Characteristics of Sedimentation Evolution Based on the Sequence Stratigraphic Frameworks in Shahezi Formation of Southern Xujiweizi Fault Depression

Many scholars in China introduced the theory of sequence stratigraphy,applying to Chinese continental fault depression lake, they have made a lot of achievements in scientific research. However, there are still a lot of controversy according to the establishment in Shahezi group of sequence stratigraphic framework in Xujiaweizi fault depression.Sequence boundary identification method in this paper is based on the “instruction of Vail’s sequence stratigraphy theory, identification of seismic unconformity, verification by using logging methords”. And, following the principle of isochronous ,sequence stratigraphic framework of this region is established clearly. The southern Xujiaweizi fault depression in Shahezi group is divided into 1 second grade sequence, in the interior distributed SQ1-SQ4 4 third grade sequences from the bottom. Developmental stages at the bottom of SQ1 and the top of SQ4, basin is small and water is shallow. However, Developmental stages in SQ2 and SQ3,water enters the lake basin continuously, formed a sedimentary background of “wide basin and deep water”. In addition, each of the three grade sequence has split structure, the lake transgressive domain and lake regression domain two system tracts. Besides, the reversed order para-sequence sets caused by the lake regression and progradation set on the positive para-sequence sets caused by the lake transgression and retrogradation. On the basis of sequence stratigraphic division and correlation, conbined with the regional construction and the supply of provenance ,the sedimentary sequence framework of evolution characteristics are studied.That fan delta,braided river delta, lacustrine are the main facies types in study area. Characteristics of sedimentary evolution there are like this: the characteristics of sedimentation evolution show framework controls sand, succession of evolution, separated-source sedimentary, contiguously distribution.