جستجوی مقالات مرتبط با کلیدواژه « Tufa » در نشریات گروه « زمین شناسی »

Shurab travertine spring is located 140 km the east of Tehran and at the beginning of the Gadook Gorge on the border of Tehran and Mazandaran provinces. This spring originates from the fractures and drainage of the Barut Formation in the train tunnel. The carbonate deposits are divided into two main categories: the first group of deposits that are forming at present time (active): and mostly of different colors such as red, yellow and orange, the second group of old (fossilized) deposits mainly adjacent to the railway line and are mostly cream-colored. The age of these deposits is less than 100 years old. The morphology of the carbonate deposits are layeres and Cascade form. Types of travertines and tufas based on morphology and environment in the stack include 1- waterfall travertine 2- travertine with layered morphology and 3- calcareous tufa or framestone phytoherm. Also, according to the petrographic results of four types of lithofacies, according to the characteristic morphologies on the ground scale and hand specimens in the travertine deposits of the saltwater travertine were identified which include: 1- lithofacies raft boundstone; 2- lithofacies algae; 3- lithofacies crystalline crusts and 4- lithofacies Bandstone shrubs. Dissolution and cementation are the most important diagenetic processes of tufa and travertine in the carbonate fascia of the region.  Hydrochemical data the water in Shurab spring is near neutral to slightly alkaline and of sodium chloride type.

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.