Tuesday, 11 July 2006 - 3:30 PM

Features and Characteristics Revealing Environmental Changes on Paleosols in the Volcanic Paleosols (Example of the Trans Mexican Volcanic Belt).

Elizabeth Solleiro-Rebolledo, UNAM, Ciudad Universitaria, Mexico, Mexico

One of the first tasks to reconstruct environmental changes in paleosol sequences is to recognize features and characteristics related to soil memory. In loess-paleosol sequences, it is well established the elements of such memory are well established and , perfectly separated from loess sediments, that themselves represent climatic signals. Soils derived from volcanic materials are known to differ considerably when formed under different environmental conditions and thus have potential for their utilization in paleoenvironmental reconstructions. Consequently, However the use of volcanic paleosols as paleoclimate proxy has brought forward some methodological questions, concerning: first, the pedogenetic speciality predetermined by specific parent material; second, the necessity to distinguish between the effects of the environmental change and those of the soil evolution related to the duration of pedogenesis (soil-forming factor time); and finally, to volcanism, that tends to mask climatic signal. Despite the fact the widespread of volcanic areas in the world, with high activity during Quaternary time, tephra-paleosol sequences have been only used for the reconstruction of Late Pleistocene–Holocene paleoclimates in several few cases, as Japan, New Zealand, central Italy and Colombia. Recently in Mexico, an extensive research has been conducted in volcanic paleosols in order to contribute to the understanding of paleoenvironmental conditions prevailing during Late Quaternary. Particulary, Pleistocene tephra-paleosol sequences of the central Trans-Mexican Volcanic Belt (TMVB) have constituted an alternative record, which could be useful to fill existing lacunas in the knowledge of Quaternary paleoenvironments. However, our reconstructions present some contradictions with other records, especially with lacustrine ones that should be taken into account. Nevertheless, study sequences in TMBV represent a very detail register of environmental change having major spatial resolution and extending over a higher larger time scale. These sequences seem to provide the paleoclimate proxies for the period before 50,000 yrs B.P. not covered by the lacustrine records; for younger periods paleosol research constitutes a register, complimentary to lake sediments. We have analyzed a set of characteristics in volcanic paleosols, we considered to constitute soil memory, that are more stable and can be related to climate change, differentiating from those assumed to be consequences of time as soil forming factor. Such properties are: morphology, texture, mineralogy (coarse and clay fractions), stable isotopes, phytolits, extractable solutions of Fe, Al, and Si, among others. In the Nevado de Toluca sequence, a complete scheme of Andosol to Luvisol transformation has been proposed as the result of interaction of both factors: climate and time.

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