Geologic units in Baraga county, Michigan

Additional scientific data in this geographic area

Baraga Group; Michigamme Formation, undivided (Early Proterozoic) at surface, covers 32 % 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 26 % of this area

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

Baraga Group; Michigamme Formation; Gray to black slate (Early Proterozoic) at surface, covers 20 % of this area

Strongly cleaved. Represents lower stratigraphic part of formation

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).

Baraga Group; Volcanic-sedimentary unit (Early Proterozoic) at surface, covers 2 % of this area

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

Menominee Group; Hemlock Formation (Early Proterozoic) at surface, covers 0.8 % of this area

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

Migmatitic gneiss and amphibolite (Late to Early Archean) (Archean) at surface, covers 0.4 % 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.

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

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