Tarim Uplift Research Articles

Tectonic relief evolution and large-scale karstification of an Ordovician supergiant reservoir, North Tarim uplift, northwestern China

Tectonic relief evolution and large-scale karstification of an Ordovician supergiant reservoir, North Tarim uplift, northwestern China

Study on sedimentation distribution based on cooperative analysis of geologic–geophysical in less well area: A case study of Suweiyi sandstone in the DB area, Kuqa Depression in Tarim Basin

The Kuqa Depression in Tarim Basin develops fan deltaic, braided river deltaic, and lacustrine sedimentation, especially extensive braided river deltaic sedimentation, in the Cretaceous-Paleogene Systems. However, fine sedimentary pattern of the Kuqa Depression and North Tarim Uplift belt since the Middle Cenozoic still needs to be studied. As a combination zone of the Kuqa Depression and North Tarim Uplift, the sedimentary characteristics of the DB area in the southern margin of the east of the Kuqa depression have been paid more attention. To better understand the sedimentary framework in the Kuqa Depression and North Tarim Uplift in the Mesozoic and Cenozoic, through joint geologic-geophysical study, sedimentation of sandstone at the bottom of the Paleogene Suweiyi Formation in the DB area and its peripheral area is investigated. Sedimentary facies and sandstone distribution in the area are identified through core observation, component analysis, logging interpretation and seismic inversion. Based on seismic facies analysis, sedimentary facies distribution in the area is delineated. Results show that sandstone at the bottom of the Paleogene Suweiyi Formation in the DB area and its peripheral area is developed in shore-shallow lacustrine beach-bar facies. The beach-bar arenaceous sediments are mainly distributed in the southern DB area and the shallow lacustrine mudstone is developed in northern DB area, showing obvious north-south differentiation characteristics.

Petrogenesis of Transitional Large Igneous Province: Insights From Bimodal Volcanic Suite in the Tarim Large Igneous Province

AbstractThe Tarim large igneous province (TLIP) corresponds to a transitional large igneous province based on the high proportion of felsic rocks, classifying between mafic and silicic large igneous provinces. Here we investigate a bimodal suite including trachydacite, rhyolite, and basanite from the Northern Tarim Uplift using petrological, geochemical, stable, and radiogenic isotopic techniques with a view to understand the formation of the TLIP. Our study reveals a multistage origin involving multiple components, although the various rock suites are genetically linked and formed under a rift incubation setting related to mantle plume. The low δ26 Mg values (−0.48‰ to −0.71‰), Fe/Mn > 60, FC3MS (FeOT/CaO‐3*MgO/SiO2) > 0.65, and high TiO2 contents (4.45–4.93 wt.%) of basanite from this suite suggest formation through partial melting of carbonated eclogite formed by recycled oceanic crust. The thick lithosphere beneath the Tarim Craton promoted extensive interaction between the underplated basaltic magmas and crust‐derived magmas leading to the formation of multistage magma chambers. Geochemical and mineralogical studies suggest that the trachydacite experienced a mixing, assimilation, storage, and hybridization process, whereas the rhyolite was produced by fractional crystallization from the associated mantle‐derived magma with significant crustal contamination. The abundance of amphibole in the trachydacite suggests a hydrous parental magma with H2O content in the range of 2.75 to 4.05 wt.%. Our results suggest that hydrous crustal components contributed significantly in the formation of voluminous felsic rocks of the TLIP.

Neotectonic evolution of the Tarim Basin Craton from Neogene to quaternary

ABSTRACTThe Tarim Basin Craton is located in the center of the Tarim Basin. Since the beginning of the Miocene, the tectonic activity has been weaker in the Tarim Basin Craton than in the marginal depression and the peripheral orogenic belts. This study investigates the tectonic movements in the Tarim Basin Craton by calculating the sedimentation rates and constructing balanced cross-sections based on well, seismic and geologic data. The tectonic movements in the Tarim Basin Craton have mainly been revealed by geological processes such as sedimentation and subsidence, structural inversion, changes in the structural feature, migration of the structural highs, and faulting. The Neogene sedimentary strata were mainly deposited in two sedimentation centers, the southern and northern sedimentation centers, and the strata in the Central Uplift Zone are relatively thin. The different depressions in different geological periods experienced wide variations in tectonic activity. Tectonic subsidence was significant and the sedimentation rates were high in the Tarim Basin Craton during the Pliocene Period (phase II). During the Neotectonic period, the stresses in the South-North direction converged in the Central Uplift Zone (the Bachu uplift–Central Tarim uplift), and the tectonic activity in this region was more intense than that in the Northern Depression and the Maigaiti Slope in the southwest. In addition, the scale of the paleo-uplift, including paleo-North Tarim Uplift and paleo-Central Uplift Zone, gradually decreased. The faults and fault systems developed zonationally in Neotectonic formations in different structural units, and always distributed discontinuously in vertical direction in sections.

Windward and leeward margins of an Upper Ordovician carbonate platform in the Central Tarim Uplift, Xinjiang, northwestern China

In the Central Uplift of the Tarim Basin, northwestern China, the Katian (Upper Ordovician) limestones of the Lianglitag Formation extend from outcrops in the Bachu area to the subsurface in the Tazhong Oil Field (TZOF) area. Reefs and inner platform deposits are the dominant facies throughout the formation. The reef composition illustrates a palaeoecologic gradient from microbial-dominated buildups on the northwestern margin to metazoan-dominated reefs on the eastern and southern margins of the platform. Between these areas no outcrops are present. In the present study, data including litho- and biofacies logs and correlations from eight wells are presented, six of them of the region between Bachu and Tazhong, and two wells along the former platform margin from the TZOF. Calcimicrobial carbonates are common in core from the inner platform part. Benthic biota documented here resembles that of the microbial mounds and bioclastic limestones in the Bachu outcrop area, and thus is considered as the eastward extension of this realm. However, metazoan-dominated boundstones formed by corals, stromatoporoids, sponges together with calcareous algae are abundant along the southern platform margin, and are similar in composition to the reefs of TZOF in the easternmost part of the platform. The palaeoecologic differentiation between microbial- and metazoan-dominated reefs suggests a strong environmental gradient from a well-oxygenated windward eastern and southern side of the platform, which favoured the open ocean and which was dominated by metazoan reefs, and the inner platform as well as the northwestern, leeward margin of the platform with warmer, less-oxygenated water, which favoured the growth of microbial carbonates. Assuming the trade winds as cause for the contrasting facies on both sides of the platform a palaeo-position of Tarim south of the ITCZ seems probable because a position north of it would require a post-Ordovician clockwise rotation of Tarim of about 90° which is possible but less probable.

A Middle Ordovician (Darriwilian) Calathium reef complex on the carbonate ramp of the northwestern Tarim Block, northwest China: A sedimentological approach

Middle Ordovician carbonates are exposed for 25km along the Lianglitag Mountains in the Tarim Basin, northwest China. They reflect platform carbonate and reef deposition along the ancient Central Tarim Uplift. The Darriwilian Yijianfang Formation, ~70m thick, was deposited in a shallow carbonate ramp setting, deepening seaward to the north in current geography. Reefal and biostromal units are constructed primarily by sessile Calathium of possible sponge affinity in the Middle Member of the formation. Patch reefs, ~10m in thickness and tens of meters in diameter, are common in the northern region. Associated shelly faunas, including trilobites, bivalves, and brachiopods, are diverse and preserved as coarse bioclastic materials together with intraclasts. Towards the south, patch reefs are smaller, <1m in thickness and with low relief. A biostrome formed by in situ Calathium framework is interpreted to act as a baffle for fine sediments, with smaller amounts of bioclasts and intraclasts. The biostrome is only ~3m thick in the southernmost section suggesting a calmer leeward setting initially. Tempestite beds composed of Calathium and nautiloid floatstones are abundant through the section, with monospecific brachiopod layers in the tempestite beds. This work demonstrates previously unrecognized paleogeographic variations of the Darriwilian Calathium reef complexes, which have larger patch reefs generally developing in the north area, smaller patch reefs dominating southward, and biostromes occurring in the southernmost locations. The reef complex was drowned due to sea-level rise, which is recorded in the upper Yijianfang Formation.

Ramp morphology controlling the facies differentiation of a Late Ordovician reef complex at Bachu, Tarim Block, NW China

A carbonate ramp in the shallow-marine northwestern part of the Central Tarim Uplift, Bachu, NW China, exhibits an extraordinary Late Ordovician reef complex along the Lianglitag Mountains, exposed for a distance of about 25 km. Seven localities within the ‘Middle Red Limestone’ of the Upper Member of the Lianglitag Formation (Katian, Late Ordovician) illustrated the changes in biofacies and lithofacies: northern, seaward-directed patch reefs are replaced towards the south by coeval grain banks. The patch reef units are dominated by microbial and calcareous algal components. The reefs at the northernmost locality are knoll-shaped, kalyptra-shaped or irregularly shaped with sizes of individual reefs increasing from about 2 m in height and diameter. Stratigraphically upward, reefs notably expand to larger structures by several mounds coalescing; they are generally about 10 m thick and tens of metres in lateral extent. The maximum thickness of the main patch reef is more than 30 m, and its diameter is around 100 m. The reefal units turn into biostromes with gentler relief southward and still further south grade into banks composed of peloids and coated grains. The southernmost locality is still a shallow-water bank, and the coastline is not documented in the study area. The present evidence indicates that the Late Ordovician palaeo-oceanography provided a number of environments for the optimal growth of carbonate build-ups; microbial-calcareous algal communities could thrive in areas where the innovative metazoan reef frameworks consisting of corals and stromatoporoids did not play a significant role. The ramp morphology, especially changes in water depth, controlled the configuration of the reef complex.

Origin of the Early Permian zircons in Keping basalts and magma evolution of the Tarim Large Igneous Province (northwestern China)

The Tarim continental flood basalts (CFBs) provide important clues about the genesis and magmatic evolution of the Early Permian Tarim Large Igneous Province (Tarim LIP) in northwestern China. Here we present results of LA–MC–ICPMS Lu–Hf isotope analysis on Early Permian (ca. 290 Ma) zircons extracted from the Tarim CFBs in the Keping area, northwest of the Tarim Basin. Zircons from two sub-groups of Keping basalts (Groups 1a and 1b) have similar Lu–Hf isotopic compositions and exhibit a relatively large range of 176Hf/177Hf ratios between 0.282422 and 0.282568. Their negative εHf(t) values (− 6.8–− 1.4) are generally lower than the whole-rock εHf(t) values of their host basalts (− 2.8–2.1), and are distinct from other known intrusive rocks (− 0.3–7.1) in the Tarim LIP and their hosted zircons (4.9–8.8). Systematic studies of Hf isotopic data from Tarim and its adjacent regions reveal that these zircons are probably xenocrysts, sourced from coeval igneous rocks in the South Tianshan Orogen (e.g., the Lower Permian Xiaotikanlike Formation volcanic and pyroclastic rock suite). This, together with the presence of Precambrian zircons in Keping basalts, clearly indicates crustal contamination during their eruptions and provides hints about the potential contaminant sources. Geochemical modeling further suggests that the earlier erupted Group 1b basalts experienced more contamination, predominantly by some high Th–U–Pb rock components, most likely from the South Tianshan Orogen. The later erupted Group 1a basalts in the Keping area have been less contaminated with mainly the Tarim Precambrian rocks. Another group of the Tarim CFBs in the Northern Tarim Uplift (Group 2) appears to have undergone negligible crustal contamination but possesses evidence for variable source compositions. The modeling also indicates that the uncontaminated parental magmas of various Tarim LIP rocks (from the picrites and basalts to ultramafic–mafic and syenitic intrusive rocks) exhibit a wide range of εNd(t) values (ca. − 5–5), reflecting source isotopic heterogeneity, which may be a consequence of plume–lithosphere interaction during the generation of the Tarim LIP.

Fault systems and their mechanisms of the formation and distribution of the Tarim Basin, NW China

This article aims to analyze the main controlling factors of development, distribution and evolution of the fault systems in the Tarim Basin. Based on the seismic profile interpretation, comprehensive analysis of the drilling and geologic data, six fault systems maybe recognized in the Tarim Basin, they are the foreland fault system of the South Tianshan Mountain, the northern Tarim uplift fault system, North Tarim depression fault system, central fault system, Southwest Tarim fault system, and Southeast Tarim fault system. It is indicated that the main differences exist at the development, evolution and distribution of the fault systems in the Tarim Basin. The sub-fault systems can be recognized according to the differences of the fault development and distribution in the interior of the fault system. It is characterized that the multi-level differential development and distribution of the fault systems exist in the Tarim Basin. The fault belt developed in the Paleozoic strata mainly distribute at the paleo-uplift and paleo-slope in the interior of the Tarim Basin, and the fault belt occurred in the Meso-Cenozoic beds mainly develop at the peripheral foreland depressions. Zonal and segment differential development and distribution of the fault systems also exist in the Tarim Basin. The formation and distribution of the Tarim fault systems is of complex controlling mechanisms. Poly-phase structural movement and tectonic transition controls the multi-phase differential development and distribution of the fault systems in the Tarim Basin. Multi-level differential development and distribution is controlled by multi-level detachment belt and regional unconformities. Zonal and segment differential development and distribution of the Tarim fault systems maybe controlled by pre-existed basement structural texture. The major direction of the fault systems in the Tarim Basin is controlled by the later stage basin-mountain coupling.

Temporal and spatial evolution analysis: The early Paleozoic Paleo-Uplifts in the Tarim basin

Twenty unconformities, primarily superimposed types, were identified based on interpretation of a 46 000 km seismic profile combined with data from over 40 drilling wells. These respectively correspond to the main tectonic evolution stages and the boundaries between those stages. Reconstruction of the original depths of eroded strata was conducted for the Middle Caledonian, Early Hercynian, Late Hercynian, Indosinian, Early Yanshanian and Late Yanshanian unconformities using the virtual extrapolation of seismic reflection. Eroded strata thicknesses were also calculated for individual periods and intervals. Based on the reconstructed data, in combination with data from research on sedimentary facies, a paleogeomorphological profile was constructed for different tectonic evolution stages of the basin during the Early Paleozoic. The profile indicates the presence of obvious regularity in the temporal and spatial evolution of these unconformities. Based on the characteristics of paleo-uplift evolution and post-layering reconstruction, the paleo-uplifts were divided into inherited (e.g., Tazhong (塔中)), residual (e.g., North Tarim) and active (e.g., Southwest Tarim and Bachu (巴楚)) types. The huge North Tarim uplift represents a typical form of residual paleo-uplift. The Paleozoic strata in the upper layers of the uplift is in poor condition for reservoir accumulation and preservation; however, the Upper Mesozoic-Cenozoic structural layer can form a secondary reservoir that is relatively rich in oil and gas. Furthermore, the flank slope area of the uplift is always a key source for oil and gas collection and the most advantageous position for the formation of the original reservoir. The Tazhong paleo-uplift has been stable since its formation in the Late Ordovician, where petroleum accumulation has been distributed not only in the uplift, but also in the deep and slope belts of the uplift. Important breakthroughs in petroleum exploration of the slope break in the North Tazhong area dating back to the Paleozoic have further confirmed the enrichment of oil and gas in this type of uplift. The Southwest Tarim paleo-uplift is a buried type, which has given it favorable properties for hydrocarbon migration over a long time. An open question is whether the large amount of oil and gas accumulated here was transported to the current Bachu uplift.

Ancient karsts and hydrocarbon accumulation in the middle and western parts of the North Tarim uplift, NW China

Abstract Ordovician karsts are well developed in the Yingmaili and Halahatang areas of the North Tarim Basin. The ancient karsts are an important factor for forming Ordovician hydrocarbon reservoirs in the central and western regions of the North Tarim Basin. They are distributed, like successive broad belts, along the south side of the North Tarim uplift and constitute a large complex ancient karst reservoir system together with the Lunnan bulge. The main controlling factors of the Ordovician karsts are uplift, interlamination parallel unconformity, fault systems, rock physical properties and high-energy sedimentary phases. The Ordovician karsts can be divided into uplift-controlled karst areas, the strata- and fault-controlled karst areas and limited karst areas while karsts of different origins can overlay each other. The ancient karsts are developed mainly in four periods: the Caledonian, Hercynian, Indo-China Yanshan, and Yanshan, and karsts of different periods overlay each other, too. The condition for developing large-scale ancient karst reservoirs exists in the area and the complex ancient karst systems can be rich in oil and gas. Along both sides of the Middle-Upper Ordovician clastic pinch-outs are the more favorable areas for large ancient karst reservoirs.

The Tarim picrite–basalt–rhyolite suite, a Permian flood basalt from northwest China with contrasting rhyolites produced by fractional crystallization and anatexis

We report major and trace element composition, Sr–Nd isotopic and seismological data for a picrite–basalt–rhyolite suite from the northern Tarim uplift (NTU), northwest China. The samples were recovered from 13 boreholes at depths between 5,166 and 6,333 m. The picritic samples have high MgO (14.5–16.8 wt%, volatiles included) enriched in incompatible element and have high 87Sr/86Sr and low 143Nd/144Nd isotopic ratios (eNd (t) = −5.3; Sri = 0.707), resembling the Karoo high-Ti picrites. All the basaltic samples are enriched in TiO2 (2.1–3.2 wt%, volatiles free), have high FeOt abundances (11.27–15.75 wt%, volatiles free), are enriched in incompatible elements and have high Sr and low Nd isotopic ratios (Sri = 0.7049–0.7065; eNd (t) = −4.1 to −0.4). High Nb/La ratios (0.91–1.34) of basalts attest that they are mantle-derived magma with negligible crustal contamination. The rhyolite samples can be subdivided into two coeval groups with overlapping U–Pb zircon ages between 291 ± 4 and 272 ± 2 Ma. Group 1 rhyolites are enriched in Nb and Ta, have similar Nb/La, Nb/U, and Sr–Nd isotopic compositions to the associated basalts, implying that they are formed by fractional crystallization of the basalts. Group 2 rhyolites are depleted in Nb and Ta, have low Nb/La ratios, and have very high Sr and low Nd isotopic ratios, implying that crustal materials have been extensively, if not exclusively, involved in their source. The picrite–basalt–rhyolite suite from the NTU, together with Permian volcanic rocks from elsewhere Tarim basin, constitute a Large Igneous Province (LIP) that is characterized by large areal extent, rapid eruption, OIB-type chemical composition, and eruption of high temperature picritic magma. The Early Permian magmatism, which covered an area >300,000 km2, is therefore named the Tarim Flood Basalt.

Differential Hydrocarbon Migration and Entrapment in the Karstified Carbonate Reservoir: A Case Study of the Well TZ83 Block of the Central Tarim Uplift Zone

The hydrocarbon migration and entrapment mechanism in the lower overlapped basins, occurring in the complex carbonate pore-fissure-fracture reservoirs, is one of the key problems that have to be solved for effective hydrocarbon exploration. The production, gas/oil ratio, and the composition of crude oils and natural gas in the TZ83 Well block are high at the intersection point of the NE and NW-strike faults and decrease gradually along the ridge of the structure. A basic model of the pore-fissure-fracture system is built according to the achievements in the research on carbonate karstification. Processes of hydrocarbon migration and entrapment in this system are analyzed, which indicate that an understanding of the complexness of differential hydrocarbon migration is the key to interpreting this phenomenon. The hydrocarbon must charge the nearest compartment before migrating further away to charge other compartments in its pathway in the complex pore-fissure-fracture system. As a result, the following two phenomena appear: (1) Gas is enriched near the hydrocarbon injection point and drives away the oil, which is enriched in the compartments farther from the injection point. (2) The complex gas–oil–water relationship is controlled by the lateral connecting networks. Based on this, this article shows that the fault intersection point is the injection point of the oil and gas, and the main pathway system is distributed along the ridge of the structure. The theory of deferential hydrocarbon migration in the pore-fissure-fracture system can be presented from two aspects: (1) In hydrocarbon exploration, the structure of the fissure-fracture system should be described first, and then the special distribution of gas–oil–water can be predicted according to the main charging point and the main pathway system. (2) Exploration should be confined to the hydrocarbon charging point and the main pathway systems. An explored area should not be abandoned merely due to failures in some wells.

North‐south Differentiation of the Hydrocarbon Accumulation Pattern of Carbonate Reservoirs in the Yingmaili Low Uplift, Tarim Basin, Northwest China

Abstract: By analyzing the characteristics of development, structural evolution and reservoir beds of the residual carbonate strata, this study shows that the residual carbonate strata in the Yingmaili low uplift are favorable oil and gas accumulation series in the Tabei (northern Tarim uplift) uplift. There are different patterns of hydrocarbon accumulation on the northern and southern slopes of the Yingmaili low uplift. The north‐south differentiation of oil reservoirs were caused by different lithologies of the residual carbonate strata and the key constraints on the development of the reservoir beds. The Mesozoic terrestrial organic matter in the Kuqa depression and the Palaeozoic marine organic matter in the Manjiaer sag of the Northern depression are the major hydrocarbon source rocks for the northern slope and southern slope respectively. The hydrocarbon accumulation on the northern and southern slopes is controlled by differences in maturity and thermal evolution history of these two kinds of organic matter. On the southern slope, the oil accumulation formed in the early stage was destroyed completely, and the period from the late Hercynian to the Himalayian is the most important time for hydrocarbon accumulation. However, the time of hydrocarbon accumulation on the northern slope began 5 Ma B.P. Carbonate inner buried anticlines reservoirs are present on the southern slope, while weathered crust and paleo‐buried hill karst carbonate reservoirs are present on the northern slope. The northern and southern slopes had different controlling factors of hydrocarbon accumulation respectively. Fracture growth in the reservoir beds is the most important controlling factor on the southern slope; while hydrocarbon accumulation on the northern slope is controlled by weathered crust and cap rock.

Poly-phase salt tectonics and hydrocarbon accumulation in Tarim superimposed basin, northwest China

The purpose of this paper is to discuss the poly-phase salt tectonics and its relation to the hydrocarbon accumulation of the Tarim superimposed basin. Several salt sequences are developed in the Tarim basin, they are: (1) the Mid-Early Cambrian salt sequence, mainly distributed in the west part of the north Tarim uplift and Keping uplift; (2) the Early Carboniferous salt sequence, mainly distributed in the south slope of the north Tarim uplift; (3) the Paleogene salt sequence, mainly distributed in the mid-west part of the Kuqa foreland fold belt and north Tarim uplift; and (4) the Miocene salt sequence, mainly distributed in the east part of the Kuqa foreland fold belt. The salt sequences deposited in the tectonically calm scenario, while the salt layers deformed during the period of intense tectonism. Although the salt sequences are characteristic of plastic flow, the differences of salt deformation styles exist in the different salt sequences because of the different deformation mechanism. It is attractive that the distribution of the large oil-gas fields or pools has a bearing upon the salt sequences and salt structures, such as the Tahe oilfield related to the Lower Carboniferous salt sequence and laterally facies changed mudstone, the Kela No.2 gas field to the Paleogene salt structures, and the Dina gas field to the Miocene salt structures. It is indicated that the large-scale hydrocarbon accumulation is controlled by the poly-phase salt sequences and structures. The deep analysis of the poly-phase salt tectonics is helpful to understanding the characteristics of the structural deformation and oil-gas accumulation of the Tarim basin.

ORGANIC PETROLOGY OF POTENTIAL SOURCE ROCKS IN THE TARIM BASIN, NW CHINA

Potential source rocks in the Tarim Basin (NW China) include Cambrian‐Lower Ordovician lagoonal carbonates and mudstones; Middle‐Upper Ordovician platform carbonates; Carboniferous‐Permian shallow‐marine carbonates and mudstones; and Triassic‐Jurassic continental deposits including coals and lacustrine mudstones. Our petrological observations show that the organic components in Cambrian‐Ordovician deposits are mainly alginites andamorphinites with minor vitrinite‐like macerals, zooclasts and solid bitumen (Type I organic matter). The organic carbon content of these rocks is 0.1–2% TOC (averaging 0.9%TOC in deeper‐water fades) and they are mature to overmature in terms of oil generation.Organic macerals in Permian‐Carboniferous source rocks are dominated by alginite with minor quantities of zooclasts andexinite derived from terrestrial higher plants (mainly Type II OM with minor Types I and III). TOC contents are 0.1–1%. These rocks are mature to highly‐mature in terms of oil generation.Macerals in Jurassic‐Triassic source rocks are dominated by vitrinite and inertinite, with V+I &gt; 50% and alginite + amorphinite &lt; 40%; exinite averages 2–5%. This organic matter type is Type III, and the sediments are immature to just mature.We have calculated the original organic matter richness of Ordovician deposits at selected locations. The original OM content appears to have been particularly high around Lunnan (in the North Tarim Uplift), in the Central Tarim Uplift and around Tadong (in the SE Uplift). These areas are therefore suggested to have particularly high exploration potential.

Structural Features of Northern Tarim Basin: Implications for Regional Tectonics and Petroleum Traps

The rhombus-shaped Tarim basin in northwestern China is controlled mainly by two left-lateral strike-slip systems: the northeast-trending Altun fault zone along its southeastern side and the northeast-trending Aheqi fault zone along its northwestern side. In this paper, we discuss the northern Tarim basin's structural features, which include three main tectonic units: the Kalpin uplift, the Kuqa depression, and the North Tarim uplift along the northern margin of the Tarim basin. Structural mapping in the Kalpin uplift shows that a series of imbricated thrust sheets have been overprinted by strike-slip faulting. The amount of strike-slip displacement is estimated to be 148 km by restoration of strike-slip structures in the uplift. The Kuqa depression is a Mesozoic-Cenozoic foredeep depression with well-developed flat-ramp structures and fault-related folds. The Baicheng basin, a Quaternary pull-apart basin, developed at the center of the Kuqa depression. Subsurface structures in the North Tarim uplift can be divided into the Mesozoic-Cenozoic and the Paleozoic lithotectonic sequences in seismic profiles. The Paleozoic litho-tectonic sequence exhibits the interference of earlier left-lateral and later right-lateral strike-slip structures. Many normal faults in the Mesozoic-Cenozoic litho-tectonic sequence form the negative flower structures in the North Tarim uplift; these structures commonly directly overlie the positive flower structures in the Paleozoic litho-tectonic sequence. The interference regions of the northwest-trending and northeast-trending folds in the Paleozoic tectonic sequence have been identified to have the best trap structures. Our structural analysis indicates that the Tarim basin is a transpressional foreland basin rejuvenated during the Cenozoic.

Structural Style and Petroleum Prospects of the Kuqa Depression, Northern Tarim Basin, Northwest China: ABSTRACT

The Kuqa depression is a 400-km {times} 100-km, east-west-trending foredeep basin located on the northern margin of the Tarim craton in northwestern China. A 10-km-thick nonmarine Mesozoic and Cenozoic sedimentary section has accumulated in the basin as the Tian Shan range to the north and has been episodically uplifted and thrust southward, tectonically loading the craton margin and providing source areas for clastic sediments. Regional mapping from Landsat images and field reconnaissance reveal important details of the structural style of the Kuqa depression. The Kuqa depression is characterized by thin-skinned deformation resulting in a series of steep, faulted, elongate folds. Thick, mobile Tertiary shale sequences and an Upper Cretaceous-lower Tertiary evaporite section in the west form detachment horizons separating disharmonically deformed structural packages. At the southern margin of the depression, the Mesozoic-Cenozoic section overrides faulted Paleozoic strata of the North Tarim uplift. Here, the Neogene Qiulitage anticline extends 250 km along the basin margin. Beginning in 1984, several important oil discoveries have been made in the Paleozoic section on the North Tarim uplift. Analysis of an oil sample indicates its compatibility with a lower Paleozoic marine source. Other potential source rocks in the Kuqa depression include Jurassic oil shales andmore » coals. Sandstone reservoir strata and structural trapping geometries are numerous, but exploration risks are complicated by the presence of the ductile evaporite and shale seals. If nonmarine source rocks are also present in the thick Cenozoic section, the Kuqa depression may be an attractive exploration target.« less