--> --> Abstract: Magnetic Stratigraphy of the Middle Miocene Bopesta Formation, Southern Sierra Nevada, Kern County, California, by S. Coles, D. R. Prothero, and J. P. Quinn; #90945 (1997).

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Abstract: Magnetic Stratigraphy of the Middle Miocene Bopesta Formation, Southern Sierra Nevada, Kern County, California

COLES, SEAN, DONALD R. PROTHERO, and JAMES P. QUINN

The middle Miocene Bopesta Formation consists of over 640 m of fluvial, lacustrine, and volcaniclastic sediments, and interbedded volcanics, exposed in the southern Sierra Nevadas south of Cache Peak. It contains both late Hemingfordian and early Barstovian faunas, especially horses. Precise chronostratigraphy of the Bopesta Formation is very important, since it is intermediate between Miocene faunas from the Mojave Desert (Barstow, Ricardo) and Transverse Ranges (Tejon Hills, Cuyama Badlands) which have previously been sampled for magnetic stratigraphy.

Magnetic sampling was conducted on the neostratotype section which spanned the thickest part of the sequence in Pine Tree Canyon, and at the late Hemingfordian Phillips Ranch locality in Sand Canyon. After removal of overprinting, the primary component of magnetization passed a reversal test, and showed no significant tectonic rotation (within the error estimates). Based on comparisons with the magnetic stratigraphy and biostratigraphy of the Barstow Formation, the Bopesta Formation appears to span Chrons C5ADn to C5Cn (14.5-16.5 Ma). The boundary between the late Hemingfordian Parapliohippus carrizoensis zone and the early Barstovian "Merychippus" stylodontus zone falls in early Chron C5Br (about 15.9 Ma), as it does in Barstow (as shown by the transition from the Rak Division to Green Hills Faunas).

Search and Discovery Article #90945©1997 AAPG Pacific Section Meeting, Bakersfield, California