Research On Tectonic Lithofacies Paleogeography And Source Rocks Characteristics Of The Carboniferous-Early Permian In The Northern Part Of Junggar Basin

The tectonic lithofacies paleogeography of Carboniferous-Early Permian in the northern part of Junggar Basin is a hot issue on the tectonic regime conversion of Paleo-Asian Ocean and its superimposed continental basin, as well as petroleum exploration. In this paper, by the field geological profile survey, the key drilling profiles description and typical sample test analysis, espically using tectonic rock geochemistry and sedimentary facies analysis, the characteristics of tectonic lithofacies paleogeographic and the source rocks of the Carboniferous-Early Permian in northern Junggar Basin are discussed. The major conclusions obtained in this thesis are as follows:Based on field geological investigation, well log observation, detrital zircon U-Pb dating and paleontology analysis of northern Junggar Basin and the adjacent areas, the structural position of the study area and the age of the controversial layers of the Carboniferous-Early Permian in previous study are clear. Also, the lithostratigraphic framework of Carboniferous-Permian in northern Junggar Basin is initially built.According to the geochemical characteristics of the late Carboniferous-early Permian volcanic core rocks of the study area, combined the regional geological background, the tectonic environment of late Carboniferous-early Permian in northern Junggar basin are analysed. The major and trace elements of the volcanic rocks show intraplate magmatic evolution characteristics. The Nb/Zr. Th/Nb and Ta/Hf、Th/Ta ratios of basalts are similar to basalts from intracontinental rift environment. In the dsiscrimination diagrams, the volcanic rocks are loaceted in intraplate environment. By comprehensive study, these volcanic rocks are from intracontinental rift environment.By sedimentary formation and tectonic magmatic activity of outcrops and drilling profiles, the tectonic lithofacies paleogeography of the Carboniferous-Early Permian in different evolution stage in northern Junggar Basin and the adjacent areas are analysed. In early Carboniferous, there are main neritic-littoral facies, and the neritic facies are mainly distributed in Wulungu depression, as well as the littoral facies are mainly distributed in Luliang uplift and northwest margin of the basin. In late Carboniferous, there are main littoral facies with large percentage of volcanic rocks. In early Permian, the north of the study area is high and the south is low, Wulungu depression is uplift old land and the Luliang uplift is shore lacustrine facies and fluvial facies. The northwest margin of the basin is shallow-deep lacustrine facies, the main subsidence area is in Mahu depression.According to the organic geochemical characteristics of source rocks and the tectonic lithofacies paleogeography, the characteristics and distribution of the Carboniferous-early Permian source rocks are anlysed. The maturity of organic matter of Carboniferous-early Permian source rocks has entered relativrly high mature stage. The organic matter types are main Ⅱ2～Ⅲ.The Carboniferous source rocks, controlled by neritic-littoral facies, are mainly distributed in Ludong-Wucaiwan and northwestern margin of Junggar Basin, while the early Permian source rocks, controlled by shallow-deep lacustrine facies, are mainly distributed in the northwestern margin of the basin.