Lacustrine sedimentology and Late Quaternary paleoclimate in the Argentinean Central Andes

GUERRA, LUCIA; MATEO MARTINI; PIOVANO, EDUARDO; ARIZTEGUI, DANIEL

Fribourg

Congreso; Twenty-sixth Meeting of Swiss Sedimentologists; 2018

We have initiated a multiproxy analysis of sedimentary cores retrieved in high altitude (> 4000m a.s.l.) shallow lakes (< 2 m water depth) located in different environments from the EasternCordillera in order to identify major sedimentological changes and to define their relationshipto regional climate. The Laguna Salada Grande (23°S/65°W) is a shallow and endorheic lakelocated at 4102 m a.s.l. at the Sierra de Aparzo, at the Argentinean Eastern Cordillera. In thisregion, precipitation is scarce (below 400 mm/year), mainly concentrated during the australsummer (December‐March) and supplied by easterly winds of the South American Monsooncirculation system (Zhou and Lau, 1998). Paleoshorelines situated several meters above thepresent lake level indicate the occurrence of deeper paleolake conditions. Analyses (ongoing)of sedimentary cores and outcrops include: petrophysical properties (magnetic susceptibilityand grain size analyses), carbon and nitrogen contents, XRF geochemistry along with aradiocarbon chronology. Preliminary results revealed the deposition of different facies: a)banded and laminated organic dark sediments, with carbonates; b) finely laminated white,light grey and ochre sediments; d) massive inorganic green muds; and d) massive consolidatedgreen muds. These facies indicate significant hydrological shifts in the lake system, withfluctuations between deep‐lake conditions and the current playa‐lake environment. Theexamination of laminated sections of the cores is as well analyzed to better understand thesedimentary and geochemical processes occurring within the lake with high resolution.Sedimentary features, such as the presence of organic rich sediments and tuff deposits, canbe traced into exposed outcrops in erosion gullies and trenches around the lake, allowing thecorrelation between sedimentary sequences and the reconstruction of the past paleolakeconfiguration. Despite its altitude, Laguna Salada Grande has not been glaciated during theLate Pleistocene permitting the comparison of its paleolimnological record withreconstructions of the cooling events obtained from glacial fluctuations at the EasternCordillera (e.g. Martini et al., 2017). Results from this research will also be compared withprevious studies of high‐altitude limnogeological records in Santa Victoria range (to the northof the study site) and Altiplano‐Puna region (west and north of the study site, e.g. Plackzek etal., 2006), as well as the records from the Pampean Plain lowlands (towards the east of thestudy site; e.g. Piovano et al., 2009). The regional and large‐scale analyses will supplysignificant information to better understand the past patterns of atmospheric circulation atmiddle latitudes of South America.