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。     

萧县黄土剖面的磁化率测量及意义

新近发现的萧县黄土剖面是关于淮河北部地区黄土堆积的初次报导．野外观察表明，该剖面可划分为４层古土壤和４层黄土．对该剖面磁化率测量表明，该剖面的磁化率曲线与古土壤一黄土系列有着高度的一致性．９个磁化率阶段的划分，说明磁化率测量比野外观察更能反映物质组成和古气候的细微变化．磁化率曲线峰谷变化的特征暗示该剖面堆积过程中气候转型事件的存在，这一剖面的的发现，填补了淮河中下游地区缺少黄土堆积的空白．     

皖南风尘堆积—古土壤序列磁化率初步研究

将北方黄土研究中广泛应用的磁化率参数引入江南第四纪风尘堆积区研究,对安徽宣城风尘堆积－古土壤序列向阳剖面进行了系统的磁化率化采样、测试,根据该剖面磁化率及其曲线的变化特征,对其古气候指示意义进行了初步的探讨．     

S2以来下蜀黄土沉积序列磁化率记录与深海氧同位素记录的对比

对镇江下蜀黄土剖面进行了系统的磁化率测试,并同深海氧同位素记录进行了对比。结果表明,S2以来下蜀黄土磁化率记录与深海氧同位素记录存在良好的对应关系。首次在下蜀黄土记录中发现了相当于深海氧同位素5a,5b,5c,5d和5e亚阶段的波动特征;下蜀黄土S2磁化率记录则可与深海氧同位素7阶段进行细节上的详细对比。对比揭示,最近20多万年以来,下蜀黄土堆积区对全球古气候变化有着积极的响应;同时,下蜀黄土记录的古气候变化在某些阶段又具有明显的区域特征,可能反映的是全球气候变化效应与东亚古季风气候影响的叠加作用。镇江下蜀黄土剖面能获得精度较高的全球变化信息与其特定的地理位置、纬度位置和地貌条件有关。     

中亚塔吉克斯坦南部黄土剖面上下部地层磁化率明显差异原因浅析

中亚塔吉克斯坦南部的黄土序列与中国黄土高原相似, 呈现黄土?古土壤交替的特征, 前人研究发现塔吉克斯坦黄土序列中以PC3为界的下部黄土与古土壤单元磁化率明显低于上部地层, 目前对这一现象尚无合理的古气候解释。本文对中亚塔吉克斯坦南部Darai Kalon黄土剖面的典型样品进行系统的矿物磁学研究以及漫反射光谱测量, 结果表明, 从黄土序列的下部到上部, 亚铁磁性矿物的总量以及超顺磁与单畴磁性颗粒的含量均呈增长的趋势, 与此同时, 硬磁性组份(如赤铁矿或针铁矿)的含量逐渐减少, 这可能指示成壤作用强度随时间增强。赤铁矿的适宜生长条件为高温干燥环境, 因此黄土序列下部的较高赤铁矿含量可能支持气候逐渐变湿的推论, 即下部地层沉积时期气候偏干, 成壤作用较弱, 古土壤中含较少的亚铁磁性矿物, 超顺磁与单畴磁性矿物颗粒较少, 故下部地层的磁化率较低。然而, 光谱测量数据显示, 下部地层针铁矿含量高于上部地层, 由于针铁矿的适宜生长条件为湿润环境, 其含量向上逐渐降低的趋势当指示气候逐渐变干。因此, PC3以下地层的较低磁化率也可能是过于湿润的环境溶解超顺磁和单畴磁性矿物颗粒造成的。尽管高场(达2 T)等温剩磁结果显示上部地层中以赤铁矿为主的硬磁性矿物含量较少, 但上部地层红度(a*)与赤铁矿含量之间较弱的相关性指示基体效应可能对光谱测量结果产生强烈的影响, 导致对赤铁矿光谱数据的解释存在很大的不确定性。针铁矿含量与磁化率的良好负相关性的确指示从下至上气候变干的趋势, 这一趋势与该地区前人的孢粉学和地球化学研究结果一致。以上研究结果表明, 对于中亚塔吉克斯坦南部黄土?古土壤序列的磁化率乃至矿物磁学数据的古气候解释非常复杂, 在中亚黄土研究中应用基于中国黄土磁学研究的模式需要谨慎, 有必要结合多指标进行综合分析。     

土壤频率磁化率与矿物粒度的关系及其环境意义

对土壤频率磁化率(xfd)与磁性矿物颗粒大小的关系及其环境意义进行了讨论．频率磁化率主要反映超顺磁性(SP)—稳定单畴(SSD)过渡态磁性颗粒的数量,对风化成土过程中形成的土壤成因磁性矿物具有指示作用．结果表明热带亚热带土壤表现为随风化成土作用的进行SP和SSD颗粒逐渐增多,其xfd和非滞后剩磁(ARM)逐渐增大,导致土壤磁化率增大．统计分析证明,土壤磁化率与xfd和ARM呈极显著正相关．土壤的xfd与游离氧化铁含量呈极显著正相关,与DCB处理的磁化率损失量呈极显著指数正相关,认为DCB处理的磁化率损失量与xfd有相同的环境意义．根据DCB处理的磁化率损失量分析可将xfd 10％作为土壤中存在相当数量SP颗粒的指标．对xfd在环境变迁、古气候演变、土壤性态、土壤侵蚀和环境污染方面的应用及其潜力进行了探讨。     

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。     

伊犁盆地晚更新世黄土—古土壤磁化率特征

新疆伊犁河谷海拔高度不同的两个晚更新世黄土剖面磁化率特征存在显著差异:位于海拔1400 m处的库尔德能布拉黄土剖面,其磁化率特征与黄土高原黄土相同,而海拔850 m处塔勒德黄土剖面的磁化率特征则与黄土高原相反.对两个剖面黄土-古土壤磁化率特征等分析研究认为,造成两个剖面S1古土壤磁化率差异的主要原因是末次间冰期土壤发育时期前者降水量大于后者.     

中国风尘沉积环境磁学研究现状

中国黄土-古土壤-红黏土序列完整记录了7.5 Ma以来东亚季风演化历史。黄土-古土壤的低频磁化率已成为东亚夏季风演化的代用指标之一,并得到广泛的应用和全球对比。虽然古土壤磁化率增强的成土观点已得到广泛认可,但磁化率与成壤强度的相关性还不是十分清楚,磁化率应用方面仍存在问题。磁化率与成壤强度、生物化学作用和古气候关系尚在研究中。     

Mineral magnetic and pedogenic studies of the paleoclimatic record of the upper part of the loess/paleosol sequence at Jiaodao

Most researchers agree that pedogenesis plays a significant role in determining the vertical distribution of magnetic susceptibility in soils and in the loess/paleosol sequences found in the People's Republic of China. Magnetic susceptibility distribution from Jiaodao on the Chinese central loess plateau matches other published magnetic susceptibility curves. Using the CBD method and a mixing model, the lithogenic and pedogenic components of magnetic susceptibility from Jiaodao were quantified. The estimated lithogenic component showed a long-term decrease with depth and had short-term periodic fluctuations in tune with the occurrence of paleosol and loess strata. The results of the mixing model suggest that interpretations based only on fluctuations in total magnetic susceptibility will be in error and that a single estimate of average lithogenic susceptibility is not an accurate basis for adjustment of the total susceptibility.     

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。     

汉江上游谷地黄褐土粒度组成特征及其意义

对汉江上游谷地河流一级阶地上黄褐土的粒度组成进行了分析.结果显示:剖面下部黄土的粒度参数数值(σ=1.72,Kg=1.03,S=1.15)和粒度分布曲线与古土壤的参数(σ=1.73,Kg=1.03,S=1.15)和曲线一致,而与区内典型洪水滞流沉积物洪水SWD(σ=1.9,Kg=1.10,S=1.20)不同;在粒度成分三角图中,黄土和古土壤集中落在小的区域内,而洪水SWD呈分散分布;黄土的Y值均小于—2.741 1,而洪水SWD大多数样品Y值大于—2.741 1.这证明汉江上游谷地古土壤S0继承了黄土的基本特征,两者具有风成堆积物的特性.与渭河谷地典型黄土对比,汉江上游谷地的黄土粒度与其十分相似,说明二者具有同源性.     

Paleoclimatic significance of mineral magnetic properties of loess sediments in northeastern Qinghai-Tibetan Plateau

Loess deposit in the northeastern Qinghai-Tibetan Plateau offers an excellent record of climate and environment changes in this region.We have conducted multiparameter mineral magnetic analyses of smaples of loess deposits from the Dongchuan,Lalakou and Panzishan sections.The methods used include magnetic susceptibility,fre-quency-dependent suceptibility,temperature-dependent susceptibility,isothermal remanent magnetization acquisibility.Maghemite and hematite is also present in the loess layers and paleosol horizons.The higher concentration of maghemite in paleosols suggests that the formation of maghemite occurred during in situ pedogenesis,which plays an important role in the enhancement of the magnetic susceptibitily.Similar to that in the Chinese Loess Plateau lying to the east of the Liupan Mountains,magnetic granulometry in the studied loess and paleosols is predominantly pseudo-single-domain(PSD). However,the mean grain-size of the ferrimagnetic minerals in loess is evidently coarser (larger PSD and multiomain-like) than in paleosols (mainly PSD).The magnetic susceptibility of loess and paleosols is positively correlated with the content of ultrafine magnet-ite/maghemite grains,and hence with the intensity of in situ pedogenesis.Therefore,the enhanced magnetic susceptibility in the studied loess-paleosol sequences can be interpreted as being due to climatically induced in situ pedogenesis.     

Comparisons of grain size characteristics of red earth from southern China with that of loess and dune sand from Beijing region

The comparisons of grain size distributions among eolian deposits along the monsoon wind trajectory are a fundamental task for the reconstruction of the past wind regimes. Here the authors sampled the dune sands in Hunsandak desert, loess deposits in Beijing region and red earth in southern China. Grain size analyses show that the distribution models of the loess and dune sand samples are unimodal whereas the red earth and paleosol are polymodal. The red earth, paleosol, loess and dune samples are distinguished and closely related to one another in grain size parameter diagrams. Moreover, the grain size distributions and parameters of the red earth and paleosol are similar, implying that the red earth in southern China and the paleosol in northern China had the same origin.     

Comparisons of grain size characteristics of red earth from southern China with that of loess and dune sand from Bering region

The comparisons of grain size distributions among eolian deposits along the monsoon wind trajectory are a fundamental task for the reconstruction of the past wind regimes. Here the authors sampled the dune sands in Hunsandak desert, loess deposits in Beijing region and red earth in southern China. Grain size analyses show that the distribution models of the loess and dune sand samples are unimodal whereas the red earth and paleosol are polymodal. The red earth, paleosol, loess and dune samples are distinguished and closely related to one another in grain size parameter diagrams. Moreover, the grain size distributions and parameters of the red earth and paleosol are similar, implying that the red earth in southern China and the paleosol in northern China had the same origin.     

咸阳市区晚更新世黄土微结构特征及其环境意义

目的揭示咸阳市区晚更新世黄土的微结构特征,探讨黄土微结构特征与其形成环境的关系,为区域环境提供科学依据。方法应用粒度分析和扫描电子显微镜对咸阳市区晚更新世黄土．古土壤系列的微结构进行分析研究。结果粒度小于0．005 mm的黏粒级含量在黄土与古土壤中差异最大,S1古土壤高达39．7％,而L1黄土仅24％;S1古土壤黏粒中大量铁质黏粒胶膜呈流胶状出现并有次生伊利石的产出,结构密实;L1黄土微骨架颗粒相互支架,黏粒胶结物含量较少,胶结程度差,土质疏松。结论咸阳市区晚更新世S1古土壤形成在湿热的森林环境,L1黄土形成于干冷的草原环境,S0黑垆土形成于凉湿气候环境。     

The magnetic properties of Serbian loess and its environmental significance

This paper reports a loess-paleosol sequence located in the Danube River basin,Serbia,which formed at least since the latest part of the early Pleistocene,and before the paleomagnetic B/M boundary.Various magnetic parameters of the Serbian V-L1-V-S4 loess-paleosol sequence have been measured and analyzed in the Titel Loess Plateau.These parameters show a very similar magnetic behavior compared with that of the Chinese loess.There is a general positive relationship between magnetic susceptibility() and pedogenesis.The main contributors to are the magnetic grains of SP(superparamagnetic) and SD(single domain) magnetic domains,while MD(multi domain) contributes only a small percentage.The difference in between loess and paleosol mainly is caused by pedogenesis.The very fine magnetic minerals increase gradually with increasing soil development(from loess to soil),and they lead to higher.The thermomagnetic curves show thatmagnetic minerals in the loess layers are magnetite and maghemite,both providing a major contribution to.In contrast the paleosol layers mainly are composed of magnetite,with almost no or a very small amount of maghemite,as implied by a reversible thermomagnetic behavior.This indicates that pedogenic conditions during V-S3 and V-S4 strong soil development have resulted in maghemite that is no longer stable,and has been resolved or converted to other stable phase minerals.This likely indicates that soil moisture during V-S3 and V-S4 development exceeded a critical condition of maghemite stability.     

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.