关键词: 杭州湾北岸, 第四纪, 孢粉, 沉积环境, 古气候

Abstract: The BZK04 borehole (237.80 m deep) is located in the south wing of the Yangtze River Delta and the north bank of Hangzhou Bay. The core contains a relatively complete and continuous sedimentary sequence since the Pleistocene. In this study, the sediment lithology, micropaleontology, sporopollen assemblage, particle size content, paleomagnetism and OSL dating of the core were analyzed comprehensively, the characteristics of depositional environment evolution and paleoclimatology changes since the Pleistocene in the research area were discussed, and the framework of quaternary multiple stratigraphic divisions and correlatiosn was established. The results show that from bottom to top, the BZK04 core can be divided into carbonaceous mudstone （Ech） of the Changhe Formation, and the Jiaxing Formation（N-Qp1j）, Qiangang Formation（ Qp2q）, Dongpu Formation（ Qp3d）, Ningbo Formation （Qp3n） and Zhenhai Formation （Qhzh） since the early Pleistocene epoch; Foraminifera of 17 species in 11 genera were identified , including 16 benthonic foraminifera and 1 planktonic foraminifera; The ostracod of 8 species in 8 genera was identified ; Pollen analysis reveals that there were 37 types of pollen, including 18 woody plant pollen, 11 herbaceous pollen, and 8 fern spore; The content of woody plants was the highest in the palynological assemblage (85.1%), followed by fern spores (8.7%) and herb pollen (6.3%). According to the comprehensive analysis of the sedimentary environment of borehole by lithologic stratification features, sedimentary facies, sporopollen, foraminifera and ostracodes, and grain size distribution frequency curve, the depositional environmental record is characterized by 18 pollen assemblages and 7 paleoclimatic cyclic changes, among which the early Pleistocene is dominated by fluvial and lacustrine facies deposits, indicating two paleoclimatic cycles from the third warm period to the fourth cold period; The middle Pleistocene was dominated by fluvial facies, lacustrine facies, and fluvial and lacustrine facies, revealing two paleoclimatic cycles from the fifth warm period to the sixth cold period; The late Pleistocene is dominated by the tidal-flat facies, estuarine facies and neritic facies, corresponding to two paleoclimatic cycles from the seventh warm period to the eighth cold period; In the Holocene, there were tidal-flat facies, fluvial and lacustrine facies, corresponding to the Atlantic and boreal periods. This study provides an important basis for further understanding the changes in quaternary sedimentary environment, the stratigraphic divisions and the paleoclimate evolution since the Pleistocene in the southern side of the Yangtze River Delta.

Key words: north shore of Hangzhou Bay, Quaternary, sporopollen, sedimentary environment, paleoclimate