滇东地区下寒武统筇竹寺组细粒岩中结核类型与成因分析

Types and formation mechanism of concretion from the Qiongzhusi formation of lower Cambrian in eastern Yunnan

本文针对滇东地区下寒武统石岩头段与玉案山段细粒岩中的结核进行了研究。主要通过结核与围岩的成分、形态、产状、结核与围岩的接触关系进行了分类及成因分析。发现该区域主要为同生结核及成岩结核,其中砂质结核属同生结核、部分泥质结核及黄铁矿结核属成岩结核。在成因上发现砂质结核的形成与底流溶解—胶结作用有关;泥质结核的形成是早期成岩过程中收缩、层内微拉、机械压实等综合作用的结果;黄铁矿结核主要形成在强还原环境中,沉积作用末期成岩作用早期弱固结的泥岩孔隙中Fe^(2+)与H_2S反应生成胶黄铁矿后进一步结晶脱水,此后在均一性较好的泥质围岩中以"物以类聚"的方式持续生长形成球状黄铁矿结核。本次结核的研究对揭示沉积物早期埋藏和成岩环境有重要意义。

The concretions in the fine-grained rocks of the lower Cambrian Shiyantou section and Yuanshan section have been distinguished in eastern Yunnan.On the cause of formation,the formation of the sandy concretions is associated with underflow dissolution-cementation.The formation of muddy concretions is the result of the synergetic effect of shrinking, layering and mechanical compaction during early diagenesis. The formation of pyrite concretion occurs mainly in the strong reduction environment, during the early diagenesis and sedimentation end, Fe2+in the pores of the consolidated mudstone react with H2 S to form pyrite and further crystallize and dehydrate. After that, they continue to grow in a "cluster-like" manner and are formed in the muddy surrounding rock with good homogeneity.This study of concretions is of great significance in revealing the early burial and diagenetic environments of sediments.