Paleopedology of middle Wisconsin/Weichselian paleosols in the Merida Andes, Venezuela

Buried Spodosols (podzols) within a thick lithostratigraphic section in the northern Venezuelan Andes are interbedded with tills and a succession of m ulticyclic lacustrine clays, silts and sands from the early and middle stad es of the Wisconsinan/Weichselian Glaciation. The peats, dated by AMS radio carbon, allow calculations of the time required for pedogenesis. These Spod osols 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 weather ed 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 de veloped with an E/Bs horizon sequence. With still longer time spans of a fe w 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 eithe r clay transformations, or silt accretion from airfall influx, apparent fro m the particle size analysis. XRD analysis of the clay fraction shows minor weathering of illite to vermiculite and chlorite in the Bs horizons. Chemi cally extractable forms of Fe and Al show increases of both soluble and ins oluble minerals from the E to the Bs horizons in the buried Spodosols, a co nsiderably different trend compared with the surface soils (Entisols). Geoc hemical trace element analysis shows a moderate degree of translocation of soluble chemical elements from the E to the Bs horizons. (C) 2001 Elsevier Science B.V. All rights reserved.