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Abstract
The Early Permian Yierxitu Formation widely distributed in Turpan-Hami area of Xinjiang provides a record of paleocli-mate, paleogeography, basin and tectonic evolution in the Early Permian period. There exists much controversy concerning sedimen-tology, basin evolution and tectonic background of the Yierxitu Formation. This paper briefly reviewed previous researches on the Yierxitu Formation in Turpan-Hami area. Furthermore, on the basis of geological survey, the authors studied stratigraphy, sedimentary facies, provenance and paleocurrents of the Yierxitu Formation, and the results indicate that the Yierxitu Formation was spatially and temporally involved in an evolution of sedimentary facies from alluvial fan or river to shallow lake, semi-deep or deep lake in upward succession. Volcanic lithological associations of the Yierxitu Formation are characterized by the bimodal volcanic rock assemblages of olivine basalt, basaltic andesite and rhyolite. The distribution of lithofacies and lithological associations indicates that the volcanic constituents of the Yierxitu Formation gradually increase from west to east, which means the volcanic activities were stronger in the east than in the west. Meanwhile, marine flysch formations intercalated with volcanic rocks were developed in the northern Bogda Mountain. Petrologic characteristics and geochemistry show that, in the northern Bogda Mountain, there existed bimodal volcanic rock assemblages. Studies show that marine rift existed in the northern Bogdashan Mountain whereas a continental rift occurred in the southern Bogda Mountain. Paleocurrents show a bio-direction pattern, and currents from the northern and southern Bogda Mountain were concentrated in the central Bogda Mountain area (the center of the rift). Provenance analysis shows that conglomerate sediments of the Early and Middle Permian period in northern Turpan-Hami area are mainly composed of andesite, tuffs and rhyolitic volcanics as well as sandstone, silica or limestones, suggesting that they were derived from the underlying Devonian and Carboniferous strata.
... Extensive and intensive tectonic movements occurred in Eastern Xinjiang (i.e. the Eastern Junggar Basin and the Turpan-Hami Basin areas) and had been active until the late Early to early Middle Permian, associated with the final closure of the Paleo-Asian Ocean in this region (Deng et al., 2009;Shi et al., 1995;Wartes et al., 2002;Wei et al., 2016). The sedimentary setting of the Turpan-Hami Basin had remarkably changed and gradually evolved from marine into continental, which was dominated by fluvial-lacustrine facies (Liu et al., 2006;Mu, 1993;Stratigraphical Lexicon of China compiling commission, 2000;Xu et al., 2013). In addition, the organic geochemical characteristics of Permian mudstones have also aroused the great interest of scholars (Miao, 2001;Zhou, 2008). ...
... However, the knowledge of the depositional environments (especially to provenance, paleoclimate, paleosalinity and so on) during the Permian (especially during the Middle-Late Permian, i.e. the closure and post-closure period of the Paleo-Asian Ocean) is still limited and lack systematicness. For example, studies on the provenance were mainly based on petrological characteristics (Shao et al., 1999;Xu et al., 2013) but there is lack of the evidences from elemental geochemistry (such as rare earth and trace metal elements). Miao (2001) noted that the Eastern Xinjiang area belonged to an overall warm climate during the Permian, but the shorter-term vertical changes of paleoclimate have not been studied. ...
... Yang (2013) proposed that several depressions and salients (i.e. the Taoshuyuan Depression in the north (Figure 1(c)), the Keyayi Depression, Boolean Salient, Taibei Depression, and Tainan Depression in the middle, and the Toksun Depression and Luxi Salient in the south) were developed in the northwestern Turpan-Hami Basin (Figure 1(b)). Permian filling successions contain Yierxitu and Daheyan Formations in Lower Permian, Taerlang Formation in Middle Permian, and Quanzijie, Wutonggou, and Guodikeng Formations in Upper Permian (Shao et al., 2001;Stratigraphical Lexicon of China compiling commission, 2000;Xu et al., 2013) (Figure 2). The Permian consists of continental clastic-pyroclastic rocks and a few limestones deposited mainly in a fluvial-delta-lacustrine environment (Shao et al., 2001;Stratigraphical Yang, 2013). ...
Studies have found that the Permian is another important stratum for petroleum exploration except the Jurassic coal measures within Turpan–Hami Basin recently. However, the knowledge of the depositional environments and its petroleum geological significances during the Middle–Late Permian is still limited. Based on the analysis about the sedimentological features of the outcrop and the geochemical characteristics of mudstones from the Middle Permian Taerlang Formation and Upper Permian Quanzijie Formation in the Taoshuyuanzi profile, northwest Turpan–Hami Basin, this paper makes a detailed discussion on the Middle–Late Permian paleoenvironment and its petroleum geological significances. The Middle–Upper Permian delta–lacustrine depositional system was characterized by complex vertical lithofacies assemblages, which were primarily influenced by tectonism and frequent lake-level variations in this area. The Taerlang Formation showed a significant lake transgression trend, whereas the regressive trend of the Quanzijie Formation was relatively weaker. The provenance of Taerlang and Quanzijie Formations was derived from the rift shoulder (Bogda Mountain area now) to the north and might be composed of a mixture of andesite and felsic volcanic source rocks. The Lower Taerlang Formation was deposited in a relatively hot–dry climate, whereas the Upper Taerlang and Quanzijie Formations were deposited in a relatively humid climate. During the Middle–Late Permian, this area belonged to an overall semi-saline water depositional environment. The paleosalinity values showed stepwise decreases from the Lower Taerlang Formation to the Upper Quanzijie Formation, which was influenced by the changes of paleoclimate in this region. During the Middle–Late Permian, the study area was in an overall anoxic depositional environment. The paleoenvironment with humid climate, lower paleosalinity, anoxic condition, and semi-deep to deep water during the deposition of the Upper Taerlang Formation was suitable for the accumulation of mudstones with higher TOC values.
... Recent studies have identified Permian strata within the Turpan-Hami Basin as exploration targets (Zhang et al., 2014). However, the depositional environment during the Permian in the basin is unclear, which has hindered petroleum exploration (Xu et al., 2013). Therefore, the article presented here focuses on depositional environments during the Permian. ...
The tectonic evolution and sedimentary characteristics of the Carboniferous-Permian rocks of the Turpan-Hami Basin have been analysed. Initially, a joint inversion of gravity, magnetic, seismic data and the established model of electrical profiles was synthesized to create a new geological interpretation. Discussion on the tectonic characteristics of piedmont zone in the northern part of the basin then followed. According to the analysis of balanced cross-sections, the tectonic evolutionary history of Carboniferous-Permian sedimentary rocks of the Turpan-Hami Basin can be divided into three stages: an extensional stage in the Carboniferous, a tectonic transition stage in the Early Permian, and a compression and inversion stage after the Middle Permian. It is found that the tectonic evolution controlled the sedimentary facies under these three stages and the sedimentation evolution has undergone marine facies, marine-lacustrine transitional facies and lacustrine facies. Meanwhile, based on the recent seismic, gravity, magnetic and electrical data, and combined with the field surveying of outcrops, the residual distribution of Carboniferous-Permian strata is characterized by the widely distributed residual Upper Carboniferous, except for the southern Liaodun Uplift and locally in the eastern area, and the denudation of Middle Permian strata mainly distributed in the Turpan Depression and the Turpan-Hami Depression. After comprehensive analysis of the sedimentary facies and erosion of Permian strata, it is concluded that the tectonic evolution and sedimentation of the Turfan-Hami Basin can be used as a constraint on Permian subduction-related accretionary orogenesis of northern Xinjiang, NW China and the closure time of the Paleo-Asian Ocean.
A diverse and well-preserved fossil wood assemblage is described, for the first time, from the Middle Permian Taerlang Formation and the Upper Permian Quanzijie Formation in the vicinity of the Tianshan Town, Hami City of northwestern China. On the basis of wood microstructure, the fossil woods are classified into three genera and five species, including one new genus: Prototianshanoxylon gen. nov. and two new species: Prototianshanoxylon erdaogouense sp. nov., Prototianshanoxylon hamiense sp. nov. The new genus is characterized by window-like cross-field pitting and mixed tracheid radial wall pitting that suggest a transitional type between araucarioid-type and protopinoid-type pittings.
Phytogeographically, the fossil wood assemblage is characterized by an admixture of elements of both temperate Angaran (represented by wood specimens with moderately to well defined growth rings in their secondary xylem) and tropical–subtropical north subregion of the Cathaysian floras (with wood specimens lacking well-defined growth rings). Such a phytogeographically mixed fossil wood assemblage is interpreted to represent a transitional and complex climate condition between a cool temperate and tropical to subtropical zones, showing both seasonal variation and unstable climate conditions. Previously, similarly mixed floras have already been found to exist widely in northern China ranging in age from Early to Late Permian, but the mechanisms thought to be responsible for their formation were varied and remain controversial. In this study, the formation of these mixed Permian floras of North China is linked to the closure of the Tianshan–Hingan seaway coupled with the collision and amalgamation of Siberia with North China and the Tarim block, in a manner much like closing a pair of scissors with the closure of the seaway proceeding gradually and progressively from west to the east.
Lacustrine organic-rich mudstones of the Upper Permian Lucaogou Formation are a significant petroleum source bed throughout most of the Junggar basin in northwest China, and paleomagnetic data may provide insight into tectonic conditions prevalent during their deposition. Secondary magnetizations were removed from 180 samples from 29 sites within the South Junggar basin. Characteristic magnetizations of these samples were either revealed directly during thermal demagnetization or were calculated from great circle trajectories. The primary nature of the characteristic magnetization is attested to by a positive fold test, by exclusively reversed magnetizations which are consistent with the mid-Carboniferous to Late Permian Kiaman reversed interval for the geomagnetic field, and by relatively low levels of thermal maturity found in the mudstones. Tectonically corrected remagnetization circles and direct observations combined give a steep direction (I=-61.9°, D=163.0°, k=17, n=78 specimens). The steep mean inclination recorded within the lacustrine organic-rich mudstones suggests that Junggar was situated near its present-day latitude during deposition of the mudstones in Late Permian times, consistent with the marginal ocean basin origin for Junggar that has been proposed based upon stratigraphic relationships. Our data suggests that Junggar may always have been associated with the northern continents of Laurasia, initially as a pre-Permian marginal ocean basin north of the Tethys and subsequently as a Permian, Mesozoic, and Cenozoic nonmarine foreland basin.