华东地区早—中三叠世海相地层划分和对比

华东地区三叠纪海相沉积仅存在于早―中三叠世时期。它们既是区域构造控盆沉积作用下的产物,也能够反演区域印支构造运动的作用型式和演变历程。华东地区的海相三叠系可以划分为2个地层区和6个地层分区。各地层分区内的地层序列可以按照地层的时间属性和连续的空间沉积古地理分异,整合为一套统一的岩石地层单元,仅局部岩相差异较大的地质体可采用单独的地层名称。借助于生物和环境事件标志,可以进行区域地层对比。地层序列的时空分异表明,印支构造运动的第一幕或序幕可能始于早三叠世晚期,这时在扬子地块的北部已与华北地块对接形成一系列局限的次级边缘海盆,并于最后于中三叠世晚期彻底关闭;与此同时,扬子地块南缘与华夏地块之间也于早三叠世晚期逐步被挤压变陡,形成台-坡-盆沉积体系,并且于早三叠世末被关闭,从而在中三叠世形成统一的沉积盆地。

Division and Correlation of Marine Lower-Middle Triassic Strata in East China

Marine Triassic sedimentation of east China occurred only in the Early-Middle Triassic time. The marine Lower-Middle Triassic successions not only are the depositional products in the sedimentary basins controlled by the regional tectonism but also represent the tectonic pattern and process of the Indosinian movement in the region. The Triassic strata of east China can be divided into two stratigraphic regions and six stratigraphic subregions. The stratigraphic sequences within each stratigraphic region can be unified into a uniform lithostratigraphic system according to the time attribute and lithofacies paleogeographic affiliation of the stratigraphic units, except for some specific geological bodies of quite distinctive lithofacies that can be separately named. The lithostratigraphic sequences can be well correlated on the basis of the integrated study of some characteristic paleontological and environmental events. The spatial and temporal variation of stratigraphic sequence indicates that the first episode or prologue of the Indosinian movement should have taken place in the late Early Triassic period, which resulted in the formation of a series of secondary marginal seas in the northern part of the Yangtze block due to its suturing with the North China block after that time, and the suture zone was finally closed in the late Middle Triassic. In the meantime, the southern margin of the Yangtze block became steepened to form a platform-slope-basin sedimentary system during the late Early Triassic with the compression of the Cathaysia block, and the deep basin was finally closed at the end of the Early Triassic, whereas united clastic sedimentary basins across the blocks occurred in the Middle Triassic.