再论安徽沿江地区中二叠统栖霞组砾屑灰岩的成因

Re-discussion on the Origin of the Rudstone in Middle Permian Qixia Formation along Lower Yangtze River of Anhui Province

安徽沿江地区中二叠统栖霞组地层厚度大,有机质含量高,保存条件良好,其广泛发育的砾屑灰岩也是人们重点关注的对象。但对砾屑灰岩的成因一直存在不同的观点,这对下扬子地区二叠纪古地理恢复及油气勘探等无疑是一种制约。因此,确定栖霞组砾屑灰岩的成因及沉积相意义重大。根据砾石的颜色、含量、产出形态、粒径和圆度等,本文将栖霞组砾屑灰岩分出四种不同类型。综合国际上对砾屑灰岩的成因认识及前人对本区的研究成果,并结合本文研究,对栖霞组砾屑灰岩的成因进行深入讨论。讨论结果显示,砾屑灰岩应为斜坡沉积产物。另外,由于斜坡坡度的差异,分别发育不同的砾石形态、砾石与基质的组合及岩相特征。栖霞组砾屑灰岩的斜坡相沉积可以进一步分为斜坡上部、斜坡中部和斜坡下部。

The Middle Permian Qixia Formation along Lower Yangtze River in Anhui province is very thick, with high organic content and well-preserved condition, the well-developed rudstone is also the key attention object. But about the origin of the rudstone has different viewpoints. Undoubtedly, this is an imperfection for reconstruction of the Permian paleogeography and oil--gas exploration along Lower Yangtze River area. Therefore, it is significant to ascertain the origin and sedimentary facies of the rudstone in the Qixia Formation. According to the colour, content, appearance, size and roundness, writers differentiate 4 types of rudstone. Summarizing international understanding of the origin of rudstone and previous study of this area, combining with this study, in-depth discussion has been made on the origin of the rudstone. The result showing that the rudstone is formed in slope. In addition, because of the difference of gradient, it respectively developed different gravel shapes, gravel and matrix assemblages, and microfacies＇characters. Clinothem facies of the rudstone can be further divided into upper slope, middle slope and lower slope.