Polynostratigraphy and palaeoenvironments across the Oligocene-Miocene boundary within the Centinela Formation, southwestern Argentina

Abstract

Abstract Palynological analysis of the Centinela Formation, exposed in the foothills of the Patagonian Andes, has revealed the presence of pollen, dinoflagellate cysts, and chlorococcalean and prasinophycean algae. These groups are here reported from the Centinela Formation for the first time. Sporomorph and dinoflagellate cyst assemblages suggest a Late Oligocene and Early Miocene age. These results coincide with a 87 Sr/ 86 Sr age close to the age of the Oligocene-Miocene boundary obtained from the lower part of the section. Palynological information from the Centinela Formation permits correlation with Upper Oligocene and Lower Miocene units cropping out along the Atlantic Patagonian coast. Assemblages from the lower part of the section suggest that the beds were deposited under marine, near-shore palaeoenvironmental conditions with a strong continental influence. In the middle part of the section, high dinoflagellate cyst ratios coincide with a maximum flooding surface recorded in the Centinela Formation. Towards the top of the Centinela Formation, the sporomorph assemblages reflect the development of vegetation adapted to coastal environments, which agrees with the sparse occurrence of marine palynomorphs. A new dinoflagellate species, Hystrichostrogylon sulcatum , is proposed. This species appears to range across the Oligocene-Miocene boundary and is particularly abundant in the lowest Miocene.