Age and depositional setting of the type Lospe Formation (Lower Miocene), Santa Maria basin, central California

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

OSTI ID:6674905

Stanley, R G ^[1]; Johnson, S Y; Obradovich, J D; Tuttle, M L ^[2]; Thornton, M L.C.; Vork, D R; Filewicz, M V ^[3]; Mason, M A ^[4]; Swisher, III, C C ^[5]

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1. Geological Survey, Menlo Park, CA (USA)
2. Geological Survey, Denver, CO (USA)
3. Unocal Oil and Gas Div., Ventura, CA (USA)
4. Univ. of California, Berkeley (USA)
5. Berkeley Geochronology Center, CA (USA)

The Lospe Formation is an 800-m-thick sequence of sedimentary and minor volcanic rocks at the base of the petroliferous Neogene Santa Maria basin of central California. In its type area in the Casmalia Hills, the Lospe rests unconformably on Jurassic ophiolite, is conformably overlain by the lower Miocene (Sauceian and Relizian) Point Sal Formation, and is of earliest Miocene (Saucesian) age on the basis of palynomorphs, benthic foraminifers, and radiometric dating of tuffs. Alluvial fan and fan-delta facies at the base of the Lospe are as much as 200 m thick and consist mainly of conglomerate and sandstone derived from nearby fault-bounded uplifts of Mesozoic rocks. These coarse sediments grade upward into a sequence of interbedded turbidite sandstone and mudstone that accumulated in a lake or restricted coastal embayment. Lenses of tuff as much as 20 m thick occur sporadically throughout this sequence and contain blocks of Jurassic ophiolite up to 50 m long and 20 m across. The uppermost 30 m of the Lospe consist of storm-deposited sandstone and mudstone containing shallow marine microfossils. That these shelf deposits are abruptly overlain by black shale of the Point Sal Formation indicates rapid deepening to oxygen-poor bathyal environments. Overall, the Lospe Formation is a fining-upward sequence that records active faulting, volcanism, and a change from nonmarine to marine depositional environments during the initial formation of the Neogene Santa Maria basin. This history is consistent with several competing tectonic models that variously explain the origin of the basin as the result of regional rifting or local rotation of small crustal blocks.

• OSTI ID: 6674905
• 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

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58 GEOSCIENCES
580000 -- Geosciences
CALIFORNIA
CENOZOIC ERA
CONGLOMERATES
DEPOSITION
FEDERAL REGION IX
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC FORMATIONS
GEOLOGIC STRUCTURES
MINERAL RESOURCES
NORTH AMERICA
PETROLEUM DEPOSITS
RESERVOIR ROCK
RESOURCES
ROCKS
SANDSTONES
SEDIMENTARY BASINS
SEDIMENTARY ROCKS
TECTONICS
TERTIARY PERIOD
USA