Abstract: Wetland as a transitional area between land and water area (e.g. lake, ocean) is a significant type of sedimentary facies. In this paper, the wetland is redefined and reclassified, and divided into two types from the view point of sedimentology, and divided into two types, i.e. swamp wetland (swamp in brief) and wet plain wetland (wet plain in brief). The deposit of the former is coal, while that of the latter is mudstone with rich plant fossils. Many researchers always classified dark mudstone into underwater reduction environment (lake) sediment and regarded it as potential source rock. This is definitely incorrect. Because some dark mudstones can be wet plain sediments and can not become as source rocks. So, to know well the depositional model and recognition feature of wetland and exactly distinguish wet plain and lake deposits or sediments are of great significance for basin oil genetic potential evaluation and lake basin evolution history understandings.

Key words: wetland, wet plain, swamp, depositional model