ALBERT

Description: Dada la importancia que revisten los suelos en los procesos que ocurren en la zona crítica (zona de interacción entre agua, suelo, aire, organismos), en este trabajo presentamos la distribución temporal y espacial de una secuencia de paleosuelos arcillosos con carbonatos secundarios (capas de caliches y carbonatos diseminados) en el sector nororiental de la Cuenca de México, particularmente en el valle de Teotihuacán. El propósito de este trabajo consiste en reconstruir la distribución temporal y espacial de la cubierta de suelos del pasado para entender su relación con la estructura actual de suelos y sedimentos en este sector semiárido de la cuenca de México. Con esta información, determinar la participación de estos materiales en la Zona Crítica (ZC). Para ello, se ha llevado a cabo un transecto de dirección norte-sur, que inicia en las elevaciones del Cerro Gordo, cruza el valle de Teotihuacán y termina en la Sierra Patlachique, describiendo perfiles de suelo en diferentes posiciones geomorfológicas. El marco cronológico se ha establecido con base en fechamientos de radiocarbono realizados en las capas de caliches. De acuerdo a la cronología, al tipo y grado de pedogénesis, y a los procesos de sedimentación, se han reconocido cuatro unidades. La primera unidad, denominada Paleosuelos del Pleistoceno, fase I (50000 – 20000 años AP), está compuesta de paleosuelos arcillosos, los cuales son Luvisoles crómicos y estágnicos, dependiendo de su posición en el paisaje. Estos paleosuelos muestran tanto carbonatos secundarios diseminados y en fracturas, como capas de caliches. En la segunda unidad, Paleosuelos del Pleistoceno, fase II (20000 –10000 años AP), dominan los sedimentos sobre los suelos; únicamente en el fondo del Valle, se han encontrado Gleysoles cortados por canales aluviales. La unidad, Paleosuelos del Holoceno, fase I (10000 a 1000 años AP) se caracteriza por presentar suelos poligenéticos (Vertisoles), fuertemente modificados por los procesos antrópicos, durante las diversas fases de ocupación pre-hispánica. La última unidad, Suelos del Holoceno, fase II, abarca el último milenio, en donde se destacan procesos de erosión e inestabilidad del paisaje. La tendencia principal en la distribución espacial de los paleosuelos es la siguiente: las unidades antiguas (Luvisoles, capas de caliches y Vertisoles) están sepultadas profundamente en el fondo del valle. Sin embargo, en los taludes y elevaciones montañosas, pueden aparecer cerca o directamente sobre la superficie, siendo incorporados en el manto de suelos actual. Las interrelaciones entre los diferentes paleosuelos a lo largo del transecto estudiado, junto con las observaciones micromorfológicas, apoyan la hipótesis de una relación evolutiva entre los Luvisoles pleistocénicos y los Vertisoles del Holoceno. Consideramos que estas diferentes unidades repercuten en los procesos hidrológicos en el valle y que las capas de caliche formadas en los ambientes pleistocénicos pueden afectar la geoquímica del agua subterránea así como sus firmas isotópicas.

Description: As soils are important elements for the processes involved in the critical zone (the zone of interaction between water, soil, air, and organisms), in this work we present the temporal and spatial distribution of a clayey-paleosol sequence with secondary carbonates (layers of caliche and disseminated carbonates) in the northeast sector of the Mexico Basin, particularly in the Teotihuacan Valley. The goal of this paper is the temporal and spatial reconstruction of the past soil cover to understand its relationship with the present day soils and sediments in this semiarid sector of the Mexico Basin. With this information the involvement of these materials in the critical zone could be determined. To comply with these objectives, a north-south transect was carried out, starting in the Cerro Gordo, crossing the Teotihuacan valley and ending in the Sierra Patlachique, describing soil profiles located in different geomorphological positions. The chronological framework has been established with radiocarbon dates of the caliche layers. According to this chronology, the type and degree of pedogenesis, as well as the sedimentation processes, four units have been recognized. The first unit is named the Pleistocene Paleosols, phase I (50000 – 20000 years BP), and is composed of clayey paleosols, chromic and stagnic Luvisols, depending on their position in the landscape. These paleosols contain pedogenic carbonates, disseminated and in fractures, and caliche layers. In the second unit, the Pleistocene Paleosols, phase II (20000 –10000 years BP), sediments predominate over soils; only in the valley floor some Gleysols are found to be cut by alluvial channels. The unit, Paleosols of the Holocene Paleosols unit, phase I (10000 to 1000 years BP), is characterized by polygenetic soils (Vertisols) strongly modified by anthropic processes during distinct phases of pre-hispanic occupation. The last unit, the Holocene Soils, phase II, covers the last millennium when erosional processes and unstable landscape dominate. The paleosols (Luvisols, caliche layers, and Vertisols) are deeply buried at the bottom of the valley. However, on the slopes and hilltop positions, they can appear close to or directly on the surface, being incorporated in the present day soil mantle. Spatial interrelations of different paleosols along the studied transect together with micromorphological observations support the hypothesis of an evolutionary link between the Pleistocene Luvisols and the Holocene Vertisols. We propose that these different units are involved in the hydrological processes in the valley and that the caliche layers, formed in the Pleistocene environments, can affect the geochemistry of the groundwater as well as its isotopic signatures.

Description: A detailed study of a loess-paleosol sequence in Oberlaab, Upper Austria, is presented with emphasis on macro- and micromorphological features, grain size distribution, rock magnetism properties, and weathering degree that allows correlation with other loess-paleosol sequences in neighboring areas, and interpretation of main pedogenic trends. The studied sequence comprises four paleosol complexes, which likely developed during four interglacial stages MIS 11, 9, 7 and 5e, and a modern soil. The oldest paleosol complex (OL5) represents three phases of soil formation, and distinct sedimentary events never reported in the area, with strong reductomorphic properties. The OL4 profile also results from three phases of pedogenesis with increased reductomorphic features in the deepest zone (affected by cryoturbation events). OL3 has abundant features related to gleyic/stagnic processes, but shows signs of clay illuviation. OL2 (Eemian soil) correlates with the MIS 5e. This paleosol shows higher degrees of clay illuviation and weathering, and fewer features related to reductomorphic processes. The modern soil is also polygenetic and constitutes a pedocomplex. Its lowermost part is formed by Würmian glacial deposits, where no well-developed soils are found; only reworked materials and pedosediments. Main pedogenic trends in the sequence are clearly differentiated. All of the paleosols were formed in humid environments, but differing in drainage conditions. The base, with OL5 and OL4 paleosols, was more affected by gleyic processes, while in the upper paleosols, especially OL2, clay illuviation is dominant. We interpret such differences to be caused by the topographic position. The basal paleosols were more affected by fluvioglacial processes due to their position on top of the terrace. The upper paleosols received increased amounts of sediment through fluvial, colluvial and aeolian (loess) input.

Description: research