Quaternary landscape development of the Rio Magdalena basin between Neiva and Bogotá (Colombia): A reconstruction based on evidence derived from paleosols and slope deposits

Abstract

The Quaternary landscape development of part of the middle Magdalena basin is reconstructed from evidence provided by paleosols and slope deposits preserved on glacis surfaces. The paleosols were formed during stable periods with tropical conditions which we have correlated with the Interglacials. The slope deposits were mainly formed during unstable periods with alternating very dry and very wet conditions which we have correlated with the Glacials. If these correlations are correct, it appears that, with the progress of the Quaternary, the (seasonal) variability of the Glacial climates became less pronounced and that of the Interglacial/Postglacial climates more pronounced, leading to a gradually diminishing amplitude of the Quaternary climatic fluctuations. The glacis were formed during periods of pronounced landscape instability (Phase 1, possibly Early or Middle Pleistocene Glacials). Next came a period of landscape stability which left a ferric hydromorphic soil formed in a humid climate (Phase 2, possibly Middle Pleistocene Interglacial(s)). This was followed by an unstable period during which the surfaces of the glacis were somewhat enlarged and covered by coarse slope deposits (Phase 3, presumably penultimate Glacial). After this, part of the area was raised by tectonic movements, streams incised into the glacis surfaces, and stream terraces were formed (Phase 4). During a stable period, plinthic hydromorphic soils and red ferrallitic soils were formed which show the effect of dry seasons (Phase 5, presumably last Interglacial). They were covered with slope deposits formed from shallow mass movements and soil erosion (Phase 6, presumably last Glacial). The sedimentation of volcanic materials began in this period and continued into the first part of the Holocene (Phase 7). Also continuing into the Holocene were (soil) erosion and the deposition of colluvium (Phase 8). During the Holocene, loss of clay due to alternating dry and wet conditions became a more important aspect of soil formation (Phase 9).