Light microscope characterization of the structure and biostratigraphy of some cretaceous species of the Calyptrosphaeraceae family (calcareous nannofossils) recognized in brazilian marginal basins

Abstract

- The purpose of this study is to present L.M. (light microscope) descriptions ofsome holococcoliths species,
recognized in Cretaceous strata of Brazilian marginal basins, in order to optimize their use in routine biostratigraphic
dating. In the specialized Iiterature most of the nannolith species object of this study present insufficient L.M. taxonomic
descriptions, and the few papers on this subject generally show illustrations that are not clear enough. Part of these
holococcoliths species are mentioned in Cretaceous international biozonal schemes (Risatti, 1973; Sissingh, 1977;
Perch-Nielsen, 1985) but in those schemes adopted by PETROBRAS, only some of them are used in routine dating of
the Cretaceous strata from Brazilian marginal basins. Ali the studied nannofossils have been recovered from core of the
Albian / Maastrichtian section of 11 boreholes from Campos, Ceará, Potiguar, Santos and Sergipe basins (eastern
Brazilian continental margin). Eight species were identified and they belong to the following genera: Calculites, Munarinus,
Octolithus, Okkolithus, Orastrum, Ottavianus and Owenia, ali of them are assigned to the Calyptrosphaeraceae family.