塔里木盆地下奥陶统白云岩类型及其成因

Classification and origin of the Lower Ordovician dolostone in Tarim Basin

下奥陶统白云岩是塔里木盆地最现实的重点勘探领域。文中在分析塔里木盆地早奥陶世构造、沉积及古气候等地质背景的基础上,以前人对白云岩的结构分类为基础,从白云岩发育产状出发,将塔里木盆地下奥陶统白云岩划分为灰岩中零散白云石、灰岩中斑状白云石、层状白云岩和沿断裂分布白云岩4类,白云石含量层位上自下而上具有总体减少的趋势。各类白云岩在岩石学特征和发育分布上具有较为明显的差异,局部可重叠出现。灰岩中零散白云石和斑状白云石的岩石学和地球化学及发育分布特征均反映其主要由浅埋藏白云石化作用形成;层状白云岩和沿断裂分布白云岩形成于中深埋藏白云石化作用;各类白云岩的产状特征差异受控于沉积期海平面变化、海水性质及埋藏条件等因素。沿断裂分布白云岩的形成和分布与断裂密切相关,是重要的储集岩石类型。白云岩储集层的形成主要是后期改造的结果,埋藏白云石化作用并未对大规模白云岩储集层的形成起到建设性作用,伴生或后期流体再运移导致的溶蚀作用为其主要成因。

Dolostone of the Lower Ordovician in the Tarim Basin is the most practical exploration target.In this paper,based on the Early Ordovician of tectonic,sedimentary,and palaeoclimate setting of the Tarim Basin,considering the former classifications of dolostone according to the structure,the Lower Ordovician dolostone of the Tarim Basin according to the development and occurrence has been classified as： scattered dolomite in limestone,mottled dolomite in limestone,bedded dolostone,and dolostone related to faults,and the content of dolomite in strata decreases upward.Four dolostones have different features of lithology and occurrence,and they can occur superposably.Features of lithology,geochemistry and occurrence of scattered,mottled dolomite in limestone have revealed their origin of shallow burial dolomitization,and bedded dolostone and dolostone related to faults are formed during moderate-deep burial dolomitization.Their origin and occurrence diversity are controlled by the changes of seawater level,seawater property,and burial environment.Dolostone related to faults,which constitutes important reservoirs,appear to be related closely to the faults in origin and/or in occurrence.Furthermore,it is concluded that the burial dolomitization failed to exert the constructive effects on the formation of dolostone reservoir,while the dissolution caused by migration of fluids in late periods is the main origin.