Nanofósseis calcários e a bioestratigrafia do oligoceno-plioceno da margem continental brasileira

Abstract

In the last fifty years, calcareous nannofossils have been frequently used to divide Mesozoic distal marine sedimentary sections around the world. Various international biozonation schemes established in exposed and cored strata are the standart references for this subdivision. To study subsurface sediments, the oil industry uses regional biostratigraphic schemes in which the biohorizon boundaries are fixed by successive disappearances (“last occurrences”) of species. We present here an Oligocene-Pliocene nannofossil zonation established for the Brazilian Continental Margin, as conceived by Richter and colleagues, and relate it to the classical Martini and Okada & Bukry’s proposals. Of the eighteen recognized biozones, six are associated with the Oligocene, ten with the Miocene, and two with the Pliocene. In this study, photomicrographs of the key-species for the biostratigraphy of the interval are shown which were obtained by optical microscopy from a selected group of thin sections are representative of the Brazilian coastal basins. The present paper contributes to the dissemination of knowledge on Cenozoic calcareous nannofossils applied to South Atlantic basins.