Mesozoic Calcareous nannofossils from Northern Southamerica and Antarctica.

CONCHEYRO, A

Mendoza

Simposio; Gondwana 12; 2005

Centro de Investigaciones Geológicas

Until the last decade, Mesozoic calcareous nannofossils studies from Southern Southamerica and Antarctica have been almost unknown o very scarce, but systematic and continuous samplings conducted during the last years in these Austral basins, have demostrated the importance of this group for dating Jurassic and Cretaceous marine sequences. After analyzing more than 40 Mesozoic marine sections located in Neuquén, Austral, Malvinas and James Ross basins, a series of bioevents of varying stratigraphic reliabilities have been identified and establish to construct a biostratigraphic framework which can be compared with the current worldwide nannofossil biostratigraphy. Jurassic calcareous nannofossils have been recovered from Neuquén and James Ross basins, and their nannofossils confirm a Toarcian –Tithonian and Tithonian ages respectively for these deposits (Bown, 1996; Concheyro and Scasso, 1999; Scasso and Concheyro, 1999). Lower Cretaceous calcareous nannofossil associations have been extensively studied in Neuquén, Malvinas and Austral basins and they precise the Berriasian - Barremian interval as well as the Aptian - Albian (Bown and Concheyro 2004; Angelozzi and Concheyro, 2002; Concheyro and Angelozzi, 2002). All these assemblages are mainly composed by nannofossils with Tethyan affinities that indicate sporadic seaway connections during those times. Upper Cretaceous nannofosils are also well distributed in Neuquén, Austral, Malvinas and James Ross basins, and they precise the Turonian-Maastrichtian interval. Nannofossils show an austral distribution and it is possible to distinguish some Austral markers as Lucianorhabdus cayeuxii, Biscutum mangnum, Biscutum coronum, Nephrolithus frequens, Cribrosphaerella daniae and Prediscosphaera stoveri among the most representatives (Concheyro and Villa, 1996; Concheyro, 2002; Concheyro, 2004; Concheyro and Angelozzi, 2002). New studies are being performed with the aim to use austral calcareous nannofossil data as one source of palaeobiogeographic Information.