Cloverly Formation

Cloverly Formation Stratigraphic range: Aptian - Albian PreЄ Є O S D C P T J K Pg N
Brightly colored strata of the Himes Member of the Cloverly Formation near Shell, Wyoming.
Type	Geological formation
Underlies	Thermopolis Shale
Overlies	Morrison Formation
Thickness	150-400 ft
Lithology
Primary	Mudstone
Other	Conglomerate, sandstone
Location
Region	Wyoming, Montana, Colorado, Utah
Country	USA
Type section
Named for	Cloverly post office, Wyoming
Named by	Nelson Horatio Darton, 1904

The Cloverly Formation is a geological formation of Early Cretaceous age (Aptian to Albian stage) that is present in parts of Montana, Wyoming, Colorado and Utah in the western United States. It was named for a post office on the eastern side of the Bighorn Basin in Wyoming by N.H. Darton in 1904. The sedimentary rocks of formation were deposited in floodplain environments and contain vertebrate fossils, including a diverse assemblage of dinosaur remains.

The Cloverly Formation rests disconformably on the Morrison Formation and is conformably overlain by the Thermopolis Shale. It is subdivided into a variety of members, depending on the location. In the Bighorn Basin along the Montana-Wyoming border, the Cloverly is divided into the following three members:

Radiometric dating by the fission track method has yielded dates of 115 ± 10 Ma (million years ago) for the lower part of the Little Sheep Member and 108.5 ± 0.2 Ma near the top of that member, confirming that the Cloverly Formation is of Aptian to Albian age.

The sediments of the Cloverly Formation were deposited in alluvial and floodplain environments. The basal conglomerates probably represent braided river deposits, while the sandstones were deposited in fluvial channels. The mudstones that contain most of the fossils represent overbank, lacustrine, and pedogenic deposits.