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Main characters and active ages of the Serikbuya and Kangxi faults in the western Tarim Basin
Abstract
The western segment of boundary fracture between the Markit Slop and the Bachu Fault-Uplift in the western Tarim Basin was once called the Serikbuya fracture zone. Based on a systematic analyses of seismic profiles, the paper thought that the Serikbuya fracture zone included, actually, two faults with obviously different dissected depth, dipping and active age. The western sector of the fracture zone was still named the Serikbuya fault, which was a basement-involved fault, composed of a series of lower-order back-thrusts and became narrower south-eastwards. The major Serikbuya fault dipped to the northeast and activated in Miocene, with some branch back-thrusts activating in Pliocene. The eastern sector of the fracture zone was renamed the Kangxi fault by the paper, which was a fault of superficial detachment. The Kangxi fault, dipped to the southwest and activated in the Caledonian movement, which rejuvenated in Pleistocene after a long-term stabilization. Regionally, the Serikbuya fault attached to the Bachu NNW-striking fracture system which created in Miocene and stretched northwards into the Kalpin area (the South Tianshan Cenozoic intracontinental orogen), while the Kangxi fault attached to the Tazhong (central Tarim) NW-striking fracture system which created in the Caledonian orogeny. The recent study demonstrated that the Central Tarim Lower Uplift was a multiple oil-gas accumulation play, so the new understanding for the former Serikbuya fracture zone might support a new thinking for oil-gas exploration in the Markit Slop. The obduction of the Bachu Fault-Uplift along the Serikbuya fault resulted in the Paleozoic and Eogene of the Markit Slop area deepend buried further, and the thick mudstone and siltstone of Pleistocene was a good capping bed for oil-gas. To analyse the role of Serikbuya fault both in early stage of petroleum accumulation and later stage of gas-filling adjustment, the oil-gas exploration in the Markit Slop area should have a new breakthrough in near future.
... Following terrestrial sediment deposition in the Triassic (Lin et al. 2012;Zhu et al. 2013b), and uplift related to the late Indosinian orogeny (Tang et al. 2014;Zhao et al. 2014), two regional unconformities formed as a result of the Yanshanian orogeny at the end of the Jurassic (Middle Yanshanian) and at the end of the Cretaceous (Later Yanshanian) (Tang et al. 2014) (Fig. 2). Although Meso-Cenozoic thrust faults dominate (Zhang et al. 1996;Sobel and Dumitru 1997;Yin et al. 1998;Bullen et al. 2003;Meng et al. 2008;Li et al. 2009Li et al. , 2010Zheng et al. 2009), the Tarim Basin also experienced local extension in the Jurassic-Early Cretaceous when maximum compression was NE-SW, forming left-lateral ENE and right lateral north-south transtensional fault zones . Under NNE-SSW maximum principal compression (σ 1 ) , pre-existing faults in this orientation would have experienced opening, providing further volume for hydrocarbon storage. ...
At >7 km depths in the Tarim Basin, hydrocarbon reservoirs in Ordovician rocks of the Yijianfang Formation contain large cavities ( c . 10 m or more), vugs, fractures and porous fault rocks. Although some Yijianfang Formation outcrops contain shallow (formed near surface) palaeokarst features, cores from the Halahatang oilfield lack penetrative palaeokarst evidence. Outcrop palaeokarst cavities and opening-mode fractures are mostly mineral filled but some show evidence of secondary dissolution and fault rocks are locally highly ( c . 30%) porous. Cores contain textural evidence of repeated formation of dissolution cavities and subsequent filling by cement. Calcite isotopic analyses indicate depths between c . 220 and 2000 m. Correlation of core and image logs shows abundant cement-filled vugs associated with decametre-scale fractured zones with open cavities that host hydrocarbons. A Sm–Nd isochron age of 400 ± 37 Ma for fracture-filling fluorite indicates that cavities in core formed and were partially cemented prior to the Carboniferous, predating Permian oil emplacement. Repeated creation and filling of vugs, timing constraints and the association of vugs with large cavities suggest dissolution related to fractures and faults. In the current high-strain-rate regime, corroborated by velocity gradient tensor analysis of global positioning system (GPS) data, rapid horizontal extension could promote connection of porous and/or solution-enlarged fault rock, fractures and cavities.
Supplementary material: Stable isotopic analyses and the velocity gradient tensor and principal direction and magnitude calculation are available at https://doi.org/10.6084/m9.figshare.c.4946046
Thematic collection: This article is part of the The Geology of Fractured Reservoirs collection available at: https://www.lyellcollection.org/cc/the-geology-of-fractured-reservoirs
... Therefore, the structural characteristics and evolution of the whole Piqiang-Selibuya Fault system are still not completely understood. A summary of the current state of knowledge of the two faults is as follows: (1) The Piqiang Fault experienced three stages of activity: Palaeozoic normal faulting, early Cenozoic fault inversion, and late Cenozoic strike-slipping (tearing) (He et al. 2002;Turner et al. 2011); and (2) the Selibuya Fault underwent multiple stages of significant thrusting activity during the end of the Ordovician, the end of the Middle Devonian, the end of the Permian, the Mesozoic, the end of the Miocene, and the Pliocene (Xiao et al. 1998(Xiao et al. , 2005bMeng et al. 2008;Cao et al. 2009;Yao et al. 2013;Tang et al. 2014;Yang et al. 2014). ...
The Piqiang–Selibuya Fault is the most significant fault in the NW Tarim Basin, China. It has attracted increasing attention because of the discovery of a series of oil (gas) fields in and around the fault zone. The structural characteristics and evolution of the Piqiang–Selibuya Fault remain controversial. Field geological surveys and seismic data interpretation reveal that the fault has experienced three stages of activity. The thicknesses of the Permian and Miocene strata on opposing sides of the fault are clearly different, and these reveal that the fault has experienced two stages of significant thrusting. The first stage took place at the end of the Triassic and was associated with the Qiangtang Block amalgamated to the south margin of Eurasia. The second stage occurred at the end of the Miocene and might have been caused by the northwards overthrusting of the Pamir. These two stages of thrusting led to the lower–middle Cambrian detachment layer in the eastern part of the Keping thrust belt being 2 km shallower than in the western part. Since the Pliocene, the southern Tien Shan orogenic belt has been reactivated and thrust towards the interior of the Tarim Basin, and a series of ENE–WSW-trending thrust sheets have formed in the Keping thrust belt. Because of the different depth of the detachment layer on the opposing sides of the Piqiang–Selibuya Fault, the number and spacing of thrust sheets formed to the east of the fault differ from those to the west. This dissimilar deformation led to the strike–slip displacement on the Piqiang–Selibuya Fault. The three stages of fault activity record three important tectonic events in the NW Tarim Basin. Qualitative analysis of this activity helps us better understand the influence of the far-field effect of the collisions that occurred on the southern margin of the Eurasia plate on the structural deformation of the NW Tarim Basin.
... The orogenic belts surrounding the Tarim Basin, either developed during the collisional orogenic period in Paleozoic or the mountain building stage in Late Cenozoic, were all created under regional compressional tectonic background, and thus compressional thrust structures are dominant and became the focus of attention (Sobel and Dumitru 1997;Yin et al. 1998;Bullen et al. 2001;Li et al. 2009Li et al. , 2010Zhang et al. 1996). Investigations on structural deformation within the Tarim Basin are also focused on the compressional thrust structures Meng et al. 2008). Few Meso-Cenozoic extensional structures have been investigated in the study area, in spite of some early studies on Meso-Cenozoic extensional structures along the Yaha and Luntai fault zones (1 and 2 in Fig. 3) (Tang et al. 1999;Tang and Jin 2000;Wei et al. 2001). ...
Late Cenozoic transtensional fault belt was discovered on Shajingzi fault belt, NW boundary of the Awati Sag in the northwestern Tarim Basin. And numerous Quaternary normal faults were discovered on Aqia and Tumuxiuke fault belts, SW boundary of Awati. This discovery reveals Quaternary normal fault activity in the Tarim Basin for the first time. It is also a new discovery in the southern flank of Tianshan Mountains. Shajingzi transtensional fault belt is made up of numerous, small normal faults. Horizontally, the normal faults are arranged in right-step, en echelon patterns along the preexisting Shajingzi basement fault, forming a sinistral transtensional normal fault belt. In profile, they cut through the Paleozoic to the mid-Quaternary and combine to form negative flower structures. The Late Cenozoic normal faults on the SW boundary of Awati Sag were distributed mainly in the uplift side of the preexisting Aqia and Tumuxiuke basement-involved faults, and combined to form small horst and graben structures in profile. Based on the intensive seismic interpretation, careful fault mapping, and growth index analysis, we conclude that the normal fault activity of Shajingzi transtensional fault belt began from Late Pliocene and ceased in Late Pleistocene (mid-Quaternary). And the normal faulting on the SW boundary of Awati Sag began from the very beginning of Quaternary and ceased in Pleistocene. The normal faulting on Awati’s SW boundary began a little later than those on the NW boundary. The origin of Shajingzi transtensional normal fault belt was due to the left-lateral strike-slip occurred in the southern flank of Tianshan, and then, due to the eastward escape of the Awati block, a tensional stress developed the normal faults on its SW boundary.
... The orogenic belts surrounding the Tarim Basin, either developed during the collisional orogenic period in Paleozoic or the mountain building stage in Late Cenozoic, were all created under regional compressional tectonic background, and thus compressional thrust structures are dominant and became the focus of attention (Sobel and Dumitru 1997;Yin et al. 1998;Bullen et al. 2001;Li et al. 2009Li et al. , 2010Zhang et al. 1996). Investigations on structural deformation within the Tarim Basin are also focused on the compressional thrust structures Meng et al. 2008). Few Meso-Cenozoic extensional structures have been investigated in the study area, in spite of some early studies on Meso-Cenozoic extensional structures along the Yaha and Luntai fault zones (1 and 2 in Fig. 3) (Tang et al. 1999;Tang and Jin 2000;Wei et al. 2001). ...
Meso-Cenozoic extensional structures are important for understanding the tectonics of the Chinese Central Asia. This paper presents a systematic investigation on the Meso-Cenozoic extensional structures in the Northern Tarim Basin. Close interpretations of seismic data reveal that the Meso-Cenozoic extensional structures were widely developed in the Northern Tarim Basin. These extensional structures are regionally composed of many small normal faults, which usually group into left- or right-step en echelon and form several transtensional fault zones. Combinations of normal faults in profile become small graben-horst or staircase-like cross-sections. Based on the areal distribution, structural style, combination relationship, formation and evolution time, and formation mechanism of the extensional structures, we found that the Meso-Cenozoic extensional structures in Northern Tarim Basin can be classified into two conjugate normal fault systems, which were formed separately in Jurassic-Early Cretaceous and Late Cretaceous-Neogene. The former is likely associated with the stress relaxation after a collisional orogeny accompanied with a certain degree of anticlockwise rotation of the Tarim block relative to the South Tianshan; the latter is possibly induced by the east by south tectonic escape of the Tarim block with a certain degree of clockwise rotation relative to the South Tianshan triggered by the far-field effect of the Himalayan orogeny.
The Bachu Uplift is one of the most important oil and gas exploration area in the Tarim Basin, but the realization of its structure characteristics and evolution as well as the oil and gas exploration are serious constrained by its exceptionally complex faults structure and evolution. Based on the fine structural interpretation of seismic data, the tectonic setting of Traim Basin's evolution, the new wells data and outcrops, the paper reveals that the activity characteristics of the faults in Bachu Uplift has great difference in different period, different area, and different fault belt, different parts of the same fault, different stratigraphic. There are mainly four periods of the faults differential activities: Transtensional faults activities in Early Caledonian, positive inversion of early transtensional faults in Late Hercynian, strong strike-slip and thrust and different deform in Middle Himalayan, different transformation and superposition in different parts and stratigraphic in the southwest faults belt in Late Himalayan. Fault evolution is mainly controlled by the tectonic movements of the Early Caledonian, the Late Hercynian and the Middle-Late Himalayan, as well as the opening and closing of oceans surrounding the Tarim paleo-continent and the orogenic movements in the corresponding period. The Middle Himalayan is the critical period for faults activities in the Bachu Uplift, because of the strong compressive stress come from the West Kunlun Mountains and the Southwest Tianshan Mountains, faults in the western part thrust uplift and strike-slip rotation, faults in the eastern part thrust like an arc and tilting to the southward. The Late Himalayan is the deformation period of the faults and it mainly occurs in the northwest edge and the southwest edge of Bachu Uplift, especially in the southwest edge, because of the strong compressive stress comes from the West Kunlun Mountains, strong different deformation and superposition occur in different parts of the southwest faults belt.
2-D seismic data interpretation combined with structural analysis was used to build a geometry model and determine active ages of the Gudongshan fault belt. The formation and evolution of this fault belt with complicated tectonic deformation may be closely related to the evolution of oceanic basins and orogenic belts around Tarim Basin. Faulting activities were the most obvious in key tectonic periods of Tarim Basin, namely the Middle Caledonian, Early Hercynian, Middle Hercynian, Early Himalayan and Later Himalayan. Faults No. 1 and No. 2 in the Gudongshan fault belt control the thickness of the Palaeozoic strata on both sides of the belt and also show signs of multiple-stage activities. Fault No. 1 was active during phase I and III of the Middle Caledonian and shows feature of progress intensification of its activity. Fault No. 2 was developed in the Early Hercynian and successively experienced negative inversion in the Carboniferous and positive inversion at the end of Paleogene. Fault No. 3 was formed in the Early Himalayan and controlled the tectonic framework of the Precambrian basement which is higher in southwest and lower in northeast. Faults No. 4 and No. 5 were developed in the Later Himalayan. The former has a thrust displacement up to 20 km and a denudation-caused monocline at the hanging wall.
Through a profound interpretation of 3D seismic data, this study provided a detailed analysis of the fault characteristics of Yubei thrust belts, proposed that it was active at early episodes of Middle Caledonian of the main faults. Seven structure stages were redefined, that is, Early Caledonian, Middle Caledonian Early Episodes, I Episodes of Middle Caledonian, III Episodes of Middle Caledonian, Late Caledonian-Early Hercynian, Late Hercynian and Himalayan. Furthermore, they can be divided into 2 types on the basis of the differential of structure stages: 1) inactive after Middle Caledonian; and 2) active after Middle Caledonian. The faults were of strong activities in Middle Caledonian, and then became weak. In a whole, the movement of the faults is stronger in the north than in the south across the strike, and more intense in the east than in the west among the 6 NE strike thrust belts. The basement faults and decollement thrust faults consist of the migration pathway to cross the gypsum rock and salt rock of the middle and lower Cambrian in the form of docking together, because of which were stable distribution and high sealing performance. But it is different to the controls of Poly-phase fault activities on hydrocarbon accumulation. The faults activities in Middle Caledonian, Late Hercynian and Himalayan were beneficial to the hydrocarbon migration and accumulation. Especially, the Hercynian faults are the most advantageous for the hydrocarbon reservoir, and the Himalayan faults are the main influence on the adjustment of hydrocarbon.
The Bashituopu fault was once a segment of southern boundary of the Bachu Fault Uplift in Mesozoic. It experienced two generations of deformation. The early one in Mesozoic was indicated by interlayer-gliding along the Middle Cambrian gypsum-salt bed accompanied with fault-bend folding in the upper wall,then the thrusting cut the Paleozoic and accompanied fault-propagating folding. The Serikbuya fault zone became the southern boundary instead of the Bashituopu fault during Oligocene and Miocene when the latter seemed un-mobile. The younger deformation of the Bashituopu fault occurred in Pleistocene, as a sub-order back-thrust in the West Kunlun fold-and-thrust belt. As a lower strain area and having relatively good petroleum geological conditions, the Bashituopu structural belt should be beneficial to oil-gas exploration.
Based on systematic interpretation of seismic profiles and a comparative study to central area of the Tarim Basin, the active modes and mechanisms of the Paleozoic faultings in western Tarim were explored in the paper. The NE-striking Madong (Badongnan) fault zone, as a part of southeastern boundary of the Bachu Fault-Uplift, was a superficial décollement fold-and-thrust belt, and expanded southeastwards. The piggy-back thrusting occurred in the end of Ordovician. The NW-striking Badong fracture (or the No. 2 Tumxuk fracture), the eastern boundary of the Bachu Fault-Uplift, was a basement-involved thrust, with the thrusting occurring in the ends of Ordovician and Middle Permian respectively. The Baxi and South of Well Tacan 2 fractures in north part of the Markit Slope were Hercynian normal faults. The Paleozoic development of the Tarim paleo-plate was constrained by the neighbouring orogenic evolution. The thrusting of nearly W-E and NE-striking fractures in early Caledonian, related to subduction of the West Kunlun ocean, might inherit the basement structures. The NW-striking fractures in central Tarim was neogenic in Late Cambrian, in which two episodes of Caledonian deformation could be recognized: the early thrusting in the end of Ordovician and late thrusting and strike-slipping during Late Silurian to Middle Devonian. The later deformation should be resulted from the activation of the Paleo-Altun shearing orogen, so as to obviously become weeker westwards. Some NW-striking fractures in west Tarim, for example, the Kangxi fracture, attached to the Tazhong(central Tarim) NW-striking fracture system. The NE-striking Madong fault zone was a transfer fault between the Tumxuk fault zone (thrusting towards the north to east) and the Wells Tazhong 8-1 and Tazhong 5 fault zone (thrusting towards the south to east).
The Cenozoic Kuqa foreland fold-and-thrust belt in Xinjiang could be divided, in southward order, into the basement thrusting belt, box anticline belt, comb anticline belt and bended folding belt. And along the W-E orientation, it could be divided into the western, middle and eastern segments. The paper described deformation features of each segment, and thought that the deformation became weakened and the topographic relief tended to planation eastwards since the box anticline belt being not developed in the eastern segment and the Qiultag mountains(the southmost anticlinal row of the comb anticline belt) did not stretched into the eastern segment. There were two main periods of thrusting for creation of the fold-and-thrust belt, occurred in Miocene and Early (-Middle) Pleistocene respectively. Correspondingly, the Kuqa area attached separatedly to the northern and southern basin-orogen sub-systems, and some diversities in stratigraphic record, deformation generations and deformation mechanism between the both sub-systems were summarized. In addition to the S-N compressive stress field resulted from thrusting and expanding of the Chinese South Tianshan, the deformation of the fold-and-thrust belt was constrained by the basemental fractures and diapir structuring of the gypsum-salt layers. The NW-striking, as well as the conjugate NE-striking fractures played a role of transfer zone in the Cenozoic S-N compressional stress field. The diapir of the gypsum-salt layers controlled the creation of the Qiultag mountains (a compressive structural belt by vertical stress field), and also, it played an important role in the segmentation of the Kuqa fold-and-thrust belt. Furthermore, the paper discussed the relation between the deformation and morphogenesis, as well as the guidance to the oil-gas exploration.
Hetian-Kekeya structural belt is away from Mazartagh structural belt in Tarin Basin about 200 km, they are almost parallel. Mazartagh structural belt is leading edge of Hetian-Kekeya structural belt, the Cenozoic compressive deformation of Hetian-Kekeya along the gypsum-mudstone of Aertashi Formation slide to Mazartagh and transformed to Fault-propagation-folds, leaded obvious topographic rise in Tarim Basin. So, the Cenozoic fold and thrust belt in eastern section of the piedmount of west Kunlun is 270 km in width and 220 km in length, it consisted of Hetian-Kekeya structural belt, Maigaiti slope and Mazartagh structural belt. Maigaiti slope is almost 200 km in length, but it hasn't obvious deformation, and taper wedge angle of this fold and thrust belt is less than those active orogenies, it's means the gypsum-mudstone of Aertashi Formation and the shape of Cenozoic deposition are key factors, the gypsum-mudstone controls α of taper wedge, the shapes of basement and dispositive wedge control β of taper wedge.
Shajingzi structural belt is a boundary structural belt between Awati sag and Wensu uplift at NW margin of Tarim Basin. It is one of the poorest studied large fault structural belts in Tarim Basin. On the basis of fine interpretation of seismic data, Shajingzi structural belt is consisted of 3 sets of fault systems; the deep-buried wedge-shipped thrust system, the narrow-sense Shajingzi fault system and the extensional tectonics near the Earth surface. The deep-buried wedge-shipped thrust structure was formed by the NW dipped fore-thrust fault and its SE dipped back thrust fault in Silurian-Devonian. The wedge is composed of Precambrian metamorphic rocks. The front of the wedge penetrated into the Cambrian caused the upper rocks lifting toward the northwest and forming a slope. The narrow sense Sahjingzi fault, i.e., the traditionally named Shajingzi fault is a basement-involved compressive strike-slip fault with high dip angle formed from latest Permian to beginning Triassic. It cut off the ancient thrust wedge. The extensional tectonics near the Earth surface was formed in Earl-Middle Quaternary. A series of normal faults arrange in right lateral en echelon along narrow sense Shajingzi fault, and constitute 2 sinistral tenso-shear normal fault zones. The deep buried thrust wedge and the Quaternary extensional tectonics are new discoveries of this paper.
The Kalpin thrust belt or Kalpin fold-and-thrust belt, located in the northwestern margin of the Tarim Basin, is a part of the South Tianshan fold-and-thrust system. On the basis of field investigation and seismic section interpretation, the main features of the Kalpin thrust belt could be summerized as the follows. 1) Only the Paleozoic rocks were involved into the thrusting , which meant that the major detachment fault was gypsum-salt layer in the Middle Cambrian. 2)The belt was characterized by imbricated thrusting, with a relatively simple inner texture. 3)The belt had an exposed thrust front, since it did not create till Pleistocene. 4) The fault-propagation folds once occurred, which were experienced violently denuded. 5) The belt was a piggyback one, with the thrusting expanded southwards. 6) A molasse basin once occurred during Pliocene, with the geological records being conglomerate of the Xiyu Formation, but the basin had been disrupted by the Pleistocene thrusting-nappe structuring. The Kalpin thrust belt consisted of the northern fold sub-belt and the southern thrust-nappe structural subbelt, and for the latter, the balanced section analysis revealved the minimal shortening rate being 29. 1% to 40. 7%.
Based on the interpretation of the new drilling and seismic data, the structural characteristics of the Selibuya fault and Kangtakumu fault, which are the boundary faults between the western Bachu uplift and Maigaiti slope, are analyzed in this paper. The Selibuya and Kangtakumu faults are basement-involved thrust faults interacting by soft-linkage. Along the SE strike, the displacement of the Selibuya fault gradually decreases, while the displacement of the Kangtakumu fault increases. The transform zone between the two faults transferred their displacements, and kept the conservation of fault displacements in western part of the Bachu Uplift. The transform zone belongs to the synthetic overlapping zone which is in the evolution stage of complex. There are much secondary faults and fractures, which is good basis for the formation of fractured-type reservoirs and hydrocarbon migration. The transform zone is the favorable objective for petroleum exploration in the Bachu area.
There is a NE-SW extend saddle-shaped lower ridge between Awati and Manjiaer sags, central Tarim Basin. It is proposed as the separate boundary between these two sags. The faults of this ridge are studied on the basis of 3D seismic data interpretation. The faults development in the ridge are classified into 4 stages: 1) Nanhua-Ordovician normal faults are related to the breakup of Rodinia supercontinent, and can be further divided into 2 sub-stages, Nanhua-Sinian and Cambrian-Ordovician. Nanhua-Sinian normal faults directly related to the breakup of Rodinia, forming graben-horst structures. Cambrian-Ordovician normal fault were formed under the gentle extensional background of Tarim wandering in paleo-Tethys. These faults usually form negative flower structure. 2) Terminal Ordovician-Middle Silurian faults composed of terminal Ordovician-beginning Silurian detachment-thrust faults and compressive strike slip faults, forming fault-propagation fold and flower structure. The faults of this stage is related to the Kunlun Caledonian collisional orogeny. 3) Late Silurian-Carboniferous normal faults form typical negative flower-structure and usually group into transtensional fault zones. The formation of this stage normal fault is associated with the stress relaxation after Kunlun Caledonian collisional orogeny. 4 ) Permian normal faults were formed under the continental-rifting background of Tarim, and often deformed by the rift-related magmation. Permian normal faults usually group into graben-horst structure and negative flower structure, and form transtensional fault zones. Some Permian faults may inherit the Late Silurian-Carboniferous faults.
The Gudongshan fault belt is situated in the Bachu rise, west part of the Tarim Basin, with NW-orientated striking and elongating beyond 140 km. Based on careful interpretation of seismic profiles, four generations of structural deformation have been recognized, i.e., the Cambro-Ordovician normal faulting, the Permian normal faulting, the Miocene thrusting and Pliocene-Pleistocene thrusting, and the latter being accompanied by normal faulting. The basement-involved thrusting in age of Miocene is main-controlling structure of the Gudongshan fault belt and consists of the main body of the belt, where the deformation style is fault-propagation folding. The Cambro-Ordovician normal faulting, firstly represented by this paper, makes up a compound horst and is buried beneath the Miocene fractures. The Permian normal faulting is accompanied with magmatism. The Miocene thrusting of the Gudongshan fracture is obviously constrained by the pre-existed normal faults and magmatic rocks, meanwhile, the Miocene fractural structures are reformed by the later faulting, i.e., the Pliocene-Pleistocene thrusting and normal faulting. The southeast terminal of Gudongshan fault belt connect the west terminal of Mazhatag structural belt, but they are not one fault belt.
Study on Mesozoic and Cenozoic extensional structure deformation is a weak part in Central Asian geological research. As one of the important Mesozoic and Cenozoic sedimentary basins, the research about Tarim basin has no exception. Some fine seismic interpretation shows that a large number of extensional tectonics which are composed of a set of small normal faults arise in Mesozoic and Cenozoic in northern Tarim basin. The small normal faults are clearly seen to array in en ethlon form, composing a series of fracture belts in planes, and their pattern in profile is a ladder and graben or horst. Based on their spatial distribution, structural styles, composite relations, the ages of growth strata, and genetic mechanism, the formation of normal faults can be divided into two phases: Jurassic-Early Cretaceous and Late Cretaceous-Neogene extensional tectonics. The former is a product of the stress releasing after the orogenic period of southern Tianshan, and the latter is caused by the escaping structures of Tarim basin towards east by south relative to South Tianshan, which were produced by the long distance effect of Himalayan collisional orogeny.
[1] This paper deals with the Tertiary tectonic and sedimentary evolution of the western Tarim basin based on an integrated stratigraphic, sedimentary, structural, and tectonic analyses. Basin evolution is divided into three stages: Paleogene, Miocene, and Pliocene. The western Tarim basin was the easternmost part of the Tethyan realm from Late Cretaceous to Paleogene, and marine sedimentation continued into the Early Miocene. Miocene development of the western Tarim basin was chiefly governed by West Kunlun right-slip faulting and the simultaneous northward thrusting of the Pamir salient and Tianshuihai terrane. Yecheng subbasin developed as a pull-apart basin owing to synchronous activity of the West Kunlun and the Shache-Yangdaman right-slip faults. Hotan foreland basin formed in response to northward displacement of the Tianshuihai terrane, and another might have developed in front of the advancing Pamir salient in the Miocene. Basinward thrusting became predominant in the orogenic belts adjacent to the western Tarim basin in the Pliocene. North-directed displacement and uplift of the Tiklik thrust terrane fragmented the preexisting Hotan foreland basin, and collision of the Pamir with the southern Tian Shan deformational fronts caused complete destruction of the Miocene Pamir foreland basin. Eastward displacement of the Qimugen fold-thrust system led to flexural subsidence of the Yecheng subbasin in the Pliocene. Kashi subbasin developed as part of the southern Tian Shan foreland basin, and was controlled by the eastern Pamir as well. A tectonic scenario is proposed to illustrate complicated interplay of the western Tarim basin with its peripheral orogens in the Tertiary.
The Lunnan Lower Uplift, a sub-unit of the North Tarim Rise in the Tarim Basin, was characterized with multiple productive reservoirs, various pool types and multi-phases of hydrocarbon generation, migration and filling to the pools. Superimposed vertically and located one next to another in lateral, the pools of various types in the Lunnan Lower Uplift constituted a typical multiple oil-gas accumulation play. The petroleum geological theory of multiple oil-gas accumulation play was inducted out from the petroleum exploration and development in the Bohai Sea Basin. It was successfully applied in the petroleum exploration in the rift petroliferous basins in East and South China. The Lunnan multiple oil-gas accumulation play indicated that this theory could also bright prospect of application and development in the compressive petroliferous basins in West China.
The Central Tarim (Tazhong) Lower Uplift, a sub-unit of the Central Rise of Tarim Basin, is characterized with multiple productive reservoirs, various pool types and multi-phases of hydrocarbon generation, migration and filling to the pools. Superimposed in vertical and located one next to another in lateral, the pools of various types in the Central Tarim Lower Uplift constituted a typical composite hydrocarbon accumulation play. It was another typical composite hydrocarbon accumulation play in the Tarim Basin, similar to the Lunnan Lower Uplift, a subunit of the North Tarim Rise. The paper described the regional tectonics briefly, discussed the source rocks, oil-gas fillings, reservoir-cap associations, migration systems, traps and pool types, analysed the main controlling factors for the oil-gas pools, and sum up the main features of the Central Tarim composite hydrocarbon accumulation play. The petroleum geological theory of composite hydrocarbon accumulation play was inducted out from the petroleum exploration and development in Bohai Bay Basin, a rift depression in East China. It has been successfully applied in the petroleum exploration in the rift petroliferous basins in East and South China. The Central Tarim and Lunnan composite hydrocarbon accumulation plays demonstrated that this theory also has bright prospect of application and development in the compressive petroliferous basins in West China.
The concept of "multiple oil-gas accumulation play" for the Lunnan Lower Uplift, Tarim Basin, promoted the oil-gas exploration and development in the area. The paper aimed to develop the theory of multiple oil-gas accumulation play, and to promote the oil and gas exploration and increase the production and reservoir by analyzing an example of the Ordovician in the eastern slope of the Lunnan Lower Uplift. Based on the recent achievements of regional petroleum geology, and to integrate the recent fruits of new technique and method such as imaging logging, high resolutional 3D seismic description on fault systems, and organic geochemistry, the paper systematically studied the key geological factors for the multiple oil-gas accumulation play in area of the Lunnan Lower Uplift, comprehensively described complicated features of the fault systems in the Lunnan Lower Uplift. It was represented that the reservoirs of Ordovician, Carboniferous, Triassic, and Jurassic might be from the same hydrocarbon supply of the Cambrian marine origin, and it was confirmed that during the formational process of the multiple accumulation play, the fault systems might be either the migration pathways in early petroleum accumulation, or the migration pathway of gas-filling adjustment in later stages. Especially for the Lunnan Lower Uplift the fault systems were effective reservoir space, as well as the important factor to improve the reservoir behaviors and to enhance the connectivities. Two models for the oil-gas accumulation under the control of multiple-activity of complicated fault systems in the Lunnan Lower Uplift were put forward, namely, the gradual-episodic model and the leaping and dynamic model. Three main aspects as the mechanics for the multiple oil-gas accumulation play were explored, namely, the paleo-uplift being a prerequisite, the multiple reservoir-cap rock associations being a foundation, and the fault systems being a key. Furthermore, the paper pointed out the strike-slip fault zone in the eastern slope of Lunnan Lower Uplift should be a realistic field for expanding the scale of Lunnan multiple oil-gas accumulation play and nature gas exploration.
The eastern Qiultag structural belt, which was on the southern edge of Kuqa foreland basin, has occurred tense tectonic compression and subsidence during Cenozoic. The tectonic evolution history was analyzed by means of the balanced cross section, the growth strata and the numerical modeling of some key wells' subsidence history. The results showed that the tectonic movement was relatively weak and the subsidence rate was minimal during sedimentary stage of the Kumugeliemu Group in age of Paleocene to Eocene. The tectonic activity began to enhance and the subsidence rate increased, and therefore developed some thrusts with small fault displacement during sedimentary stage of the Suweiyi Formation in age of Oligocene. The tectonic movement enhanced further and the subsidence rate increased again during Miocene, so that deposited thick salt layer of the Jidike Formation, then the salt layer flowed by tectonic compression and formed salt pillow during the sedimentary stage of Kangcun Formation, when the growth strata occurred. Subsequently, the studied area subsided quickly during depositional stage of the Kuqa Formation in age of Pliocene. With the South Tianshan Mountains uplifted rapidly, the thrust expanded southwards rapidly, and the front of the Kuqa fold-and-thrust belt arrived the eastern Qiultag structural belt in Early Pleistocene when the regional tectonics fell into its pattern. To sum up, the tectonic deformation was tense in this area where developed many thrusts, and the salt layer flowed evidently and formed salt nappe.
The Kelatuo nature gas in the Kashi Sag, southwestern Tarim Basin, was mainly composed of crude oil dissolved gas, or wet gas, with methane content ranging from 74.59% to 85.58%, where only the nature gas of the Wells Ke 4 and Ke 30 was wet gas with a little leaning to dry. The δ13C1 values ranged from -41.2‰ to -40.6‰, and δ13C2 values from -30.0‰ to -27.4‰ for the Kelatuo gas. The comparison between the gas and source rocks showed that the Kelatuo gas might be mainly derived from lacustrine source rocks of the Middle Jurassic Yangye Formation, which was different from the Akemo natural gas generated by Carboniferous source rocks in the Kashi Sag. The hydrocarbon-generating history indicated that the Jurassic source rocks in the Kashi Sag became mature-high mature from immaturity because of huge deposits of the Neogene, and the generated oil and gas gathered in the Kelatuo anticline traps. The hydrocarbon accumulation process should be so called "late hydrocarbon accumulation", with the character of continuous gas gathering. By the end of Plioence, the peripheral mountains of the Kashi Sag began to rise, which resulted in the destruction of early reservoir and forming the present oil and gas seeps or oil sandstones.
Based on accurate structural analysis of four seismic profiles across Kashi area in western Tarim Basin, a tectonic model for Cenozoic fold-and-thrust belts in the area was established. The area was controlled by southward thrusting of the Chinese South Tianshan in Late Cenozoic, in addition, the area was influenced by northward thrusting of the West Kunlun mountains. Namely, the Cenozoic fold-and-thrust zone there could be divided into two parts: the northern part attached to the foreland thrusting system of the Chinese South Tianshan, and the southern one to the foreland thrusting system of the West Kunlun mountains. The former was named the Artux foreland fold-and-thrust belt in the paper, which was composed of three rows of main thrusts and related anticlines, and their evolutional process was briefly discussed. By technique of balanced section, the structural shortening was calculated, which was more than 43.7 km in the northern part and 4 km in the southern part respectively, with a total shortening ratio of the profile being fifty percent. To synthesize regional tectonic evolution and reservation conditions, it was thought that the relatively better potentials might be deeper layers in the northern part (the Artux fold-and-thrust belt), and the key factor for oil-gas exploration should be good-quality reservoirs there.
The Wushi Sag situated to the south of the western segment of the Chinese South Tianshan, with the East Sub-Sag being its main body, and generally being regarded as westward extension of the Kuqa Depression (a Cenozoic molasses basin of intracontinental orogeny in South Tianshan area). Controlled by the Cenozoic intracontinental orogeny in area of the Tianshan Mountains, the Wushi Sag created with the same basin-forming dynamics of the Kuqa Depression. In Wushi, the Cenozoic deformation had different features from the Kuqa Depression, because there was the Wensu Rise, to the south of the Wushi Sag, which resisted southward expanding of the compressional stress, and a NW-striking structural transfer belt (the West Qiultag structural belt) separated the Wushi Sag from the Kuqa Depression. The Meso-Cenozoic strata in the Wushi Sag could be divided, by the gypsum-salt bed in the Miocene Jidike Formation, into two structural layers. Generally speaking, the deformation in the upper structural layer was characterized with back-thrust, and a basement-evolved ramp thrust occurred in the lower structural layer. In addition, a thrust in the Pre-Mesozoic basement should be emphasized, since the Wensu Rise acted once a provenance to the Wushi Sag during Meso-Cenozoic. These deformation features in Wushi might be related to westward migration of the Cenozoic compressional stress, and some thrust deformation absorbed by the strike-slipping along the northern and southern boundaries of the Wushi Sag, which indicated an inheritance of Cenozoic structures to the Hercynian-Indosinian collisional tectonics in the Chinese South Tianshan. The paper expressed briefly tectonic evolution of the South Tianshan orogen, introduced main chatacterictics of boundary fractures of the Wushi Sag, reconstructed Meso-Cenozoic evolution of the Wushi Sag and compared with that of the Kuqa Depression. Based on what mentioned, the paper explored the basin-formation dynamics, analysed the coupled evolution between the Wushi Sag and the South Tianshan orogen, and pointed out that the main target for the oil-gas exploration in Wushi should be Triassic Huangshanjie Formation.
Seismic data in the complicated geological area can't intuitionally reflect the actual geometries of surface and subsurface structures, hence, identification of dip domains and axial surfaces analysis, together with seismic reflection profiles and surface structural measurements, have been used to define the quantitative geometrical relationship between shape of fold and fault, which is an effective method to structural interpretation of poor seismic images. Geometrical and kinematical analyses based on structural interpretation will contribute to understand deformation process, time and dynamic mechanism, and quantitatively simulate the kinematic process of imbricate thrusting and their related folds of multi-order and multi-phase. We presented four examples, in which the above methods were effectively applied, from the southern margin of the Junggar Basin and the periphery of Tarim Basin. The steps of fine interpretation using dip domains and axial surfaces analysis were detailedly expounded in the first example. The quantitative relationship among the displacement and shape of fault and fold on the kinematic process of Wuboer thrust belts in the northern margin of Pamir were discussed from perspective of geometry and kinematics in the second example. The break-forward thrusting was recognized by the gradually younger of the base of growth strata on the forelimb of the three anticlines in the Fusha thrust belt in the front of the West Kunlun Mountains in the third example, and kinematic model of the distortion in the middle part of the Qiultag anticline were constructed using structural trend analysis in the last example.