中-上扬子地区奥陶系层序地层格架

在系统分析典型露头剖面的岩性和沉积序列发育特征的基础上，结合古生物牙形石、全岩碳同位素和氧同位素、岩石薄片分析以及典型钻井、测井和地震的综合层序分析，将中-上扬子地区奥陶系海相地层划分为8个区域上可对比的三级层序，即层序OSQ1-层序OSQ8。建立了年代地层、牙形石生物地层、岩石地层与层序地层之间的相互关系。识别出Ⅱ型及Ⅲ型（淹没不整合型）2种层序界面。区域上以发育Ⅱ型层序界面为主，仅层序OSQ7的顶界面（即临湘组与五峰组的分界面）属典型的Ⅲ型层序界面。中-上扬子地区奥陶系碳酸盐台地/缓坡相沉积的淹没是一个渐进发展的过程，从早奥陶世晚期至晚奥陶世晚期，持续时间超过25 Ma。通过对比反映全球海平面相对变化的全岩碳同位素旋回和反映沉积古水深相对变化的沉积旋回，分析揭示，在古气候和沉积充填速率影响不大的背景下，中-上扬子地区下奥陶统下部层序OSQ1的发育主要受控于全球海平面变化，而层序OSQ2-层序OSQ8的发育主要受控于区域构造运动，即扬子板块向华夏板块的俯冲会聚所产生的挤压构造作用，属于较为典型的前陆挤压层序。

Ordovician sequence stratigraphic framework in the Middle-Upper Yangtze area

Based on systematically analyzing the typical outcrop lithology and sedimentary sequence developing characteristics, further analyzing the conodonts (ancient animal fossils), carbon and oxygen isotopes of whole rocks, and rock thin sections, in combination with the comprehensive analyses of typical drilling, logging and seismic sequences, the Ordovician marine strata in the Middle-Upper Yangtze area are divided into 8 third-order sequences regionally correlated, i.e., OSQ1-OSQ8 sequences. In addition, this study establishes the mutual relationship between chronostratigraphy, conodont biostratigraphy, rock strata and sequence stratigraphy. The sequence boundaries of type Ⅱ and type Ⅲ (submerged unconformity type) have been identified. On a regional level, the type Ⅱ is dominant. Only the top of sequence OSQ7, i.e., the boundary between Linxiang Formation and Wufeng Formation, is typically show as the type Ⅲ. The Ordovician carbonate platform or ramp in the Middle-Upper Yangtze area underwent a gradual submerging process, lasting for more than 25 Ma from the late period of Early Ordovician to the Late Ordovician. Based on the comparison between the whole rock carbon isotope cycle and the sedimentary cycle reflecting the relative change of eustatic sea level and sedimentary paleo-water depth, respectively, the analysis results indicate that less affected by the paleoclimate and sedimentary filling rate, the development of the Lower Ordovician sequence OSQ1 in the Middle-Upper Yangtze area is mainly controlled by eustatic sea level change, while the OSQ2-OSQ8 sequences are mainly controlled by the regional tectonic movement, i.e., a compressive tectonic process produced by the subduction from Yangtze plate to Huaxia plate, so that they are belong to the typical foreland compressive sequences.