黄河上游靖远金坪段全新世古洪水沉积物特征  

Sediment Characteristics of the Palaeoflood Slackwater Deposits at Jingyuan-Jinping Site in the Upper Reaches of the Yellow River

作　　者：赵雪如 黄春长[1] 庞奖励[1] 查小春[1] 郭永强[1] 胡贵明[1] 

机构地区：[1]陕西师范大学旅游与环境学院,陕西西安710062

出　　处：《山地学报》2016年第2期173-180,共8页Mountain Research

基　　金：国家自然科学基金项目(41471071);教育部博士点基金优先发展领域项目(20110202130002)~~

摘　　要：通过对黄河上游靖远-景泰峡谷段进行系统地全新世古洪水沉积学和水文学考察,确定金坪村剖面含有一组14层古洪水滞流沉积层。同时在该河段多处发现2012年大洪水洪痕和滞流沉积物的尖灭点。对两种沉积物进行采样和分析测试,结果表明古洪水滞流沉积物粒度成分分类为粘土质粉沙和细沙质粉沙。其粒度分布集中,分选性良好,与现代大洪水滞流沉积物完全相同,明显不同于晚更新世马兰黄土和全新世中期古土壤。这些特征表面他们是黄河上游古洪水悬移质泥沙在高水位滞流环境下缓慢沉积的产物,记录了黄河上游靖远-景泰峡谷段一期14次特大古洪水事件。该剖面全新世古洪水滞流沉积物的磁化率很低、烧失量小、Ca CO3含量低,与现代洪水滞流沉积物对应指标相似。说明这组古洪水滞流沉积物在沉积之后很快被坡积石渣土覆盖保存,没有受到地表风化成壤作用的影响。并且经过OSL测年,本期特大古洪水事件发生在3 200—3 000 a B.P.,这些研究结果对于揭示黄河上游特大洪水沉积物性质和泥沙来源、开展黄河流域全新世古洪水水文学研究,揭示黄河上游洪水水文泥沙过程对于全球变化的响应规律具有重要的意义。Field investigation was carried out along Jingyuan -Jingtai Gorges in the upper reach of the Yellow River. Typical palaeoflood slackwater deposits of the Holocene age were identified at the base of the bedrock valley slopes in the Jinpingcun（JPC） site. According to its sedimentary features during our fieldwork, 14 beds palaeoflood slackwater deposits are confirmed. Meanwhile, several modem flood slack water deposits and its end points were found in the same reach. These deposits were consisted of the sandy silt and silt fine. The particle-size distribution of the palaeo- flood SWD was centralized and well sorted, which was totally same with modem flood slack water deposits hut different from loess and palaeosoil. All these characteristics indicated that the palaeoflood slackwater deposits were actually suspended sediment load in flood flow deposited in areas of flow separation and preserved after the flood recession. 14 extraordinary palaeoflood events were recorded by these newly deposited and unaffected deposits in Jingyuan -Jingtai Gorges in the upper reaches of the Yellow River. Besides, the magnetic susceptibility,loss-on-ignition of palaeoflood slackwater deposits were particularly low, which similar with modem flood slack water deposits. This indicated that they were not much affected by weathering and pedogenesis after deposition. Though OSL dating,this events occurred in 3 200 - 3 000 a B. P.. Our study has great significance to reveal the flood slackwater characteristic, distinguish the origin of sediment and provide important data in understanding the interactions between regional hydro-climatic systems and global change in semi-arid and sub-humid regions.

关 键 词：环境变迁 古洪水滞流沉积物 沉积特点 黄河上游 全新世 

分 类 号：P512.2[天文地球—地质学] P539.6