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ABSTRACT: Chronostratigraphic Assignment of Volcanopelagic Strata Above the Coast Range Ophiolite

HULL, DONNA MEYERHOFF, University of Texas at Dallas, Richardson, TX, CHARLES D. BLOME, U.S. Geological Survey, Denver, CO, and EMILE A. PESSAGNO, JR., University of Texas at Dallas, Richardson, TX

Volcanopelagic strata at selected localities of the Coast Range Ophiolite have been dated using the radiolarian biostratigraphic zonation of Pessagno et al. Chronostratigraphic assignments range from lower Oxfordian to uppermost Tithonian. In the southern Coast Ranges of California, oldest sediments have been recovered from Cuesta Ridge, where Radiolaria assignable to superzone 1, zone II (lower Oxfordian) occur at the base of the succession. Overlying strata at Cuesta Ridge contain Radiolaria that range from zone 2, subzone 2 beta to zone 3, subzone 3 alpha (middle Oxfordian to lower Tithonian). Radiolaria from the Point Sal remnant of the Coast Range Ophiolite are middle Oxfordian to lower Tithonian; the Llanada remnant is considerably younger, yielding Radiolaria of zone 3, subzone 3 beta to zone 4, subzone 4 alpha (uppermost Kimmeridgian to uppermost Tithonian). In the northern California Coast Ranges, tuffaceous cherts from Black Mountain, Sonoma County, contain middle/upper Oxfordian to upper Kimmeridgian Radiolaria.

The most complete succession of the Coast Range Ophiolite is the Stanley Mountain remnant, San Luis Obispo County, California. At this locality, the basaltic member of the Coast Range Ophiolite is overlain by more than 130 m of volcanopelagic strata gradationally overlain by 130 m of strata of the Great Valley supergroup. Samples collected from the volcanopelagic succession have yielded greater than 400 species of Radiolaria ranging in age from middle Oxfordian to uppermost Tithonian.


AAPG Search and Discovery Article #91016©1992 AAPG-SEPM-SEG-EMD Pacific Section Meeting, Sacramento, California, April 27-May 1, 1992 (2009)