Devonian stratigraphic sequence in the Daguan area of Yunnan Province and its resource potentials of industrial quartz sand

The Devonian System in Daguan County of Yunnan Province is rich in quartz sand resources. The study of stratigraphic sequence in this area can not only contribute to the in-depth analysis of the paleogeographic environment and its variation characteristics of quartz sand formation, but also can reveal the formation and distribution rules of quartz sand with the help of tectonic background, and finally provide theoretical basis for the development of silicon industry. Therefore, based on the field stratigraphic profiling and core logging of shale gas wells, and combined with the paleotectonic background, this paper studied the Devonian profile characteristics in Daguan and Yanjin counties in northeast Yunnan Province with a straight-line distance of less than 50 kilometers. This area is located in the northern margin of Dianqiangui rift in Late Paleozonic, where controlled by the edge facies zone, two sets of high maturity quartz sandstone were deposited in Posongchong Formation and Suotoushan Formation. In general, seven Devonian formations were deposited, including Posongchong, Pojiao, Qingmen, Suotoushan, Hongyapo, Qujing, Zaijieshan from bottom to top in order, but these seven formations are often incomplete and vary very frequently at different locations. Controlled by the pattern of uplift and depression in the rift basin and syngenetic fractures, the sedimentary sequence is often inconsistent in different locations. The Devonian strata witnessed two regressive and transgressive depositional processes, reflecting the formation process from continental shelf construction to carbonate platform, and the strata of each formation are similar to those of stratotype section with certain variety characteristics. On the whole, the resource potential of Suotoushan Formation is better than that of Posongchong Formation. Zhonghe Town of Yanjin County is the most promising development prospect of industrial quartz sand for the Posongchong Formation, and Mugan Town and Huangjingba Town of Daguan County are the most promising prospects for the Suotoushan Formation, which are of guiding significance to the exploration of Devonian quartz sand.