Enigmatic uppermost Permian-lowermost Triassic stratigraphic relations in the northern Bighorn basin of Wyoming and Montana

Conference · Sat Jun 01 04:00:00 EDT 1991 · AAPG Bulletin (American Association of Petroleum Geologists); (United States)

OSTI ID:5862808

Paull, R A; Paull, R K ^[1]

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1. Univ. of Wisconsin, Milwaukee (United States)

Eighteen measured sections in the northern Bighorn basin of Wyoming and Montana provide the basis for an analysis of Permian-Triassic stratigraphic relations. This boundary is well defined to the south where gray calcareous siltstones of the Lower Triassic Dinwoody disconformably overlie the Upper Permian Ervay Member of the Park City Formation with little physical evidence of a significant hiatus. The Dinwoody is gradationally overlain by red beds of the Red Peak Formation. The Dinwoody this to zero near the state line. Northward, the erathem boundary is enigmatic because fossils are absent and there is no evidence of an unconformity. Poor and discontinuous exposures contribute to the problem. Up to 20 m of Permian or Triassic rocks or both overlie the Pennsylvanian Tensleep Sandstone in the westernmost surface exposures on the eastern flank of the Bighorn basin with physical evidence of an unconformity. East of the exposed Tensleep, Ervay-like carbonates are overlain by about 15 m of Dinwoody-like siltstones interbedded with red beds and thin dolomitic limestone. In both areas, they are overlain by the Red Peak Formation. Thin carbonates within the Dinwoody are silty, coarse algal laminates with associated peloidal micrite. Carbonates north of the Dinwoody termination and above probably Ervay are peloidal algal laminates with fenestral fabric and sparse coated shell fragments with pisoids. These rocks may be Dinwoody equivalents or they may be of younger Permian age than the Ervay. Regardless, revision of stratigraphic nomenclature in this area may bed required.

• OSTI ID: 5862808
• Report Number(s): CONF-9107109--
• Conference Information: Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (United States) Journal Volume: 75:6
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
CARBONATE ROCKS
DEVELOPED COUNTRIES
FEDERAL REGION VIII
GEOLOGIC AGES
GEOLOGIC FORMATIONS
GEOLOGIC STRUCTURES
GEOLOGY
LITHOLOGY
MESOZOIC ERA
MONTANA
NORTH AMERICA
PALEOZOIC ERA
PERMIAN PERIOD
ROCKS
SEDIMENTARY BASINS
SEDIMENTARY ROCKS
SILTSTONES
STRATIGRAPHY
TRIASSIC PERIOD
USA
WYOMING