Sedimentary Characteristics And Tectonic Background Of The Jurassic In The South And East Margin Of The Junggar Basin

The south and east margin of the Junggar Basin in Jurassic developed well and have clear sedimentary characteristics, which is the ideal stratum of the study on Jurassic sedimentary environment and tectonic background. According to the research of 5 profiles in the south and east margin of the Junggar Basin, we can determine the depositional facies types and characteristics, analyse the source area of the sediment, and remodel the tectonic and sedimentary evolution process of the east margin of Junggar Basin.The main typies of rocks in the study area are conglomerate, sandstone, siltite, mudstone and argillaceous limestone. The main typies of depositional facies in the study area are braided fluvial facies, braided fluvial delta facies, meandering fluvial delta facies and lacustrine facies. In the sediment source area, the Jurassic’s sources of the south margin of Junggar Basin come from Tianshan orogenic belt’s branch-Bogda Mountain; while the Jurassic’s sources of the east margin of Junggar Basin come from Karamori orogenic belt. In the tectonic and sediment area, by the effect of uplift of Bogda Mountain and Karamori Mountain, at different times of Jurassic, the south and north sides of the basin’s eastern part showed different sedimentary facy combinations. In early Jurassic, both the Bogda mountain which on the south side of Junggar basin and the Karamori mountain which on the northeast side of Junggar basin uplifted quickly, then both of the south margin and the northeast margin of Junggar Basin were braided fluvial delta facies, and the interior part of the basin developed semi deep lacustrine- deep lacustrine facies. During this time, Junggar Basin suffered several large scale lake lake transgression, most part of the basin was flooded by lakes, coal seam didn’t develop, and the supply of source is less. In the early middle Jurassic, both the uplift speed of Bogda mountain which on the south side of Junggar basin and the Karamori mountain which on the northeast side of Junggar basin were not fast, then the north and south margin of Junggar Basin are meandering fluvial delta facies. From the late of middle Jurassic to late Jurassic, the Bogda mountain which on the south side of Junggar basin uplift faster, and the south margin of Junggar Basin developed the Tou Tunhe Formation-Ka Lazha Formation’s braided fluvial facies-braided fluvial delta facies; While the Karamori mountain which on the northeast side of Junggar basin uplifted slower, and the northeast margin of Junggar Basin developed the Shi Shugou Group’s meandering fluvial delta facies. During this time, the uplift of the mountains on both sides caused the lake level to fall, the water depth became shallow, and the interior part of the basin changed from semi deep lacustrine facies to Shallow lacustrine facies. At that time, the climate was warm and wet, and the plants growed most prosperous, and the internal basin developed a large area of the marsh environment, when the coal seam development reached the golden period.