Soil genesis in a marine terrace sequence of Sicily, Italy

Abstract

Knowledge about the rates of pedogenic processes is essential to understand landscape development\nand history. It can be attained by the quantitative investigation of soil chronosequences. In this work, the\ndevelopment of Chromic Luvisols in the Mediterranean is addressed. The soils investigated are located\non fi ve uplifted Pleistocene marine terraces in south-western Sicily, and have developed on calcareous\nmarine and fl uvial sediments. The soil on the highest terrace is a Ferri-Profondic Luvisol, while soils on\nthe lower terraces represent a Chromi-Profondic Luvisol (Bathifragic), a Chromi-Profondic Luvisol and\ntwo Bathicalci-Chromic Luvisols. The soils on the 1st (lowest) and 2nd terrace are 100 cm thick, the one\non the 3rd terrace, 160 cm and those on the 4th and 6th (highest) terrace more than 200 cm. All soils\nare decalcifi ed, while greater CaCO3 contents in the Ap horizons of the soils on the three lower terraces\nare due to deposition of younger calcareous fl uvial sediments. Soil pH (water) drops from pH 7.7¿8.9\nin the soils on the three lower terraces to values below pH 7 in the soils on the two higher terraces. In\ngeneral, the chemical alteration and the leaching of silicic acid increase with elevation, and are most\npronounced on the 4th and 6th terrace. Clay illuviation and associated translocation of Fe, Al and K is\npronounced in all soils. The clay minerals include kaolinite, illite and expandable three-layer silicates.\nIrregularly interstratifi ed clay minerals are composed of illite, vermiculite, smectite and chlorite, and\nusually constitute 20¿40 % of all clay minerals, indicating proceeding soil development. The comparatively\nmore advanced weathering and the high kaolinite content on the most elevated terrace point to soil\ndevelopment under warmer and wetter climate, that is early Pleistocene or earlier. The soil on the 4th\nterrace is more developed than the soils on the less elevated terraces.\nThe 3rd terrace was exposed to local rejuvenation by sedimentation in a lagoon/lacustrine\nenvironment. Above the lacustrine layer, the Chromi-Profondic Luvisol on the 3rd terrace shows a similar\ndevelopment as the soils on the two lower terraces. Therefore, we assume that the marine terraces around\nMenfi in south-western Sicily emerged at least at three different time steps; the 6th terrace and the 4th\nterrace developed at different times, whereas the lower three terraces formed at similar times. The latter\nmay have formed also at the same time, and later dislocated to different elevations by tectonics.