长江口水下三角洲Y7柱样磁性特征及其影响因素

以长江口水下三角洲380cm长的Y7柱样为对象,在磁性测量、地球化学和粒度分析的基础上,探讨了近百年以来长江口水下三角洲沉积物磁性特征变化及其影响因素.研究结果表明,磁铁矿是主导Y7柱样磁性特征的主要矿物,相比常量元素和粒度的均一组成,磁性特征存在显著的垂向变化.220cm以下,频率磁化率(χfd)、非磁滞剩磁磁化率(χARM)、磁化率(χ)、饱和等温剩磁(SIRM)、χARM/χ以及χARM/SIRM随深度增加而下降,而退磁参数S-100mT和S-300mT则呈相反变化趋势;220cm以上,χfd,χ,χARM/χ,χARM/SIRM以及S-100mT和S-300mT随深度变化不大,而SIRM和χARM则随深度增加呈现下降趋势.Y7柱样中硬剩磁(HIRM)随深度变化不大.结合Mn/Fe比值的变化,研究认为Y7柱样300cm以下层位,随深度增加沉积物磁性减弱和超顺磁颗粒急剧减少,还原成岩作用是重要因素之一,不完整反铁磁性矿物因相对稳定而导致其在磁性矿物组合中的比例上升.此外,长江中上游主要支流泥沙贡献率的变化可能会对Y7柱样磁性特征有一定影响,但尚需进一步的工作支持.     

直流场和交变场对泥岩磁化率的影响

磁化率值不仅受控于天然岩石和环境物质中磁性颗粒的组合特征,还与实验室内的处理过程有关,包括热处理过程和加场处理过程.热处理过程通常改变磁性矿物的类型,使样品的磁化率值发生明显变化,因而备受关注.但加场处理过程对样品磁化率的影响在于改变其中所含磁性颗粒的磁畴结构,这种变化是微观的,目前尚未受到应有的重视.本文选择8块泥岩样品进行了加场处理对其磁化率影响的研究.样品取自松辽盆地松科1井青山口组一段,主要携磁矿物为准单畴( PSD)或多畴(MD)磁铁矿.在逐步获得等温剩磁直至饱和的过程中,逐步测量样品的磁化率值.随后对其进行单轴系统交变退磁,逐步测量剩磁后,完成磁化率测量.结果发现:1)直流场使样品的磁化率值增大.在低于50mT的外加场中,随外加场的增强,样品的磁化率值快速增大;之后,随外加场的增强,样品的磁化率值基本不变,直到600mT; 600mT ～ 1T之间样品的磁化率值又大幅增大;最终,样品的磁化率较初始值(x0)增大0.84％ ～ 3.40％.这种磁化率值的增大受控于样品内PSD或MD磁铁矿磁畴结构的改变,与磁铁矿的含量无关.2)样品获得SIRM后进行的逐步交变退磁使其磁化率值有所降低,随交变场的增强,其降低的幅度也增大,但是,交变场达到100mT时,样品的磁化率值仍较x0高.经逐步交变退磁后,样品的磁化率较x0增加0.03％ ～ 2.42％.因而,天然样品在进行磁化率测量之前,不能将其置于任何直流场或交变场中处理.     

镇江下蜀土的岩石磁学特征及磁化率变化机制

对镇江59.4m厚的下蜀土剖面的磁化率、χ-T曲线、等温剩磁获得曲线和磁滞回线等岩石磁学性质进行了研究,结 果表明：1）全剖面磁化率变幅较大,变化于（6.4~186.3）×10-8m3·kg-1之间;其中,剖面下段（24~59.4m）平均值为 34.7×10-8m3·kg-1,远低于上段（0~24m）的平均值126.1×10-8m3·kg-1;2）代表性样品的岩石磁学特征大致可以分为两类： 一类具有较高的磁化率,χ-T曲线呈明显的磁铁矿的居里点特征,IRM获得曲线在300mT时接近饱和,反向场退磁曲线显 示具有较低的剩磁矫顽力（25~40mT）,磁滞回线表现出细高的形状,在600~800mT之间闭合,显示含有较多的亚铁磁性 矿物（如磁铁矿和磁赤铁矿）;另一类样品则具有较低的磁化率,χ-T曲线初始磁化率较低,IRM获得曲线在300mT时达到 饱和剩磁的69%~82%,具有较高的剩磁矫顽力（70~135mT）,磁滞回线呈蜂腰状,提示含有较少的亚铁磁性矿物和较多的 高矫顽力矿物（如赤铁矿和针铁矿）,且可能含有铁的硫化物;3）岩石磁学特征表明下蜀土堆积的不同时段可能受到不同 环境的控制,中更新世中期之前曾出现多期过度湿润的气候条件,导致成土环境偏向还原条件,磁铁矿和磁赤铁矿逐渐转 化为弱磁性矿物,使得磁化率异常降低,与西伯利亚黄土变化模式类似;中更新世中晚期以来则以较干燥的氧化环境为 主,主要受成壤作用控制,有利于细小磁铁矿和磁赤铁矿的生成,与中国黄土高原的成土模式相似。     

武汉市东湖沉积物的磁性特征与重金属含量之间的关系

对武汉市东湖主湖区的郭郑湖和塘林湖114个沉积物样品的磁化率与代表性样品的频率磁化率系数、磁滞回线参量和重金属元素进行系统分析, 综合区域环境背景, 探讨应用岩石磁性方法技术评价大型城市内陆湖泊沉积物污染程度的可行性及其效果.结果表明, 在主成分中, 郭郑湖沉积物没有一个主成分占绝对优势, 仅有少数重金属元素含量与磁化率相关, 磁化率χ与重金属富集强度的相关性较差; 而塘林湖沉积物有一个“工业源”的主成份占绝对优势, Fe (全铁)、Co、V、Mn、Ti、Ba、Cr、Ni、Cu等元素与饱和等温剩磁SIRM、χ关系密切(相关系数大于0.87).郭郑湖与塘林湖的沉积物的饱和等温剩磁与重金属富集强度的相关程度高于磁化率, 因此, 可以用其(SIRM) 作为环境污染程度的指示参量.      

中国西北地区典型钢铁工业城市表土重金属污染的环境磁学响应

以嘉峪关市为研究靶区,系统采集城区表土样品58件,对其进行环境磁学和重金属元素（Cd、Cr、Cu、Mn、Pb、V、Zn、Fe）质量分数分析。结果表明：嘉峪关市表土以低矫顽力磁铁矿为主导,磁晶粒度以较粗的假单畴（PSD）和多畴（MD）颗粒为主;城区表土亚铁磁性矿物浓度和磁性颗粒大小远高于国内综合型大城市表土;市区反映磁性矿物含量的参数呈现出以酒钢厂和废渣场为中心的高值区域,并随着污染源距离的增加向周围递减;嘉峪关市表土重金属Cd、Cr、Cu、Mn、Pb、V、Zn、Fe质量分数与反映磁性矿物含量的参数具有显著共变性,二者的高值分布与反映磁晶粒度参数的高值分布成盈缺呼应关系。然而嘉峪关市土壤母质磁性颗粒本底值较粗,与污染土壤特征相似,因此对西北地区而言,亚铁磁性矿物浓度相对磁晶粒度可以更好地指示钢铁厂周边土壤重金属的污染程度。     

三门峡会兴沟剖面黄土—古土壤序列的岩石磁学研究

岩石磁学是古地磁学和环境磁学研究的基础,是鉴定岩石和沉积物中磁性矿物种类、粒度和含量的有效途径。对黄土高原东南部三门峡盆地的水沟—会兴沟旧石器遗址会兴沟剖面黄土—古土壤序列(S_0~S_8)进行系统的岩石磁学研究表明:本剖面沉积物的主要载磁矿物为磁铁矿、磁赤铁矿和赤铁矿,显示准单畴(PSD)磁性颗粒特征。所有磁学参数曲线均表现出基本一致的变化特征,与深海氧同位素曲线能够很好的对应,反映了第四纪以来的冰期—间冰期旋回中,东亚季风影响下的风尘黄土堆积中磁性矿物种类、粒度和含量的周期性变化特征。黄土中高矫顽力磁性矿物的相对含量要高于古土壤中的,而随着成土作用的加强,在古土壤中细粒的低矫顽力磁性矿物显著增加的同时,其中高矫顽力磁性矿物的绝对含量也相应增加。质量磁化率(χ)与非磁滞剩磁磁化率(χ_(ARM))和饱和等温剩磁(SIRM)及磁粒度参数χ_(ARM)/SIRM和χ_(ARM)/χ均呈明显的正相关关系,表明由成土作用产生的单畴(SD)颗粒和较小PSD颗粒对磁化率增强有显著的贡献。     

南海深海平原柱状样QD189磁化率、非磁滞剩磁、粒度、碎屑矿物丰度之间的主要关系

磁学可能是南海深海平原古环境研究取得突破的关键方面之一。众多磁学参数中,磁化率是最基本、最综合反映沉积物磁性矿物总体状况的参数,非磁滞剩磁对单畴颗粒含量敏感,而且单畴颗粒是剩磁的主要携带者,结合粒度、碎屑矿物丰度等数据探索南海深海平原柱状样QD189磁化率和非磁滞剩磁地质含义。在磁化率大于45×10-5层位和481 cm以浅的磁化率小于45×10-5的层段,磁化率、2~5粒级含量、ARM和ARM@20m T变化一致性较好,2~5粒级软磁性多畴颗粒含量变化可能是这些层位磁化率变化的主要原因。在808~488 cm层段内,小于45×10-5的磁化率与2~5粒级含量、ARM和ARM@20m T变化总体上一致性较差,磁化率变化机制有待进一步研究。2~5粒级是QD189重要的较粗粒级组分,大体上以深度350 cm为界具有下层段含量较高且粒度变化大、上层段含量较低且粒度变化小的特点。ARM@20m T比ARM更加真实地表示QD189单畴颗粒含量,除了单畴颗粒外,9~12粒级假单畴、多畴颗粒矿物对665~48 cm层段的ARM可能有一定贡献,其中,层段548~310 cm的ARM中可能还有6~9粒级多畴颗粒的贡献。通过碎屑矿物丰度、火山玻璃丰度和(或)磁化率异常峰值的对应关系识别出6次火山活动,火山玻璃丰度的分布特点还揭示出QD189中普遍发生生物扰动作用。     

中亚地区现代表土磁学特征及其古环境意义*

在中国西北地区主要沙漠、绿洲和戈壁及蒙古国南部戈壁等亚洲中部粉尘源区采集了表土(包括沙漠和土壤)样品,系统分析了样品的磁学性质(包括磁化率、无磁滞磁化率、等温剩磁、磁滞回线和热磁曲线)。结果表明,中亚地区表土样品中主要磁性矿物是铁磁矿,含有赤铁矿和磁赤铁矿,并伴有少量顺磁性矿物;磁性矿物粒度主要是准单畴(PSD)和多畴(MD),超顺磁性颗粒含量较低,接近于中国西部黄土地层含量。中亚地区表土磁性矿物含量总体都较低,磁性矿物含量在空间上与降雨量成正比。研究结果指示西部地区(准噶尔盆地和南部塔里木盆地)表土样品较北部地区(鄂尔多斯高原、阿拉善高原以及蒙古高原)表土样品,其粗颗粒磁性矿物含量高,而细颗粒磁性矿物含量低。本研究结果为黄土地层古土壤磁性增强源自成土过程提供了最直接的证据。     

Application of Borehole Core Magnetic Susceptibility and PXRF Measurement to the Moon Mountain Copper-Iron Mining Area in Chile and Prospecting Prediction

以智利月亮山铁氧化物铜金型矿床为例,利用磁化率K对铁磁性矿物及蚀变岩的现场识别能力和X射线荧光分析仪（PXRF）快速分析元素含量功能,结合矿床地质以闪长岩（5．5×10-3SI〈K〈17．9×10-3SI）、角砾岩（0．35×10-3SI〈K〈0．7×10-3SI）、磁铁矿（K〉753．4×10-3SI）、磁赤铁矿（313．3×10-3SI〈K〈753．4×10-3SI）、赤铁矿（0．78×10-3SI〈K〈1．62×10-3S1）、镜铁矿（0．67×10-3SI〈K〈0．78×10-3SI）等划分闪长岩亚相、角砾岩亚相、磁铁矿微相、磁赤铁矿微相、赤铁矿微相、镜铁矿微相;以PXRF现场测量铁含量〉30％,铜含量〉0．5％为含矿（化）界限,确定磁化率-铁铜含量对应关系：高磁化率-高铁含量-磁铁矿型、低磁化率-高铁含量-赤铁矿型（镜铁矿）、低磁化率-低铁含量-蚀变岩型,及岩相学找矿标志-矿物标志、构造标志、闪长岩标志、蚀变分带标志和矿物蚀变标志等,对月亮山矿区进行深部找矿预测。     

塔里木盆地西北缘库孜贡苏剖面晚白垩世-早中新世沉积物岩石磁学研究

对塔里木盆地西北缘库孜贡苏剖面晚白垩世-早中新世沉积物进行了热退磁及岩石磁学研究,结果表明岩石热退磁及岩石磁学特征随沉积环境可分为三种类型:潮下、台地边缘浅滩相岩石主要磁性矿物为磁铁矿及少量针铁矿、磁赤铁矿,磁性矿物含量较少、颗粒较小（假单畴）,其天然剩磁强度较小,一般小于1×10-2 A/m,在250℃~500℃能获得稳定特征剩磁方向,特征剩磁由磁铁矿携带;潮间、潮上带岩石主要磁性矿物为磁铁矿,〖JP2〗并含有少量磁赤铁矿、赤铁矿、针铁矿,磁性矿物颗粒为假单畴和多畴,天然剩磁强度一般在1×10-2 ~1 A/m之间,在250℃~580℃能获得稳定特征剩磁方向,特征剩磁由磁铁矿携带;河湖相岩石主要磁性矿物为磁铁矿、赤铁矿,并含有少量磁赤铁矿、针铁矿,磁性矿物含量较多、颗粒较小（假单畴）,天然剩磁强度一般在1×10-1 A/m以上,多数样品特征剩磁由赤铁矿携带,少数由磁铁矿与赤铁矿共同携带。岩石磁学研究对于在沉积环境复杂剖面进行古地磁研究具有重要的意义。     

The terrestrial fauna of the Late Triassic Pant-y-ffynnon Quarry fissures,South Wales,UK and a new species of Clevosaurus (Lepidosauria: Rhynchocephalia)

Pant-y-ffynnon Quarry in South Wales yielded a rich cache of fossils in the early 1950s, including articulated specimens of new species (the small sauropodomorph dinosaur Pantydraco caducus and the crocodylomorph Terrestrisuchus gracilis), but no substantial study of the wider fauna of the Pant-y-ffynnon fissure systems has been published. Here, our overview of existing specimens, a few described but mostly undescribed, as well as freshly processed material, provides a comprehensive picture of the Pant-y-ffynnon palaeo-island of the Late Triassic. This was an island with a relatively impoverished fauna dominated by small clevosaurs (rhynchocephalians), including a new species, Clevosaurus cambrica, described here from a partially articulated specimen and isolated bones. The new species has a dental morphology that is intermediate between the Late Triassic Clevosaurus hudsoni, from Cromhall Quarry to the east, and the younger C. convallis from Pant Quarry to the west, suggesting adaptive radiation of clevosaurs in the palaeo-archipelago. The larger reptiles on the palaeo-island do not exceed 1.5?m in length, including a small carnivorous crocodylomorph, Terrestrisuchus, and a possible example of insular dwarfism in the basal dinosaur Pantydraco.     

Définition d'une limite multicritère ; stratigraphie du passage Campanien–Maastrichtien du site géologique de Tercis (Landes,SW France)Definition of a multi-criteria boundary; stratigraphy of the Campanian–Maastrichtian interval of the geological site at Tercis (Landes,SW France)

Lithostratigraphy, physicochemical stratigraphy, biostratigraphy, and geochronology of the 77–70 Ma old series bracketing the Campanian–Maastrichtian boundary have been investigated by 70 experts. For the first time, direct relationships between macro- and microfossils have been established, as well as direct and indirect relationships between chemo-physical and biostratigraphical tools. A combination of criteria for selecting the boundary level, duration estimates, uncertainties on durations and on the location of biohorizons have been considered; new chronostratigraphic units are proposed. The geological site at Tercis is accepted by the Commission on Stratigraphy as the international reference for the stratigraphy of the studied interval. To cite this article: G.S. Odin, C. R. Geoscience 334 (2002) 409–414.     

The effect of water on accessory phase solubility in subaluminous and peralkaline granitic melts

The solubilities of columbite, tantalite, wolframite, rutile, zircon and hafnon were determined as a function of the water contents in peralkaline and subaluminous granite melts. All experiments were conducted at 1035 °C and 2 kbar and the water contents of the melts ranged from nominally dry to approximately 6 wt.% H₂O. Accessory phase solubilities are not affected by the water content of the peralkaline melt. By contrast, solubilities are affected by the water content of the subaluminous melt, where the solubilities of all the accessory phases examined increase with the water content of the melt, up to 2 wt.% H₂O. At higher water contents, solubilities are nearly constant. It can be concluded that water is not an important control of accessory phase solubility, although the water content will affect diffusivities of components in the melt, thus whether or not accessory phases will be present as restite material. The solubility behaviour in the subaluminous and peralkaline melts supports previous spectroscopic studies, which have observed differences in the coordination of high field strength elements in dry vs. wet subaluminous granitic glasses, but not for peralkaline granitic glasses. Lastly, the fact that wolframite solubility increases with increasing water content in the subaluminous melt suggests that tungsten dissolved as a hexavalent species.     

Quaternary stresses revealed by calcite twinning inversion: insights from observations in the Savonnières underground quarry (eastern France)

Calcite samples were extracted both from the rock matrix and the superficial coating of a karstified fault plane of an underground quarry, located in the eastern border of the Paris basin. The karstification is dated as Quaternary. Analysis of mechanical calcite twinning reveals that only the calcite matrix has also undergone a compression trending WNW that can be attributed to the Mio-Pliocene alpine collision. Both coating and matrix have undergone a strike-slip regime with σ₁ roughly trending north–south, that could correspond to the regional present-day state of stress, a strike-slip compression rather trending NNW, modified by local phenomena. To cite this article: M. Rocher et al., C. R. Geoscience 335 (2003).     

HYDROGEOLOGY

正20141756 Chen Ruige(Mathematical College,China University of Geosciences,Beijing100083,China);Zhou Xun Numerical Simulation of Groundwater Level Fluctuation in a Coastal Confined Aquifer with Sloping Initial Groundwater Level Induced by the Tide(Geological Bulletin of China,ISSN1671-2552,CN11-4648/P,32(7),2013,p.1099-1104,6 illus.,16 refs.) Key words:confined water,groundwater level     

METAMORPHIC PETROLOGY

正20141408 Cai Jia(Institute of Geology,Chinese Academy of Geological Sciences,Beijing100037,China);Liu Fulai Petrogenesis and Metamorphic P-T Conditions of Garnet-Spinel-Biotitebearing Paragneiss in Danangou Area,Daqingshan-Wulashan Metamorphic Complex Belt(Acta Petrologica Sinica,ISSN1000-0569,CN11-1922/P,29(7),     

SERIALS

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GEOPHYSICAL EXPLORATION

正20142386An Guoying(China Aero Geophysical Survey and Remote Sensing Center for Land and Resources,Beijing 100083,China)Application of Satellite Remote Sensing in Regional Hydrogeological Investigation:Taking Cenozoic Strata in Wenquan Sheet(1∶250 000)of Karakoram Range as an Example(Geosci-     

QUATERNARY GEOLOGY & GEOMORPHOLOGY

正20141016An Chengbang(Key Laboratory of Western China’s Environmental Systems,Ministry of Education,Lanzhou University,Lanzhou 730000,China);Zhao Yongtao Lake Records during the Last Glacial Maximum from Xinjiang,NW China and Their Climatic Impli-     

PETROLEUM GEOLOGY

正20141538 Cao Qing(School of Earth Sciences and Engineering,Xi’an Petroleum University,Xi’an 710065,China);Zhao Jingzhou Characteristics and Significance of Fluid Inclusions from Majiagou Formation,Yichuan Huangling Area,Ordos Basin(Advances in Earth Science,ISSN1001-8166,CN62-1091/P,28(7),2013,p.819-828,7 illus.,3 tables,43 refs.)