A geochemical approach on reconstructing Upper Pleistocene environmental conditions from wadi deposits - an example from the Wadi Sabra (Jordan)

Stratified Upper Pleistocene sediment sequences have been geochemically investigated in the arid environment of the Wadi Sabra (Southern Jordan). The wadi fills are associated to archaeological finds of Upper Palaeolithic to Epipalaeolithic age and intended for a reconstruction of palaeoenvironmental conditions during and after the time of the initial human occupation. As the mineralogical and sedimentological composition of the sediments is highly influenced by the nature of the local source rock, the significance of provenance analysis and depositional processes is limited. Therefore, geochemical characteristics were consulted as indicators for secondary alteration and weathering processes. A combined approach of CNS analysis, carbonate fractionation, electrical conductivity, and colour spectrophotometry supported by selective XRF scanning and chemical iron extraction was used to elaborate the nature and characteristics of various fine grained calcrete horizons. Although a detailed palaeoenvironmental interpretation of these deposits was complicated by an inhomogeneous distribution of precipitated solutes, a diversity of source materials, and potential sedimentation gaps, the results indicate that most of the fine grained deposits represent fossil and relict palaeosol horizons. Consequently, the study area might have experienced repeated phases of landscape stability and initial soil development during the latest phase of the Upper Pleistocene before a change in hydrological conditions initiated a distinctive erosional period that prevailed during most of the Holocene until modern times.