ABSTRACT
There are two types of coal forming during sea transgression, that is, (1) coal formed in the sea transgression process and (2) coal formed under transgression events. As for the first type, the formation of coal was transferred gradually toward the land during the transgression and peat formed in advance was submerged in sea water and the horizon of peat accumulation went upward gradually. So, coal seams formed are of diachronism. The second type means that the sea transgression events caused coal accumulation and the sea transgression process was relatively short compared with the interval of the infilling of the basin. So the transgression can be thought to be isochronic which is a unique characteristic of the epicontinental sea basin. The transgression layer was spatially stable, isochronic, and widespread. Therefore, it is of actual significance in dividing sequences and their inner units, especially in high-resolution sequence stratigraphic classification.
