末次冰期晚期半干旱环境下黄河阶地上的河流与风沙沉积交互过程

末次冰期晚期半干旱环境下黄河阶地上的河流与风沙沉积交互
过程
马俊飞;王先彦;弋双文;戴岩;刘全玉;鹿化煜
【期刊名称】《高校地质学报》
【年(卷),期】2017(023)004
【摘要】风沙与河流地貌过程的交互作用是半干旱环境典型的地表过程.位于半干旱区的黄河兰州至银川段,现代风沙与河流沉积过程相互影响剧烈,而该区域地质历史时期风沙与河流交互过程的沉积记录还鲜有报道.文章对该区域黄河二级河流阶地堆积序列(河道砾石-具水平层理砂层-沙丘砂-条带状粉砂)进行了详细的沉积学分析.结果表明,流水作用形成的水平砂层之上覆盖的厚2～3.8 m的沙丘,由成分均匀的极细砂和粗粉砂组成;发育块状结构,而未见流水沉积结构;为典型风成沙丘.其上覆盖的粉砂层,粒度组成与该地区砂质黄土有相似性,以粗粉砂颗粒为主;但其还含有少量的粘土和极细砂组分,分选差,且发育薄层条带状纹层(层厚约5～10 cm);为河漫滩环境下主要为风尘输入的颗粒在静水条件下沉降形成的河漫滩相沉积.风成沙丘的众数粒度值略小于下伏水平状河流砂众数粒度,而粗颗粒组分和细颗粒组分含量都略小于下伏河流砂,表明风成沙丘可能是由风力分选、搬运下伏河流砂,就地堆积形成.风成沙丘与下伏河流砂的主量元素组成基本一致,而与该区域物质来源于较大范围的风成砂黄土主量元素的组成相差较远,也表明该阶地堆积序列中发育的风成沙丘物质来源于局地下伏的河流砂层.光释光年代测试的结果表明,风成沙丘堆积于距今约21～16 ka期间,而上覆河漫滩堆积于距今约14～13 ka期间.末次盛冰期,干旱气候和强劲的冬季风导致早期河漫滩上发育风成沙丘,而随后的冰消期夏季风的加强和相对暖湿的气候,使得末次盛冰期形成的沙丘被河漫滩沉积覆盖.该区域黄
河二级阶地由辫状河砾石(夹砂透镜体)-河漫滩砂-风成沙丘-河漫滩粉砂构成的沉积序列是该区域末次盛冰期以来风沙与河流交互作用形成的良好记录,反应了半干旱地区地表过程(风沙和河流交互)对气候环境变化的响应.%The interactions of fluvial and Aeolian processes are a pronounced feature in dry land environments, which can significantly change Earth surface morphology. The interactions of fluvial and Aeolian processes are common in the Lanzhou-Yinchuan reach of Huanghe river catchment at present, but it is rarely reported in the geological time. Here, we analysis the sedimentology including grain size distribution of a sediment sequence on the T2 terrace of the Huanghe River in this area. Aeolian sand dunes (2-3.8 m thickness) situated between fluvial coarse sands and floodplain silts are distinguished, which show mass structure, and mainly composed of well sorted very fine sand. The poor sorting laminar silt mixed with clay and very fine silt covers these dunes. We consider this sediment unit (laminar silt) as floodplain sediment including some aeolian dust input, settling from static water. The grain size of the aeolian dune is slightly smaller than that of the underlying horizontal fluvial sand. Both of the amounts of the coarse and fine component in the sand dunes are less than that in the underlying fluvial sand. These may indicate that the aeolian sand dunes in this region are built through the wind eroding, sorting, carrying the underlying fluvial sand and accumulating in situ. The elemental compositions of the aeolian sand dunes are consistent with the underlying fluvial sand and different from the sandy loess in this area. This also indicates that the source of the dunes on the terrace is the fluvial sand below the dunes. The OSL ages
show that the aeolian dunes were deposited during 21～16 ka, and the covering floodplain silts deposited during 14～13 ka. The correlation of the deposit of dunes with climate change records in this area show the sand dunes were built during the period of strong winter monsoon with cold and dry climate during the Last Glacial Maximum (LGM). And the dunes were covered by floodloam later, when the period of strong summer monsoon with warm and wet climate during the last deglaciation. The sediment sequence composed by fluvial gravel, sand, aeolian dune, floodloam on the second terrace of the Huanghe river in this area show the interactions of fluvial and Aeolian process as a response to the climate and environment changes since LGM in this semi-arid environments.
【总页数】9页(P750-758)
【作者】马俊飞;王先彦;弋双文;戴岩;刘全玉;鹿化煜
【作者单位】南京大学地理与海洋科学学院,南京210023;南京大学地理与海洋科学学院,南京210023;南京大学地理与海洋科学学院,南京210023;南京大学地理与海洋科学学院,南京210023;安康学院,安康725000;南京大学地理与海洋科学学院,南京210023
【正文语种】中文
【中图分类】P931
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