Cretaceous and Paleogene radiolarians from the brazilian continental margin basins: biostratigraphical importance and diagenetic aspects

Abstract

Cretaceous to Paleogene radiolarian assemblages have been recognized through the study of samples from 19 exploratory wells drilled in the eastern Brazilian continental margin, in Pelotas, Santos, Campos, Espírito Santo, Mucuri and Sergipe basins. The distribution of radiolarians along the wells is discontinuous, with intervals showing an expressive number of specimens and others with low numbers. The systematical analysis permitted to identify three orders, 40 families, 108 genera and 281 infra-generic taxa. Among the identified species it was possible to recognize important index-fossils of the different stages from the mid to Upper Cretaceous (Aptian-Maastrichtian), as well as from the Paleogene (Paleocene-Eocene). The analysis of the stratigraphical distribution of taxa made it possible to identify the bioevents, specially the first and last occurrences of taxa that represented the basis for the recognition of the international biozones. Faunistic similarities were observed with cretaceous assemblages elements from California (United States), north of the Apeninnes Mountains (Italy), Betic Cordillera (Spain) and Russian Platatform. The Paleogene species were compared to typical elements from the assemblages found in sediments from the tropical regions in the Gulf of Mexico, in the western region of Cuba, in the Caribbean Sea, in the Phillipines, in the central region of the Indian Ocean, in the eastern Pacific and in the eastern and western North Atlantic. Several bioevents identified in the studied wells permitted the correlation of the brazilian basins assemblages with the Cretaceous to Paleogene standard zonation established to low and middle latitude regions. This survey reports part of the results obtained during the development of the project integrant of the Applied Micropaleontology Network: Projeto Radiolários - Prorad (Radiolarians from the Brazilian continental margin. High resolution biostratigraphy of the Albian to the Paleogene) - carried out through an agreement between Petrobras and UFRJ.