Leachate Lithium Characteristics of Loess-paleosol Sequences on the Chinese Loess Plateau and their Paleoclimatic Significance

The geochemical components of the leachate from loess-paleosol deposits can provide information about climaterelated post-depositional processes.For example,leachate lithium([Li]_(leachate))is a potential paleoclimate proxy because lithium is a typical lithophile element that is readily adsorbed by clay minerals during weathering and pedogenesis,and thus stratigraphic variations in[Li]leachatecan reflect these processes.We investigated the[Li]leachatevalues of two loess-paleosols profiles(the Luochuan and Weinan sections),on a north-south climatic gradient on the Chinese Loess Plateau.Independent paleoclimate information was provided by measurements of magnetic susceptibility,grain size,Rb/Sr ratios,and clay mineral content.During the last glacial-interglacial period,[Li]leachateincreased from 0.39 to 1.97μg/g at Luochuan and from 0.67 to 2.45μg/g at Weinan,mainly due to increasing pedogenesis.Based on these results we developed a conceptual model to explain the variations in[Li]leachate,Li^(+)within loess layers is mainly derived from dust input and the decomposition of primary minerals,influenced by the East Asian winter monsoon,while in paleosol layers Li is mainly derived from clay mineral adsorption during pedogenic processes,influenced by the East Asian summer monsoon.

Red Ratings for Loess-Paleosol Sequences on China’s Loess Plateau and Their Paleo-Climatic Implications

Comparisons of red ratings (RR) with Fe_d, Fe_d/Fet, clay content, andmagnetic susceptibility (x) of two loess-paleosol sequences at Luochuan and Lingtai on China's LoessPlateau were conducted to study the possible relationship between RR and pedogenic degrees of thetwo loess-paleosol sequences, and to discuss whether the RR could become new paleo-climaticindicators. Results showed that the RR of the two loess-paleosol sequences had positive, highlysignificant (P < 0.01) correlations with: 1) citrate-bicarbonate-dithionite (CBD) extracted iron(Fe_d), 2) ratios of CBD extracted iron to total iron (Fe_d/Fet), 3) clay (< 2 mum), and 4) magneticsusceptibility (x). This suggested that the RR of these loess-paleosol sequences could indicatedegreesof loess weathering and pedogenesis and were potential paleo-climatic proxies. The strongcorrelations of RR to Fe_d and x also implied that during pedogenic processes, pedogenic hematite inloess and paleosols were closely related to the amount of total secondary iron oxides and pedogenicferrimagnetic minerals (predominantly maghemite).

A preliminary study of the quantitative couplingbetween loess-paleosol sequences and summermon soon changes

The Loess Plateau-Northeastern Tibetan Plateau in China is famous for its deep andcontmuous distributed loess, in which soils (developed from loess) vary gradually with differentbiological climates changing from subhumid to arid, which provide a natural proving ground forstUd}' the coupling of loess-paleosol and climatic changes quantitatively. Thirty-two sections weresampled (collected) for measuring chemical element contents, clay content (and other items) and 60sections were collected for carbonate analysis to establish transfer functions between pedogenesisand climate. Finally, we estimated the paleoclAnate (P/T) in the region with transfer functions,It isrevealed that the variation of paleocldriate reflected by transfer functions accorded closely with theclimatic pattern resulted from recent work. Specifically, it was about 140 ha BP that summermonsoon reached Lanzhou or further, paleosol S1 (equaling to MIS 5 in deep sea records) developedstrongly in a large scale, even touching upon northeanstern Tibetan Plateau. And, the estimated P/Tinformation also indicated the cold and humid period during 50-30 ka BP, mean annual Precipitationwas about 400-500 nun in Angutan recorded by mega-interstadial paleosol Sm.

Magnetostratigraphy of a Loess-Paleosol Sequence from Higher Terrace of the Daduhe River in the Eastern Margin of the Tibetan Plateau and Its Geological Significance

The eolian deposits distributed in the river valleys in the eastern margin of the Tibetan Plateau （TP） are very useful in neotectonic and paleoclimatic studies. Firstly, the climate in the eastern margin of the TP is mainly controlled by the Indian summer monsoon, and detailed studies on the loess-paleosol sequences in this region can provide valuable terrestrial evidence of past changes in the Indian summer monsoon. Secondly, the river terraces in the eastern margin of the TP are considered to be a sensitive recorder of neotectonism to reflect the timing and amplitude of the TP uplift.

Comparison of paleotemperature reconstructions using microbial tetraether thermometers of the Chinese loess-paleosol sequence for the past 350000 years

The recently proposed global and local calibrations for the mean annual air temperature(MAT) reconstruction on the basis of 5-and 6-methyl brGDGTs have rarely been applied to the Chinese LPS yet, leaving the applicability of these calibrations unclear. Here, we used the improved chromatography method to analyze 198 loess-paleosol samples from the Weinan section in the southern CLP for the past 350 kyr. The 6-methyl brGDGTs comprise a major proportion of total brGDGTs, pointing to alkaline conditions for most soil samples from the Weinan LPS. The decoupled profile variation of MBT′6ME and MBT′_(5ME) suggests their response to different enviromental factors, possibly soil pH(or soil moisture) and temperature, respectively. This discrimination further corraborates that temperature and monsoonal precipitation were not in phase during the last four deglaciations on the CLP. Temperature estimates for the six calibrations tested show similar trends but remarkably differ in amplitudes. The soil moisture appears to affect the global MBT′/CBT calibration, the global MATmr calibration(a calibration based on the multiple linear regression) and the Chinese local SSM(Stepwise Selection Method) calibration, resulting in a significant underestimation of late Holocene temperature. In contrast, the dry climate has no effect on the global MBT′5ME calibration. Of the six calibrations,only the Chinese local SSM calibration and global MATmr calibration produce temperature variation amplitude over the past 350 ka that is consistent with other independent proxy data. The recently proposed local calibrations based on 5-and 6-methyl brGDGTs for North China yield the amplitude of temperature changes that is much larger than the results determined by other approaches.All the six calibrations have their own weakness in the MAT reconstruction, due partly to the inconsistency between the brGDGT distribution in the Weinan LPS and the modern soils used to establish these calibrations.

Paleo-environmental study on the growth of magnetotactic bacteria and precipitation of magnetosomes in Chinese loess-paleosol sequences

405 samples were collected from L5-S5-L6 in consideration of obvious variations in susceptibility of the geological sections, which are section Xifeng in Gansu Province and section Duanjiapo in Shaanxi Province for study of magnetotactic bacteria (MB) and magnetosomes (MS) in Chinese loess-paleosol sequences. MB in each sample were observed by TEM after being cultured under 8-18℃, room temperature (RT), 25℃, 26℃ and 30℃ conditions. In general, MB are distributed widely in loess-paleosol sequences, fewer in loess layers with predomination of vibriod in shape. However, there are more MB in paleosol layers with morphological varieties such as roddish, vibriod and occasionally approximately coccus. The magnetosomes (MS) in MB of paleosol are usually arranged in chains along the cells. It was also found that MB growth and MS formation are associated with the environment in which MB live. It can be inferred from the distributions of MB and MS that the paleoclimates fluctuated during the formation of

Geochemical characterization of loess-paleosol sequences:Comparison between the upper reaches of the Hanjiang and Weihe river valleys,China

This paper aims to compare the geochemical characteristics of loess-paleosol sequences in the upper reaches of the Hanjiang and Weihe river valleyswhich are located in the semi-humid temperate zone and humid subtropical zonerespectively. The Mituosi（MTS） profile in the upper reaches of the Hanjiang River valley and the Yaohecun（YHC） profile in the Weihe River valley were selected for this comparative research. The stratigraphic characteristicscompositionchemical weathering intensityleaching rates of Ca and Namobility of major elementsand transport features of Na and Fe were analyzed with respect to depth and compared between the two profiles. This study reached the following conclusions.（1） The composition of the loess-paleosol sequences in two regions are quite similar to the average composition of the upper continental crust（UCC）indicating that the loess in the two regions came from multiple sources and was mixed well. Thereforethe loess in the two regions is considered aeolian loess.（2） Compared with the loess-paleosol sequence in the Weihe River valleythe loess-paleosol sequence in the upper reaches of the Hanjiang River valley features a darker color; a higher chemical index of alteration（CIA） value; higher leaching rates of Na and Ca; higher migration ratio（relative to K） of AlSiMgand Na; and lower migration ratio of Fe and Ca. This evidence indicates that the loess-paleosol sequence in the humid subtropical environment experienced stronger chemical weathering intensity than the loess-paleosol sequence in the semi-humid temperate zone.（3） Both the YHC profile and MTS profile record a period of climate deterioration at 6000–5000 a BP. The period punctuated the mid-Holocene Climatic Optimum（8500–3100 a BP） in the study area.

晚第四纪风尘物质成分的变化及其环境意义

对长武和宜川晚第四纪黄土-古土壤序列的高分辨率铁含量分析表明，不同时期的风尘在化学成分上具有较明显的区别。在排除成壤过程中CaCO3淋溶和淀积的相对影响后，研究剖面的铁含量基本反映了原始风尘的铁含量。已有研究表明，西部源区的气溶胶和现代地表流沙中铁的相对含量显著高于东部源区。本文认为，风尘铁含量的变化反映了西部沙漠风尘对黄土堆积的相对贡献。由于西风带北支是西部源区风尘的主要搬运者，风尘中全铁含量可能反映了西风带北支气流的强度，并明显存在着千年尺度的变化。

洛川黄土—红粘土序列铁氧化物组成及其古气候指示

对洛川黄土、古土壤和红粘土中磁性矿物组成、成因和相关系进行了研究。结果表明:黄土磁性矿物以风尘磁铁矿为主,少量的成土赤铁矿和成土磁赤铁矿;古土壤磁性矿物以成土磁赤铁矿为主,成土赤铁矿次之,少量的风尘磁铁矿和赤铁矿;红粘土磁性矿物以成土赤铁矿为主,风尘磁铁矿和成土磁赤铁矿次之,少量风尘赤铁矿。黄土、古土壤和红粘土磁性矿物组成差异,反映了其形成期不同的古气候特性以及不同气候条件下生物地球化学作用强度的差异。干冷的冰期,黄土弱成土作用形成了以粗颗粒的风尘磁铁矿核+赤铁矿边的磁化率载体。间冰期的温暖湿润的古气候最有利于生物活动,强烈生物活动导致古土壤中大量纳米超细磁赤铁矿/磁铁矿产生,形成以磁赤铁矿为主,风尘磁铁矿核+赤铁矿边为辅的磁化率载体。红粘土成壤期,强降雨强蒸发的长干短湿的高温炎热的古气候使得红粘土化学风化强烈,生物地球化学活动较弱,形成以磁铁矿核+赤铁矿边和磁赤铁矿核+赤铁矿边的磁化率载体。黄土、古土壤和红粘土磁性矿物组成、磁性矿物相关系是其形成期独特的古气候指示。

兰州地区晚第三纪磁性地层与古环境意义

兰州地区位于黄土高原和青藏高原的过渡带,其第三纪地层对研究风尘沉积发育和青藏高原隆升都有着特殊的意义.本研究以0.5 m间距对兰州盆地皋兰山剖面240 m的晚第三纪地层进行古地磁样品采集,古地磁样品共计422个;以50℃为间隔从室温至500℃用热退磁仪和超导磁力仪完成了皋兰山剖面样品的系统热退磁和剩磁测量.结果表明皋兰山剖面上部地层的实测极性柱出现2个负极性大段中间夹着4个正极性小段,其特点与Gilbert时的典型特征完全一致,并且两端未完全出露的正极性分别与Chron2A.3n和Chron3An.1n相对应,最终确定皋兰山剖面的年代为6～3.5 Ma.由此推断,皋兰山剖面顶部的五泉砾岩形成大约开始于3.5 Ma,五泉砾岩底界年代的确定,为青藏高原的A幕运动提供了地质证据.皋兰山剖面深度602 m处出现由河湖相砂岩向以风成红粘土为主常夹有薄层砂岩的地层转变,通过岩性地层及年代的推断,兰州地区的风尘序列堆积发育的年代至少为7 Ma,与黄土高原风尘序列堆积底界8～7 Ma基本一致,说明了兰州地区与黄土高原在风尘序列堆积过程中具有统一性.

风成沙丘间沉积成因类型与风成垂向层序——以鄂尔多斯早白垩世内陆古沙漠为例

依据鄂尔多斯早白垩世内陆古沙漠沉积实例,探讨了沙丘间的成因分类,按照沙丘间底床的表面环境,将沙丘间划分为干旱型、潮湿型和覆水型三种沉积类型,并阐明了其沉积和组合特征;在此基础上,提出了风成垂向层序模式;鉴于沙漠同一相带的沙丘间类型及其沉积组合具有一定的共性特征,进一步建立和阐明了古沙漠分带的风成层序样式。

古沙漠沉积及其层序单元——以鄂尔多斯白垩纪内陆古沙漠盆地为例

古沙漠是以风成沉积为特征的一种特殊环境的充填 ,由于风成沉积与水成沉积机制不同 ,目前以湖泛面为依据所开展的陆相湖盆层序地层研究的原则不能完全适用于古沙漠地层 .分析讨论了基于地下潜水面为沉积基准面的古沙漠沉积作用过程及其控制因素 ,探讨了古沙漠层序地层的构成及其单元的划分 ,并提出了古沙漠成因地层及沉积学研究的有关概念和方法 .

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．

Millennial-scale monsoonal climatic change from paleosol sequences on the Chinese western Loess Plateau and Tibetan Plateau: a brief summary and review

This paper summarizes the work from the INQUA 1997 Project "Response of soilformation to short-warm-episodes of Asian summer monsoon" and its seeded related internationaland domestic grants. It reviews the effects of the millennial monsoonal changes on the loess-paleosols of the Chinese Loess and Tibetan Plateaus. High-resolution proxy records ofpedogenesis and monsoons demonstrate that both Asian winter and summer monsoons wereunstable and synchronously and inversely coupled during the last glaciation. During that timerapid episodic cycles of cold surges and warm enhancements spanned only ca. 1-2 ka in high-frequency domain. Sub-Milankovitch cycles (6-8 ka) of progressive cooling or weakening in low-frequency domain generally resembled the pattern of the North Atlantic climatic change. However,during the last interglacial, Asian winter and summer monsoons seemed to vary independently, theformer being stable and the later unstable. Soil formation seems to occur in surprisingly fastresponse to the summer monsoon warm enhancements, resulting in weakly or moderatelydeveloped paleosol sequences. North Atlantic and polar cold air surges though the westerlies andother paths, and the north-south swing of the westerlies beside the Tibetan Plateau, may be thealternative mechanisms for the rapid monsoonal changes during the last glacial. But in the lastinterglacial, the summer monsoons worked largely independently.

Red Clay Sediment in the Central Chinese Loess Plateau and Its Implication for the Uplift of the Tibetan Plateau

The widely distributed red clay sediment underlying the Chinese Loess Plateau truly records the Neogene environmental evolution, and its genesis and development are intrinsically related to the uplift processes of the Tibetan Plateau and the evolution of East Asia monsoon system. In this paper, a detailed magnetostratigraphy of a loess-red clay section （107°13′E, 35°02′N） from the central Loess Plateau is reported. The loess-red clay sequence is composed of 175 m Quaternary loess-paleosol sequence and 128 m Neogene red clay sediments. Based on the correlation with the standard geomagnetic polarity time scale, the paleomagnetic results indicate that the age of Chaona red clay sequence extends to 08.1 Ma, which is the older red clay deposition in the central Chinese Loess Plateau. The commencement of red clay at -8.1 Ma may imply that the Ordos planation surface was broken by the movement of the Haiyuan-Liupanshan Faults, which was related to the uplift of the Tibetan Plateau induced by the collision of India Plate and Eurasian Plate. And the western part adjacent to the Tibetan Plateau was uplifted to form the embryo of the Liupan Shan （Mts.） and the eastern part was down-faulted to receive red clay deposition. We link this faulting to an initial uplift of the Tibetan Plateau. The undulating nature of the broken Ordos planation surface may explain the chronological differences and depth discrepancies among various cross-sections of red clay.

Transformation relationship among different magnetic minerals within loess-paleosol sediments of the Chinese Loess Plateau

The dominant magnetic minerals and carriers of magnetic signals within the Chinese Loess Plateau are magnetite, maghemite, hematite, and goethite. In this study, we investigated the provenance and evo- lution of magnetic minerals during loess pedogenesis, using X-ray diffraction (XRD) and optical and electron microscopy, including field emission scanning electron microscopy (FESEM) and high- resolution transmission electron microscopy (HRTEM). Our results reveal that single- and multiphase mineral assemblages among magnetic minerals in the loess-paleosol sequence have been formed. Partial oxidation of coarse eolian magnetite has occurred in the desert source area and the oxidation degree is enhanced after deposition of the dust upon the Chinese Loess Plateau. This mode of origin resulted in a microtexture consisting of an inner magnetite core surrounded by a hematite rim, and strongly affected the magnetic characteristics of the loess. Goethite coexists with hematite in the loess and paleosol, and nanometer-scale hematite is formed upon goethite rims via dehydration. Our study provides direct mineralogical evidence of the magnetic record and paleoclimatic implications of the loess–paleosol sequence of the Chinese Loess Plateau.

广东东海岛大岭剖面风沙沉积序列及化学特征分析

利用广东省东海岛大岭剖面海岸风沙沉积元素地球化学分析,结合14C测年结果,探讨了大岭剖面采样部分的沉积序列、地球化学特征以及环境意义。结果表明:(1)常量元素组成主要为SiO_(2)、Al_(2)O_(3)和Fe_(2)O_(3)三种;(2)活跃元素相对全球上陆壳含量有所减少,相对稳定元素Al、Fe的含量往上呈现减少趋势;(3)化学蚀变指数(CIA)反映了剖面形成时处于中等风化程度,化学风化三角图(A-CN-K图)样品点的分布集中紧凑,体现气候条件较为稳定;(4)大岭剖面(⑨—①层)所反映的气候环境整体向干凉方向发展,期间划分两个阶段:第一阶段,表现为暖湿环境,其中含有一个温度湿度有所减少的时期;第二阶段,相比上阶段温度湿度都有所减少,海岸风沙活动加强。

江苏金坛和尚墩旧石器遗址地层的古地磁年代与磁化率研究

北方黄土研究中磁化率分析已越来越多运用到第四纪风尘堆积研究中。采用古地磁极性柱结合磁化率曲线比对定年的方法,初步确定江苏金坛和尚墩遗址750cm厚的地层年龄为330kaBP,对应磁化率曲线判断该区域分别经历了24kaBP左右、110kaBP左右、190—240kaBP左右、300kaBP左右的4个暖湿期,其中间隔有3个干冷时期,具有完整的3个气候旋回。对应地层发育的4个古土壤层、3个黄土层的风尘堆积—古土壤序列。研究表明,虽然古地磁极性定年的方法有一定的局限性,但在以磁化率信息为辅助的条件下,可在一定程度上消除这些局限,获得较为准确的地层年代,多种证据表明这种方法是可靠的。

Pedosedimentary events in loess of China and Quaternary climatic cycles

In the Loess Plateau of China, the orbitally induced climatic oscillations are generally expressed by alternation of pedogenetic and sedimentary events (pedosedimentary events). In the last years, investigations at different localities revealed that complete loess-soil sequences contain 37 major soil stratigraphic units which are spatially correlativ. Recent studies have demonstrated that many of these soil units are polygenetic (polycyclic), which were formed by several pedogenetic stages interrupted by dust deposition stages, evidencing climatic oscillations within the interglacial periods. Some loess units contain also clearly ex-

Magnetic property of Chinese loess and its paleoclimate significance

The magnetic minerals of paleosol unit S8 and loess unit L8 in Weman section have been studied. The experiments show that the remanent magnetization of Chinese loess is mainly carried by magnetite, with small amounts of a higher coercivity mineral, presumable hematite, also present. The remanent stability is not affected by maghemite presenting loess and paleosol with instability property. The grain size of the magnitic minerals is dominated by pseudo-single domain (PSD). The coercivity (Hc), remanent coercivity (Hrc) and saturation magnetization (Mr) gradually change from paleosol to loess, which indicates that the change of the -egional climate from the interglacial to glacial stage is a gradual process.