Palynology and alluvial facies from the mid-Cretaceous of Patagonia, subsurface of San Jorge Basin, Argentina

Facies associations distinguished in the Caleta Olivia Member of the Cañadón Seco Formation, San Jorge Basin, reveal an ancient sandy multichannelled fluvial system with moderate sinuosity and well developed proximal (natural levee, splay) and distal (shallow ponds, backswamp) overbank deposits. A palynological assemblage was recovered from these sediments and dated as late Albian-Cenomanian. This is the first palynological dating of sediments of this age for this basin and Argentina. The pollen assemblage is characterized by primitive types of non-magnolioid angiosperms: Tricolpites minutus (Brenner) Dettmann, Nyssapollenites cf. squamosus Dettmann, Phimopollenites pannosus (Dettmann & Playford) Dettmann, Cupuliferoidaepollenites cf. parvulus (Groot & Penny) Dettmann, Rousea georgensis (Brenner) Dettmann. A humid, continental mild to warm climate is suggested for this region during the mid-Cretaceous. To the Cañadón Seco Formation (and its equivalents on the north flank of the basin and marginal areas) is assigned a late Albian-Cenomanian age; the uppermost section may be early Turonian in age.