Depositional environment of the Upper Cretaceous Mokelumne River Formation, Sacramento basin, California

Conference · Tue May 01 04:00:00 EDT 1990 · AAPG Bulletin (American Association of Petroleum Geologists); (USA)

OSTI ID:6685414

Johnson, D S ^[1]

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1. 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--
• Conference Information: Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (USA) Journal Volume: 74:5
• Country of Publication: United States
• Language: English

Related Subjects

03 NATURAL GAS
030200* -- Natural Gas-- Reserves
Geology
& Exploration
58 GEOSCIENCES
580000 -- Geosciences
CALIFORNIA
CLAYS
CRETACEOUS PERIOD
DEPOSITION
FEDERAL REGION IX
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC FORMATIONS
GEOLOGIC STRUCTURES
GEOLOGIC TRAPS
MESOZOIC ERA
MINERAL RESOURCES
NATURAL GAS DEPOSITS
NORTH AMERICA
RESERVOIR ROCK
RESOURCES
ROCKS
SANDSTONES
SEDIMENTARY BASINS
SEDIMENTARY ROCKS
SHALES
USA
WELL LOGGING