FORAMINIFEROS NUEVOS O CARACTERISTICOS DEL EOCENO MEDIO DE CUENCA AUSTRAL: SIGNIFICADO PALEOZOOGEOGRAFICO

Abstract

Among the three major Paleogene transgressions occurred in southemmost South America in the Lower Paleocene, Middle Eocene and Oligocene, the second one contained the most endemic benthic shallow foraminiferal assemblage. The apparent appearance in the Middle Eocene of typical genera as Cribrorotalia, Boltovskoyella and Notorotalia, already known from Australasia and particularly from New Zealand, signed the austral character but they had an independent speciation. The scarce species common to both areas are unfrequent or monotypical. A sequential biogeographic changing, from almost cosmopolitan assemblages in the Danian to endemic ones in the late Middle Eocene and subantarctic influenced assemblages in the Oligocene, is related to the evolution of the Paleogene ocean. The biotic changes occurred in response to the distinct water masses that have bathed southern South America. The marked Middle-Late Eocene endemism seems to be related to the transitional conditions of the oceanic circulation and the development of well defined currents. The most conspicuous and characteristic middle Eocene species from the Austral Basin are considered. The SEM study of the genus Nummodiscorbis reveals that it belongs to the Family Glabratellidae, and the genus Planoglabratella becomes a junior synonym. Five new species are described: Bulimina fueguina n. sp., Elphidium rioturbiense n. sp., Caucasina selknamia n. sp., Uvigerina manaikense n. sp. and Astrononion pseudorusticum n. sp.