塔中地区中上奥陶统礁、滩相隐蔽圈闭研究

根据基准面旋回变化控制层序形成和展布的有关规律，并结合钻井、测井和地震等资料，综合分析建立了塔中地区奥陶系的层序地层格架，共包括5个三级层序。该地区中、上奥陶统可分为3个三级层序，沉积旋回总体显示出不对称的特点，海平面以上升过程为主。钻井证实，在层序地层格架中，塔中地区奥陶系有着多种类型的隐蔽圈闭（古岩溶圈闭、生物礁圈闭等）。其中礁、滩相隐蔽圈闭的发育在纵向上受基准面旋回变化的制约，形成于各层序单元的下部；在平面上受海平面以及古隆起、坡折带等古地貌格局的双面控制，主要发育在碳酸盐岩台地边缘，分布于两个相带，一个是碳酸盐岩台地内的地形由平坦向较陡处转折的斜坡带，另一个是碳酸盐岩台地向台地斜坡过渡的台地边缘。

STUDY ON THE MIDDLE-UPPER ORDOVICIAN SUBTLE TRAPS OF REEF-BEACH FACIES IN TAZHONG AREA

Based on the principles that the cyclic change of base level controls the formation and distribution of sequences and in combination with the comprehensive analyses of drilling, logging and seismic section, the Ordovician sequence stratigraphic framework in Tazhong area is established. It consists of 5 third-order sequences, of which the Middle-Upper Ordovician can be divided into 3 third-order sequences. As a whole, the cycles are asymmetrical and the change of sea level is dominated by ascending process. Drilling data verify that the Ordovician in Tazhong area has various types of subtle traps in the sequence stratigraphic framework. Vertically, the subtle traps of reef-beach facies are controlled by the change of base level cycle and are mainly developed in the lower part of each sequence unit. While laterally, they are controlled by both sea level and palaeogeomorphology such as palaeohigh and slope break zone, and are mainly developed on the margin of carbonate platform. They are distributed in two facies belts, one of which is the slope zone where the carbonate platform changes from flat to relatively steep, and the other is the platform margin where the carbonate platform transits to platform slope.