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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. [ABSTRACT FROM AUTHOR]

The Altyn Tagh fault plays an important role in growth of the north-western Tibetan plateau, but the timing of its inception and magnitude of left-lateral displacement are not well constrained. This study provides new independent constraints by correlating stratigraphic development and spatial distribution of the neighbouring Tarim and Qaidam basins. It is shown that the Tarim and Qaidam basins experienced quite similar stratigraphic and sedimentary evolution from late Sinian to early Palaeogene times. This fact indicates that the Tarim and Qaidam basins were a single block, at least until Oligocene time, which was then offset by the Altyn Tagh fault. Early Palaeozoic and Late Triassic suture zones within the East and West Kunlun and pinch-outs of Mesozoic strata are chosen as piercing lines. Restoration of these lines gives total offset estimates of 350–400 km across the south-western and central segments of the Altyn Tagh fault. [ABSTRACT FROM AUTHOR]

Fifty-four oils and 20 gas condensates from the cratonic region of the Tarim Basin, NW China were quantitatively analyzed by gas chromatography–mass spectrometry to elucidate the influence of thermal maturation, multiple charges and mixing, and thermochemical sulfate reduction (TSR) on the relative distributions of alkyldibenzothiophenes (DBTs) vs alkylphenanthrenes, which are widely used to interpret depositional environment and lithology. Concentrations of DBTs relative to DBTs in the aromatic hydrocarbon fraction and ratios of dibenzothiophene/phenanthrene (DBT/P) exhibit wide variations in the studied samples. Field observations, coupled with a suite of oil sand pyrolysis experimental results, suggest that DBTs are more easily released from kerogen and/or asphaltenes and are more easily destroyed in oil than the alkylphenanthrenes. The DBT/P ratio initially increases during early maturation and then decreases in the post mature stage. Concentrations of DBTs are low in samples from the cratonic region of the Tarim Basin (most samples have DBT/P ratios < 1) because of their high maturity. The unusually high concentration of DBTs in some gas condensates from the Tazhong Uplift is possibly the result of back reaction of H 2 S formed by TSR with hydrocarbons. A typical TSR-altered sample represented by ZS1C has a DBT/P ratio as high as 22.3 with DBTs representing 63.6% of components in the aromatic hydrocarbon fraction. Mixing of a TSR-altered late charge with previously existing oils is responsible for the wide range of variation of DBT concentrations and DBT/P ratios. The influence of TSR on DBT/P ratios is easily distinguishable from thermal maturation because the former increases the ratio while the latter decreases the ratio. Consequently, the DBT/P ratio is not valid as a parameter to interpret source rock lithology and depositional environment in the present case study. [ABSTRACT FROM AUTHOR]

Late Silurian–Carboniferous extensional structures have been discovered after careful interpretation of seismic reflection data in western Manjiaer Sag, Central Tarim Basin in central Asia. The extensional structures comprise numerous small normal faults in nearly N–S strike direction. Groups of normal faults in profile show features suggestive of negative flower structures and small horst-graben structures. Based on growth index calculation, these extensional structures formed in the Late Silurian period, continued activity in the Devonian and Carboniferous and then ceased at the end of Carboniferous. The peak-stage of normal fault activity occurred in Late Silurian. Late Silurian–Carboniferous normal faults also developed in the Tazhong and Tabei areas, which implies that Tarim Basin were under regional extensional tectonic setting during that periods. The extensional structure in southern Tarim resulted from the post-orogeny stress relaxation of the Kunlun Early Paleozoic orogenic belt, and those in northern Tarim resulted from the Paleozoic back-arc rifting which led to the opening of South Tianshan ocean. [ABSTRACT FROM AUTHOR]