Stratigraphy and environments of the Upper Quaternary of the El Abra corridor and rock shelters (Colombia)

Abstract

A study of the stratigraphy and depositional environments of the Upper Quaternary in the El Abra area (part of the high plain known as the Sabana de Bogotá in the Eastern Cordillera of Colombia), combined with the results of an extensive palynological study of the same sediments, and of radiocarbon dating, led to a reconstruction of the history and palaeoecology. After a description of the stratigraphic sequence in the El Abra rock shelters, the principal guide horizons are mentioned. The stratigraphy of the El Abra “corridor” is reconstructed in a number of transections, showing amongst others the former erosion levels and gullies, fan-like accumulations of coarse-grained sediments, and the relation of the sequence in the rock shelters with that of the level part of the “corridor”. Three major episodes may be distinguished. The first episode most probably began before 100,000 B.P. and may have ended shortly after 50,000 B.P. The region formed part of an extensive marshy area, with marsh forests, and there was no permanent open water. The second episode lasted from shortly after 50,000 B.P. to approximately 37,000 B.P. The water table was considerably higher and the area formed part of the large Sabana Lake. The third episode comprises the time from approximately 37,000 B.P. to the present. The lake had disappeared from the area, and after the local erosion of the old surface, a sequence of soils, inundation clay, volcanic ashes etc. was deposited; only now and then there were short intervals with a higher water table. During these three episodes there were important and frequent changes of vegetation, caused by the changing average annual temperatures and precipitation.