鄂尔多斯盆地奥陶系马五_(5)亚段沉积微相与古地理演化

Microfacies and Paleogeographic Evolution of Ma_(5)^(5) Member in the Ordovician,Ordos Basin

碳酸盐岩微相分析有利于认识沉积相展布特征和古地理演化规律,对油气勘探具有指导意义。通过大量薄片、岩心资料在鄂尔多斯盆地奥陶系马五_(5)亚段划分出MFT1—MFT7七种沉积微相类型及MA1—MA4四种沉积微相序列,沉积微相与生物遗迹化石指示马五_(5)亚段为潮坪环境。结合沉积前古地形及古海平面变化信息,以单因素图件为基础,采用优势相法编制马五_(5)^(2)层(Ⅰ)、马五_(5)^(1)层(Ⅱ)岩相古地理图,沉积环境受沉积前古地形控制而分异:潮上带、潮间上带、潮间下带及潮下带自西向东依次分布,盆地东部高地形处发育潮间带沉积;随古海平面下降,马五15期沉积相带向东迁移,东部潮间带连片分布。

Analysis of carbonate microfacies is helpful for understanding the distribution of sedimentary facies and the evolution of paleogeography,which is of guiding significance in oil and gas exploration.Based on a large number of thin-section data and core information,seven types of microfacies(MFT1MFT7)and four types of sedimentary array(MA1MA4)were defined in the Ordovician Ma^(5)^(5) member of the Ordos Basin.Microfacies and trace fossils show that the environment of the Ma_(5)^(5) member was a tidal flat.Paleogeographic maps of layers I and II were compiled,indicating that the environments were controlled by the paleotopography:a supratidal zone,an intertidal zone and a subtidal zone occur in sequence from west to east;the intertidal zone was also found in high terrain in the eastern basin.As the sea-level fluctuated,the facies migrated to the east,and the intertidal zone in the east was contiguous.