EGI OpenIR
罗布泊盐湖沉积物磁性特征及其古环境记录研究
Alternative TitleMagnetic properties of sediments of saline lake Lop Nur and its implications for paleo-environmental change
李文
Subtype博士
Thesis Advisor穆桂金
2019-06-30
Degree Grantor中国科学院大学
Place of Conferral北京
Degree Discipline理学博士
Keyword盐湖沉积 罗布泊 磁性特征 早期成岩作用 古气候变化 Saline lake sediments Lop Nur Magnetic properties Early diagenesis paleo-environmental change
Abstract盐湖沉积物是干旱-半干旱地区过去不同时间尺度气候和环境变化的重要信息记录载体。 罗布泊是世界知名的盐湖沉积区域,位于塔里木盆地东端,亚欧大陆腹地干旱核心区,是青藏高原北侧最大沉降盆地的沉积-汇水中心,记录了区域数百万年以来的气候环境历史。历史上孕育了以小河文化和楼兰文化为代表的灿烂古文明,也是古丝绸之路的交通枢纽。 提取可靠的环境记录指标,重建罗布泊地区的高分辨率环境记录对于理解全球气候环境变化和人地关系至关重要。沉积物磁学性质被广泛应用于湖泊沉积研究,常用反映沉积环境和古气候变化,但在盐湖环境中,沉积物磁性特征及其成因机制尚未清晰解译。 本文对采集自罗布泊盐湖的 LB(深度 378 cm) 和 LOP1(深度 163 cm) 两个剖面,以及罗布泊盐湖表层沉积物, 罗布泊西岸地区的雅丹、风成砂和红柳沙包沉积物进行了系统的环境磁学研究,结合年代学测试、粒度、有机质、碳酸盐、色度、 X 射线衍射 (XRD)、扫描电镜和能谱分析(SEM/EDS)等手段,系统分析了罗布泊盐湖沉积物的磁性特征及其影响因素,阐明了磁性特征的沉积学和古环境意义,利用磁性特征重建了罗布泊地区全新世以来的气候环境变迁历史,并探讨了罗布泊地区全新世气候环境变迁与全球变化之间的关系。获得以下主要结论和新认识:根据磁性特征可将罗布泊盐湖沉积物分为三类, 磁学特征分别为多畴(MD)颗粒磁铁矿主导, 单畴(SD)颗粒胶黄铁矿主导和多畴(MD)颗粒黄铁矿主导。 其中由磁铁矿主导磁性特征的沉积层位,磁性矿物主要来源于陆源碎屑输入。磁性特征(包括磁性矿物类型组合,晶粒和矿物含量) 与罗布泊西岸地区以及物源区塔里木盆地的沉积物一致,体现了沉积物物源的影响, 同时表明这些层位沉积物磁性特征未受到沉积后次生作用的改造, 可视为罗布泊盐湖沉积物磁性特征的背景水平。此外, 磁铁矿主导层沉积物中相对较低的 S-300mT和较高的 HIRM-300mT,显示不完整反铁磁性矿物(主要为赤铁矿)贡献较高。 该类型沉积物中,磁性参数的变化主要与粒度组成变化有关,分粒级提取样品的磁性测量结果以及磁性参数与粒度相关关系分析表明在该类型沉积物中, 粗粒级组分(粗粉砂和砂)沉积物磁性较强。这是因为罗布泊沉积物磁铁矿主要以多畴(MD)为主,较粗的 MD磁性颗粒主要赋存于沉积物粗颗粒组分中, 粗粒级组分沉积物含量越高,磁性矿物含量越高,反之亦然。早期成岩作用是罗布泊盐湖沉积物磁性特征发生变化的最重要因素。 LB 和LOP1 剖面都鉴定到了早期成岩作用成因的次生铁硫化物(胶黄铁矿、黄铁矿)的存在,并导致沉积物磁性特征产生了显著的变化。 单畴(SD)颗粒胶黄铁矿生成和保存导致沉积物具有明显较高的 χ, χARM, SIRM, HIRM-100mT, S-100mT, S-300mT,χARM/χ 以及 SIRM/χ, 而 MD 颗粒黄铁矿则导致了极低的 χ, χARM, SIRM,HIRM-100mT, S-100mT, S-300mT, χARM/χ, 这显示了盐湖环境中硫酸盐还原成岩作用对磁性特征的显著影响。通过多沉积记录指标综合分析和野外岩性观察,判定罗布泊盐湖早期成岩作用成因的次生铁硫化物生成于高湖面(相对湿润)阶段,此阶段流域内湿度较高,增加的有机质输入促使了硫酸盐成岩作用的发生。罗布泊湖盆内早期成岩成因胶黄铁矿及其相关磁学参数(如 SIRM/χ) 可以作为区域水文和气候历史变化的指标。 LB 剖面 8150-7000, 5300-4900, 3600-3100, 2750-2550 和 1820-1680 Cal. yrBP 期间生成和保存了大量 SD 胶黄铁矿颗粒,显示这些沉积阶段罗布泊和塔里木河流域水量较丰,罗布泊处于高湖面阶段。对比前人研究成果,发现这五个胶黄铁矿生成阶段在时间序列上对应或略晚于全新世北大西洋冷事件(5~1)。冷事件期间强度增加并且南移的西风急流为塔里木盆地带来更多降水, 流域湿度和有机质增加, 导致了胶黄铁矿的生成保存。这显示罗布泊地区全新世以来的气候环境变化与高纬度地区的气候突变事件具有关联性。此外, 罗布泊沉积物磁学和沉积学研究表明该地区由早中全新世向中晚全新世的气候过渡呈现突变特点,而非渐变,转折时间约为 4000 cal. yr BP 左右。总体上 4000 cal. yr BP 之前, 区域气候干燥而相对稳定; 4000 cal. yr BP 之后, 湿度增加而波动剧烈,这一气候模式得到大量前人研究结果的支持。 该区域全新世气候变化可能同时受到厄尔尼诺-南方涛动(ENSO)和北大西洋涛动(NAO)的共同影响,后者又影响了西风急流的位置和强度,也对该区域的气候变化产生影响。此外地域性因素(主要是指山地冰川) 的影响也需要考虑,尤其在全新世早期。
Other AbstractSaline lakes are useful repositories for paleo-climatic records in arid-semiaridregion. China’s Lop Nur is one of the world’s largest saline lake, located in theeastern Tarim Basin, was the terminal lake of Tarim River and Kongque River, thelargest waterbody known in west China. Lop Nur is at the convergence of sedimentsand salts from throughout the Tarim Basin, and therefore bears rich information aboutthe environmental evolution of the Tarim Basin and surrounding regions. Lop Nurwas crossed by the famous Silk Road, and was the political, economic, and culturalcenter of western China (e.g. ancient Loulan Civilization). Lacustrine sedimentaryrecords from Lop Nur region are of paramount importance for understanding theQuaternary paleoenvironment of this area and have revealed significant information.In environmental magnetism, rock and mineral magnetic techniques are used toinvestigate the formation, transportation, deposition, and postdepositional alterationsofmagnetic minerals under the influences of a wide range of environmental processes.In recent years, environmental magnetic methods, which include the characterizationof mineralogy, concentration, and the grain size of magnetic minerals, has beenwidely applied to establish paleoenvironment change in diverse environmentalsettings (e.g. lake sediments). However, magnetic properties of saline lake sedimentsand its influence factors have not been determined so far.In this study, LOP1 profile (163 cm) and LB profile (378 cm) were collectedfrom Lop Nur saline lake. The surface sediments, Yardangs sediments, aeolian sanddunes and Tamarix cone sediments were collected from west bank of Lop Nur. Rockmagnetism were carried on those samples, in combination with analyses of geologicaldating, particle size, total organic matter, carbonate content, chroma characteristic,X-ray diffraction (XRD), scanning electron microscope/energy dispersive X-rayspectroscopy (SEM/ EDS). The aim of this study is to assess the influence factors ofmagnetic properties in Lop Nur and its environmental significance. The conclusionsare as follows:According to the magnetic properties, sediments of Lop Nur saline lake can bedivided into three groups, magnetic properties dominated by multi-domain (MD)magnetite, single domain (SD) greigite and multi-domain pyrite, respectively.Magnetic measurements results reveal that the multi-domain (MD) magnetite ofLop Nur sediments are mainly come from Tarim Basin. The magnetite dominatedlayers are largely unaffected by early diagenesis and consistent with those of sourcematerials from Tarim Basin, can be regarded as the typical background signal of LopNur sediments. The magnetic parameters variations of magnetite dominated layers remainly controlled by particle size and hydrodynamic sorting. In those layers, coarsefraction (i.e. coarse silt and sand) have higher magnetic minerals concentrations. It isdue to the fact that the magnetic minerals are mainly exhibit MD characteristic, thecoarse MD grains are enriched in the coarse fraction sediments. Meanwhile, themagnetite dominated layers have relatively low S-300mT and relatively high HIRM-300mT,indicate that the anti-antiferromagnetic minerals (e.g.hematite) have relatively highcontribution in oxidizing environments.Early diagenesis is the major influence factors of magnetic properties in Lop Nursaline lake. In reducing environment layers of LB profile and LOP1 profile,authigenic greigite and pyrite are identified within organic-rich sediments, whichformed in the early diagenesis processes. The authigenic greigite and pyrite aresignificantly impact the magnetic properties. The formation of single domain (SD)greigite resulted the markedly high χ, χARM, SIRM, HIRM-100mT, S-100mT, S-300mT,χARM/χ and SIRM/χ. The formation of multi-domain(MD) pyrite resulted thesignificantly low χ, χARM, SIRM, HIRM-100mT, S-100mT, S-300mT, χARM/χ. This indicatethat early diagenesis is the mainly influence factor on magnetic properties of Lop Nursaline sediments. The different authigenic iron sulfide contents in different layers arerelated to sedimentary environment changes. Sufficient supplies of organic matter andsulphate and low sedimentation rates favour the pyritization process. Moreover, ifpyritization was constrained, intermediate greigite formed and was preserved.In LB profile, five layers with relatively high values of χ, χARM, SIRM, S-ratio,χARM/χ and SIRM/χ are identified within organic-rich sediments; the five layers aredated to ca. 8150-7000, 5300-4900, 3600-3100, 2750-2550 and 1820-1680 cal. yr BP.Authigenic greigite is the dominant magnetic mineral within the five layers and it ispresent in the stable single domain state. Combined with results of a previous study,we infer that the greigite-bearing sediments were deposited during cold and wetperiods which were probably related to the North Atlantic cold events during the past8400 yr. During these periods, greigite formation was likely driven by an enhancedorganic matter supply, but pyritization was constrained by the decreased sulfatecontent and high sedimentation rate. The greigite and its diagnostic magneticparameters (e.g., SIRM/χ) can be regarded as an indicator of the hydrological andclimatic evolution of the Tarim Basin.The magnetic properties and sedimentology characteristics of Lop Nur sedimentsdemonstrated that the Holocene moisture conditions variations in Lop Nur and itssurrounding region show an abrupt change pattern, the transition time was dated to~4000 cal. yr BP. Before 4000 cal. yr BP, the climate conditions characterized byrelatively dry and very stable. In contrast, after 4000 cal. yr BP, moisture conditionsexhibited an increasing trend and accompanied by large fluctuation. This imply that inLop Nur and its surrounding region, the major forcing factors of climate changebetween early to middle Holocene and late Holocene might be obvious different. TheEl Niño -Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO) mayplay the dominated role in the determining moisture variability in Lop Nur and itssurrounding region.
Subject Area自然地理学
Language中文
Document Type学位论文
Identifierhttp://ir.xjlas.org/handle/365004/15337
Collection中国科学院新疆生态与地理研究所
研究系统
Affiliation中国科学院新疆生态与地理研究所
First Author Affilication中国科学院新疆生态与地理研究所
Recommended Citation
GB/T 7714
李文. 罗布泊盐湖沉积物磁性特征及其古环境记录研究[D]. 北京. 中国科学院大学,2019.
Files in This Item:
There are no files associated with this item.
Related Services
Recommend this item
Bookmark
Usage statistics
Export to Endnote
Google Scholar
Similar articles in Google Scholar
[李文]'s Articles
Baidu academic
Similar articles in Baidu academic
[李文]'s Articles
Bing Scholar
Similar articles in Bing Scholar
[李文]'s Articles
Terms of Use
No data!
Social Bookmark/Share
All comments (0)
No comment.
 

Items in the repository are protected by copyright, with all rights reserved, unless otherwise indicated.