ENSAMBLES DE MICROFÓSILES (FORAMINÍFEROS Y NANOFÓSILES CALCÁREOS) CRETÁCICOS DEL SUBSUELO DE LA CUENCA DE MAGALLANES, ISLA DE TIERRA DEL FUEGO, CHILE

Abstract

Foraminifera and calcareous nannofossils were studied in washed drill-cuttings of three wells from the Chilean sector of the Magallanes Basin. This contribution aims to identify, characterize and illustrate microfossil assemblages throughout the Cretaceous sedimentary record to integrate foraminiferal and the nannofossil data and improve further biostratigraphic studies in the basin. The analyzed Cretaceous succession in these wells corresponds to five discrete foraminiferal and nannofossil assemblages, which were recognized and are described here. The Valanginian–Hauterivian assemblage is characterized by a low diversity of benthic foraminifera typical of this age, like Lenticulina nodosa and Astacolus gibber, and nannofossil markers Lithraphidites bollii and Eiffellithus striatus; then, the Aptian–Albian begins with a predominance of radiolarians and transitions into a highly diverse assemblage comprising mainly gavelinellid benthics as well as abundant planktic foraminifera, which include Muricohedbergella delrioensis and M. portsdownensis, and diverse calcareous nannofossils with the marker Sollasites falklandensis. The Cenomanian can be distinguished by the presence of the nannofossil Corollithion kennedyi and also abundant planktic foraminifers; whilst the Coniacian–Campanian assemblage is characterized by planktic foraminifera like Costellagerina bulbosa, C. pilula, and Planoheterohelix reussi, as well as a diverse benthos and the nannofossil species Reinhardtites anthophorus, Eiffellithus eximius, and Eprolithus floralis. Finally, the Maastrichtian assemblage is characterized by mainly agglutinated foraminifera and few poorly preserved nannofossils. A detailed systematic list of both foraminiferal and nannofossil species is presented, intended to serve as a catalogue that will help to identify the different Cretaceous assemblages of the basin in future studies.