Mid-Atlantic Ridge coccolith and silicoflagellate biostratigraphy, Deep Sea Drilling Project Sites 558 and 563.

Low-latitude coccolith zonation can be used for biostratigraphy at Mid-Atlantic Ridge sites DSDP 558 (lat. 38°N) and DSDP 563 (lat. 34°N). The low-latitude zonal sequence from lower Oligocene to Holocene is interrupted by coolwater assemblages in upper middle Miocene and by hiatuses that removed the lower Pliocene and part of the upper Pliocene. A gap in the range of zonal guide fossil Discoaster druggii in the lower Miocene, also identified in other ocean basins, occurs at both DSDP 558 and 563. Coccoliths are abundant and moderately overgrown at both sites. Pentaliths occur in the Oligocene at DSDP 563 but are missing at DSDP 558, probably the result of diagenesis. New taxa of coccoliths identified include Cyclolithellai neoaprica Bukry, n. sp., and Sphenolithus calyculus Bukry, n. sp.

Silicoflagellates are limited to the upper Quaternary at DSDP 558 with warm-water assemblages of the Dictyocha aculeata Zone and possibly the upper Mesocena quadrangula Zone, as indicated by the presence of Dictyocha lingii. A new silicoflagellate species, Distephanus floridus Bukry, n. sp., is described.