Niger Termit Basin experienced the first and second rifting cycles during the Early Cretaceous and Eocene-Oligocene,respectively.The two cycles originated through different geodynamic and kinematical mechanisms;as a result,they have different structural styles and basin features.This paper analyzed the geodynamic origin,kinematical features and structural styles of the second rifting cycle,as well as implications of these factors in hydrocarbon accumulation in the Termit Basin,Niger.The findings are the following.During the Eocene-Oligocene,and under the regional compression stress field caused by the Africa-Arab and Eurasia plate collision,the Termit Basin moved as an extrusion from the inner Africa plate in the NEE-SWW direction and acted as typical strike-slip with extensional characteristics.Building on the NW-SE fault system in the first rifting cycle,the second rifting cycle developed the NNW-SSE fault system in the Termit Basin.The basin has primarily graben-horst and half graben structures,with graben style in the north,and Domino half graben style in the south.The Eocene-Oligocene transtension formed a series of en echelon normal faults-connected by soft linkage-and developed a large number of strike slip transfer structures at both basin and sub-basin levels.The Paleogene structure transfer zones could be divided into three basic styles,i.e.,parallel,anti-parallel and back to back styles,of which,overlapping parallel,anti-parallel and back to back overlapping transfer zones are the main structural styles observed in the Termit Basin.The second rifting cycle controlled the Eocene-Oligocene depositional system of the Termit Basin.During the Eocene initial rifting stage,delta system was formed in Sokor-1 Fm.;and during the Oligocene-Early Miocene deep-rifting stage,lacustrine mudstone was deposited in the Sokor-2 Fm.,which generated the most advantage reservoir-seal assemblage in the Termit Basin.Meanwhile,structural transfer in the second cycle helped to form many fault blocks and noses and faulted anticline structures,which account for the main types of traps in the Termit Basin.Furthermore,during the Oligocene-Early Miocene deeprifting stage,the main active fault became connected to the Cretaceous source kitchen,this led to extensive vertical and lateral hydrocarbon migrations in the Termit Basin.The growth indices of the main faults implied that the Paleogene hydrocarbon distribution and accumulation were controlled by the fault activity during the Oligocene-Early Miocene deep-rifting stage.Based on above analysis,the lithological traps of the Sokor-1 and mid-lower Sokor-2 Fms.—located on the strike slope of transfer zones,and new petroleum system in the Upper Sokor-2 Fm.,all have hydrocarbon potentials and could be further explored.%尼日尔Termit盆地主要发育早白垩世和始新世一渐新世两个裂陷旋回,其起源于不同的动力学背景和运动学机制,相应表现出不同的盆地性质.其中古近纪始新世—渐新世第二裂陷旋回受区域挤压应力环境下的非洲板块内部局部应力释放控制,具有逃逸盆地的性质,在盆地内部表现为典型走滑伸展特征.该旋回在第一期NW-SE控盆断裂基础上发育了NNW SSE断裂体系,盆地整体呈现地堑-地垒和半地堑结构,北部为双断结构地堑,南部为西断东超多米诺半地堑结构.古近系断裂的斜向拉张作用形成了大量雁列式正断层,以软连接方式相连,在二级构造单元内发育了大量构造调节带,分为同向型、对向型和背向型3大类,以同向叠覆型、对向平行型和背向叠覆型为主,成为Termit盆地最主要的构造调节带样式.古近纪始新世渐新世第二裂陷旋回及其构造样式控制了盆地沉积体系,在始新世Sokor1初始裂陷期形成了三角洲-湖泊沉积体系、渐新世—早中新世Sokor2深陷期沉积了湖相泥岩,形成了盆地主力储盖组合.同时,该旋回的构造调节作用形成了大量断块和断鼻/断背斜构造,成为Termit盆地的主要圈闭类型.渐新世早中新世的深陷期导致断层沟通白垩系成熟烃源岩,在盆地内发生广泛的垂向和侧向运移,该时期断层的活动强度决定了古近系油气分布和富集程度.Sokor1和Sokor2段中下部岩性圈闭及Sokor2段成藏组合是Termit盆地的下步勘探领域.
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