Brule Formation

Brule Formation Stratigraphic range: Rupelian PreЄ Є O S D C P T J K Pg N
Brule Formation in Badlands National Park
Type	Geological formation
Underlies	Sharps Formation, Arikaree Formation
Overlies	Chadron Formation
Thickness	6 to 65 m.
Lithology
Primary	Fine grained clastic rocks
Other	Freshwater limestone, Tuff, Sandstone
Location
Region	North Dakota, South Dakota
Country	United States

The Brule Formation was deposited between 34 and 30 million years ago, roughly the Rupelian (Oligocene). It is a sequence of fine grained clastic rocks (claystones, mudstones, siltstones) interbeded with freshwater carbonates, volcanic ash (tuff), and sandstone.

The sandstones layers, which are up to 3 m thick, can contain mammalian fossils (e.g. the Fitterer bed). The most important fossils sites are:

Cat fish, several mammals such as nimravids and hesperocyon and sunfish fossils are known from the Brule Formation in Badlands National Park. Notable among the local fauna are bathornithid birds, ranging from the highly varied wetland-dwelling Bathornis species to the gigantic Paracrax.