The Analysis Of Prototype Basin Of Kongquehe Region In Tarim Basin

Tarim basin has been rebuilt by the tectonic movements many times throughout its whole geological history and constructed into a superposition basin including certain basin types. It is important to analyze the basin types in each stage of Tarim development for studying the tectonics and sedimentary controls. The original basin types developed in Kongquehe area of Tarim basin discussed from three aspects are as follows: local structural style, tectonic evolution and sedimentary fillings of basins in. this paperFour sorts and eight kinds of local structural styles identified are as follows in this paper: 1 .basement—involved structural assemblage including a. thrust block— fault structural assemblage (Longkou 3rd anticline), b. fault—terrace reverse structural assemblage (Laokaiping 1st anticline), c. compressive thrust structural assemblage (Line a222—952), d. middle compressive fault—folds structural assemblage (Weimake 2nd anticline) and e. buried hill drape structural assemblage (Kunan buried hill drape structural zone), 2.cover — detachment structural assemblage including a. Imbricate thrust structural assemblage (Kunan structural zone) and b. compressive thrust folds structural assemblage, 3.slightly deformed folds of detachment structural assemblage (Caohu sag), 4.diapiric folds structural assemblage (Line Tbb91—n203). On plane, these local structures are shown as dome, long—axis anticline, fault nose and fault anticline. The distributions of local structural styles are analyzed on the four reflecting surfaces: T₉⁰ ,T₇⁰ ,T₅⁰ and T₃¹ separately, corresponding to four main stage of basin development : Cambrian— Devonian ( ∈—D) , Carboniferous—Triassic(C—T), Jurassic—Cretaceous (J—K) and Tertiary—Quaternary (R—Q) .Balancing cross sections is an important method to study tectonic evolution.The tectonic evolution is generalized into three tectonic cycles and seven evolution stages by studying six balanced cross sections (E—W: Line CH03—113EW, Line KQH02—948EW, Line KQH02—952, S—N: Line CH03—140-148.9SN , Line KQH02—225SN, Line KQH02—302SN) as follows: I .Sinian—Devonian (Z—D) breakup—close cycle of craton including 1 .Sinian—Ordovician craton's marginal aucolgon developing stage, 2.Silurian—Devonian (S—D) compressive uplift stage, II .Carboniferous—Triassic (C—T) breakup—close cycle of craton including 1 .Carboniferous — Early Permian intecraton's depressive stage, 2.1ate early Permian hinterland thrust —strike slipping stage, 3.late Permian—Triassic foreland stage, III Jurassic—Quaternary(J—Q) extension—compression cycle including 1.Jurassic—Paleogene downwarping faulted stage, 2.Neogene—Quaternary rebirth foreland developing stage.Tectonic evolution in every stage was controlled by the regional tectonic background at that time. In Sinian, northeast margin of Tarim plate was passive continental margin. Extensional movement of the continental margin constructed Kuruktag—Manjaer aucolgon. The aucolgon began in Sinian and early Cambrian and ended in late Ordovician. During Silurian—Carboniferous, the northern Tarim plate was active continental margin. Northern paleooceanic plate subducted under the continental margin of northern Tarim plate, which formed a complicated island arc—trench—back-arc basin (marginal sea basin)system. In early Permian, the south of Tarim plate was next to paleotethyan plate. The subduction of the paleotethyan plate made accretionary subductional melange and volcanic arc of Kunlun continental margin formed. The main plate activity in Triassic was collision between Tarim plate and Qiangtang block. During Jurassic—early Tertiary, there was a collision between Himalaya—Gangdisi mountain arc and Eurasian plate. The sea ofYaluzangbu river had finally closed during Neogene—Quaternary.The characteristics of the basin fillings can reflect its development of basin at that time. So sedimentary fillings in this area are analyzed according to the characteristics in both vertical development and panel distributions.From Cambrian to Ordovician, sedimentary facies are that of trough—basin on the background of craton breakup. Lithology is mainly black quartzite and argillite, containing abyssal biofossil assemblage such as radiolarian and so on. However, in middle and late Ordovician, Kuman aucolgon was being on filling stage, so thick rift sediment deposited in the basin.During Silurian—Devonian, the region was in compressive and uplift stage. Seawater became shallow, and formed a sort of shallow —shelf —shore line facies. The lithology is gray, gray—green, red silt-sandstone. In Devonian seawater became shallower than before, furthermore climate was very torridity and sediment supply was abundant. As a result, a sort of brown—red, aubergine sandstone n siltstone and mudstone deposited. In latter, mudstone decreased and sandstone increased at the same time.In Carboniferous, the facies of the northeast of Tarim were open platform facies , restricted platform and tidal flat, moreover sediments distributed widely throughout all the basin. Lithology were conglomerate—bearing sandstone, mud limestone, sand—bearing limestone and so on.In Triassic, the study area was in foreland basin developing stage, sedimentary assemblage were with obvious characteristics of foreland basin. The sedimentary area of Triassic was smaller than before, and sediments were mainly composed of sandstone , mudstone including conglomerate and coal. The sedimentary facies were lacustrine and delta facies. The depressive center located onKuche depression and Manjiaer sag in front of paleotianshan mountain. Sedimentary thickness became thinner from north to south with from 500 to 1500m. The characteristics of foreland depressive basin are very obvious.The sedimentary area were large, and distributed widely at Jurassic .Most of wells encountered this set of strata. The wells' sequence of Caol,. Cao4 and Cao6 suggests that the sedimentary facies of Jurassic are shore lake , swamp, shallow lake, semi—deep lake facies. Lithology is sandstone, siltstone and mudstone including coal.The study area was in the extensional background. During Cretaceous. The characteristics was peneplanation and the sedimentary environments were steady lake and river with gentle layers. Its thickness increased slowly toward basin and tectonic movements were slight.prototype basin analysis of each stage of Kongquehe area in Tarim basin are according to local structual styles, balanced cross sections, basin fillings1 .Sinian rift basinIn early Sinian, Tarim block occurred extension, and the rift basin (inte— continental rift) developed in the margin. There was obvious difference between south and north bounded by Xingdi fault.2.Cambrian—early Ordovician rift or aucolgon basinIn early Cambrian, the aucolgon depressed to a large extent and deposited a sort of abyssal basin sediments reflecting a lower supply.3.Middle and Late Ordovician compressive flexure basinJunggar oceanic plate subducted forwards the South of Middle Tianshan block, accompanied by arc and volcanism. The backarc extension occurred in the Southern Tianshan ocean to the north of Tarim block, resulted a compressive background in atthe north margin of Tarim blockt. The Kunlun ocean started to subduct forwards the Kunlun block in the south of Tarim block, forming Middle Kunlun island arc. So in that case, Tarim block is concerned, there is a press from the south. The basin had changed from extension to compressive flexure. During late Ordovician, sedimentary style with lower supply disappeared gradually. The basin had been turn into filling basin, and the sedimentary thickness were very large.4.Silurian—Devonian compressive flexure basinIn Silurian, Northern Kunlun ocean plate subducted forwards Kunlun block. Middle Kunlun island arc and Tarim plate occurred arc—continent collision. Junggar oceanic plate subducted forwards Middle Tianshan block, Southern Tianshan oceanic plate subducted under Middle Tianshan oceanic plate. In Devonian, the southern margin of basin were in inter—continent compressive background owing to a collision between Tarim plate and Kunlun island arc.5.Carboniferous inter—continental depressive basinThe study area is inter—continental depressive basin under the influence of the closes of South Tianshan oceanic6.Permian basin with foreland charactersIn the last stage of ealy Permian, the basin formation resulted in the intense compression and erosion due to the oblique collision between the northern margin of Tarim plate and Middle Tianshan island arc resulting in that strong compression and thrust and forming large-scale nappe, accompanied by slid-strip leftwards.7.Triassic foreland basinIn Triassic, it is main driving factor of foreland basin's development that subduction of paleotethyan plate and Qiangtang block and Tarim block collide.8. Jurassic and Cretaceous depressive basin...