Deposition mechanism of delta Carboniferous-Permian in Ordos area

Abstract：Based on the observation and description of outcrop and drill cores, correlation of well logging, granularity analysis, identification of rock thin section, the delta formed from Carboniferous to Permian were divided into four types. Variety factors, which control the deposition mechanism of delta, are considered in this classification scheme. These types and fea- tures of delta were controlled by many factors, for instance, paleotopography, river type, den- sity difference between river water and water basin, hydrodynamic condition of water basin, etc. The results are as follows. In the Taiyuan stage of the early Permian, shallow water me- andering river delta develops with epicontinental sea background, and has the characteristics of plane jet, weak underflow and low extension of sand body. It develops shallow water meander- ing river delta in the residual epicontinental sea-coastal lakes background in the Shanxi stage of the early Permian, with the features of axial jet, significant river-controlling effect and lobate plane. Shallow water braided river delta formed in coastal inland lakes grows in Shihezi stage of middle Permian. The sand body extends relatively far due to plane jet~ and mult-stage erosion and overlay are obvious. There is the inland lake delta developed in the Shiqianfeng stage of late Permian.