New Miocene mammal assemblages from Neogene Manantiales basin, Cordillera Central, San Juan, Argentina

LÓPEZ GUILLERMO M.; VUCETICH, MARÍA GUIOMAR; CARLINI A. A.; BOND MARIANO; PÉREZ M. E. ; CIANCIO MARTÍN R. ; PÉREZ D. J. ; ARNAL MICHELLE; OLIVARES I. A.

Cenozoic Geology of the Central Andes of Argentina

Universidad Nacional de Salta

Año: 2010;

The discovery of abundant fossil mammals from two different levels of the lowest third of the Chinches Formation (Manantiales basin) located in Cordillera Frontal of San Juan, between 32°30’ and 33°S, is reported. These synorogenic Miocene deposits were deposited by the structural evolution of Cordón de La Ramada fold and thrust belt. Two diverse fossil mammal assemblages have been recognized, one from the lowest bearing horizon, informally named «Chinches bearing level» (CBL), and other, stratrigraphically higher, informally named «Las Hornillas bearing level» (LHBL). Marsupials, Xenarthra (Cingulata and Tardigrada), Notoungulates (four families), Litopterns and six groups of rodents are represented in both mammal assemblages. The presence of Eocardia montana, E. excavata and Nesodon conspurcatus strongly suggests that the bearing levels may be referred to the Santacrucian SALMA (South American Land Mammal Age), late early Miocene in age. The morphology of Stenotatus sp.,Hapalops sp., Protypotherium sp., Neoreomys cf N. austrlis, and the mesotheriines is comparable to that of Santacrucian species. Although both assemblages are referred to the Santacrucian SALMA, differences in composition among them suggest slight differences in age. This temporal reference matches with studies of fission-track and magnetostratigraphy, and sedimentological data of this sequence. The latitudinal intermediate location together with the particular taxonomic composition of these assemblages may provide the clue to understand the differences between Miocene faunas from Patagonia and the Altiplano (Chile and Bolivia). As well, these assemblages are a new important source of information for the comprehension of the phyletic and geographic relationships of several taxa, and the paleoenvironmental changes associated with the uplift of the Andes.