Largest known microbialites discovered in Lake Van, Turkey

Abstract

MICROBIALITES are organosedimentary deposits produced by benthic microbial communities interacting with detrital or chemical sediments1. Calcareous cyanobacterial microbialites defined as stromatolites and thrombolites were common in ancient shallow marine environments2. Today, they are restricted to a few lacustrine and perimarine settings. This restriction may result from changes in seawater chemistry through time3–6, particularly from alteration in supersaturation with respect to carbonate minerals7. The largest known calcareous microbialites (several metres high) were formed in the late Precambrian8. Here we report the discovery of enormous (∼40 m high) tower-like microbialites from alkaline (pH>9.7) Lake Van, eastern Anatolia. Growth is by mats of coccoid cyanobacteria (Pleurocapsa group) permineralizing in situ with aragonite and by inorganically precipitated calcite. Certain aspects of these microbialites resemble Proterozoic marine stromatolites9.