Prototype And Evolution Of Shihezi Formation,Yanchang Formation Basin In Southern Ordos And Its Adjacent Region

Southern Ordos and its adjacent region is the geological area, which is located south of the Caobi-Laolongshan-Shengrenqiao tectonic belt and north of Shangdan tectonic belt. Geologically, it includes the area of Weibei uplift in Ordos basin,Weihe graben,Xiaoqinling structural belt and North Qinling tectonic belt. Where was the south border of Ordos Basin in Shihezi formation and Yanchang formation sedimentary periods had always been one of the hot and key issues in geological research of southern Ordos Basin. The solution of this problem will affect and determine not only the confirmation of the nature and scope of Middle Permian and Late Triassic Ordos Basin, but also the objective recognition to the distribution of the sedimentary facies belts of Shihezi and Yanchang formation in southern Ordos basin. The research of this thesis will focus on solving two problems,one is the south border restoration of Ordos Basin in Shihezi formation and Yanchang formation sedimentary periods; the other is to discuss Middle Permian and Late Triassic structural formation and evolution of North Qinling tectonic belt influence on tectonic-sedimentary characteristic in the same period of southern OrdosTaking plate tectonics and basin analysis as guiding theory,ground geological survey as basis,geochemical analysis and test of relevant rock samples in research area as method, combining with systematical explaination and analysis of existed exploration wells and geophysical data, using the way of drawing up the figures of strata thickness,tectonic pattern of each sedimentary stage,constitutional diagram of heavy mineral,clastic constitution triangular plot and major element,trace element geochemical diagrams,this paper makes a analysis and contrast of Shihezi formation and Yanchang formation substance source of southern Ordos Basin with North Qinling region and also discuss the strcutural attribute of source area.Based on above studies,reappear the prototype and evolution process of southern Ordos and its adjacent region in Shihezi formation and Yanchang formation sedimentary periods.The results of the study show that Shihezi formation of the southern margin of Ordos basin and Shihezi formation of North Qinling region have the similar source provenance composition and consistent tectonic background; Yanchang formation of the southern margin of Ordos basin and Yanchang formation of North Qinling region also have the similar source provenance composition and consistent tectonic background.So deduce that the south border of Ordos Basin had crossed Luonan tectonic belt and maybe reached North Qinling and the more southerly region in Shihezi formation and Yanchang formation sedimentary periods.