Geologic units in Wisconsin (state in United States)

Additional scientific data in this geographic area

Cambrian, undivided (Cambrian) at surface, covers 31 % of this area

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

Sinnipee Group (Ordovician) at surface, covers 8 % of this area

Dolomite with some limestone and shale; includes Galena, Decorah, and Platteville Formations

Silurian, undivided (Silurian) at surface, covers 8 % of this area

Dolomite, undivided; includes Cayugan, Niagaran, and Alexandrian series

Prairie du Chien Group (Ordovician) at surface, covers 8 % of this area

Dolomite with some sandstone and shale; includes Shakopee and Oneota Formations

Mafic metavolcanic rocks (Early Proterozoic) at surface, covers 6 % of this area

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.

Mafic to felsic metavolcanic rocks (Early Proterozoic) at surface, covers 5 % of this area

Volcanic rocks in areas of sparse geologic data and nondefinitive magnetic and gravity data

Ancell Group (Ordovician) at surface, covers 4 % of this area

Orthoquartzitic sandstone with minor limestone, shale and conglomerate; includes Glenwood and St. Peter Formations

Chengwatana Volcanic Group (Middle Proterozoic) at surface, covers 3 % of this area

Gray basalt flows, interflow breccia, tuff, and minor sedimentary rocks

Granite-tonalite (Early Proterozoic) at surface, covers 3 % of this area

Gray to pinkish-gray, medium-grained, generally equigranular granite to tonalite and granitoid gneiss; locally includes diorite. Intrudes older metavolcanic rocks. Zircon ages range from 1852 +/- 15 to 1862 +/- 5 Ma

Wolf River batholith; Wolf River Granite (Middle Proterozoic) at surface, covers 2 % of this area

Red, coarse-grained rapakivi granite consisting of large (1-3 cm) ovoid alkali feldspar sporadically mantled by plagioclase, interstitial plagioclase, quartz, biotite, hornblende, and ilmenite

Copper Harbor Conglomerate (Middle Proterozoic) at surface, covers 1 % of this area

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.

Maquoketa Formation (Ordovician) at surface, covers 1 % of this area

Shale, dolomitic shale and dolomite; includes overlying Neda Formation (age uncertain) consisting of oolitic iron oxides and shale

Migmatitic gneiss and amphibolite (Late to Early Archean) (Archean) at surface, covers 1 % of this area

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.

Oronto Group; Freda Sandstone (Middle Proterozoic) at surface, covers 1 % of this area

Mainly reddish-brown, medium- to fine-grained lithic arkosic sandstone, siltstone, and micaceous silty shale.

Bayfield Group; Chequamegon Sandstone (Middle Proterozoic) at surface, covers 1 % of this area

Poorly sorted arkosic sandstone

Gneiss, migmatite, and amphibolite (Late Archean) at surface, covers 1 % of this area

Quartzofeldspathic gneiss and less abundant amphibolite and migmatite. Includes granitoid rocks. Granitic gneiss at Port Edwards, WI on Wisconsin River has a U-Pb zircon age of 2870 +/- 13 Ma, and gneiss at Jim Falls in Chippewa River valley has a U-Pb zircon age of 2522 +/- 22 Ma (Sims and others, 1989)

Biotite schist (Early Proterozoic) at surface, covers 1 % of this area

Metamorphosed graywacke in poorly exposed areas in northwestern Wisconsin. Sample at one locality (near Blockhouse Lake, 10 km northeast of Park Falls, T. 40 N., R. 1 E.) has a U-Pb zircon age of 1852 +/- 6 Ma (Sims and others, 1985b)

Wolf River batholith; Red River Granite (Middle Proterozoic) at surface, covers 1.0 % of this area

Contains alkali feldspar phenocrysts (0.5-2 cm), subordinate plagioclase and quartz, and rare clusters of biotite with or without hornblende

Baraga Group; Michigamme Formation, undivided (Early Proterozoic) at surface, covers 0.8 % of this area

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

Gneiss and amphibolite (Late Archean) at surface, covers 0.8 % of this area

Interlayered quartzofeldspathic gneiss and amphibolite in Marenisco, Mich., area and northwestern Wisconsin. Protoliths are bimodal intermediate and mafic volcanic rocks (Sims and others, 1984).

Bayfield Group; Orienta Sandstone (Middle Proterozoic) at surface, covers 0.7 % of this area

Poorly sorted arkosic sandstone

Barron Quartzite (Early Proterozoic) at surface, covers 0.6 % of this area

Pink to maroon to light-gray, medium-grained, moderately sorted quartzite. Red argillite (pipestone) interbedded locally. At least 213 m thick

Granodiorite-tonalite (Early Proterozoic) at surface, covers 0.5 % of this area

Gray, medium-grained intrusive rocks, including intrusion breccias. Exposed in central Wisconsin. Zircon ages range from 1837 to 1847 Ma

Alkali feldspar granite of 1835 Ma age group (Early Proterozoic) at surface, covers 0.5 % of this area

Red to pink, medium-grained leucocratic alkali feldspar granite; contains miarolitic cavities; biotite is altered to opaque oxide minerals; contains fluorite locally. Called red granite previously (Sims, 1990). Exposed in both Pembine-Wausau and Marshfield terranes.

Wolf River batholith; Hager Formation; Rhyolite member (Middle Proterozoic) at surface, covers 0.5 % of this area

Gray to reddish-gray, slightly foliated, porphyritic rhyolite containing aligned phenocrysts of alkali feldspar and lesser amounts of plagioclase in a fine-grained matrix of feldspar, biotite, amphibole, and sparse quartz

Wolf River Batholith; Anorthosite (Middle Proterozoic) at surface, covers 0.5 % of this area

Gray, coarse-grained (1-20 cm) plagioclase-rich (An45-53) rock containing interstitial orthopyroxene, clinopyroxene, Fe-Ti oxides, and apatite.

Felsic metavolcanic rocks of 1835- to 1845-Ma age group (Early Proterozoic) at surface, covers 0.5 % of this area

Rhyolite to dacite and, locally, andesite tuff, breccia, and minor sedimentary rocks, including conglomerate. Exposed in central Wisconsin.

Gneiss and amphibolite (Early Proterozoic) at surface, covers 0.5 % of this area

Interlayered quartzofeldpathic gneiss and amphibolite between Athens shear zone and Owen fault, central Wisconsin

Milladore Volcanic Complex (Early Proterozoic) at surface, covers 0.5 % of this area

Succession of poorly exposed interlayered metavolcanic and metasedimentary rocks. Lithic units described in Sims (1990)

Athelstane Quartz Monzonite (Early Proterozoic) at surface, covers 0.5 % of this area

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)

Bimodal mafic and felsic metavolcanic rocks (Early Proterozoic) at surface, covers 0.4 % of this area

High-aluminum basalt to low-silica andesite pillowed flows and interlayered dacite to rhyolite tuffs and porphyries in Monico and Mountain areas, northeastern Wisconsin. A rhyolite porphyry at Jennings (Oneida County) has an age of 1869 +/- 6 Ma. Rocks are host to massive sulfide deposits (Crandon and Pelican River)

Metagabbro (Early Proterozoic) at surface, covers 0.4 % of this area

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

Granitic rocks of 1760-Ma age group (Early Proterozoic) at surface, covers 0.4 % of this area

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).

Wolf River batholith; Waupaca Granite (Middle Proterozoic) at surface, covers 0.4 % of this area

Rapakivi granite (wiborgite) containing 70-80 percent coarse (1.5 -5 cm) ovoid alkali feldspars mantled by plagioclase, coarse anhedral quartz, and interstitial hornblende and biotite

Rhyolite (Early Proterozoic) at surface, covers 0.4 % of this area

Ash-flow tuffs and interbedded volcaniclastic sedimentary rocks and cogenetic granite (unit Xga) exposed as inliers in southern Wisconsin. In central Wisconsin pink, flow-banded rhyolite and chert-cemented breccia inferred to be 1760 Ma.

Menominee Group; Blair Creek Formation (Early Proterozoic) at surface, covers 0.4 % of this area

Dominantly dark-gray, massive, porphyritic tholeiitic basalt. Includes a basal conglomerate and a lean iron-formation in middle of formation

Puritan Quartz Monzonite (Late Archean) at surface, covers 0.3 % of this area

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)

Felsic volcanic and volcanogenic rocks (Early Proterozoic) at surface, covers 0.2 % of this area

Tuff, argillite, graywacke, and minor volcanic rocks of lower greenschist-facies in southern Rusk County. Could be younger in age than adjacent metavolcanic rocks.

Gabbroic rocks of Keweenawan affinity (Middle Proterozoic) at surface, covers 0.2 % of this area

gabbro, anorthosite, granite, peridotite

Granitic rocks, undivided (Early Proterozoic) at surface, covers 0.2 % of this area

Gray, weakly foliated to massive granite in poorly exposed areas.

Metabasalt (Late Archean) at surface, covers 0.2 % of this area

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.

Porphyritic granite (Early Proterozoic) at surface, covers 0.2 % of this area

Granite containing plagioclase, microcline, and quartz phenocrysts in a fine-grained granophyric matrix. Probably subvolcanic intrusions related to volcanic rocks of 1835- to 1845-Ma age group

Powder Mill Group; Kallander Creek Volcanics (Middle Proterozoic) at surface, covers 0.2 % of this area

Basalt, andesite and lesser rhyolite flows. Basalt flows near base of the formation contain plagioclase phenocrysts, some in radiating clusters

Bayfield Group; Devil's Island Sandstone (Middle Proterozoic) at surface, covers 0.2 % of this area

Well-sorted quartzose sandstone

Traverse Group (Middle Devonian) at surface, covers 0.2 % of this area

Traverse Group

Quartz diorite (Early Proterozoic) at surface, covers 0.1 % of this area

Includes Marinette Quartz Diorite of Dunbar Dome (Sims and others, 1985a) and nearby Twelve Foot Falls Quartz Diorite

Wolf River Batholith; Belongia Granite (Middle Proterozoic) at surface, covers 0.1 % of this area

Red to pink granite consisting of both a coarse-grained and a fine-grained facies. Probably an epizonal intrusion

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

Massive to layered intrusive gabbroic rocks; weakly metamorphosed and deformed. Exposed in both Pembine-Wausau and Marshfield terranes

Fault rocks (Archean to Early Proterozoic) at surface, covers 0.1 % of this area

Mylonitic rocks of uncertain lithology in Eau Pleine shear zone

Wausau Pluton; Granite near Nine Mile Swamp (Middle Proterozoic) at surface, covers 0.1 % of this area

Orange to pink, coarse-grained massive granite composed of alkali feldspar sporadically mantled by plagioclase, quartz, and biotite; contains miarolitic cavities

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

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.

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

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

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

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).

Wolf River batholith; High Falls Granite (Middle Proterozoic) at surface, covers 0.1 % of this area

Gray to pink, equigranular to porphyritic granite to granodiorite containing microcline microperthite, concentrically zoned plagioclase, quartz, biotite, and hornblende

Wausau Pluton; Quartz syenite (Middle Proterozoic) at surface, covers 0.1 % of this area

Contains flow-oriented xenoliths of biotite schist and sillimanite-bearing quartzite

Granite near Cherokee (Early Proterozoic) at surface, covers < 0.1 % of this area

Pink, coarse-grained granite consisting of microcline microperthite and oligoclase phenocrysts in a fine-grained matrix of quartz, potassium feldspar, and oligoclase. Hornblende and (or) biotite occur in clots

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

Oronto Group; Freda Sandstone; Conglomerate member

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

Maroon but locally white, gray, and red quartzite (quartz arenite) with a basal quartzose conglomerate. At Flambeau Ridge (Chippewa County) consists of conglomerate. Distinguished from other quartzite units in being strongly deformed and metamorphosed. Includes Flambeau, Rib Mountain, McCaslin, and Thunder Mountain Quartzites of local usage

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

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

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

Medium-gray, mottled, medium-grained, equigranular tonalite and granodiorite. Intrudes rocks of the Milladore Volcanic Complex.

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

Granophyre

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

Lava flows, mostly basalt, andesite and felsite flows and subordinate interflow sedimentary rocks.

Spikehorn Granite and Bush Lake Granites, undivided (Early Proterozoic) at surface, covers < 0.1 % of this area

Gray to pinkish-gray, fine- to medium-grained, massive granite containing scattered phenocrysts of potassium feldspar. Exposed in northeastern Wisconsin

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

Mafic to felsic flows, pyroclastic rocks, impure quartzite, and conglomerate in Eau Claire River, Eau Claire and northern Clark Counties. Rhyolite has zircon ages of 1,858 +/- 5 Ma. Possibly correlative with Milladore Volcanic Complex.

Wausau Pluton; Granite near Big Eau Pleine Reservoir (Middle Proterozoic) at surface, covers < 0.1 % of this area

Pink to red, medium- to fine-grained granite containing miarolitic cavities

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

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

Stettin pluton (Middle Proterozoic) at surface, covers < 0.1 % of this area

Pyroxene syenite, amphibole syenite, tabular syenite, and nepheline syenite. Age approximately 1520 Ma (Sood and others, 1980).

Rhyolite at and near Cary Mound and near Brokaw (Early Proterozoic) at surface, covers < 0.1 % of this area

Flow-banded rhyolite, welded tuff, volcanic conglomerate, and volcanogenic sedimentary rocks. Exposed in both Pembine-Wausau and Marshfield terranes.

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

Gray, green, and brown lithic siltstone, shale, and sandstone. Copper sulfides and native copper occur locally near base

Baraga Group; Michigamme Formation; Banded cherty and slaty iron-formation (Early Proterozoic) at surface, covers < 0.1 % of this area

Baraga Group; Michigamme Formation; Banded cherty and slaty iron-formation

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

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

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

Wausau Pluton; Aplite (Middle Proterozoic) at surface, covers < 0.1 % of this area

Pale-orange to pink, fine-grained porphyritic aplite

Tuff breccia schist and minor iron-formation (Late Archean) at surface, covers < 0.1 % of this area

Pink and gray, layered quartzofeldspathic schist of intermediate volcanic composition and associated thin iron-formation. Felsic gneiss at Arbutus Dam on Black River at Hatfield has U-Pb zircon age of about 2800 Ma (Sims and others, 1989)

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

Mellen Intrusive Complex; Granite (about 1000 Ma)

Peshtigo Mangerite in the Wolf River batholith; Peshtigo Mangerite (Middle Proterozoic) at surface, covers < 0.1 % of this area

Brown to dark-gray, coarse-grained (0.3-1.5 cm) inequigranular monzonite containing subhedral, zoned plagioclase, alkali feldspar, mafic silicates (fayalite, hypersthene, ferroaugite-hedenbergite, hornblende, and biotite), and interstitial quartz

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

Interlayered gabbro, mafic accumulates, gabbroic anorthosite and anorthosite (Cummings, 1984) in Eau Claire River (T. 27 N., R. 8 W.). Age uncertain, but interpreted as Archean (Sims, 1990).

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

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

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

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

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

Medium-grained granodiorite gneiss in northwestern Marathon County.

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

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

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

Mapped where units are too thin to show separately on map (Gogebic Range). Palms Formation includes Bad River Dolomite and Sunday Quartzite of Chocolay Group

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

Pale-red, medium- to fine-grained, leucocratic, mylonite gneiss exposed near Neillsville, Wisc.

Mellen Intrusive complex; Olivine gabbro (Middle Proterozoic) at surface, covers < 0.1 % of this area

Mellen Intrusive complex; Olivine gabbro

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

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

Diabase, gabbro, and ferromonzodiorite (Mesoproterozoic) at surface, covers < 0.1 % of this area

Diabase, gabbro, and ferromonzodiorite. Primarily sills including the Endion, Lester River, Silver Cliff, Stony Point, Split Rock, Lafayette Bluff, Lake Clara–Lichen Lake, Pigeon River, and Reservation River intrusions.

Wolf River batholith; Hager Formation; Quartz porphyry member (Middle Proterozoic) at surface, covers < 0.1 % of this area

Contains 30-45 percent resorbed quartz phenocrysts (3-4 mm) and less abundant alkali feldspar and plagioclase phenocrysts (4-5 mm) in a fine-grained matrix of quartz, two feldspars, biotite, and hornblende

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

Exposed in northeastern Wisconsin

Basalt and basaltic andesite (Mesoproterozoic) at surface, covers < 0.1 % of this area

Basalt and basaltic andesite. Includes the Leif Erickson, Lakeside (~1,098 Ma), Sucker River, Larsmont, Two Harbors, Crow Creek, Gooseberry River, Gustafson Hill, Baptism River, Good Harbor Bay, Cascade River, Croftville, Red Cliff, and Marr Island lavas.

Schroeder-Lutsen basalts (Mesoproterozoic) at surface, covers < 0.1 % of this area

Unconformably overlies units described below (Mns, Mnu, Mnr, and Mnb).

Middle and Upper Cambrian (Middle and Upper Cambrian) at surface, covers < 0.1 % of this area

Sandstone, siltstone, and shale; includes the Wonewoc Sandstone, Eau Claire Formation, and Mt. Simon Sandstone.

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

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

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

Poorly exposed. Includes Clarksburg Volcanics member which is mostly mafic to intermediate pyroclastic rocks in Marquette trough, between Marquette Bay and Champion

Banded iron-formation and associated volcanogenic rocks (Late Archean) at surface, covers < 0.1 % of this area

Magnetite-quartz iron-formation and associated talc schist in aluminous quartzofeldspathic schist (unit Wt)

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

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

Wonewoc Formation (Middle-Upper Cambrian, upper Marjuman-Steptoean (formerly upper Dresbachian-lower Franconian)) at surface, covers < 0.1 % of this area

Surface exposures limited to northeastern Allamakee County; subcrops beneath Mississippi River alluvium in Allamakee County. Includes Ironton and Galesville members. Primary lithology: sandstone, fine to coarse grained, upper part fossiliferous (Ironton). Thicknesses: 125-155 ft (38-47 m).

Jordan Sandstone, St Lawrence and Lone Rock formations (Upper Cambrian, upper Steptoean-Sunwaptan-lower Skullrockian [formerly middle Franconian-Trempealeauan)) at surface, covers < 0.1 % of this area

Surface exposures limited to Allamakee and northeast Clayton counties; subcrops beneath Mississippi River alluvium in southern Allamakee and Clayton counties. Primary lithologies: sandstone, very fine to coarse grained, quartzose to feldspathic (Jordan); silty dolomite to dolomitic siltstone (St. Lawrence); sandstone, very fine to fine grained, glauconitic to very glauconitic, common greensands (Lone Rock). Secondary lithologies: siltstone, part argillaceous (St. Lawrence, Lone Rock). Minor: silty shale partings (St. Lawrence, Lone Rock); dolomite, part sandy; intraclastic dolomite, sandstone, and siltstone. Maximum thicknesses of total interval: 260-310 ft (79-95 m). Formation thicknesses: Lone Rock Fm, 110-140 ft (34-43 m); St. Lawrence Fm, 60-80 ft (18-24 m); Jordan Sandstone, 80-110 ft (244-34 m).

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

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

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

Red, brown, and white quartzose sandstone, and minor siltstone, shale and conglomerate

Prairie Du Chien Group and St. Peter Sandstone (Prairie du Chien, Lower Ordovician, Ibexian (Tremadocian-lower Floian); St. Peter, Middle-Upper Ordovician, Whiterockian (upper Darriwilian-lower Sandbian).) at surface, covers < 0.1 % of this area

Prairie du Chien Group includes Oneota Fm (Coon Valley, Hager City members) and Shakopee Fm (New Richmond Sandstone, Willow River members); St. Peter Sandstone includes Readstown and Tonti members. Sub-St. Peter erosional surface bevels and locally truncates Prairie du Chien strata. Primary lithologies: dolomite, part cherty, part sandy, mostly unfossiliferous, common voids and vugs (Prairie du Chien); sandstone, quartzose, very fine to medium grained (St. Peter, Shakopee). Secondary lithologies: dolomite, laminated to stromatolitic, part intraclastic; dolomite, fossil molds (primarily mollusks); interbedded very fine to fine sandstone and dolomite (Coon Valley, Shakopee); conglomerate, dolomite and chert clasts in sandy matrix (Readstown). Minor: oolitic dolomite and oolitic chert (Shakopee); shale, green, part sandy (Shakopee); shale, green-brown to gray, part laminated, silty to sandy, part fossiliferous (locally in St. Peter of Winneshiek Co.); coarse sand grains (St. Peter, Shakopee); breccia, dolomite-chert clasts; chalcedony/quartz nodules. Maximum thicknesses total interval: generally 300-400 ft (90-120 m), may reach thicknesses to 700 ft (210 m) (locally thick St. Peter in Winneshiek Co.). Unit thicknesses: Prairie du Chien Group, 225-335 ft (69-102 m), locally thinner where overlain by thick St. Peter; Oneota Fm, 130-225 ft (40-69 m), locally thinned beneath thick St. Peter; Shakopee Fm, 55-100 ft (17-30 m), locally thinned to absent beneath thick St. Peter; St. Peter Sandstone, generally 40-75 ft (12-23 m), varies 25-225 ft (8-69 m), may locally reach thicknesses to 700 ft (210 m) in Winneshiek Co.

Migmatitic gneiss and amphibolite (Late to Early Archean) (Archean) at surface, covers < 0.1 % of this area

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.

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

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.

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

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

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

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.

Sandstone, siltstone, and local conglomerate (Mesoproterozoic) at surface, covers < 0.1 % of this area

Sandstone, siltstone, and local conglomerate. Includes the Hinckley Sandstone and Fond du Lac (youngest detrital zircons ~1,000 Ma) and Solar Church Formations; deposition in eolian, fluvial, and lacustrine environments.

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

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

Anorthositic intrusions and inclusions, undifferentiated (Mesoproterozoic) at surface, covers < 0.1 % of this area

Anorthositic intrusions and inclusions, undifferentiated (~1,099 Ma).

Trempealeau Formation (Late Cambrian) at surface, covers < 0.1 % of this area

Trempealeau Formation

Munising Formation (Late Cambrian) at surface, covers < 0.1 % of this area

Munising Formation

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

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

Eau Claire Formation (Middle Cambrian, upper Marjuman (formerly Dresbachian)) at surface, covers < 0.1 % of this area

Subcrops beneath Mississippi River alluvium in Allamakee County; surface exposures absent. Primary lithologies: sandstone, very fine to fine grained, part argillaceous; shale, silty, gray to green-gray, part glauconitic. Secondary lithology: siltstone, part argillaceous, part dolomitic. Minor: dolomite. Thicknesses: 120-145 ft (37-44 m).

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

Sandstone, siltstone, shale, and dolostone; includes the Jordan Sandstone and St. Lawrence Formation, and the Mazomanie, Lone Rock, and Davis Formations of the Tunnel City Group.

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

Lava flows, mostly basalt, andesite and felsite flows and subordinate interflow sedimentary rocks.

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

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

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

Red, brown, and white quartzose sandstone, and minor siltstone, shale and conglomerate

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

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).

Ferromonzodiorite forming the upper contact zone (Mesoproterozoic) at surface, covers < 0.1 % of this area

Ferromonzodiorite forming the upper contact zone.

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

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)

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

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.

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

Trenton Limestone

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

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

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

Dominantly dark-gray, massive, porphyritic tholeiitic basalt. Includes a basal conglomerate and a lean iron-formation in middle of formation

Gneiss and amphibolite (Late Archean) at surface, covers < 0.1 % of this area

Interlayered quartzofeldspathic gneiss and amphibolite in Marenisco, Mich., area and northwestern Wisconsin. Protoliths are bimodal intermediate and mafic volcanic rocks (Sims and others, 1984).

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

Basalt, andesite and lesser rhyolite flows. Basalt flows near base of the formation contain plagioclase phenocrysts, some in radiating clusters

Copper Harbor Conglomerate (Middle Proterozoic) at surface, covers < 0.1 % of this area

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.

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

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

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

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

Poorly exposed. Includes Clarksburg Volcanics member which is mostly mafic to intermediate pyroclastic rocks in Marquette trough, between Marquette Bay and Champion

Clam Falls volcanic sequence (Mesoproterozoic) at surface, covers < 0.1 % of this area

Clam Falls volcanic sequence (~1,102 Ma).

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

Mainly reddish-brown, medium- to fine-grained lithic arkosic sandstone, siltstone, and micaceous silty shale.

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

Mapped where units are too thin to show separately on map

Gabbro (Mesoproterozoic) at surface, covers < 0.1 % of this area

Gabbro. Includes the Western Margin, Greenwood Lake, Bald Eagle (~1,098), Lake One, Lake Three, Wilder Lake, and Osier Lake intrusions.

Minong volcanic sequence (Mesoproterozoic) at surface, covers < 0.1 % of this area

Minong volcanic sequence (~1,095 Ma).

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

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

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

Gray, green, and brown lithic siltstone, shale, and sandstone. Copper sulfides and native copper occur locally near base

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

Exposed in northeastern Wisconsin

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

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

Mt. Simon Sandstone (Middle Cambrian undifferentiated) at surface, covers < 0.1 % of this area

Subcrops beneath Mississippi River alluvium in northeastern Allamakee County; surface exposures absent. Overlies erosional surface on Precambrian granitic basement rocks. Primary lithology: sandstone, very fine to very coarse grained, part iron-stained. Minor: shale, silty to sandy, gray, red, green; quartz granules; granitic pebbles. Thicknesses: 365-405 ft (111-123 m).

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

Oronto Group; Freda Sandstone; Conglomerate member

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

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

Chengwatana volcanic rocks (Mesoproterozoic) at surface, covers < 0.1 % of this area

Primarily mafic flows.