Analysis of Sequence and Sedimentary Facies in Simen Formationin of Lower Carboniferous in the North-central Guizhong Depression

Based on the detailed observation of 20 field outcrop profiles of Shuiyuan Tangxian bisect and Zhongdu Changsheng bisect, and the data of the borehole of Dongtang 1 in the north-central Guizhong depression, this paper, combined with the data of rock sheet, granularity analysis and previous studies, researches the types and its evolution characteristics of the clastic rocks sedimentary facies in the research area. The results show that:①The Simen formation can be divided into one third-order cycles of sedimentation and four fourth-order cycles of sedimentation in the north-central Guizhong depression.②Clastic onshore-tidal flat deposits are widely developed in the Simen formation. There are some lagoon microfacies deposits in some areas. The Shaping microsedimentary deposits are mainly developed in the north of Huanjiang and east of Liuzhou. The microfacies of the Hunjiping is more developed in the whole area. The Niping microfacies is mainly developed in the west of Nandan, the periphery of Yizhou, the north of Liucheng and the edge of Xiangzhou.③In the late Lower Carboniferous, a sedimentary model has been developed in Simen formation of the study area,the onshore-tidal flat phase being widely developed. The above studies revealed the sedimentary evolution rule of Simen formation and meanwhile provided a geological basis for oil-gas exploration.