Biostratigraphic studies using planktonic and benthic foraminifers, calcareous nannofossils, radiolarians, diatoms, and silicoflagellates are summarized for the four main sequences (Sites 572 to 575) collected during DSDP Leg 85 in the central equatorial Pacific. Upper Eocene through Quaternary reference sections were recovered at Sites 573 and 574, and middle Miocene through Quaternary and lower Miocene through Quaternary reference sections were cored at Sites 572 and 575, respectively. Detailed graphic correlation plots suggest that Site 573 may contain as many as nine short hiatuses. Site 572 in the fertile eastern equatorial Pacific is apparently free of hiatuses, and Sites 574 and 575 have hiatuses (two each) only in the compressed upper sections.Few inconsistencies exist in the various microfossil stratigraphies. Diachronous species occurrences are identified, and age estimates for 66 late Eocene through Quaternary microfossil datums have been extrapolated from age-vs.-depth plots constructed from 63 datums with direct and/or indirect ties to paleomagnetic stratigraphy.An addendum presents an alternative biostratigraphic time scale for the middle and late Miocene based on a correlation of paleomagnetic Anomaly 5 with paleomagnetic Chron 11.

Leg 85 of the Deep Sea Drilling Project recovered Cenozoic nannofossils from the central and eastern parts of the Pacific equatorial high-productivity area. The low-latitude zonation of Bukry (1973a) was used for dating uppermost Eocene to uppermost Pliocene samples. At two sites (573 and 574) the Eocene/Oligocene boundary was reached, enabling accurate study in spite of an unconformity and strong calcite dissolution. Some unconformities and/or intervals of very low rates of sedimentation are described in detail and correlated from one site to another. The high abundance of species belonging to Reticulofenestra and Dictyococcites permitted the accurate study of these taxa; their morphologic differences and their stratigraphic occurrences are described in detail. A short, tentative, ecological study was made by using the nannofossil dissolution index, the total nannofossil abundance, and the abundance of some taxa. The easternmost site (Site 572) contains some species that are restricted to this site and are characteristic of upwelling areas. Discoasters are totally absent in a sediment interval apparently deposited during a period of unstable climate when glacial to interglacial oscillations were occurring in Antarctica.

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At the northern exit of the Vema Channel, in the Southern Brazil Basin, deep currents linked with Antarctic Bottom Water flow (AABW, below 4200 m) have formed contouritic accumulations along the continental rise. Lithologic and textural investigations were carried out on a Kullenberg core in order to establish a chronology of late Pleistocene‐Holocene fluctuations in AABW flow. The core, spanning the last 600,000 years, was recovered from a field of sediment waves. The deposits consist of fine grained muds. Carbonate contents are very low because deposition takes place near the present‐day carbonate compensation depth. The core stratigraphic framework is based on calcareous nannofossil and excess 230Th analyses. Two main types of facies can be identified: (1) yellowish brown muds, with frequent manganese enrichments forming dark laminae, and (2) homogeneous gray‐green muds. Two indicators of paleocurrent activity have been considered: (1) erosional sediment features that give evidence for high amplitude and short‐term current events, and (2) grain size fluctuations (percentage of panicles greater than 10 µm), indicating low amplitude and long‐term variations. Two periods can be defined. The first one (circa 600 to circa 350 kyr B.P.) is characterized by an instability in current activity, with strong flow events recorded as erosional surfaces. Long‐term fluctuations reveal the existence of several episodes of increased velocity occurring approximately every 50 kyr. The second period (350 kyr B.P. to present) is marked by globally weaker current activity and long‐term fluctuations of lower amplitude and longer duration. Maximum velocities occur preferentially during periods of climatic cooling. These fluctuations might be correlated with the 100 kyr eccentricity cycle of the Earth's orbit.

At Holes 548 and 549A, almost complete sections of Quaternary deposits were recovered. Floral associations were studied in closely spaced samples. Nannofossils are moderately well preserved and contain few reworked forms. The following nannofossils were studied in detail: Gephyrocapsa (closed Gephyrocapsa with G. producta, G. sinuosa, and G. caribbeanica; open Gephyrocapsa: G. doronicoides, subdivided into five variants, and G. ocβanica; G. protohuxleyi; small Gephyrocapsa: G. ericsonii and G. aperta), Pseudoemiliania lacunosa (a round and an elliptical type), Helicopontosphaera (H. sellii, H. gr. kamptneri, and H. neogranulata), Cyclococcolithina (three variants of C. leptopora and two variants of C. macintyrei), Coccolithus pelagicus (C. pelagicus s.s. and two variants). These taxa were used to define supplementary datum levels to be added to the conventional nannofossil datums and to the paleomagnetic events on the curves of sediment accumulation rate for each site. Thus, it is possible to establish a tentative, very detailed nannofossil stratigraphy for the Quaternary. The influence of glaciation on the calcareous phytoplankton is evident, especially during the last 500,000 yrs. The nannofossil total-abundance curve shows fluctuations that resemble closely the fluctuations in the major climatic cycles described by Ruddiman and Mclntyre (1976).