Depositional environments of Upper Cretaceous Fox Hills Formation, Niobrara and Weston counties, east-central Wyoming
The Upper Cretaceous Fox Hills Formation on the southeastern flank of the Powder River basin, Wyoming, was deposited along a regressive, northeast-trending, low-energy, tidally affected, wave-dominated coastline. The Fox Hills Formation consists of rocks deposited successively in marine transitional-lower shoreface, upper shoreface, foreshore, and tidal-flat environments. The marine transitional-lower shoreface beds are characterized by generally highly bioturbated, very fine-grained sandstone and silty claystone with interbedded siltstone, silty shale, and shale. The amount of sandstone in them increases landward. The upper shoreface deposits consist dominantly of sandstone and have minor amounts of siltstone, silty claystone, and shale. The sandstone generally becomes coarser and better sorted upward. The deposits of the foreshore (intertidal) consist of moderately sorted to well-sorted fine-grained sandstone that has seaward-dipping wedge-planar cross-bedding. Tidal-flat deposits are common in the upper part of the section in the northern part of the study area. At one locality, these deposits consist of at least 75 ft (23 m) of intercalated fine-grained sandstone and claystone that have lenticular to flaser bedding. The majority of these deposits show a high degree of bioturbation and are considered to be intertidal. These sediments are overlain by approximately 15 ft (4.5 m) of fine-grained silty sandstone and claystone which have plant root casts and a high content of carbonaceous material, and which could represent supratidal deposits. Overlying these deposits is a 12 ft (3.7 m) sandstone bed having a scour base, lag of clay clasts and woody fragments, parallel bedding that grades upward into trough cross-bedding, and a 6 ft (1.8 m) bed of oyster shells near its top.
- Research Organization:
- Geological Survey, Denver, CO
- OSTI ID:
- 6433167
- Report Number(s):
- CONF-8309274-
- Journal Information:
- Am. Assoc. Pet. Geol., Bull.; (United States), Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Vol. 67:8; ISSN AAPGB
- Country of Publication:
- United States
- Language:
- English
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CRETACEOUS PERIOD
FEDERAL REGION VIII
GEOLOGIC AGES
GEOLOGIC HISTORY
GEOLOGIC STRUCTURES
GEOLOGY
MESOZOIC ERA
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SEDIMENTARY BASINS
SEDIMENTARY ROCKS
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