Tithonian Calcareous Nannofossils Assemblages from Southern Argentinian basins and Antartica

CONCHEYRO, A; LESCANO, M.

Trelew

Simposio; V Simposio Argentino del Jurasico; 2013

Museo Paleontológico Egidio Feruglio

The Late Jurassic calcareous nannofossil assemblages are becoming more important in stratigraphy together with calpionellids and absolute ages, due to the accuracy provided by nannoconids, which are especially valuable for the Tithonian to Early Cretaceous transition. These nannofossils had a worldwide distribution, with some cosmopolitan species, and more endemic ones, depending on their paleogeographic position and latitude. New studies on the Tithonian nannoflora of the Neuquén and Larsen basins (Patagonia and Antarctica, respectively) are considered with the aim to establish stratigraphic correlations with other southern Mesozoic basins and comparisons with global chronostratigraphic standards. In the Neuquén Basin, the Tithonian-Berriasian calcareous nannofossil associations comprise the interval between the NJ20 to NK1 Biozones, characterized by eight Tithonian bioevents: FOs of Polycostella beckmanii, Polycostella senaria, Zeugrhabdotus embergeri, Eiffellithus primus, Hexalithus noeliae, Umbria granulosa, Raghodiscus asper, Nannoconus wintereri and five Berriasian bioevents: FOs of Nannoconus kampneri minor, Cruciellipsis cuvillieri and N. kamptneri kamptneri and LOs of Polycostella senaria Thierstein y Nannoconus wintereri. They also include the occurrence of six species of nannoconids with Tethyan affinities that indicate sporadic seaway connections during that time. In the Larsen basin, Antarctica, calcareous nannofossils are recovered from Antarctic Peninsula and the western area of James Ross Island. Their assemblages are partially dissolved, they show low diversity and abundance and contain Polycostella beckmanni, which indicates middle Tithonian age and allows correlation with the Neuquén Basin. Nannofloras in the Austral Basin or Malvinas have not yet been recognized.Polycostella beckmanii, Polycostella senaria, Zeugrhabdotus embergeri, Eiffellithus primus, Hexalithus noeliae, Umbria granulosa, Raghodiscus asper, Nannoconus wintereri and five Berriasian bioevents: FOs of Nannoconus kampneri minor, Cruciellipsis cuvillieri and N. kamptneri kamptneri and LOs of Polycostella senaria Thierstein y Nannoconus wintereri. They also include the occurrence of six species of nannoconids with Tethyan affinities that indicate sporadic seaway connections during that time. In the Larsen basin, Antarctica, calcareous nannofossils are recovered from Antarctic Peninsula and the western area of James Ross Island. Their assemblages are partially dissolved, they show low diversity and abundance and contain Polycostella beckmanni, which indicates middle Tithonian age and allows correlation with the Neuquén Basin. Nannofloras in the Austral Basin or Malvinas have not yet been recognized.