Paleosol-sedimentary records of contrasting environmental changes in the Sabana de Bogotá, Colombia, during the late Pleistocene – Holocene

Abstract

The Sabana de Bogotá, located on a high plateau (2600 masl), is a slightly dissected plain of lacustrine origin surrounded by quarzitic Cretaceous sandstone ridges. Due to the high altitudes, the Sabana represents a special case in the tropical belt near Ecuador with unique characteristics. Several studies have been conducted to reconstruct paleoenvironmental conditions during the late Pleistocene and the Holocene, mainly from lacustrine and glacial records. However, the Sabana also contains a rich register of paleosols. In this work, we analyzed the paleopedological record found in the lower foot of a quarzitic ridge. In various sections, we identified prominent, well-developed paleosol units interlayered with colluvial sedimentary strata mixed with pyroclastic components covering the interval from Marine Isotope Stage 2 (MIS 2) to MIS 1. Two profiles were selected, located just some meters apart. The first (profile 6) contains a complete pedological record with the modern soil and three paleosols forming a pedocomplex, while the second profile (6a) represents a case where sedimentation overlaps pedogenesis. Selected methodologies were applied (macro and micromorphological description, color, grain size distribution, magnetic susceptibility, total organic carbon, bulk chemical composition, X-ray diffraction, and radiocarbon dating) to differentiate pedogenetic trends and sedimentary sources. The results show the studied paleosols contain similar properties, although with variable intensity and some differences in their expression and specific processes for some selected units or horizons. All paleosols evidence illuviation and redoximorphic (stagnic) processes; however, with a clear multiphase development. We interpret these paleosols as formed mainly in cold and humid conditions. One remarkable finding in the sequence was a human bone embedded in the third paleosol, aged around 11,000 cal yr BP, representing one of the most ancient individuals in Colombia.