PALEOZOIC AND MESOZOIC ROCKS OF GROS VENTRE, TETON, HOBACK, AND SNAKE RIVER RANGES, WYOMING
Published:July 01, 1955
HAROLD R. WANLESS, RALPH L. BELKNAP, HELEN FOSTER, 1955. "PALEOZOIC AND MESOZOIC ROCKS OF GROS VENTRE, TETON, HOBACK, AND SNAKE RIVER RANGES, WYOMING", Paleozoic and Mesozoic Rocks of Gros Ventre, Teton, Hoback, and Snake River Ranges, Wyoming, Harold R. Wanless, Ralph L. Belknap, Helen Foster
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The Gros Ventre, southern Teton, northern Hoback, and Snake River ranges and Grayback Ridge of the Wyoming Range, and the buttes of southern Jackson Hole display a remarkably long and nearly complete stratigraphic column. Archean granites and gneisses are strikingly displayed in the eastern fault scarp and high peaks of the Teton Range and the southeast front of the Gros Ventre Range. Paleozoic rocks, representing all periods with the possible exception of the Silurian, aggregate about 6000 feet, and the Triassic, Jurassic, and Cretaceous are represented by more than 12,000 feet of strata.
The Paleocene and Eocene are represented by a maximum of about 20,000 feet in the Hoback basin between the Hoback and Gros Ventre ranges, and in the Mt. Leidy highlands north of the Gros Ventre ranges and east of Jackson Hole. The Oligocene is apparently unrepresented except farther north in Jackson Hole, but the Miocene and early Pliocene are represented by the Camp Davis formation several thousand feet thick in Bryan Flats between Hoback Range and Grayback Ridge, in Jackson Hole, and in Star, Grand, and Swan valleys west of the Snake River Range. Volcanic rocks of Tertiary age are intercalated with the sediments in Jackson Hole and Grand and Star valleys, and there are late Tertiary intrusives in the Snake River Range. The Pleistocene is recorded by the Buffalo, Bull Lake, and Pinedale drifts of Kansan, Iowan and Mankato ages.
The Gros Ventre and Teton ranges are within the stable platform or foreland area with Paleozoic and early Mesozoic sections of moderate thickness and comparatively simple structures. The faults are largely high-angle reverse faults with pressures from the north and east. The Hoback and Snake River ranges and Grayback Ridge belong to the borders of the southern Idaho geosyncline with a Cambrian (Gros Ventre) to Cretaceous (Frontier) section nearly 90 per cent thicker than the foreland section. Structurally this area is marked by a series of subparallel low-angle thrusts from the south and southwest including the Jackson, Little Granite, Game, Bear, Darby, Absaroka, Ferry Peak, and St. John thrusts. Although the amount of crustal shortening involved in the individual thrusts of this belt is unknown, the effects of this shortening, combined with marked southward and westward thickening of the sedimentary columns, bring about significant differences in succession and thickness in several formations even between points now only a few miles apart.
During several field studies at the University of Michigan Rocky Mountain field station, at Camp Davis, Wyoming, detailed stratigraphic sections were measured in the exposed formations in each of the ranges. These sections show numerous persistent thin diagnostic strata not previously noted, and give a clearer picture of the facies changes between the foreland and geosyncline. These variations are shown by graphic sections of the strata of each system. Single measured sections of the Devonian, Mississippian, Pennsylvanian, and Permian successions and of the Bear River and Aspen formations of the Upper Cretaceous are included in the text, and other measured sections have been placed on open file at the office of The Geological Society of America, where they may be consulted.