Soil evolution in basaltic parent materials under successive climate changes, Saudi Arabia

Abstract

This study was designed to investigate the successive effects of the early Pleistocene subhumid and early to middle Holocene semi-arid paleoclimates and late Holocene to present day arid/hyperarid conditions on pedogenesis and evolution in Harrat Ithnayn volcano in the Arabian Shield, Saudi Arabia. The investigations were conducted using pedological macro and micro-features, physicochemical characteristics, elemental geochemistry, weathering indices and mineralogical analyses for light and heavy sand and clay fractions. The targeted soils developed in a subhumid paleoclimate and are classified as vitric Andisols, which are little to moderately weathered. Subhumid climate effects were evident through the presence of pedogenic Fe (crystalline oxides, Fed = 25 to 58 g kg─1), fairly high Feo/Fed (0.24 to 0.87), and the predominance of hydroxy-Al smectite and kaolinite. Residual primary minerals and modern arid conditions simultaneously led to accumulation of secondary salts and carbonates. Exchangeable Ca and Mg pools contributed 21–56 % of total Ca and Mg contents, while exchangeable K contributed only up to 4 %. Soil processes thus involved andisolization, salinization, and calcification. These processes were due to successive moist paleoclimates and the current arid conditions, thus revealing their formation under multiple climates.