长江三角洲地区晚第四纪古土壤及其记录的古环境

The Late Quaternary stiff mud of the Yangtze Delta is considered as a paleosol based on multidisciplinary studies of sedimentology, micromorphology, and micropaleontology. Their parent materials were inferred to be floodplain deposits, and started deposition at early stage of the last high-stand of sea level before Last Glaciation. When sea level was still higher enough, the floodplain could be covered during flooding events and received layers of fine sediments settling out of the water body. These fine-sediment layers occurred pedogenesis when the floodplain exposed after floods. Paleosol sections record alternation of deposition and pedogenesis, representing flooding and exposing stages. As sea level falling went on and coastline retreated seaward, incised valley became deeper and deeper. When the incised valley was deep enough, the river water was completely limited in the river channels and even floods could not overflow the channel to the floodplain. Thus, deposits on the floodplain were completely exposed to weathering and came into a new stage of on-going pedogenesis. At the stage when sea level reached its lowest level, huge incised valley was formed in the modern Yangtze deltaic area. Pedogenesis on the exposed floodplains did not terminate until they were flooded again by the Holocene transgression.　 Incised valley was infilled when sea level rose during the Holocene transgression, and then the floodplain can be inundated again by floods to accept new deposition covering the paleosols. The paleosols were covered successively by estuarine and deltaic deposits, changes from pedogenesis to early diagenesis. Therefore, the paleosols underwent three stages: period of alteration of deposition and pedogenesis as sea level fell, period of on-going pedogenesis during lower sea level, and period of being buried and reformed (early diagenesis) when sea level reach relative higher level during postglacial transgression. These three stages occurred opposite to formation of incised Yangtze valley, infill of the incised valley, and development of the Yangtze Delta. This complete sequence of Last Glacial regression and Post Glacial transgression was studied in detail first time in the Changjiang Delta, and has never been reported from studies of other deltas as far as we know.

运用多学科先进的方法技术，取得长江三角洲晚第四纪埋藏古土壤的宏观和微形态，地球化学，碳氧同位素，古生物学及放射性测年等资料，确定古土壤类型。研究古土壤沉积，成壤和早期成岩作用及其与海平面变化的关系。恢复古土壤形成埋藏的古环境，探讨我国东部沿海地区末次冰期的干冷程度，降雨量，地下水位升降，以及古气候的影响。