Sedimentary Environment, Diagenesis and Geochemistry of the Fahliyan Formation in the Type Section (Fahliyan Anticline) and Gachsaran Oil Field

The Fahliyan Formation with the age of Lower Cretaceous (Berriasian-Hauterivian) were studied for microfacies analysis, diagenesis and original carbonate mineralogy in the type section at Fahliyan Anticline and subsurface section in well number 55 of Gachsaran Oil Field. Petrographic studies led to the recognition of 10 microfacies that were deposited in four facies belts: tidal flat, lagoon, shoal and open marine. The observed facies patterns indicated a homoclinal carbonate ramp depositional environment. Recognition of different type of cements shows that the Fahliyan Formation has mostly undergone meteroric diagenesis. Major and minor elements and carbon and oxygen isotope values indicate that aragonite was the original carbonate mineralogy in the Fahliyan Formation, and suggests that alteration occurred in a closed diagenetic system, with low water/rock interaction.