GEOLEX

Summary of Citation: Montana

Publication:
Eldridge, G.H., 1888, On some stratigraphical and structural
   features of the country about Denver, Colorado: Colorado
   Scientific Society Proceedings, v. 3, pt. 1, p. 86-118

Usage in Publication:
Montana group*

Modifications:	Geologic Province:	Dominant Lithology:
Overview	Denver basin

Summary:
Name Montana group will be used for the Fort Pierre and Fox Hills, and the Fox Hills will include both the Fort Pierre and the Fox Hills as Meek and Hayden defined them in a forthcoming in American Journal of Science (footnote on p. 93-94). Called a "member of the Cretaceous."

Summary of Citation: Montana

Publication:
Stebinger, E., 1914, The Montana group of northwestern Montana:
   U.S. Geological Survey Professional Paper, 90, p. 62-68

Usage in Publication:
Montana group*

Modifications:	Geologic Province:	Dominant Lithology:
Revised	Sweetgrass arch

Summary:
In northwest MT in and near the Blackfoot Indian Reservation, Glacier Co on the Sweetgrass arch, the formations in the Montana group are very different from those on the Missouri and Musselshell Rivers in the central part of the state. A section in valley of Two Medicine River from its mouth in T31N, R5W to a point 3 mi above T31N, R9W studied. Section starts above Colorado shale. Montana group above the Colorado is divided into (ascending): Virgelle sandstone (first used), Two Medicine formation (first used), Bearpaw shale, and Horsethief sandstone (newly assigned to Montana group). Cross section shows relations of the sequence in Two Medicine River valley with units between southern Alberta and the Black Hills. Virgelle is equivalent to the lower Eagle of central MT. Two Medicine tongues into the Claggett and Judith River of central MT. Horsethief is equivalent to Lennep of central MT. Overlain by rocks of continental origin designated "St. Mary River beds of Dawson." Late Cretaceous age inferred.

Summary of Citation: Montana

Publication:
Bowen, C.F., 1915, The stratigraphy of the Montana group, with
   special reference to the position and age of the Judith River
   formation in north-central Montana: U.S. Geological Survey
   Professional Paper, 90, p. 95-153

Usage in Publication:
Montana group*

Modifications:	Geologic Province:	Dominant Lithology:
Revised	Central Montana uplift Sweetgrass arch

Summary:
Revised in that the lower massive persistent sandstone member of the Eagle sandstone, basal formation of the Montana group, is named Virgelle sandstone member. Overlies Colorado shale. Underlies Lance formation. Divided into the (ascending): Eagle sandstone, Claggett formation, Judith River formation, and Bearpaw shale. Geologic map of area from Judith on the Missouri River in Fergus Co south to Musselshell in Musselshell Co, MT on the Central Montana uplift. Virgelle member named for locality on the Missouri River, Chouteau Co, MT on the Sweetgrass arch. Late Cretaceous age.

Summary of Citation: Montana

Publication:
Darton, N.H., 1919, Description of the Newell quadrangle, South
   Dakota: U.S. Geological Survey Geologic Atlas of the United
   States, Newell folio, no. 209, 7 p.

Usage in Publication:
Montana group*

Modifications:	Geologic Province:	Dominant Lithology:
Areal limits	Williston basin

Summary:
Name extended to Black Hills region, Butte and Meade Cos, SD in Williston basin, to include Pierre shale and overlying Fox Hills sandstone. Underlain by Niobrara formation; overlain by Lance formation. Late Cretaceous in age.

Summary of Citation: Montana

Publication:
Schultz, A.R., 1920, Oil possibilities in and around Baxter
   basin, in the Rock Springs uplift, Sweetwater County, Wyoming:
   U.S. Geological Survey Bulletin, 702, 107 p.

Usage in Publication:
Montana group*

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

Summary:
Revised in that Montana group divided into (ascending): the Baxter shale (new), Blair formation (new), Mesaverde formation, and Lewis shale in Sweetwater Co, WY in the Greater Green River basin. Ranges from 3,500 to 6,300 ft thick in report area. Geologic map. Stratigraphic charts. Only Blair and Baxter described. Of Late Cretaceous age.

Summary of Citation: Montana

Publication:
Lavington, C.S., 1933, Montana group in eastern Colorado: American
   Association of Petroleum Geologists Bulletin, v. 17, no. 4,
   p. 397-410

Usage in Publication:
Montana group

Modifications:	Geologic Province:	Dominant Lithology:
Revised	Las Vegas-Raton basin

Summary:
Divided into Pierre shale (base) and Fox Hills sandstone (top). Is 4,300 to 6,000+ ft thick. Contact between Pierre and Fox Hills is gradational. Pierre divided into 5 zones (ascending): barren zone, rusty zone, tepee zone, cone-in-cone zone, and transition zone. Cross sections. Barren zone includes a 20 ft thick sandstone called Apache sandstone member (first used); the new member attributed to an unpublished report by H. W. C. Prommel. Report area concerned with Denver and Las Vegas-Raton basins. Of Late Cretaceous age.

Summary of Citation: Montana

Publication:
Viele, G.W. and Harris, F.G., III, 1965, Montana Group stratigraphy,
   Lewis and Clark County, Montana: American Association of
   Petroleum Geologists Bulletin, v. 49, no. 4, p. 379-417

Usage in Publication:
Montana Group

Modifications:	Geologic Province:	Dominant Lithology:
Revised Overview	Montana folded belt province

Summary:
Typically consists of (ascending) Telegraph Creek Formation, Virgelle Sandstone, Two Medicine Formation, Bearpaw Shale, Horsethief Formation, St. Mary River Formation, and Willow Creek Formation; totaling about 5,000 ft in thickness in the Disturbed belt of northern Lewis and Clark Co, MT in Montana folded belt province. Revised along western margin of Disturbed belt in that the Big Skunk Formation (new), comprised of 2,100 ft of volcanic-rich, arkosic sedimentary rock, occupies the upper two-thirds of the Two Medicine stratigraphic interval. Age is Late Cretaceous.

Summary of Citation: Montana

Publication:
Gill, J.R. and Cobban, W.A., 1973, Stratigraphy and geologic
   history of Montana Group and equivalent rocks, Montana,
   Wyoming, and North and South Dakota: U.S. Geological Survey
   Professional Paper, 776, 37 p.

Usage in Publication:
Montana Group*

Modifications:	Geologic Province:	Dominant Lithology:
Revised	Montana folded belt province Central Montana uplift Williston basin Powder River basin

Summary:
Revised to include Hell Creek Formation as uppermost unit because of its lithogenetic similarities to underlying Cretaceous units; Miner Creek and St. Mary River Formations, Hell Creek equivalents, are not included within Montana. Telegraph Creek Formation considered basal part of Montana. Study area is within central MT in Lewis and Clark and Meagher Cos (Montana folded belt province), Wheatland, Golden Valley, and Fergus Cos (Central Montana uplift), Garfield Co (Williston basin), and Bighorn Co (Powder River basin). West-east cross section A-A' across central MT from Dearborn River to Porcupine dome (a distance of 300 mi) shows Montana Group to consist of (ascending) Telegraph Creek Formation, Virgelle Sandstone, and Two Medicine Formation, in Dearborn River area; Telegraph Creek, Virgelle Sandstone Member of Eagle Sandstone, main body of Eagle, Judith River Formation, Claggett Shale, Parkman Sandstone, Bearpaw Shale, Horsethief Sandstone, Lennep Sandstone, and Hell Creek Formation, in Bruno siding area; Gammon Shale, Claggett, Parkman, Bearpaw, Fox Hills Sandstone, and Hell Creek, in Porcupine dome area. Ammonite zones on cross sections. Cross section B-B' shows rocks equivalent to Montana Group in WY; section C-C' correlates Montana Group rocks in MT with equivalent rocks in WY. Table of stratigraphic nomenclature for MT and WY (fig. 12). Age is latest Santonian to late Maestrichtian (Late Cretaceous).

Summary of Citation: Montana

Publication:
Ruppel, E.T., O'Neill, J.M. and Lopez, D.A., 1993, Geologic map
   of the Dillon 1 degrees x 2 degrees quadrangle, Montana: U.S.
   Geological Survey Miscellaneous Investigations Series Map,
   I-1803-H, 1 sheet, scale 1:250,000

Usage in Publication:
Montana Group

Modifications:	Geologic Province:	Dominant Lithology:
Not used

Summary:
Rocks formerly assigned to the Montana Group in the Dillon area, southwest MT in the Montana folded belt province, are designated unnamed upper and lower parts of an unnamed sedimentary rock sequence of Early and Late Cretaceous age. These sedimentary rocks are younger than the Blackleaf Formation and older than the Beaverhead Group. Name Montana Group not used.