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In November 2002, a fieldwork coring campaign in Lake Chungará allowed us to recover 15 cores up to 8 m long. The sampling was carried out with a Kullemberg coring system installed on a floating platform from the Large Lake Observatory (USA). Core Chun02-10 was selected for study since it preserves the most complete record of the Middle Holocene aridity crisis.

A total of 332 samples were used to determine the Total Organic Carbon (TOC) and Nitrogen (TN), as well as C and N isotopic compositions (13C and 15N), on bulk sediment samples and using a Finnigan delta Plus EACF-IRMS spectrometer at the Serveis Cientifico-Tècnics of the Universitat de Barcelona (SCT-UB). The samples were previously de carbonated using an acid attack. A preliminary characterization of the diatom assemblages was made using semiquantitative (rank-abundance) data (Sancetta, 1979) of the main euplanktonic (species) and periphytic taxa (genera or species). Cluster analyses were applied to geochemical samples and variables with the statistical package SPSS to both classify the samples in homogeneous geochemical behavior zones as well as to define the major environmental phases making up the studied period. The age model is based on Giralt et al.(2008).