Characterization of modern dolomite stromatolites from hypersaline Petukhovskoe Soda Lake, Russia

Abstract

Microbialites occur in a number of modern soda lakes, but the formation of dolomite stromatolites in these environments is rare. Microbial metabolic activities are considered to influence precipitation of carbonate minerals (including dolomite) in marine, hypersaline and slightly alkaline environments due to their capacity to buffer pH of the local environmental settings. Hydrochemical features of hypersaline alkaline Petukhovskoe Soda Lake are already favourable for the precipitation of carbonate minerals, and the metabolic activities of microorganisms may not be significant in this type of environment. Stromatolites from this lake provide an excellent opportunity for the study of recent natural dolomite formation in the highly saturated soda environment. To understand the genesis of these stromatolites and to provide insight into environmental aspects of its formation, we have made a detailed structural and mineralogical description with the use of light and scanning electron microscopy, infrared spectroscopy and X-ray analysis. Due to the special fluctuating conditions of sedimentation in the lake, stromatolites contain both layers with chemogenic precipitation of minerals and layers with fossilized algal, cyanobacterial and coccoid bacterial forms. The presence of dolomite, calcite and Mg calcites with different content of magnesium is detected. The primary independent binding of Mg and Si with the following binding of Ca in the pericellular and released exopolysaccharides is shown. Extracellular polymeric substances (EPS) and fluctuating hydrological regimen of the Petukhovskoe Soda Lake are considered to play the key role in the precipitation of Ca–Mg carbonates including dolomite.