Limnogeological reconstructions in subtropical South America using high-altitude lake sediments at the Argentinean Eastern Cordillera

FRANCISCO MUÑOZ; DANIEL ARIZTEGUI; MATEO ANTONIO MARTINI; EDUARDO LUIS PIOVANO; LUCÍA GUERRA; ELISEO FLORES

Toulouse

Encuentro; International Meeting of Sedimentologists 2017; 2017

International Association of Sedimentologists

Subtropical South America east of the Andes provides an ideal setting for limnogeological reconstructions to understand changes in past atmospheric circulation patterns. Previous paleolimnological research in Northwestern Argentina has been carried out in meadows, proglacial, playa and landslide-formed lakes. However, the regional correlation of the reconstructed climate oscillations remains highly controversial. The lack of agreement between these reconstructions has reinforced the interest to pursue a regional limnogeological analysis to evaluate the synchrony or lack of it among lacustrine systems located at different latitudes. In particular, the Eastern Cordillera from Argentina (22°-26°S) has a strategic position at the southern limit of the South American Monsoon system (SAMS), which regulates the precipitation in large areas of the subtropics. We have initiated a multiproxy study of sedimentary cores retrieved in high altitude (> 4000 m a.s.l.) shallow lakes (< 2 m water depth) located in different environments from Zenta and Santa Victoria ranges. Combined micro-sedimentological, geochemical and mineralogical investigations will be used to identify climatic transitions and abrupt events during the Holocene. Laguna Salada Grande (23°S/65°W) is a shallow lake (~1.5 m water depth) with an endorheic watershed located at 4100 m in the Zenta range. Paleoshorelines situated several meters above the present lake level indicate the occurrence of major paleohydrological changes. Preliminary analyses revealed the deposition of different facies: a) banded and laminated, organic dark sediments; b) finely laminated light sediments; d) massive inorganic green sediments; and d) massive inorganic clays. Sedimentary features such as the presence of organic rich sediments and tuff deposits can be traced from the cores into exposed profiles outcropping in erosion gullies and trenches around the lake, allowing to correlate and better understand the former watershed configuration. Despite its altitude, Laguna Salada Grande has not been glaciated during the Late Pleistocene permitting the comparison of its paleolimnological record with the cooling events reconstructed from glacial fluctuations reported at highest altitudes of the Eastern Cordillera. Our results from this study site will be compared to high altitude limnogeological records from other wetlands at Santa Victoria range and Altiplano-Puna region. These lacustrine records from Eastern Cordillera will supply novel and critical information that combined with former reconstructions from other subtropical archives will greatly improve existing scenarios of former SAMS activity at middle latitudes of South America.