DINOFLAGELLATE CYSTS FROM GREAT VALLEY SUPERGROUP

The Great Valley Supergroup (GVS) of Northern California Coast Ranges consists of 15 km thick monotonous siliciclastic turbidities with interspersed tuff horizons and micritic nodules. The age of GVS ranges from late Tithonian up to Maastrichtian, and its strata contain Radiolaria, Calcareous nannofossils, as well as bivalve Buchia and Ammonites.

Paleontological investigation has established precise biozonations for fossil contents of GVS. Six Buchia biozones are introduced in the Tithonian to Hauterivian interval (Jones et al. 1969). Radiolarian biostratigraphy in dating the Lower Cretaceous portion of GVS is demonstrated by Pessagno (1977 b). Calcareous nannofossils zonation has been established for Tithonian to Albian interval of GVS (Bralower 1989).

Dinoflagellate cysts are recovered while the samples of micrite nodules from Albian interval were processed to extract calcified Radiolaria (Mohsen Kariminia, research for Ph.D. dissertation in progress). Unlike standard palynological methods, just acetic acid is utilized, and cysts are recovered from dried residue. Abundance and preservation of cysts are remarkable. Reviewing the records of the last four decades indicates that dinoflagellates within the GVS have received far less consideration than other fossil groups. While the age determinations of GVS is fully intertwined with biostratigraphic studies of other groups of fossils(e.g. Radiolaria, Calcareous nannofossils, Buchia), and because of Boreal nature of the radiolarian faunas of the GVS, integration of the new findings on dinoflagellates with existing data of other groups will enhance the biostratigraphy of dinoflagellates in the Late Jurassic and Early Cretaceous Boreal realm.