Palaeoenvironmental Evolution and Multi-stratigraphic Division and Correlation of Yangtze River Delta Plain since Pleistocene: Evidence from BZK03 Borehole

Based on the analysis of sediment isotope dating, sporopollen assemblages, microfossils, grain size and magnetism of the samples from BZK03 borehole in the Yangtze River Delta plain, this paper discusses the sedimentary environment evolution, sedimentary facies and paleoclimate characteristics since Pleistocene, and then the Quaternary multi-stratigraphic division and correlation framework of the borehole has been established. The results show that, from bottom to top, the samples of drilled holes are weathered siltstone of Cretaceous Quxian Formation and Quaternary sedimentary strata of Jiaxing Formation, Qiangang Formation, Dongpu Formation, Ningbo Formation and Zhenhai Formation. Sporopollen assemblages can be divided into 18 sporopollen zones. According to the cycle law of warm, humid, cold, dry paleoclimate cycles, BZK03 borehole shows that there are 6 paleoclimate cycles in this region. In line with lithologic stratification, sedimentary environment and paleoclimate, the division and correlation of borehole multiple strata reveals that 144.6~198.5m is Jiaxing Formation strata with alternating fluvial and fluvial-lacustrine sedimentary environments in early Pleistocene, and there are two climatic cycles. 88.3~144.6m is the Qiangang Formation stratum of Middle Pleistocene fluvio lacustrine face-fluvial face-fluvio lacustrine face-fluvial face sedimentary environment, including two climatic cycles. 16.6~88.3m is late Pleistocene deposition, and the sedimentary environment is the Ningbo Formation of fluvial-littoral-fluvial-tidal-fluvial facies and the Dongpu Formation of estuarine-neritic facies, including two climatic cycles. 0~16.6m is Zhenhai Formation stratum of fluvial-lacustrine-shallow-fluvial-tidal flat sedimentary environment.