Late Cretaceous Archaeomonadaceae, Diatomaceae, and Silicoflagellata from the South Pacific Ocean, Deep Sea Drilling Project, Leg 29, Site 275

Abstract

Pacific, at the southeast margin of Campbell Plateau, on a relatively elevated bottom eroded by bottom currents. Under a thin layer of Recent-Pleistocene foraminiferal ooze, Late Cretaceous siliceous sediments were drilled: a bright-yellow upper unit is 14.5 meters thick and is underlain by a dark-brown unit down to 62.0 meters. At this depth further drilling was prevented by hard siliceous shale. The two units are distinctly different both lithologically and paleonto- logically. Unit 1, down to 14.5 meters, consists of diatom-radiolarian ooze with abundant siliceous microfossils, mostly of cold-water oceanic plankton, such as Archaeomonadaceae, Diatomaceae, Radiolaria, Site 275 of the Deep Sea Drilling Project is located in the South Microfossils make up 60%-90% of the sediment. The underlying Unit 2 consists of olive-gray partly detrital clayey silt with thin inter- calcations of lithified siliceous shale. It yielded Radiolaria, Dino- flagellata, and colonies of green algae, but no Archaeomonadaceae, Diatomaceae, or Silicoflagellatae. Silicoflagellatae, with accessory sponge spicules. Unit 1 were examined and evaluated in detail. Thus far, 158 species have been determined, including 4 new genera, 57 new species, and 3 new combinations, all extinct. The sediment is of Late Cretaceous age. Based on the abundance and vertical ranges of the species, 9 biozones and 12 subzones have been established.