Isotopic and elemental geochemistry of Bahram Formation (Middle-Upper Devonian) in east of Iran

In this research, paleo-climatic conditions and diagenetic system of Bahram Formation (Middle-Upper Devonian) have been investigated using geochemical data of major and minor elements and also oxygen and carbon stable isotopes. For this purpose, three stratigraphical sections of this formation including Cheshmeh-shir section (north east of Tabas) with a thickness of 180 m, Kamar-kuh section (south of Kashmar) with a thickness of 188 m and Hoze-dorah section (east Tabas) with a thickness of 192 m have been studied.The studied sections have been composed of thin to thick bedded, gray colored fossiliferous limestones. Based on the obtained geochemical data, the insubstantial values of δ18O isotope (mean -7.66‰ at Kamar-kuh, -8.11‰ at Cheshmeh-shir and -8.21‰ at Hoze-dorah section) in most of samples and also normalized ratio by calcite for strontium versus iron and manganese values indicate a relatively open system and high rate of water-rock interactions.The combination of elemental analysis results (including low ratio of Sr/Mn and high Mn content) and the trend of carbon and oxygen isotopes values reveal that the meteoric diagenesis has had the most important effect on these deposits.
The calculated sea water temperature at the time of deposition of the studied sections using δ18O values has been estimated between 41° and 45° Celsius which is somewhat higher than the expected temperature for this period of time and might be due to the effect of diagenesis.