Carbonate and organic matter sedimentation and isotopic signatures in Lake Chungará, Chilean altiplano, during the last 12.3 kyr.

Abstract

Sediments in lakes in the Andean volcanic setting are often made up of diatomaceous ooze together with volcaniclastics and small amounts of carbonates. Despite their scarcity, carbonates along with organic matter provide significant paleoenvironmental information about lake systems. This study focuses on the carbonates in Lake Chungará, their morphologies, distribution and origin deduced from the isotopic markers. These markers re flected changes in the water and the biomass between the onset of the Holocene and around 9.6 calkyr BP. These changes are marked by general increases in TOC, TN,and TN-δ15 NAIR, andby fluctuating values of TOC-δ13 CVPDB in its sediments and are probably related to major shifts in the lake surface/volume associated with rises in lake level. An increase in salinity around 10 cal kyr BPis thought to be linked toa short dryperiod, giving rise to the onset of carbonate production. The mid-Holocene arid period between 7.3 and 3.5 cal ka BP, with a maximum of aridity around 6.0 cal kyr BP, was deduced from δ18O VPDB values in the endogenic carbonates. These results match the reconstructions in Lake Titicaca based on benthic diatoms and paleoshore levels.