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Facies characterization of the Basal Antelope shale in the Monterey Formation at Elk Hills and surrounding fields: San Joaquin Basin, California
The Antelope shale consists of fine-grained, deep-marine, organic-rich, diagenetic, biosiliceous shales, and clastic turbiditic sandstones in the San Joaquin basin. This heterogeneity in lithology is challenging when characterizing and correlating these facies within neighboring fields. An integrated approach is required to analyze these rocks. This integration requires paleontological data, mudlogs, gamma logs, natural spectral gamma logs, elemental capture spectroscopy logs, density logs, neutron logs, cores, and x-ray diffraction analysis. From this combined approach, the relative distributions of biosiliceous chert, detrital sand, and shale facies were determined for the basal Antelope Shale at Elk Hills and surrounding fields. The results from this study highlighted an abundance of chert and shale facies at Railroad Gap and Asphalto field. At the Elk Hills and Buena Vista fields, an abundance of sandstone facies appeared to replace the chert facies with depth. The interpretation from these facies distributions suggested that Railroad Gap and Asphalto represented banktop to upper slope facies while Buena Vista and Elk Hills represented lower slope to basinal facies. This interpretation corresponds to the depositional model established by previous studies done within the San Joaquin basin on the Antelope shale and associated Stevens sandstone.
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