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

Conference · Fri Feb 01 04:00:00 EST 1991 · AAPG Bulletin (American Association of Petroleum Geologists); (United States)

OSTI ID:5199568

Stanley, R G ^[1]; Johnson, S Y; Tuttle, M L; Obradovich, J D ^[2]; Mason, M A ^[3]; Swisher, III, C C ^[4]; Thornton, M L.C.; Vork, D R; Filewicz, M V ^[5]; Cole, R B ^[6]

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1. Geological Survey, Menlo Park, CA (United States)
2. Geological Survey, Denver, CO (United States)
3. Univ. of California, Berkeley (United States)
4. Berkeley Geochronology Center, CA (United States)
5. Unocal Corp., Ventura, CA (United States)
6. Univ. of Rochester, NY (United States)

The type Lospe Formation in the Casmalia Hills is an 800-m-thick sequence of sedimentary and minor volcanic rocks. The Lospe is entirely of early Miocene (Saucesian) age on the basis of palynomorphs, benthic foraminifers, and {sup 40}Ar/{sup 39}Ar ages of 17.70 {plus minus} 0.03 Ma (mean of seven determinations) and 17.39 {plus minus} 0.12 Ma (mean of six determinations). The {sup 40}Ar/{sup 39}Ar ages were measured on water-laid tuffs; these tuffs may have erupted from the same volcanic source as a welded tuff yielding an {sup 40}Ar/{sup 39}Ar age of 17.79 {plus minus} 0.10 Ma (mean of five determinations) from the Tranquillon volcanics on Tranquillon Mountain in the westernmost Transverse Ranges. Alluvial fan and fan-delta facies within the basal part of the Lospe are as thick as 200 m and consist mainly of conglomerate and sandstone derived from nearby fault-bounded uplifts of Mesozoic rocks. These coarse-grained facies grade upward into a sequence of interbedded sandstone and mudstone that accumulated in a shallow lake. Gypsum layers in the lake deposits contain sulfate depleted in {sup 34}S (0 to +3{per thousand}), suggesting that the sulfur had a hydrothermal origin. The uppermost 30 m of the Lospe consists of storm-deposited sandstone and mudstone containing shallow-marine microfossils. The shallow-marine deposits are abruptly overlain by bathyal marine shale of the Point Sal Formation. The Lospe Formation records active faulting, volcanism, hydrothermal activity, and rapid subsidence during initial formation of the Neogene Santa Maria basin. These events may have resulted from crustal extension related to the beginning of clockwise rotation of the western Transverse Ranges about 18 to 17 Ma.

• OSTI ID: 5199568
• Report Number(s): CONF-9103128--
• Conference Information: Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (United States) Journal Volume: 75:2
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
AGE ESTIMATION
ANIMALS
ARGON 39
ARGON 40
ARGON ISOTOPES
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CALIFORNIA
CENOZOIC ERA
CONGLOMERATES
CORRELATIONS
DEVELOPED COUNTRIES
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
FORAMINIFERA
GEOLOGIC AGES
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
GEOLOGIC STRUCTURES
GEOLOGY
INVERTEBRATES
ISOTOPE DATING
ISOTOPES
LIGHT NUCLEI
MICROORGANISMS
MIOCENE EPOCH
NORTH AMERICA
NUCLEI
ORIGIN
PALEONTOLOGY
PALYNOLOGY
PROTOZOA
RADIOISOTOPES
ROCKS
SANDSTONES
SARCODINA
SEDIMENTARY BASINS
SEDIMENTARY ROCKS
STABLE ISOTOPES
STRATIGRAPHY
TERTIARY PERIOD
TUFF
USA
YEARS LIVING RADIOISOTOPES