Mineral Formation in Cyanobacterial Mats of the Barguzin Basin Alkaline Hot Springs (Baikal Rift Zone)

摘要

The oldest lithified cyanobacteria found in sediments date back to 3.6 Ga, and large-scale formation of stromatolitic structures associated with copious cyanobacterial mats is known at 2 and 1 Ga [1, 2]. Today's cyanobacteria have been expelled to extreme habitats, such as hot springs where thermophilic communities can live. Many hot springs vent in the Bar-gusin basin of the Baikal Rift Zone [3-5].They are alkaline waters with high silica concentrations and a nitrogen-dominated gas phase. The water-bearing rocks are sheared outsized granites or granodiorites. Microbial populations have been recognized at all venting sites [6] (more than ten within the Barguzin basin), but travertine occurs at three sites only (Alia, Garga, and Gusikha) [7].The thickest carbonate (travertine) framework at the Garga spring has been attributed to the microbial activity [8]. Yet, minerals deposited immediately in the hot-spring environments of the basin have never been described. We investigated microbial populations of five springs (Alia, Kuchiger, and Umkhei on the right side of the Barguzin valley, and Garga and Uro on its left side) and discovered bacteria-mediated precipitation of amorphous silica and calcite in the Alia and Garga springs, just where travertine is formed. Our objective was to study the morphology of minerals and the laws of their formation in microbial communities.