Late Quaternary history of Laguna Llancanelo area, Argentina

GARCIA, ADRIANA; CHIVAS, ALLAN; D'AMBROSIO, SABINA; PAUL CONOLLY

Congreso; 34th International Geological Congress; 2012

Laguna Llancanelo (35°38´S, 69°08´W) is a shallow saline lake located ~400 km south of Mendoza, and ~70 km east of the Andes. The lake developed within the Llancanelo and Payunia back-arc volcanic fields, an area characterised by the existence of ~800 volcanic eruption sites which were active between 2 Ma and 7 ka years ago, perhaps also, in younger times. A multidisciplinary study of sediment cores from the lake is underway, with nine undisturbed long cores up to 10 m long collected in 2010 from the eastern and western margins, and representing at least the last 30 ka (the onset of MIS 2) of the lake’s history. Grain size analyses, XRD/XRF analyses and micropalaeontological analyses (particularly charophytes and plant remains, in this study) were performed on three long cores on both margins of the lake. Preliminary geochemical analyses allow the recognition of three explosive volcanic events preserved in the lake, as well as the finding of some sections where organic remains (oospores of Tolypella, a charophyte; and emergent aquatic plants) are excellently preserved. The hypothesis about the past larger size of the lake, has been proved for at least its pre-LGM stage with the identification of active palaeodrainage channels on the eastern side of the lake (on the western side, the watercourses are still active), while for the Holocene, the lake became substantially drier and subject to periodical subaerial exposure (increasing deflation, gypsum precipitation and higher salinity).