Pedostratigraphy and pedological and geochemical characterization of Las Carreras loess-paleosol sequence, Valle de Tafí, NW-Argentina

The Las Carreras loess-paleosol sequence is considered the most complete Quaternary pedostratigraphic record in South America. It consists of 32 paleosols formed during the past 1.15 Ma. Chronological control is provided by magnetostratigraphy. Sediment and paleosol characterization is based on a variety of methods, including soil chemistry, geochemistry, and micromorphology. The main pedogenic processes identified are carbonate leaching and reprecipitation, ped formation, and translocation of clay and organic matter. In many cases, the boundaries between individual paleosols are not clearly defined due to indistinct transitional zones. Based on both pedological and sedimentological characteristics the sequence was subdivided into three units, with paleosols in Units I and III designated as Luvisols and paleosols in Unit II tentatively classified as (Luvic) Kastanozems. This subdivision reflects environmental changes associated with the mid-Pleistocene transition. Overall geochemical variability is low and largely related to pedogenesis. The homogeneity suggests a rather constant provenance that seems to be linked to the Central Andes pursuant to the Chaco Model of Iriondo [1997. Models of deposition of loess and loessoids in the Upper Quaternary of South America. Journal of South American Earth Sciences 10, 71-79], and includes direct volcanic ash falls and local sources in a subordinate manner. In a paleoclimatic context, loess-paleosol alternation is interpreted to reflect climatic cycles that were primarily caused by the variability of the South American Monsoon System.