فهرست مطالب fatemeh goleij

Travertine deposits are a kind of continental carbonates that form in specific chemical, physical and biological conditions. Garab travertines in southeast of Mashhad are studied based on field, geochemistry (elemental and stable isotope analysis) and hydro-geochemistry analysis. Field and petrographic characterization led to recognize of crystalline crust, raft, foam, shrub, laminated, black mud and tufa lithofacies. These lithofacies are composed of calcite and aragonite mineralogy. They have high concentrations of Ca, Mg, S, Fe, Na and Sr and low concentration of Mn, P and Si. These lithofacies are enriched with respect to δ13C and depleted with respect to δ18O that can be related to algal origin and meteoric water, respectively. The type of Garab springs water is Ca- HCO3- - SO42- and Na- Cl. This water is saturated with respect to bicarbonate and sulfate. The water composition and dissolved ions have a close relation to geological units (carbonate and evaporite) in Garab area.

Tufa is the non- marine carbonates that formed from cold to low temperature freshwater at low depth and low energy flow conditions. Abgarm’s tufa is a typical kind of these deposits. Field and microscopic studies led to recognize of seven allochthonous and autochthonous lithofacies. The presence of dense plant covering river margins, increasing use of dissolve CO2 in water and providing chemical conditions due to turbulence are factors that are important in the formation of tufa. Based on concentrations of dissolved ions, the type of Abgarm water is Ca- Mg- HCO3. Based on ions ratio, the water with primary meteoric origin is affected by passing through dolomitic limestone and evaporite of the Mozduran and Shurijeh formations. The high concentrations of these ions caused the carbonate to be trapped between algae filamentous and formed a kind of active tufa. The presence of gastropod species show a dominance wet climatic conditions when these deposits formed. At the next step, decreasing rainfall and increasing temperature and evaporation, caused the death of two gastropods species (Melanopsis praemorsa and Galba truncatula) in the studied area. Isotopic analysis of oxygen and carbon show the effects of meteoric waters and Mozduran aquifer limestone formation in isotopic compositions of tufa in Abgarm area.