Characteristics of sedimentary microfacies of the Weining formation and its evolution in the Well Ziye-1, located in southern Guizhou Province，China

The sedimentary rock of the Weining formation in the Ziyun area is characterized by platform margin algal mound deposits. Intensive study of borehole core from the well Ziye-1 shows that the sedimentary facies of the Weining formation is in total an upward grading sequence due to sea regression taking place under platform marginal reef to open platform environment. Meantime, it includes three subfacies as platform margin algal mound, restricted platform and open platform subfacies which can be further divided into six microfacies, i.e. biological bounded stone (SMF7), bioclastic argillaceous limestone with skeletal fragment/grain lime-argillaceous limestone (SMF10), oncolite rudstone/grained limestone (SMF13), aggregate grained limestone (SMF17)、homogen abiological micrite (SMF23)and clastic floating rock/ rudstone/breccia(SMF24).Sedimentary filling sequence of the Weining formation also consists of six sedimentary cycles which is lithologically similar to the above sedimentary microfacies. Each sedimentary cycle mainly comprises limestone algae clot formed under a platform marginal reef environment. However, the lithology slowly changes to bioclastic limestone produced in upward open platform condition. The results indicated that the Weining formation had experienced at least six times of sea-level fluctuation; Furthermore, The emergence of the Weining formation marked the end of the organic-rich mud shale of Dawuba formation produced at a slope facies along the northwest trough-basin margin in Luodian-Shuicheng area.