CRETACEOUS ORGANIC-WALLED DINOFLA-GELLATE CYSTS FROM THE SOUTHERMOST PART OF SOUTH AMERICA: PALAEOBIOGEOGRAPHIC AFFINITIES.

MARIA VERONICA GULER

Congreso; IV INTERNATIONAL PALAEONTOLOGICAL CONGRESS; 2014

Organic-walled dinoflagellate cysts have been useful for the Mesozoic biostratigraphy of southern South America, particularly for the Lower Cretaceous marine rocks which integrate the most important oil-systems of the Austral/Magallanes and Neuquén basins in Argentina and Chile. Diverse and well-preserved assemblages were recorded from the Springhill and Río Mayer formations deposited during the regionally-extensive marine episodes occurred in the late Valanginian?Albian time interval, related to the thermal subsidence stage of the Austral Basin. The Early Cretaceous dinoflagellate cyst assemblages from the Austral Basin show similarity with those of Australia and Antarctica. The sequence of the age-diagnostic dinoflagellate cyst events that define the biostratigraphy of the Austral Basin is nearly the same as those recorded in wellcalibrated sequences of Australia and Antarctica. Also, the Australian dinoflagellate cyst zonation schemes are clearly applicable. Therefore, assemblages from the Austral Basin reflect strong austral palaeobiogeographic affinities, and support marine connections between southernmost South America, southern and western Australia, and Antarctica in the Early Cretaceous. During the Late Jurassic to Cretaceous the Neuquén Basin was a retro-arc depocentre developed under active convergence of the western margin of South America, connected to the Pacific Ocean. Dinoflagellate cyst assemblages from the late early Valanginian ? earliest Barremian Agrio Formation, well dated by ammonoids and calcareous nannoplankton, closely resemble coeval assemblages from western Europe, exhibiting clear Tethyan affinity. Thus, dinoflagellate cysts constitute another evidence of the extensive exchange of marine biota between the Neuquén Basin and the Tethyan Realm,in agreement with the distribution of echinoids, bivalves and ammonoids. The Late Cretaceous dinoflagellate cyst record is limited to the late Campanian?Maastrichtian interval in the south of South America. Late Campanian? early Maastrichtian and late Maastrichtian assemblages from the Cerro Cazador and Calafate Formations, respectively, southwestern Patagonia (Austral Basindomain), compare well with those from southern Australia, New Zealand, Antarctica, Maud Rise, Kerguelen Plateau and Georgia Basin. Furthermore, in the north of Patagonia, the Jagüel and Pedro Luro Formations (Neuquén and Colorado Basins, respectively) yielded late Maastrichtiandinoflagellate cysts which have little commonality with those from the Calafate Formation. Hence,dinoflagellate cysts assemblages from the southernmost tip of South America would integrate the South Polar Province based on the south high-latitudes Maastrichtian dinoflagellate cyst distribution and denote oceanic connections with the circum?Antarctic regions during the latest Cretaceous.