重庆綦江藻渡中二叠统沉积微相

Study of sedimentary microfacies of the Middle Permian at Zaodu section, Qijiang County, Chongqing, China

探讨重庆綦江藻渡地区中二叠统沉积微相组合的特征及沉积环境演化。以野外地质剖面和室内薄片鉴定为基础,对藻渡地区中二叠统碳酸盐岩开展系统的岩石颗粒组分、岩石类型和沉积环境分析,并绘制相关图件。根据Dumham的碳酸盐岩沉积结构分类方案,主要有7种类型:生物碎屑颗粒灰岩、生物碎屑泥粒灰岩、泥灰岩、含生物碎屑泥粒灰岩、有孔虫泥粒灰岩、中-细晶白云岩和生物碎屑粒泥灰岩。研究区在中二叠世一直处于碳酸盐台地环境,发育了陆棚、台地边缘和开阔台地相,在栖霞组早期处于持续海侵过程,而栖霞组晚期经历了海退,到茅口组早期快速上升到最高点,茅口组中期开始下降,在茅口组晚期海平面大幅度快速下降到最低点。

Based on the investigation of field geological section and identification of rock thin sections,the particle compositions of carbonate rock,rock types and sedimentary environment of the middle Permian at Zaodu area of Qijiang County are systematically analyzed so as to discuss its characteristics of sedimentary microfacies assemblage and sedimentary environment evolution.7 types of carbonate rocks,including bioclastic granular limestone,bioclastic packstone,marlstone,bioclastic-bearing packstone,foraminiferal marl limestone,medium-fine crystalline dolomite and bioclastic packstone,are recognized through the study of petrological characteristics and the application of Dumham structure classification for carbonate rocks.It reveals that the studied area was in a carbonate platform environment in the middle Permian Period with the development of continental shelf,platform edge and open platform facies.Continuous transgression occurred in the early period of Qixia Formation and followed by regression in the later period of Qixia Formation.In the early period of Maokou Formation,the sea levels rapidly rise to its highest level and sea levels began to fall in the middle period of Maokou Formation and the falling of the sea levels reached its highest point in the late period of Maokou Formation.