中晚全新世黄河下游湖泊沉积物磁性特征及河道变迁

Abnormal monsoon rainfall caused by global climate change poses a serious threat to the course in the lower reach of the Yellow River (CLYR). The correct understanding of the changing history of the CLYR and the further clear clarification of its regularity is the basis for scientific management about the Yellow River. A series of lakes located in the north-flow path (such as Daluze Lake, Aze Lake, and Dayeze Lake) and south-flow path (such as Luoma Lake) of the CLYR since the middle to late Holocene are important sedimentary archive for the research of course changes. Previous studies have relied on the coarse-grained fluvial or flooded material deposits in these lakes to explore the breaching and shifting history of the CLYR. However, in addition to Yellow River, other regional rivers can also bring coarse-grained sediments to these lakes, leading to a misunderstanding of the CLYR’s changing history which been reconstructed by the coarse-grained deposits. For this reason, we propose a source analysis of the coarse-grained sediments in these lakes using the environmental magnetic indicators. We aim to find out the difference of magnetic characteristics between the Yellow River inputted and other rivers inputted coarse-grained sediments. Then effectively identify the coarse-grained sediments which from the Yellow River, so as to obtain a reliable history of the CLYR’s changes from middle to late Holocene. This research provides important data for investigating the CLYR’s changing regularity and driving mechanism, and lays scientific basis for preventing the natural disasters accompanied by course changing that caused by abnormal flood under the background of global warming.

全球气候变化引起的季风降雨异常使黄河下游河道面临严重威胁。正确认识黄河下游河道变迁历史、厘清变迁规律是科学治理黄河的基础。中晚全新世以来发育在黄河北流路径上的大陆泽、阿泽和大野泽以及南流路径上的骆马湖，是探究黄河下游河道变迁历史的极佳沉积载体。以前的研究多基于这些湖泊中的粗颗粒河流相或洪泛物质沉积层来探究黄河决溢改道历史。然而除了黄河输入物质外，区域内其他入湖河流也可以为这些湖泊带来粗颗粒沉积物，从而可能导致基于粗颗粒沉积层获得的黄河决溢改道记录失真。为此，我们提出利用环境磁学指标对这些湖泊中的粗颗粒沉积层进行物源分析。找到黄河与其他河流带入的粗颗粒沉积物的磁性特征差异，并有效识别出湖泊中来自黄河的粗颗粒沉积物，从而得到中晚全新世黄河下游河道可靠的变迁历史，为深入理解其变迁规律与驱动机制提供重要数据，为应对全球变暖背景下异常洪水导致的河道变迁及相伴灾害提供科学依据。

苏北平原黄墩洼地记录了黄河决溢改道历史。本研究基于多种粒度描述性参数和BEMMA端元分析手段，成功揭示黄墩洼地沉积物多物源属性，并将3个组分单独提取出来。通过与现代黄河以及山东黄土的综合对比分析，阐明了各组分具体来源。其中组分1为流域内河流、冲洪积和极端暴雨导致的地表径流输入的物质，组分2为后期成壤作用改造的远距离输入粉尘物质，组分3为黄河贡献的典型物质。基于这些物质的变化并结合环境磁学、TOC等指标，揭示中-晚全新世以来黄墩洼地沉积环境发生巨变。由稳定的陆相沉积环境转变为河流相沉积。在典型河流相沉积序列中，识别出4个频繁的黄河决溢改道阶段以及8次重要事件。这一研究，第一次从地质记录中厘清了黄河南流路径上的演变过程。为探究黄河更新世全面贯通以来的演化研究提供借鉴。同时，为应对季风降雨异常导致的黄河下游河道决溢风险提供理论依据。