Abstract

The Knoxville series, the latest West Coast Jurassic, is best developed and best preserved and exposed in its type area on the west border of the Sacramento Valley, in Tehama County. It consists of deltaic deposits having a maximum thickness of 16,300 feet and an average thickness of 11,600 feet. It forms three major stratigraphic groups, each characterized lithologically and stocked with appropriate faunas of marine invertebrates, which occupy a chronological span from early-middle Portlandian to latest Tithonian time of the European scale. In part the series crops out at intervals on the west border of the Great Valley for nearly 300 miles. Outside this valley it is traceable southward to the Santa Ynez Range and northward to partly correlative deposits in western Oregon, Washington, British Columbia, and southern Alaska. The Knoxville series contrasts strongly in composition, structures, faunistic features, and geologic history with the next older, the Franciscan and Mariposa groups, both of which occupy distinct geographical areas.

Historically the Knoxville epoch is a distinct chronological unit between the Nevadan orogeny at the close of the Mariposa-Mount Jura epoch and the earliest Cretaceous epoch, the deposits of which occupy distinct areas on the West Coast. It includes the earliest marine deposits laid down in the Great Valley trough and in other troughs developed farther north by the Nevadan orogeny. Correlative deposits occur in many parts of the world—Cutch, southwest India; the Lower Volga basin, Russia; in western Germany; at Speeton, England; and in Japan.

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