EL DANIANO MARINO DE PATAGONIA (ARGENTINA): PALEOBIOGEOGRAFIA DE LOS FORAMINIFEROS BENTONICOS

Abstract

In the Danian, 234 species of benthic foraminifera are recognized, as the result of a taxonomic revision of the microfauna from the Colorado-Neuquén, Golfo San Jorge, and Austral Basins, based on bibliographic data and mainly authors' unpubIished reports. Among the formerly proposed 37 new names, most of the species have few morphologic differences from well-known cosmopolitan species and seven are considered to be junior synonyms. Only a group of forms is clearly endemic: Buliminella ex gr. B. isabelleana Camacho, widespread in the Colorado-Neuquén Basins (f. tuberculata), San Jorge Basin (f. typica and pascuali), and in the Austral Basin and Antarctic Peninsula (f. procera). These forms composed frequent monospecific assemblages of shallow environments that characterized the marine Danian of the austral region. The recent homeomorph Buliminella elegantissima d'Orb., infaunal, opportunistic, detritivorous and dominant in polluted environments such as the discharge aureole and sewage fields, is used as a paradigmatic element. Similar extreme environments such as the hypersaline waters of the Neuquén-Colorado Basins were inhabited by B. isabelleana, f. tuberculata, and the remainder forms, without ornamentation, disaerobic to anoxic waters represented by laminated deposits of the San Jorge Basin and Antarctic Peninsula. The Jaccard similarity values among the different Basins show: a) higher similarity between adjacent Basins, b) apparent decreasing similarity between Basins at higher latitudes. The paleogeographic map based on the foraminifera distribution defines an area, emerged at present, covered by the Danian sea of 507.000km2, being the major Paleogene transgression in southern South America.

KEY WORDS. Danian. Foraminifera. Paleogeography. Paleobiogeography. Patagonia.