Coccoliths, as the dominant constituent of many Deep Sea Drilling Project cores, have provided the means of rapid and detailed biostratigraphic zonation to help guide ocean-sediment coring operations aboard D.V. Glomar Challenger. The Cenozoic has been divided into 50 to 60 zones and subzones which are most effective for middle- and low- latitude sites. Because key stratigraphic coccoliths have proved more resistant to diagenetic change than planktic foraminifers, they contributed to dating of sedimentary beds within and just above basalt, directly demonstrating the correctness of the sea-floor spreading hypothesis. An unexpected discovery of Braarudosphaera beds in the South Atlantic produced valuable speculation on the response of coccolithophorids to paleoceanographic changes.
Samples from the diversity of oceanic terrains explored by early cruises of Glomar Challenger helped in the recognition of the effects of differential preservation —etching and overgrowth from species to species —and in the determination of biogeographic ranges which would affect the taxonomic, paleoecologic and biostratigraphic assignments of coccoliths. DSDP sites have provided the matrix needed to outline depth sequences based on dissolution rank, and paleotemperature sequences based on abundance along latitudinal traverses. New Hydraulic Piston Corer capabilities will make possible application of magnetic reversal stratigraphy to undisturbed cores where coccolith evolutionary transitions and datum-interval stratigraphy can be established.
