Examination of climatic orbital changes and sedimentation rate in the Ilam Formation in the Kupal oilfield, Dezful Embayment

Carbonate successions are considered archives for recording the palaeoclimatic proxies and so they are suitable for understanding climatic patterns and identifying the Milankovitch cycles and cycles’s impacts on sea-level changes during Phanerozoic. In the current study, the carbonate successions of the Ilam Formation (Santonian) and their spectral gamma-ray data were chosen to identify the cycles and influencing factors on the sedimentation in one of the oilfields in the Dezful Embayment, southwest of Zagros mountains. According to available evidence, all of Milankovitch cycles contributed to changes in climatic conditions simultaneously with development of the Ilam Formation, however, the long Eccentricity cycles were dominant and have played a greater role in this issue. The sedimentation rate was estimated at 4-5.5 cm/kyr on average in the Ilam Formation. Considering the sedimentation rate and number of identified long Eccentricity cycles, it could be said the deposition in the Ilam Formation lasted in 1.13-1.8 Ma. Our results indicate that the relative sea-level changes in the studied wells correspond to the eustatic sea level. The deposition process in the Ilam Formation was largely affected by the performance of long Eccentricity cycles, eustatic sea level, and tectonic events during the Upper Cretaceous.