Lacustrine sedimentology and Late Quaternary paleoclimate in the Argentinean Central Andes

MATEO ANTONIO MARTINI; EDUARDO LUIS PIOVANO; DANIEL ARIZTEGUI; LUCÍA GUERRA

Fribourg

Congreso; Twenty-sixth Meeting of Swiss Sedimentologists; 2018

University of Fribourg

We have initiated a multiproxy analysis of sedimentary cores retrieved in high altitude (> 4000 m a.s.l.) shallow lakes (< 2 m water depth) located in different environments from the Eastern Cordillera in order to identify major sedimentological changes and to define their relationship to regional climate. The Laguna Salada Grande (23°S/65°W) is a shallow and endorheic lake located at 4102 m a.s.l. at the Sierra de Aparzo, at the Argentinean Eastern Cordillera. In this region, precipitation is scarce (below 400 mm/year), mainly concentrated during the austral summer (December‐March) and supplied by easterly winds of the South American Monsoon circulation system (Zhou and Lau, 1998). Paleoshorelines situated several meters above the present lake level indicate the occurrence of deeper paleolake conditions. Analyses (ongoing) of sedimentary cores and outcrops include: petrophysical properties (magnetic susceptibility and 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 consolidated green muds. These facies indicate significant hydrological shifts in the lake system, with fluctuations between deep‐lake conditions and the current playa‐lake environment. The examination 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, can be traced into exposed outcrops in erosion gullies and trenches around the lake, allowing the correlation between sedimentary sequences and the reconstruction of the past paleolake configuration. Despite its altitude, Laguna Salada Grande has not been glaciated during the Late Pleistocene permitting the comparison of its paleolimnological record withreconstructions of the cooling events obtained from glacial fluctuations at the Eastern Cordillera (e.g. Martini et al., 2017). Results from this research will also be compared with previous studies of high‐altitude limnogeological records in Santa Victoria range (to the north of the study site) and Altiplano‐Puna region (west and north of the study site, e.g. Plackzek et al., 2006), as well as the records from the Pampean Plain lowlands (towards the east of the study site; e.g. Piovano et al., 2009). The regional and large‐scale analyses will supply significant information to better understand the past patterns of atmospheric circulation at middle latitudes of South America.