| Abstract: | Lithological and paleontological studies of outcrops of Upper Cretaceous formations were conducted at 12 localities in eastern Wyoming, central Colorado, and northeastern New Mexico. The sequence extends upward from the top of the Mowry Shale, or age-equivalent rocks, through the Graneros Shale, Greenhorn Limestone, Carlile Shale, Niobrara Formation, Pierre Shale, and Fox Hills Sandstone, or age-equivalent formations, to the top of the Laramie Formation, or laterally equivalent formations. The strata are mainly siliciclastic and calcareous, with thicknesses ranging from about 3,300 ft in northeastern New Mexico to as much as 13,500 ft in eastern Wyoming. Deposition was mainly in marine environments and molluscan fossils of Cenomanian through Maastrichtian ages are common. Radiometric ages were determined from beds of bentonite that are associated with fossil zones. The Upper Cretaceous formations at the 12 study localities are herein divided into three informal time-stratigraphic units based on fossil content and contact relations with adjacent strata. The basal unit in most places extends from the base of the Graneros to the top of the Niobrara, generally to the horizon of the fossil Scaphites hippocrepis, and spans a period of about 14 million years. The middle unit generally extends from the top of the Niobrara to the approximate middle of the Pierre, the horizon of the fossil Baculites gregoryensis, and represents a period of about 5 million years. The upper unit includes strata between the middle of the Pierre and the top of the Upper Cretaceous Series, which is the top of the Laramie Formation or of laterally equivalent formations; it represents a period of deposition of as much as 11 million years. Comparisons of the collections of fossils from each outcrop with the complete sequence of Upper Cretaceous index fossils can indicate disconformable contacts and lacunae. Widespread disconformities have been found within the Carlile Shale and between the Carlile Shale and the Niobrara Formation. Less extensive disconformities are within the Greenhorn Formation, the Niobrara Formation, and the Pierre Shale. |
| Genre: | USGS Numbered Series |
| ProdID: | 70005715 |
| Citation Author: | Merewether, E. A.; Cobban, W. A.; Obradovich, J. D. |
| Citation Contributing Office: | Geology and Environmental Change Science Center |
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| Citation Language: | English |
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| Citation Online Only Flag: | Y |
| Citation Phsyical Description: | Sheet 1: 66.30 inches x 36.64 inches; Sheet 2: 65.40 inches x 30.74 inches: Pamphlet: iii, 10 p.; Figure 1; Figure 2; Figure 3 |
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| Citation Publisher: | U.S. Geological Survey |
| Citation Series: | Scientific Investigations Map |
| Citation Series Code: | SIM |
| Citation Series Number: | 3175 |
| Citation Search Results Text: | Biostratigraphic data from Upper Cretaceous formations-eastern Wyoming, central Colorado, and northeastern New Mexico; 2011; SIM; 3175; Merewether, E. A.; Cobban, W. A.; Obradovich, J. D. |
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| Citation Year: | 2011 |
| Type: | citation/reference |
| Text: | Biostratigraphic data from Upper Cretaceous formations-eastern Wyoming, central Colorado, and northeastern New Mexico; 2011; SIM; 3175; Merewether, E. A.; Cobban, W. A.; Obradovich, J. D. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/sim_3175.png |
| URL (INDEX PAGE): | http://pubs.usgs.gov/sim/3175/ |
| Date Other: | Tue, 11 Oct 2011 00:00 -0500 |
| Publisher: | U.S. Geological Survey |
