Geologic units in Marquette county, Michigan

Migmatitic gneiss and amphibolite (Late to Early Archean) (Archean) at surface, covers 24 % 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.

Gneiss and amphibolite (Late Archean) at surface, covers 19 % 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).

Jacobsville Sandstone (Middle Proterozoic) at surface, covers 10 % of this area

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

Trempealeau Formation (Late Cambrian) at surface, covers 8 % of this area

Trempealeau Formation

Black River Limestone (Late Ordovician) at surface, covers 6 % of this area

Black River Limestone

Prairie du Chien Group (Early Ordovician) at surface, covers 6 % of this area

Prairie du Chien Group

Baraga Group; Michigamme Formation; Gray to black slate (Early Proterozoic) at surface, covers 6 % of this area

Strongly cleaved. Represents lower stratigraphic part of formation

Metabasalt (Late Archean) at surface, covers 5 % 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.

Baraga Group; Michigamme Formation, undivided (Early Proterozoic) at surface, covers 5 % 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

Munising Formation (Late Cambrian) at surface, covers 3 % of this area

Munising Formation

Menominee Group, undivided (Early Proterozoic) at surface, covers 2 % of this area

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

Menominee Group; Negaunee Iron-formation (Early Proterozoic) at surface, covers 2 % of this area

Highly metamorphosed banded iron-formation. Principal iron-formation in Marquette trough and nearby areas. Includes abundant metadiabase sills.

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

Trenton Limestone

Menominee Group; Composite unit of Siamo Slate and Ajibik Quartzite (Early Proterozoic) at surface, covers 1 % of this area

Siamo Slate is laminated green siltstone and argillite. Ajibik Quartzite is white, buff, and pink orthoquartzite and less abundant sericite quartzite.

Chocolay Group, undivided (Early Proterozoic) at surface, covers 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

Baraga Group; Michigamme Formation; Mafic to intermediate flows and pyroclastic rocks, including Clarksburg Volcanics member (Early Proterozoic) at surface, covers 0.5 % 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

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

Predominantly mafic to intermediate volcanic flows and pyroclastic rocks with interlayered slate and tuff beds

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

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