汉江上游一级阶地风成黄土光释光测年研究及意义
发布时间：2018-10-19 19:49
【摘要】：黄土是第四纪气候变化研究的三大载体之一,黄土—古土壤序列记录了第四纪以来诸多气候环境演变信息。汉江上游地区地处秦岭南侧,是我国南北气候环境的过渡地带,对环境响应敏感,其河流阶地上的黄土包含了阶地形成以来的气候和地貌演变信息,值得深入探究；同时,随南水北调中线工程的建设,对此区域未来环境变化研究和预测成为研究热点。气候研究的关键是测年问题,但目前有关阶地地层年代序列的系统研究还较少,对阶地黄土沉积过程中气候环境变化规律的研究造成一定困难。在对汉江上游河谷进行野外考察的基础上,选择汉江上游安康——郧县段分布于河流两岸的4个典型一级阶地剖面以及位于南水北调中线的汉江支流丹江一级阶地1个剖面共5个剖面作为研究对象,进行详细可靠的光释光测年研究及气候替代性指标测试。针对样品的不同释光特征对测年方法和测年条件进行选择,检验光释光测年方法对于汉江一级河流阶地沉积物的适用性,对样品最终年代的可靠性进行验证,尝试不同测年方法相互对比,以获得较为可靠的年龄数据。主要结论如下：(1)主要运用快速组分得出等效剂量(De)值的单片再生剂量法(SAR)为适合汉江上游样品测试的最佳方法,使用回授信号来获得De值的TT-OSL法由于其光释光信号较弱且难以与本底区分而不适合汉江上游石英样品的测年。(2)40～63μm(中粒)和90～125μm(粗粒)的黄土样品均可用于汉江上游样品的测年：90～125μm适合用于未饱和样品的测年,40～63μm适合用于饱和样品的测年；240～260℃为样品De值测试的普遍适用温度坪区,cutheat选择小于预热温度40℃。(3)汉江上游一级阶地雏形开始出现于55 ka B.P.,最终形成于25 ka B.P.。阶地形成初期(55-25 ka B.P.),区域地貌演变以新构造抬升与河流下切为主,此期间河漫滩相沉积物时而高于河面接受风尘堆积,时而被河水淹没而出现风成黄土—冲积砂的交互层。阶地发展稳定后(25-0 ka B.P.),新构造抬升趋于停止,区域地貌演化以阶地面稳定接受风尘堆积为特征,形成了厚层风成黄土覆盖层。(4)汉江一级阶地上55 ka B.P.以来的沉积序列记录了此区域末次冰期和全新世的气候变化。末次冰期以内,汉江上游区域以干冷气候为主,气候波动频繁,在LJT、MTS等剖面出现多期次的风成黄土—冲积砂的交互层；进入全新世以后,随着东南季风的进退,全新世又分为三个不同的气候期：11.3～8 ka的全新世早期升温期；8～3ka左右的全新世适宜期；3ka以来的降温期。汉江黄土地层中记录了全新世6～5ka的气候恶化事件,发育了黄土层；并记录了0.38ka左右的古洪水事件,发育了古洪水滞留沉积层。
[Abstract]:Loess is one of the three major carriers in the study of Quaternary climate change. The loess paleosol sequence records a lot of climatic and environmental evolution information since the Quaternary. The upper reaches of the Hanjiang River, located in the southern side of Qinling Mountains, is a transitional zone between north and south climate environment in China. It is sensitive to the environment. The loess on the river terrace contains the information of climate and geomorphology evolution since the terrace was formed, so it is worth further exploring. With the construction of the middle route project of South-to-North Water transfer Project, the research and prediction of the future environmental change in this area has become a research hotspot. The key of climate research is dating, but there are few systematic studies on terrace stratigraphic chronological sequence at present, which makes it difficult to study the regularity of climate and environment change in terrace loess sedimentary process. On the basis of a field survey of the upper Hanjiang River valley, Four typical first-order terraces in the upper reaches of Hanjiang River, Ankang-Yunxian section, and one section of Danjiang first terrace, a tributary of Hanjiang River in the middle line of South-to-North Water diversion Project, are selected as the research objects. A detailed and reliable study of optical luminescence dating and climate substitution index testing was carried out. According to the different luminescent characteristics of the samples, the dating method and the dating conditions are selected, the applicability of the optical luminescent dating method to the first-order river terrace sediments of the Hanjiang River is tested, and the reliability of the final age of the samples is verified. In order to obtain reliable age data, we try to compare different dating methods with each other. The main conclusions are as follows: (1) the monolithic regenerative dose method (SAR), which mainly uses the fast component to obtain the equivalent dose (De) value, is the best method for sample testing in the upper reaches of the Hanjiang River. The TT-OSL method for obtaining the De value by using the back credit number is not suitable for the dating of quartz samples in the upper reaches of the Hanjiang River due to its weak optical luminescent signal and difficult to distinguish from the background. (2) the loess samples of 400.63 渭 m (medium grain) and 90,125 渭 m (coarse grain) can be used in Han Dynasty. The dating of the samples in the upper reaches of the Yangtze River: 90 ~ 125 渭 m is suitable for the dating of unsaturated samples, and 40 ~ 63 渭 m is suitable for the dating of saturated samples; The De values of the samples were measured at 240 鈩，
本文编号：2282180
[Abstract]:Loess is one of the three major carriers in the study of Quaternary climate change. The loess paleosol sequence records a lot of climatic and environmental evolution information since the Quaternary. The upper reaches of the Hanjiang River, located in the southern side of Qinling Mountains, is a transitional zone between north and south climate environment in China. It is sensitive to the environment. The loess on the river terrace contains the information of climate and geomorphology evolution since the terrace was formed, so it is worth further exploring. With the construction of the middle route project of South-to-North Water transfer Project, the research and prediction of the future environmental change in this area has become a research hotspot. The key of climate research is dating, but there are few systematic studies on terrace stratigraphic chronological sequence at present, which makes it difficult to study the regularity of climate and environment change in terrace loess sedimentary process. On the basis of a field survey of the upper Hanjiang River valley, Four typical first-order terraces in the upper reaches of Hanjiang River, Ankang-Yunxian section, and one section of Danjiang first terrace, a tributary of Hanjiang River in the middle line of South-to-North Water diversion Project, are selected as the research objects. A detailed and reliable study of optical luminescence dating and climate substitution index testing was carried out. According to the different luminescent characteristics of the samples, the dating method and the dating conditions are selected, the applicability of the optical luminescent dating method to the first-order river terrace sediments of the Hanjiang River is tested, and the reliability of the final age of the samples is verified. In order to obtain reliable age data, we try to compare different dating methods with each other. The main conclusions are as follows: (1) the monolithic regenerative dose method (SAR), which mainly uses the fast component to obtain the equivalent dose (De) value, is the best method for sample testing in the upper reaches of the Hanjiang River. The TT-OSL method for obtaining the De value by using the back credit number is not suitable for the dating of quartz samples in the upper reaches of the Hanjiang River due to its weak optical luminescent signal and difficult to distinguish from the background. (2) the loess samples of 400.63 渭 m (medium grain) and 90,125 渭 m (coarse grain) can be used in Han Dynasty. The dating of the samples in the upper reaches of the Yangtze River: 90 ~ 125 渭 m is suitable for the dating of unsaturated samples, and 40 ~ 63 渭 m is suitable for the dating of saturated samples; The De values of the samples were measured at 240 鈩，
本文编号：2282180
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