渭河临潼段与长江宜都段全新世古洪水沉积学对比研究

【作者】 王娟；

【导师】 黄春长；

【作者基本信息】 陕西师范大学 ， 自然地理学， 2012， 硕士

【摘要】 本文通过对渭河临潼段与长江宜都段的野外考察,选取渭河临潼陈东村剖面和长江宜都尾笔村2个剖面和渭河2010年现代洪水沉积物作为研究对象,这两个剖面均含有典型的古洪水滞流沉积物,共采集到样品59个,在陕西师范大学沉积学实验室对其进行粒度、磁化率、碳酸钙含量、烧矢量、吸湿水和化学元素含量的沉积学实验,利用沉积学方法分析对比了渭河临潼陈东村剖面和长江宜都尾笔村剖面古洪水滞流沉积物的特征,并获得了以下结论：(1)观察两个剖面古洪水滞流沉积物的野外特征表明,发现古洪水滞流沉积保存于古河道的回水湾处。在渭河临潼CDC剖面上,古洪水SWD呈浊橙色,颜色上与上层风成黄十与下层古土壤比较接近,但质地和层理明显不同。古洪水SWD呈粘土质地,致密坚硬,具有水平或者波状层理,碎块具有贝壳状状断口,这与剖面上黄十与古十壤不同；在长江宜都WBC剖面上,古洪水SWD呈浊黄橙色,是纯净均匀的松软粉沙,这在颜色质地上与当地古土壤和黄十都有显著区别。(2)对野外采集到的样品进行了沉积学实验,通过粒度实验分析表明,渭河临潼CDC剖面中的古洪水滞流沉积物属粉沙质亚粘十,粒度组成较细,以粉沙含量为主,分选较好；磁化率、烧失量和吸湿水含量低于古十壤,高于马兰黄十；CaCO3含量高于古十壤,低于马黄十,这均说明了渭河临潼CDC剖面的古洪水SWD经历过了洪水的搬运和重新分配。长江宜都WBC剖面中存在二期古洪水SWD,其中,古洪水SWD2属于沙质亚粘土,古洪水SWD1和SWD3属于粉质亚沙土,三层古洪水SWD颗粒粒级均较粗,尤其是古洪水SWD2,粉沙、细沙和沙含量较多。在三层古洪水SWD中,古洪水SWD1和SWD3比古洪水SWD2的分选更好。三层古洪水SWD烧失量和吸湿水含量均低于古土壤和近代风成黄土,其中,古洪水SWD2含量最低,CaCO3含量均高于古土壤和近代风成黄土,其中,古洪水SWD2含量最高,说明古洪水SWD发生时水动力强大,携带了大量泥沙,尤其是古洪水SWD2时期。(3)古洪水SWD中的地球化学元素含量与黄十和古十壤也存在明显的差异,说明古洪水在发生时发生了很好的分选。其中,渭河临潼CDC剖面常量元素与微量元素的UCC曲线与古十壤均很相似,说明当地洪水的元素组成主要是由当地成十母质决定的。长江宜都WBC剖面常量元素与微量元素的UCC曲线既与古十壤不同,也与现代风成黄十不同,说明长江洪水物质来源更为复杂,支流的洪水汇入对该地的元素组成也有较大的影响。两个剖面的沉积物都具有典型古洪水滞流沉积物的特征。(4)渭河临潼CDC剖面和长江宜都WBC剖面中的古十壤与马兰黄十、现代黄十在沉积学特征上存在着显著的差异。在粒度组成上,古土壤的粘粒和细粉沙含量较多,粗粉沙、细沙、沙三者含量较小,中值粒级和平均粒级较小；磁化率、烧失量和吸湿水含量均较高。长江宜都WBC剖面古土壤磁化率较低是由于长江中下游地区地势较低,长期处于还原环境,土壤潜育化,形成较多的氧化亚铁,所以磁化率较低；同时CaCO3含量较低,这与马兰黄土和现代黄土止好相反,说明在古土壤形成时期夏季风盛行,气候温暖湿润,生物作用较强,土壤粘粒胶体较多,而黄土堆积形成时期冬季风盛行,气候寒冷干燥,以粉尘堆积为主。(5)通过OSL测年断代,同时对比渭河上游宝鸡峡固川镇剖面底层年代,确定渭河临潼CDC剖面古洪水发生在3200～3000a BP之间,这个时期正是全新世大暖期结束之际,也就是我国历史上商代末期,气候由暖变冷；长江宜都WBC剖面古洪水SWD位于现代黄土之上,夹杂与表土层之中,通过OSL测年分析,结合320cm处(L0)发现的东汉文化层的陶片测年年代,确定古洪水SWD1、SWD2和SWD3分别为宋、元、清代洪水。本文研究成果和方法具有非常重要的理论意义；通过OSL测年技术,结合考古资料,确定古洪水SWD的发生年代,进而对长江和渭河SWD的沉积学特征进行对比,这一对比结果为这些地区的水利工程建设、交通工程建设、水资源调控、防洪减灾以及流域内生态环境综合治理等方面提供了重要依据,丰富了古洪水水文学对比研究。更多还原

【Abstract】 We have done some field survey on the Weihe River and Changjiang river, and we got fifty nine sedimental samples from two profiles which contain several slackwater deposits and paleostage indicators. They were analyzed in the sedimentologic laboratory in Shaanxi Normal University, including Grain-size distribution, magnetic susceptibility, loss-on-ignition, CaCO3, hydroscopic water and chemical elements content. We contrast the characters of Holocene paleoflood Deposits in two profiles by sedimentologic analysis. The main results are as following:(1) After detailed observation, we found that the Holocene paleoflood Slackwater Deposits were kept at the ancient river water in the bay. In the CDC profile, the color of the Holocene paleoflood Slackwater Deposits is turbid orange, which is close to the upper eolian loess and the lower paleosol. But the texture and bedding are both markedly different. The Holocene paleoflood Slackwater Deposits are clay quality of a material and have the level or wavy bedding, dense hard and the fragments with shell-liked fracture. In the WBC profile, The Holocene paleoflood Slackwater Deposits are pure uniform loose silty sand and have the color of turbid yellow orange. These features are different from loess and paleosol.(2) Through particle size experimental analysis, the results show that the Holocene paleoflood Slackwater Deposits in CDC profile are silty clay, size of a fine, sorting better than other sediments; magnetic susceptibility, loss-on-ignition and hydroscopic water content are both lower than paleosol, higher than malan loess; CaCO3content is opposite. These features show that the Holocene paleoflood Slackwater Deposits in CDC profile have experienced the flood of transportation and redeposition. There are three sections paleoflood Slackwater Deposits in WBC profile. SWD2is silty clay, SWD1and SWD3are both sand clay. Three layers of paleoflood Slackwater Deposits are coarse granularity especially SWD2, Whose sorting is better than SWD1and SWD3. Three layers of paleoflood Slackwater Deposits’ loss-on-ignition and hydroscopic water content are lower than paleosol and eolian loess especially SWD2. The CaCO3content of paleoflood Slackwater Deposits is larger than paleosol and eolian loess especially SWD2. The results show that hydrodynamic force is very strong and transports a lot of sand when paleoflood happened.(3) In CDC and WBC profiles, the chemical elements content of paleoflood Slackwater Deposits is different from loess and paleosol. The result shows that the material source of the Holocene paleoflood Slackwater Deposits is different from loess. In CDC profile, the Curves of major element and trace element standardized by UCC are similar to paleosol. The composition of the local flood’s element is mainly decied by local soil parent material. In WBC profile, the Curves of major element and trace element standardized by UCC are different from paleosol and loess. These features show that the source material of the Changjiang river flood is more complex and tributaries into flood in the area of the elements had great influence. The sediments of two profiles are both typical paleoflood Slackwater Deposits.(4) The sedimentation characteristics of paleosol and loess are significant different in two profiles. In CDC profile, paleosol contains more clay and fine silt, less coarse silt and sand. Median grain of level and average level is lower. Magnetic susceptibility, loss-on-ignition and hydroscopic water content is higher. In WBC profile, because the middle and lower reaches of Changjiang river are low-lying, staying in reduction environment in a long time, soil gleying, FeO forming, so magnetic susceptibility is lower. The CaCO3content of paleoflood Slackwater Deposits is also lower. These features are opposite to loess. These results shows that the paleosol formation period summer monsoon prevail, warm and humid, stronger biological function, more soil clay. The loess formation period winter monsoon prevail, cold and dry, dust accumulation.(5) In CDC profile, OSL dating shows that these palaeoflood events occurred between3200to3000a BP, exactly the same time as that documented in the upper reaches of the Weihe River. This time was the ending of the mid-Holocene climatic optimum, and also the ending of the Shang Dynasty in Chinese history. In WBC profile, OSL dating and archeology shows that three palaeoflood events occurred in Song, Yuan, Qing dynasty.These research results and methods have important theoretical significance; Through OSL dating and archeology, we determine the time of these palaeoflood events and contrast the sedimentology characteristics of paleoflood Slackwater Deposits in Changjiang river and Weihe river. The contrastive results for these regions hydraulic engineering construction, traffic engineering construction, water regulation, flood control and watershed ecology, and so provide an important basis, and enrich the comparison study of paleoflood.更多还原