川东南地区中二叠统茅口组沉积相特征

Sedimentary Facies Characteristics of the Middle Permian Maokou Formation in Southeastern Sichuan

摘要: 通过对川东南地区中二叠统茅口组钻井岩心、薄片、野外剖面、测井资料的综合分析，结合前人研究，重新梳理构建了研究区沉积相类型、分布特征及平面分布演化。川东南地区茅口组发育泥晶灰岩、生屑灰岩、泥质灰岩、硅质岩及白云岩等岩性，在碳酸盐岩缓坡型台地沉积模式下沉积相可划分为外缓坡、中缓坡、内缓坡及开阔台地共4种。茅一段沉积初期，川东南地区发生大规模海侵，水体普遍较深，主要发育中缓坡–外缓坡沉积，受川中古隆起的影响，局部发育低能生屑滩；茅二下亚段沉积期，沉积相继承了茅一段沉积特征，中缓坡相呈北西向展布，相较内缓坡水体较深，滩体发育少；茅二上亚段沉积期，受构造–沉积分异作用的影响，川东南地区沉积相由碳酸盐缓坡转变为开阔台地，分布广泛，高能生屑滩较发育；茅三至茅四段沉积期，沉积相延续了茅二上亚段地层的沉积模式，仍为开阔台地相沉积，沉积相带展布转变为北西–南东向，台地内生屑滩继承茅二上亚段位置，水体深度加大，台地分布更加广泛。研究区茅口组沉积期受区域海平面升降、构造活动和沉积相类型的控制，有利沉积相带主要发育在茅二上亚段沉积期，高石梯–荷包场一带发育具有勘探价值规模性的高能生屑滩。

Abstract: Based on the comprehensive analysis of drilling cores, thin sections, field profiles and logging data of Middle Permian Maokou Formation in southeastern Sichuan, combined with previous studies, the types, distribution characteristics and plane distribution evolution of sedimentary facies in the study area are reorganized and constructed. There are micrite limestone, bioclastic limestone, argillaceous limestone, siliceous rock and dolomite in Maokou Formation in southeast Sichuan. Under the carbonate gentle slope platform sedimentary model, the sedimentary facies can be divided into four types: outer gentle slope, middle gentle slope, inner gentle slope and open platform. In the early stage of Mao-1 Formation, large-scale transgression occurred in the southeast of Sichuan, and the water body was generally deep, mainly developing moderate slope-outer gentle slope deposits. Due to the influence of the Middle Paleozoic uplift in Sichuan, low-energy bioclastic beaches developed locally. During the sedimentary period of the second lower member of Mao-2 Formation, the sedimentary facies inherited the sedimentary characteristics of the first member of Mao-2 Formation, and the middle gentle slope facies distributed in the northwest direction, which was deeper than the inner gentle slope water body and less developed beach body. During the sedimentary period of the upper sub-member of Mao-2 Formation, influenced by tectonic-sedimentary differentiation, the sedimentary facies in southeastern Sichuan changed from carbonate gentle slope to open platform, which was widely distributed and developed with high-energy debris beach. During the sedimentary period from Mao-3 to Mao-4 member, the sedimentary facies continued the sedimentary model of the upper sub-member of Mao-2, and it was still open platform facies deposition. The distribution of sedimentary facies belt changed to NW-SE, and the debris beach on the platform inherited the position of the upper sub-member of Mao-2, and the water depth increased and the platform was more widely distributed. The sedimentary period of Maokou Formation in the study area is controlled by regional sea level fluctuation, tectonic activity and sedimentary facies types, and the favorable sedimentary facies belt is mainly developed in the sedimentary period of the upper second member of Mao-2 Formation, high-energy bioclastic beach with exploration value is developed in Gaoshiti-Hebaochang area.