Carlile Shale

The Carlile Shale is a Turonian age Upper/Late Cretaceous series shale geologic formation in the central-western United States, including in the Great Plains region of Colorado, Kansas, Nebraska, New Mexico, North Dakota, South Dakota, and Wyoming.

History of investigation
The Carlile Shale was first named by Grove Karl Gilbert for exposures at Carlile Spring, located about 21 mi west of Pueblo, Colorado. He described it as a medium gray shale, capped with limestone or sandstone, and assigned it to the Benton Group. By 1931, William Walden Rubey and his coinvestigators had mapped it into Kansas and the Black Hills. Rubey also first assigned it to the Colorado Group. C.H. Dane assigned it to the Mancos Shale in New Mexico in 1948.

Description
The formation is composed of marine deposits of the generally retreating phase (hemi-cycle) of the Greenhorn cycle of the Western Interior Seaway, which followed the advancing phase of the same cycle that formed the underlying Graneros Shale and Greenhorn Formation. As such, the lithology progresses from open ocean chalky shale (with thin limestones) to increasing carbonaceous shale to near-shore sandstone. Near the center of the seaway, currents in the remnant shallows sorted skeletal remains into a mass of calcareous sand. The contact between the Carlile Shale and the overlying Niobrara Formation is marked by an unconformity in much of the outcrop area, but where an unconformity is not discernible, the boundary is typically placed at the first resistant, fine-grained limestone bed at the base of the Niobrara Formation.

Fossil content
Upper Turonian series plesiosaur remains are among the fossils that have been recovered from the strata of its Blue Hill Shale Member in Kansas. The Carlile in eastern South Dakota contains shark teeth, fossil wood and leaves, and ammonites.