Oolitic Iron Deposits of Kazhdumi Formation in Central Persian Gulf: Depositional Environment and Sea-level Change

Sedimentological characteristics, sedimentary environment and see-level change of the middle Cretaceous oolitic ironstones of one hydrocarbon field in central Persian Gulf were analyzed in this study. The analyses include petrography, XRD and size analysis using laser particle sizing. Core analysis of the sequence shows that it is composed of shaly limestone, limy shale, carbonate cemented sandstones, shale and oolitic ironstones from bottom to top. The dominant minerals of these deposits at the upper part are goethite, phosphate, calcite, clay minerals and siderite. These analyses showed that the studied ooids were deposited in a shallow marine environment with bidirectional currents and occasional storms. Lack of limestone relics, the presence of marine ooids, change in iron minerals from siderite to goethite in sediment sequence from bottom to top and high roundness and symmetry of grains confirms such environment. Deposition of a shale layer just above this complex has protected them from considerable diagenetic changes with creating two impermeable layers around this unit. The sea-level falls toward the oolitic ironstone layer and rises again after the deposition of this layer. If this sequence be present at the other parts of the Persian Gulf, it could be used as a key bed in stratigraphic studies and correlations in Persian Gulf area.