The extensional dextral strike-slip duplex of JZ27-33 Block in Liaodong Bay
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Three main NNE-striking strike-slip faults are developed in JZ27-33 block of Liaodong Bay,i.e.,Liaozhong 3 fault(or Liaozhong 1 fault),Liaozhong 2 fault and Liaodong 2 fault.These 3 faults assume en echelon distribution on the plane,with many secondary normal faults of strike-slipping nature developed between them.These normal faults strike NE or NEE and obliquely intersect main strike-slip faults,and the sharp angle between them indicates the corresponding stratigraphic moving direction on the plane.Negative flower structure is another important feature of the giant strike-slip faults.It is therefore concluded that the faults of the study area have characteristics of on the plane and negative flower structure on the cross-section,and that the faults in JZ27-33 block of Liaodong Bay formed a typical extensional dextral strike-slip duplex system,with the main controlling factors composed of the dextral strike-slip and plane distribution of Tanlu fault,the multi-phase tectonic movement and the brittle sedimentary layers.Keywords:
Transform fault
Echelon formation
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Shaleitian uplift is located in the western Bohai Bay. The lithology of the buried hill is Archaeozoic granite, which covered by Neogene fluvial sandstone and mudstone directly. New multiazimuth 3D seismic data show that a strike-slip fault cut through Shaleitian uplift in Neogene. The strike-slip fault of NNE trend is 20 km long. There are many EW- trending branch fractures around the main strike-slip fault which is cut by the small faults or combined into negative flower structures. From the analysis of the seismic slice and the interpretation results, the strike-slip zone can be divided into 3 parts in plane. There are two movement stages from the study of the strike-slip fault and branch fractures evolution, namely strike-slip stage and extensional stage. The multi-period activities in study area not only generated good anticline closures, but produced good migration conditions.
Neogene
Lithology
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Transpression
Transtension
Echelon formation
Strain partitioning
Transform fault
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Through analysis of the pre-Mesozoic faults in the southern slope of Huimin Sag based on fault distribution ichnography and on 3D seismic sections, it is recognized in this paper that a group of NNW faults are parallel to one another in the ichnography and showing sectional negative flower structures. Analytical results of the shapes of the negative flower structures and the stratigraphic features of the formations indicate that the strike-slip fault group have undergone two different courses of shearing activities, including strong sinistral shearing during the Mesozoic, followed by dextral shearing during the Cenozoic; Evolution of this fault group is similar to that of the NNW-trending strike-slip faults in the Luxi block, as they belong to the same brush fracture system controlled by the slip activity of Tan-Lu fault. It can be deduced that the formation and evolution of the fault group is mainly engendered by the sinistral strike-slip of Tan-Lu fault in the Mesozoic and the dextral strike-slip of Tan-Lu fault in the Cenozoic.
Shearing (physics)
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Buried hills in the Shaleitian bulge of the western Bohai offshore are composed of Archaeozoic granite,which is immediately covered by Neogene fluvial clasolites.In this area there is a well-developed NE dextral strike-slip fault that stretches for about 20km and slantingly cuts through the whole Shaleitian bulge.The angle between the NE and NW strike-slip faults within the buried hills is about 100°.The major NE strike-slip fault keeps unceasingly active,while NW faults being no longer active in Neogene extend discontinuously with partial segments displayed as channels.Strike-slip faults in this area commonly show a minus flower structure and the Neogene tectonic movement induced numerous approximately-EW dextral extensional minor faults near the major strike-slip fault,which cut the major strike-slip fault occasionally.Based on detailed interpretations of high-resolution seismic data,we divided the evolution of faults in this area into three stages: the formation of base strike-slip faults in pre-Neogene,the formation of feebly-en-echelon faults in cover strata in early Neogene and the formation of tenso-shear and strongly-en-echelon faults in cover strata in late Neogene.Multiperiodic activities of strike-slip faults in the uplifted area not only formed faulted-anticline traps but also controlled Paleogene deposits on both sides of the faults,exerting an influence on the accumulation and redistribution of hydrocarbons.
Neogene
Echelon formation
Anticline
Paleogene
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Based on the analysis of high-resoulution 3D seismic data and drilling wells, this paper studies the NNE trending fault and associated structures. The NNE trending faults show an echolon arrangement on horizontal. The different tectonic deformation and strata units exist in the both side of the fault zone. The NNE fault has associated folds by the side of the fault zone. The faults are characterized by flower structure on the seismic profiles. Therefore, the faults have strike-slip movement. The NNE trending faults, which parallel to the Tanlu fault, were possible formed during Indo-China movement. It was active as a right strike-slip fault during Late Jurassic and Early Cretaceous. It controlled the Magan ejection and development of Late Mesozoic sedimentary basin. The faults express as normal fault by right strike-slips movement during Censozoic except tectonic inversion.
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Through fault structure analysis and chronology study, we discuss the origin and growth mechanisms of strike-slip faults in the Tarim Basin. (1) Multiple stages strike-slip faults with inherited growth were developed in the central Tarim cratonic basin. The faults initiation time is constrained at the end of Middle Ordovician of about 460 Ma according to U-Pb dating of the fault cements and seismic interpretation. (2) The formation of the strike-slip faults was controlled by the near N-S direction stress field caused by far-field compression of the closing of the Proto-Tethys Ocean. (3) The faults localization and characteristics were influenced by the pre-existing structures of the NE trending weakening zones in the basement and lithofacies change from south to north. (4) Following the fault initiation under the Andersonian mechanism, the strike-slip fault growth was dominantly fault linkage, associated with fault tip propagation and interaction of non-Andersonian mechanisms. (5) Sequential slip accommodated deformation in the conjugate strike-slip fault interaction zones, strong localization of the main displacement and deformation occurred in the overlap zones in the northern Tarim, while the fault tips, particularly of narrow-deep grabens, and strike-slip segments in thrust zones accumulated more deformation and strain in the Central uplift. In conclusion, non-Andersonian mechanisms, dominantly fault linkage and interaction, resulted in the small displacement but long intraplate strike-slip fault development in the central Tarim Basin. The regional and localized field stress, and pre-existing structures and lithofacies difference had strong impacts on the diversity of the strike-slip faults in the Tarim cratonic basin.
Tarim basin
Thrust fault
Transpression
Stress field
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Echelon formation
Growth fault
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As an important fault type in the Liaodongwan Depression,strike slip faults are components of the Tan-Lu fault zone,and they have exerted major influences on the structural framework and hydrocarbon accumulation in the depression.Based on detailed 3D seismic interpretation,this paper reveals the spatial distribution and segmented differential deformation characteristics of the strike slip faults in the Liaodongwan Depression. The strike slip faults mainly occur in the eastern and central Liaodongwan Depression,trend northeast as a whole,and have good continuity. They appear as flower structures on sectional view,while appear as strike slip duplex and imbricated structures on plane view. Comparison of deformation features of strike slip faults in different areas shows that the strike slip fault zone features in obvious segmented differential deformation. The strike slip faults can be divided into two segments,namely transpressional segment in the south and uplifting segment in the north. The uplifting segment can be subdivided into complex-uplifting,buried-uplifting and single-uplifting segments according to the shapes of the uplift. The development of the Liaodong uplift was mainly controlled by the transpressional movement of the strike slip faults,but the Liaoxi uplift with earlier initiation of uplifting was influenced by extensional stresses resulted from mantle uplifting.
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Based on the 3D seismic structure interpretation of Bohai Sea, combined with physical modeling of structure, structural style analysis and apatite fission track simulation, the structural characteristics and genetic mechanism of the Cenozoic strike-slip faults in Bohai Sea were investigated. The results show that Tanlu strike-slip fault experienced three stages of strike-slip activities in the Cenozoic, and the transition from left-lateral strike to right-lateral strike-slip was completed at the end of the fourth member of the Shahejie Formation. The strike-slip faults in the Bohai Sea have the characteristics of multi-stage and multi-strength stress superposition. According to the superimposed forms of different strengths, different properties and different ratios, they can be divided into three major genetic types, extension and strike-slip superimposition, extension and extrusion superimposition, extrusion and strike-slip superimposition, and fifteen typical structure patterns. Affected by multiple changes in the direction and rate of subduction of the Cenozoic Pacific plate, the difference between the Cenozoic extension and the strike-slip in the Bohai Sea area leads to the diversity of the fault system and the zoning of the depression structure. According to superimposition features of faults, the Bohai Sea area can be divided into the Liaoxi S-type weak strike-slip zone, Liaodong braided strong strike-slip zone, Boxi conjugated medium strike-slip zone, Bodong brush structure medium strike-slip zone and Bonan parallel strong strike-slip zone. These zones differ in oil and gas accumulation features.
Superimposition
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