MAMMALIAN BIOSTRATIGRAPHY AND BIOCHRONOLOGY AT GRAN BARRANCA: THE STANDARD REFERENCE SECTION FOR THE CONTINENTAL MIDDLE CENOZOIC OF SOUTH AMERICA

CARLINI, A. A.1, MADDEN, R.H.2, VUCETICH, M.G.1, BOND, M.1, LÓPEZ, G.1, REGUERO, M.1 AND SCARANO, A.1

La Plata, Buenos Aires

Congreso; XVI Congreso Geológico Argentino, Simposio Gran Barranca; 2005

MAMMALIAN BIOSTRATIGRAPHY AND BIOCHRONOLOGY AT GRAN BARRANCA: THE STANDARD REFERENCE SECTION FOR THE CONTINENTAL MIDDLE CENOZOIC OF SOUTH AMERICA Carlini, A. A.1, Madden, R.H.2, Vucetich, M.G.1, Bond, M.1, López, G.1, Reguero, M.1 and Scarano, A.1 1Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, Paseo del Bosque, 1900 La Plata (Argentina) 2Duke University Medical Center, Durham, NC (USA) The Sarmiento Formation at Gran Barranca is composite section containing over 49 different fossil-bearing levels. 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 mammalian guide taxa permit recognition of the standard sequence of middle Cenozoic SALMAs at Gran Barranca. Clear stratigraphic relationships between fossil mammals, dated tuffs and lavas, magnetic polarity intervals, and unconformities of constrained temporal duration, permit establishing a refined biochronology. The Casamayoran “Barrancan” is essentially as Cifelli established, and its upper temporal limit can be established. An assemblage of intermediate taxonomic composition occurs at the top of the “Barrancan” interval. The Mustersan is represented by two levels directly dated. An unconformity separates the Mustersan from overlying fossil levels. Knowledge of the “Astraponoteen plus Superieur” of Ameghino is significantly improved. A rich pre-Deseadan and post-Tinguirirican level with guide taxa of both faunal units and primitive rodents must be accomodated. The Deseadan has been one of the least well-known parts of the section at Gran Barranca. The rich Colhuehuapian levels are the best constrained temporally. The topmost fossil levels at Gran Barranca yield a “Pinturan” assemblage.