Palaeoenvironmental use of silicophytoliths in soils and palaeosols associated with Holocene volcanic ash deposits in north-western Argentina
We compare the silicophytolith record of current soils and Holocene palaeosols from two sedimentary sequences in a region between the Chaco-Pampean Plain and the Puna (Tolombón section in Santa María Valley, and Tafí del Valle section in Tafí Valley), NW Argentina. These two geographic areas are separated by the Aconquija-Cumbres Calchaquíes ranges, a climatic barrier to the wet Atlantic winds. These sequences contain volcanic ash deposits recording two large eruptions occurred during Holocene in the Southern Puna in the Central Volcanic Zone of the Andes, from the Cueros de Purulla volcano (ca. 7820 BP) and the Cerro Blanco Volcanic Complex (ca. 4200 cal BP). These ash-fall deposits buried soils and preserved their silicophytolith record, allowing the use of this palaeoenvironmental proxy to clarify the vegetation prior these two volcanic events. The silicophytolith assemblages yield evidence for a mega/mesothermal xerophytic grassland when Tolombón palaeosol was formed, similar to the present-day environment in the Santa María Valley, with presence of C4 grasses (Chloridoideae and Panicoidae). Instead, the climate was cooler and wetter ca. 4200 cal BP than currently in the Tafí Valley, increasing over time aridity and abundance of C4 grasses (Chloridoidae, Panicoideae), and decreasing the quantity of C3 grasses (Pooideae). Prehistorical and historical land use also contributed to this change. The impact of these large volcanic ash-falls on vegetation did not translate in an abrupt change on phytodiversity. Results point out a stable arid environment during Holocene in the Santa María Valley whereas the Tafí Valley was more sensitive to environmental changes due to its location in the eastern slopes of Aconquija-Cumbres Calchaquíes ranges, more exposed to the wet Atlantic winds. ; MINECO, Spain, CGL2011-23307, Project QUECA Agencia-Ministerio de Ciencia y Técnica, Argentina, PICT-1583-2013 Universidad Nacional de Mar del Plata, EXA 643/13 Canary Islands Government, ULPGC, Research Consolidated Group GEOVOL Generalitat de Catalunya, 2017 SGR 1494, Research Consolidated Group GEOPAM ; Peer reviewed