Did transgressions occur during the Late Cretaceous and Early Tertiary in eastern China? And how were the transgressions related to hydrocarbons? The two questions are of interest to many geologists. Through many years of study of fora-minifers as well as other fossils such as Dinoflagellates, stromatoliths, Polychaeta burrows, marine ostrocods, bivalves, nannofossils and fishes, the authors hold that in the Late Cretaceous and Early Tertiary there occurred respectively two phases of transgression, which resulted in the formation of brackish deposits. They are as follows in ascending order: 1)the 1st member of the Qingshankou Formation in the Songliao basin in the Senomanian; 2 ) the 1st and 2nd members of the Nenjiang Formation in the Songliao basin and the Zhutian Member of the Nanxiong Forma-tion in the Nanxiong basin in the Turonian to early Senonian; 3 ) the 2nd member of the Taizhou Formation and Funing Formation i.n the Subei-South Yellow Sea basin, the 2nd member of the Buxin Formation in the Sanshui basin and the Yuan-Jiang Formation in the Dongting depression of the Jianghan basin in the Paleo-cene to early Eocene; 4 )the Chunhuazhen, Shahejie and Dongying Formations in the Bohai Gulf subsidence area, the Nadu Formation of the Baise basin and Nanning basin in the Beibu Gulf subsidence area and the Qianjiang and Jinghezhen Formations in the Qianjiang depression of the Jianghan basin in the late Eocene to Oligocene. These specious brackish deposits are favorable for the generation and accumulation of hydrocarbons, and mostly constitute the main source formations of the Mesozoic-Cenozoic petroleum-bearing basins in eastern China.