Characteristics of sedimentary microfacies of the Weining formation and its evolution in the Well Ziye-1, located in southern Guizhou Province, China
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摘要: 贵州南部紫云地区的威宁组以台地边缘藻丘沉积为主要特征.紫页1井钻孔岩芯显示:威宁组总体由台地边缘礁(丘)向局限台地、开阔台地过渡的海退进积层序,其间包括台地边缘藻(丘)、局限台地、开阔台地三个亚相,发育生物粘结岩(SMF7)、有骨屑颗粒的生屑灰泥质颗粒石灰岩/颗粒质灰泥石灰岩(SMF10)、核形石砾屑碳酸盐岩/颗粒灰岩(SMF13)、集合颗粒灰岩微相(SMF17)、均质无生物泥晶灰岩微相(SMF23)、岩屑漂浮岩/砾屑碳酸盐岩/角砾岩微相(SMF24)六个微相;威宁组的沉积充填序列由六个岩性组合基本相同、沉积环境、沉积微相特征大致相似的沉积旋回构成.每一个沉积旋回均以台地边缘礁(丘)相的藻凝块灰岩为主体,向上则渐变为局限台地、开阔台地相的生物碎屑灰岩,表明威宁组至少经历了六次海平面升降变化过程;威宁组的出现代表了罗甸—水城北西向槽盆边缘斜坡相的打屋坝组富有机质泥页岩的终结.Abstract: 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.
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