## 2 Geological Setting  
The Kuqa Foreland Basin is situated along the northern margin of the Tarim Basin, adjacent to the Tianshan orogenic belt (Figure 1b). This basin extends approximately northeast-southwest (NEE-trending) over 500 km, with north-south widths ranging from 80 km (maximum) to 30 km (minimum), encompassing an area of approximately \(3.7\times 10^{4}\) km\({}^{2}\). Internally, the basin is subdivided into three sags: the Wushi Sag, Baicheng Sag, and Yangxia Sag [39; 40]. The Kuqa foreland thrust belt underwent polyphase tectonic evolution. Closure of the South Tianshan Ocean during the Late Permian-Early Triassic transition exerted fundamental control on the development of Late Carboniferous-Indosinian nappe structures [39; 40]. Late Cretaceous regional isostatic adjustment provoked extensive uplift, accompanied by virtually complete denudation of Upper Cretaceous sedimentary units [41; 42]. Paleocene tectonism manifested as post-collisional crustal reorganization under a weak extensional regime. Neogene-Quaternary continental collision between the Eurasian and Indian plates drove pronounced uplift of the South Tianshan orogen, generating intense thrust propagation that ultimately shaped the current structural architecture [43; 44; 45]. The study area, the Wushi Sag, constitutes the western sector of the Kuqa Foreland Depression--a NE-SW-trending subsiding depression bounded by distinct structural units (Figure 1a) [40; 41; 42]. Its northern margin abuts the Tianshan orogenic belt along thrust faults, while the Wushi Fault demarcates its southern boundary against the Wensu Uplift. Eastward, it transitions into the Qiulitage structural belt. Seismic profiles traversing its central domain reveal a classic foreland basin architecture, with south-north transitions from forebulge to foredeep to orogenic wedge domains (Figure 2). Overlying the Carboniferous basement, the Triassic succession in the Wushi Sag exhibits thickness variations ranging from 430 m along the southern margin to 1550 m in foredeep exposures, displaying an overall northward-thickening wedge geometry (Figure 2). Based on well data and outcrop observations, the Cretaceous sequence is largely absent across most of the sag. The Triassic stratigraphy comprises, in ascending order: the Lower Triassic Ehuobulake Formation (250-240 Ma); Middle Triassic Kelamayi Formation (240-230 Ma); and Upper Triassic Huangshanjie Formation (230-190 Ma) (Figure 3) [43; 44; 45]. Unconformably overlying Carboniferous limestone, the Ehuobulake Formation features two repetitive cycles, each alternating between greenish-gray mudstone-sandstone intervals and purplish-red sandstone-conglomerate interbeds with mudstone, capped by basal purplish-red conglomerates. The Kelamayi Formation is characterized by rhythmic alternations of pebbly sandstones and variegated (purplish-red to greenish-gray) mudstones with marked lateral thickness variations. The Huangshanjie Formation contains two fining-upward cycles transitioning from basal massive sandstones upward into carbonaceous mudstones and gray-black shales, reflecting progressive waning of sedimentary energy during Late Triassic lacustrine-dominated basin filling (Figure 3). Figure 1: Map of study area. **(a)** Tectonic Elements Map of the Wushi Sag and Neighboring Areas in the Northwestern Tarim Basin. The map illustrates the major tectonic units in the Wushi Sag and its surrounding regions. **(b)** Schematic diagram of the structure of the Tarim Basin; gray area shows the position of the Kuqa Depression; the black box shows the position of the Wushi Sag. Figure 3: Comprehensive Stratigraphic Column of the Wushi Sag Based on the TLK Outcrop Profile. Figure 2: Interpreted NE-trending seismic profile traversing the central study area and Well ST1, with its position indicated in Figure 1a’s line A–A’.