Quistes de dinoflagelados y polen asociado del Cretácico Inferior (Formación Springhill) de la Cuenca Austral, Plataforma Continental Argentina

Abstract

Well preserved and moderately diverse, early Cretaceous dinoflagellate cyst assemblages were recovered from the Springhill Formation at wells MLD3 and MLD4, of southeastern Argentina. The relative dating of the sequences is based on the first and last occurrences of age-diagnostic dinoflagellate cysts taxa. These bioevents are, in ascending order: last occurrence of Kleithriasphaeridium fasciatum, first occurrence of Prolixosphaeridium parvispinum, last occurrence of Phoberocysta neocomica, first occurrence of Herendeenia postprojecta, first occurrence of Odontochitina operculata, last occurrence of Cassiculosphaeridia magna and last occurrence of Kaiwaradinium scrutillinum and support a late Barremian age for both stratigraphical sequences. The last occurrence of K. fasciatum and the first occurrence of P. parvispinum recorded at the lower part of the marine interval in the MLD3 well and the upper part of the MLD4 well, constrain the age of the beginning of the transgressive episode around the early/late Barremian transition, not younger than the early late Barremian. In these intervals, the upper part of the Australian Muderongia testudinaria Zone Helby can be indirectly recognized. The top of the Muderongia australis Zone was recognized at the uppermost marine part of the MLD3 well, assigned to the late Barremian. First occurrences of primitive angiosperm pollen grains like cf. Clavatipollenites, Spinizonocolpites sp., Arecipites sp., Asteropollis, Foveomonocolpites and Tricolpites were recorded too in both wells.