Geological Society of America Memoir 194 2001 Sedimentary record of Mesozoic deformation and inception of the Turpan-Hami basin, northwest China Todd J. Greene* Department of Geological and Environmental Sciences, Stanford University, Stanford, California, 94305-2115, USA Alan R. Carroll* Department of Geology and Geophysics, University of Wisconsin, 1215 West Dayton Street, Madison, Wisconsin 53706, USA Marc S. Hendrix* Department of Geology, University of Montana, Missoula, Montana 59812, USA Stephan A. Graham* Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305-2115, USA Marwan A. Wartes* Department of Geology and Geophysics, University of Wisconsin, 1215 West Dayton Street, Madison, Wisconsin 53706, USA Oscar A. Abbink* Laboratory of Palaeobotany and Palynology, Utrecht University, Utrecht, The Netherlands ABSTRACT The Turpan-Hami basin is a major physiographic and geologic feature of north- west China, yet considerable uncertainty exists as to the timing of its inception, its late Paleozoic and Mesozoic tectonic history, and the relationship of its petroleum systems to those of the nearby Junggar basin. To address these issues, we examined the late Paleozoic and Mesozoic sedimentary record in the Turpan-Hami basin through a series of outcrop and subsurface studies. Mesozoic sedimentary facies, regional un- conformities, sediment dispersal patterns, and sediment compositions within the Turpan-Hami and southern Junggar basins suggest that these basins were initially separated between Early Triassic and Early Jurassic time. Prior to separation, Upper Permian profundal lacustrine and fan-delta facies and Triassic coarse-grained braided-fluvial–alluvial facies were deposited across a contigu- ous Junggar-Turpan-Hami basin. Permian through Triassic facies were derived mainly from the Tian Shan to the south, as indicated by northward-directed paleocurrent di- rections. This is consistent with the sedimentary provenance of Triassic sandstone (mean & Qm29F29Lt42, Qp23Lvm49Lsm28, and Qm51P25K24) and conglomerate ( 32% granitic clasts) in the northern Turpan-Hami basin. We interpret a relative increase in quartz and feldspar concentration and a relative decrease in volcanic lithic grains in the northern Turpan-Hami basin to reflect unroofing in the Tian Shan and exposure of late Paleozoic granitoid rocks. In addition, two basinwide unconformities of Late Permian–Early Triassic and Early Triassic–middle-Late Triassic age attest to deformation within the Turpan-Hami basin and associated continued uplift and erosion of the Tian Shan. *E-mails: Greene, [email protected]; Carroll, carroll@geology. wisc.edu; Hendrix, [email protected]; Graham, [email protected]. edu; Wartes, [email protected]; Abbink, [email protected]. Greene, T.J., et al., 2001, Sedimentary record of Mesozoic deformation and inception of the Turpan-Hami basin, northwest China, in Hendrix, M.S., and Davis, G.A., eds., Paleozoic and Mesozoic tectonic evolution of central Asia: From continental assembly to intracontinental deformation: Boulder, Colorado, Geologi- cal Society of America Memoir 194, p. 317–340. 317 318 T.J. Greene et al. By Early Jurassic time, the Turpan-Hami basin and the southern Junggar basin became partitioned by uplift of the Bogda Shan, a major spur of the Tian Shan. In contrast to the thoroughgoing northward-directed Permian-Triassic depositional systems, Lower through Middle Jurassic strata begin to reflect ponded coal-forming, lake-plain environ- ments within the Turpan-Hami basin. These strata contain paleocurrent indicators re- flecting flow off the intervening Bogda Shan. Abasinwide Lower Jurassic– Middle Jurassic unconformity in the Turpan-Hami basin suggests continued uplift and erosion of the Bogda Shan, consistent with a return to more lithic-rich sandstone and volcanic-rich conglomer- ate compositions. These sedimentary facies, paleocurrent, and provenance data sets pro- vide the best available constraints on the initial uplift of the Bogda Shan and the first documentary evidence of intra-Mesozoic shortening within the basin. INTRODUCTION by the Bogda Shan, a major mountain range containing peaks as high as 5570 m (Fig. 1A). Few published data bear directly on The present-day Turpan-Hami basin is a major physio- the initiation of the Turpan-Hami basin or its premodern physio- graphic feature of central Asia. It contains the second lowest el- graphic and depositional history. Post-Carboniferous sedimen- evation on earth (-154 m), yet is bounded on its northern flank tary facies, paleocurrent dispersal patterns, and sandstone A. E86° E92° CHINA N JUNGGAR BASIN 0 100 km DUSHANZI N44° N44° + + NORTH + + + + + + TIAN URUMQI S B HAN O BA GD AN RKO A SH L TAG TIAN SHAN TURPAN-HAMI H BASIN TURPAN HAMI CENTRAL TIAN TIAN N42° SOUTH SHAN SHAN N42° + +++ + + + + KUQA KORLA K TARIM BASIN URUK TAGH CHINA PRE-MESOZOIC TRIASSIC JURASSIC CRETACEOUS CENOZOIC E86° E92° E86° E88° E90° E92° E94° B. N44° K (Li and Jiang, 1987) N44° J T-P T-P C C southern Junggar Basin Urumqi Jimsar B OG DA SHAN Zaobishan Taoshuyuan T2-3 Shisanjianfang Sandaoling Ha-3 T T2-3 P-T1 * P1-2 P2-T1 C Kekeya 5 C Aiweiergou C 6 Taibei Sag 4 P1 - 9 J1-T Taican-2 8 F T Hami Baiyanghe lam * P2 Turpan in TURPAN-HAMI g M T88-625 tn K C Tokesun . Ancan-1 K (Mu, 1994) J2 J1-T3 T88-635 * J2-3 BASIN Sag J2 T-P T2-3 T2-3 J2-3 C T84-200 T-P T1 C P2 CHOL TAGH N42° N42° E86° E88° ° E90 ° E92 E94° 50 km N Taoshuyuan study locality Legend fault Upper Jurassic (J3) Permian-Triassic (P2 - T1) Late Paleozoic granitoid rocks T88-635 seismic line Lower-Middle Jurassic (J1 + J2) Permian (P1 + P2) Paleozoic gabbroic rocks * well Cenozoic Middle-Upper Triassic (T2 + T3) Carboniferous volcanic rocks Pre-Mesozoic igneous and sedimentary depression Cretaceous (K1 + K2) metamorphic rocks Figure 1. A: Location map of study area within Xinjiang Uygur Autonomous Region, northwestern China. Boxed area is shown in detail in B. B: Geologic map of Turpan-Hami basin, showing various study locations in basin, location of seismic lines and wells referred to in text, and two main western sedimentary depressions, Tokesun Sag and Tabei Sag (adapted from Chen et al., 1985). Solid black circles show general strati- graphic relationships and unconformities of Carboniferous through Cretaceous strata at various locations; data for each black circle are from this study unless otherwise noted. Fault locations are adapted from Chen et al. (1985) and Allen et al. (1993). Sedimentary record of Mesozoic deformation and inception of the Turpan-Hami basin 319 compositions from the southern Junggar and northern Tarim et al. (1993) also identified two Mesozoic compressional basins (Hendrix et al., 1992; Carroll et al., 1995) suggest that the episodes in the Turpan-Hami basin and suggested that Lower Junggar and Tarim basins have existed as discrete physiographic Permian marine facies in the northern Turpan basin were de- features, separated by the intervening Tian Shan, since late posited as a foreland basin fill related to north-vergent thrust Paleozoic time. However, previous interpretations of the time of faults in the Tian Shan region. inception and early structural style of the Turpan-Hami basin Key to understanding the tectonic and sedimentary history vary widely. Hendrix et al. (1992) suggested, on the basis of of the Turpan-Hami basin is better documentation of the record paleocurrents, sedimentary facies, and isopach data, that the of sedimentary fill within the basin, combined with information Turpan-Hami basin was established as a discrete physiographic regarding the history of uplift and unroofing of the Bogda Shan. feature by Early Jurassic time, in response to compressional up- Unfortunately, very little information has been published about lift of the Bogda Shan. Allen et al. (1995) proposed that the Tur- the structure of the interior of the Bogda Shan; access to key ex- pan basin was one of several major depocenters created by posures is difficult, and there are no seismic lines that transect transtensional rotation within a Late Permian–Triassic sinistral the range. Tectonic interpretations from the Turpan-Hami basin shear system. In determining the sedimentary provenance of are largely limited either to specific reports on a focused northern Turpan-Hami deposits, Greene et al. (1997) and petroleum-related topic (Huang et al., 1991; Wang et al., 1993, Greene and Graham (1999) suggested that granitic cobbles con- 1998; K. Cheng et al., 1996; L. Liu et al., 1998), or regional tained within Lower Triassic deposits were derived solely from interpretive syntheses that lack detailed data sets and hence are the Central and South Tian Shan blocks, south of the Turpan- impossible to evaluate critically (Fang, 1990, 1994; Li and Hami basin, and inferred that the ancestral Bogda Shan had not Shen, 1990; Shen, 1990; Chen, 1993; Tao, 1994; Allen et al., been uplifted by that time. 1995; Shao et al., 1999b). Shao et al. (1999b), for example, used Better timing constraints for the initiation of the Turpan- basin subsidence curves to infer a period of Late Permian ther- Hami basin are especially important because they bear directly mal subsidence that was followed by a Middle-Triassic to early on the lateral extent of thick, organic-rich Upper Permian la- Tertiary period of flexural subsidence for the Turpan-Hami custrine shale in the southern Junggar basin. Carroll et al. (1992) basin. However, error bars for age control are absent, and paleo- and Clayton et al. (1997) demonstrated that these and equivalent elevation level is set at sea level for the past 250 m.y. in their strata are the source of oils produced at the Karamay oil field analysis. Likewise, numerous Chinese authors have published and other fields along the northwestern Junggar basin margin, reports on Early-Middle Jurassic depositional history and se- which collectively are thought to contain reserves of 2–3 billion quence stratigraphy, mainly due to its importance in petroleum barrel oil fields (Taner et al., 1988).