Research On Jurassic Sedimentary And Tectonic Evolution Of The East Sector Of Northern Qaidam Basin

With an average elevation nearly3000m, Qaidam basin is a Meso-Cenozoic intracontinentalbasin, which is in the north of Tibet Plateau, bounded by the Qilian thrust belt in the north, theElashan fault zone in the east, the Altyn tagh fault zone in the northwest, and the Eastern KunlunMountain in the south. What is a critical key to the exploration of the east sector of NorthernQaidam basin is the range and sedimentary features of Jurassic strata in the area, and which is stillunsure. To make the crucial factor clearly, therefore, with the guide of sedimentology and tectonicgeology and the help of the research results acknowledged, the thesis shows a conclusion aboutJurassic tectonic and sedimentary evolution in the area, which is based on outcrop observation andsorts of lab analyses.According to geological surveys in the fields, combined with well and seismic data, Jurassicstrata in the area has been divided into four formations, whose lithology features, marker bed andthe thickness and range have been definite. At the same time, sedimentary factors and facies havebeen identified, with fan-delta and braided-river delta as a primary role in the area.Based on seismic interpretation, the results of balanced cross section and regional geologymaterials, the Jurassic basin tectonic evolution in the east sector of Northern Qaidam basin isdivided into three periods as two stages: rifted basin stage in Early and Middle Jurassic period andcompressive depression basin stage in Late Jurassic period. In the early period of Jurassic, Qaidamplate and surrounded mountains are in an extensional tectonic environment, which is considered asan effect of apotectonic in orogenics. In the Early Jurassic, half-graben fault basin is onlydiscovered in Hongshan area. However, half-graben fault basin has not been extended to the wholeeast sector of Northern Qaidam until Middle Jurassic, and there are several depocenters: Hongshan,Yuqia and Delingha, etc. In Late Jurassic, the weather has changed from wet to dry, and the wholebasin has been uplifted, which has been in a compressive depression basin stage. The three stages of Jurassic basin tectonic evolution is connected with sedimentary evolution, and there are threeJurassic sedimentary cycles in Dameigou:“alluvial fan-braided river-braided-river delta”riftedbasin transgression cycle in Early Jurassic,“fan delta–braided river delta-lacus” rifted lacustrinebasin wide development cycle in Middle Jurassic and “flood plain-shore-shallow lake”depressionwithered cycle in Late Jurassic.Uplifting of Saishiteng Mountain and denudation of J3+K were due to Late Yanshan tectonicmovement. Owing to strong Himalayan movement, abundant intense deformation structures areeasily found in fore-mountain belt like Yuqia, Dameigou, etc, and Aimunike and OlongbulakMountains are uplifted. Today’s tectonic framework that alternating uplifts and depressions isestablished and Jurassic basin has been seriously broken.There are two groups of faults in the area with strike of NW and NE. The fault group of NEcontrols the half-garben basin in Early Jurassic and the fault of NW not only controls thehalf-garben basin in Middle Jurassic, but also controls the strong denudation since Late Mesozoic.Jurassic strata are considered to be reserved well in the lower position in succession since Jurassicera.