Paleopedology of Middle Wisconsin/Weichselian paleosols in the Mérida Andes, Venezuela

Buried Spodosols (podzols) within a thick lithostratigraphic section in the northern Venezuelan Andes are interbedded with tills and a succession of multicyclic lacustrine clays, silts and sands from the early and middle stades of the Wisconsinan/Weichselian Glaciation. The peats, dated by AMS radiocarbon, allow calculations of the time required for pedogenesis. These Spodosols were studied to determine compositional changes from initial to full soil development. During lake low water stands, peats of variable thickness developed, along with soils belonging to the Spodosol order. On a relative time scale, the initial stage of soil genesis produced peat with a weathered mineral zone (Bs)—initial spodic horizon of a few centimeters thickness. With a longer time for soil genesis of a few centuries, a thin Spodosol developed with an E/Bs horizon sequence. With still longer time spans of a few thousand years, between 55 and 60 ka, more mature Spodosols with E/Bs/Cox/Cu profiles formed beneath very thick peat in conjunction with groundwater fluctuations. The lowermost peat (VII) in the section varies from 15 to 26.5 cm in thickness. The paleosols are sandy, with little evidence of either clay transformations, or silt accretion from airfall influx, apparent from the particle size analysis. XRD analysis of the clay fraction shows minor weathering of illite to vermiculite and chlorite in the Bs horizons. Chemically extractable forms of Fe and Al show increases of both soluble and insoluble minerals from the E to the Bs horizons in the buried Spodosols, a considerably different trend compared with the surface soils (Entisols). Geochemical trace element analysis shows a moderate degree of translocation of soluble chemical elements from the E to the Bs horizons.