Palaeogeography and palaeoenvironments of northern Patagonia from the Late Cretaceous to the Miocene: The Palaeogene Andean gap and the rise of the North Patagonian High Plateau

Abstract

We summarize the geotectonic history of the southern (mostly Patagonian) Andean Cordillera, and its possible influence on the regional expression of global climates, biogeography, and important aspects of mammalian evolution in South America. The northern Patagonian segment of the Andes contrasts with neighbouring sections in that, during Palaeogene times, there was a transform margin stage; this influenced the Andean climate in addition to global climate changes. This segment underwent alternating subduction and transform episodes that suggest the existence of a proto-Andes and an Oligocene Andean gap for the San Carlos de Bariloche area. Coeval with this gap (and at the backarc region of this segment), the 1200-1500m uplift of the Northern Patagonian Massif took place, resulting in an altiplano (high plateau), or Northern Patagonian High Plateau (NPHP), of 100000km2, which dominated northern Patagonia during the Oligocene. It is estimated that, by these times, climate in the NPHP was humid and seasonally cool, in contrast to the seasonally more uniform, humid climates of the lower lands peripheral to it. The NPHP may have acted as a biogeographical barrier between central and southern Patagonia, on one side (as part of the Austral Biogeographical Kingdom), and the rest of South America (Holotropical Kingdom) on the other. The most important Paleogene mammalian turnover transpired at the Early Oligocene, concomitantly with the full opening of the Drake Passage and associated global cooling. The latitudinal climate gradient that began at the Eocene-Oligocene transition affected sharply the entire Patagonian region, an effect that was enhanced by the uplift of the NPHP. © 2011 The Linnean Society of London.