The Salt-Related Structures And Their Formation Mechanisms In The Qiulitag Structural Belt, Kuqa Depression

The Paleogene Kumugeliemu Formation and Neogene Jidike Formation attain thick halite layers in the Qiulitag structural belt which is located in the most frontal range of the Kuqa depression. Influenced by the subsalt basement tectonics, differential loading and compressional stresses, the halite layers easily flowed from one place to another, and then formed numerous salt-related structures in the Qiulitag structural belt, which had important influences on the hydrocarbon migration and accumulation.The superimposed structural models composed of the subsalt, salt and suprasalt sequences of the Qiulitag structural belt have been carried out using data from seismic profiles interpretation based on the fault-related folding and salt tectonics. In vertical direction, subsalt, salt and suprasalt structures have been classified, and in plane, the differential deformation and segmentation of the salt-related structures are obvious.The Pre-Paleogene basement in the western Qiulitag structural belt appears as a paleo-uplift controlled by basement boundary faults. The basement paleo-uplift initially presented in the Ordovician, and developed during the Silurian to Triassic followed by the termination in the Jurassic. The Pre-Paleogene basement tectonics influenced the development of salt-related structures.According to the balanced cross sections, the salt-related structures mainly formed within the Kuche period to Quaternary. In the Kuqa depression, the SN- striking shortening strains are 20~35 km which occupied the ratio of 20%~35% of the total sections. The different shortening rates in varying tectono-stratigraphic layers and belts are prevalent in the depression where the salt layers could act as detachment and adjusting during the differential deformation of the subsalt and suprasalt layers.On the whole, the salt structures in the northern part of the Kuqa depression formed earlier than those in the south, and the salt structures in the western Qiulitag structural belt also formed earlier, with larger size, and in the eastern portion, the salt structures developed later, with smaller size. The model of elastic-viscous plate indicated that differential loading induced by the thicker sediments in the Baicheng sag dominated in the early stage of salt structural development. At the present, however, the compressional stresses should play largest effects on the salt structures.The physical modelling also showed that the basement faults, paleo-uplift and structural slopes and steps influenced the salt flowage which resulted in the salt thicken on top of the paleo-uplift and the formation of large-scaled north-dipping detachment faults. During the structural distortion, salt bodies acted mainly as the detachment layer and filled the anticline crest, and few salt diapirs formed in the analogue modelling.By the integrated analysis of the influences of salt-related structures on the hydrocarbon migration and accumulation in the Qiulitag structural belt, the reservoir formation models have been documented, and favorable exploration objectives have also been predicted.