Position of Oil Fields of Southwest Iran with Respect to Relevant Sedimentary Basins

Abstract The uneven distribution of factual data is stressed; much is known from the mountain outcrops, but little below the foothills and plains where knowledge is restricted to a few bore hole sections. The Paleozoic can be treated as basement, its major contribution to oil field position probably being the influence of a Cambrian salt group on the growth of the Tertiary folds in which the oil concentrated. The first important negative area can be recognized in the Turonian and Lower Cretaceous; it was aligned northwest-southeast with an axis about 40 miles northeast of the oil-field belt. This trough was separated from the Basra-Kuwait area of thick deposition by a positive area about which little is known. In Upper Cretaceous/Eocene time the axis of the sedimentary trough was about 70 miles northeast of the oil field belt. During Lower Miocene time an important basin developed, in which the Lower Fars evaporites were laid down, with an axis about 20 miles northeast of the oil field belt. After Middle Miocene time orogenesis developed rapidly, local structural features assumed control, and great thicknesses of continental beds were deposited in individual synclines. Concurrently with the development of the anticlines and synclines a major upwarping of the Zagros Mountains occurred, and a downwarping of the foothills and plains areas. The southwest limit of the pre-Fars outcrops, "The Mountain Front," marks the approximate hinge line of this great geoflexure, which in the oil field area had an amplitude of about 40,000 feet. It is shown that the oil fields of South Iran are situated high up on the southwest flank of the depositional basins in which the source material must have accumulated, but that their present position is on the northeast flank of the late Tertiary basin in which sediments are still accumulating. The presence of the oil can be explained by long distance or local oil migration.