During the sea level low stand of the last glaciation maximum, the present Changjiang Delta area could correspondingly be subdivided into two palaeogeographical units: incised valley and palaeointerfluve. Erosional surface at the base in theincised valleys and the surface of the stiff clay (palaeosol) at the paleointerfluves constitute the lower boundary of the post-glacial transgressive sedimentary cycle, which corresponds to sequence boundary in sequence stratigraphy. The maximum flooding surface lying in estuarine-shallow marine muddy unit demarcates the underlying transgressive sequence and overlying regressive sequence. With the falling of sea level of δ18O stage 3 the Changjiang River began to down-cut, and a huge incised valley was formed during the lowest sea level of the stage 2. The postglacial transgression caused by sea level rising led to infilling of the incised valley and formation of the river channel, floodplain-estuary, estuarine-shallow marine and deltaic stratigraphical units. The retrogressive aggradation was the main process resulting in fluvial depositional units. The presence of tidal laminae and small-sized foraminiferas within muddy deposits of the floodplain unit demonstrated the influence of marine factors. Estuarine-shallow marine muddy deposits were basically formed during maximum transgression, then delta progradation created the deltaic sequences with multi-stage mouth sand bars. The stiff clay on the palaeointerfluve, belonging to floodplain facies, underwent deposition alternating with pedogenesis, ongoing pedogenesis and early diagenesis, which roughly correspond to stage 3, stage 2 and stage 1 of δ18O respectively. The stiff clay, overprinted by all these processes, contains abundant information on late Quaternary palaeoenvironment changes in the Changjiang Delta region. During the period of ongoing pedogenesis, river base level and groundwater remained lower, the annual precipitation was about 500～800 mm, which corresponded to that of modern temperate zones, drying-wetting cycles were apparent and groundwater was frequently fluctuated. All of these demonstrated that the climate was not arid at that time.
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