Pedogenic information from fine-sand. A study in Mediterranean soils

Abstract

The fine sand fraction (50–250μm) of Mediterranean soils from southern Spainprovides valuable information on soil genesis and the origin of their parentmaterials. This study considers the whole fine sand and heavy fine sand(ρ> 2.82 g cm−3) of Luvisols, Calcisols and Fluvisols, which form achronosequence (ages from 600 to 0.3 ka) of the River Guadalquivir terrace sys-tem. Advanced techniques (X-ray diffraction, inductively coupled plasma massspectrometry, inductively coupled plasma atomic emission spectroscopy, vari-able pressure scanning electron microscope with an energy dispersive X-rayspectroscopy system and Raman analysis) were employed. Inheritance is theprincipal pedogenic process. The whole fine sand consisted of carbonates (cal-cite and dolomite), tectosilicates (quartz, K-feldspar and plagioclases),phyllosilicates (illite/moscovite, biotite, Na-mica, chlorite, kaolinite, inter-stratified vermiculite-chlorite, vermiculite-illite and smectite-illite) and ironoxides (goethite and haematite). The minor minerals (rutile, anatase, ilmenite,zircon, staurolite, monazite, barite, apatite, andalusite, garnet and titanite) areconcentrated, also through inheritance, in the heavy fine sand. However, thereis also substantiated evidence for neoformation of rutile in these soils, neverreported previously. In addition, we report that (a) the geochemical indices cal-culated in fine sand (SiO2/CaO, Chemical Index of Weathering (CIW),Weathering Index of Parker (WIP), Weathering Index (WI), Base DepletionIndex (BDI), Weathering Ratio (WR) and Sr/Zr) are closely related to soil age,allowing chronofunctions to be established, and (b) geochemical indices pro-vide information on the origin of soils and permit the establishment of a“criti-cal point”corresponding to“time zero;”that is, the start of pedogenicalteration of the parent material