Palaeontology of the Cerros Bayos section, Roca Formation (Danian), La Pampa Province, Argentina

Abstract

New mollusc and echinoid faunas are recorded from exposures of the Roca Formation at Cerros Bayos (La Pampa Province) and assigned to the Maastrichtian - Danian (CC26 - NP3 Zones of Martini 1971) on the basis of the associated nannofossil assemblages. The macroinvertebrate assemblages show increased diversity and abundance of molluscs from Zones NP1 to NP3. One new Danian echinoid, the spatangoid Bolbaster argentinensis sp. nov., is described. At least 19 molluscan genera are recognized; 14 of these, together with seven species, are identified for the first time from Danian exposures of La Pampa Province. An equivocal record of Pyropsis tumida Wilckens, 1905 may extend the range of this tudiclid gastropod from the latest Cretaceous into the Danian. The Cerros Bayos exposures substantially increase our knowledge of diversity trends and biotic recovery immediately following the Cretaceous - Paleogene boundary event, and provide clues to the composition of the little-studied earliest Paleogene faunas in southern Patagonia.