History of pedogenesis and geomorphic processes in the Valley of Teotihuacán, Mexico: Micromorphological evidences from a soil catena .

M. Lourdes González-Arqueros, Jorge E. Gama Castro, Sergey Sedov, Lorenzo Vázquez-Selem, Emily McClung de Tapia


The paper provides new evidence on the pedogeomorphic history of the Valley of Teotihuacán, Mexico. The soil landscape here consists of Luvisol and "black soil", the micromorphology of which allowed us to (a) distinguish between in situ and inherited processes and (b) establish spatial relationships of erosion and sedimentation along a toposequence of three soil profiles. Soil profiles sites were selected by photointerpretation followed by verification on a toposequence from middle mountain slope to colluvial piedmont. Samples of these profiles were characterized by physical and chemical analyses, including micromorphological observation under a petrographic microscope. The results are summarized as geomorphic observations, description and analysis of soil profiles along a catena, and micromorphological features. The final data set permits recognition and interpretation of both present-day pedofeatures and inherited pedofeatures due to past hillslope processes. In the “black soil”, the key processes include development of vertic features, humification and CaCO3 accumulation; while micromorphology revealed fragments of illuvial clay along with disorthic ferruginous nodules. In the Luvisol, clay illuviation dominates and is associated with redoximorphic features. Strongly weathered pumice fragments and less weathered mineral and rock fragments were observed in the vertic horizons. Because the pedofeatures of the “black soil” strongly differ from those of the Luvisol, we can readily identify the cases where Luvisol materials were inherited by the “black soil”. Thus, the micromorphological observations allow us to propose that the “black soil” was likely to incorporate Luvisol materials that were earlier colluviated. The presumed erosional phase may correspond with climatic aridization.
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