黄河前套盆地TMZ05钻孔沉积记录的古水文变化研究

Paleohydrological variations revealed from the TMZ05 Borehole in the Qiantao Basin of the Yellow River

  • 摘要: 古水文是研究评估流域灾害风险的重要历史参照。以黄河前套盆地土默特右旗段1个深约19 m的钻孔岩芯(TMZ05)为载体,通过对沉积物粒度和元素等指标的分析,构建了粒度的U值(p(16~80 μm) / p(2~16 μm))、粒度端元组分的FEI值((pEM4+pEM5)/(pEM3+pEM4+pEM5))以及元素ln(Zr/Rb)值作为古水文强度的代用指标,基于光释光(OSL)和AMS14C测年技术,重建了该区19 ka以来古水文的演变过程,进而探讨了区域古水文演化阶段及其对气候系统的响应关系。结果发现,末次冰盛期以来该区古水文事件的频率和幅度呈现出总体降低的趋势,在阶段性上表现出18.5~14 ka与8.5~6 ka古水文为低频低幅的特征,而14~8.5 ka古水文为强烈的高频高幅的变化,6 ka之后,古水文的强度和变率呈上升的趋势。FEI和ln(Zr/Rb)指标具有更高的分辨率,揭示了5个古水文事件的高频高幅期,即19~16.5 ka、14~11.7 ka、11~9.7 ka、9.4~8.5 ka和4.2~1.6 ka,期间黄河流域的灾害性洪水事件频发。综合区域古环境数据的对比,发现古水文高频高幅的时段即黄河流域洪水灾害的频发总体对应于气候系统的转型时段,说明水文气候系统的不稳定性会影响河道形态的平衡。

     

    Abstract: Paleohydrology serves as a critical historical reference for studying and assessing flood risks in river basins. We analyzed a ~19 m deep borehole core (TMZ05) from Tumote Right Banner in the Qiantao Basin of the Yellow River and reconstructed the paleohydrological evolution over the past 19 ka using sediment grain size and geochemical proxies, including the grain-size U value (U=p(16~80 μm) / p(2~16 μm), flood energy index (FEI=(pEM4+pEM5)/(pEM3+pEM4+pEM5)) from grain size end-member components, and ln(Zr/Rb) values. Optically stimulated luminescence (OSL) and accelerator mass spectrometry (AMS) 14C dating were applied to establish the chronological framework. Results reveal that since the Last Glacial Maximum (LGM), the frequency and magnitude of paleohydrological events in the region have been generally decreased but exhibited distinct phases. Periods of 18.5~14 ka and 8.5~6 ka were characterized by low-frequency and low-amplitude fluctuations, while 14~8.5 ka showed intense high-frequency and high-amplitude hydrological variability. After 6 ka, both the intensity and variability of paleohydrology were gradually increased. Furthermore, five high-frequency and high-amplitude paleohydrological phases: 19~16.5 ka, 14~11.7 ka, 11~9.7 ka, 9.4~8.5 ka, and 4.2~1.6 ka indicated by high-resolution proxies (FEI and ln(Zr/Rb)), during which catastrophic flood events occurred frequently in the Yellow River Basin. Regional paleoenvironmental comparisons indicate that these high-frequency and high-amplitude hydrological phases corresponded to intensified flood disasters, and occurred mainly during the transitional periods of climate system, implying that the instability in hydroclimatic regime could seriously disrupt the equilibrium of fluvial morphology.

     

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