Depositional facies and geochemistry of the Kangan formation in the South Pars Field, Persian Gulf (Iran)

Abstract

The Kangan Formation is one of the largest carbonate reservoirs located in the South Pars Field, which is one of the major gas fields in the central basin of the Persian Gulf. Facies analyses indicate that the Kangan carbonates are formed in four microfacies belts: tidal flat, lagoon, shoal, and shallow open marine, in a platform ramp environment. The predominance of tidal flat sediments along with the oolitic shoal facies and lack of a large shoal reef indicate a homoclinal-ramp system. Major and minor elements and carbon and oxygen isotope values were used to determine the original carbonate mineralogy of the Kangan Formation. The data indicate aragonite carbonate mineralogy in a closed diagenetic system. The Kangan Formation displays a gradual upward increase in δ13C values and variation in δ18O with changing lithologies. Palaeotemperature calculation, based on the heaviest δ18O values in limestone micrites and dolomicrites, range from 36 to 44 °C, respectively. The isotopic compositions of the Kangan carbonates indicate that they were deposited in shallow tropical waters. Stratigraphic analysis indicates four major transgressive and regressive events of nearly two million years’ average duration, which controlled the development of two depositional sequences and their systems tracts.