorite

Menominee Group; Hemlock Formation (Early Proterozoic) at surface, covers 0.2 % of this area

Menominee Group; Hemlock Formation - Predominantly mafic to intermediate volcanic flows and pyroclastic rocks with interlayered slate and tuff beds

Lithology: basalt; andesite; pyroclastic; slate; tuff

Paleozoic undivided (Paleozoic) at surface, covers < 0.1 % of this area

Paleozoic undivided

Lithology: limestone; dolostone (dolomite); sandstone

Badwater Greenstone (Early Proterozoic) at surface, covers < 0.1 % of this area

Lithology: basalt; pyroclastic

Powder Mill Group; Kallander Creek Volcanics (Middle Proterozoic) at surface, covers < 0.1 % of this area

Powder Mill Group; Kallander Creek Volcanics - Basalt, andesite and lesser rhyolite flows. Basalt flows near base of the formation contain plagioclase phenocrysts, some in radiating clusters

Lithology: basalt; andesite; rhyolite

Salina Group (Silurian) at surface, covers < 0.1 % of this area

Salina Group - Dolomite, gray, yellow-gray to olive-gray, laminated to thin bedded; occasional thin bed and laminae of dark gray shale and anhydrite and/or gypsum; brecciated zones in part.

Lithology: dolostone (dolomite); shale; evaporite

Salina Group (Late Silurian) at surface, covers < 0.1 % of this area

Salina Group

Lithology: evaporite; shale; dolostone (dolomite)

Athelstane Quartz Monzonite (Early Proterozoic) at surface, covers < 0.1 % of this area

Athelstane Quartz Monzonite - Pink, coarse-grained granite to granodiorite containing nearly equal amounts of microcline microperthite, plagioclase, and quartz and 5-10 percent biotite and (or) hornblende. Mafic minerals are interstitial and give a clotty appearance. (1836 +/- 15 Ma)

Lithology: granite; granodiorite

Puritan Quartz Monzonite (Late Archean) (Late Archean) at surface, covers 0.2 % of this area

Puritan Quartz Monzonite (Late Archean) - Pink to pinkish-gray, medium- to coarse-grained, equigranular to inequigranular granite to granodiorite in Puritan batholith south of Gogebic Range. Age 2710 +/- 140 Ma (Sims and others, 1977)

Lithology: granite; granodiorite

Menominee Group; Blair Creek Formation (Early Proterozoic) at surface, covers < 0.1 % of this area

Menominee Group; Blair Creek Formation - Dominantly dark-gray, massive, porphyritic tholeiitic basalt. Includes a basal conglomerate and a lean iron-formation in middle of formation

Lithology: basalt; iron formation; conglomerate

Metagabbro (Early Proterozoic) at surface, covers < 0.1 % of this area

Metagabbro - Mafic to ultramafic bodies defined and delineated principally by positive magnetic and gravity anomalies; includes diorite bodies. Comagmatic with unit Xmi

Lithology: gabbroid; ultramafic intrusive rock; diorite

Porcupine Volcanics; Rhyolite (Middle Proterozoic) at surface, covers < 0.1 % of this area

Porcupine Volcanics; Rhyolite

Lithology: rhyolite

Rhyolite to dacite (Early Proterozoic) at surface, covers < 0.1 % of this area

Rhyolite to dacite - Massive to flow-banded rocks of greenschist metamorphic grade in northeastern Wisconsin; virtually undeformed.

Lithology: felsic metavolcanic rock

Sunbury and Bedford Formations, Undivided (Devonian and/or Mississippian) at surface, covers < 0.1 % of this area

Sunbury and Bedford Formations, Undivided - Shale and siltsone; shale, black to brownish-black, carbonaceous in upper one third of interval, gray to bluish-gray, clayey with occasional siltstone lamina and thin beds in lower two-thirds of interval.

Lithology: shale; black shale; siltstone

Traverse Group (Devonian) at surface, covers < 0.1 % of this area

Traverse Group - Dolomite and shale interbedded with limestone; upper part dolomite; gray to light brown; thin to medium bedded; abundant chert; lower part shale interbedded with limestone; olive gray; thin to medium bedded; very fossiliferous; as much as 170 feet thick.

Lithology: dolostone (dolomite); shale; limestone; chert

Granitic rocks of 1760-Ma age group (Early Proterozoic) at surface, covers < 0.1 % of this area

Granitic rocks of 1760-Ma age group - In northern Wisconsin, granite to granodiorite of varied texture. In southern Wisconsin (not mapped separately), red to pink alkali-feldspar granophyric granite associated with rhyolites of both peraluminous and metaluminous affinities (unit Xr of Marshfield terrane).

Lithology: granite; granodiorite

Metagraywacke (Late Archean) (Late Archean) at surface, covers < 0.1 % of this area

Metagraywacke (Late Archean) - Gray, fine-grained, thin- to thick-bedded, commonly graded graywacke and slate in Marenisco, Mich. area

Lithology: metasedimentary rock; slate

Baraga Group; Tyler Formation (Early Proterozoic) at surface, covers < 0.1 % of this area

Lithology: sandstone; siltstone; iron formation; argillite

Biotite schist (Lake Archean) (Late Archean) at surface, covers < 0.1 % of this area

Biotite schist (Lake Archean) - Quartz-plagioclase-biotite schist of probably intermediate volcanic protolith in area south of Gogebic Range

Lithology: mica schist; gneiss

Basaltic and andesitic breccia (Early Proterozoic) at surface, covers < 0.1 % of this area

Basaltic and andesitic breccia - Exposed in northeastern Wisconsin

Lithology: volcanic breccia (agglomerate)

Metabasalt (Late Archean) (Late Archean) at surface, covers < 0.1 % of this area

Lithology: meta-basalt; tuff; schist

Mellen Intrusive Complex; Granite (about 1000 Ma) (Middle Proterozoic) at surface, covers < 0.1 % of this area

Mellen Intrusive Complex; Granite (about 1000 Ma)

Lithology: granite

Portage Lake Volcanics (Middle Proterozoic) at surface, covers < 0.1 % of this area

Portage Lake Volcanics - Lava flows, mostly basalt, andesite and felsite flows and subordinate interflow sedimentary rocks.

Lithology: basalt; andesite; rhyolite; mudstone

Dundee Limestone (Devonian) at surface, covers < 0.1 % of this area

Dundee Limestone - Limestone; olive gray to brown; upper part thin bedded, lower part medium to thick bedded; fossiliferous in upper part becomes cherty dolomite in lower part; as much as 105 feet thick.

Lithology: limestone; dolostone (dolomite)

Chocolay Group, undivided (Early Proterozoic) at surface, covers < 0.1 % of this area

Lithology: quartzite; dolostone (dolomite); slate

Paint River Group; Lower part (Early Proterozoic) at surface, covers < 0.1 % of this area

Paint River Group; Lower part - Includes Stambaugh Formation, Hiawatha Graywacke, Riverton Iron-formation, and Dunn Creek Slate (James and others, 1968). Correlated with lower part of Baraga Group

Lithology: graywacke; iron formation; slate

Menominee Group; Ironwood Iron-formation (Early Proterozoic) at surface, covers < 0.1 % of this area

Menominee Group; Ironwood Iron-formation - Interbedded cherty and slaty iron-formation. Locally, secondary enrichment has formed "soft ore" bodies. In eastern part of Gogebic Range, Ironwood Iron-formation is intercalated with pyroclastic rocks of Emperor Volcanic Complex, and in eastern half of T. 47 N., R. 43 W. (where mapped within unit Xip) consists entirely of black slate

Lithology: iron formation; slate

Puritan Quartz Monzonite (Late Archean) (Late Archean) at surface, covers < 0.1 % of this area

Lithology: granite; granodiorite

Powder Mill Group; Kallander Creek Volcanics; Upper rhyolite member (Middle Proterozoic) at surface, covers < 0.1 % of this area

Powder Mill Group; Kallander Creek Volcanics; Upper rhyolite member

Lithology: rhyolite

Gabbroic rocks of Keweenawan affinity (Middle Proterozoic) at surface, covers < 0.1 % of this area

Gabbroic rocks of Keweenawan affinity - gabbro, anorthosite, granite, peridotite

Lithology: gabbro; anorthosite; peridotite; granite

Dacite and volcanogenic graywacke (Early Proterozoic) at surface, covers < 0.1 % of this area

Dacite and volcanogenic graywacke - Includes andesite tuff. Occurs in northeastern Wisconsin. Dacite has age of 1866 +/- 39 Ma.

Lithology: dacite; graywacke; andesite

Athelstane Quartz Monzonite (1836 +/- 15 Ma) (Early Proterozoic) at surface, covers < 0.1 % of this area

Athelstane Quartz Monzonite (1836 +/- 15 Ma) - Pink, coarse-grained granite to granodiorite containing nearly equal amounts of microcline microperthite, plagioclase, and quartz and 5-10 percent biotite and (or) hornblende. Mafic minerals are interstitial and give a clotty appearance.

Lithology: granite; granodiorite

Powder Mill Group; Kallander Creek Volcanics; Upper rhyolite member (Middle Proterozoic) at surface, covers < 0.1 % of this area

Powder Mill Group; Kallander Creek Volcanics; Upper rhyolite member

Lithology: rhyolite

Cambrian, undivided (Cambrian) at surface, covers < 0.1 % of this area

Cambrian, undivided - Sandstone with some dolomite and shale, undivided; includes Trempealeau, Tunnel City, and Elk Mound Formations

Lithology: sandstone; dolostone (dolomite); shale

Accessibility FOIA Privacy Policies and Notices

U.S. Department of the Interior | U.S. Geological Survey
URL: http://mrdata.usgs.gov/geology/state/fips-unit.php?state=MI
Page Contact Information: pschweitzer@usgs.gov
Page Last modified: 10:03 on 08-May-2012