浅滩碳酸盐岩发育镶边台地的沉积约束——川东北镇巴地区寒武统龙王庙组为例

Sedimentary Constraints of Rimmed Platform Developed in Shoal Carbonate Rocks—The Cambrian Longwangmiao Formation in Zhenba Area of Northeastern Sichuan as an Example

摘要: 目前资料表明，川东北镇巴地区下寒武统龙王庙组储层发育与川中地区存在较大的差异，且关于川北地区寒武系储层研究较少。文中以川东北镇巴地区龙王庙组野外露头剖面为研究对象，利用野外勘测、岩石样品等资料，探讨了镇巴地区下寒武统龙王庙组的沉积相类型及特征，并结合前人资料分析镇巴地区下寒武统龙王庙组沉积模式及川北地区下寒武统龙王庙组平面展布规律。得出以下几个认知：1) 镇巴地区下寒武统龙王庙组发育台地边缘和斜坡2种沉积相带，并根据岩性特征、沉积构造、岩层厚度等多方面因素，将进一步细分为台缘滩、滩间海、上斜坡、下斜坡等4种次相；2) 川北地区下寒武统龙王庙组砂屑滩主要发育于剖面上部，且在镇巴地区捞旗河与星子山剖面存在明显厚度差异具有坡度明显变陡的沉积特征，根据前人总结沉积相展布规律，认为镇巴地区下寒武统龙王庙期的沉积环境由碳酸盐缓坡转变为镶边碳酸盐台地。

Abstract: The current data show that the reservoir development of the Lower Cambrian Longwangmiao Formation in Zhenba area of northeastern Sichuan is quite different from that in central Sichuan, and there are few studies on the Cambrian reservoirs in northern Sichuan. In this paper, the outcrop section of Longwangmiao Formation in Zhenba area of northeastern Sichuan is taken as the research object. The types and characteristics of sedimentary facies of Longwangmiao Formation of Lower Cambrian in Zhenba area are discussed by means of field survey and rock samples. Combined with previous data, the sedimentary model of Longwangmiao Formation of Lower Cambrian in Zhenba area and the plane distribution law of Longwangmiao Formation of Lower Cambrian in northern Sichuan are analyzed. The following conclusions are drawn: 1) Two sedimentary facies belts, platform margin and slope, are developed in the Lower Cambrian Longwangmiao Formation in Zhenba area. According to the lithological characteristics, sedimentary structure, rock thickness and other factors, they are further subdivided into four sub-facies: platform margin beach, inter-beach sea, upper slope and lower slope. 2) The lower Cambrian Longwangmiao Formation in the northern Sichuan area is mainly developed in the upper part of the section, and there is a significant thickness difference between the Laoqihe and Xingzishan sections in the Zhenba area. The sedimentary characteristics of the slope are obviously steeper. According to the previous summary of the distribution of sedimentary facies, it is considered that the sedimentary environment of the lower Cambrian Longwangmiao period in the Zhenba area is changed from carbonate gentle slope to rimmed carbonate platform.