Evolution of soil porosity in loess-palaeosol sequences of the Ebro Valley, NE Iberia

Abstract

Structure development and porosity evolution are closely related key processes in the formation of soils on loess. In order to better understand changes in soil porosity with time, four loess-palaeosol sequences (LPS) of the Ebro Valley were investigated using micromorphological and multiscalar images of soil thin sections combined with luminescence dating. Scanned and high-resolution mosaic images of thin sections using circular polarized light and backscattered electron scanning images were used to characterize the structural and textural porosity. The results were compared with physical and chemical analyses, and detailed micromorphological descriptions. The main results of our research revealed that 1) the change in loess particle packing, from enaulic to porphyric coarse/fine (c/f) related distribution, is the first process giving cohesion to the loess material and 2) that soil development during stabilization periods is associated with higher bioporosity. Gypsum accumulation is also a relevant process contributing to the increase of packing porosity within channels and chambers in the studied soils. Our results provide new insights into soil formation processes in Mediterranean loess and open new fields of research such as the possibility of using the quantification of bioporosity as an additional palaeoenvironmental marker.