黔北务川-正安-道真地区上奥陶统五峰组-下志留统龙马溪组沉积相分析

ANALYSIS OF SEDIMENTARY FACIES OF THE UPPER ORDOVICIAN WUFENG FORMATION-LOWER SILURIAN LONGMAXI FORMATION IN THE WUCHUAN-ZHENG′AN-DAOZHEN AREA,NORTHERN GUIZHOU PROVINCE

在充分收集、整理黔北务川-正安-道真地区区域地质背景基础上,通过野外多条露头剖面的实地观测、岩相信息的记录及样品镜下分析等方法研究该区沉积岩物质质组成、构造和结构,明确岩石类型。综合沉积物颜色、岩性、结构构造等相标志,识别研究区上奥陶统五峰组、下志留统龙马溪组的沉积相与亚相,进而精细划分其沉积微相。依据连进剖面对比,认为黔北务正道地区上奥陶五峰组至下志留龙马溪组沉积于局限浅海沉积环境,沉积相为陆棚相。在垂向上,自下而上水体逐渐变浅,从深水陆棚亚相向浅水陆棚亚相过渡;进一步细分,其自下而上依次发育微相有碳质泥棚、含粉砂碳质泥棚、钙质泥棚、含粉砂钙质泥棚和钙质粉砂质泥棚。在横向上,整体表现为由南向北的水体逐渐加深,由深水陆棚逐渐演化为浅水陆棚。最终确认了陆棚相沉积体系为黔北务正道地区五峰组-龙马溪组的沉积模式。

On the basis of collection and synthesis of regional geological background data,the material compositions,textures,structures and lithological types in the Wuchuan-Zhengan-Daozhen area,northern Guizhou Province are studied through field observation of several outcrop profiles,record of lithofacies information and microscopic analysis of samples.The sedimentary facies and subfacies of upper Ordovician Wufeng Formation and lower Silurian Longmaxi Formation in the study area are identified by integrating facies markers,such as color,lithology and structure of sediments,and then the sedimentary microfacies are finely subdivided.The correlation of continuous well profile indicates that the upper Ordovician Wufeng Formation and lower Silurian Longmaxi Formation were deposited in the limited shallow sea with a shelf facies sedimentary environment.In the vertical direction,the water gradually became shallower from the bottom to the top,and transited from deep water shelf subfacies to shallow water shelf subfacies ones.The microfacies were further subdivided into carbonaceous mud shelf,silt carbonaceous mud shelf,calcareous mud shelf,silt calcareous mud shelf and calcareous silt mud shelf from the bottom to top.In the horizontal aspect,the water body gradually deepened from south to north,and the deep-water shelf gradually evolved into the shallow-water shelf.It is proposed that the shelf facies depositional system is the depositional model of the Wufeng Formation-Longmaxi Formation in the Wuchuan-Zheng′an-Daozhen area in northern Guizhou Province.