四川盆地下奥陶统桐梓组白云岩多元成因

四川盆地下奥陶统桐梓组白云岩的成因研究较少,模式存在多样性,尚未达成共识.通过系统的岩心观察、薄片鉴定、地球化学分析等方法,在四川盆地桐梓组识别出晶粒白云岩、颗粒白云岩和含石英白云岩及含白云质石英砂岩等与白云石相关的岩石类型.地球化学分析揭示不同类型白云岩具有不同的地球化学特征及白云石化机理,晶粒白云岩的MgO含量与C...

Multi-Origin of Dolomite in Lower Ordovician Tongzi Formation of Sichuan Basin,Western China

The origin of dolomite in Tongzi Formation of Lower Ordovician in Sichuan Basin has been studied less,and there are various models,and no consensus has been reached.Through the system’s core observation,thin slice identification,geochemical analysis and other methods,dolomite-related rock types such as dolomite,granular dolomite and quartz dolomite and dolomitic quartz sandstone are identified in the Tongzi Formation of the Sichuan Basin.Geochemical analysis reveals different geochemical characteristics and different dolomitization mechanisms of different types of dolomite.MgO and CaO values of grain dolomite show obvious positive correlation,with relatively highδ¹⁸O_PDBvalue,δ¹³C_PDBvalue,Sr value and higher Mg/Ca ratio,and lower Fe and Mn values,which is considered to be the cause of dolomite evaporation pump dolomitization.Class A containing quartz dolomite and dolomitic quartz sandstone has similar geochemical characteristics to grain dolomite,and also formed in the quasi-simultaneous period of dolomitization.The MgO and CaO contents of the granular dolomite show a weak negative correlation.Theδ¹³C_PDBvalue and theδ¹⁸O_PDBvalue are basically consistent with the distribution range of seawater carbon and oxygen isotope values.The Sr content is relatively high,which is considered to be the cause of reflux infiltration of dolomitization.Class B containing quartz dolomite and dolomitic quartz sandstone develops only in the local area near the provenance,and the contents of MgO and CaO are positively correlated.Theδ¹³C_PDBvalue and theδ¹⁸O_PDBvalue show a significant negative bias.Compared with other two types of dolomite,Class B has higher Al₂O₃,Fe,Mn contents and relatively lower Sr content,and are affected by the mixing of terrestrial debris.In summary,it is believed that it is the dolomitization of mixed water.The Tongzi Formation in the Sichuan Basin has coexistence characteristics of three types of dolomitization,and the mechanism of the Upper Cambrian dolomitization is inherited.