320 A revised radiolarian zonation for the Upper Jurassic of western North America

An accurate radiolarian zonation for the Upper Jurassic is critical to unraveling the stratigraphy and tectonic history of much western North America. To meet this end a revised zonation is presented for the Upper Jurassic of the California Coast Ranges. Zone 1, 2, 3 and 4 of Pessagno (1977a, 1977b) are redefined and related as accurately as possible to Upper Jurassic chronostratigraphic units. Discrepancies between European, Deep Sea Drilling Project, and North American biostratigraphic and chronostratigraphic data are analyzed. We conclude that many of the problems surrounding the correlation of North American Jurassic strata with those in the Mediterranean area are due to paleo-oceanographic factors closely related to plate tectonics. Even if preservational and taxonomic problems are excluded, correlation of Tethyan European Upper Jurassic radiolarian assemblages with those of either Boreal or Tethyan North America will continue to be a difficult problem. The southern European Tethyan faunas differ from Tethyan faunas of eastern Mexico by lacking Parvicingula Pessagno, 1977, and may be representative of a lower latitude province within the Tethyan Realm.

One new genus, Vallupus Pessagno and Blome, and four new species: Vallupus hopsoni Pessagno and Blome, Hsuum mclaughlini Pessagno and Blome, Parvicingula colemani Pessagno and Blome, and P. excelsa Pessango and Blome, are described from volcanogenic-pelagic strata overlying the Stanley Mountain remnant of the Coast Range ophiolite. These taxa as well as many others are pertinent to the definition of Upper Jurassic zonal units in California and elsewhere in wester North America.

E.A. Pessagno, Jr., C.D. Blome, J.F. Longoria

Pages: 52, 5 pls., 3 text-figs., appendix