Geologic Unit: Benton

Usage:

Benton Shale (CO*,MN*,MT*,NE*,NM,ND*,SD*,WY*)
Benton Formation (CO*,MT*,NM*,SD*,WY*)
Benton Group (CO*,SD)
Called Fort Benton in early reports.

Subunits:

GROUP STATUS (alphabetical): Carlile Shale (CO*,SD), Graneros Shale (CO*,SD), Greenhorn Formation (SD) or Greenhorn Limestone (CO*,SD).
FORMATION STATUS (alphabetical): Codell Sandstone Member (CO*), Graneros Member (CO*), Greenhorn Limestone Member (CO*,NM,SD,WY*), Juana Lopez Member (CO*), Mowry Member (CO).

Geologic age:

Late Cretaceous*

Type section, locality, area and/or origin of name:

Named from Fort Benton, on upper Missouri River, about 40 mi below Great Falls, [central Chouteau Co.], MT. Stratigraphic limits of formation based largely on sections along Missouri River in northern NE, where the Benton Shale rests on Dakota Sandstone and is overlain by Niobrara Limestone (Meek and Hayden, 1862; Wilmarth, 1938).

AAPG geologic province:

Sweetgrass arch*
North Park basin*
Denver basin*
Green River basin*
South Park basin*
Wind River basin*
Powder River basin*