Sedimentary Characteristics and Development Model of Shallow-water Delta of Salt Lake in Qianjiang Depression

The Qianjiang depression of Jianghan basin develops a sedimentary system in shallow-water delta. Its formation, evolution and development model have some similarities and also differences with the freshwater environment because of high salinity of the lake basin. Based on 3D seismic, well logging, core and geochemical data, this paper clarified the depositional characteristics and development model of shallow water deltas in this area. The lacustrine mudstone of Qianjiang Formation in Qianjiang depression is lighter in color; light red mudstone can be seen in some wells, and mud cracks are common in mudstone with high Mn/Fe ratio and Sr/Ba ratio, being shallow sedimentary environment of salt lake. Detrital materials are transported over long distances by means of the strong sand-carrying capacity of the salt lake water body. The relatively high-density sand-carrying water masses sink to form underwater distributary channel sand bodies or turbidite sand bodies. The relatively low-density sand-carrying water masses are suspended or floating under the support of the salt water in the lake basin and are further transported towards the lake basin, forming beach bar sand or sheet sand bodies on the far shore. The study area is mainly shallow-water delta front subfacies, including various types of microfacies such as the end of underwater distributary channel, mouth bars, sheet sandsand distal bars. Thus, a shallow delta sedimentary model on the far shore of the salt lake was established during the deposition of the Qianjiang Formation. This model clarifies the distribution characteristics and development mechanism of the sand bodies, and provides a theoretical basis for rolling exploration and later development in the study area.