NOT THE ROSETTA STONE

Discovery of the Paleocene index fossil Turritella infragranulata pachecoensis and subsequent exposure of an estimated 3,000-feet of foraminifer-bearing mudstone above and below the Turritella bed at Cement Hill northeast of Fairfield, California, led to speculation that this area could be the “Rosetta stone” for understanding Paleocene stratigraphy and paleontology in northern California. This dream evaporated when the mudstones were dated by coccoliths, foraminifers, and radiolarians and were found to be predominantly Eocene. The “section” turned out to consist of several fault blocks with repetitions of both overturned and normal sequences of Paleocene and Eocene sandstones and mudstones capped by Late Cretaceous radiolarian shale. Existing geologic maps of the region show an eastward-dipping monocline of Late Cretaceous and Eocene rocks extending nearly 100 miles northward from Fairfield. This new, very complex structure is anomalous in a petroleum province generally characterized by relatively simple structure.