Phototrophic microorganisms of the Pamukkale travertine, Turkey: Their distribution and influence on travertine deposition

Abstract

The travertines at Pamukkale contain a diverse assemblage of phototrophs: 17 species of cyanobacteria, 16 diatoms, and 5 Chlorophyceae. Two communities were recognized on the active travertines: (1) surficial mats dominated by filamentous cyanobacteria, particularly Lyngbya (Phormidium) laminosum forming soft weakly mineralized layers to 10 mm thick, and (2) a predominantly endolithic assemblage, also dominated by cyanobacteria developing 2–5 mm below the travertine surface. The distribution of these communities is determined largely by water flow and the de‐greee of desiccation. Two further communities are briefly described from nondeposit‐ing areas. Most of the active travertine consists of alternating layers of micrite and sparite 0.25–0.75 mm in thickness, which probably result from short‐term fluctuations in water flow rather than diel events (photosynthesis, temperature). The presence of needle‐fiber calcite in surface samples suggests that evaporation of water may play some part in travertine formation. The phototrophs appear to influence the travertine fabric only locally, where the surficial growths contain strings of calcite crystals adhering to the filaments, forming irregularly laminated layers. The hot‐spring water is believed to be contaminated with sewage and agricultural effluent, but there was no evidence to suggest that this is currently affecting the travertine deposits. The water is supersaturated with respect to calcite when it contacts the travertine, and precipitation is primarily the result of carbon dioxide evasion. Water chemistry and discharge measurements indicate a total travertine deposition rate of 35 tonnes per day.