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Transition Element Ratios in Organic Matter from Monterey Formation: Transition Element-Lithofacies Correlations

John R. Odermatt, Joseph A. Curiale, Richard W. Hurst

A suite of four transition elements (Cr, Mo, Ni, and V) was analyzed in the organic matter (kerogen and extract) of cores from the Union Leroy 51-18 well, Santa Maria Valley field, California. Elemental concentrations in kerogens were found to vary systematically with depth when normalized to elemental carbon contents. This may suggest that these elements are bound to the organic matter of kerogen concentrates and may be useful in characterizing sedimentary organic matter from the Monterey Formation. Concentration ratios of these elements [e.g., V/(V + Ni); Mo/(Mo + Cr)] were used to divide the sedimentary organic matter into two populations. These populations correspond almost exactly to the siliceous and phosphatic lithofacies. These populations are valid for both solub e organic matter and kerogen concentrates. The observed pattern in these elements may be related to the Eh-pH conditions of the depositional environment. If these trace element zones are shown to be laterally recognizable, the transition element stratigraphy of sedimentary organic matter will be useful for subsurface correlations in the Monterey Formation in the Santa Maria basin.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.