Paleoenvironmental evolution and East Asian monsoon records through three stages of paleochannels since the mid-pleistocene in the Western Bohai Sea, North China

Abstract

Three stages of paleochannels development, dating back to the Mid-Pleistocene, have been identified in the western Bohai Sea (BS) region. However, the factors controlling their sedimentary formation remain unclear. This study analyzed samples from DZQ01 and adjacent boreholes to establish a chronological framework through AMS ¹⁴C and OSL dating, complemented by grain size and geochemical analyses. End-member analysis using the Generalized Weibull method successfully separated three components: EM1, EM2, and EM3. EM3 (<26.28 μm) reflects the influence of the East Asian Summer Monsoon (EASM), while EM2 (26.28–105.1 μm) is indicative of the East Asian Winter Monsoon (EAWM). Geochemical indicators, such as the Rb/Sr ratio, reflect the impact of paleoclimatic changes. This study identified five major glaciation events since the Mid-Pleistocene. The DU6 unit recorded two glacial stages (300–272 cal. ka B.P.), characterized by a weakened EASM and a stronger EAWM. Similarly, the DU4 unit recorded two glacial stages (165–127 cal. ka B.P.), also marked by a subdued EASM and an enhanced EAWM. The DU2 unit reflects a prolonged glacial stages (71–14 cal. ka B.P.), dominated by the EAWM, resulting in cold and dry conditions. Overall, the uplift of the Tibetan Plateau and sea-level fluctuation significantly influenced the formation and evolution of paleochannels, with the sedimentary characteristics closely tied to the intensities of the East Asian Monsoon (EAM).