Geologic units in Cass county, North Dakota

Additional scientific data in this geographic area

Belle Fourche-Skull Creek, Undivided (Lower to Upper Cretaceous) at surface, covers 49 % of this area

Belle Fourche Formation (as described in Kb). Mowry Formation: medium- to dark-gray shale; marine offshore sediment; as thick as 55 metres (180 feet). Newcastle Formation: light-gray, fine- to medium-grained sandstone; marine shoreline and offshore sediment; as thick as 45 metres (150 feet). Skull Creek Formation: medium-gray to dark-gray shale; marine offshore sediment; as thick as 40 metres (140 feet).

Greenhorn Formation (Upper Cretaceous) at surface, covers 24 % of this area

Dark-gray calcareous shale; marine offshore sediment; as thick as 45 metres (150 feet).

Precambrian Rocks (Precambrian) at surface, covers 13 % of this area

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

Belle Fourche Formation (Upper Cretaceous) at surface, covers 6 % of this area

Medium- to dark-gray, silty to sandy shale; marine offshore sediment; as thick as 105 metres (350 feet).

Carlile Formation (Upper Cretaceous) at surface, covers 5 % of this area

Dark-gray shale; marine offshore sediment; as thick as 120 metres (400 feet).

Inyan Kara (Lower Cretaceous) at surface, covers 2 % of this area

Light-gray, fine to coarse sandstone and gray shale; river, lake, and nearshore marine sediment; as thick as 135 metres (450 feet).

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

Granitic intrusion. Includes the Sacred Heart (~2592, 2,603 Ma) and Ortonville granites, the Shannon Lake Granite (~2,674), and other intrusions having low gravity and magnetic signatures.

Granitoid intrusion (Neoarchean) at surface, covers < 0.1 % of this area

Granitoid intrusion. Constrained solely by low gravity and magnetic signatures.

Mowry-Skull Creek, Undivided (Lower to Upper Cretaceous) at surface, covers < 0.1 % of this area

Mowry, Newcastle, and Skull Creek Formations (as described in Kbs).

Granite to granodiorite (Neoarchean) at surface, covers < 0.1 % of this area

Granite to granodiorite. Variably magnetic.

Undifferentiated (Cenomanian to Campanian) at surface, covers < 0.1 % 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.