【摘要】：黃土是第四紀氣候變化研究的三大載體之一,黃土—古土壤序列記錄了第四紀以來諸多氣候環(huán)境演變信息。漢江上游地區(qū)地處秦嶺南側(cè),是我國南北氣候環(huán)境的過渡地帶,對環(huán)境響應(yīng)敏感,其河流階地上的黃土包含了階地形成以來的氣候和地貌演變信息,值得深入探究；同時,隨南水北調(diào)中線工程的建設(shè),對此區(qū)域未來環(huán)境變化研究和預(yù)測成為研究熱點。氣候研究的關(guān)鍵是測年問題,但目前有關(guān)階地地層年代序列的系統(tǒng)研究還較少,對階地黃土沉積過程中氣候環(huán)境變化規(guī)律的研究造成一定困難。在對漢江上游河谷進行野外考察的基礎(chǔ)上,選擇漢江上游安康——鄖縣段分布于河流兩岸的4個典型一級階地剖面以及位于南水北調(diào)中線的漢江支流丹江一級階地1個剖面共5個剖面作為研究對象,進行詳細可靠的光釋光測年研究及氣候替代性指標(biāo)測試。針對樣品的不同釋光特征對測年方法和測年條件進行選擇,檢驗光釋光測年方法對于漢江一級河流階地沉積物的適用性,對樣品最終年代的可靠性進行驗證,嘗試不同測年方法相互對比,以獲得較為可靠的年齡數(shù)據(jù)。主要結(jié)論如下：(1)主要運用快速組分得出等效劑量(De)值的單片再生劑量法(SAR)為適合漢江上游樣品測試的最佳方法,使用回授信號來獲得De值的TT-OSL法由于其光釋光信號較弱且難以與本底區(qū)分而不適合漢江上游石英樣品的測年。(2)40～63μm(中粒)和90～125μm(粗粒)的黃土樣品均可用于漢江上游樣品的測年：90～125μm適合用于未飽和樣品的測年,40～63μm適合用于飽和樣品的測年；240～260℃為樣品De值測試的普遍適用溫度坪區(qū),cutheat選擇小于預(yù)熱溫度40℃。(3)漢江上游一級階地雛形開始出現(xiàn)于55 ka B.P.,最終形成于25 ka B.P.。階地形成初期(55-25 ka B.P.),區(qū)域地貌演變以新構(gòu)造抬升與河流下切為主,此期間河漫灘相沉積物時而高于河面接受風(fēng)塵堆積,時而被河水淹沒而出現(xiàn)風(fēng)成黃土—沖積砂的交互層。階地發(fā)展穩(wěn)定后(25-0 ka B.P.),新構(gòu)造抬升趨于停止,區(qū)域地貌演化以階地面穩(wěn)定接受風(fēng)塵堆積為特征,形成了厚層風(fēng)成黃土覆蓋層。(4)漢江一級階地上55 ka B.P.以來的沉積序列記錄了此區(qū)域末次冰期和全新世的氣候變化。末次冰期以內(nèi),漢江上游區(qū)域以干冷氣候為主,氣候波動頻繁,在LJT、MTS等剖面出現(xiàn)多期次的風(fēng)成黃土—沖積砂的交互層；進入全新世以后,隨著東南季風(fēng)的進退,全新世又分為三個不同的氣候期：11.3～8 ka的全新世早期升溫期；8～3ka左右的全新世適宜期；3ka以來的降溫期。漢江黃土地層中記錄了全新世6～5ka的氣候惡化事件,發(fā)育了黃土層；并記錄了0.38ka左右的古洪水事件,發(fā)育了古洪水滯留沉積層。
[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，

本文編號：2282180