中上扬子地区二叠纪缺氧环境

摘要

The anoxic environments of the Permian of Middle and Upper Yangtze Area are well developed, and the rocks of anoxic deposits are mainly composed of black shale, black thin-bedded siliceous rocks, dark grey to grey black thin to medium bedded lime-mud limestones and mud bearing limestones.The former three rocks always form the dark color shale, thin-bedded siliceous rocks and lime-mud limestones assemblage, and mud bearing limestone is the “eyelid” part of eyeball-shaped limestones. Then the petrological, palaeontological and geochemical characteristics of these two assemblages have been studied, and origins of the anoxic environments have been analyzed. The results reveal that the former assemblage is the product of basin, basin margin or slope environments, and the anoxic environment is formed by the great scale transgression; and the “eyelid” part of eyeball-shaped limestones should be the product of carbonate open platform environment, and its anoxic environment results from the upwelling.%中上扬子地区二叠纪缺氧环境较为发育,缺氧沉积的岩石类型主要为黑色泥页岩、黑色薄层硅岩、深灰色-灰黑色中-薄层泥晶石灰岩和含泥石灰岩.前3种岩石类型常形成暗色泥页岩-薄层硅岩-泥晶石灰岩组合,而含泥石灰岩则主要为眼球状石灰岩的"眼皮"部分.分别对这两种组合的岩石特征、古生物特征及地球化学特征进行了研究,并分析了各自的沉积环境以及缺氧环境的成因.分析认为暗色泥页岩-薄层硅岩-泥晶石灰岩组合为盆地、盆地边缘或斜坡环境的产物,其缺氧环境主要为大规模的海侵形成;眼球状石灰岩的"眼皮"部分应为碳酸盐岩台地的产物,其缺氧环境应为上升流作用形成.