A MULTI-PROXY RECONSTRUCTION OF A MIO-PLIOCENE PALEO-LAKE OUTCROP FROM THE LAUCA BASIN, NORTHERN CHILE

The Mio-Pliocene world experienced large-scale changes in climate and tectonics. Major mountain chains were uplifted (Andes, Himalayas), modern oceanic gateways opened and closed, and greenhouse gas concentration shifted. The Altiplano between the eastern and western cordillera of the Andes, was uplifted between ~10-6 Ma, and Mio-Pliocene lake sediments from the region provide an excellent opportunity to study how the tectonic and associated climatic shifts affected local environments and ecology.

The loosely termed “Lauca Formation” in the Lauca Basin of the Northern Chilean Altiplano spans the last ~8.7 Ma. Previous research documents an ephemeral lake system in the basin responding to shifts in the precipitation-evaporation balance. Here, we provide a high-resolution record of environmental change from the Lauca Formation dated by new U-Pb analysis of detrital zircons between ~5.7-5.4 Ma. We used sedimentology, petrology, diatoms, pollen, and isotope geochemistry to reconstruct the environmental and climatic history of the lake. The data suggest variability in lake depth and chemistry through the sequence, with a relatively deeper fresher lake at the base of the outcrop. Tree taxa characteristic of modern high-elevation environments are present throughout the sequence, but increase in abundance toward the top of the section.