安徽巢湖下三叠统殷坑组瘤状灰岩成因研究

Genesis of nodular limestones from the Lower Triassic Yinkeng Formation in Chaohu region

从碳、氧同位素、化学成分、矿物组成及岩石的结构、构造等特点出发,探讨安徽巢湖地区下三叠统殷坑组瘤状灰岩特征及成因机制。结果表明殷坑组瘤状灰岩在纵向上表现为成分组成及结构、构造有差异的瘤体和基质2部分呈明显的韵律性发育的特征,碳、氧同位素等地化特征表明瘤状灰岩是在较深的水体中沉积,其形态受沉积环境所控制形成了上斜坡带断续状瘤状灰岩、下斜坡及深水盆地的顺层条带状瘤状灰岩,形成机制是沉积和成岩作用改造依次增强的结果,形成过程主要受气候变化及周期性的瞬时动荡水体(洋流、底流)的作用形成瘤状灰岩锥形,再经过成岩差异压溶作用的“细颈化”作用,最终形成了巢湖地区宏观结构特征鲜明、微观演化特征差异的瘤状灰岩沉积。

Based on the characteristics of carbon-oxygen isotope,chemical composition,mineral composition and rock structure,this paper discusses the characteristics and genetic mechanism of nodular limestone from Yinkeng Formation of the lower Triassic in Chaohu region,Anhui province.The results show that the nodular limestone in the Yinkeng Formation in this area was composed of different tumor bodies and matrix with obvious rhythmic development in the longitudinal direction.The carbon-oxygen isotopic geochemical characteristics indicate that nodular limestone is deposited in deep water,whose shape is controlled by sedimentary environment.There are two types of nodular limestone in this area including intermittent limestone formed in slope zone and banded nodular limestone in deep water basin.Its development is the result of the gradual enhancement of deposition and diagenetic transformation.The formation process is mainly affected by climate change and periodic instantaneous turbulent water bodies(ocean currents and bottom currents)to form nodular limestone rudiments.Through the“necking”of diagenetic differential pressure and dissolution,the nodular limestone deposit was finally formed with distinct characteristics in macro-structure and in micro-evolution and different characteristics in micro-evolution.