Geologic units in Traverse county, Minnesota

Undifferentiated (Cenomanian to Campanian) at surface, covers 73 % of this area

Conglomerate, sandstone, mudstone, shale, marlstone, siltstone, and minor lignite, deposited in marine and non-marine settings; likely Cenomanian to Campanian age. Unit outline is the product of contouring the stratigraphic top and base, from which an isopach grid was created. Because the distribution is patchy, unit boundaries were drawn from the gridded data to represent locations where more than 25 feet (8 meters) of thickness occurs. As a result, many areas outside of the unit boundaries may be overlain by thin Cretaceous strata and the unit is depicted without a contact line.

Volcaniclastic rocks of felsic to intermediate composition (Neoarchean) at surface, covers 11 % of this area

Volcaniclastic rocks of felsic to intermediate composition.

Foliated to gneissic tonalite, granodiorite, and diorite (Neoarchean) at surface, covers 10 % of this area

Foliated to gneissic tonalite, granodiorite, and diorite. Includes the Lookout Mountain tonalite (~2,718 Ma) of the Giants Range batholith and other intrusions within batholithic complexes defined by a low-to-moderate gravity signature with magnetic foliation apparent from aeromagnetic maps.

Schist and tonalitic to granodioritic paragneiss (Neoarchean) at surface, covers 4 % of this area

Schist and tonalitic to granodioritic paragneiss. Typically adjacent to large batholithic complexes.

Mafic metavolcanic rocks (Neoarchean) at surface, covers 0.7 % of this area

Mafic metavolcanic rocks. Includes minor volcaniclastic and hypabyssal intrusive rocks metamorphosed to lower greenschist to lower amphibolite facies; includes the Ely Greenstone (~2,722 Ma).

Granitic intrusion of unknown age (Archean or Paleoproterozoic) at surface, covers 0.5 % of this area

Granitic intrusion of unknown age. Low gravity and magnetic expression.

Schist of sedimentary protolith (Neoarchean) at surface, covers 0.2 % of this area

Schist of sedimentary protolith. Metamorphosed to upper greenschist to amphibolite facies.

Graneros Shale (Upper Cretaceous) at surface, covers 0.1 % of this area

Dark-gray, noncalcareous, pyritic, poorly fossiliferous shale, with numerous sandstone layers at the base. Thickness up to 110 ft (36 m).

Carlile Shale (Upper Cretaceous) at surface, covers < 0.1 % of this area

Dark-gray to black, silty to sandy shale with several zones of septarian, fossiliferous, carbonate concretions. Contains up to three sandstone units in the upper portion of the formation and sandy calcareous marl at the base. Thickness up to 330 ft (100 m).

Precambrian Rocks (Precambrian) at surface, covers < 0.1 % of this area

Greenschists and amphibolites; banded iron formation; stretched pebble conglomerates; metabasalt; serpentinite; felsic tuff; mylonite; intermediate felsic plutonic rocks; migmatite; layered gneiss.

Greenhorn Formation (Upper Cretaceous) at surface, covers < 0.1 % of this area

Gray shale, mudstone, marl, calcarenite, and shaly limestone grading upward into light-gray to tan, alternating marl and thin-bedded, fossiliferous limestone. Thickness up to 40 ft (12 m).

Mafic intrusions including pyroxenite, peridotite, gabbro, and lamprophyre (Paleoproterozoic) at surface, covers < 0.1 % of this area

Mafic intrusions including pyroxenite, peridotite, gabbro, and lamprophyre. Defined largely by magnetic signature. One intrusion in Morrison County is ~1,791 Ma, and lithologically similar intrusions cut the Foley Granite (~1,774 Ma).