黄河沉积物中稀土元素(REE)组成的粒度效应*

依据Stokes颗粒沉降原理将黄河利津水文站和汊河清八站的表层沉积物分别提取为<2μm,2~4μm,4~8μm,8~16μm,16~32μm和32~63μm的6个粒级,采用ICP-MS法对各个粒级沉积物的15个稀土元素进行测试。结果表明:黄河沉积物两个样品REE含量随粒度增大的变化趋势有细微差别,但总体随粒度大小呈"高—低—高"的不对称马鞍型分布,其中最高REE含量和最低REE含量分别位于<4μm的粘土粒级和4~16μm细粉砂粒级中; 各粒级沉积物经北美页岩标准化后,REE的配分模式一致,呈平缓的右倾型,相对富集轻稀土,明显的Eu正异常和Ce负异常。对各个粒级样品进行X射线衍射分析及体视镜下观测,石英含量随粒级增大而增加, 长石在8~16μm中含量最高,在16~32μm中,碳酸岩含量最高,随着粒级增大,重矿物含量逐渐增加,黄河沉积物REE随粒度的变化特征与粘土矿物对其吸附及流域碎屑沉积物不同粒级的矿物成分密切相关。     

巴丹吉林沙漠石英δ18O值及其物源意义

巴丹吉林沙漠是世界上沙丘最高大的沙漠,其沙源研究对认识沙漠形成、高大沙山发育和防沙治沙工程有重要意义。石英是沙漠沉积物中常见的矿物,其氧同位素值可示踪物源。采集沙漠西北部、东部、东南部高大沙山、丘间低地与湖泊以及雅布赖山前的表层沉积物,测定了样品不同粒级的石英δ18O值。结果表明:①石英δ18O值随粒级减小有增大趋势,同一样品不同粒级石英δ18O值存在较大差异,相同粒级石英δ18O值也有变化。②石英δ18O值介于9.4‰~19.3‰,均值为13.3‰（n=55）;其中沙丘沙的石英δ18O值介于9.5‰~16.6‰,均值为12.9 ‰（n=39）;湖相沉积物的石英δ18O值介于9.4‰~19.3‰,均值为14.2‰（n=16）。③区域内,<16 μm粒级的石英δ18O值与16~64 μm、125~154 μm、200~250 μm、> 300 μm粒级的石英δ18O值都存在显著差异,但200~250 μm与 > 300 μm粒级的石英δ18O值没有显著差异;经区域对比,巴丹吉林沙漠 < 16 μm粒级的石英δ18O值与柴达木盆地沙漠、蒙古戈壁风成沉积物 < 16 μm石英δ18O值无显著差异,但巴丹吉林沙漠16~64 μm粒级的石英δ18O值与蒙古戈壁风成沉积物16~64 μm石英δ18O值存在显著差异;这似乎暗示研究区的细颗粒物质可能是远源的。巴丹吉林沙漠沉积物的石英δ18O值位于火成岩石英、砂岩和变质岩石英δ18O值分布阈值内,受区域地质条件、物源混合、粒级效应等因素的影响,砂粒级的石英δ18O值所指示的母岩成份特征与祁连山区岩石的岩性有较好吻合。     

长江与黄河沉积物稀土元素随粒度变化对比研究

依据Stoke定律将长江小于63 μm的沉积物分成4个粒级.将黄河小于63 μm的沉积物分成6个粒级.采用ICP-MS法分别测试了分粒级沉积物的REE含量,结果显示：相同粒级中长江沉积物的∑REE均高于黄河沉积物.长江沉积物REE的丰度遵循元素的“粒度控制律”,即随粒度变细∑REE含量依次增高;黄河沉积物∑REE呈“高-低-高”的不对称马鞍型分布;北美页岩标准化分布曲线均呈右倾状,轻重稀土分馏明显,相对富集LREE,具弱Ce亏损,明显的Eu正异常.长江与黄河沉积物REE组成特征差异与两条河流流域的风化作用及沉积物的矿物组成密切相关,黄河∑REE的马鞍型分布是细粒级中黏土矿物吸附及粗粒级中相对高含量的重矿物富集作用的结果,而长江沉积物随粒级增大∑REE的衰减趋势主要是随粒级增大逐步增加的石英和长石含量的稀释作用所造成.     

应用石英释光灵敏度溯源的研究现状和展望

应用石英释光灵敏度进行物源研究是释光技术发展的新方向。回顾了石英释光灵敏度在测年研究中的发展现状,对其产生的机制、实验中的影响因素及其在测年中对灵敏度的监测、矫正等进行了介绍,详细介绍了空间尺度上不同沉积物(冰碛物、风成沉积物、水成沉积物)石英释光灵敏度的差异和时间序列上风成沉积物释光灵敏度的变化特征。据现有的研究成果分析,沉积历史和母岩来源对沉积物中石英的释光灵敏度的高低有重要的影响,因此可用它来追溯石英的物源。探讨该技术在物源研究领域存在的问题,对其发展前景进行了展望。     

物源—河流过程—化学风化对松花江水系沉积物重矿物组成的影响

松花江水系作为我国七大水系之一,对其沉积物组成的深入探究对揭示源区控制因素和沉积物的搬运—沉积过程具有重要意义。重矿物蕴含着源岩母岩的重要信息,是解开由源到汇过程和物源示踪的重要工具。为了评估物源、河流过程和化学风化对重矿物组成的影响,我们从松花江水系干流和支流的边滩以及阶地共取32个样品,进行分粒级(<63μm、63~125μm和125~250μm)的重矿物分析。结果表明,松花江水系源区母岩信息在嫩江各支流(诺敏河最为典型)的重矿物组成中得到很好的反映,但在嫩江干流中没有得到反映,这表明物源对重矿物组成的控制受到河流过程的影响。松花江水系的重矿物组成以角闪石、绿帘石、钛铁矿和榍石为主。河流沉积物的重矿物组成主要富集在63~125μm组分,同一河流的不同河段的重矿物组成存在显著差异(巴兰河尤为典型),表明了河流搬运—沉积过程对重矿物组成起到重要控制。哈尔滨松花江T2阶地沉积物(弱风化)的重矿物组成基本保留了现代河流砂特征,讷谟尔河T1阶地沉积物(中等风化)的重矿物受到一定程度的改造,而受到严重化学风化影响的通河松花江T3阶地的重矿物组成已遭受严重破坏,不稳定矿物(角闪石和辉石)以及蕴含的母岩信息已完全消失,表明了重矿物组成明显受到沉积物化学风化程度的影响。由于源—汇过程中重矿物的混合和由此导致的稀释作用,使得沉积物携带的物源信息经过长距离搬运之后逐渐变得模糊。因此,我们认为,在进行河流重矿物源—汇过程研究中,宽粒度分析窗口和足够多的样品数量需要考虑以充分获取源区完整的重矿物组成信息。同时,在利用河流阶地重矿物组成进行源—汇联系和古水系演化研究时,需要首先评估阶地沉积物的化学风化程度。     

乌梁素海湖泊沉积物粒度特征及其环境指示意义

结合放射性同位素测年,在对乌梁素海湖泊沉积物粒度的分析基础上,结合黄河以及河套地区相关文献资料,探讨乌梁素海在自然和人类活动共同作用下的演变过程。乌梁素海沉积物中黏土（<4 μm）平均含量28.7%、细粉砂（4～16 μm）平均含量34.4%、中粉砂（16～32 μm）平均含量17.3%、粗粉砂（32～64 μm）组分平均含量14.1%、砂质组分（>64 μm）含量整体较低,平均含量为5.5%。沉积物不同粒级范围颗粒含量的相关性分析表明,在1965年左右（岩芯深度20 cm）乌梁素海沉积物组分特征发生了明显变化。基于此,结合前期对湖泊沉积物中元素含量特征的分析,利用粒径-标准偏差方法,通过对比黄河泥沙以及流域沉积物的粒度特征,研究了约1965年前后两个时段的沉积物来源。尽管乌梁素海湖泊沉积物主要来源于黄河携带的泥沙以及河套平原灌溉退水携带的大量流域表土侵蚀物质,但同一物源组分在1965年前后这两个不同的演化阶段具有不同的粒级特征。1965年之前,<19.95 μm的粒级组分反映了河套平原灌溉退水携带的流域表层侵蚀物质组分特征,而19.95～181.97 μm的粗颗粒组分反映了黄河径流携带的泥沙,后者决定了乌梁素海沉积物的粒级特征。1965年以来,这两种不同来源组分的粒级变细,灌溉退水携带的流域表土侵蚀物质（<5.71 μm组分）控制了湖泊沉积物的粒度特征,并与总排干入乌梁素海的水量变化、围湖建堤以及扬水站的修建等人类活动强度密切相关。总体来看,上世纪六十年代以来,乌梁素海湖泊沉积物的粒度组成受人类施加的影响已经超越了自然作用的影响。     

长江河口水下三角洲沉积物组成变化及其环境意义

三角洲不同年代的沉积物组成记录了流域-河口-近海沉积物源汇过程动态变化信息.文章以长江河口水下三角洲A3-1和A6-6柱样为对象,进行了光释光(OSL)年代、粒度和元素地球化学分析,探讨了不同年代沉积物地球化学组成差异及其影响因素.研究结果表明,柱样长度为1.58 m的A3-1沉积物年龄为1070±50～1180±30...     

南京周家山下蜀黄土石英颗粒特征及其物源意义

下蜀黄土的成因和物源一直是学术界研究的热点。对南京周家山下蜀黄土的石英粒度和石英表面微结构进行分析,结果显示:粉砂粒级石英颗粒（5~50 μm）占绝对优势;<20 μm组分平均含量为42.76%,<30 μm组分平均含量为62.98%;粒度分布曲线和累积曲线总体具有颗粒偏细,呈正偏态,分选较差,峰形尖锐,双峰曲线不对称的特征;粒级-标准偏差曲线呈“双峰”分布,两个明显的标准偏差峰值分别出现在7.962 1 μm和39.905 2 μm。石英颗粒表面形态主要以次棱角状为主;表面机械结构具有丰富的蝶形坑、曲脊、贝壳状断口,部分表面出现平行节理面、V形坑;不同粒级组分表面形态和机械结构特征存在差异。分析表明,南京周家山下蜀黄土属典型风成成因堆积物,是多源区物质高度混合搬运堆积的结果。     

内蒙古黄旗海全新世湖泊沉积物中Rb 、Sr分布及其环境意义

内蒙古黄旗海 H3剖面中发育黄旗海全新世高湖面时形成的湖相粉砂质沉积。对全样、77~20μ m 粒级、小于20 μm粒级沉积物的 Rb、Sr含量,以及小于20 μ m 粒级样品中碳酸盐矿物种类及含量的测试结果 表明,全新世早、中期形成的湖泊沉积物中,自生富锶文石是Sr在沉积物中含量较高的主要原因。各粒级沉积 物中Rb 、Sr含量与沉积物粒度组成的关系表明：Sr 倾向富集于黏粒 （ ＜4 μ m）中,可能与湖泊自生碳酸盐以泥 晶为主有关,而 Rb倾向富集于 4～28 μ m 颗粒粒级中,可能与其硅酸盐矿物碎化过程的特点有关;Sr 与 Rb存 在粒度效应,且二者粒度效应明显不同。Rb／Sr 与湖泊、流域的诸多过程及沉积物粒度效应有关,在不同湖泊演 化阶段,其具体的环境含义不同,这是湖泊沉积与风化壳的不同之处。     

释光年代学样品前处理流程

释光测年是第四纪年代学中应用较广泛的重要测年方法。释光技术的发展经历了热释光(Thermoluminescence,简写TL)阶段到光释光(Optically Stimulated Luminescence,简写OSL)阶段,测年研究的载体矿物主要是长石和石英。因测试目的不同,前处理方法有一定的差异。本文主要在前人工作的基础上,针对沉积物、陶瓷、暴露岩石三种释光测年样品的长石或石英获取方法进行总结,以期对释光测年样品前处理起到参考作用。     

台湾山溪性小河流碎屑重矿物组成及其示踪意义

台湾山溪性小河流每年向边缘海输入巨量沉积物,对东海陆架的沉积过程产生了显著的影响。本文分析台湾两条典型河流(兰阳溪和浊水溪)沉积物的全粒级碎屑重矿物组成,共鉴定出20种重矿物,但重量百分含量较低,为0.004%~0.116%。兰阳溪的主要重矿物组合为:锆石-菱镁矿-赤褐铁矿-锐钛矿-黄铁矿,浊水溪为:锆石-石榴石-赤褐铁矿-钛铁矿-锐钛矿-白钛石。研究流域的碎屑重矿物组成存在明显的沿程不均一性,指示出多数沉积物主要受到近源影响,从上游至下游重矿物组成的继承性较差。因此,基岩性质是河流碎屑重矿物组成的主要控制因素:兰阳溪和浊水溪的下游地区主要受各自流域内第四纪碎屑沉积物的贡献,上游地区则主要受到中央山脉庐山组的贡献。基岩控制起主导作用也使得重矿物指数如ATi、GZi和ZTR等难以恰当地应用于台湾山溪性小河流中。并且,大陆东部典型入海河流的重矿物组成与台湾河流存在明显区别:大陆入海河流中主要重矿物为磁铁矿和绿帘石;与之不同的是,兰阳溪河口富集锆石、菱镁矿和黄铁矿,浊水溪河口富集锆石和石榴石。这种差异主要反映了流域内基岩性质的不同。     

Chronology of desert margin in western India using improved luminescence dating protocols

The present study provides improved chronology for the desert margin fluvial sediments of semi-arid region located in the Mahi river basin, western India. The sequence has preserved a near-continuous record of climate change since the Last Interglacial. An earlier attempt of dating based on feldspar IRSL chronology shows a combined effect of anomalous fading and unbleached components resulting in age inversions. The present work tries to explore the possibility of using blue light stimulated luminescence (BLSL) of quartz, infra-red stimulated luminescence (IRSL) of feldspar and the newly developed methodologies, like natural correction factor based single aliquot regeneration (NCF-SAR) protocol and decision making schemes based on distribution of doses and beta heterogeneity concept for luminescence dating of sediments. Observations suggest that quartz suffered from significant sensitivity changes during natural signal measurement and partial bleaching. A combination of NCF-SAR protocol and sample specific equivalent dose computation helped in arriving at better age estimate for present samples. The study also compares the criteria for the selection of different age models that are used at present. The age of the alluvial sequence is now bracketed between 10 ka (upper aeolian unit) and 75 ka (lowermost fluvial unit).     

Towards single grain ESR dating of sedimentary quartz: first results

In optically stimulated luminescence dating, apparent ages of individual grains are thought to reflect a wide distribution of initial bleaching levels in hard to bleach sediments. Although having a larger age range (up to 1 Ma and beyond), this approach has not been used yet in electron spin resonance (ESR) dating. Here we report on the first results of ESR measurements on single sedimentary quartz grains. Initial bleaching levels are evaluated for two different River Meuse deposits in Limburg, NE Belgium. Measurements were done with a Q-band ESR spectrometer on transparent quartz grains of sufficiently large diameter (0.5–0.7 mm). Single crystal ESR properties were used to identify different ESR active centres. In about 50% of the selected grains an Al and/or Ti–Li signal was detected and the latter has been selected for further measurements. Artificial bleaching experiments show a strong signal decrease with UV light exposure. After gamma-ray irradiation, a number of different signal intensity vs. artificial dose curves could be observed: exponential growth, exponential saturation, linear, with inflexion points, and unclear ones. Many grains show increasing ESR signals with doses up to 1000 Gy, suggesting that the age range could be extended over 1 Ma, covering the Middle Pleistocene and part of the Early Pleistocene. Accumulated doses of individual grains were calculated using the additive dose method. The results show a large dose distribution of individual grains for both deposits. It is concluded that insufficiently bleached grains can be detected using single grain ESR measurements of sedimentary quartz in a fluvial environment.     

Luminescence dating of neotectonic activity on the southwestern coastal plain,Taiwan

The southwestern coastal plain of Taiwan is heavily urbanised, with a population of more than 6 million. The area is known to be subsiding, and the resulting basin is filled with thick fluvial deposits, of at least 200 m thickness. In the past century, three large earthquakes have occurred in the area; two caused surface ruptures, and resulted in large property loss and more than 2000 casualties. There is an urgent need for an understanding of the dynamics and recurrence intervals of this neotectonic activity, but little is known of the chronology of the late Pleistocene deposits. Recently more than 20 cores longer than 250 m were taken from the coastal plain as part of a large hydrogeological investigation, and basic data on lithology, hydrogeology and palaeobiology were collected. The base of these cores is beyond the ¹⁴C age limit, and so the application of luminescence dating to these sediments has been investigated.Optically stimulated luminescence methods have been applied to quartz sand-sized grains extracted from 29 samples. Dosimetry based on gamma spectrometry is also compared with ICP-MS and XRF analyses. In the age range up to ∼40 ka, radiocarbon ages are compared with the luminescence results, to give confidence that the initial bleaching of these sediments was sufficient. The luminescence ages are then discussed and differential rates of basin subsidence are deduced. It is clear from these data that the study area is tectonically active, and it may be that regions of similar subsidence rate correlate with identifiable geological structures.     

Rare earth elements in fine-grained sediments of major rivers from the high-standing island of Taiwan

Thirty-eight sediment samples from 15 primary rivers on Taiwan were retrieved to characterize the rare earth element (REE) signature of fluvial fine sediment sources. Compared to the three large rivers on the Chinese mainland, distinct differences were observed in the REE contents, upper continental crust normalized patterns and fractionation factors of the sediment samples. The average REE concentrations of the Taiwanese river sediments are higher than those of the Changjiang and Huanghe, but lower than the Zhujiang. Light rare earth elements (LREEs) are enriched relative to heavy rare earth elements (HREEs) with ratios from 7.48 to 13.03. We found that the variations in (La/Lu)_UCC–(Gd/Lu)_UCC and (La/Yb)_UCC–(Gd/Yb)_UCC are good proxies for tracing the source sediments of Taiwanese and Chinese rivers due to their distinguishable values. Our analyses indicate that the REE compositions of Taiwanese river sediments were primarily determined by the properties of the bedrock, and the intensity of chemical weathering in the drainage areas. The relatively high relief and heavy rainfall also have caused the REEs in the fluvial sediments from Taiwan to be transported to the estuaries down rivers from the mountains, and in turn delivered nearly coincidently to the adjacent seas by currents and waves. Our studies suggest that the REE patterns of the river sediments from Taiwan are distinguishable from those from the other sources of sediments transported into the adjacent seas, and therefore are useful proxies for tracing the provenances and dispersal patterns of sediments, as well as paleoenvironmental changes in the marginal seas.     

冰川沉积释光测年： 采样策略与测试选择

释光测年是可对冰川地貌进行直接定年的一种测年技术,已被广泛应用于冰川沉积测年中,推动了第四纪冰川研究的深入发展。但冰川沉积释光测年还没有达到标准化的程度,实际应用中仍有不少问题需要探究,其中最受关注的是冰川沉积物释光信号晒退不完全的问题,即样品在埋藏前因曝光机会有限导致信号没有归零或仅部分归零。冰川沉积释光信号晒退程度与地貌部位和沉积环境密切相关。冰川沉积释光采样需注意几个方面：（1）详细的地貌学和沉积学调查及对采样点的选择;（2）较适合释光测年的冰水沉积和冰缘风成沉积采集及其与冰川作用期次的联系;（3）冰碛夹层中的冰水砂透镜体的选取;（4）冰碛垄采样时垂直与水平方向上的考量;（5）岩石释光测年的发展使砾石成为当前第四纪冰川释光测年采样的一种选择。室内进行释光等效剂量测试时,也有几个关键的选择：（1）粗颗粒石英光释光测年是末次冰期以来冰川作用的首选方法;（2）如果样品年代老于石英测年上限,或者石英不适合测试,则可考虑钾长石后红外高温释光测年方法;（3）单颗粒、小测片和岩石释光埋藏测年技术可以鉴别样品的晒退情况,是目前最适合冰川沉积释光测年的几种选择;（4）如有条件,尝试用不同矿物、不同粒径、不同方法进行测试对比和交叉检验。要获得第四纪冰川释光测年的最佳年代学结果,地貌学、沉积学和年代学的结合是非常必要的。     

Sedimentary evidence and luminescence and ESR dating of Early Pleistocene high lake levels of Megalake Tengger,northwestern China

The timing of high lake-level stands during the Late Pleistocene in western China remains controversial. Here we report new results from Megalake Tengger based on a study of palaeo-shorelines and a drill core from Baijian Lake in the northwestern Tengger Desert. Multiple dating methods, based on luminescence signals (quartz optically stimulated luminescence, K-feldspar post infrared-infrared stimulated luminescence) and electron spin resonance signals of quartz, were used to date beach sands from palaeo-shoreline profiles at altitudes of ~1310 m (+20 m above lake level), ~1320 m (+30 m) and ~1350 m (+60 m), and from the top 20 m of sandy sediments from the drill core obtained from the modern beach of Baijian Lake. The dating results show that high lake-level stands associated with the previously reported Megalake Tengger (~1310–1320 m) occurred during the late Early to Middle Pleistocene, which is much earlier than previously reported. In addition, no geomorphological evidence of shorelines and sedimentary evidence from the drill core profile were found to support the previously reported Late Pleistocene lake levels. Our results indicate that the exact age of the previously reported ‘high lake level event’ in a large part of northwestern China during the Late Pleistocene needs to be re-evaluated.     

Establishing the Late Pleistocene-Holocene sedimentation boundary in the southern North Sea using OSL dating of shallow continental shelf sediments

This paper provides insight into the fate of Late Weichselian and Early Holocene sediments accumulated in the German sector of the southern North Sea. A combination of optically stimulated luminescence (OSL) dating and radiocarbon dating was applied to set up the chronology. Seven cores were studied to obtain ten quartz OSL samples and ten radiocarbon samples. The core locations were chosen along a southeast to northwest transect along the western side of the Elbe palaeovalley, giving a good coverage of the entire German North Sea area. All samples for OSL dating showed a significant scatter in the equivalent dose (D_e) distribution of quartz due to heterogeneous bleaching. The Minimum Age Model (MAM-3) was found to be the most suitable to extract true burial ages. It was inferred from the study that sedimentation did still occur during the late deglaciation period in many areas. These are mainly Late Weichselian glaciofluvial or glaciolacustrine sediments directly overlain by early Holocene fluvial and/or transgressive deposits and followed by modern marine sands. However, considerable late Weichselian erosion or a possible period of non-deposition was observed in the highland area to the northeast of the Dogger Bank and a small discontinuity in the near-shore region was noticed, probably due to early Holocene fluvial erosion. Relicts of a palaeo-river bank or terrace were identified in core 14VC to the east of the Dogger Bank. A possible interpretation of the Pleistocene-Holocene interface along the core transect is provided based on lithology and measured OSL and radiocarbon ages.