Microstratigraphy and paleoenvironmental implications of a Late Quaternary high-altitude lacustrine record in the subtropical Andes

GUERRA, LUCÍA ; MARTINI, M.A.; HENDRIK VOGEL; EDUARDO L. PIOVANO; IRKA HAJDAS; RICARDO ASTINI; ANTOINE DE HALLER; ANDREA MOSCARIELLO; DANIEL ARIZTEGUI

SEDIMENTOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2021

0037-0746

High-mountain lake records in arid to semiarid settings, such as the Andes of Northwestern Argentina, are highly restricted and often deprived of well-preserved microstratigraphic information to analyze detailed paleoenvironmental changes and their causes. Laguna La Salada Grande (LSG, 23ºS/65ºW, 4063 m a.s.l.) is a closed shallow lake located at Cordillera Oriental, Northwestern Argentina with a unique depositional record, including geomorphic and stratigraphic evidence of past lacustrine environmental changes. In this study, limnogeological multi-proxy analyses (magnetic susceptibility, X-ray fluorescence scans, organic and inorganic carbon contents, and grain size) together with radiocarbon AMS based chronology were applied on two composite sedimentary cores from LSG. In order to better understand the depositional dynamics of this small lacustrine system at different time-scale resolutions we analyzed and interpreted microfacies through sub-centimetric exams of thin sections and samples using novel automated methods (including elemental mapping and automatic QEMSCAN mineralogy) from retrieved laminated and massive records dated back to the Late Pleistocene. Five major sedimentary intervals represent wide multi-millennial-scale changes from relatively deep, stable and organic matter productive paleolake before ~34 ka (ka=1000 years before 1950), to a highly fluctuating shallower-paleolake with frequent detrital influxes after ~34 ka. Lamination analysis allowed the recognition of non-regular and probably sub-centennial high-energy flood-events for the period between 31 and 25 ka. At ~21 ka LSG shifted to deeper lake conditions with fine grained deposits and limited delivery of coarse-grained sediments, followed by a period of an abrupt lake level drop and shifting to the current shallow lake setting. Correlation of LSG units with other paleoclimate records around the region, suggests a close link between LSG evolution and multi-millennial changes in the past South American Summer Monsoon dynamics.