A CASE STUDY FROM THE ZAGROS AREA IN SOUTHWEST IRAN EXAMINES THE GEOCHEMISTRY, FACIES FEATURES, AND PALAEOENVIRONMENTAL CIRCUMSTANCES OF THE STORM-DOMINATED PHOSPHATE-BEARING DEPOSITS OF THE EASTERN TETHYAN OCEAN

Abstract

The South Tethyan Phosphogenic Province, a vast carbonate-dominated stratum that stretches across the Middle East, has phosphate resources in south-western Iran. The Tethyan phosphorites of Iran are classified as low-grade ore deposits globally and date to the Eocene-Oligocene (Pabdeh Formation). The Pabdeh Formation was formed on a carbonate ramp setting as a distally steepened ramp, according to the depositional conditions of the facies. In such a setting, turbidity currents carried phosphate particles from the deeper middle and outer ramp of the ocean to the back-shoal setting where they were suspended and deposited as shell-lag and phosphate lamination. Microfacies investigations show that turbidity currents helped all the phosphatic ooids and phosphatized foraminifera, fish scales, bones, and phosphatic intraclasts relocate from shallow to deeper sections of the Tethyan Ocean. REE+Y and P2O5 exhibit a positive correlation in all analyzed sections, which attests to their high geochemical group coherence, according to analysis and interpretation of the data. Negative Ce anomalies define the shale normalized REE patterns of Mondun phosphorites. In contrast, Nill sections with Ce enrichment suggest circumstances of somewhat deeper water sedimentation. This anomaly indicates that the depositional environment was oxic and intensively reworked, bioturbated with greater energy levels during phosphate deposition. These geochemical results are consistent with microfacies analyses, which show that the Mondun section is in a shallow and high energy state with negative cerium anomalies, whereas the Nill and Siah sections are in a deep ramp setting with positive cerium anomalies in REE patterns.