Study On The Restoration Of Erosion Thickness And Palaeostructural Evolution In The Key Tectonic Period Of Multiple Unconformity Plane Overlapping Areas In The Tabei Area

The Tabei area is one of the most oil and gas-rich blocks in the Tarim Basin.Clastic rock structures and carbonate karst oil and gas reservoirs are the two most important types of reservoir formation in this area,such as formation lithology and deep subsalts.Subtle oil and gas reservoirs have become the main exploration targets in the future.The area has experienced multiple periods of intense tectonic movement and stratigraphic erosion.The Cambrian subsalt dolomite and Ordovician karst and overlying clastic rock accumulations have all received the transformations and impact of ancient structures in various periods.Due to multi-stage tectonic uplifts and denudations,the Upper Cretaceous of the Yakela fault block is directly overlying the Proterozoic metamorphic rocks and some Sinian-Cambrian systems.It is not clear how the extremely thick Ordovician-Triassic system was eroded.Therefore,the staged erosion thickness restoration and paleo-structural studies are very important for understanding the hydrocarbon accumulation in this area,especially the deep Cambrian-Sinian oil and gas exploration in the Yakela uplift.Affected by the South Tianshan Mountains,the northern Tarim area has many erosion stages,large thicknesses,multiple strata involved,complex truncation relationships and rapid plane changes,making it difficult to recover the erosion volume using existing methods.In this study,through in-depth dissection of the development history of the Luntai fault in the southern boundary of the Yakela fault convex,the types and methods of the basin boundary in the study area at various stages,and other methods,we strive to accurately restore the amount of erosion in each key tectonic period,including the Yakela fault block.Three dimensional seismic data of yakla area show that Luntai fault is continuous in east-west direction and its activity intensity gradually increases from west to East.It is mainly developed in the late Hercynian,which is the result of the scissor type orogeny of the South Tianshan Ocean from east to west.During this period,the hanging wall of the fault experienced a sharp uplift,which is the main reason for the lack of pre Jurassic strata on the eastern side of the Yakela fault block.Since then it was further affected by the Indosinian movement,but the activity intensity is much less than before.The results of erosion thickness restoration at the end of Silurian in the south of the fault show a trend of thinning to the north,indicating that the Luntai fault did not form or the distance between faults was small during this period,which did not have a great impact on the erosion thickness restoration.The basin boundary types of each period in the study area can be divided into four types: sedimentary boundary,denudation boundary,sedimentary boundary and denudation boundary,sedimentary boundary in the study area was destroyed.The Upper Jurassic is the sedimentary boundary.the Yuqi Formation,Sinian,Middle and Lower Ordovician are the denudation boundary.The Middle Lower Jurassic and Upper Devonian are the denudation and sedimentary boundary.The Permian,Lower Carboniferous and Upper Ordovician Middle Lower Devonian are the fourth types.Combined with the characteristics of multiple basin boundary types and complex geological structures in Tabei area,it is subdivided into two models based on the methods of sedimentary thickness restoration.Model 1 is the same as the previous trend analysis method,and the model 2 is to restore the original sedimentary thickness with the aid of the original sedimentary thickness of 0 denudation point and the basin boundary.In view of the lack of pre Jurassic strata on the east side of the Yakela fault block,this paper proposes a method of correlation of denudation intensity based on the main activity history of the fault,and uses it to split the denudation amount.By using this method,the denudation amount in the key structural period in the northern Tarim area can be recovered.the denudation intensity was the biggest in the late Hercynian,followed by the Early Hercynian and Indosinian,followed by the first act of middle Caledonian?the third act of middle Caledonian and the Yanshanian.The denudation range is the smallest in the first and third episodes of middle Caledonian,followed by the Early Hercynian,and almost the whole area experienced denudation in the late Hercynian,Indosinian and Yanshanian.From middle Caledonian to Early Hercynian,the denudation center moved to Southeast.In the late Hercynianhe denudation center moved to Yakela fault block.In Indosinian,it inherited the basic pattern of Early Hercynian,and in Yanshanian it moved out.According to the paleostructural map and equilibrium section of each key interface,the prototype of Shaya uplift has been basically formed in the middle Caledonian period,and the pattern of two convexes and two depressions appears in the Early Hercynian period.In the late Hercynian period,Yakela fault block and Korla nose convexity are the secondary structural units of Shaya uplift,which are separated by faults.From the perspective of denudation and paleostructural recovery,the high-yield wells of Middle and Lower Ordovician are mainly located in the x-conjugate fault in the middle Caledonian and the denudation area in the Early Hercynian,and the oil and gas reservoirs of Triassic are located in the southwest of the Yanshanian paleoanticline.