Tectono-Sedimentary Evolution And Its Controls On Basic Petroleum Geological Condition Of South Margin Of Junggar

As important component of foreland basin of Central-western China, piedmont structural zone of south margin of Junggar and adjacent area have became the research focus and frontier field. Because of special tectonic position, superimposed and restricted respectively by structure system of multi-stages and synch-stages of Variscan period, Indosinian period, Yanshan period and Himalaya period, margin of Junggar and adjacent area finally became a composite superposition basin, mainly composed of continental deposit of late Paleozoic and Meso-Cenozoic. By the research of the relation between tectonic evolution and enrichment of hydrocarbon, it is conduced to confirm the dynamic process of basin formation action and transformation action of different stage, and provide the sufficient evidence for objective evaluation of the hydrocarbon resource and exploration object optimize.Guided of the dynamics theory of sedimentary basin, approached of the structure-sedimentary research, based on the surface geology, underground geology, geophysical, geochemistry and various analyzing and testing data, mainlined on basin formation action and transformation action, structure character, basin prototype of difference cycle, the structure deformation and 3D structure form and the relation to the enrichment of hydrocarbon of the key time of Meso-Cenozoic are being studied deeply.According to the rock geochemistry and geophysical data, it shows that there are triple basements in Juggar basin: ancient ctystallization basement of Precambrain, folded basement of late-Caledonian and folded basement of Variscan. The structural character since late Carboniferous indicates that there are seven critical moments of tectonic regime conversion between north Tianshan and south margin of Juggar: end of the middle Permian, end of the early Triassic, end of late Triassic, end of Bajocian stage of middle Jurassic, end of late Jurassic, end of early Cretaceous and end of Miocene. Based on critical moments, tectonic sequence in the study area can be divided into four: tectonic sequence of late Variscan period, Indosinian period, Yanshan period and Himalaya period.The main formation time for foreland basin of south margin of Juggar and inner continental orogen-basin formation of north Tianshan area is Himalaya period of Meso-Cenozoic. Tectonic units in the study area can be divided into six parts: Bogda piedmont thrust belt, Yishan piedmont thrust belt, Sikeshu depression, Fukang depression, Changji depression and Santai depression. Bogda piedmont thrust belt is an overthrust nappe, formed in Himalaya period. Yishan piedmont thrust belt is subdivided into two parts: fault-fold belt of Yishan front characteristic of thick-skinned structure and decllement zone of piedmont of Yishan characteristic of thin-skinned structure. Sikeshu depression is divided into three parts: monocline in the south, fold belt in the middle and monocline in the north. According to the basin prototype, tectonic stage can be divided into eight: continent rift vally stage from late Carboniferous to Middle Permian, thrust depression stage from early Permian to early Triassic, concentrating stage in mid-late Triassic, weak extension stage in early-middle Jurassic, thrust depression stage in mid-late Jurassic, depression stage in Cretaceous, steady depression stage from Paleocene to Miocene, the formation stage of intense overthrust belt and foreland basin form Pliocene to Quaternary.According to the relation between structure of Himalaya stage and enrichment of hydrocarbon, three sets of source reservoir cap assemblage are divided: lower assemblage from Permian to Triassic, middle assemblage from Jurassic to Cretaceous, upper assemblage from Cretaceous to Neogene. The tectonic activity of Mio-Cenozoic characteristic of inheritance squeezing action is the main element for hydrocarbon enrichment and reservoir forming.