Stage characteristics for the development of late Quaternary paleosols in the Yangtze Delta area

The late Quaternary paleosols in the Yangtze Delta area developed in the period of 25 000–12 000 aBP. Phytolith ratios (value A) of contents of fan, square and rectangle types indicating the warm and humid climate to those of bar, hat and point types indicating cold and dry climates decrease upwards overall on profiles of the paleosols, suggesting that the climates turned from warm and humid to cold and dry. So, the paleosols developed mainly during the regression before the last glacial maximum. Changes of value A indicate no trend of warming, suggesting that the transgression was rapid after the last glacial maximum. The development of the paleosols exhibited obvious stages, which were controlled remarkably by transgression and regression: I. Period of alternation of deposition and pedogenesis, which was from the occurrence of regresson before the last glacial maximum to the time when sea levels fell close to the lowest; II. Exposure period with continual pedogenesis, which was terminated when the paleosols were drown in the post-glacial transgression; III. Period of being drown and buried, the paleosols were buried by marine sediments, and reworked by early diagenesis.