Mammalian biostratigraphy and biochronology at Gran Barranca: the standadr reference section for the continental middle Cenozoic of South America.

CARLINI A.A.; BOND, M.; LÓPEZ, G.; REGUERO, M.; SCARANO A.C.; MADDEN, R.H.

Denver EU

Simposio; 64th Annual Meeting Society of Vertebrate Paleontology; 2004

SVP

The Sarmiento Formation at (iran Barranca is a 21(5m thick composite section containing over 43 different fossil-bearing les els. Based on the stratigraphic occurrences of standard index and guide taxa, there are at least six different faunal zones. The occurrences of Notostylops, Astraponotus Pyrotherium, Colpodon and Astrapothericulus together with other mammalia guide taxa permit recognition of the standard sequence of middle Cenozoic South America Land-Mammal Ages at Gran Barranca. In addition, clear stratigraphic relationships betwee fossil mammals. dated tuffs and lavas, magnetic polarity intervals, and unconformities of cot strained temporal duration, permit establishing a refined biochronology for assemblages Ar biozones. The Barrancan is essentially as Cifelli established based on Sitnpson´s collections at stratigraphy. and its upper temporal limit can he established. An assemblage of intermedia taxonomic composition occurs at the top of the Barrancan interval, if amenable to age contri may warrant recognition. The Mustersan is represented by two levels directly dated and brat eted by dates from overlying and underlying tuffs. An unconformitylseparates the Musters, from overlying fossil levels. Knowledge of the Astraponotcen plus Superieur of Ameghino significantly improved and stratigraphy suggest the age of the base of a Tinguirirican Land Mammal Age may be more precisely constrained at Gran Barranca. A rich pre-Deseadan and post-Tinguirirican level with guide taxa of both faunal units and primitive rodents must be accommodated. The Deseadan has been one of the least well-known parts of the section at Gran Barranca. Deseadan levels can be precisely located with respect to the basalt complex and associated unconformities. The rich Colhuehuapian levels are the best constrained temporally. The topmost fossil levels at Gran Barranca yield a Pinturan assemblage older than that of the type area.