华北平原HS1钻孔第四纪冲洪积物地球化学特征及古气候意义

选用华北平原地区长时间序列的HS1钻孔, 在对其沉积物主、微量元素含量、相关程度及地球化学指标分析的基础上对区内古环境变化、古气候演化进行了讨论。结果表明, 自上新世晚期(3.50 Ma)以来HS1钻孔所在区域经历了温暖湿润—温和偏湿—寒冷略干—寒冷干旱—温和偏干—温凉潮湿—温和偏干—温暖潮湿8个气候演化阶段, 整体趋势由湿润变为干旱, 这与孔内孢粉、碳-氧同位素和粒度记录具有同趋性。区域对比结果显示, 重建长时间尺度内的气候变化, 地球化学可作为孢粉的更优等效指标, 短时间序列内的气候变化则以高分辨率的孢粉记录最优。区内整体处于陆缘弱氧化的沉积环境, 且第四纪时期化学风化程度相较古土壤层发育的上新世晚期更弱。HS1钻孔不同地质时期冲洪积物的元素地球化学组成的差异性, 主要取决于其母质来源和搬运距离; 具体表现为一方面与受地形地貌影响、一级构造调节转换带及次级构造单元控制的古水流有关, 另一方面与受气候变化影响的沉积环境、水动力条件、化学风化和成土作用等有关。

Geochemical Characteristics and Paleoenvironmental Significance of Quaternary Alluvial-pluvial Deposits in Borehole HS1 in the North China Plain

The paleoenvironmental changes and paleoclimate evolution were discussed based on the analysis of the content, correlation degree, and geochemical index of the major and trace elements in the sediments of the HS1 borehole in the North China Plain. The results demonstrated that since the Late Pliocene (3.50 Ma), the area surrounding the borehole HS1 has undergone eight climatic evolution stages: warm and humid, moderately humid, cold and slightly dry, cold and drought, moderately dry, moderately cool and humid, moderately dry, and warm and humid. The overall climatic tendency has changed from wet to dry, which is consistent with the pollen grain size and carbon-oxygen isotope records of borehole HS1. The results of the regional comparison revealed that geochemistry can be used as a better equivalent index for pollen to reconstruct climate change on a long-time scale and that climate change on a short-time scale is best recorded by high-resolution pollen. The entire area was in a weak oxidation sedimentary environment on the continental margin and the degree of chemical weathering in the quaternary period was weaker than that in the late Pliocene. The distinction in the geochemical element composition of alluvium in different geological periods of borehole HS1 primarily relied on its parent material source and transport distance. On the one hand, it was associated with the ancient water flow controlled by topography and geomorphology, primary tectonic adaptation, transformation zone, and secondary tectonic unit. On the other hand, it was related to the sedimentary environment, hydrodynamic conditions, chemical weathering, and soil formation influenced by climate change.