Foreland Basin Sedimentary Environment along the Main Zagros Thrust Suture Zone in the Eastern Zagros Orogen

The Upper Oligocene-Neogene collisional succession in the SE segment of the Zagros Fold-Thrust Belt records progressive flexural subsidence related to topographic loading along the Main Zagros Thrust. Detailed analysis of lithofacies and clay mineral assemblages reveals vertical and lateral changes in the depositional environment of the foreland sedimentary rocks, spanning the shallow-marine carbonates of the Jahrum Formation and the alluvial-fan strata of the Bakhtyari Formation. Tectonic uplift and associated activity along the Main Zagros Thrust to the northeast have driven this shallowing-upward transition. The relatively uniform distribution of clay minerals suggests that mineralogy is primarily controlled by provenance rather than environmental fluctuations. The sedimentary environment can be generally modeled as a fan delta with various facies belts, i.e., proximal fan delta, mid fan delta, transition facies, delta slope, distal fan facies, shallow marine, and fluvial-alluvial systems. Lateral irregular variations in the sedimentary environment and thickness (10-250 m) during the Late Oligocene to Early Miocene along the Main Zagros Thrust can be attributed to the irregular shape of the Arabian plate and differing subsidence rates. However, the significant thickening of the Guri Member from the northwest to the southeast (2 to 700 m), coupled with a deepening sedimentary environment trend toward the southeast of the MZT, suggests that the Minab-Zendan Fault may have contributed to modulating accommodation space from the Middle Miocene onward. While this structure likely influenced the subsequent deposition of the Mishan and Aghajari formations, these patterns may also reflect broader regional subsidence variations.