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

Modem travertine deposits are observed in the Sicakcermik hot springs locat ed northwest of Sivas, central Anatolia. They are the carbonate deposits of crustal (spongy) and/or alabaster-textured formations controlled by both o rganic and inorganic processes. The structures formed under the influence o f inorganic processes include the accumulations an the fissure and joint ri dges. These structures are adjacent to the hot water emergence spots repres enting the points of rapid hot water flow and sudden release of CO2. The st ructures developed under the influence of organic processes form in areas a t relatively farther distances from the hot water emergence points. These s tructures were described to be "waterfall or cascade deposits"; "terrace-mo und travertines"; and "shallow lake fans" by different researchers. They ar e recognized in the field by special identifying trails such as manganous-f errous travertine shrubs resembling ivy, siliceous stromatolites, and ferro us pisoids, 3 to 12 mm in diameter. All the modem travertine samples examined are dominantly farmed by subidiom orphic prismatic-tabular calcite crystals. Scanning Electron Microscopy rev ealed that calcite crystals forming the pisoids are characterized by zonal growth. Stromatolitic formations, on the other hand, bear regular joints de veloped as a consequence of sudden cooling and some special structures indi cative of bacterial activity (in the farm of nodule, spheroid, ellipsoid, c olumn, filament and honeycomb or grape bunch structures). In addition, seco ndary dissolution vugs and poles giving way to the release of CO2 are assoc iated structures with the stromatolitic formations. The data collected from all the utilized techniques suggest that the microbiological formations ob served in the travertines of Sicakcermite hot spring were produced by the s ulfate-reducing, boring-budding bacteria such as Coccoids, Pedomicrobium, B eggiatoa 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 thickess. The hot water eme rgence points and their flowpaths manifest seldom-found natural features. T hese 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 preser ved. If accomplished, a modem natural monument similar to that in Pamukkale (Turkey) and Yellowstone National Park (Wyoming, USA) could develop within a reasonable length of time.