In section, map, and 3D views, the strike-slip faults have distinctive characteristics that set them apart from dip-slip faults. The primary fault planes of strike-slip faults typically developed vertically in seismic profiles and combined with the minor nearby faults to generate the flower structures, either positive or negative (Harding, 1974; Chritie-Blick and Biddle, 1985; Harding, 1985; Swanson, 2005). In map view, as the displacement occurred along the strike, the abrupt cut-off of markers, such as the relics of paleo rivers and facies of igneous rocks, presents across the fault planes (Ramadan et al., 2014). Strike-slip faults also frequently appear in various shapes, including linear, oblique, feather, en-echelon, X-shape, and broom-shape. Dolphin and ribbon effects in the 3D image help identify strike-slip faults (Graham et al., 1984; Harding, 1985; Romeo et al., 2005).

Interpretations of the Tabei Uplift (TO₃) reveal that most faults display a linear structure, while horsetail and en-echelon occurred sparsely across the Tabei Uplift at the tip of some strike-slip faults (Figure 5C). The seismic sections (Figure 6) across the Tabei Uplift show that most faults are subvertical and develop a flower structure with intense deformation near the bottom of Upper Ordovician, the seismic reflection interface of TO₃. In summary, the Tabei Uplift developed a complicated strike-slip fault system with severe deformation during the Paleozoic.

The complicated strike-slip fault system is distributed widely in the Tabei Uplift as two sets of intersected X-type faults (Figures 1, 5). The distribution patterns of the strike-slip system were identified in various interfaces, from deep to shallow, and present distinctive characteristics: the bottom of the Lower Cambrian (TЄ₁), the bottom of the Upper Cambrian (TЄ₃), the bottom of the Upper Ordovician (TO₃), and the bottom of the Silurian (TS).

The strike-slip faults appear segmented, linear, but intermittent on the coherence slices of interface TЄ₁ (Figures 5A, E), where the NW-trending faults dominate the fault system with stronger activity and wider distribution. Strike-slip faults on the surface of TЄ₃ share characteristics with the interface of TЄ₁ but comprise longer linear fault segments. Meanwhile, NE-trending faults exhibit broader distributions and extend over longer planes compared to the TЄ₁ interface (Figures 5B, F). Additionally, the initial configuration of the two sets of X-type faults, intersecting at a small angle (∼40°), is discernible on the interface. The strike-slip faults are linear and longer but more continuous on the interface of TO₃, with intense activity (Figures 5C, G). Subordinate faults developed along the principal displacement zone of major faults, such as the Riedel shear, and displayed in horsetail splay, oblique, and feathered. The intersection relationship of these X-type faults indicates that the NE faults are left lateral, whereas the NW faults are right lateral. On the surface of TS (Figures 5D, H), en-echelon faults are displayed along the trending of deep strike-slip faults. Most en-echelon faults exhibit left-stepping in a NW linear configuration, and the average intersection angle with the underlying strike-slip faults is 45°, demonstrating that the en-echelon faults belong to T fractures (Tondi et al., 2012; Han et al., 2017; Deng et al., 2019), which develop when NW strike-slip faults are reactivated with dextral movements.

Several seismic profiles were selected to represent the features of fault systems in the Tabei Uplift (Figures 1B, 5, 6). The overall fault characteristics in the seismic sections, from north to south, are similar (Figures 6A–C), displaying layered deformation structure, from deep to shallow (Table 1). Three deformation layers were recognized: the deep structural layer (Sinian–Middle Cambrian, basement–TЄ₃), the middle layer (Upper Cambrian–Middle Ordovician, TЄ₃–TO₃), and the shallow layer (Upper Ordovician–Carboniferous, TO₃–TP).

The deep structural layer comprises the Sinian rift system, weak deformed strike-slip faults, and salt-related structures. On the seismic section, several normal faults in high-dip angles emerged in the Sinian rift system. The strike-slip faults display subvertical fault planes propagating from the basement, and many developed along the margin of normal faults or followed the preexisting fault planes (Figure 6B), showing that basement structures influenced the development of strike-slip faults. Besides, the faults inserted into the basement are more in the NW-trending than in the NE-trending. Some minor or secondary faults formed in the Lower–Middle Cambrian, connected to the major fault planar, and are interpreted as flower structures, such as F2 and F13 (Figures 6A, B). In response to localized tectonic stress alterations within the fault deformation zone and the distinctive physical characteristics of salt, the Middle Cambrian strata underwent a variety of deformational expressions, characterized by localized amplification and reduction in thickness, as exemplified by the emergence of salt domes and sag structures (Figure 6A, F4 and F7).

The middle structural layer, Upper Cambrian–Middle Ordovician, comprises strike-slip faults deformed intensely near the bottom of the Upper Ordovician (TO₃) and is expressed as a flower structure or linear shape. The fault planes predominantly terminate near the bottom of the Upper Ordovician (TO₃), with branching secondary faults extending downwards to the intersect with the primary fault. Anticlines and synclines developed in the carbonate strata, forming positive and negative flower structures (Figure 6A, F6, and F7). Some strike-slip faults were linear when they experienced weak deformation (Figure 6B and F15).

The shallow structural layer, Upper Ordovician–Carboniferous, comprises clastic rocks and develops normal faults, forming graben and half-graben. In some cases, the shallow normal fault penetrated through the Upper Ordovician strata, extending into the Ordovician carbonate rocks, and disrupted the underlying anticlines and positive flower structures below, resulting in the formation of complicated flower structure (Figure 6A, F9 and F7).

Researchers have extensively studied the evolving histories of the orogenic belts around the Tarim Basin, as it significantly affects the tectonic stress field in the basin. Most authors believe the basin was under a passive continental margin with an extensional tectonic stress field from the Cambrian to the Early Ordovician after the breakup of the Rodinia supercontinent (Jia, 1997; Wang, 2004). From the Middle to Late Ordovician, the ancient Kunlun and North Altyn Ocean subducted successively (Zhang et al., 2002; Wang, 2004; Li et al., 2009), and the basin was under an intensive compressive stress field in the NS direction. This subduction brought about the formation of the Tabei and Tazhong Uplifts with an EW orientation. The distribution patterns of unconformities were studied, which correlated well with the regional tectonic evolution studies (He et al., 2011; Lin et al., 2012; He et al., 2016). Nevertheless, research on the tectonic stress field patterns in the Tabei Uplift is insufficient, especially in the Early Paleozoic.

The bottom of the Lower Cambrian (TЄ₁) was selected, which was relatively stable and seldom affected by later denudation. According to the thickness of residual strata, the map of paleotectonic restoration of TЄ₁ during tectonic evolution were restored, including the late of Early Cambrian (Figure 8A), the late of Middle Cambrian (Figure 9A), and the late of Middle Ordovician (Figure 10A).

The map of paleotectonic restoration comprises most regions of the Tabei and Manxi Low Uplifts according to the 3D seismic data provided by the CNPC. In the late of Early Cambrian, the paleotectonic map displayed high uplifts in the east, and most areas of the Tabei Uplift were in a depression, whereas the depression structure was not uniform. Some NW and NE-trending grooves developed and arranged linearly (Figure 8A) in the middle of the Tabei Uplift, reflecting the structural characteristics of the basement, correlating well with the trending of the two sets of strike-slip faults. On the seismic section, the structural patterns of the Precambrian rift are clear and affect the deposition of the overlying Lower Cambrian strata (Figure 8B). In the late of Middle Cambrian, the paleotectonic map exhibits a similar overall structural pattern as the late of Early Cambrian; however, the upheaval of the northeastern part of the Tabei Uplift occurred, and the sags in the Manxi Low Uplift oriented NW (Figure 9A), implying the direction of compressive stresses derived from the NE–SW in the north. The seismic profile shows that the strata thickness gradually decreases from the southwest to the northeast (Figure 9B). In the late of Middle Ordovician, the paleotectonic map feature changed dramatically. The overall structure framework was high in the north due to the considerable upheaval of the northern Tabei Uplift (Figure 10A), indicating that the direction of compressive stress transferred from north to south. The seismic profile shows that the thickness of the strata gradually thins from south to north (Figure 10B). Furthermore, the unconformity features in the Tarim Basin, developed from the Silurian to the Permian, have been systemically documented (Lin et al., 2012; He et al., 2016). The direction of compressive stress, from the Silurian to the Carboniferous, was demonstrated by patterns of erosion thickness (Figure 11A). The profile characteristics show that the large unconformity is widely developed in the Devonian (Figure 11B). The compressive stress primarily comes from the northeast and southeast (Figure 11A), corresponding to the closure of the south Tianshan and Altyn Oceans (Lin et al., 2012).

Numerous studies have been conducted to study the timing and formation mechanism of the X-shaped faults due to the significant hydrocarbon exploration findings along the strike-slip faults in the Tabei Uplift and the unique phenomena of small-angle X-type faults. Most authors consider the overall pattern of fault system controlled by a pure shear model, while the features of each fault correlate with the simple shear model. The faults were initiated in the Late Ordovician and developed a two-stage evolution (Wu et al., 2018; Deng et al., 2019; Ma et al., 2019; Wu et al., 2020b). However, debates exist about the controlling factors for the deviation of the dihedral angles of conjugate faults. Some authors propose that the lithology might significantly influence the dihedral angles of conjugate faults (Deng et al., 2018; Deng et al., 2019) because the internal friction coefficient varies with different lithologies. Besides, some scholars propose that fault reactivation and major fault orientation is a controlling factor for dihedral angles in the Tabei Uplift; the NW-trending faults significantly influence the dihedral angles (Wu et al., 2018; Wu et al., 2020a). Nevertheless, few studies have been conducted on the effects of preexisting basement structures on developing the strike-slip fault system in the Tabei Uplift.

Structure evolution and fault formation mechanisms in the Tabei Uplift were postulated in the study based on comprehensive interpretations of fault geometry features, analysis of tectonic stress field patterns, and features of the preexisting basement structures in the basin. The Precambrian normal faults in basement were detected on cross-sections from high-quality seismic data (Figures 3, 6, 8) (Neng et al., 2016; Yi et al., 2020; Chen et al., 2022). The map of paleotectonic restoration (Figure 7A) of the Lower Cambrian (TЄ₁) at the late of Early Cambrian revealed that the rifts developed in the Tabei Uplift, distributed in the NW and NE directions (Figures 8A, B). This result correlates well with the trending of strike-slip faults, demonstrating that basement formations might significantly influence the Tabei Uplift’s strike-slip fault evolution. Following the breaking of the Rodinia supercontinent, the paleo ocean formed around the Tarim Block, and the basin was in a passive continental margin environment under an extensional setting from the Precambrian to the Early Ordovician. But there are still some uncertainties in the activity of orogenic belts around the basin in the Cambrian (Li et al., 2013; Wan et al., 2018). The latest researches proposed that at the end of the Middle Cambrian, the Proto-Tethys Ocean and the Paleo-Asian Ocean initially subducted (Xu et al., 2011; Ge et al., 2014; Han et al., 2015). The West Kunlun and Altyn Oceans gradually subducted in the south (Xiao et al., 2003; Liu et al., 2014), and the south Tianshan Ocean subducted southward in the north, resulting localized compressive–reverse movements occurred in the Middle–Late Cambrian (Gao and Fan, 2014). During the Middle to Late Cambrian, the Tabei Uplift experienced compressional tectonic stress from the northeast and south. This stress reactivated the basement rift systems, leading to the formation of NW- and NE-trending strike-slip faults. The angle between these two sets of rift systems is approximately 40° (Figure 8A), which resulted the formation of X-shaped fault system with small dihedral angles (Figures 12A, B).

Compressive stress emerged in the central Tarim Basin from the Middle to Late Ordovician due to the closure of the Ancient Kunlun and Altyn Oceans (Zhang et al., 2002; Li et al., 2009), the north Tianshan Ocean subduction towards the Central Tianshan microcontinent (Jia and Wei, 2002; Gao and Fan, 2014) and the continuous southward subduction of the south Tianshan Ocean (Han et al., 2015; Han et al., 2016). The Tabei Uplift was under a compressive tectonic stress field in N–S direction (Figure 10A). The Tabei Uplift was lifted and tilted southward during the period, verified by the thickness of the Upper Ordovician in the cross-section (Figure 10B). Under the compressive stress, the strike-slip faults were reactivated with a more significant deformation magnitude than previous stages (Figure 12C), punctured upward based on the underlying fault system, presented flower structures on the cross-section, and displayed linear segments with subordinate faults forming various patterns on the map view. The horsetail splay occurred at the south tip of the strike-slip faults (Figure 5C), indicating that the faults propagated from the north to the south and the compressive stress from the north was the dominant dynamic source of the Tabei Uplift.

The Tarim and Central Tianshan–Yining Blocks collided throughout the Silurian to the Carboniferous, and the South Tianshan Ocean gradually closed at the Carboniferous with a scissor-like form from east to west (Gao et al., 1998; Gao et al., 2006; Gao et al., 2009; Gao and Fan, 2014). The en-echelon normal faults formed within the period and most exhibit NE-trending with left-stepping in a NW linear arrangement parallel to the underlying strike-slip faults, interpreted as the tensional fracture from the progressive dextral movement of the NW-trending faults (Figure 12D). Moreover, the direction of compressive stress is indicated by the strike of en-echelon normal faults unveils the tectonic stress field was under a NE–SW compressional stress, consistent with the unconformity distribution characteristics (Figure 11).

Significant hydrocarbon discoveries in the ultra-deep (>5,000 m) Paleozoic carbonate rocks were achieved around the Manjiaer depression. Most petroliferous wells were drilled within 1 km from the strike-slip fault (Wang et al., 2020; Tian et al., 2021; Wang et al., 2021). Many researchers have extensively studied the controlling factors of hydrocarbon accumulation. Most agreed that the Yuertusi Formation is the dominant source rock (Zhu et al., 2016; Wang et al., 2021; Zhu et al., 2022), developed in the Lower Cambrian, and the major hydrocarbon generating periods include the Late Caledonian, the Late Hercynian, and the Himalayan (Wang et al., 2020). Furthermore, the geometric patterns of strike-slip faults considerably influence the accumulation of hydrocarbons, influencing the development of reservoirs, including fractures and caves related to erosion (Deng et al., 2018; Wang et al., 2020; Deng et al., 2022). However, the role of layered deformation structure of strike-slip fault in hydrocarbon accumulation process remains unclear and why strike-slip faults in the Tabei Uplift are significantly hydrocarbon-enriched in various directions still controversial.

Based on detailed interpretations, three distinct deformation layers can be identified, each playing a different role in hydrocarbon accumulation and together constituting an independent petroleum system (Figure 13). The deep layer (below the TЄ₃) comprises Yuertusi Formation, which generates oil and gas, and the Middle Cambrian, a thick layer of salt and gypsum, which significantly influences the upward migration of hydrocarbon. The middle layer (TЄ₃–TO₃) developed a solution-fracture reservoir, mostly distributed in the Yinshan and Yijianfang Formations. The shallow layer (TO₃–TP) comprises thick mudstones and functions as caprock controlling the preservation of hydrocarbons. The evolutions of strike-slip faults correspond to the vertical deformation layers. The Middle-Late Cambrian deformation cut through the thick salt and gypsum layer and provided the channels for hydrocarbon upward migration in subsequent periods. The Middle-Late Ordovician deformation generated a damage zone in the carbonate strata along the faults, provided meteoric water and hydrothermal fluids paths to penetrate and erode, and formed a fracture-solution reservoir. The en-echelon faults, which have been active from the Silurian to the Carboniferous, resulted from the underlying strike-slip fault system being reactivated. They might cut through the caprock and cause hydrocarbon leaks. In addition, the reactivation of strike-slip faults might enhance the hydrocarbon upward migration and restore the migration efficiency of sealed fault panels from the Cambrian source rock to the Ordovician carbonate reservoir, especially during the accumulation periods.

The Tabei Uplift’s reservoir development is in good condition (Ma et al., 2019; Wu et al., 2020a), and the carbonate fracture-cave reservoir is developed along the strike-slip fault damage zone. The NW-trending fault activity is stronger, and the internal reservoir is significantly better. However, most high-efficiency wells are found in the NE-trending strike-slip faults (Chen et al., 2023), whereas NW-trending strike-slip faults offer inferior conditions for hydrocarbon enrichment (Figures 14A, B).

NW- and NE-trending strike-slip faults have suitable conditions for reservoir development (Chen et al., 2023). The distribution characteristics of wells show that the number of efficient wells and effective wells in the south is much more than that in the north, while more failed wells are distributed in the north (Figure 14A). The difference in fault-controlled hydrocarbon enrichment might be affected by the distribution characteristics of source rocks and hydrocarbon migration conditions (Figures 15, 16).

Accordingly, the sedimentary center of the Yuertus Formation is primarily in the Manxi Low Uplift (Tian et al., 2021; Wang et al., 2021), gradually thinning to the Tabei Uplift (Figure 15). The hydrocarbon generation center is in the Manxi Low Uplift and serves as a source for hydrocarbon migration to the paleo uplift. The bottom of Upper Ordovcian in the Tabei Uplift is inclined to the southwest (Figure 14A) (Ning et al., 2020), and the NE direction becomes dominant for hydrocarbon migration due to the influence of potential energy. It is advantageous for hydrocarbon migration along the NE direction that the large strike-slip faults through the Tabei and Manxi Low Uplifts are NE-trending (Figure 1B). Furthermore, the en-echelon normal faults, which developed along the NW-trending strike-slip faults from the Silurian to the Carboniferous, may have cut through the caprock, leading to hydrocarbon leakage (Figures 4D, 16). Also, the NE-trending fault fully accepted the hydrocarbon filling due to reactivation during the Yanshan and Himalayan periods (Deng et al., 2018, 2022), which corresponds to the stages of hydrocarbon charging (Figure 16).