Sedimentary Facies and Paleoenvironment Significance of Hole BZK01 in the Yangtze River Delta Plain Since Pliocene Based on Big Data Analytics

Abstract

The analysis of the sediment 14C dating, grain sizes, sporopollen and micropaleontology in the BZK01 borehole in the Yangtze River Delta Plain was carried out. The sporopollen assemblages, the sedimentary environment evolution, the sedimentary facies and the paleoclimate characteristics revealed by the borehole since the Pliocene were discussed in combination with the gamma logging and the lithologic stratigraphy, and the quaternary multiple stratigraphic division of the borehole was established. The results show that the study area has undergone many environmental changes since Pliocene due to the influence of the primitive topography, the sea level changes, the land-sea changes, the paleoclimate changes and the Neotectonic movement. From bottom to top, the drilling holes reveal that the lithology and the strata are bedrock Changhe Formation, the Neogene-Quaternary sedimentary Jiaxing Formation, the Qiangang Formation, the Dongpu Formation, the Ningbo Formation and the Zhenhai Formation in turn. The sporopollen assemblage can be divided into 16 sporopollen belts. According to the periodic variation of the paleoclimate cycle during the warm, the humid and the cold and the dry periods, BZK01 drilling reflects that in the total area there are seven paleoclimatic cycles. The multi-stratigraphic division and correlation of the boreholes revealed that 151.9–278.0 m is the Pliocene-Early Pleistocene period of the alternating fluvial and lacustrine deposits, and there are two climatic cycles; 83.5–151.9 m is the Middle Pleistocene of the fluvial-lacustrine-shallow lacustrine depositional environment, which includes two climatic cycles. 15.4–83.5 m is the Late Pleistocene and sinks. From bottom to top, the sedimentary environment is the estuarine-fluvial-tidal-flat-littoral-fluvial facies, corresponding to Wangdian-Hangzhou transgression period, including two climatic cycles. 0–15.4 m is Holocene of the estuarine-fluvial-lagoon facies sedimentary environment, corresponding to Fuyang transgression, including one climatic cycle.