奥陶纪为我国地史上最大的海侵期,其海陆分布的大致轮廓,特别是在早期基本上和晚寒武世的相似,表现了明显的继承性。较大的变化发生在中、晚奥陶世逐渐形成的大规模海退过程中,以致在北方出现了广阔的华北大陆,在西南有滇黔桂古陆的隆起。在整个奥陶纪作为古地理的正单元而长期高出海面的古陆,在我国北方有内蒙古陆、东北古陆、辽胶古陆、熊耳——伏牛古陆和淮阳古陆。在南方主要有华夏古陆和台湾古陆(它们向南延伸与可能存在于中国南海一带的古陆相接)、康滇古陆、阿坝古陆和江南列岛。接受沉积的古地理负单元包括海盆和海槽,前者主要有华北海、扬子海,喜马拉雅海和塔里木海,可能还有藏北海,后者则有内蒙——兴安海槽、天山海槽、祁连海槽、秦岭海槽、昆仑海槽、藏东——滇西海槽和华南海槽。根据古地理环境和古构造性质的不同,中国奥陶纪沉积可划分为两种基本类型,即稳定沉积类型与不稳定沉积类型。前者可据岩相特征分为均一相型(如华北海内呈均一分布的碳酸盐沉积)和由碳酸盐岩、砂岩、页岩交互成层的混合相型沉积(如见于扬子海的沉积)。后者可视岩系中火山岩的发育与否而分为优地槽型与冒地槽型沉积。如祁连山海槽、天山海槽、内蒙——兴安海槽、昆仑海槽和秦岭海槽西段都有广泛发育的火山岩,属于优地槽型。华南海槽、藏东滇西海槽和秦岭海槽东段则不见火山岩产出,属于冒地槽型沉积。有些地区,如鄂尔多斯西缘及江南列岛地区,其沉积特征介于上述两种基本类型之间,可称为过渡型沉积(见图Ⅱ、Ⅲ)。中国奥陶系各种不同沉积型相的分布,概略地表明在图Ⅰ中了。从图中优地槽型沉积的分布看来、中国奥陶纪明显地存在着三个火山活动带,它们分别与天山——内蒙兴安海槽、祁连山海槽和昆仑——西秦岭海槽相吻合。至于如何运用板块构造模式阐明其固有的机理和发展过程,则尚待进一步的工作和研究。 Ordovician is the largest transgression period in the history of our country. Its outline of sea-land distribution is similar to that of Late Cambrian, especially in the early stage, which shows obvious succession. The larger changes took place in the gradual formation of the Middle and Late Ordovician sea retreat, so that in the north appeared a vast North China continent, in the southwest of Yunnan, Guizhou and Guangxi ancient land uplift. In the entire Ordovician as the positive unit of paleogeography and long-term sea surface over the ancient land, in Inner Mongolia in our land, Inner Mongolia, Liao plastic ancient land, Bear ear - Funiu ancient land and Huaiyang ancient land. In the south, there are mainly Huaxia ancient land and Taiwan ancient land (they extend southward to the ancient land that may exist in the South China Sea), Kangdian ancient land, Aba ancient land and Jiangnan archipelago. Negative paleogeographic units undergoing sedimentation include the basin and trough, with the former mainly including the North China Sea, the Yangtze Sea, the Himalayas and the Tarim Sea, possibly the northern Tibet, and the latter with the Inner Mongolia-Xing’an Trough, the Tianshan Trough and the Qilian Sea Trough, Qinling Trough, Kunlun Trough, Tibet-East-West Trough and South China Trough. According to the paleogeographic environment and paleo-structural properties, the Ordovician sediments in China can be divided into two basic types, that is, stable sedimentary types and unstable sedimentary types. The former can be divided into homogeneous facies types (eg, carbonate sediments distributed uniformly in North China) and mixed facies sediments (such as sediments found in the Yangtze Sea) stratified by carbonate rocks, sandstone and shale according to lithofacies characteristics ). The latter can be visualized in the development of volcanic rocks in the rock or not and is divided into excellent trough type and risking trough deposition. For example, Qilian Mountain Trough, Tianshan Trough, Inner Mongolia - Xing’an Trough, Kunlun Trough and western Qinling Trough have extensively developed volcanic rocks, which are excellent trough type. The South China Trough, eastern Tibetan basin in western Yunnan and the eastern section of the Qinling Trough are not seen volcanic output, belong to the sag-type sediments. In some areas, such as the western margin of the Ordos and the Jiangnan Islands, the sedimentary characteristics lie between the two basic types mentioned above and may be called transitional sediments (see Figures II and III). The distribution of various sedimentary facies in the Ordovician in China is shown schematically in Figure I. From the distribution of well-shaped trough sediments in the picture, there are obviously three volcanic activity zones in Ordovician in China, which are respectively related to Tianshan-Inner Mongolia Xinganhaikou, Qilian Mountain Trough and Kunlun-West Qinling Trough Anastomosis. As for how to use the plate tectonic model to clarify its inherent mechanism and development process, remains to be further work and research.