Evidence of microbiologic activity in modern travertines: Sicakcermik geothermal field, central Turkey

• Published in: Carbonates and evaporites 2000-01, Vol.15 (1), p.18-27
• Main Authors: Tekin, Erdogan, Kayabali, Kamil, Ayyildiz, Turhan, Ileri, Ozden
• Format: Article
• Language: English
• Subjects: Alabaster; Algae; Aquatic plants; Budding; Budding bacteria; Calcite; Carbon dioxide; Carbonates; Crystals; Cyanobacteria; Deposits; Diameters; Electron microscopy; Emergence; Formations; Hot springs; Hot water; Joints (timber); Lakes; National parks; Ridges; Scanning electron microscopy; Shrubs; Stromatolites; Structures; Terraces; Travertine; Water flow; Water springs; Waterfalls
• ISSN: 0891-2556; 1878-5212
• DOI: 10.1007/BF03175645

Modern travertine deposits are observed in the Sicakçermik hot springs located northwest of Sivas, central Anatolia. They are the carbonate deposits of crustal (spongy) and/or alabaster-textured formations controlled by both organic and inorganic processes. The structures formed under the influence of inorganic processes include the accumulations on the fissure and joint ridges. These structures are adjacent to the hot water emergence spots representing the points of rapid hot water flow and sudden release of CO2. The structures developed under the influence of organic processes form in areas at relatively farther distances from the hot water emergence points. These structures were described to be “waterfall or cascade deposits”; “terrace-mound travertines”; and “shallow lake fans” by different researchers. They are recognized in the field by special identifying trails such as manganous-ferrous travertine shrubs resembling ivy, siliceous stromatolites, and ferrous pisoids, 3 to 12 mm in diameter.All the modern travertine samples examined are dominantly formed by subidiomorphic prismatic-tabular calcite crystals. Scanning Electron Microscopy revealed that calcite crystals forming the pisoids are characterized by zonal growth. Stromatolitic formations, on the other hand, bear regular joints developed as a consequence of sudden cooling and some special structures indicative of bacterial activity (in the form of nodule, spheroid, ellipsoid, column, filament and honeycomb or grape bunch structures). In addition, secondary dissolution vugs and pores giving way to the release of CO2 are associated structures with the stromatolitic formations. The data collected from all the utilized techniques suggest that the microbiological formations observed in the travertines of Sicakçermik hot spring were produced by the sulfatereducing, boring-budding bacteria such as Coccoids, Pedomicrobium, Beggiatoa sp., Thiobacillus sp., as well as blue-green algae (Cyanobacteria).The travertine occurrences produced by both organic and inorganic processes have an annual average of 3–5 cm deposition in thickness. The hot water emergence points and their flowpaths manifest seldom-found natural features. These natural monuments are irresponsibly destroyed for several reasons. The authors argue that these formations, significant from the point of view of their occurrence mechanism as well as their final products, must be preserved. If accomplished, a modern natural monument similar to that