Abstract: In order to determine sedimentary characteristics and model of the EarlyMiddle Jurassic in Jiyang depression, the authors studied sedimentary features, core section, well logging of the EarlyMiddle Jurassic in Jiyang depression. There are many sedimentary facies in EarlyMiddle Jurassic of study area, such as river facies with fining upward cycle, delta facies with higher maturity of debris composition and texture , fan delta facies with lower maturity of debris composition and texture, coastal and shallow lacustrine subfacies with dominanttly mottle mudstone and biogliph, lake bay subfacies with dominanttly black mudstone and plant remains and swamp facies with dominanttly thin coal layers. The results indicate that EarlyMiddle Jurassic Jiyang depression was composed of several isolated basins, which were controlled and divided up by northwest faults. Lake levels of these isolated basins were instable, but on the whole, coastal and shallow lake is in the mojority.

Key words: Jiyang depression, EarlyMiddle Jurassic, sedimentary facies, intramountainous lake basins