川中地区龙王庙组洞穴充填物特征及油气地质意义

摘要

依据洞穴充填物岩性、孢粉化石、主元素、痕量元素和稀土元素特征分析，结合区域构造演化资料，探讨了川中下寒武统龙王庙组大型洞穴的形成时期和充填过程。洞穴充填泥中孢粉化石时代为石炭纪—早白垩世，泥质岩具有高 B 含量、低 Sr／Ba、稀土元素配分模式差别大的元素地化特征。认为龙王庙组洞穴主要形成于石炭纪—早二叠世古隆起大规模隆升暴露期，为风化壳喀斯特作用和顺层喀斯特作用叠加形成的，并经历了石炭纪—早二叠世的沉积充填和潜流携带古隆起高部位物质充填，及中生代—新生代构造活动期地表水携带溶解残余物沿断裂下渗充填过程。邻近龙王庙组尖灭线，受石炭纪—早二叠世风化壳喀斯特作用和顺层喀斯特作用影响的颗粒滩发育带为川中龙王庙组储层发育最有利地区。%Large scale paleo-caves occur in the rocks of Lower Cambrian in the central Sichuan Basin. Based on the analysis of lithology,sporopollen fossils,major elements,trace elements,rare elements and regional tectonic evolution,the forming time of paleo-caves and their filling processes are studied. It reveals that the sporopollen fossils belong to Carboniferous to early Cretaceous,and element geochemistry of the argillaceous rock shows high B content,low Sr/Ba and various rare earth elements distribution.Superimposed processes of weathering and bed-parallel karstification involved in the formation of paleo-caves during Carboniferous to early Permian.It experienced sedimentation and filling of materials brought by underflow from exposed high lands.Also,surface water carried dissolved materials migrating along the faults during Mesozoic to Cenozoic period.Grain shoal belts, near Longwangmiao Formation pinch-out line which is affected by Carboniferous to early Permian weathering and bedded karstification,are favorable areas for formation of reservoir in central Sichuan Basin.