MORPHOLOGIC DIVERSITY AND PALEOGEOGRAPHIC SIGNIFICANCE OF THE FAMILY PARVICINGULIDAE (RADIOLARIA)

Radiolaria of the Family Parvicingulidae Pessagno (Suborder Nassellaria) are described from the lower member of the Taman Formation, east-central Mexico and from volcanopelagic strata overlying the Stanley Mountain remnant of the Coast Range ophiolite in the southern Coast Ranges of California. One new genus and twenty-one new species are documented. In addition, radiolarian assemblages from eighteen limestone, chert and siliceous mudstone samples from Stanley Mountain have been analyzed quantitatively to evaluate middle Oxfordian to upper Tithonian trends in the Family Parvicingulidae and the Family Pantanelliidae. Results show (1) confirmation of a previously observed increase in abundance and diversity of parvicingulids in younger strata; (2) fluctuations in pantanelliid abundance and diversity with maximum abundance occurring within the parvicingulid-dominated part of the succession; and (3) a significant influence of rock type and/or processing techniques on the composition of radiolarian thanatocoenoses. As proposed by the Pessagno and Blome radiolarian paleogeographic model, Parvicingula and Praeparvicingula are useful indicators of mid- to high-latitude deposition during the Upper Jurassic. Ristola holds true to the model as a lower-latitude indicator, but the Family Pantanelliidae, also believed to be indicative of low- to mid-latitudes, varies significantly in abundance, diversity and distribution within the Tethyan Realm and Southern Boreal Province. Such variability indicates that its presence is controlled largely by taphonomic processes and the paleoceanographic regime.