Characteristics And Evolution Of Salt-related Faults In The 1506 Block Of Lower Congo Basin

Block 1506 is located in the northern part of the lower Congo basin,straddling tensile stress,stress transition and a small area of compressive stress.The faults developed in the block,and the faults at different levels play a significant role in the control and transformation of the formation and development of the structures and the distribution of sedimentary facies since the late cretaceous.The main faults controlling the uplift and depression tectonic belt divid the block into diapir area,growth fault development area and multi-stage graben area from west to east,with the multiple faults controlling the tectonic belt in the growth fault development zone divide the tectonic units into blocks from south to north,make the whole block presents the strike-slip feature of "east-west zoning and north-south zoning".The activity and evolution of faults in the block are closely related to the influence of tectonic evolution and salt activity.Read and calculate the growth index and the drop of 34 sites on the growth faults in the block,and draw diagrams.It was found that there was fault activity in the block in different periods,the most intense and numerous active faults,and the most obvious control of active faults on sedimentation occurred during the Oligocene to Miocene sedimentary period.During this period,the Congo basin entered the stage of passive continental margin drift.Under the turbulent deep-water environment,the thick salt deposited in the early stage were vigorously active,and the interaction with the fault activity promoted stronger activities.The key active period of growth faults in block 1506 was determined around MioceneAccording to the tectonic maps of four reflectors in the area(the paleogene Oligocene top interface,the neogene lower Miocene top interface,the meso-miocene top interface and the upper Miocene top interface),it is observed that the sedimentary centers are mostly distributed near the eastern active fault in the study area in each period.Based on the sedimentary data,summarizing the activity of salt-related faults and their control rules on the development degree and distribution of the reservoir of the waterway or turbidite sand,It can be found that the salt in the western part of the block are generally in the late period(before and after the late Miocene)with a single arch,mostly due to the channels provided by faults developed in the prophase(Oligocene),tensile fractures were developed at the top of the diapir nucleus,or radial fractures were induced in the plane around the diapir.The salt in the middle grows with the formation deposition and controls the settlement zone in a small area,for example,“rim syncline”.Some of the salt stopped growing halfway and developed tensile growth fractures at the top of the diapir nucleus,individual diapirs are not related to fractures.The control effect of the eastern salt body on sedimentation was mainly reflected in the late period(the beginning of the late Miocene)when the salt flows westward to provide the space for subsequent stratigraphic deposition.With the gradual weakening of this phenomenon from south to north,the main sedimentation control function of the fault began to appear.According to the contribution degree of fault and salt activity to sedimentary control,the models of salt-related fault structure controlling sedimentation are further divided into four categories.It is concluded that the contribution rate of fault activity to sediment control is higher than that of salt activity.