湖南慈利江垭中-上二叠统岩石特征及沉积环境分析

湖南慈利江垭剖面中 上二叠统自下而上可以分为栖霞组、茅口组、吴家坪组和大隆组，总厚度为4617 m。该剖面岩以石灰岩为主，含少量的硅岩、泥岩、页岩和白云岩。石灰岩进一步分为砾屑灰岩、砂屑灰岩、粉屑灰岩、生物碎屑粒泥灰岩以及生物碎屑泥粒灰岩。砾屑灰岩主要分布于栖霞组及茅口组中，为斜坡沉积作用的产物。白云岩主要为同生和准同生白云岩，为局限台地环境的产物。根据岩性、微相分析，可划分出滨岸、局限台地、开阔台地、台地边缘、斜坡及盆地6种沉积环境。沉积演化表明，研究区二叠纪发生了两次大规模的海侵，主要发生于栖霞期早期—茅口期晚期以及吴家坪期早期—长兴期晚期。值得指出的是，栖霞组及茅口组中斜坡沉积的发现，对于重新认识研究区中二叠世古地理分布、演化及斜坡的迁移具有重要的意义。

Petrological characteristics and sedimentary environment analysis of the Middle-Upper Permian of Jiangya section,Cili County,Hunan Province

The Permian of Jiangya section at Cili County，Hunan Province is composed of the Qixia，Maokou，Wujiaping and Dalong Formations，with a thickness of 4617 m.The rock types of this section include limestone，silicalites，mudstone，shale，dolomite.Limestone can be further divided into calcirudite，calcarenite，calcisiltite，bioclastic wackestone，bioclastic packstone.Calcirudite developed in Qixia and Maokou Formations formed in carbonate slope environment and dolomite occurred in restricted platform.According to the comprehensive analyses of lithology and microfacies，six kinds of sedimentary environments were identified.They were shore zone，restricted platform，open platform，edge of platform，slope and basin.The sedimentary evolution shows there were two cycles of transgression and regression occurred in Permian，mainly from the early Qixia period to the end late Maokou period and the early Wujiaping period to the late Changxing period.There is no doubt that the recognition of slope facies in the Qixia and Maokou Formations is of great significance for a new awareness of the distribution and evolution of the middle Permian palaeogeography and the migration of slope in this region.