LANDSCAPE CHANGES IN NORTHERN SOUTH AMERICA DURING THE NEOGENE

Neotropical rainforests hold one of the highest levels of biodiversity in the world. Orogenic activity and climatic fluctuations have triggered major changes in the landscape by shaping the evolution of their biota during the Neogene. But, how these physical processes have affected plant species composition in neotropical forests? We studied the palynostratigraphy of three Neogene sequences from northern South America located in eastern Colombia and western Venezuela, in which savannas and xerophytic vegetation, respectively, dominate the landscape at present. These sequences reach 8 Km of thickness providing a detailed record of environmental change over the Neogene. One of the most striking findings from our fossil record is the presence of a wet forest over the Miocene instead of those biomes that characterize both areas now days. The expansion of neotropical savannas began in the Pliocene as recent phenomenon, that can be linked to a continuous reduction in rainforest areal coverage over the past five million years. The dynamic of the landscape is also reflected by two discrete and well-defined flooding events occurred in the early and middle Miocene stages. These events are associated to marine incursions and the presence of a large-scale fresh water already reported for the northwestern Amazonia.