Paleogeography and paleoenvironments of Central Patagonia from the Late Cretaceous to the Miocene: The Paleogene Andean gap and the rise of the Northpatagonian Altiplano.

ARAGÓN E., F. J. GOIN, Y. E. AGUILERA, M. O. WOODBURNE, A. A. CARLINI, M. F. ROGGIERO

LA PLATA

Workshop; Paleogeography and Paleoclimatology of Patagonia: effects on biodiversity; 2009

FAC. CS. NATURALES Y MUSEO - DALHOUSIE UNIVERSITY

In its large expanse, the Andes comprise a barrier that affects in many ways the distribution of climate in the region. From a geological perspective, the Andean mountain system is a supra-subduction feature at the active South American plate margin. This plate margin has been active since the Late Jurassic. The modern configuration of the Andes and its large N-S variations are the result of post-Miocene tectonic processes and the particular characteristics of each segment (subduction angle, angle of convergence, thickness of the oceanic plate, relationships between the segments, composition of the continental crust, etc.). For this reason, it is necessary to review the pre-Miocene orogenic development and its potential regional geographic role for each segment in particular and whether or not there was a marine connection between the Atlantic and Pacific oceans. The northern Patagonian segment of the Andes preserves a geotectonic history which differs from its neighbors in that it behaved as a transcurrent margin during the Paleogene. This episode was characterized by extension, with the evolution of forearc, arc, and backarc basins and the migration of calcalkaline volcanism toward the backarc. The Andean uplifted segment was eroded and deactivated and permitted the flow of humid air from the Pacific to the extra-Andean regions. Simultaneously in the backarc region of this segment, the 1200-1500 m uplift of the North Patagonian Massif took place, resulting in an Altiplano of 100,000 m2 which dominated the area during the Oligocene. It is estimated that the climate in the Altiplano was humid, seasonally cool, in contrast to the seasonally more uniform humid climates to the south. The most important mammalian turnover that happened during the Paleogene occurred at the early Oligocene, concurrently with the full opening of the Drake Passage and the global cooling. The latitudinal climate gradient that began at the Eocene- Oligocene transition affected sharply the whole Patagonian region, and at least at these times the mammalian turnover affected the mammalian associations both East and West of the Andean Range. This work considers the possible changes in the geographic segments during the Cenozoic for the Northern Patagonian region and their effect on climate control, as well as a consideration of the principal sedimentary and magmatic cycles, global climatic events and main faunal cycles.