塔里木盆地玉北地区上奥陶统碳酸盐岩沉积微相及沉积环境

Sedimentary microfacies and setting of the Upper Ordovician carbonates in the Yubei area,Tarim Basin

采用微相分析的方法,对玉北地区12口钻井上奥陶统恰尔巴克组、良里塔格组碳酸盐岩的微相类型和沉积环境进行了研究。通过在显微镜下对其颗粒成分、生物组合、基质类型及结构特征等进行深入观察,划分出8种碳酸盐岩微相类型。依据各微相类型组合特征,并结合钻测井、地震剖面、古生物及地球化学等资料,认为玉北地区上奥陶统碳酸盐岩主要形成于开阔台地、台地边缘与台缘斜坡3种沉积环境,晚奥陶世的沉积相带呈东西向分异:大致以玉北5-胜和2-皮山北2井南一线为界,东部为台缘斜坡-陆棚相,中西部为碳酸盐岩台地相。玉北地区晚奥陶世纵向沉积演化为开阔台地—台地边缘—台缘斜坡—陆棚,其沉积环境的演变主要受控于区域构造运动。

We studied the microfacies types and sedimentary settings of carbonate rocks of the Upper Ordovician Qrebake and Lianglitage Formations from 12 wells of the Yubei area,by means of microfacies analysis.Eight kinds of carbonate microfacies have been identified based on the microscopic observation of grains,biological assemblies,matrix and structural characteristics.Based on how the microfacies types are associated to each other,combined with drilling and logging data,as well as seismic profile,palaeontological and geochemical analyses,we believed that the Upper Ordovician carbonate rocks are mainly developed in the sedimentary environments of open platform,platform margin and marginal-platform slope.The sedimentary facies in the Late Ordovician differ from the east to the west.The boundary is delineated along Well YB5 - Well SH2 - the south of Well PSB2,with marginal-platform slope-continental shelf facies in the east,and carbonate platform facies in the center and the west.In conclusion,the Upper Ordovician in the Yubei area has evolved from open platform,to platform margin,to marginal-platform slope,and then to continental shelf facies in vertical sequence,and the variation of sedimentary environments in the area is mainly controlled by regional tectonic movements.