TTE43

ADN de Lago Serrano, Laguna Verde y de Los Cisnes: un análisis…

ABSTRACT Environments where microbialites have been identified, have shown that not all of them share the same characteristics, showing a variety of abiotic factors that allow this organo-sedimentary structures to grow, reason why they could be considered to have their own “DNA”. Between the parameters that influence carbonate precipitation by biologic activity are temperature, pH, alkalinity, evaporation and mixing of waters with different compositions. North of Porvenir, Isla Grande de Tierra del Fuego, it is possible to find three water bodies: Lago Serrano, Laguna Verde and Laguna de Los Cisnes, from north to south. Between these three, only the last one shows domical structures formed by biologically induced carbonate precipitation, known as microbialites. It was proposed to carry out major element análisis, water physicochemical analysis, and hydrometeorological parameters and soil studies, with the objective of determining which are the factors that influence and allow the growth of microbialites exclusively at Laguna de Los Cisnes. Hydrologic balance results show that annual precipitation is 324,1 mm/year, from which a major part is evaporated, a minor percentage is infiltrated and there is no surface runoff. This hydrologic deficit is related to the direct action of the westerly winds. Low precipitation and high evaporation, along with dominant salinity marked by sodium and calcium in the Laguna de Los Cisnes waters, would be the factors allowing the current growth of microbialite in the said water body. Such salinity could be strongly influenced by a salt water intrusion coming from the Magellan Strait, helped by the type of substrate where Laguna de Los Cisnes is emplaced and, to a lesser extent, by saline particles transported from the west by strong winds. The beginning of microbial activity in that site, the southernmost with those types of rocks known to date, could be related to the releasing of a great amount of CO 2 to the atmosphere, by the ending of the Last Glacial Period, creating ideal environment conditions to start carbonate precipitation by biological activity, just as once occurred in the beginning of the history of our planet.

2