SUBASSEMBLAGES OF BENTHIC FORAMINIFERA AND PALAEOENVIRONMENTAL IMPLICATION IN THE YANGTZE RIVER ESTUARY SINCE HOLOCENE

According to quantitative statistics interpretation on the foraminiferal assemblages, combined with AMS ¹⁴C dating, grain size and geochemistry data of the YD-0903 borehole collected from the offshore of the Yangtze River estuary, this paper discusses the evolution of Holocene palaeoenvironment of the estuary. 6 stages of sedimentary environmental evolution of the studied area are defined, i.e. 11 260~10 150 cal.aBP, dominated by Ammonia beccarii vars, indicating an estuarine and nearshore environment; 10 150~7 730 cal.aBP, dominated by Epistominella naraensis-Ammonia beccarii vars, indicating an estuarine, nearshore to shallow shelf environment; 7 730~3 610 cal.aBP, dominated by Epistominella naraensis-Florilus spp., indicating a hypoxia shallow shelf environment; 3 610~2 930 cal.aBP, characterized by Quinqueloculina spp., indicating a relatively high temperature and high salinity shallow shelf environment; 2 930~2 150 cal.aBP, characterized by Bolivina spp., indicating a hypoxic and nutrient-rich prodelta to a shallow shelf environment; and 2 150~220 cal.aBP, dominated by Protelphidium tuberculatum, indicating a low temperature prodelta environment.