Sedimentary Environmental Evolution in the Western Bohai Sea since the Middle Pleistocene: Integrating Geochemical and Paleontological Records

Shuyu Wu^*Jun Liu^*Yongcai FengJidong Yuan

• Yantai Center of Coastal Zone Geological Survey, China Geological Survey, Yantai, China

The western Bohai Sea (BS) preserves a continuous Quaternary succession sensitive to orbital-scale climate and sea-level change. This study present a 300-kyr high-resolution geochemical and microfossils records from core DZQ01, and identified elemental proxies such as Rb/Sr, Mg/Ca, and Ni/Co ratios to quantify paleoclimate, paleosalinity, and paleoredox variabilty. Six depositional units (DU6–DU1) are identified: DU6 (300–272 cal. ka B.P.) record cold-arid fluvial deposition, and persistent suboxic conditions; DU5 (272–205 cal. ka B.P.) captures an initial shift toward warmer, more humid conditions followed by renewed cooling and arid conditions, recorded in tidal-flat to shallow-marine facies; DU4 (205–90 cal. ka B.P.): is dominated by cold and arid conditions punctuated by a short-lived warming event; DU3 (90–57 cal. ka B.P.) exhibits elevated temperatures and sea levels, fully marine conditions marked by abundant benthic foraminifera and ostracods; DU2 (57–14 cal. ka B.P.) documents cold-arid conditions, incised-valley fills, and diminished biogenic activity; and DU1 (14 cal. ka B.P. to present) reflects warm-humid climate, widespread euryhaline assemblages, and high biological productivity in intertidal to shallow-marine setting. Glacial-interglacial cycles are driven by complex interactions among orbital forcing, greenhouse-gas concentrations, and ocean-atmosphere feedbacks. Glacials are marked by global cooling, expanded continental ice sheets, and decreased atmospheric CO2, whereas interglacial exhibit global warming, reconfigured oceanic circulation, and northward-shifted Intertropical Convergence Zone position.