The Brule Formation is a sequence of fine grained clastic rocks (claystones, mudstones, siltstones) interbedded with freshwater carbonates, volcanic ash (tuff), and sandstonein South Dakota, Nebraska, Colorado, North Dakota, and Wyoming. It was deposited between 34 and 30 million years ago, roughly the Rupelian age (Oligocene). It occurs as a subunit of the White River Group.
Historical description The formation was named by N. H. Darton "for the Brule Indians, who once roamed over Pine Rldge Ind. Res. in southern S. Dak., where the fm. covers large areas, and that it is not present in Brule Ind. Res., which occurs farther NE In S. Dak." Darton's first description stated, "The White River beds In their extension from S. Dak. Into Nebr. present some differences in strat. range and relations. They expand considerably and include, at top, beds which appear not to be represented in the typical regions. Accordingly, to afford distinct definitions for the members in Nebr. I have Introduced the designation Brule clay and separated the underlying Titanotherium beds as Chadron fm. The Brule consists mainly of a hard, sandy clay, of pale-pink color. Thickness about 600 ft. In vicinity of Wyo. line, but diminishes greatly eastward; in vicinity of 103° mer. in NW. comer of Nebr. it is 320 ft. Has not been recognized E. of long. 101°30', where it appears to sink beneath the surface In Platte Valley. Extends far to NB. in So. Dak. Is upper fm. of White River group." N. H. Darton, 1898 (D, 8, G, S, 19th Ann, Eept., p t 4, pp. 736, 766–759). (Abbreviations are in source document.)Lexicon of Geologic Names of the United States, Part 1, A-L. United States Department of the Interior, Geological Survey Bulletin 896, USGS Bulletin 896, 1
Fossil record The sandstones layers, which are up to thick, can contain mammalian fossils (e.g. the Fitterer bed). The most important fossils sites are: Fitterer Ranch Obritsch Ranch M&M Ranch Little Badlands in Stark County, ND Chalky Buttes (including White Butte) in Slope County, ND
Prehistoric catfish, several mammals such as nimravids and Hesperocyon, and sunfish fossils are known from the Brule Formation in Badlands National Park.Hunt, ReBecca K., Vincent L. Santucci and Jason Kenworthy. 2006. "A preliminary inventory of fossil fish from National Park Service units." in S.G. Lucas, J.A. Spielmann, P.M. Hester, J.P. Kenworthy, and V.L. Santucci (ed.s), Fossils from Federal Lands. New Mexico Museum of Natural History and Science Bulletin 34, pp. 63–69.
Notable among the local fauna are Bathornithid birds, ranging from the highly varied wetland-dwelling Bathornis species to the gigantic Paracrax.
Fauna
Fauna reported from the Brule Formation Genus Species Location Stratigraphic position Material Description ImagesProscalops Proscalps tertius Numerous, including upper incisor and molar. Species holotype likely located here.HesperocyonH. gregariusHyaenodonH. horridusHyracodon H. nebraskensisSD, ND, NEJaw fragments, skullsEarly rhinocerosSubhyracodon S. occidentalisNE, SD, ND, WYTeeth and skullsEarly rhinocerosEporeodon E. majorSDIncredibly rareLarge oredodontLeptauchenia L. decoraSD, NETeeth and skullsSmall OreodontMerycoidodon M. culbertsoni M. gracilisSD, ND, NE, WYSkulls, limb bones, and skeletonsOreodontPoebrotherium P. wilsoniSD, ND, NE, WYBones, jaw fragmentsEarly camelLeptomeryxSD, NE, WYTeethDeer-like mammalArchaeotherium A. mortoniWYTeeth and skullsEntelodont
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