This paper examines carefully the sedimentary features

biological associations and characteristics of organic carbon of the Upper Permian Dalong Formation in the northern margin of the MiddleUpper Yangtze region. We also discuss the relationship between regressive sequences and highquality source rocks. According to the study

we believe that the depositional setting of the Upper Permian Dalong Formation belong to regressive continental shelf facies which changes from the outer shelf in the early period to the inner shelf in the middletolate period. The change of facies belt brought about shallowwater organism

especially plenty of bacillusalga

which continuously provided organic materials for the development of highquality source rocks in the Dalong Formation in the MiddleUpper Yangtze region. The organic carbon content in the upper part is higher than that in the lower part of the Dalong Formation. In addition

ascending current repeatedly brought nutritious salt from deep water to sallow water

which made the biological groups thrive and promoted the productivity of organic matter. Therefore

highquality source rocks developed in large scale in the Dalong Formation. From this study we come to the conclusion that the regressive continental shelf is also an important location for the development of source rocks.