Late Maastrichtian to Danian organic-walled dinoflagellate cysts and calcareous nannofossils from eastern Austral Basin, Patagonia, Argentina

Abstract Late Maastrichtian to Danian dinoflagellate cyst and calcareous nannofossil biostratigraphy was analyzed at the Sur Rio Chico borehole, Austral Basin, Argentina. Two stratigraphical intervals from the 965 to 1003 m below ground surface of the drilled section were defined. The co-occurrence of Manumiella bertodano, M. seelandica and M. conorata in the 990–1000 to 1000–1003 mbgs interval, associated with the top of the nannofossil Neprolithus frequens miniporus Zone indicated a late (probably latest) Maastrichtian age. The acme of the presumed heterotrophic Manumiella spp. and the acme of the mesotrophic cool-water nannofossil Prediscosphaera stoveri, together with other cool-water taxa Arkhangelskiella cymbiformis, Kamptnerius magnificus and Nephrolithus frequens may indicate cool nutrient–rich waters in this interval. Finally, the co-occurrence of dinoflagellate cyst taxa Carpatella cornuta, Cerodinium diebelii, Danea californica, Senoniasphaera inornata and Palaeoperidinium pyrophorum linked to the nannofossil NP3 Zone, suggest a middle Danian age for the 965–970 to 985–990 mbgs interval. An acme of P. pyrophorum herein related to the Pp2 of New Zealand, might reflect an episode of cool temperature during the Danian in the Austral Basin. The sedimentary succession is represented by the Campo Bola Formation within which two discontinuities were recognized; the older is of early-late Maastrichtian, and the younger the latest Maastrichtian to the earliest Danian. A third discontinuity involving the middle to late Paleocene separates the Campo Bola Formation from the overlain Eocene Man Aike Formation.