Formation and evolution of oblique anticline in eastern Niger Delta

Based on the three-dimensional seismic interpretation data,this paper analyzed the formation mechanism and the growth process of the oblique anticline AE of the M region of the eastern Niger Delta,as well as the evolution process of the associated fault systems.The study results show that the stratigraphic sedimentary period between reflector H4-H6 of the middle and late Miocene was the initial fold-thrust stage,the anticline AE was a half-graben controlled by oblique extensional faults derived from the oblique extensional transfer structure formed by local initial differential fold-thrusting.At the same time the tear faults developed as a result of the differential sliding.During the stratigraphic sedimentary period between reflector H1-H4 of the late Miocene to Pliocene,the large-scale folding and thrusting occurred,differential contractional deformation resulted in the pre-existing extensional half-graben became AE anticline by oblique tectonic inversion,then the anticline grew continually and the crest of the anticline migrated gradually.The newly formed fault systems consist of a small number of associated tear-normal faults caused by differential thrusting and gravity-driven domino normal faults predominantly induced by the slope inclination of the anticline limb.During the stratigraphic sedimentary period between reflector H0-H1 of the Pleistocene to Holocene,as the growth of the anticline ceased,the area entered post-fold thrusting stage.The formation and distribution of conjugated faults were controlled by the local gravity return collapse,local differential sliding and reactivation of pre-existing positive inversion faults jointly.The research results of genetic mechanism of the oblique inversion anticline and evolution of associated faults are helpful to reveal the key factors controlling the accumulation and distribution of oil and gas.