Microbial processes forming daily lamination in a stromatolitic travertine

Thirty-hour continuous observation revealed that cyanobacterial metabolism caused daily lamination of a stromatolitic travertine in the Shionoha hot spring, SW Japan. The travertine is mainly composed of dendritic calcite crystals intercalated with bands of micritic particles at sub-millimeter intervals. Cyanobacteria remained in the spaces between the calcite crystals during the daytime, rose to the travertine surface to receive illumination as light decreased and formed a biofilm around sunset. A micritic band developed on the biofilm where glutinous substances trapped detrital ferrihydrite-rich particles transported from upcurrent. The trapped particles covered the biofilm, and in-situ precipitation of calcite crystals became dominant before mid-night. The depositional model of daily lamination of the Shionoha travertine may provide insight into the poorly understood origins and depositional rate of ancient stromatolites. (C) 2008 Elsevier B.V. All rights reserved.