川黔湘交境早寒武世“变马冲组”沉积层序与古环境

ORDOVICIAN-SILURIAN DEPOSITIONAL SEQUENCES AND THEIR RELATIONS WITH TECTONIC MOVEMENT IN SOUTH CHINA

川黔湘交境早寒武世“变马冲组”为一套陆源碎屑岩沉积，是在三角洲环境中形成的．该组相当于一个Ⅱ型三级层序，由陆棚边缘体系域、海侵体系域和高水位体系域组成，分别代表了三角洲发育、萎缩和再发育的３个演化阶段．陆棚边缘体系域期，发育河流相、三角洲前缘相和前三角洲相，以三角洲前缘相为主；海侵体系域期，发育三角洲前缘相和前三角洲相，以前三角洲相为主；高水位体系域期，发育三角洲平原相、前缘相和前三角洲相，以三角洲平原相为主．研究区西北部的秀山古岛是主要物源区，由此向东南呈现出水体渐深，沉积物渐细的变化趋势．

The aim of this study is to discuss the depositional sequences and their relations with tectonic movement during the Ordovician and Silurian by comparison of division of sequence stratigraphy from the northwestern Hunan and southeastern Guizhou with definite tectonic phase. Three second-order depositional sequences can be recognized in Ordovician and Silurian of South China. Reseach result indicates that second-order sequences are mainly affected by regional tectonic movements and sea level changes from third-order depositional sequences. On the basis of the data of depositional sequence, paleogeographic changes and stratigraphy, it is inferred that regressive event of Huixingshao Period (early Middle Silurian) was the last phase of Caledonian cycle in South China.