Abstract: Lithologic Variation of the Rare Biomarker Compound 28, 30-Bisnorhopane Within the Miocene Monterey Formation in the Texaco Anita-14 Well, Santa Barbara County, California

Jeffrey Brenner

The rare geological marker compound 28, 30-bisnorhopane is commonly found in the oils and rocks of the Miocene Monterey Formation of central and southern California. In the offshore Texaco Anita-14 well of the Santa Barbara coastal area, the most significant concentrations of 28, 30-bisnorhopane are restricted to a small interval of organic-rich, calcareous/phosphatic shale. Onshore exposures of the Monterey Formation in this area are commonly subdivided into five lithologic members, all of which have been identified in the Anita-14 well based on visual examination and XRD analysis of the core and cuttings coupled with electric log interpretations. Soluble organic matter was extracted from several core and cuttings samples from each lithologic member and analyzed for hopanes by standa d gas chromatographic-mass spectrometric (GC-MS) techniques. Preliminary results reveal minor, but somewhat variable concentrations of 28, 30-bisnorhopane in all of the Monterey members but one. The greatest concentration of 28, 30-bisnorhopane occurs within a small interval of poorly laminated, organic-rich calcareous/phosphatic shale that also contains the highest amount of extractable organic matter in the core. Furthermore, within this organic-rich member, bisnorhopane concentrations appear to be higher in the more strongly laminated rocks as opposed to those that are weakly laminated or massive.

This evidence supports the proposition that 28, 30-bisnorhopane may be of use as an indicator of depositional conditions for one of the more organic-rich source rocks of the Monterey Formation.

AAPG Search and Discovery Article #90981©1994 AAPG Pacific Section Meeting, Ventura, California, April 27-29, 1994