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Cenozoic Planktonic Foraminiferal Biostratigraphy of the Southwestern Atlantic (Rio Grande Rise): Deep Sea Drilling Project Leg 72

1983; Linguagem: Inglês

10.2973/dsdp.proc.72.129.1983

C. Pujol,

Atmospheric and Environmental Gas Dynamics

Our study focuses on the biostratigraphy of Cenozoic planktonic foraminifers sampled during Leg 72.We located the sites of interest on the Rio Grande Rise and its surroundings (southwestern Atlantic).A rich assemblage of the microfauna and the recovery of a good Cenozoic sequence offered an opportunity for gathering documentary evidence on the planktonic biostratigraphy of this area.Site 515 was drilled in the Brazil Basin at a depth of 4250 m.The planktonic foraminifers were generally poorly preserved, with the exception of a short lower Eocene sequence at the base of Hole 515B.The equivalent of Zones P9..to P6b were identified at the base of Hole 515B.Holes 516 and 516A and Sites 517 and 518 contain a good Pliocene sequence in which Subzones PL1 to PL6 were differentiated.At Hole 516, the cores range from lower to upper Miocene, and there is probably a brief gap at the base of the upper Miocene.Despite the extensive lower Miocene section, stratigraphic refinement according to Blow's zones was difficult because of a high-latitude component.The spiny morphotype of Globoquadrina as in Site 357 (Perch-Nielsen et al., 1977) and Globorotalia zealandica group are the typical components of this lower Miocene high-latitude fauna.G. miozea conomiozea morphotypes have a long stratigraphic range occurring from lower-middle Miocene to the base of the Pliocene.Hole 516F contains a complete succession between the basal Miocene and the Cretaceous/Tertiary boundary.Again, stratigraphic definition for the Eocene-Oligocene is somewhat difficult because of the high-latitude fauna.The zones between P10 and P20 are difficult to differentiate on species data.Orbulinoides beckmanni is not recognized, and some genera like Hantkenina seem to have an unusual stratigraphic distribution.In the middle and upper Eocene, Globigerinita forms are very common.The Globigerinatheka genus is also well represented, especially by G. subconglobata and G. index.Such an assemblage is typical for a temperate-water fauna.A thick Cretaceous slump occurs in the lower Eocene and disturbs the microfauna near the Paleocene/Eocene boundary.Finally, the Paleocene section is complete, allowing differentiation of Zone PI in spite of bioturbation and reworked sediment.