Modern stromatolites from the Andean lakes: Unlocking ancient stromatolitic sedimentary models

Abstract

Modern carbonate-stromatolite occurrence has often related with the sea (e.g., Shark Bay, Australia; Exuma Sound, Bahamas in the Caribbean sea) or with littoral pools or channels (e.g., Lagoa Salgada, Brazil; Laguna Bacalar, Mexico; Lagoon Coorong, Australia; Solar Lake, in the Sinai Peninsula, Egypt), always connected with the sea. The discovery of modern gypsum-stromatolites from Cuatro Ci´enagas, Mexico, in a continental playa-lake (800 masl) and carbonate-stromatolites in Andean Lakes from Argentina and Chile (more than 3500 masl) have been considered as a significant advance in their scientific knowledge. These stromatolites in the Puna region are been growing in very extreme environmental conditions in the Socompa, Diamante, Tolar Grande and Negra lakes (Argentina) and Tebenquiche and La Brava lakes in Chile. The Puna represents a large basin that is fragmented into a system of minor interrelated basins demarcated by mountains. Its climate is arid, with annual precipitation less than 350 mm, and daily temperatures range from -10 to 20◦C in summer and -15 to 10◦C in winter. Due to its high altitude and low latitude geographical position, the Puna region is exposed to high solar irradiance (∼165% of the value at the sea level), especially in the UV-B region, where the instantaneous flux can reach up to 17 W/m2 . Due to the extreme environmental conditions, such as residual volcanic activity associated with sulphur availability, hypersalinity, high UV irradiation, low O2 pressure and low nutrient availability, these modern stromatolite-like ecosystems constitute excellent models to study geochemical cycles and biogeochemical interactions during the early Earth. Moreover, these lakes are good laboratories to try to test the hypothesis that similar microbial mat community produce different organosedimentary structures depending of the physico-chemical environmental conditions (Logan’s stromatolite model). By the other hand, during the Precambrian deposition of Villa M´onica Formation, Tandilia System, Argentina, and the Mina Verd´un Group, Uruguay, the stromatolite morphology distinguished suggest that the mesoscale arrangements have been produced by the sedimentological condition as Logan’s ideas said.