Using X-ray fluorescence core scanning to assess acid sulfate soils

During the formation of acid sulfate soils (ASS), several chemical elements in the sediment are mobilised. These elements are removed from the sediment or become enriched as precipitates in distinct horizons. The stratigraphic depth in which these precipitates accumulate is element-specific and is located either within the oxidised or in a transitional zone between the oxidised and the reduced zone. Aim of this study is to demonstrate how X-ray fluorescence core scanning, together with detailed sediment descriptions, can be used to perform an initial assessment of these different zones in ASS in a fast and cost-effective manner. We measured the chemical element signatures of K, Fe, Pb, Sr, Zn, Ni, Y, Mn and Ca in two sediment cores from Western Australia where ASS are suspected to occur. The oxidised zone in both cores is characterised by the occurrence of jarosite, which is indicated by pale straw yellow mottling and synchronous peaks in Fe/Ti, K/Ti, Pb/Ti and Sr/Ti, and of other secondary Fe-oxides, which are indicated by reddish mottling and synchronous peaks in Fe/Ti and Pb/Ti. The transition zone into reduced material is marked by synchronous peaks in Zn/Ti, Ni/Ti, Y/Ti and Mn/Ti. Based on these characteristic signatures, we broadly estimated the depth of the oxidised and the transitional zone at both sites.