High-resolution strontium isotope stratigraphy and biostratigraphy of the Miocene Monterey Formation, central California

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

OSTI ID:7091523

Finger, K L ^[1]; DePaolo, D J ^[2]

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1. Chevron Oil Field Research Co., La Habra, CA (USA)
2. Univ. of California, Berkeley (USA)

Detailed biostratigraphic and Sr isotope studies on two outcrop sections of the Miocene Monterey Formations of California demonstrate the applicability of the Sr isotope method for detailed biostratigraphic ages. These ages generally agree with Sr-isotope ages determined by correlating {sup 87}Sr/{sup 86}Sr ratios with a standard {sup 87}Sr/{sup 86}Sr vs. age curve constructed of data from Deep Sea Drilling Project (DSDP) Sites 575 and 590. Diagenetic modification of Sr-isotope ratios of the Monterey Formation was negligible. In the lower Miocene, strontium isotopes provide age resolutions of 0.1 to 0.2 Ma and reversals within a general trend of increasing {sup 87}Sr/{sup 86}Sr coincide with minor faults and slump structures. Biostratigraphy yields the more definitive age assignments in the younger siliceous rocks where diatoms in particular have more utility than the corresponding flat and polytonic portion of the isotopic curve. Strontium isotope correlation of the basal Monterey Formation with DSDP Site 575 indicates that Monterey deposition commenced 17.85 {plus minus} 0.10 Ma (within planktic foraminiferal zone N6 and calcareous nannofossil zone CN2). This event dates 0.35 {plus minus} 0.10 Ma before the beginning of the pronounced shift of {delta}{sup 13}C observed at Site 575, which argues against a causal link between the two. It is evident that Sr-isotope stratigraphy is a valuable supplement to biostratigraphy; the techniques are complementary in refining chronostratigraphic interpretations.

• OSTI ID: 7091523
• 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

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