Abstract: Whether or not there occurred transgressions in the Jiyang depression,Shandong and its adjacent areas during the Early Tertiary has long been an open question.Exemplified by the Jiyang depression,the emphasis in this paper is placed on the evolution of the first and second members of the Lower Tertiary Shahejie Formation in the depression on the basis of sedimentary and palaeontological information.A new concept tsunami is put forward to explain the formation of the alluvial facies in the upper part of the second member of the Shahejie Formation throughout the Bohai Bay Basin and the reason for maximum lake flooding in the first member of the Shahejie Formation from the Tertiary onwards.It is in-ferred that the origin of tsunami interpreted as the accidental events may well allow to be related to the collision of celestial bodies with the earth.