Organically bound metals and biomarkers in the Monterey Formation of the Santa Maria Basin, California

Systematic variations in metal concentration ratios and biomarker ratios are observed with depth in cores of the Monterey Formation of the Union Leroy 51-18 well in the Santa Maria Basin, California. Specific metal ratios— V ( V + Ni) and Mo ( Mo + Cr) —correlate between kerogen and extractable organic matter. Further, the organic matter in the two predominant lithofacies (siliceous shales vs. phosphatic shales) can be distinguished based upon metal concentration ratios (e.g., V ( V + Ni) and certain biomarker characteristics (e.g., sterane/terpane, mono/triaromatic steroid hydrocarbon ratios). Maximum 28,30- bisnorhopane hopane ratios occur over a narrow range of V ( V + Ni) ratios in kerogen concentrates and extractable organic matter. This suggests that metal ratios (in kerogen concentrates and EOM) may be useful for oil-source rock correlation studies in the Monterey. Further, while kerogen parameters (metals) are discontinuous at the lithofacies boundary, extract parameters (biomarkers) are gradational at this boundary, suggesting about 30 ft. (9 m) of vertical hydrocarbon migration across the lithofacies contact.