Characteristics of Tidal Action Depositional System and Distribution of Sand Body of Silurian in Tazhong Area, Tarim Basin

The 3rd upper sub-member of the Silurian Kepingtage formation is an important exploration and development set in Tazhong area, Tarim Basin, of which the sedimentary system and sand body distribution have been researched in... [ view full abstract ]

The 3rd upper sub-member of the Silurian Kepingtage formation is an important exploration and development set in Tazhong area, Tarim Basin, of which the sedimentary system and sand body distribution have been researched in detail based on the data of core, logging, seismic, outcrop, experimental analysis and the theory of sequence stratigraphy. The results show that it was overlap and edge away layer by layer from northwest to southeast. On the background of transgression, the depositional systems of tidal flat, estuary and tidal delta were developed and controlled by palaeogeomorphology, while different types of sand bodies and sedimentary formations were developed owing to the types and energy of main action water bodies. In the depositional system of tidal flat, the main types of sand bodies are subtidal channels and intertidal sand flat, where subtidal channels show significantly banded distribution vertical to the coast with a complete three-tier structure composed by the lower part of the retention deposition of waterway, the middle of the large cross bedding of medium-fine sandstone and the upper of siltstone and mudstone. The thickness is about 1.5~3m and decreases in the estuary direction, also the particle size becomes fine. This feature was confirmed in the outcrop area. In the estuary deposition system, the sand bodies of channels and tidal bars are common and extend far parallel to the axis of the estuary with thin layers of mudstone. The morphology of the whole estuary is like a bell mouth. The sand bodies of underwater distributary channels are developed with silica, flint gravel layers and large erosion surfaces in the tidal delta depositional system. By above research, the depositional model of tidal flat-estuary-delta in Tazhong area was established and the distribution of favorable sand bodies could be predicted.