| The main purpose of this paper is to discuss the formation and tectonic evolution of Bachu-Markit area and Hetian palaeohigh affected by multi-periods tectonic movements. Based on the detailed analysis of the main fault zones and fault styles, the relationship between tectonic evolution, fault structural styles and hydrocarbon accumulation have been studied, aiming to predict the favorable prospects and targets.Bachu-Markit area is located at the southeast of Tarim basin, including Bachu uplift and Markit slope two structural units. Bachu uplift is a large NNW to NWW striking faulted-uplift. Based on the characteristics of the evolution history and faults distribution, it can be divided into two structural subunits of the east and the west. Markit slope is a regional slope, which is a monoclinal structure, northwest trend, southeast dip.Bachu-Markit area is a extremely complex tectonic zone controlled by both the southwest and the north foreland system of Tarim basin. According to the recovery of structural evolution sections, it shows that Bachu uplift is a active palaeohigh, which was in slight extensional structural environment of early Caledonian and elevated from late Hercynian. Himalayan movements made it rapid uplift, so that the tectonic framework turned to high in the northwest and low in the southeast. Since the middle Caledonian to the early Hercynian, Bachu area is a north dipping slope of Hetian palaeohigh. Markit slope dipped north in the early Paleozoic as well, and was tilted in south-north orientation in Hercynian. During this period, Hetian palaeohigh developed in Markit area. However the true reason that Markit slope are so steep to southeast is the result of intense tectonic movement of the late Himalayan.Bachu-Markit area mainly develops NW, NWW and NE fault systems. The deformation and typical structural styles distribution of main faults can be comprehensively researched in the paper. The faults in Bachu uplift are well developed. From west to east, the strike of boundary faults change from NWW to nearly EW distribution gradually, the quantity of faults is fewer from the plane view. On the longitudinal section, the deep faults are more developed than the shallow faults. In Himalayan Period, the boundary faults thrusted and dextral strike-slip associated concurrently. Relatively, the faults of Markit slope hardly developed and mainly distributed in Paleozoic strata. The structural type in Bachu-Markit area includes both basement involved and cover strata decollement. Different fault systems and different faulted segments of the same fault have different structural styles and activity ages. Most of the faults are basement involved, they can provide the favorable channel for hydrocarbon moving upward. Shallow cover strata decollement faults mainly developed in the south edge of Bachu uplift, forming the well preservation conditions for hydrocarbon.The formation of Bachu uplift is the result of the compression of tectonic movements of Caledonian, Hercynian and Himalayan etc. Different tectonic stresses of each period lead to the different structural deformation between the south and north edge of the area. This paper start s from the differentiation of regional evolution, mainly describe the fault shape and styles of structural transfer zone in the south of Bachu uplift. The structural transfer zone contains two types, which are the opposite-thrusting transfer zone in the Selibuya fault belt and the back-thrusting transfer zone between the Selibuya and Kangtakumu fault belts. The complex structure deformation interior of structural transfer zone can control the distribution of strata, be used as the favorable channel for hydrocarbon, and then form effective hydrocarbon traps. In addition, the rapid uplift of Bachu area in Himalayan resulted in the sharp structural slope-break zone develops along the strong thrust fault zone in the north and south sides, which significantly controlled the distribution of depositional system and sand bodies.Through the multi-stage tectonic transforms, the strata are eroded strongly and the eroded strata thickness distribute uneven in Bachu--Markit area. We have divided the filled strata into three first-order unconformity and six second-order unconformity. With the study of the structural deformation characters and unconformity interfaces distribution, we use the tendency method of deposional thickness and structural extrapolation of seismic section method to calculate the eroded strata thickness and paleogeomorphology of Bachu-Markit area. It can figure out the ranges of the palaeohigh and palaeslope in different stages through the palaeogeomorphological features. Combination of the onlap phenomena, it is put forward that Hetian palaeohigh formed in the middle Caledonian, then developed continually from the late Caledonian to the early Hercynian, and disappeared accompanied with the strong uplift of Bachu uplift in the middle to the late Hercynian. Across the evolutionary time, Hetian palaeohigh migrated from southwest to northeast, the range became lager, the trend turned to NE. Hetian palaeohigh as a disappeared palaeohigh is the important place for the early hydrocarbon accumulation.The tectonic evolution of Bachu-Markit area is in closely related to the hydrocarbon accumulation, trap matching, condition of preservation and the source of oil and gas. According to the former analysis, the trap in Bachu uplift is mainly the structural traps controlled by the fault belts, and the trap in Markit slope is usually to be the palaeokarst trap formed under the early Hetian palaeohigh and palaeslope. Putting the development of the tectonic as a clue and tc consider from the favorable structural styles controls the reservoir, combined with the known hydrocarbon accumulation mode, we believe that the favorable zone for exploration in Bachu-Markit area including the shallow overthrust belt in the north of Markit slope, structural transfer zones in south edge of Bachu uplift, Kangtakumu, Gudongshan and Kalashayi fault belts, Manan and Madong fault belts of Markit slope, volcanic zone of PSB1well. |
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