MAGNETIC STRATIGRAPHY OF THE LOWER-MIDDLE EOCENE DOMENGINE, YOKUT, AND AVENAL SANDSTONES, WESTERN SAN JOAQUIN BASIN, CALIFORNIA: IMPLICATIONS FOR THE DOMENGINE MOLLUSCAN STAGE

The Domengine, Yokut, and Avenal Sandstones are relatively thin (30-100 m thick) but widespread nearshore and deltaic sands found along the western margin and in the subsurface of the San Joaquin and Sacramento basins. Molluscs from the Domengine Sandstone formed the basis for the middle Eocene "Domengine Stage", the highest diversity of molluscs ever reported from the Pacific Coast. The Domengine Sandstone has also yielded extensive deposits of coal and oil. Based on their molluscs, the underlying Yokut Sandstone, and the nearby Avenal Sandstone, have also been assigned to the Domengine Stage. Magnetic analysis of samples from these units revealed a stable remanence held in both magnetite and hematite which passed a reversal test. The Yokut Sandstone is entirely of normal polarity, while the Domengine and Avenal Sandstones are entirely of reversed polarity. Based on calibration from calcareous nannofossils, the Yokut Sandstone is correlated with latest early Eocene Chron C22n (49.0-49.9 Ma), while the Domengine and Avenal Sandstones correlate with earliest middle Eocene Chron C21r (47.9-49.0 Ma).