Palynomorphs in the first paleosol layer in the Yangtze Delta and their paleoenvironmental implication

The relatively abundant palynomorphs were recovered from the samples of the first paleosol layer of core CY in Shanghai for the first time. A total of 55 genera and families of spore, pollen and phytoplankton were identified. According to the characteristics of the palynological assemblages, the depositional conditions in the development period of the paleosols were discussed and the microfossil evidence to study the origin of the paleosols in the Yangtze Delta area was provided as well. The research results show that paleosols should be freshwater deposits. The palynological assemblage sequence in the first paleosol layer reveals fluctuations of freshwater palynomorphs, mainly Concentricystis, and terricolous herbs pollen, reflecting the alternations of deposition and exposure in the development period of the paleosols. Concentricystis developed prosperously in the period of flood, while terricolous herbs grew on the emerged land in the period of exposure. The variations in the palynological assemblages suggest that the depositional conditions were various during the formation of the paleosols, and resulted in obvious stage characteristics of the paleosol’s development. The dinoflagellate cysts occur in low abundance in the palynological assemblages of the first paleosol layer of core CY, indicating that the area where core CY lies was influenced by seawater in the depositional period of the parent materials of the paleosols.