ABSOLUTE CHRONOLOGY OF THE PLIOCENE-QUATERNARY SEDIMENT SEQUENCE OF THE BOGOTA AREA, COLOMBIA

A revised geochronological framework is presented for the sequence of unconsolidated sediments present in the Bogota area (Eastern Cordillera, Colombia). This is based on 11 fission track dates on zircons that were obtained both from exposed ash layers and from a series of ashes from the Funza II borehole, which reached 586 m below the surface of the high plain. The 3 dates obtained from the exposed ash layers provide control for the older part of the sequence (6-2.5 Ma). The 8 dates from the Funza II core give control for the younger part of the sequence (3-0 Ma). Acceptance of these new fission track dates on volcanic zircons means that many of the tephra dates obtained from the Funza I core (that included fission track dates on glass shards and K-Ar dates using the mineral fractions in the ashes, published in 1984), are rejected. It also confirms earlier climate-stratigraphical dating. The Neogene-Quaternary sediments of the Bogota area span a period of at least the last 6 Ma. The fluvial-lacustrine sediment record registers major tectonic uplift of the Eastern Cordillera for the period between 5 and 3 Ma, the development of the large sedimentary basin of Bogota after 3.5 Ma, with an important phase of tectonic adjustment at about 1 Ma, and a long period of strong climatic fluctuations that started shortly after 2.7 Ma.