Eustatic and tectonic control on the evolution of the Jurassic North Qiangtang Basin, northern Tibet, China: Impact on the petroleum system

The Qiangtang Basin is the largest Mesozoic marine hydrocarbon-bearing basin in China. Investigating its tectonic and sedimentary evolution is therefore relevant for hydrocarbon exploration. Here we present a detailed stratigraphic and sedimentological analysis of five Jurassic stratigraphic sections in the North Qiangtang Basin. Nineteen facies associations were identified and allowed us to reconstruct changes of water-depth. The North Qiangtang Basin experienced two transgressive-regressive cycles during the Jurassic. The first cycle started in the mid-Jurassic (Bajocian-Bathonian), with braided-river and floodplain sediments passing up-section to tidal flat and eventually inner-to mid-ramp deposits. Tidal-flat deposition resumed during the Callovian. The second cycle began in the Late Jurassic (Oxfordian) with transgressive inner-to mid-ramp sediments followed by a shallowingupward trend during the late Oxfordian, leading again to tidal-flat sedimentation in the Kimmeridgian-Tithonian. Petrographic analysis and detrital-zircon geochronology indicate provenance constantly from the Hoh Xil-Songpan Ganzi terrane, Kunlun arc, and central Qiangtang. Because Jurassic magmatic activity and active syn-depositional faults have not been reported, and steady detrital supply indicates a stable tectonic environment, eustatic change is inferred to represent the principal control on sedimentary evolution in the North Qiangtang Basin during the Jurassic. A comparison with the Amu Darya Basin in central Asia, characterized by similar sedimentological conditions and distribution of reservoir and source rocks, emphasizes the importance of eustatic control for the development of the source-reservoir-seal system of the North Qiangtang Basin.