Neogene ecology of the Salto de Tequendama site (2475 m altitude, Cordillera Oriental, Colombia): the paleobotanical record of montane and lowland forests

Abstract

A paleobotanical and palynological study of Neogene fluvial sediments of sections Salto de Tequendama I and II, located in the area of the high plain of Bogotá (Cordillera Oriental, Colombia) at 2475 m altitude was carried out. Several other sections of Miocene and Pliocene age were analysed for microfossils and macrofossils and evidence for the uplift of the Cordillera Oriental of Colombia was evaluated. Using modern vegetation zonation, with caution, as a reference, the fossil assemblages are interpreted and the elevation of the site during intervals of the Neogene is inferred. The pollen assemblages of sections Salto de Tequendama I and II include taxa such as Mauritia, Iriartea, Humiriaceae, Amanoa, Virola, Ceiba, indicating a lowland environment. These taxa are presently found on the alluvial plains in lowland areas, e.g. Amazonia. The pollen assemblage of section Salto de Tequendama I contains, in addition to lowland taxa, also montane taxa (e.g. Podocarpus, Clethra, Symplocos, Compositae, Ericaceae), suggesting presence of mountains in the region. Macrofossils representing mainly Humiriaceae in section I emphasize the allochthonous character of the plant assemblage. The peaty flood basin deposits of section II show fossil spectra indicative of swamp forest, dominated by Mauritia. The dominance of Cyperaceae and Cyclanthaceae seeds supports the conclusion that the plant assemblages of section II are autochthonous. Biostratigraphical evaluation suggests a Middle Miocene age for the sediments of the sections Salto de Tequendama I and II, although an Early Pliocene age cannot be ruled out. Paleovegetation characteristics suggest a paleoelevation below 700 m, compared to the present elevation of the site at 2475 m. This difference may be explained in terms of climatic change, and tectonic uplift. However, warming during the Miocene and Pliocene accounts at most for 3°C, corresponding to a shift of vegetation belts of c. 500 m. The remaining difference in elevation of 1300 m is an approximation for the minimal uplift of the Cordillera Oriental during the Middle Miocene and Pliocene. Plant macrofossils, mainly fruits and seeds, and pollen types new to the study area are described and illustrated.