湖北大峡口剖面下三叠统岩石学特征及沉积环境

湖北大峡口剖面下三叠统层位齐全,界线清楚,出露良好,沉积构造发育,是研究鄂西地区下三叠统的理想剖面。该区下三叠统自下至上可划分为大冶组和嘉陵江组,总厚度1 204.47m,是一套碳酸盐岩沉积,以石灰岩和白云岩为主。研究表明,早三叠识别出了开阔台地、局限台地、盆地、斜坡、浅滩等环境。沉积相的纵向演化为盆地-斜坡-台地,整体上是一个海平面下降、水体变浅的过程,期间偶有短暂的海平面上升的过程。在岩石特征、沉积环境分析的基础上建立了大峡口剖面下三叠统盆地-斜坡-开阔台地-浅滩-局限台地的沉积模式。

Lithology and Sedimentary Environment of the Lower Triassic Series in the Daxiakou Section,Xingshan,Hubei

The Daxiakou section in Xingshan,Hubei characterized by a complete development of the Lower Triassic,clear boundaries,favorable exposure and good development of sedimentary structure is an ideal section for the study of the Lower Triassic in west Hubei.The Lower Triassic is composed of the Daye and the Jialingjiang Formations consisting of limestone and dolomitite,with a thickness of 1204.47 m.The limestone may be divided into micrite limestone,worm limestone and grain limestone.The worm limestone formed by the resolution was mainly developed in the second and the third Member of the Daye Formation.The dolomitite was mainly developed in the Jialingjiang Formation.The research shows that open platform,restricted platform,open continental shelf,slope,shoal and other environment can be identified in the Early Triassic.The vertical evolution of sedimentary facies is open continental shelf-slope-platform,the whole process is sea level drop and shallow water,with occasional and short time sea level rise.A sedimentary model of open continental shelf–slope-open platform-shoal-restricted platform for the Lower Triassic in the Daxiakou section is established on the basis of lithology and sedimentary environment.