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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
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Shallow-water mollusks from the Temblor Range, central California, represent five, or possibly six, provincial mega-invertebrate stages. This molluscan sequence is unique because (1) elsewhere in the California Coast Ranges Oligocene and early Miocene sedimentary sequences are dominantly of nonmarine or deep-water facies, and (2) the mollusks are interbedded with deep-water benthonic foraminifers representing at least as many microfaunal stages. Only in the southern part of the San Joaquin basin is there a reasonably complete sequence of shallow-water invertebrate assemblages of Oligocene and early Miocene ages. The molluscan biostratigraphy of this entire sequence previously has not been studied in detail, but the foraminiferal assemblages are well documented and represe t a complete sequence of late Oligocene and Miocene microfaunal stages.
The Oligocene and Miocene molluscan sequence is based largely on assemblages from the Temblor Formation; the basal shale member contains Bruclarkia columbiana, an index species for the "Lincoln Stage" of Weaver. The overlying "Phacoides reef," formerly assigned to the "Vaqueros Stage," represents a previously unrecognized post-"Lincoln," pre-"Vaqueros" molluscan stage in California. The lowest occurrence of "Vaqueros" mollusks is in the stratigraphically higher Agua Sandstone Member; the highest is in the Carneros Sandstone Member. The button beds at the top of the Temblor Formation and sandstone lenses in the overlying Monterey Shale include mollusks restricted to the "Temblor Stage." Mollusks from the Santa Margarita Formation in the southwest part of the range are referable to the Margaritan Stage," stratigraphically higher assemblages from this formation are referable to the "Jacalitos Stage."
Pectinids (Aequipecten, Lyropecten, Pecten s.s., and Vertipecten) are the most useful mollusks in biostratigraphic subdivisions and provincial correlation of this sequence, i.e., Phacoides "reef"--P. sanctaecruzensis, V. n. sp., Agua Sandstone Member--L. magnolia, V. perrini; Carneros Sandstone Member--L. crassicardo, L. miguelensis, V. nevadanus; button beds--A. andersoni, L. crassicardo; and Santa Margarita Formation--L. estrellanus, L. crassicardo.
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