Late Quaternary paleosols in the western and central Cordillera of Colombia

More or less well preserved paleosols were studied in the submontane and montane zone of the Western and Central Cordillera, Departamento del Valle, Colombia. Their Pleniglacial age was ascertained by radiocarbon analysis of charcoal which was, in several sections, found associated with the basis of volcanic ash deposits. The two ash periods which provided the bulk of the volcanic parent material seem to have occurred about 30 000 and 10 000 yr. B.P. The paleosols developed before and immediately after the older period (Middle Pleniglacial). The characteristic morphological traits — a uniform grey horizon of low humus content and with a basal iron pan — indicates a cold humid environment of low evapotranspiration and low organic turnover. Such soils do not form today but were characteristic for the Middle Pleniglacial soil cover from altitudes of 1500 to 3500 m. Increasing stable humus content in paleosols after 30 000 yr. B.P. apparently indicate a turn towards drier conditions, i.e. a growing influence of Gramineae after a predominance of wooded vegetation, quite in agreement with the pollen-based paleoclimatic concept of Van der Hammen. This paper demonstrates the distribution of truncated and transported paleosols relicts as a result of the great degradational phase which reshaped the soil mantle probably between 20 000 and 10 000 yr. B.P. The type of paleopedological soil formation process is discussed in some detail.