Abstract

ABSTRACT The Llamara Basin (21230S – 69370W) (LlB) is one of the oldest and largest saline basins in northern Chile. It has been described as a former lake (Lago Soledad) in Upper Miocene times and today it still receives a huge amount of sediments trough the Arcas Alluvial Fan, the largest described in northern Chile. The importance of this basin is based on the fact that through its geological history, it provides ample information on critical issues in the geological, paleoclimatic and geomicrobiological evolution of the Atacama Desert. These issues, between others, are: i. LlB is closely related to the genesis of fossilized Salar Grande. This salt flat corresponds to a NaCl massive body (120 km2 area and 80/90 m average depth) and is considered unique world around. ii. It is related to a huge fault system that appears as the main brine feeders of associated saline basins. iii. The mass balance between the Arcas Alluvial Fan and the LlB plus the lake/salt flat association provides information about the paleoclimate during Upper Miocene. iv. Its basement partly corresponds to nitrate & iodine deposits. Their relationship provides new information about the evolution of these unique deposits. v. Its development is associated with the Rio Loa, the only river crossing the Atacama Desert and partly draining the LlB and taking its water up to the sea. vi. The high capacity for molecular preservation of the salt crusts evidenced by the hugh diversity of specialized halophilic microorganisms revealed in metagenomic analysis allows us to complete the evolution in reduced time scale. vii. Current gypsum biotic and abiotic precipitation in the sink holes (locally called “puquios”) provides additional information about evaporates genesis in the LlB. Our studies up to now conclude that i) from the geological viewpoint a much wider basins systems was evolving during the Upper Miocene-Pliocene due to important climate changes. That geomorphological features were the same recognized today; ii) that brines circulation was partially trough some fault systems; iii) in the relationship with Nitrate and Iodine deposits it looks that important part of them were related with former lakes and were not removed from their original basins; iv) that the microbial diversity inside salt crusts, microbial mats and gypsum structures allows us to assume the participation of microorganisms in carbon, nitrogen and sulfur turnover in the LlB.