Stratigraphy and paleoenvironmental changes in the Yangtze Delta during the Late Quaternary

The Yangtze Delta area may be subdivided into paleo-valley and paleointerfluves of the last glaciation. The postglacial transgressive sedimentary cycle (PTSC) on the front zones of the paleointerfluves is composed of marsh-nearshore and barrier-lagoon, shallow marine and nearshore-tidal flat units, with a basement in stiff clay. The PTSC in back zones of the paleointerfluves consists of lacustrine-marsh deposits. The PTSC in the incised valley contains river channel, floodplain-estuary, estuarine-shallow marine and deltaic units, with an erosional surface at its bottom. The stiff clay and the erosional surface constitute the PTSC lower boundary. The stiff clay, consisting of a paleosol, experienced deposition alternating with pedogenesis during the falling of sea-level during δ¹⁸O stage 3; ongoing pedogenesis in the sea-level lowstand of δ¹⁸O stage 2; and early diagenesis after paleointerfluve inundation by the sea-level rise of δ¹⁸O stage 1. The climate during the paleosol formation was temperate with more than 500-mm a^-1 rainfall and frequently fluctuating groundwater. The Yangtze River incised its course during falling sea level of stage 3, and a huge incised valley was formed during the sea-level lowstand (stage 2). The filling of the incised valley took place during the postglacial sea-level rise, and delta formation occurred at a late stage of PTSC development. (C) 2000 Elsevier Science Ltd. All rights reserved.