GEOLEX

Summary of Citation: Chadron

Publication:
Darton, N.H., 1899, Preliminary report on the geology and water
   resources of Nebraska west of the one hundred and third
   meridian: U.S. Geological Survey Annual Report, 19, p.
   721-785

Usage in Publication:
Chadron formation*

Modifications:	Geologic Province:	Dominant Lithology:
First used	Denver basin Chadron arch	Clay Gravel

Summary:
Rocks assigned to Chadron formation, lower formation of White River group, in this report were known as "Titanotherium beds" in earlier reports because of the occurrence of bones and teeth in the formation. Intent to name, source of geographic name, and type locality not stated. Extends as a narrow outcrop zone across northern portion of state (geologic map) in Sioux Co, NE, Denver basin; Dawes and Sheridan Cos, NE on the Chadron arch. Is exposed along North Platte River near the WY state line. Known to underlie parts of CO and SD, but does not extend very far east in NE. Is absent along Republican River. Consists of light green-gray sandy clay and dark red gravel beds several ft thick. Varies from 30 to 60 ft thick. Overlies Pierre shale or clay. Underlies Brule clay (named). Many sketches of stratigraphic sections and photographs. Of Tertiary age.

Summary of Citation: Chadron

Publication:
Smith, W.S.T., 1903, Description of the Hartville quadrangle
   [Wyoming]: U.S. Geological Survey Geologic Atlas of the United
   States, Hartville folio, no. 91, 6 p.

Usage in Publication:
Chadron formation*

Modifications:	Geologic Province:	Dominant Lithology:
Areal limits Overview	Denver basin

Summary:
Geographically extended from the Scotts Bluff area, NE into the Hartville area, Platte Co, WY in the Denver basin. Exposures of Chadron confined to the Goshen Hole area, southwest corner of the geologic map where it is 60+ ft thick. Is younger than the Cretaceous Graneros formation (also extended into the map area) and underlies Oligocene Brule formation (extended into map area) in report area. Consists of clay, sand, and sandstone of various colors. The sandstones are hard, ridge forming, coarse and cross-bedded. The upper limit of the formation is uncertain. Teeth of the fossil TITANOTHERIUM are abundant in different beds. Columnar section. Oligocene age.

Summary of Citation: Chadron

Publication:
Nace, R.L., 1939, Geology of the northwest part of the Red
   Desert, Sweetwater and Fremont Counties, Wyoming: Wyoming
   Geological Survey Bulletin, no. 27, 51 p.

Usage in Publication:
Chadron formation

Modifications:	Geologic Province:	Dominant Lithology:
Revised	Wind River basin Greater Green River basin

Summary:
Revised in that the basal conglomerate formerly called Sweetwater member is renamed Beaver Divide conglomerate member of Chadron formation of White River group. Name Sweetwater is preempted. Beaver Divide overlain by an unnamed upper part of Chadron. Beaver Divide is about 68+/-ft thick. The upper part is about 450 ft thick. Geologic map; cross section; stratigraphic table. Lower contact also revised in that Beaver Divide disconformably overlies the newly named Continental Peak formation. Mapped in Fremont Co in the Wind River basin and in Sweetwater Co in the Greater Green River basin. Oligocene age.

Summary of Citation: Chadron

Publication:
Clark, J., 1954, Geographic designation of the members of the
   Chadron formation in South Dakota: Carnegie Museum Annals,
   v. 33, art. 11, p. 197-198

Usage in Publication:
Chadron formation

Modifications:	Geologic Province:	Dominant Lithology:
Revised	Williston basin

Summary:
Standard section for Chadron in Big Badlands is the south fork of Indian Creek, Pennington Co, SD, Williston basin from sec 34, T3S, R12E to sec 10, T4S, R12E. Designation lower, middle and upper members changed to Ahearn, Crazy Johnson, and Peanut Peak members (all new). No descriptive information included with new members. [All three not adequately defined.] Of early Oligocene age. [Term White River Group not used.]

Summary of Citation: Chadron

Publication:
Bump, J.D., 1956, Geographic names for members of the Brule
   formation of the Big Badlands of South Dakota: American
   Journal of Science, v. 254, no. 7, p. 429-432

Usage in Publication:
Chadron formation

Modifications:	Geologic Province:	Dominant Lithology:
Revised	Williston basin

Summary:
Revised in that Chadron formation, lower formation of White River group, underlies the newly named Scenic member of the Brule formation in the Big Badlands area, south of Scenic, Pennington Co, SD in the Williston basin. Oligocene age. Lower part of Scenic is the 36 ft thick pink-gray clay fossiliferous unit of the lower nodular zone that weathers brown gray and that lies above limestones and clays of the Chadron.

Summary of Citation: Chadron

Publication:
Malhotra, C.L. and Tegland, E.R., 1960, A new Tertiary formation
   in Harding County, South Dakota: South Dakota Academy of
   Sciences Proceedings, 60th series, v. 38, no. 2, p. 263-274

Usage in Publication:
Chadron formation

Modifications:	Geologic Province:	Dominant Lithology:
Revised	Williston basin

Summary:
Revised in that the lower 39 ft formerly included in the Chadron is removed from the Chadron and named Slim Buttes formation in the area of Slim Buttes, Harding Co, SD in the Williston basin. These rocks now assigned to the Slim Buttes are the predominately white sandstone that have a Duchnesean or basal Oligocene vertebrate fauna and that on the basis of heavy mineral studies were determined as derived from igneous rocks probably in the Big Horn Mountains. No true Chadron known in the northern Slim Buttes or the report area. Chadron is early Oligocene age which author distinguishes from basal Oligocene. Term White River group not mentioned.

Summary of Citation: Chadron

Publication:
Hickey, L.J., 1977, Stratigraphy and paleobotany of the Golden
   Valley Formation (early Tertiary) of western North Dakota:
   Geological Society of America Memoir, 150, 181 p.

Usage in Publication:
Chadron Formation

Modifications:	Geologic Province:	Dominant Lithology:
Revised	Williston basin

Summary:
Lower contact revised in that the Oligocene Chadron Formation, basal formation of the White River Group, unconformably overlies the newly named Camels Butte Member of Golden Valley Formation in western ND in the Williston basin. Lower Chadron is an arkosic, fine- to coarse-grained, angular, non-calcareous, somewhat tuffaceous sandstone. The grains are mostly quartz and feldspar. Conglomerate lenses in the sandstone contain clasts that range from granules to cobbles of volcanics (welded tuff, quartz latite porphyry, and rhyolite) transported from the Absaroka volcanic field in northwest WY. Other constituents in the conglomerate are granite, chert, petrified wood, crystalline rocks, and some granules of clinker. Where reworked Golden Valley material present in lower Chadron, the lower Chadron contact difficult to select. The underlying upper Camels Butte has been leached and oxidized to depth of 7 to 30 m beneath the unconformity. Brilliant colors developed in the zone of weathering. Camels Butte was designated upper member of Golden Valley in earlier reports. Correlation chart. Mapped as White River Group [undivided] on the geologic map. White River is as much as 76 m thick in the map area. Chadron underlies Brule Formation of the White River. White River underlies Arikaree Formation.

Summary of Citation: Chadron

Publication:
Retallack, G.J., 1983, Late Eocene and Oligocene paleosols from
   Badlands National Park, South Dakota: Geological Society of
   America Special Paper, 193, 82 p.

Usage in Publication:
Chadron Formation

Modifications:	Geologic Province:	Dominant Lithology:
Overview	Williston basin Sioux uplift

Summary:
Rests on Slim Buttes Formation unconformably and underlies Brule Formation unconformably in Williston basin and Sioux uplift. Includes Ahearn Member, a volcanic ash at base which has an age of 37.2 +/-0.7 m.y. date. Has popcorn-weathered surface. Is largely claystone breccia. Some sandstone channels. Has numerous paleosols. Most of formation in Pinnacles area of the Park is probably equivalent to Peanut Peak Member of Chadron farther west. Climate was probably humid and subtropical to subhumid and warm temperate. Root traces indicate a woodland area. Deposited on floodplains. Vertebrate fossils from stream and near stream deposits. Fossil root traces. Is of early Oligocene age.

Summary of Citation: Chadron

Publication:
Prothero, D.R. and Swisher, C.C., III, 1992, Magnetostratigraphy
   and geochronology of the terrestrial Eocene-Oligocene transition
   in North America, IN Prothero, D.R., and Berggren, W.A.,
   eds., Eocene-Oligocene climatic and biotic evolution: Princeton
   University Press, p. 46-73

Usage in Publication:
Chadron Formation

Modifications:	Geologic Province:	Dominant Lithology:
Age modified Isotopic dating	Wind River basin

Summary:
40Ar/39Ar dates on biotite from the "Purple White Layer" (PWL) yielded a mean age of 33.91 +/-0.06 Ma (latest Eocene). PWL is an ash that marks boundary between Chadron Formation and overlying Orella Member of Brule Formation and marks the Chadronian-Orellan North American Land Mammal "Age" boundary and the Eocene-Oligocene boundary. Thus, the Chadronian and Chadron are now latest Eocene age and the Orellan and lower part of Brule are earliest Oligocene age. Ash samples taken from Flagstaff Rim section in Natrona Co, south-central WY, Wind River basin. Tables of isotopic dates.

Summary of Citation: Chadron

Publication:
Swinehart, J.B. and Diffendal, R.F., Jr., 1997, Geologic map of
   the Scottsbluff 1 degrees x 2 degrees quadrangle, Nebraska
   and Colorado: U.S. Geological Survey Miscellaneous Investigations
   Series Map, I-2545, 1 sheet, scale 1:250,000

Usage in Publication:
Chadron Formation*

Modifications:	Geologic Province:	Dominant Lithology:
Mapped 1:250k (Scottsbluff quad, NE)	Denver basin Chadron arch	Claystone Mudstone

Summary:
Mapped as upper Eocene formation in western NE (Denver basin). Chadron is lower formation of White River Group (lower Oligocene and upper Eocene). Chadron described as claystone and mudstone, gray, greenish-gray, and pink; bentonitic. Underlies almost all of quad but crops out only in very small area near northwest corner of quad; lower part not exposed. Drill-hole data reveal fine- to coarse-grained sandstone, claystone, and mudstone in paleovalleys. Is oldest unit mapped in quad; underlies Brule Formation (lower Oligocene) of White River. Exposed thickness is 25 ft; maximum thickness in subsurface is about 270 ft.