Andean uplift and climate change

Abstract
Sedimentological data indicate that a semi-arid/arid climate prevailed across the Central Andes from 15 Ma to 4 Ma. Between 4 and 3 Ma a switch to hyperaridity occurred along the western margin of South America. Palaeoaltitude data suggest that a substantial proto-Central Andean mountain range was in place between 15 and 9 Ma. These data support the idea that the Andean rain shadow existed by 15 Ma and that it reinforced the pre-existing climatic regime rather than changing it. The change to hyperaridity in western South America is attributed to a combination of global climate cooling and enhanced upwelling of the Humboldt current generated by closure of the Central American Seaway between 3.5 and 3 Ma, and not to the Andean rain shadow.