DEPOSITIONAL HISTORY, DIAGENESIS AND GEOCHEMISTRY OF THE TALE-ZANG FORMATION, SOUTH OF LURESTAN

Carbonate sequences of the Taleh-Zang Formation mainly consist of large benthic foraminifera (e.g., Nummulites and Alveolina) along with other skeletal and non-skeletal components. In this formation, the water depth during deposition was determined based on the variation and different types of benthic foraminifera and other components in different facies. Microfacies analysis led to the recognition of 10 microfacies that are related to 4 facies belts such as: tidal flat, lagoon, shoal and open marine. The absence of turbidite deposits, reefal facies, gradual facies changes and widespread tidal flat deposits indicate that the Taleh-Zang Formation was deposited in a carbonate ramp environment. Due to the great diversity and abundance of larger benthic foraminifera, this carbonate ramp is referred to as "foram-dominated carbonate ramp system". Comparison between elemental and isotopic compositions of biotic (benthic foraminifera) and abiotic (micrite) components in Taleh-Zang Formation shows an equilibrium condition due to minor biological fractionation and kinetic effects such as growth rate or other unknown factors. Thus, palaeotemperature calculation of seawater based on heaviest oxygen isotope values of biotic and abiotic carbonates are similar. Petrographic and geochemical studies illustrate that these carbonates were affected by weak meteoric digenesis in a closed diagenetic system with a low water/rock interaction.