Depositional environment of the Upper Cretaceous Mokelumne River Formation, Sacramento basin, California
- Washoe Natural Resources, Clovis, CA (USA)
The Upper Cretaceous Mokelumne River formation of the southern Sacramento basin is a fluvial-deltaic sequence deposited during the late Maestrichtian epoch. Quartzose-feldspathic sediments, sourced from the rising proto-Sierra Nevada terrain toward the east, were deposited within a fore-arc basin tectonostratigraphic setting. The Mokelumne River formation contains interbedded sands and shales in the northern area which grade into massive sands in the southern area, indicating a change in depositional environments. The upper contact of the unit is an unconformity which separates the Mesozoic and Cenozoic eras. The lower contact is an unconformity in the north which grades into a conformable contact with the underlying strata toward the south. The present study examines the depositional characteristics of the Mokelumne River formation in the northern area. Wireline log analysis indicates the presence of the following lower delta-plain deposits: distributary channels, natural levees, crevasse splays, and marshes with associated lignite beds, Subaqueous delta-plain deposits include the basal sand unit, locally termed the Bunker sand. The Bunker sand exhibit a coarsening-upward sequence on wireline logs and is interpreted to represent a prodelta distal bar. The sand-shale ratio decreases northward and westward and increases toward the south. The Modelumne River formation is productive in 29 fields and has produced in excess of 500 bcf of natural gas. Hydrocarbon accumulations are formed by updip fault truncation, stratigraphic traps, and updip erosional traps sealed by overlying clays.
- OSTI ID:
- 6685414
- Report Number(s):
- CONF-900605-; CODEN: AABUD
- Journal Information:
- AAPG Bulletin (American Association of Petroleum Geologists); (USA), Vol. 74:5; Conference: Annual convention and exposition of the American Association of Petroleum Geologists, San Francisco, CA (USA), 3-6 Jun 1990; ISSN 0149-1423
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
58 GEOSCIENCES
CALIFORNIA
GEOLOGIC FORMATIONS
NATURAL GAS DEPOSITS
DEPOSITION
RESERVOIR ROCK
CLAYS
CRETACEOUS PERIOD
GEOLOGIC TRAPS
SANDSTONES
SEDIMENTARY BASINS
SHALES
WELL LOGGING
FEDERAL REGION IX
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC STRUCTURES
MESOZOIC ERA
MINERAL RESOURCES
NORTH AMERICA
RESOURCES
ROCKS
SEDIMENTARY ROCKS
USA
030200* - Natural Gas- Reserves
Geology
& Exploration
580000 - Geosciences