Facies, sedimentary environment and sequence stratigraphy of the lower Upper Cretaceous in the Dezful Embayment, southwestern Iran:

Authors

1 Ph. D. student of Sedimentology and petrology of sedimentary rocks, Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran

2 Prof., Dept., of Sedimentary Basins and Petroleum, Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran

3 National Iranian Oil Company, Tehran, Iran

Abstract

The Upper Cretaceous (Upper Albian-Lower Torunian) Sarvak Formation (and its equivalents) is the second most important carbonate reservoir in Iran that was developed under the warm tropical climate. The Sarvak Formation with the predominant limestone lithology in the Omid, Mansuri, and Ahvaz Oil Fields was conformably overlies the shaly Kazhdumi Formation and overlain by the Ilam Formation. Detailed petrographical studies led to determine twelve carbonate microfacies that indicate deposition on a homoclinal ramp-type carbonate setting. The identified ramp-type setting was composed of four main facies belts including inner, middle and outer ramp associated with an intrashelf basin. Biostratigraphic assemblage zones, facies analysis, depositional sub-environments, and wire-line logs assisted in mapping the paleogeography of the study area into four third-order stratigraphic sequences. The upper boundary of third and forth depositional sequences (DS3-4) in all studied oil fields defined as a disconformity confirmed by the evidence of extensive dissolution and other meteoric diagentic features that reveal a platform exposure. The other sequence boundaries defined as a correlative unconformity. The modified sequences and sequence boundaries of the Sarvak succession are clearly correlatable with sequence boundaries and surfaces derived from the Arabian Plate sequenc stratigraphy in Iran and adjacent Arabian countries.

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