Isotopic composition and growth rate of microbialites in Laguna Turquesa, a high-altitude lake in the Central Andes

Abstract

This study investigates the isotopic characterization of microbialites from Turquesa Lake located in the arid, high-altitude region of the Central Andes (3752 m.a.s.l.). Stable isotope analyses (δ¹³C and δ¹⁸O) were conducted on three microbialite levels (M1, M2, and M3), with complementary radiocarbon dating revealing ages of 11,830 ± 170 years BP for the outer layer of M1 and 13,140 ± 120 years BP for its core. Findings indicate variable microbial growth rates, peaking in the core (0.12 mm/year) and decreasing towards the outer layers (0.027 mm/year), with internal structures reflecting reticulate intervals in central zones and laminated patterns in outer layers. δ¹³C values ranged from 11.86 to 9.93 ‰ and δ¹⁸O from 10.60 to 6.22 ‰. The results suggest that M1 and M2 formed when Turquesa and Peinado lakes were connected, displaying complex isotopic fractionation influenced by evaporation and photosynthesis, while M3 formed under evaporative conditions associated with the separation of the lakes due to evaporation. Nevertheless, M3 appears to be less evaporative than M1 and M2, as indicated by its lower δ¹⁸O values. This research provides new insights into how extreme environmental conditions in the Puna have influenced the isotopic evolution and formation of microbialites.