INVESTIGADORES
ALVAREZ maria fernanda
congresos y reuniones científicas
Título:
Silicophytoliths in buried paleosols by volcanic ash located at the west of Tucumán, Argentina
Autor/es:
OSTERRIETH M.,; ALVAREZ M.F.; GALLARDO J.J.; FERNÁNDEZ-TURIEL J. L; SAAVEDRA J
Lugar:
Bruselas
Reunión:
Congreso; 9th International Meeting For Phytolith Research; 2014
Institución organizadora:
International Phytolith Society
Resumen:
Recurrent volcanic eruptions have occurred during the Quaternary in the Andes and, in particular, in the Northern sectors of Argentina and Chile, generating of net environmental impacts in the region. Soils buried by ashes are good indicators of environmental conditions until the time of the eruption, as the vegetation associated to these soils evidences climatic and environmental conditions till the moment of the burial. The silicophytoliths are amorphous silica hydrated generated by biomineralizations; they are produced by a large number of plant communities around the world; therefore, they are good indicators of the plant-soil-environment relationship. The objective of this study was the analysis of the contents of silicophytoliths in both, soils and paleosols, present in an area close to Tafí del Valle (Tucumán, Argentina), for estimating the intensity and type of pedogenetic processes that generated them; and, in the case of paleosols, post-pedogenetic also processes that occurred after the volcanic eruption. The studied paleosol was covered by a deposit of volcanic ash, dated middle Holocene, coming from the volcanic complex of Cerro Blanco (South of the Puna). Soil samples from the current soils and the paleosols buried by volcanic ash, integrated and sieved, were analyzed and their silicophytoliths identified. For the determination of the percentage of silicophytoliths against the total sum of mineralogical components, 5.00 g soil samples were taken from each layer of soil and paleosol, according to routine techniques. In Entisols, silicophytolith percentages range between 3 and 4 % in relation to the total amount of mineralogical components of the soil. The main silicophytolith morphotypes are Elongates and Rondels, in minor proportion Bilobates, Saddle and Bulliforms with good preservation. These morphotypes are linked to very few grasses plant communities and shrubs xerophytes, associated with extreme environmental conditions, such as periods of water deficit and aridity. The silicophytoliths present in the paleosol are substantially higher than those found in the current soil, with values of 30 % of the total amount of mineralogical components. The dominant morphotypes are elongated, with varied sizes with crenate to smooth edges; Bilobated with varied sizes and smooth ends, convex and concave, indicators of Panicoideas type C3 and C4 grasses and C3 grasses. Saddles indicators, morphotypes communities C4 with metabolic pathways, were also found. There are also common Bulliforms, indicating large and medium-size typical of grasses; and typical conductive tissue cells. A significant amount of Elongated, smooth silicophytoliths, are articulated and mainly associated with sharp thorns morphotypes characteristic of epidermis of grasses. These articulated silicophytolits are associated generally to environmental conditions with high stability, topographically flat areas, and/or processes of rapid burials, as occurred in this case study. Volcanic glasses are abundant in both soils studied. For these reasons, the qualitative and quantitative presence of silicophytoliths in current and buried soils analyzed indicate conditions of high environmental stability and net pedogenetic processes, which held a major grass cover, for a considerable time span, just until the burial produced by the dated middle Holocene eruption of Cerro Blanco Volcanic Complex; this is clearly different to the current soils, with only incipient pedogenetic processes due to the extreme aridity.