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Recently, a significant breakthrough in natural gas exploration was achieved in well Qiatan-1 in the Permian carbonate strata of the Western Tianshan thrust belt in the piedmont depression of southwestern Tarim Basin, marking the discovery of a new exploration layer in the area. However, this region is characterized by multiple sets of source rocks and extremely complex sedimentary and structural features. Research on the genesis and source of the natural gas in well Qiatan-1 is insufficient, restricting its further natural gas exploration. Therefore, the study systematically investigated the genesis and source of the natural gas in well Qiatan-1 based on regional geological background, geochemical characteristics of the gas, and potential source rock features. The measured results showed that the natural gas in well Qiatan-1 was mainly composed of methane (83.53%), with a gas dryness coefficient (C1/C1-5) of 0.992, and contained relatively high levels of N2 (8.36%), CO2 (7.28%), and He (0.110%). The carbon isotope values of methane, ethane, propane, and CO2 in the gas were -27.8‰, -20.2‰, -18.4‰, and 1.7‰, respectively. Based on the natural gas composition and alkane carbon/hydrogen isotope composition, the natural gas in well Qiatan-1 was determined to be coal-type gas in the high to over-mature stage. Considering the distribution, organic matter abundance, type, thermal maturity of its potential source rocks, the gas in this well was mainly sourced from Permian source rocks in the Permian Qipan Formation, and may also be mixed with a small amount of carbon isotopes, forming heavier inorganic hydrocarbon gases. In addition, the components and isotopic evidence of non-hydrocarbon gases such as N2, CO2, and He showed that a certain proportion of inorganic gas had mixed into the natural gas in well Qiatan-1. The helium isotopic composition suggested that the proportion of mantle-derived helium was about 14.6%, and the He content had reached the standard for helium-rich natural gas (He ≥ 0.100%).

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The intensifying exploration for deep-buried oil and gas reserves in the southwestern Tarim Basin accelerates the necessity to understand how the structure and evolution of the Precambrian basement affect the development and distribution of Precambrian strata. However, the lack of systematic and comprehensive understanding of the structural characteristics of the Precambrian basement in the southwestern Tarim Basin restricts further advancements in the exploration of ultra-deep oil and gas reserves in this area. Based on the previous research results, this study analyzed the lithology, age, structure, and evolution of the Precambrian basement in the southwestern Tarim Basin by utilizing integrated research methods of geology and geophysics and in combination with the U-Pb dating results of the Precambrian basement. The results reveal that the structure of the Precambrian basement in the Bachu uplift region is characterized by Paleozoic strata overlying directly on the Paleo-proterozoic metamorphic rocks/granites. In the Maigaiti slope and southwestern depression, it exhibits a typical three-tier structure: the Paleoproterozoic metamorphic rocks/granites at the bottom, overlain by sedimentary build-ups from the rifting to depression evolution of the Nanhua-Sinian system. Evolution of the Precambrian basement in the southwestern Tarim Basin was primarily transpired in five phases: continental rifting in the Columbia supercontinent (> 1.1 Ga), assembly of the southwestern Tarim block and the Australian plate (about 1.0 Ga), assemblage between the northern and southern Tarim blocks (900-800 Ma), Nanhua rifting period (760-640 Ma), and Sinian depression period (< 635 Ma). The uplift and downwarping structures during the Nanhua rifting period dictated the development of the Sinian-Lower Cambrian sedimentary strata. In-depth research into the structure and evolution of the Precambrian basement in the southwestern Tarim Basin, as presented in this study, provides important theoretical basis for deep oil and gas exploration in the region, and helps to promote further development of ultra-deep oil and gas exploration.

Based on well horizon calibration, the typical seismic profiles in southwestern Tarim Basin were interpreted systematically, regional geological sections were established, and the regional denudation thickness of each tectonic period was restored. On this basis, the plane morphology maps of ancient structures of the Cambrian pre-salt dolomites in different periods were compiled, and the spatial distribution, development, evolution and migration of paleo-uplift in the late Early Paleozoic were analyzed. In the late Early Paleozoic, there existed a unified regional paleo-uplift widely distributed in southwestern Tarim Basin, which is called the southwestern Tarim plaeo-uplift. The “Tarim SW paleo-uplift” and “Hetian paleo-uplift” proposed in previous literatures are not independent, but the result of the spatio-temporal migration and evolution of the southwestern Tarim paleo-uplift identified in this paper. The southwestern Tarim paleo-uplift emerged at the end of Middle Ordovician, and took its initial shape with increased amplitude in the Late Ordovician. During the Silurian, the southwestern Tarim paleo-uplift rose steadily and expanded rapidly to the east, incorporating Pishan—Hetian and other areas, with the structural high locating in the Pishan—Hetian area. During the Devonian, the southwestern Tarim paleo-uplift began to shrink gradually, to a limited range in the Pishan—Hetian area in the southern part of the basin. During the Carboniferous, the southwestern Tarim paleo-uplift became an underwater uplift, that is, the paleo-uplift gradually died out. The southwestern Tarim paleo-uplift belongs to the forebulge of the southwestern Tarim foreland basin in the late Early Paleozoic, and its formation and evolution are related to the early Paleozoic orogeny of the West Kunlun orogenic belt in the south of the Tarim Basin. The migration of the southwestern Tarim paleo-uplift from the northwestern part of the southwestern Tarim Basin to the Pishan—Hetian area indicates the early Paleozoic orogenic process of the West Kunlun orogenic belt, which started in the western section at the end of Middle Ordovician and extended from west to east in a “scissor” style. The migration and evolution of the southwestern Tarim paleo-uplift controlled the development of unconformities at the end of Middle Ordovician, the end of Late Ordovician, and the end of Middle Devonian, and the spatial distribution of dissolved fracture-cave reservoirs in weathered crust below the unconformities in the southwest of Tarim Basin. The migration of the structural high of the southwestern Tarim paleo-uplift also played an important role in controlling the development of dissolved fracture-cave reservoirs in weathered crust.

Based on seismic data, outcrop evidence, logging data and regional aeromagnetic data, the distribution of Nanhua–Sinian rifts in the southwestern Tarim Basin was analyzed, and on the basis of restoration of lithofacies paleogeography in different periods of Neoproterozoic–Cambrian, the evolution model of the proto-type rift basin was discussed. The Neoproterozoic Rodinia supercontinent split event formed the trigeminal rift system at the edge and inside of the craton in the southwestern Tarim Basin located in the Kunlun piedmont and Maigaiti slope. The rift in Kunlun piedmont zone was distributed along the E-W direction and was the oceanic rift in the trigeminal rift system. Two decadent rifts in N-E strike developed in the Luonan and Yubei areas of Maigaiti slope, and the interior of the rifts were characterized by a composite graben-horst structure composed of multiple grabens and horsts. The Neoproterozoic–Cambrian proto-type basin evolution in the southwestern Tarim Basin can be divided into three stages: rift in the Nanhua, embryonic passive continental margin in the Sinian, and stable passive continental margin in the Cambrian. Despite the regional tectonic movements in the end of Nanhua and Sinian, the tectonic framework of the southwestern Tarim Basin had not changed significantly, the sedimentary center of Nanhua rift basin showed the characteristics of succession in the Sinian–Early Cambrian. The Nanhua rift in Kunlun piedmont evolved into a craton marginal depression during the Sinian–Early Paleozoic, while the Luonan decadent rift in the midsection of Maigaiti slope evolved into a sag inside platform in Early Cambrian, constituting the paleogeographic framework of “two paleouplifts and one sag” with the paleouplifts in east and west sides of the slope. The later evolution of the Luonan decadent rift in the midsection of the Maigaiti slope formed two sets of reservoir-forming assemblages, the Sinian and the Lower Cambrian ones, which are important exploration targets in future.

The southwestern Tarim Basin in western China is one of the most dynamic areas of basin-range coupling in the Cretaceous. This study presents the first attempt to simulate the tectono-sedimentary evolution of the southwestern Tarim Basin during the Cretaceous in three dimensions using a basin and landscape dynamics modeling approach. We have simulated the evolution of the southwestern Tarim Basin and the West Kunlun Orogenic Belt (WKOB) during the Cretaceous over a period of 79 million years. Apart from numerous local fans and streams perpendicular to the mountain front, a major paleo-drainage system paralleling to WKOB was developed within the depression during the Early Cretaceous. It subsequently evolved into two drainage systems by a topographic high within the depression in the Late Cretaceous, forming two river channels flowing to the northwest and southeast, respectively. During the Cretaceous the southwestern Tarim Basin was infilled by sediments of up to 3500 m thick. WKOB contributed the bulk sediments to the basin (75.53%), whereas the Markit Slope to the north contributed 24.23%. The sedimentary centers were located mainly in the areas of the southeastern Wupoer and the northwestern Qibei structural belts. The closure of the Paleo-Tethys Ocean towards the end of Triassic around 200 Ma caused the development of paleouplifts in the region and a subsequent overlapping of the Jurassic by the Cretaceous strata. During the Cretaceous, the tectonic movement was relatively quiescent. Only the topmost sediments were subject to erosion at the end of the Cretaceous, as a result of the subduction of the Neo-Tethys Ocean to the south. Paleoclimate and/or precipitation controlled the denudation rate of the orogenic belts while tectonic subsidence controlled the thickness of sediments within the basin. This finding provides new insights for quantitatively evaluating geomorphic and landscape evolution and source-to-sink systems in the southwestern Tarim Basin. • Using Badlands to provide new insights on tectono-sedimentary evolution. • Paleoclimate and precipitation appear to have controlled the denudation rate of the orogenic belts. • Differential tectonic uplift and subsidence of the orogenic belts and depression controlled the amount of sedimentation. • The sedimentary provenances were sourced from the West Kunlun Orogenic Belt (75%) and the Markit Slope (24%). • Simulation reveals a main paleo-drainage system evolved into a two-channel river system. [ABSTRACT FROM AUTHOR]

A detailed investigation of potential provenance is still lacking in the southwestern Tarim Basin, which restricts our complete understanding of Cenozoic source-to-sink relations between the basin interior and the Pamir salient - western Kunlun Mountain Range. Debate also exists concerning the potential sources of the Paleogene and Cretaceous igneous detritus present in the Cenozoic sedimentary sequences. Here, we present U-Pb (LA-ICP-MS) ages of detrital zircons from the continuous Eocene-Pliocene sediment series in the well-exposed Aertashi section to investigate changes in sediment provenance through time. The U-Pb detrital zircon ages range widely from 45 to 3204 Ma and can be divided into seven main groups: 45–65 Ma (sub-peak at 49 Ma), 67–103 Ma (sub-peak at 95 Ma), 196–251 Ma (sub-peak at 208 Ma), 252–416 Ma (sub-peak at 296 Ma), 417–540 Ma (sub-peak at 446 Ma), 550–1429 Ma (sub-peaks at 614 Ma, 828 Ma and 942 Ma) and 1345–3204 Ma (sub-peaks at 1773 Ma and 2480 Ma). These zircons were mainly derived from the western Kunlun Mountain Range and northern Pamir salient to the west and south. The evolution of the provenance and source-to-sink relationship patterns in the southwestern Tarim Basin can be divided into three stages: (1) The Middle Eocene to Lower Oligocene sediments display a wide variety of detrital zircon ages, suggesting that the source area was extensive. (2) A major change in provenance occurred during the Late Oligocene to Early Miocene and was characterized by an abrupt increase in the proportion of Triassic and Lower Paleozoic igneous components, implying a significant adjustment in topography induced by the initial uplift and exhumation of the western Kunlun Mountain Range and northern Pamir salient. (3) In the Late Miocene, the source-to-sink system transformed again, and contributions of Triassic to Lower Paleozoic material weakened substantially due to the sufficient indentation of the Pamir salient. Our integrated analyses of zircon geochronology indicate that the main source terranes of the Paleogene and Cretaceous igneous detritus are the central and southern Pamir salient, respectively, which are speculated to have been continuously connected to the study area during Eocene-Pliocene times, although such detritus is scarce in certain formations and has not yet been detected. [ABSTRACT FROM AUTHOR]

The Miocene Aertashi Debris-Avalanche Deposits at the southwestern Tarim Basin, the foreland basin of the Eastern Pamir (NW Tibetan Plateau), have an incredibly long-runout distance (much longer than 130 km) and provide critical constraints on the evolution of drainage patterns, tectonics, and geochronological framework of the region. To investigate when and how the deposits formed, we conducted extensive field and microstructural observations, as well as geochronologic analyses. The deposits are massive, poorly sorted, and matrix-supported, containing massive blocks, jigsaw-fractured clasts, and fluidal-shaped cataclastic lava bodies. Some cataclastic lava bodies up to ~25 m across are compact on the hand-specimen scale but are pervasively fragmented on the microscale. Microstructural observations of particles show abundant diagnostic features of highly-energetic collisions, such as conchoidal fractures and microcracks. Both field and microstructural observations indicate that the deposits were derived from a debris avalanche. Pervasive cataclasis of many fluidal-shaped lava bodies is interpreted to record intense shear of hot, semisolid lavas close to the glass-transition temperature, in which phenocrysts deformed brittlely while the glassy components mainly deformed plastically and controlled the rheology of the bodies as ductile material. The mechanical properties of clasts are important in controlling their deformation within debris avalanches. The presence of abundant hot, semisolid lavas in the studied deposits may be critical for the survival of megaclasts after a long-runout distance. The field and microstructural observations and geochronologic analyses show that debris-avalanche deposits can aid in constraining regional geochronologic framework. These results consistently confirm that the Aertashi Debris-Avalanche Deposits were deposited at ~11 Ma, during rather than long after the eruptive period. • The massive, poorly-sorted volcaniclastic deposits within the Xiyu Formation at Aertashi was formed by a debris avalanche. • The intense cataclasis of many fluidal-shaped lava bodies occurred when they cooled close to the glass-transition. • The mechanical properties are critical in controlling debris-avalanche clasts fragmentation behaviors during transport. • The Aertashi debris-avalanche deposits were emplaced at ~11 Ma, rather than long after the volcanic activity ceased. [ABSTRACT FROM AUTHOR]