Tithonian–Berriasian calcisphere (calcareous dinoflagellate cysts) zones in the Neuquén Basin, Argentina: correlation between Southern Andes and Tethyan regions

Abstract

This work presents a regional biostratigraphic study on the calcisphere (calcareous dinoflagellate cysts) zones of the Tithonian–Berriasian in the Neuquén Basin, Western Argentina. This stratigraphic interval is mostly represented by a thick rhythmic succession of marlstone and limestone, with an abundant fossil content and a remarkable stratigraphic continuity along several hundred meters, known as Vaca Muerta Formation. This formation was originated in distal hemipelagic setting of a carbonate ramp and is one of the most important unconventional hydrocarbon reservoirs in the world. The detailed study of six stratigraphic sections, allowed the elaboration of a reliable biostratigraphic scheme and its correlation with Andean ammonites, calpionellids, and polarity zones. Calcareous dinoflagellate cysts within the Vaca Muerta Formation are moderately preserved. Despite that, twenty-nine species and nine biozones have been identified: Committosphaera pulla, Parastomiosphaera malmica, Colomisphaera tenuis, Colomisphaera fortis, Stomiosphaerina proxima, Stomiosphaera wanneri, Colomisphaera vogleri and Colomisphaera conferta. These results allow to contribute to an increasingly solid chronostratigraphic framework in the Neuquén Basin.