Cenozoic Bathyal and Abyssal Calcareous Benthic Foraminiferal Zonation

Deep-sea (bathyal-abyssal) benthic foraminifera provide a potential supplement to planktonic biostratigraphy. Benthic foraminifera are more resistant to dissolution and are often found in upper bathyal, lower abyssal, and higher latitude sediments which contain impoverished planktonic faunas. The biostratigraphic utility of benthic foraminifera was previously limited by poor understanding of their taxonomy and paleobathymetric distributions. During the past ten years, study of deep-sea benthic foraminifera from Deep Sea Drilling Project (DSDP) and industry wells has provided an improved taxonomic base and empirical observations of age-depth distributions. Building on this data base, we establish 14 bathyal and 12 abyssal zones for the Cenozoic deep sea. Biostratigraphic resolution is higher in the abyssal realm during the Paleogene (9 abyssal versus 6 bathyal zones) and higher in the bathyal realm during the Neogene (3 abyssal versus 8 bathyal zones). During periods of accelerated taxonomic turnover (e.g., in the middle Miocene bathyal zone), deep-sea benthic foraminifera yield fairly refined zonations; in contrast, slow taxonomic turnover occurred during the Paleocene in the bathyal and abyssal realms and in the late Neogene in the abyssal realm, yielding few biostratigraphic subdivisions.