Holocene landscape transformation of lake basins of Central Mexico based on volcanic soil development: a first exploratory study from micromorphology to magnetic mineralogy

Abstract

Iron oxides can be produced in soils due to chemical weathering/pedogenesis and are related to climatic conditions and also anthropogenic alterations. In this research, four soil profiles (TAC1, TAC2, TAC3 and LV1) were analyzed in areas with different climatic conditions in two lake basins of volcanic environments: the Alberca de Tacámbaro (TAC) in the state of Michoacán, with a warm-subhumid climate and Lago Verde (LV) in the state of Veracruz with a warm-humid climate. The objective of this study was to generate preliminary information on the transformation of the landscape in the two lake basins, taking into account the site-specific pedogenic processes on a centennial-millennial time scale and the possible impact of recent anthropogenic activities on the soils of these lakes’ basins. Differences in the degree of pedogenesis in soils were analyzed from magnetic mineralogy studies that were complemented and compared with studies of micromorphology, bulk rock mineralogy, clay identification, color, and texture of soil horizons. 14C dating was also obtained in organic matter from several of the horizons to, together with the micromorphological features, interpret the possible landscape changes in these basins due to anthropic impact. It was identified that in the TAC and LV soils, the pedogenetic processes were not sufficient to erase the magnetic signal of the volcanic minerals. The magnetic mineralogy in the profile is dominated by low coercivity ferrimagnetic minerals; magnetite and titanomagnetite in the case of the TAC profiles and also maghemite in the case of the LV1 profile. The characteristics of the LV1 profile, such as the presence of a Bt-type horizon, clay illuviation, and the presence of Fe oxides, suggest a more advanced pedogenic development than in the TAC profiles. In both the TAC and LV profiles, the reworking of the edaphic material and several cycles of soil formation related to the possible anthropic impact were observed. In profiles TAC1 and TAC2, the above was evidenced by the presence of charcoal fragments and the ages of the BC horizons of 1955 cal AD, while in profile TAC3, three cycles of sedimentation and soil formation were observed. In profile LV1, at a depth of 90 cm, an age of 2007 cal AD was obtained for the 2Cb1 horizon, and the reworking of the edaphic material was observable by the presence of clay soil fragments and fresh minerals in the modern soil (Ah -AB-Bt). All the data obtained will help to establish soil-sediment relationships for paleoclimatic studies on lake sediments from the central region of Mexico.