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8 条 记 录,以下是 1-8
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三峡地区二叠系牙形石的U-Th-Pb定年及古海水信息
2010年
利用激光剥蚀电感耦合等离子质谱(LA-ICP-MS)对三峡地区二叠系茅口组牙形石的U-Th-Pb同位素年龄进行测定。结果表明该地层中牙形石的208Pb/232Th放射年龄为269±44,Ma,207Pb/235U放射年龄为256±39,Ma,接近二叠系茅口组的生物地层年龄。206Pb/238U的年龄为196±6,Ma,虽然准确度较高,但与前人推测的地层年龄相比偏低。此外,作者对牙形石的稀土元素(REE)组成进行了分析,并且发现牙形石的REE组成和Ce异常与古海水氧化还原条件有一定的相关性,可以指示古海水的信息。
王瑾周炼胡兆初赵来时张海强陈孝红李志红
关键词:二叠系牙形石古海水
扬子克拉通北缘显生宙碎屑沉积岩Mo同位素初步研究及其地质意义被引量:3
2008年
通过对扬子克拉通北缘西乡-碑坝小区寒武纪-侏罗纪碎屑沉积岩的Mo、Nd同位素进行测定,结合微量元素数据分析,结果表明,该区寒武纪-侏罗纪碎屑沉积岩的δ98Mo变化范围在?0.65‰^+1.87‰之间,εNd(t)变化范围在?1.46~?10.90之间.茅口组晚期一个样品(4820)具有相对偏正的δ98Mo和εNd(t)(0.97‰,?1.46),有可能与二叠纪晚期峨眉山地幔柱的喷发过程中,扬子克拉通北缘古海水中富集的大量硫化氢有关,此时海水中的MoO42?转变为MoS42?,并具有偏正的Mo同位素组成.晚二叠世长兴期样品(4814)也具有明显偏正的δ98Mo(1.87‰),但εNd(t)相对偏负(?10.90),并具有相对较高的总有机碳(TOC)含量和总硫含量(TS)(分别为1.52%,2.02%),暗示该时期具有较高的初级生产力和有机碳埋藏量,似乎表明脱硫酸还原作用产生的大量HS?,H2S与同期海相沉积岩明显偏正的δ98Mo有一定的耦合性.研究显示,古大陆边缘碎屑沉积岩的Mo同位素变化,与区域构造活动及产生的环境效应存在一定的相关性,可以作为指示区域古环境演化的有效示踪剂.
周炼高山Chris HawkesworthCorey Archer谢树成
关键词:MO同位素碎屑沉积岩
Nd Isotopes and Geochemistry of Phanerozoic Clastic Sedimentary Rocks from the Yangtze Block and Their Tectonic Implications
2007年
This article presents Sm-Nd and geochemical data on fine-grained sediments of the northern margin from the Yangtze block, China, to understand the variations of Nd isotopic compositions and crustal evolution history in this area. The results are as follows: (1) Nd isotopic compositions for clastic sedimentary rocks of the Middle-Late Proterozoic have relatively positive Nd(t) values (+ 2.72 to + 0.69), with Nd model ages from 1.38 Ga to 1.55 Ga, corresponding to the contemporaneous volcanic rocks from the Xixiang (西乡) Group. This indicates that the arc-related materials from Middle-Late Proterozoic dominate the provenances of the Middle-Late Proterozoic periods. (2) The gradual decrease in εNd(t) during the Cambrian-Carboniferous periods is likely to reflect the progressively increasing proportion of erosion materials from the Foping (佛坪) and Qinling (秦岭) complexes, corresponding to a gradually decreasing trend in the La/Th ratios. (3) A prominent increase in the εNd(t) value of the Late Permian strata probably reflects the significant incorporation of the mantle-derived materials. The trace element data are compared with data of the Emeishan (峨嵋山)flood basalts. These data indicate that the volcanic dust has been added to the Late Permian strata during the Late Permian, represented by periods of extremely high Emeishan flood basalt activity in the south-eastern margin of the Yangtze block.
周炼高山刘勇胜Corey Archer
牙形石微量元素对生物绝灭事件的响应:以二叠-三叠系全球层型剖面第一幕绝灭事件为例被引量:8
2009年
首次系统地利用浙江长兴煤山剖面牙形石化石,依托中国地质大学(武汉)地质过程与矿产资源国家重点实验室激光剥蚀等离子体质谱仪(LA-ICP-MS)获取牙形石微区原位元素含量信息.结果显示,牙形石的Ce异常和稀土总量出现快速的波动,它们均反映出P/T之交环境(氧化-还原、生态条件等)的不稳定性.这些微量元素特征可以很好地与古海洋环境和生物绝灭事件耦合.这一研究将为系统探索全球古生代末生物大灭绝及其后生物复苏的过程、时限与古海洋化学及古生态变化性质等问题的研究提供新的途径,并有望对这些重要科学问题提供有效的制约.
赵来时吴元保胡兆初周炼刘勇胜史玉芳张素新童金南袁鹏
关键词:牙形石微量元素生物绝灭事件
The environmental index of the rare earth elements in conodonts:Evidence from the Ordovician conodonts of the Huanghuachang Section,Yichang area被引量:6
2012年
High-resolution microanalysis was performed on conodonts collected from the Huanghuachang section in the Yichang area using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). This region is regarded as a standard section for the division and correlation of the Ordovician system in southern China. The results show that the values of (La/Yb)N and (La/Sm)N decrease, while the values of δCe increase as seawater deepens and energy decreases. As the sedimentary environment changes from shallow-water carbonate platform to platform margin to open continental shelf to shelf basin, rare earth element distribution curves gradually transform from a right inclined pattern to a flat pattern to a left inclined pattern and a hat-shaped pattern. The present work proves that the values and distributive patterns of rare earth elements in conodonts correspond with the sedimentary environment, and therefore provide reliable evidence for the application of rare earth element concentrations of biogenic phosphates such as conodonts for palaeoenvironmental reconstructions.
CHEN XiaoHongZHOU LianWEI KaiWANG JinLI ZhiHong
关键词:牙形石环境指标LA-ICP-MS
牙形石稀土元素的环境意义:来自湖北宜昌黄花场奥陶系牙形石的证据被引量:4
2011年
利用LA-ICP-MS对系统采自华南奥陶系标准剖面——宜昌黄花场剖面的牙形石进行了高分辨率微区分析.结果表明随着沉积环境水体加深、量能减小,牙形石稀土元素存在(La/Yb)N与(La/Sm)N值减小,而??Ce值变大的趋势.伴随沉积环境由浅水碳酸盐台地-台地边缘向广海陆棚-陆棚盆地演化,牙形石的REE配分曲线由右倾斜型逐步变为平坦型、左倾斜型和帽型.从而不仅证明牙形石稀土元素(REE)的组成特征以及配分模式具有重要的古环境指示意义,而且为牙形石等磷酸盐生物壳体的稀土元素在古环境重建中的应用提供了可靠的依据.
陈孝红周炼危凯王瑾李志宏
关键词:奥陶纪牙形石稀土元素古环境
判识缺氧事件的地球化学新标志——钼同位素被引量:29
2011年
V/(V+Ni),U自生(自生U),V/Cr,Ceanom和U/Th是传统的氧化还原判别指标,但是这些微量元素的富集不仅与氧化还原环境有关,有机质的类型、沉积速率以及后期成岩作用都有可能使得元素的赋存形式发生变化,使得这些指标对氧化还原的判别出现多解性.δ98Mo作为一个新的氧化还原条件判别指标,已经得到人们的广泛关注.本文对宜昌王家湾剖面晚奥陶世五峰组-早志留世龙马溪组和四川上寺剖面晚二叠世大隆组两套黑色岩系(硅泥质组合)的δ98Mo和微量元素进行系统测定,比较δ98Mo与传统氧化还原判别指标之间的相关性,初步结果表明,这两套黑色岩系的V/(V+Ni),U自生,V/Cr,Ceanom和U/Th等有较大变化范围,总体上处于缺氧的范围,与δ98Mo没有明显的相关性.U/Mo比值可以作为指示氧化还原条件变化的指示剂,也许与U和Mo在不同成岩阶段相对富集程度不同有关,这种规律在静水环境更加明显,表现为在滞留环境中(δ98Mo〉1.5‰),U/Mo比值明显偏小,似乎与同期以硫酸盐还原作用带为主的滞留沉积环境有关,暗示在这种静水滞留的缺氧环境下,后期生物扰动的机会要少很多.而在δ98Mo在0~1.5‰范围内,U/Mo比值有较大的变化范围,不排除在相对常氧的情况下,生物扰动和水循环改变了孔隙水的氧化还原条件,导致元素的重新分配.
周炼苏洁黄俊华颜佳新解习农高山戴梦宁腾格尔
关键词:MO同位素黑色岩系
Preliminary Mo isotope data of Phanerozoic clastic sediments from the northern margin of the Yangtze block and its implication for paleoenvironmental conditions被引量:3
2009年
Mo isotopes along with Nd isotopes and other geochemical characteristics of the Phanerozoic clastic sediments from the northern margin of the Yangtze block were analyzed by MC-ICP-MS and some other techniques, spanning the period from Cambrian to Jurassic. The δ 98Mo values and εNd(t ) in these sedimets were observed to exhibit a large range of variation (?0.65‰―+1.87‰, ?1.46―?10.90, respec-tively). Specifically, the sample from Late Permian Maokou Formation has relatively positive values in both δ 98Mo and εNd(t ) (+0.97‰, ?1.46, respectively). These elevated values are proposed to relate to the input of a large quantity of H2S and HS- into the contemporaneous seawater by the volcanic eruption of the Emeishan mantle plume. Introduction of these sulfide gases would cause MoO42? to be transferred into MoS24?, favoring the preferential deposition of the heavy Mo isotope as MoS24? and thus leaving a positive Mo isotope value. The sample from Late Permian Changxing Formation has a significantly elevated δ 98Mo value of +1.87‰, in association with the relatively negative εNd(t ) (?10.90) and remain the relatively higher content of both TOC and total sulfur (TS) (1.52%, 2.02%, respectively). This infers the presence of the enhanced primary productivity and high organic burial during the Changxing pe-riod. The production of a huge quantity of HS? and H2S by the sulfate-reducing reaction led to the ex-istence of the elevated seawater δ 98Mo values during the Changxing period. The preliminary Phanero-zoic data reported here allow us to propose that the Mo isotope signature preserved in reductive sediments is related to the regional tectonic settings and the associated environmental conditions, and thus the measurement of δ 98Mo promotes our understanding on the evolution of the paleoenviron-mental event in the Earth history.
ZHOU LianGAO ShanCHRIS HawkesworthCOREY ArcherXIE ShuCheng
关键词:钼同位素古环境显生宙
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