Palynology and paleobotany of the Early Pliocene section Río Frío 17 (Cordillera Oriental, Colombia): biostratigraphical and chronostratigraphical implications

Abstract

Organic-rich sediments of section Río Frío 17 (3165 m altitude, Cordillera Oriental, Colombia) were analyzed for pollen and plant macrofossils. Time control is based on fission-track dating of zircon from an intercalated tephra with an age of 5.3 ± 1.0 Ma. Pollen and macrofossil spectra of several outcrops and cores, including section Río Frío 17, reveal gradually cooler depositional environments during the Neogene. Obvious differences between modern and Pliocene Andean vegetation belts are taken into account. The sequence of outcrops reflects the final uplift of the Cordillera Oriental. Pollen and macrofossils of section Río Frío 17 suggest that lower subandean (lower part of lower montane belt) to tropical lowland conditions prevailed in the area during the Early Pliocene: sediment deposition occurred apparently at c. 1000 m elevation. If Pliocene average temperatures were comparable to present-day values with an amplitude of ± 3°C, an altitudinal shift of 500 m maximum is suggested. Hence sedimentation is estimated to have occurred at 1500 m elevation maximally, based on the fossil plants and the present-day ecological requirements of their extant relatives. The remaining difference in elevation is attributed to tectonic uplift by at least 1700 m. The macrofossil evidence and the presence of Hedyosmum pollen suggest that the sediments of section Río Frío 17 should be placed in Biozone II, instead of Biozone I of the biostratigraphical zonation for the high plain of Bogotá as suggested by Helmens and Kuhry (1990). The arrival of Hedyosmum in the pollen record and the final uplift of the high plain of Bogotá is now estimated at c. 5.3 ± 1.0 Ma. The age of the sediments of sections Salto de Tequendama I and II (Biozone I), estimated as Early Pliocene by Van der Hammen et al. (1973), is earlier than that date. Selected plant macrofossils, such as seeds and fruits, are described and illustrated.