Depositional environments of middle Minnelusa Leo (Middle and Upper Pennsylvanian), Wyoming, South Dakota, and Nebraska
The informal middle member of the Minnelusa Formation, commonly known as Leo, consists of a spectrum of sediments including sandstone, dolomite, anhydrite, bedded chert, limestone, and radioactive carbonaceous shale. Deposition within the upper Paleozoic alliance basin of the present day tri-state area of South Dakota, Wyoming, and Nebraska occurred in sabkha, tidal flat, and shallow subtidal environments. Major and minor cycles of eustatic sea level changes are manifest by the Leo section. Early Desmoinesian (lowermost Leo) sediments are open marine, upper subtidal limestone interbedded with restricted marine upper subtidal dolomite, anhydrite, and radioactive organic-rich dolomite. During the upper Desmoinesian and lower Missourian, most of the Alliance basin was a restricted carbonate tidal flat. Throughout the remainder of the Pennsylvanian, the prevalent environment was a restricted coastal to inland sabkha with episodic inundations intercalating intertidal dolomite and lagoonal black shale with the sabkha sediments. Prolonged periods of exposure allowed migration of eolian bypass with only isolated patches of dunes being trapped by rare topographic relief. Criteria suggesting windblown deposition of the majority of Leo sandstone include deflationary lag surfaces, low-amplitude ripples, subcritically climbing translatent cross-stratification, and sand-flow toes. Isolated eolian sandstones provide excellent stratigraphic traps for hydrocarbons generated in the organic-rich shales. The current flurry of Leo drilling that began in 1978, has affirmed the inherent potential of this play. Definition of paleodepositional trends and seismic recognition of isolated dunes are the keys to Leo exploration success.
- Research Organization:
- Mitchell Energy Corp., Denver, CO
- OSTI ID:
- 6525421
- 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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Upper part of Minnelusa Formation in outcrop near Beulah, Wyoming, and at West Mellott field, Powder River basin
Diagenesis of sandstones in Permian upper Minnelusa Formation, west Mellott field, Powder River basin, Wyoming
Related Subjects
020200* -- Petroleum-- Reserves
Geology
& Exploration
03 NATURAL GAS
030200 -- Natural Gas-- Reserves
Geology
& Exploration
EXPLORATION
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC FORMATIONS
GEOLOGIC TRAPS
GREAT PLAINS
MINERAL RESOURCES
PALEOZOIC ERA
PENNSYLVANIAN PERIOD
PETROLEUM DEPOSITS
RESERVOIR ROCK
RESOURCE POTENTIAL
RESOURCES
ROCKS
SANDSTONES
SEDIMENTARY ROCKS
SEDIMENTATION