Tectonic Feature of Manghan Sag in Songliao Basin
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By means of structure-stratigraphy method,through systematic 2 dimension structure-stratigraphy interpretation of several seismic sections,structure-stratigraphy balance recovery,and calculating extension quantity and extension rates,the developing process of Manghan sag is revealed and the tectonic features and forming mechanisms of the basin are analyzed.The results show that Manghan sag is a fault depression superimposed structure.The fault depression is mainly controlled by the faults in the Lower Cretaceous Jiufotang group,Shahai group and Fuxin group periods,and the fault depression turned into depression basin which was not controlled by the faults on both sides of the basin,and its scope of deposition is extended to the both sides,and the strata onlapped to the basin margin from Quantou group to Nenjiang group.The basin structure becomes simple from deep to shallow,and the deep structure is complicated relatively with faults and the shallow structure is simple and flat form of depression structure.Manghan sag structure characteristic fully reveals that the basin developing was controlled by the extension of the sinistral transformation.Cite
Sedimentation
Deposition
Rift zone
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Intra-sag uplift of Xujiaweizi fault depression in the Songliao basin is significantly different with the surrounding areas in respects of sedimentary-structural features.Based on the comprehensive study of seismic,well and regional geologic data and in combination with the unique geologic features of the intra-sag uplift,it is believed that the intra-sag uplift is a window opened in the shallow part of the early fossil foreland basin.Its formation,development and consumption are systematically discussed in 5 stages by using the theory of normal faults being associated with folds.Although the intra-sag uplift is contemporaneous with the faulted basin on its both sides,they belong to different geologic bodies formed in different geologic time and are the products of basins in two stages.This provides a new understanding for exploration in deep of the Songliao basin and reveals the large deep gas potential in the study area.
Geologic time scale
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Herisitai sag in Block 4 of Tenggeer depression has a low degree of prospecting and prospects of resource in Erlian basin.Analysis of tectonic evolution history is on the basis of the new basic data in the study area.The northern low-lying of Herisitai sag which is nearly parallel to the(S-type) of the strip has two main faults that are Herisitai fault and eastern fault of northern main low-lying,which can control low-lying of Herisitai sag.Tectonic evolution of Tenggeer depression has three main stages: extensional rift filling on sedimentary stage of early cretaceous Arxan Formation to Tenggeer Formation;steady sedimentary and fault renew activity on sedimentary stage of early cretaceous Saihantala Formation;lacustrine basin vanishing in cretaceous to depression stage in Cenozoic.It shows tectonic evolution is controlled by the regional structural background in the study area and specialty of lacustrine basin filling through changes in local tectonics of small low-lying.
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In this paper, the structural evolution and the responses of the basin filling, the sedimentary sequence, the sedimentary and subsidence centers to tectonic movement in Biyang Sag are summarized. The movement times of boundary faults are determined and the evolution history is restored based on the migration of sedimentary and subsidence centers. It is shown that the extension action of Yanshanian movement, the movement of boundary faults after Yanshanian movement and the deposition after Himalayan movement determine three basin filling sequences and structural sequence in Biyang Sag. Besides, sedimentary sequence is also controlled directly by the changes of accumulation space and sediment supply resulted from episode movement of faults. The studies on the changes of sedimentation and subsidence centers show that structural situation is unstable in He-2 member. The movements of the two boundary faults are all weakened greatly and the centers of sedimentation and subsidence superpose gradually in the southeast of Biyang Sag until No.1 sandstone group of He-2 member, the basin come really into atrophied rift and fault basin.
Sedimentation
Sequence (biology)
Mass movement
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In the early stage of Shiwu depression movement of Songliao basin,there was faulting and depression sedimentation,and basin reversing happened at the later stage.In this paper we simulated the formation and developing process by means of both shovel shape and linear boundary fault,which indicated that half of the graben fracture controlled by the steeper fault led to basin reversing during lateral compression.It provides a reasonable explanation for tectonic evolution of Shiwu faulted depression structure in Songliao basin,that is the normal faults formed during depression movement was compressed in laterstage reversing,which resulted in occurrence change and developed into reverse fault within sedimentary cover in depression phase.
Reversing
Depression
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By means of structure-stratigraphy method,based on the knowledge of faulting active phase,pattern of the basin edge as well as tectonic deformation traced by deposition record,with the help of systematic 2 dimension structure-stratigraphy balance recovery,it's indicated that during the developing process of Changling sag,there was clockwise rotating from NE-SW to EW along the expanding direction.This movement generally happened at the same time as formation of Lower Cretaceous Shahezi Group.Because of the special tectonic location of Changling sag on the southern edge of central Songliao basin,in this early stage,noticeable northeast expanding depression overlapped later northwest tectonic expanding,which leads to complicated tectonic pattern.During the extension period of Changling sag,strain pattern changed from pure shear which caused graben-type extension structural pattern developed in the early stage to simple shear formed half-graben-type in later.
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Nanpu sag,located in Bohai Bay Basin,is a small rift lacustrine basin. In study areas,the sand distributions were effected by the fault activity in different levels and thus study of sequence stratigraphy and sedimentary should be guided by tectonic evolution as a principal axis. Through the analysis of faulting histories in different levels,the filling characteristics of sand body inside the basin can be explained. Combining 580 m core observation and 3D seismic data which covered the entire study area,sedimentary facies and fault evolution in offshore area of Nanpu Sag were defined. Periodic rifting activity in Nanpu sag could be classified into two periods from 31 Ma to 23. 5 Ma,one is Shahejie Formation and the other is Donying Formation. Shahejie Formation can be divided into three sub-episodes which correspond with three third order sequences and only two sequences in Shahejie Formation would be discussed because of the overlying strata of study area were eroded in the course of the First member of Shahejie Formation and four third sub-episodes,which correspond to 4 third order sequences,were identified in Dongying Formation. Fandelta and nearshore subaqueous fan were formed in the hanging wall of boundary fault,and the braided river delta deposits were developed in the gentle slope belt and the gravity flow deposits were found in deep lake and semi-deep lake area. In the same tectonic unit,steep region or gentle slope,for example,though the feature of sedimentary facies evolution is inheritance,vertical stages are obvious,by analyzing the filling sequences evolution sections. Active intensity of tectonic remains constant in each sub-episode,so vertical stages of sand bodies in the form of foreset and retrograde were controlled mainly by lake-level fluctuations which also have some impact on vertical stages between each sub-episode. After calculated and analyzed the fault activity velocity of Bogezhuang Fault,Gaoliu Fault and the faults in the transition zone coupled with the plans of sedimentary facies,to make clear the control of the fault to the deposition and filling,figured out the distributions of detrital material in catchment basin are strongly controlled by different level of faults which were classified into boundary fault and secondary fault. The activity of boundary fault with timeshared and segmentation control the migration and swing of fan delta deposit around steep slope through controlling the swing of transfer zone around the margin of basin. Some gravity flow deposits caused by earthquake or delta frontal instability occurred re-distribution along the transfer zones,which belong to secondary fault between the edge and inner of the basin. As the secondary fault movement is a multi-stage process,the inner transfer zones control the redistribution of autogenic deposits. All in all,the deposition and filling of basin were controlled by the fault evolution,activity intensity and tectonic styles and structural associations. The lake-level variation and climate exchange also play a very important role in determining the vertical stages in sub-episode. The research on fault activity in different levels and its impact for the depositional sand distribution can provide a new idea for the subsequent exploration.
Sequence Stratigraphy
Fault block
Growth fault
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By means of two dimensional structure-stratigraphy interpretation of several seismic profiles,cross-section balancing,and calculation of extension amount and extension rates,the paper investigated developing process of the Binxian-Wangfu sag and analyzed the structural features and forming mechanism of the basin.The results show that Binxian-Wangfu sag was in the initial stage of rifting in the Huoshiling Formation,Shahezi Formation and Yingchengzi Formation,and the fault depression was mainly controlled by normal faults before the deposition of the Denglouku Formation.The sag onlaps to the Tangfangzhen uplift,and was also controlled to some extent by normal faulting within the basin during the deposition.The sag completely turned into depression and exhibited regional subsidence after the deposition of the Denglouku Formation,and the subsidence center was not obviously corresponding to the early fault depression,and the subsidence of the Binxian-Wangfu sag was not controlled by the early fault depression.During the Quantou Formation period,especially the third segment and the Qingshankou Formation period the sag mainly showed depressional subsidence;The general structure of the basin was clearly marked by faults in the lower section and onlap in the upper section.The basin formation was associated with the the NS-trending dextral transtension.
Onlap
Transtension
Deposition
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Based on the geological structure interpretation of the 3D and 2D seismic profiles covering the whole study area in the Huanghua depression,the architecture and evolution of the basement and cover of the basin were described and analyzed in detail.The huge Indosinian E-W trending thrust-fold structure and the Yanshanian NNE trending thrust-fold structure were also identified.It is proposed that the main Qikou sag is a rifting basin resulted from negative inversion of the Indosinian uplifting paleo-anticline.The architecture of land in the north and middle part of the Huanghua depression appears as NE striking domino style half graben system,which was faulted at the northwest margin and overlapped at the southeast slope.The offshore part of the basin is characterized by a huge complex graben of nearly W-E striking.The throw of the Cangdong fault,boundary fault of the basin,decreases gradually from south to north,and disappears to the north of the Banqiao sag,and linked with the Chadian fault by the structure transitional zone at the west slope of the Beitang sag.From the quantitative analysis of the activity of the main fault systems and subsidence history of the basin,the Cenozoic synrifting evolution of the Huanghua depression was divided into three episodes.From the episode I to episode II,the depocenter and the subsidence center migrated northwards from the onshore to offshore.Finally,combining analysis of the tectonic stress field involving the migration of the subsidence center and the regional geological features of the Bohai bay basin,the transtensional basin model is preferred to interpret the evolution of the Huanghua depression and the deforming mechanism of the Bohai bay basin during the deposition of the Kongdian Formation(Ek) and Dongying Formation(Ed).
Anticline
Thrust fault
Basement
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The structure and stratigraphy interpretation of five basin-wide 2D seismic profiles indicates that the syn-depositional framework of Suibin Sag in Sanjiang Basin was reshaped by later compression. The internal faults are mainly trending in NW and NNW, intersecting with the uplift-depression structure trending in NE. After the formation of uplift-depression structure, the basin was also undergone compression from northeast to southwest, resulting in a large number of reverse faults within Suibin Sag. Seismic interpretation reveals that Suibin Sag is bounded by normal faults to the west, south and east with trending in NE, NW/NWW, and NE respectively. These faults controlled the subsidence and deposition during Cretaceous, although some of them were converted to reverse faults later. Sanjiang Basin was undergone syn-depositional extension in all direction, i.e. the extension trending in N-S and W-E direction. The eastern and western boundaries of the basin are limited by Yilan-Yitong Fault and Dunhua-Mishan Fault, respectively. Sanjiang Basin and Amur basin to its north were right-lateral transtensional basins during early Cretaceous. The Cretaceous deposits above Dongshan Formation are missing in western Sanjiang Basin, while the eastern Dongshan Formation is unconformable with overlying Upper Cretaceous. These results indicate that the basin was undergone uplift and erosion due to tectonic reversion after Early Cretaceous.
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