The thick Neogene salt layer developed in the Eastern part of Qiulitage Belt, through the representative seismic profiles, it is reveled that the salt layer is a decollement layer and adjustes the differentiated deformation between the supra-salt layer and the sub-salt layers, the structural traps in the supra-salt layer are mainly anticline trap, thrust fault sheltering trap, etc, the traps in the salt layer are mainly the lithostratigraphic trap or the anticline trap constituted of the carbonate rock and the sandstone, the structural traps in the sub-salt layer are mainly the pop-up etc. Combining this result with analyzing of the condition of the hydrocarbon accumulation, the authors consider there is the accumulation pattern of separated source-side rejecting in the area with a transporting layer composed of faults and unconformities, there is a good relationship between the evolution history of the source rock in Yangxia Sag and the structural deformation, all these make the structural traps in the studied area capture the natural gas generated in Yangxia Sag.
This paper presents the analysis on geological characteristics of Tazhong Uplift, such as the configuration and nature of the fault structures, and the aeromagnetic anomaly, etc. The study result shows that Tazhong Uplift presents several large-scale fault belts that mainly extend in three directions: NW, approximate (approx.) EW and NNE. The NW fault belts lie in the north and northwest of the research area; the approx. EW fault belts rest in the south and southeast of the research area, whereas the NNE fault belts are mainly strike-slip faults and cut the NW fault belts into several structural segments. It is concluded that the late Caledonian and the late Hercynian period were the two major forming periods of Tazhong Uplift. In the late Caledonian period, the NW thrust faults developed in Tazhong Uplift under the tectonic compression stress from the southwest Foreland Basin. In the late Hercynian period, the subduction of Altyn Orogenic Belt influenced the central Tarim and generated the approx. EW thrust faults in the central and southern Tazhong Uplift. This subduction also forced the early-formed fault belts into an arc-shape in the central Tazhong Uplift and caused NNE strike-slip faults in the northern Tazhong Uplift. Laterally the tectonic stress decreased from the south to the north. From regional perspective, the fault belts diverge to the west and converge to the east.
Abstract: The Triassic Jialingjiang Formation and Leikoupo Formation are characterized by thick salt layers. Three tectono‐stratigraphic sequences can be identified according to detachment layers of Lower‐Middle Triassic salt beds in the northern Sichuan Basin, i.e. the sub‐salt sequence composed of Sinian to the Lower Triassic Feixianguan Formation, the salt sequence of the Lower Triassic Jialingjiang Formation and Mid‐Triassic Leikoupou Formation, and the supra‐salt sequence composed of continental clastics of the Upper‐Triassic Xujiahe Formation, Jurassic and Cretaceous. A series of specific structural styles, such as intensively deformed belt of basement‐involved imbricated thrust belt, basement‐involved and salt‐detached superimposed deformed belt, buried salt‐related detached belt, duplex, piling triangle zone and pop‐up, developed in the northern Sichuan Basin. The relatively thin salt beds, associated with the structural deformation of the northern Sichuan Basin, might act as a large decollement layer. The deformation mechanisms in the northern Sichuan Basin included regional compression and shortening, plastic flow and detachment, tectonic upwelling and erosion, gravitational sliding and spreading. The source rocks in the northern Sichuan Basin are strata underlying the salt layer, such as the Cambrian, Silurian and Permian. The structural deformation related to the Triassic salt controlled the styles of traps for hydrocarbon. The formation and development of hydrocarbon traps in the northern Sichuan Basin might have a bearing upon the Lower‐Middle Triassic salt sequences which were favorable to the hydrocarbon accumulation and preservation. The salt layers in the Lower‐Middle Triassic formed the main cap rocks and are favorable for the accumulation and preservation of hydrocarbon.
Abstract: By analyzing the balanced cross sections and subsidence history of the Longmen Mountain thrust belt, China, we concluded that it had experienced five tectonic stages: (1) the formation stage (T 3 x ) of the miniature of Longmen Mountain, early Indosinian movement, and Anxian tectonic movement created the Longmen Mountain; (2) the stable tectonic stage (J 1 ) where weaker tectonic movement resulted in the Longmen Mountain thrust belt being slightly uplifted and slightly subsiding the foreland basin; (3) the intense tectonic stage (J2.3), namely the early Yanshan movement; (4) continuous tectonic movement (K‐E), namely the late Yanshan movement and early Himalayan movement; and (5) the formation of Longmen Mountain (N‐Q), namely the late Himalayan movement. During those tectonic deformation stages, the Anxian movement and Himalayan movement played important roles in the Longmen Mountain's formation. The Himalayan movement affected Longmen Mountain the most; the strata thrust intensively and were eroded severely. There are some klippes in the middle part of the Longmen Mountain thrust belt because a few nappes were pushed southeastward in later tectonic deformation.
Abstract: Field investigation and seismic section explanation showed that the Longmen Mountain Thrust Belt has obvious differential deformation: zonation, segmentation and stratification. Zonation means that, from NW to NE, the Longmen Mountain Thrust Belt can be divided into the Songpan‐Garzê Tectonic Belt, ductile deformation belt, base involved thrust belt, frontal fold‐thrust belt, and foreland depression. Segmentation means that it can be divided into five segments from north to south: the northern segment, the Anxian Transfer Zone, the center segment, the Guanxian Transfer Zone and the southern segment. Stratification means that the detachment layers partition the structural styles in profile. The detachment layers in the Longmen Mountain Thrust Belt can be classified into three categories: the deep‐level detachment layers, including the crust‐mantle system detachment layer, intracrustal detachment layer, and Presinian system basal detachment layer; the middle‐level detachment layers, including Cambrian‐Ordovician detachment layer, Silurian detachment layer, etc.; and shallow‐level detachment layers, including Upper Triassic Xujiahe Formation detachment layer and the Jurassic detachment layers. The multi‐level detachment layers have a very important effect on the shaping and evolution of Longmen Mountain Thrust Belt.
Abstract: Thick‐skinned contractional salt structures are widely developed in the western Kuqa depression, northern Tarim basin. To understand the mechanisms that govern the development of these structures, physical experiments are conducted and the results show that they are largely governed by the activities of basement faults and the forming of paleo‐uplifts and basement slopes. The model materials in this study are dry sand, vaseline and plasticene (or hard foam), simulating the suprasalt, salt, and subsalt layers respectively. The experiments show that, due to the activities of basement faults and the forming of the paleo‐uplifts, salt bodies usually accumulate and thicken significantly on the middle top of the paleo‐uplifts which are constrained by the pre‐exiting boundary faults. The development of large‐scale thrust faults and salt nappes is favored by the basement slops with larger dips. The experiments also conclude that differential structural deformation could occur between the subsalt and suprasalt layers because of the presence of salt layers. Their geometries and the locations of structural highs are different, despite of the great similarities in the uplifted areas. The pierced salt diapir is not observed in the experiments, which indicates that the contractional shortening does not effectively accelerate the development of the salt diapir.
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