Gran Barranca, a twenty-three million year record of Middle Cenozoic faunal evolution in Patagonia.

MADDEN R.H.; KAY, RF; VUCETICH MG; CARLINI A.A.

The Paleontology of Gran Barranca: Evolution and Environmental Change through the Middle Cenozoic of Patagonia”, Madden, R.H., Carlini, A.A., Vucetich, M.g. and Kay R.F. (eds).

Cambridge University Press

Lugar: Cambridge; Año: 2010; p. 423 - 439

Explosive Plinian volcanism provided a rich local source of fine-grained volcaniclastic sediments to central Patagonia in the middle Cenozoic. The chronology of the accumulation extends from the Middle Eocene Climate Optimum (MECO) to the Middle Miocene Climate Optimum (MMCO) and includes the only southern hemisphere continental record across the Eocene–Oligocene transition (EOT) and into the Oi-1 glaciation of Antarctica. The continuity of sedimentation is broken by hiatuses of different temporal magnitude that appear to correspond chronologically with changing sea level and the intensity of erosion. The Sarmiento Formation at Gran Barranca is subdivided into six members, Gran Barranca (41.6–38.7 Ma), Rosado (38.7 Ma), Lower Puesto Almendra (37 Ma), Vera (35–33.3 Ma), Upper Puesto Almendra (31.1–26.3 Ma), and Colhue-Huapi (20.4–18.7 Ma). The sequence of fossil mammal faunas in the Sarmiento Formation at Gran Barranca is the standard sequence of South American Land Mammal Ages (SALMAs) and their subdivisions. The sequence includes the Barrancan SALM Subage, an intermediate level “El Nuevo,” the Mustersan SALMA, the Tinguirirican SALMA, an early Deseadan level “La Cantera,” the Deseadan SALMA, Colhuehuapian SALMA, and a Pinturan level. The taxonomic composition and most distinctive features of each of these levels at Gran Barranca is summarized, with special attention to the new and rich record of small mammals recovered by intensive sampling by wet washing. Given the climate intimacy between narrow peninsular Patagonia, the southeast Pacific and South Atlantic oceans, and the vast Southern Ocean today, the terrestrial environments of middle Cenozoic Patagonia were probably subject to the influence of global climate change as recorded in the marine sea-floor record. Evidence that the terrestrial biota responded to the trends and events recorded in marine sediments of the southern oceans depends on an understanding of how the magnitude and rate of this climate change drives evolutionary and biotic change, and whether