Paleoenvironmental reconstruction in the western lacustrine plain of Llancanelo Lake, Mendoza, Argentina

摘要

Lakes are key sites for studying paleoclimates. Llancanelo Lake (southern Mendoza Province, western Argentina) is an endoreic, highly saline water body located in the southern extreme of a tectonic basin, the Central or Huarpes Depression. The lake is located between the Andean Cordillera, San Rafael Block and Payenia Volcanic Field. The lake evolved as a major regional depocenter during the Pliocene-Quaternary, hence it contains important thicknesses of intra and extra basinal clastic and evaporitic sediments mainly dominated by volcaniclastic products. The main conditioning factors in the lake evolution were arc and back-arc volcanism as well as climatic changes. Geomorphological and sedimentary evidence supports the hypothesis that the lake was in past times larger than in present days. This paper estimates the lake's former extension on the western lacustrine plain using electromagnetic induction (EMI) and geo-electricity (Multielectrode Resistivity Meter) surveys, as well as shallow wells, along an 8 km long transect perpendicular to the lake's western shoreline. The geophysical and sedimentological information, as well as microfaunal studies, lab analysis and petrographic/EDAX determinations, support the presence, in the subsoil, of a lacustrine sequence at least 30 m thick composed mainly of volcaniclastic sediments. Volcanic eruptions and climatic changes influenced the evolution of the lake, producing intercalations in the lacustrine sedimentary sequences of ash layers, evaporites, soils, and eolian and swamp deposits.