干旱区生态环境知识资源中心

Existing paleophytogeographical reconstructions of the Tertiary of southern South America have concentrated preferably in the Paleogene, due to the lack of adequate Neogene outcrops. Recent paleobotanical studies carried out in the Navidad Formation and Farellones Formation. in central Chile, however, permits the extension of paleobotanical reconstructions into the Neogene period. This work seeks to contribute to the understanding of the history of southern South American forests based on a combined revision of the paleobotanical, geological and climatical records: all synthesized into a model of the climatic-vegetational evolution of southern South America. The Paleogene is characterized by the temporary and spatial succession of three types of Paleoflora: Neotropical, Mixed and Antarctic, with elements that survive at the present time in the subtropical forests and rainforests of southern south America. The succession of these Paleofloras would have been the consequence of a combination of geological and climatical events. The most important of these was the separation of Australia from Antarctica and the consecutive glaciation of East Antarctica during the Eocene/Oligocene. During the middle and upper Miocene, events such as the formation of the Drake strait, the Circumpolar Current, and the beginning of the upwelling of cold waters off the Pacific coast of South America determined important climatic changes as well, augmenting the tendency toward aridity in a large part of subtropical South America. A Subtropical Paleoflora without Nothofagus ocurred in central Chile and northern Argentina during this period, that included taxa with disjunct distributions in the present. These include taxa that are found in the sclerophyllous forest from central Chile and the Yungas forest of the NW Argentina and Bolivia, as well as the subtropical forests of southern Brazil. The final rising of the Andean Ranges in the Plio-Pleistocene, and the events at the end of the Miocene, determined the development of the hyperarid Atacama Desert along the Pacific coast and the major features of the actual climate and recent vegetation of southern South America.