Geochemistry of a soil catena developed from loess deposits in a semiarid environment, Sierra Chica de Córdoba, central Argentina

Abstract

A catenary sequence of soils formed on reworked loess under semiarid climatic conditions was studied. Four soil profiles located on the piedmont of Sierra Chica de Córdoba, central Argentina,were described, classified and geochemically analyzed. All soils, developed on summit, shoulder, backslope, and toeslope positions, were classified as Mollisols. Decarbonatation-carbonatation, melanization, and argilluviation are the main pedogenic processes recognized in these soils, which appear to control the differentiation of genetic horizons along the catena. Different geochemical approaches indicate that there are not substantial variations in the chemical composition of the studied soils along the catena, with the exception of the soil in the toeslope position, which exhibits slightly differences. In general, all profiles show weak depletions of mobile elements (Ca, Na, Mg, Sr, U) in the upper continental crust UCC-normalized diagrams which are attributed to a slight chemical alteration. Other elements, such as Fe, Cr, Co and Ni, also exhibit depletions compared to UCC, which can be explained by the alteration of ferromagnesian silicates, but can also be an inherited feature from the parent material. The significant enrichment in As compared to UCC, evident in all profiles along the catena, is also a typical feature of the pampean plains´ loess of Argentina. So, the chemical differences in the profile located on the toeslope aremainly attributed to the supply of materials from local sources, i.e., crystalline basement and sedimentary rocks, due to its position in the catena. Statistical correlations and multivariate cluster analyses reinforce the assumption that the geochemistry of the studied soils is inherited from the parent material. In addition, chemical indices (CIA, ICV), elemental ratios (Ba/Sr, Rb/Sr) and the A-CN-K ternary diagram indicate an incipient degree of chemical alteration for thesesoils, compatible with the weathering regime prevailing in the region. Thus, the differentiation of genetic horizons along the catena is the result of weak weathering and pedogenic processes, which have not been strong enough to mask the chemical imprint of the parent material.