Geohemical Study of Carbonate and Dolomite Facies of Dalan and Kangan Gas Reservoers in the Salman Oil Field

   Abstract:
     Dalan (Upper Permian) and Kangan (Lower Triassic) Formation were deposited in an extensive carbonate platform under an arid climate. These Formations makes up the essential part of the Gas reservoirs in south of Iran and Persian Gulf. Detailed field and petrographic investigation of over 1200 meter carbonate sequence of the Kangan and Dalan led to the recognition of several shallow marine (tidal flat, subtidal, lagoon, bar and open marine) facies. Environment of deposition of these limestone were a shallowing ?upward .The transition from Dalan to Kangan denotes a period of drastic change in the deposition environment and the chemical milieu of the sedimentation basin. These changes are reflected by a marked positive excursion of carbon and oxygen isotopes from Kangan to Dalan Formation. Petrographic, chemical and isotopic studies of the dolomite in the Kangan and Dalan Formations reveal that dolomitization was the result of several diagenetic events. The neomorphic alteration of these dolomites significantly modified their original chemical signatures. Dolomite in the Kangan and Dalan formed in two stages by different mechanisms. In Dalan Formation dolomitization occur in the early phase of syngenetic (pen contemporaneous) replacement of the pre-existing carbonate in an arid climate on a supratidal flat. Kangan?s dolomite formed during deep burial.