南京下蜀土剖面磁化率测量及其与深海沉积的对比

本文通过对典型样品的低温磁行为分析探讨了磁化率反映古气候的机制,并尝试把下蜀土剖面磁化率古气候记录与华北黄土及深海沉积的记录相对比。     

深海氧同位素第5阶段的气候记录:武都黄土剖面与极地冰心、深海沉积同位素记录的对比

武都地区晚更新世以来堆积了厚约１７ｍ的黄土地层，其间夹有多层厚度不一、发育程度不同的古土壤层．在剖面１３．２～１７ｍ黄土中，野外可清晰的观察到６层古土壤．通过剖面磁化率、粒度、稳定同位素、元素地球化学、ＴＬ年代、ＣａＣＯ３、有机质含量的综合分析，认为它敏感而详尽地记录了深海氧同位素第５阶段的气候变化历史．对比研究结果显示：除总体模型与中国中西部黄土高原、深海氧同位素及南极冰心记录一致外，还可以与格陵兰Ｓｕｍｍｉｔ冰心记录进行良好的细节对比，揭示了全球气候变化地质记录的统一性．     

黄土磁化率各向异性特征初探——以青海西宁大墩岭黄土剖面为例

黄土是经风力搬运而沉积的。近年来从黄土剖面中提取磁化率变化的信息进行古地理气候环境的研究已取得令人瞩目的进展,其磁化率变化曲线所反应的气候环境变化同深海氧同位素变化曲线以及南极冰岩芯的氧同位素变化曲线所揭示的古气候环境变化过程极其相似。通过研究黄土和次生黄土的磁组构特征区分沉积物的沉积环境也取得了可喜的进展。然而,从黄土剖面中提取磁化率各向异性信息,研究风成黄土的搬运作用—风(风向,风力)的研究工作尚处于起步阶段。国外虽已在用磁化率各向异性参数恢复古环境的研究中取得许多成就,但在对第四纪沉积物的研究则不多见。笔者     

基于粒度建立1.2 Ma长武黄土剖面高分辨率时间标尺

中国黄土-古土壤堆积作为研究全球古气候古环境变化的三大支柱之一,清晰地记录了第四纪时期气候的干冷与暖湿变化.若对其所蕴含的全球变化信息进行更精确地研究,需要高分辨的时间标尺作为研究基础.本文以长武黄土-古土壤剖面为研究对象,通过将黄土-古土壤磁化率变化曲线与深海氧同位素变化曲线对比获得年龄控制点,以其32μm颗粒含量作为变量,利用粒度内插方法建立黄土时间标尺.并利用两种方法加以验证,获得了一条可靠的高分辨率的黄土-古土壤时间序列.     

黄土磁化率对千年-百年尺度气候事件的记录及其古气候意义

中国黄土高原的黄土-古土壤风尘堆积序列具有粒度细、沉积速率高和连续性好等特征,是古气候学研究的重要组成部分。黄土沉积物在轨道尺度上与全球气候关系密切,可以记录千年-百年尺度的快速气候事件。中国黄土古气候学取得的核心成果之一,就是磁化率可以作为东亚夏季风替代性指标,然而,磁化率在古气候研究中存在多解性,导致其在高分辨率研究中应用较少。文中选择黄土高原的赵家川和巴谢剖面磁化率数据,通过与格陵兰冰心和中国石笋等高分辨率古气候记录进行对比,发现赵家川剖面磁化率记录了4次Heinrich事件,巴谢剖面磁化率记录了全新世以来新仙女木、9.2 ka和4.2 ka 3次气候快速恶化事件。通过对比分析巴谢剖面磁化率记录的3次快速气候事件及其可能的驱动因素,认为太阳辐射减弱可能是主要因素。     

深海氧同位素第5阶段的气候记录;武都黄土剖面与极地…

武都地区晚更新世以来堆积了厚约１７ｍ的黄土地层，其间夹有多层厚度不一，发育程度不同的古土壤层。在剖面１３．２－１７ｍ黄土中，野外可清晰的观察到６层古土壤。通过剖面磁化率，粒度，稳定同位素，元素地球化学，ＴＬ年代，ＣａＣＯ３有机质含量的综合分析，认为它敏感而详尽地记录了深海氧同位素第５阶段的气候变化历史。     

山西临猗杨范第四纪沉积剖面初步研究

通过对杨范剖面黄土地层岩性特征、沉积结构、质量磁化率和频率磁化率的分析及与深海氧同位素曲线的对比,划分了剖面地层,初步确定了黄土沉积始于1.20 Ma B P,黄土沉积以来该区发生了13次大的干冷-暖湿气候变化;沉积转型指示河流强烈加积转变为河流侵蚀,代表约在1.20 Ma B P发生过一次强烈的构造抬升事件。     

西安狄寨塬全新世的古气候环境

对西安地区全新世以来的环境演变特征进行系统研究,建立该地区全新世以来黄土—古土壤沉积年代序列,揭示其反映的东亚冬、夏季风变迁规律,为预测西安地区乃至中国和全球未来环境的发展趋势提供依据.通过对西安白鹿塬刘家坡典型剖面全新世黄土—古土壤地层的岩性描述、地层划分和对比,结合泾阳县新庄村AMS14 C的年代测定和其他学者的测年数据,建立了该地区全新世以来黄土沉积年代序列.根据磁化率气候替代指标显示的曲线特征,阐述了这一替代指标在剖面上的变化规律,探讨了该黄土剖面所反映的东亚冬、夏季风强弱变化特点,论证和详细分析了西安地区全新世以来环境变化的特征和规律,进而对该剖面磁化率曲线特征与其他学者的孢粉谱建立的温度曲线对比,对西安地区全新世以来古气候的阶段性进行了详细分析和论证.将西安地区10 000年以来的气候演变划分为7个气候阶段.     

辽南黄土晚更新世粒度敏感组分的古环境意义

选取大连市金州区北部华农村一处高度为14.5 m的黄土剖面为研究对象,进行高密度采样获得714个样品并进行粒度测试,运用粒径-标准偏差法和端元模型法提取粒度敏感组分并对其进行分析,与深海氧同位素MI S气候阶段进行对比,重建了晚更新世以来辽南地区的环境变化过程.结果表明:①端元组分EM1、EM2、EM3、EM4分别代表...     

大厂凹陷MIS3阶段以来沉积物地球化学特征分析

深海氧同位素3-1阶段是指深海沉积物有孔虫氧同位素记录的第四纪末次冰期至冰后期的一个时期,期间气候表现为间冰阶、极端寒冷、多次千年尺度气候事件至最后转暖多个变化特征,相关气候变化沉积响应及影响因素等科学问题一直以来备受关注。然而,该时期相关千年尺度气候事件的记录及讨论在华北平原地区仍有争议,为探讨华北平原西北地区在该阶段的气候特征,本研究在大厂凹陷区天然剖面进行高密度碳14断代样品测试,并开展常量和微量元素地球化学含量分析,获得地球化学数据变化趋势特征,结果表明,该剖面年代从32.5ka至8.2 ka,处于深海氧同位素3阶段末期至深海氧同位素1阶段早期。在该时段,主量元素氧化物TFe2O3、Al2O3、SiO2、MgO、CaO、Na2O与K2O与微量元素Sr、V、Ni、Co、Ga、Cu、Ba、Cr和Zn均呈现一致的变化趋势;在MIS2末次冰盛期和MIS1早期中的B?lling-Aller?d暖期和新仙女木冷期,K/Na、Al/Na、化学蚀变指数 、化学风化指数 和古温度等指标与东亚季风区气候呈现一致的变化,同时与全球尺度的事件具有同步性,因此认为晚更新世晚期华北平原的气候变化可归因于全球气候系统下东亚季风区的演化。     

末次间冰期陇西黄土记录与气候不稳定性问题的初步研究

陕西黄土高原黄土记录的分辩率较高，Ｓ１古土壤厚达８．５ｍ，主要由两个古土壤组和其间黄土层组成。临夏塬堡剖面上可分为５个古土壤层，主要黄土层记录了末次间冰期内的较干冷高粉尘堆积时期。     

Magnetic characteristics and their paleoclimatic significance of Fengzhou loess in the Qinling Mountains of China

The Fengzhou loess section is very typical in the Qinling Mountains. The section, about 82 m thick and underlain by the Neogene red clay, consists of 33 layers of loess and 33 layers of paleosol. The section covers Brunnes normal polarity zone and Matuyama reversed polarity zone, and the B/M boundary is located in the middle of L₈. Matuyama reversed polarity zone records Jaramillo, Olduvai and Reunion normal polarity subchrons. The boundary between Matuyama reversed polarity zone and Gauss normal polarity zone (M/Ga) appears in the lithological boundary between loess and the Neogene red clay. Loess accumulation in Fengzhou started before 2.48 Ma. The magnetic susceptibility curve indicates 33 cold-dry and humid-warm cycles of paleoclimatic variation in the Qinling Mountains during the last 2.48 Ma. The above climatic fluctuation may be well compared with that of the oxygen isotopic records from deep-sea deposits.     

Mid-Late Quaternary loess-paleosol sequence in Lantian’s Yushan,China: An environmental magnetism approach and its paleoclimatic significance

The application of rock magnetism methods to investigating the variations of magnetic minerals in the sediments is an important approach to the reestablishment of paleoclimate evolution. Thus we performed fine magnetic measurements on the loess-paleosol sequence (from L15 upwards to S5, in which L is short for Loess, S is short for Paleosol, the same hereinafter) of Yushan stratigraphic section, which is on the southeastern margin of Chinese Loess Plateau, in Lantian County of China’s Shaanxi Province, and the thickness of which is ca. 40 m. Our study shows that the primary magnetic carriers of loess and paleosol in this section are magnetite, maghemite, hematite and goethite. Thermomagnetic analyses on the samples of representative horizons show that the higher pedogenesis degree of the sediments, the smaller variations of magnetization there will be before and after heating, probably related to the pedogenic alteration of loess sediments. Analyses of several magnetic parameters show a significant discrepancy between the paleoclimatic conditions recorded in the strata from the loess unit L15 upward to the paleosol unit S5 in the study area and those recorded in the relative strata of other sections on the Chinese Loess Plateau, and those recorded in marine sediments, indicating the great impact of regional geological background. Similarly, the rapid and intensive change recorded in the segment from L15 to S9-1, and the significant difference between the paleoclimate evolutions of the two periods before and after the change (from L15 to S9-1, and from L9 to the base of S6) indicate the strong alteration of magnetic carriers in the study area as a result of the alternations of summer and winter monsoons in East Asia.     

下蜀土剖面磁化率反映古气候变化机制的探讨

通过对典型下蜀土样品的低温磁化率测量，探讨下蜀土剖面磁化率反映古气候变化的机制。结果表明，下蜀土构成剖面中古土壤、黄土层的磁性晶粒的大小不同，古土壤中大量的细小超顺磁颗粒的存在是其磁化率增高的主要原因，这种细小磁性颗粒在古土壤中的积聚可能与其发育及古气候的暖湿程度有关。     

Susceptibility variations of multiple origins of loess from the Ily Basin (NW China)

The magnetic susceptibility of loess from the Ily Basin,northwestern China shows maximum values in S0 paleosols but minimum values in other paleosols,the mechanism of which has been well debated.In this work,systematic magnetic measurements were made on a representative section from Neleke county.The results show that the loess horizons(L1,L2 and L3) have multi-domain magnetite grains of aeolian origin,S0 is characterized by production of pedogenetic ultrafine-grained ferrimagnetic minerals,and the other paleosols(S1,S2,and S3) are characterized by the formation of nonferrimagnetic minerals associated with waterlogging.The correlation between the low concentration of ferrimagnets,high paramagnetic content,high magnetic coercivity remanence,fine ferrimagnetic grain size and intensified pedogenesis suggest two competing processes of pedogenetic enhancement and pedogenetic depletion in the lower paleosols.Pedogenetic depletion dominates and is responsible for the low susceptibility.Changes in magnetic grain size distribution occur during pedogenetic depletion.The susceptibility variations are of multiple origins in the loess of the Ily Basin.Pedogenetic enhancement,pedogenetic depletion,and allochthonous input of magnetic minerals should all be taken into account to explain the variations of magnetic parameters.     

中国黄土中松山-高斯极性倒转事件记录的空间对比

前人古地磁学研究表明,中国黄土不同剖面中松山-高斯(M/G)地磁极性转换界线记录层位并不一致,有的记录在黄土中,有的记录在红粘土中,这种不一致现象将可能影响到基于古地磁的黄土年代框架的建立及与全球气候记录的准确对比。针对这一问题,选取目前已有的典型黄土剖面中M/G地磁极性转换研究的结果进行了对比分析,并尝试采用磁化率-深度曲线的空间对比来检验不同剖面M/G界线层位记录的差异,结果表明中国黄土中M/G界线均记录在由磁化率-深度曲线所反映的"黄土L33层",说明黄土中M/G界线层位记录不一致的现象可能主要是由于地层划分方案的差异所致。根据这一思想,论文尝试对传统的洛川、西峰黄土地层划分方案进行部分修订,并简要介绍了M/G界线记录的海陆对比差异和未来利用宇宙成因核素10Be示踪M/G极性倒转事件过程的可能性,以期为研究黄土中地磁极性转换过程和确切层位提供一种新方法。     

山西临汾盆地中对应于S_2古土壤发育前后时期的一次湖退—

临汾盆地的第四纪调查发现,在湖相沉积层之上广泛覆盖着部分L3黄土层或S2古土壤层,表明在S2古土壤发育前后时期盆地内发生了一次显著湖退;在海拔稍低的一些区域,出现晚期灰绿色湖相层覆盖在L2黄土层之上的现象,表明在L2黄土堆积时期盆地内发生了一次小幅湖侵;广大的盆地区域都存在S1古土壤广泛覆盖晚期湖相地层现象,表明这次小幅湖侵结束于S1古土壤开始发育之时.盆地的湖退—湖侵变化证明,盆地深部"上地幔强烈上隆→减弱或渐趋稳定→再次强烈上隆……"这样的构造循环是存在的.同时,盆地的湖退时序差异也初步证明了"青藏高原的阶段性隆升对其广大外围地区的地貌发育有着重大影响和控制作用".     

长江三角洲与东海岛屿黄土研究综述

黄土是记录古气候和古环境变化信息的良好载体，长江三角洲平原及东海岛屿晚更新世黄土地层剖面的发现, 证明了末次冰期以来长江三角洲地区及海域均广泛存在风尘黄土堆积的事实,研究表明长江三角洲平原埋藏黄土和东海岛屿黄土是下蜀黄土上部地层在中国东部沿海和海域的延伸和继续.中国东部风尘黄土记录了我国晚更新世以来东部沿海地区的气候变化及东亚季风演变，与中国西北地区黄土地层相比，东部黄土具有沉积厚度小、成因复杂、次生作用强烈的特点；粒度和磁化率等参数垂向变化规律没有西部明显；粘土矿物和常量化学成分显示了东部黄土经历了较强地淋溶作用.在东部风尘黄土研究过程中，更需注意区域环境特征、地貌地形特点以及沉积期后环境变化对风尘黄土沉积物的影响效应，通过多指标的综合验证才能够正确解读黄土地层赋含的环境变化信息以及认识我国东部季风区晚更新世以来的古环境演变过程及规律.     

History of the temperature-dependence of susceptibility and its implications: Preliminary results along an E-W transect of the Chinese Loess Plateau

An investigation of rock magnetic properties using the temperature-dependence of susceptibility (TDS) and the coercivity of different IRM components was conducted on samples of the Malan loess (L1) and the last interglacial soil (S1) along an E-W transect of the Chinese Loess Plateau. We find that the behavior of the TDS is useful in identifying maghemite (γ-Fe_2O_3) in both loess and paleosol, and that it can be used as a new proxy of the degree of pedogenesis, which is closely linked to climatic conditions. Based on results from the TDS, we conclude that (1) the detrital magnetite grains predominate in the L1 unit to the west of Liupan Mts, where the weathering and pedogenetic processes were weakest; (2) a comparable degree of pedogenesis exists in the L1 at the east of the Liupan Mts and the S1 at the west of the Liupan Mts; (3) a higher concentration of maghemite is found in the S1 unit at the eastern sections, suggesting that the local climate was warmer and more humid in this interval. In addition, we propose that TDS measurements can be used as a rapid means of determining the reliability of the paleomagnetic secular variation (PSV) record in loess/poleoso/sequenees.