Study On Sequence Stratigraphy And Sedimentary Facies Of The Lower Jurassic Badaowan Formation In The Northwest Of The Junggar Basin

The Jurassic strata in Northwest of the Junggar Basin is beneficial to in-situ leaching sand uranium deposit's enrichment. However, due to the previous studies on the construct of sequence framework and the identify of sedimentary system is controversial, which restricts the development of research work. Thus, this article based on sedimentology and sequence stratigraphy, and on the basis of basin outcrops,drilling cores, well logging and mud logging, we studied the petrology, sedimentary structure, logging facies and sequence stratigraphy of Badaowan Formation. Within the sequence straigraphic framework, identify the distribution rule of sedimentary system, reveals the sedimentary evolution of each period and finally established the sedimentary model of Badaowan Formation.Badaowan Formation's outcrop was good in the researching area, the thickness of strata gradually reduced from east to west, and the strata was fluctuated from northwest to southeast;regional unconformity's effect on stratigraphic distribution in this area made the thickness of formation gradually reduced and thin out from Kebai area to the northeast, southwest and northwest. Meanwhile, the thickness of formation was fluctuated from northeast to southwest, affected to fracture and internal folding deformation. Badaowan sequence stratigraphy and lithostratigraphy were significantly matched. The strata can be divided into three section from bottom to top, and JSQ1?JSQ2?JSQ3 three-grade sequence interface were matched, respectively.Different types of sedimentary facies such as fluvialfacies, braideddeltafacies and lacustrine facies were identified. The fluvialfacies in lower Formation in this area was braided fluvial facies, and main sub-facies were floodplain and riverbed,which can be divided into two micro-facies as floodplain and channel bars;braideddeltafacies in middle and top sections in this formation can be divided into braid river delta plain, braided delta front and former braided delta three types sub-facies, and the braid river delta plain can be separated into sub-facies such as braidedchannel, distributary interchannel, swamp etc. Braideddeltafacies can be separated into micro-facies as underwater distributary channel, underwaterdistributary interchannel, mouth bar etc.Micro-facies of former braided deltacan only find former braided delta mud in this area; lacustrine facies in the middle section of this formation can be divided into two sub-facies as shore-shallowlacustrine and moderate-deeplacustrine, which can be separated into micro-facies as shallow-lakesandbar, shore-shallowlacustrinemud and moderate-deeplacustrine mud etc. The main sedimentary model developed in Badaowan Formation was braided fluvial facies-braideddeltafacies-lacustrine facies.