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Calcareous plankton biostratigraphy (foraminifers and nannoplankton) and magnetostratigraphy of the upper Oligocene to Pleistocene have been studied in hydraulic piston Cores 516-1 to 516-44, 516A-5 to 516A-11, and 516F-1 to 516F-11, Rio Grande Rise (water depth 1313 m). Some 80 biostratigraphic datum events have been correlated to the magnetic polarity stratigraphy over an interval representing the Matuyama to Chron 5, and Chrons 16 to 23. Coring disturbance and biostratigraphic evidence of a condensed section preclude unambiguous identification of polarity or biostratigraphic events over an approximately 30-m interval in the middle and upper Miocene. Sedimentation rates varied considerably during the Neogene, but an abnormally thick upper Oligocene and lower Miocene section allows a high degree of magnetobiochronologic resolution. A new planktonic foraminiferal zonation for the Miocene completes the midlatitude Neogene zonation of the South Atlantic. Important magnetobiostratigraphic correlations at Site 516 and their estimated magnetochronology include: (1) Oligocene/Miocene boundary = first appearance datum (FAD) Globorotalia kugleri = last appearance datum (LAD) Reticulofenestra bisecta = mid-Anomaly 6C (Chron 23) = 23.7 Ma; (2) Aquitanian/Burdigalian boundary = LAD G. kugleri = between base Anomaly 6A and top of unnumbered anomaly between 6A and 6B (Chron 21) = 21.8 Ma; (3) Zone N6/N7 boundary = LAD Catapsydrax dissimilis (= FAD G. pseudomiozea and G. zealandica) = Chron 16/17 boundary = 17.6 Ma; (4) early/middle Miocene (= Burdigalian/Langhian) boundary = FAD Praeorbulina sicana = midpart of Anomaly 5C (Chron 16) = 16.6 Ma or FAD P. glomerosa = just above Anomaly 5C (inferred) = 16.3 Ma; (5) Zone N8/N9 boundary = FAD Orbulina suturalis above Anomaly 5C (later part Chron 16, inferred); (6) Miocene/Pliocene boundary = LAD Globoquadrina dehiscens LAD Globorotalia lenguaensis = basal Gilbert Chron = 5.3 Ma. INTRODUCTION Integrated studies on planktonic biostratigraphy and magnetobiostratigraphy in deep-sea cores and on uplifted marine sections on land are providing the framework for more refined age estimates of biostratigraphic zonal boundaries, events, and chronostratigraphic boundaries. Although we now have a relatively precise magnetobiostratigraphy for the Paleogene (Alvarez et al., 1977; Lowrie et al., 1982; Poore et al., in press) and the Pliocene-Pleistocene (Hays et al., 1969; Berggren, 1973), the Miocene remains somewhat incomplete (Ryan et al., 1974), at least in terms of the calcareous plankton. The relatively complete Neogene biostratigraphy (Pujol, this volume) and magnetostratigraphy (Hamilton and Suzyumov, this volume) of Site 516 have encouraged us to make a more detailed investigation of this site. Seven holes were drilled at Site 516 on the Rio Grande Rise in 1313 m water depth (Fig. 1). Four of these (516B to E) were abandoned with little or no recovery. The hydraulic piston corer (HPC) was used for Hole 516 to 183.3 m with 81% recovery. Hole 516A recovered the upper 69.5 m of the section with 88% recovery, and Barker, P. F., Carlson, R. L., Johnson, D. A., et al., Intt. Repts. DSDP, 72: Washington (U.S. Govt. Printing Office). Hole 516F was washed to 169.1 m and then rotary drilled with continuous coring to 1270.6 m. Thus there is an overlap of the upper 70 m of section in Holes 516 and 516A and a 13-14 m overlap between the lower part of Hole 516 and the upper part of Hole 516F. We have examined nearly 160 samples (105 from Hole 516, 40 from 516A, and 12 from 516F) from the upper Oligocene-Pleistocene at Site 516. An essentially complete Neogene stratigraphic succession appears to be present with a rich, well-preserved planktonic foraminiferal fauna and moderately to well-preserved calcareous nannoplankton floras in most samples. A markedly reduced rate of sedimentation (condensed section) is postulated over an interval of about 14 m (between 56 and 70 m sub-bottom = Cores 516-14 to 516-17), and an upper Miocene unconformity may lie between Core 516-14 and Section 516-13-2 at about 56 m sub-bottom. In this 14-m interval, many calcareous plankton taxa associated with middle-upper Miocene stratigraphy are present together, and distinct (bio)stratigraphic separation is not possible. A relatively complete Neogene polarity stratigraphy has been recorded at Site 516. Elements of the Matuyama (beginning with the Jaramillo Event), Gauss, and Gilbert chrons and the latest part of Chron 5 were identified in Cores 516-1 to 516-13 above the inferred hiatus at approximately 55 to 56 m. Cores 516-14 and 516-15 675 W. A. BERGGREN, M. P. AUBRY, N. HAMILTON

Neogene Magnetobiostratigraphy of Deep Sea Drilling Project Site 516 (Rio Grande Rise, South Atlantic)