An investigation on sedimentary facies and hydrochemistry characteristics of carbonate deposits in the Ab-e Ask region, Southeast of Damavand volcano

Calcareous springs of Ab-e Ask are located 85 km northeast of Tehran, in the southern range of the Damavand volcano. Microscopic studies represent the existence of four abiotic and two microbialite facies in the Ab-e Ask travertines. The travertines are the main deposit types of these springs. Based on sedimentation sequence and lithofacies these travertines are categorized as first type (vent and channel), second type (pound, dam, and cascade), and third type (laminated) travertines. On a δ18O versus δ13C plot (VPDB), these travertines are plotted in the oncoid and crystalline crust lithofacies fields. These facies show the character of hydrothermal spring and set the spring in the thermogenic group. Positive values of the Langelier Saturation Index (LSI) for Pashnak, Nadaali, and Zagh springs indicate that these water samples are supersaturated with respect to calcium carbonate, which leads to considerable sedimentation around the springs. In contrast, a negative LSI value at the Sare Pole spring indicates the water is undersaturated with respect to calcium carbonate. Therefore, this spring has a lesser role in travertine deposition compared to the other springs. Also, the position of the samples on the modified Gibbs and Van Wirdum diagrams, suggests that the interaction of water with carbonate and to some extent silicate rocks is considered as the most important source of Ca and Na.