Depositional characteristics and petroleum geological significance of wetland

Key words:  wetland  wet plain  depositional characteristics

Abstract:

Based on analysis and correlation of wetland in outcrops, drilling and logging information, and combined with the features of modern wetland, wetland was redefined from the view point of sedimentology as "a type of natural sedimentary environments which is flat and wet, may be covered by water less than 2 m deep, and is rich in plants". Wetland is classified into two types, swamp wetland (swamp in brief) and wet plain wetland(wet plain in brief). The sedimentary features in plain wetland and correlation among related facies were studied. The deposits of wet plain wetland are mainly dark colored mudstone, silty mudstone and carbonaceous mudstone. They are rich in plant fossils. The content of organic carbon of wet plain is high. The resistivity logging curve is notched, and the resistivity is in between those of pure mudstone and sandstone. The difference marks in geologic wet land, flood plain and lake lie in as follows:color of deposits, lithology, plant fossils and electric logs. Flood land always develops in the outside zone of wet land, while wet plain in the outer part and swamp in the central part. Correct differentiation between wet plain mudstone and lake mudstone contributes to reconstruction of paleogeography, evolution of paleoclimate, evaluation of the oil and gas potential of a basin, and guiding oil gas exploration work.