Strontium-Isotope Study of Pore Waters in San Joaquin Basin, California

S. T. Kwon, J. R. Boles, G. R. Tilton

Nineteen pore-water samples from the late Miocene and younger marine formations were analyzed for strontium contents and isotopic compositions. All samples have ⁸⁷Sr/⁸⁶Sr ratios lower than the late Miocene seawater value (0.7090). The strontium values in many of these waters reflect silicate rather than carbonate reactions. In general, the strontium contents and isotopic ratios of the pore waters are related to the depth and location of the oil fields. The strontium contents as a whole show a tendency to increase with depth, although ⁸⁷Sr/⁸⁶Sr ratios have no simple depth relationship. The strontium contents and isotopic compositions of the pore waters fall into five groups related to geographic locations. This suggests localized evolution of pore waters in a given area and limited movement of these subsurface waters.

AAPG Search and Discovery Article #91035©1988 AAPG-SEPM-SEG Pacific Sections and SPWLA Annual Convention, Santa Barbara, California, 17-19 April 1988.