贵州桐梓松坎二叠系岩石特征及沉积环境分析

 贵州桐梓松坎二叠系剖面是华南二叠系的一条代表性剖面,自下而上依次可以分为栖霞组、茅口组、龙潭组和长兴组,总厚度为484.02m.野外实测和室内研究表明：剖面岩石类型较为单调,主要为石灰岩和页岩,以及少量的白云岩和硅岩.石灰岩进一步可以分为生屑石灰岩、生屑质石灰岩、含生屑石灰岩、泥(粉)晶石灰岩和眼球状石灰岩.眼球状石灰岩主要分布于栖霞组下部和茅口组中下部,为沉积作用和成岩作用共同作用的产物,与上升流关系密切.白云岩主要为呈斑块状分布的石灰质白云岩,主要分布于栖霞组和茅口组,其可能为石灰岩经埋藏白云化作用而形成.硅岩可分为结核状、团块状、条带状硅岩和层状硅岩两种类型;二者皆为交代成因.通过岩性、古生物、沉积构造、地球化学等相标志的分析,划分出了滨岸和碳酸盐岩开阔台地两种沉积环境,其中碳酸盐岩开阔台地内局部出现浅滩环境.沉积演化表明,该地区二叠纪发生了两次较大的海进、海退旋回,第一次海侵始于中二叠世栖霞初期,结束于茅口末期;第二次海侵始于晚二叠世龙潭初期,直至长兴期末结束.

Petrological Characteristics and Sedimentary Environment Analysis of the Permian of Songkan Section, Tongzi County, Guizhou Province

The Permian of Songkan section at Tongzi County, Guizhou Province is a typical section in South China, which is composed of the Qixia, Maokou, Longtan and Changxing Formations with a thickness of 484.02m. The field measurements and lab studies show that the rock types of this section are rather simple, including limestones, shale, dolostones and siliceous rocks. Limestones can be further divided into bioclastic limestones, bioclastic-bearing limestones, microcrystalline-fine crystalline limestones and eyeball shaped limestones. The eyeball shaped limestones were mainly developed in the lower part of the Qixia Formation and the middle to lower parts of Maokou Formation. They were formed by the interaction of sedimentation and diagenesis under the influence of upwelling. The dolostones are dominated by calcitic dolostones distributed in patches. They were mainly developed in Qixia and Maokou Formation, and probably formed by burial dolomitization. Siliceous rocks can be divided into two types of the nodule-, lump-and band-like rocks and the bedded siliceous rocks, which were formed by metasomatism; and the source of silicon is related to the hydrothermal activity. According to the analyses of lithology, palaeontology, sedimentary structures and geochemistry, two kinds of sedimentary environments were identified. They include the shore zone and the carbonate platform, and locally there are shallow banks in the platform. The analysis of the sedimentary environment evolution indicates that two sedimentary cycles of transgression and regression occurred in the Permian. The first transgression began in the Early Qiaxia Age, ended in the Late Maokou Age. In the Early Longtan Age, the second transgression began and lasted until the Late Changxing Age.