塔里木盆地中央隆起中部中下奥陶统白云石类型及形成机理

根据岩心及薄片观察,按照矿物晶体的大小、形状以及自形程度的差异,将塔里木盆地中央隆起中部中下奥陶统碳酸盐岩地层中的白云石分为6种类型,包括泥微晶白云石、粉—细晶自形—半自形漂浮状白云石、粉—细晶半自行—他形白云石、粉—细晶自形(环带)白云石、细—粗晶他形白云石、粗晶鞍形白云石。综合不同类型白云石的结构特征、碳氧锶同位素值、阴极发光等特征,认为中下奥陶统白云石主要由三种成岩作用形成:泥微晶白云石主要是在准同生期由回流白云石化形成;大部分粉—粗晶白云石是在埋藏期由埋藏白云石化形成,其中浅埋藏期是大规模白云石化的阶段;粗晶鞍形白云石主要由与高温热液活动相关的热液白云石化形成。

Classification and Diagenetic Mechanism of Middle-Lower Ordovician Dolomite in the Middle Part of Central Uplift,Tarim Basin

Middle to Lower Ordovician carbonate rocks are extensively distributed in the middle part of Central Uplift,Tarim Basin.As the dominant mineral of the carbonate rocks,the dolomite is analyzed in genesis.By observation of the rock cores and thin sections,six types of dolomites can be divided according to the different size,shape and euhedral texture of dolomitic crystals.Combined with the structural feature,the stable C and O isotope and Sr isotope analysis and the microscopic cathodoluminescence,it is considered that the Middle to Lower Ordovician dolomites formed in different diagenesis.Micritic and microcrystalline dolomites are formed by refluxion dolomitization during penecontemporaneous stage.Most of microcrystalline dolomites are formed by burial dolomitization during buried stage,in which a wide scale of dolomitization was during shallow buried stage.Coarse-crystalline saddle dolomites are formed by hydrothermal dolomitization during hydrothermal stage.