川西北地区中二叠统沉积相特征

Characteristics of Middle Permian Sedimentary Facies in Northwest Sichuan

摘要: 本文探讨四川盆地西北部中二叠统的沉积相特征和沉积环境的演化特征。以研究区的野外露头剖面和钻井岩心的室内薄片为基础，对川西北中二叠统碳酸盐岩的岩石学特征、沉积相类型和沉积环境演化进行系统的研究。依据冯增昭提出的对碳酸盐岩的沉积结构的分类，将研究区的碳酸盐岩划分为9种微相：亮晶生屑灰岩、泥晶生屑灰岩、生屑微晶灰岩和含生屑微晶灰岩、泥晶灰岩、生物碎屑白云岩、粗晶白云岩、块状白云岩、燧石条带、亮晶白云岩。通过对岩石薄片的观察得出研究区中二叠统始终处于碳酸盐岩台地相沉积环境，并进一步划分为开阔台地相、台地边缘相和陆棚相。通过对研究区沉积相带的研究分析，在栖霞组初期海平面快速的上升，后面海平面缓慢下降，总体上栖霞组处于海平面上升的状态，但是变化频繁；在茅口组初期出现快速的海侵，后期海平面缓慢的下降为特征。

Abstract: This paper discusses the sedimentary facies and sedimentary environment evolution characteristics of the middle Permian in northwest Sichuan Basin. Based on field outcrop section and indoor thin section of drilling core, the petrological characteristics, sedimentaryfacies types and sedimentary environment evolution of middle Permian carbonate rocks in northwest Sichuan are systematically studied. Based on the classification of carbonate sedimentary structure proposed by Feng Zengzhao, the carbonate rocks in the study area are divided into nine kinds of microfacies: sparry raw chip crumbs limestone, micritic limestone, important raw limestone and contain important raw limestone, micrite, bioclastic dolomite, coarse grain dolostone, massive dolomite, flint stripe, sparry dolostone. Through the observation of the rock thin section, it is concluded that the middle Permian in the study area is always in the carbonate platform sedimentary environment, and it is further divided into open platform facies, platform marginal facies and shelf facies. According to the study and analysis of the sedimentary facies belt in the study area, the sea level of Qixia Formation rose rapidly at the early stage and then slowly fell. On the whole, the Qixia Formation was in the state of sea level rise, but changed frequently. The maokou Formation was characterized by rapid transgression in the early stage and slow sea level decline in the later stage.