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1.
全球末元古系建系研究是当前国际地层学研究的重要课题之一。我国宜昌峡东地区震旦系沿江剖面研究历史悠久，已有相当深入的岩石地层、生物层及层序地层研究，并被推荐为国际未元古系候选层邓剖面之一。为进一步提高其研究精度，本文系统地研究了震旦系沿江剖面碳酸盐岩同位素化学地层，研究结果表明，陡山沱组底部“碳酸盐岩帽”的δ^13C－3．1‰－3－3．7‰，向上为正偏移，至层序Ⅲ（DS3）最大值达＋6．7‰。陡山沱组顶部（DS6）再次出现偏移－2．5‰，构成一个完整的变化周期。同时，^87Sr/^86Sr值表现出向上增大的变化，由陡山沱组度部（DS1）的0．707743逐渐增高陡山沱组顶部（DS6）的0．707965；灯影组蛤蟆井段（DS7）的δ^13C值变化在－2．45‰－＋5‰之间（DS8），至石板滩段中部再降至＋1．7‰（DS），而后基本保持在＋1．7‰－3．6‰之间平衡变动。白马沱段顶部δ^13C再次降至＋0．5‰，并有向负偏移的趋势。灯影组的^87Sr/^86Sr值依然出现由老至新递增的趋势（0．708244－0．708993）与当前国际末元古系剖面的化学地层特征基本一致。 相似文献
2.
以湖南张家界田坪和大坪震旦系剖面为主要研究对象,开展了湘西北地区斜坡相区震旦系层序地层的划分和对比研究。根据斜坡相区三级层序的发育特点,将陡山沱组划分为5个三级层序(ZSQ1~5),灯影组划分为4个三级层序(ZSQ6~9)。其中,陡山沱组下部的4个三级层序(ZSQ1~4)构成震旦系下部的二级层序,陡山沱组顶部的三级层序ZSQ5和灯影组的4个三级层序(ZSQ6~9)构成震旦系上部的二级层序。斜坡相区与台地相区震旦系层序地层的划分基本一致,可实现相互对比;斜坡相区与盆地相区震旦系只能实现二级层序的对比。 相似文献
3.
三峡地区震旦系碳酸盐岩碳氧同位素特征 总被引：17，自引：0，他引：17
本文对三峡地区秭归庙河陡山沱组第一段至第三段，宜昌棺材崖陡山沱组第三段上部至灯影组底部以及四溪灯影组石板滩段和白马沱段碳酸盐岩碳氧同位素组成特点的研究结果表明，三峡地区震旦系碳同位素组成与全球新元古代广布的后Martinoan冰期地层δ^13C的分布模式基本一致，本文还讨论了地层中碳同位素组成与生物演化和地层层序发展的关系，指出陡山沱组一段白云岩中δ^13C的负异常可以作为震旦系底界划分的标志，最晚Varanger冰期在三峡地区由陡山沱组三段上部出现的三级层序界面所替代，震旦系内部陡山沱组一段和三段可能形成于Marinoan冰期之后，伊迪卡拉生物分异发展之前，而陡山沱组四段及上覆灯影峡组则大致与国外伊迪卡拉期地层对比。 相似文献
4.
5.
陡山沱组为气候变暧后的第一套沉积组合,其内化石稀少,同位素年龄数据有限,地理分布不平衡,极易造成认识上的混乱。尝试从层序地层学的角度来探讨明月剖面震旦系陡山沱组层序地层特征,继而为研究陡山沱组黑色岩系成矿性打下基础。通过野外观测和室内综合研究,并结合区域地层对比,将大巴山地区明月剖面震旦系陡山沱组地层层序划分为4个二级层序（sequence）、9个三级层序（cycle）,对层序Ⅲ又进一步划分为9个四级副层序,最后得出明月剖面震旦系陡山沱组地层层序与Hoffman等1998年提出的“雪球地球”假说所描述的基本类似,为下一步找矿指明了思路。 相似文献
6.
末元古系-寒武系底Sr、C同位素对比 总被引：14，自引：0，他引：14
测定了云南永善肖滩前寒武系-寒武系界限Sr同位素组成及湖北省三峡 剖面震旦系碳酸盐岩Sr、C同位素组成,并与蒙古、 加拿大、西伯利亚和纳米 比亚的末元古系Sr和C同位素数据进行了比较,得出末元古纪海水87Sr/86Sr和 δ13C值的演变图。通过该演变图,可以对全球末元古系地层进行对比。 相似文献
7.
碳酸盐岩中碳同位素组成的演化对于古环境研究重要意义。笔者研究了浙江煤山剖面的新元古代地层陡山沱组和灯影组中δ13C，δ18O，87Sr/86Sr以及微量元素含量的演化。所分析的87Sr/86Sr值都大于0.714，同时大多数Mn/Sr比值在4～20之间。因为Sr在海洋中的存留时间很长（约3Ma），盖帽碳酸盐的87Sr/86Sr可指示冰期海水的Sr同位素组成，而在雪球事件期间87Sr/86Sr不可能这么高。在冰期之后，由于冰期前沉积的大量碳酸盐岩和冰期时喷发的玄武岩与陆壳岩石一起风化，海洋87Sr/86Sr也不会升到如此之高，可以认为所研究地层87Sr/86Sr已被成岩改造。大多数δ13O大于－10，并且δ13O和δ13C之间不存在明显的相关关系，表明大多数样品记录了初始的碳同位素组成。δ13C的演化曲线在碳酸盐盖帽以及陡出沱组－灯影组交界呈现明显的负漂移（－4‰～－3‰），在主要的陡山沱和灯影时期则最高升至＋3‰～＋4‰。碳酸盐盖帽中的δ13C负漂移可能由多种原因造成，例如：因为在雪球事件时海洋中光合作用几乎完全中止，造成海水与海底热液中CO2（约－6‰）的δ13C值趋同；冰期后即使生物产量已经快速恢复，但是极高的碳酸盐沉积速率仍会造成较低的δ13C值；原来甲烷水合物在冰期后中释放出甲烷；冰期后原来分层的海洋发生垂向洋流。目前尚不能唯一地确定碳酸盐盖幔中的δ13C负漂移是由某一个原因造成的，可能是由几个因素共同作用的结果。随着生物产量、大气中CO2含量和洋流都在雪球事件之后逐渐恢复正常，陡山沱组碳酸盐岩中δ13C也逐渐升高到正常的正值。当大气中巨量的CO2通过风化、碳酸盐岩沉积和有机质埋藏等途径被移除以后，气候开始变冷。当气个冷到某个临界范围时，强烈的温盐环流造成的上升洋流把富集12C的深部海水带到表层海水，造成陡山沱组－灯影组交界处的δ13C表现负漂移，同时使大气中的CO2升高到正常水平。灯影时期的气候要比陡山沱稳定。大气和海洋环境在几乎整个灯影时期都维持在适合生态系统的状态中，因面灯影组的δ13C大多为正值。 相似文献
8.
华南埃迪卡拉系斜坡相带碳稳定同位素特征 总被引：1，自引：0，他引：1
为验证碳稳定同位素特征在不同沉积环境的变化,选择了斜坡相带张家界田坪埃迪卡拉系剖面进行碳同位素的研究,系统采集了110件碳酸盐岩样品,并在中国地质调查局同位素地球化学开放研究实验室通过MAT-251质谱仪完成了碳、氧稳定同位素测试。测试结果显示,张家界田坪埃迪卡拉系剖面所记录的碳稳定同位素曲线,除了陡山沱组底部的负异常外,和任何已知的这一时期的碳同位素曲线均有较大的差异。从陡山沱组二段中下部开始,δ13 C表现为长期稳定的正漂移。大致在4.0‰附近波动,变化幅度在2.0‰~6.0‰之间,这一趋势一直延续至灯影组二段的中部,随后δ13 C逐渐减小,并在灯影组三段中部降至负值。从田坪剖面所处的古地理位置等因素的综合考虑,该剖面陡山沱组碳同位素δ13C值既受控于氧化还原界面的迁移,同时,也叠加了碳酸盐岩风化作用的影响;而灯影组的碳同位素δ13C值则更多地受控于海平面的变化。 相似文献
9.
通过震旦系研究历史的回顾,在前人研究的基础上,结合近年来综合地层研究的成果,试图建立可供全球对比的中国末元古系层型剖面。我国震旦系研究历史悠久,典型剖面经历南北之争,数十年来存在多种界定意见。通过近十年的研究,笔者依然认为峡东地区震旦系剖面沉积最为连续,出露完整,具有生物演化特征明显和形态多样的特点,可与世界各地的末元古纪地层进行广泛对比。目前,其上界定位于峡东地区灯影组天柱山段小壳化石带之下(即相当云南晋宁梅树村剖面震旦—寒武系界线小壳化石带B点,年龄为539±34Ma),而底界的厘定在国内一直存在多种意见。本文通过对峡东地区震旦系剖面的综合地层研究,结合生物地层学、年代地层学、层序地层学、C/O同位素研究以及沉积相等方面的综合分析,认为震旦系底界应划定在南沱冰期之后的陡山沱期沉积的下界,重申应选定峡东地区剖面为震旦系的层型剖面。 相似文献
10.
重庆城口震旦系下统陡山沱组共分两段,主要发育浅海陆棚沉积相,包括过渡相和滨外陆棚两个微相。对区内钻井剖面及露头剖面进行分析,识别出岩性岩相转换面、陡山沱组与观音崖组之间界面两种层序界面类型,将陡山沱组划分为4个Ⅱ型三级层序。其中层序1为陡山沱组第一段底部,层序2为陡山沱组第一段中部,层序3为陡山沱组第一段上部和第二段底部,层序4为自陡山沱组第二段下部至灯影组第一段底部中厚层状白云岩。基于浅海陆棚的背景,研究区陡山沱组第四次海平面广泛上升至最大海泛面滞后时段内,在深水、还原、偏碱性的浅海滨外陆棚环境下锰矿才开始聚集,且在高燕、修齐等锰矿区成为重要的开采矿床。 相似文献
11.
Police, politics, and the right to the city 总被引：1，自引：0，他引：1
Mustafa Dikeç 《GeoJournal》2002,58(2-3):91-98
Space and spatiality have recently been at the core of debates concerning the political possibilities of the city. The arguments advanced in this paper might be seen as an attempt to contribute to these debates through a reflection on the spatiality of (in) justice, politics, and the right to the city. The case of French urban policy, with its focus on distressed urban areas, and the `suburban problem' in France are used as examples to make arguments more concrete. 相似文献
12.
E. M. Prasolov S. A. Sergeev B. V. Belyatsky E. S. Bogomolov K. A. Gruzdov I. N. Kapitonov R. Sh. Krymsky V. O. Khalenev 《Geochemistry International》2018,56(1):46-64
This paper reports the first results of a study of 11 isotope systems (3He/4He, 40Ar/36Ar, 34S/32S, 65Cu/63Cu, 62Ni/60Ni, 87Sr/86Sr, 143Nd/144Nd, 206–208Pb/204Pb, Hf–Nd, U–Pb, and Re–Os) in the rocks and ores of the Cu–Ni–PGE deposits of the Norilsk ore district. Almost all the results were obtained at the Center of Isotopic Research of the Karpinskii All-Russia Research Institute of Geology. The use of a number of independent genetic isotopic signatures and comprehensive isotopic knowledge provided a methodic basis for the interpretation of approximately 5000 isotopic analyses of various elements. The presence of materials from two sources, crust and mantle, was detected in the composition of the rocks and ores. The contribution of the crustal source is especially significant in the paleofluids (gas–liquid microinclusions) of the ore-forming medium. Crustal solutions were probably a transport medium during ore formation. Air argon is dominant in the ores, which indicates a connection between the paleofluids and the atmosphere. This suggests intense groundwater circulation during the crystallization of ore minerals. The age of the rocks and ores of the Norilsk deposits was determined. The stage of orebody formation is restricted to a narrow age interval of 250 ± 10 Ma. An isotopic criterion was proposed for the ore-bearing potential of mafic intrusions in the Norilsk–Taimyr region. It includes several interrelated isotopic ratios of various elements: He, Ar, S, and others. 相似文献
13.
I. M. Gorokhov M. A. Semikhatov M. M. Arakelyants E. A. Fallick N. N. Mel’nikov T. L. Turchenko T. A. Ivanovskaya T. S. Zaitseva E. P. Kutyavin 《Stratigraphy and Geological Correlation》2006,14(3):260-274
Clay subfractions (SFs) of <0.1, 0.1–0.2, 0.2–0.3, 0.3–0.6, 0.6–2 and 2–5 μm separated from Middle Riphean shales of the Debengda Formation are studied using the TEM, XRD, K-Ar and Rb-Sr isotopic methods. The oxygen and hydrogen isotope compositions in the SFs are studied as well. The low-temperature illite-smectite is dominant mineral in all the SFs except for the coarsest ones. The XRD, chemical and isotopic data imply that two generations of authigenic illite-smectite different in age are mixed in the SFs. The illite crystallinity index decreases in parallel with size diminishing of clay particles. As compared to coarser SFs, illite of fine-grained subfractions is enriched in Al relative to Fe and Mg, contains more K, and reveals higher K/Rb and Rb/Sr ratios. The Rb-Sr age calculated by means of the leachochron (“inner isochron”) method declines gradually from 1254-1272 Ma in the coarsest SFs to 1038-1044 Ma in finest ones, while the K-Ar age decreases simultaneously from 1225–1240 to 1080 Ma. The established positive correlation of δ18O and δD values with dimensions of clay particles in the SFs seems to be also consistent with the mixing systematics. The isotopic systematics along with data on mineral composition and morphology lead to the conclusion that mixedlayer illite-smectite was formed in the Debengda shales during two periods 1211–1272 and 1038–1080 Ma ago. The first period is likely close to the deposition time of sediments and corresponds to events of burial catagenesis, whereas the second one is correlative with the regional uplift and changes in hydrological regime during the pre-Khaipakh break in sedimentation. 相似文献
14.
Influences of the unsaturated,saturated, and riparian zones on the transport of nitrate near the Merced River,California, USA 总被引：1，自引：0，他引：1
Joseph L. Domagalski Steven P. Phillips E. Randall Bayless Celia Zamora Carol Kendall Richard A. WildmanJr Janet G. Hering 《Hydrogeology Journal》2008,16(4):675-690
Transport and transformation of nitrate was evaluated along a 1-km groundwater transect from an almond orchard to the Merced River, California, USA, within an irrigated agricultural setting. As indicated by measurements of pore-water nitrate and modeling using the root zone water quality model, about 63% of the applied nitrogen was transported through a 6.5-m unsaturated zone. Transport times from recharge locations to the edge of a riparian zone ranged from approximately 6 months to greater than 100 years. This allowed for partial denitrification in horizons having mildly reducing conditions, and essentially no denitrification in horizons with oxidizing conditions. Transport times across a 50–100-m-wide riparian zone of less than a year to over 6 years and more strongly reducing conditions resulted in greater rates of denitrification. Isotopic measurements and concentrations of excess N2 in water were indicative of denitrification with the highest rates below the Merced River. Discharge of water and nitrate into the river was dependent on gradients driven by irrigation or river stage. The results suggest that the assimilative capacity for nitrate of the groundwater system, and particularly the riverbed, is limiting the nitrate load to the Merced River in the study area. 相似文献
15.
扬子北缘马元铅锌矿床闪锌矿微量元素及S-Pb-He-Ar-C同位素地球化学研究 总被引：7，自引：3，他引：4
马元铅锌矿床是近年扬子陆块北缘铅锌找矿的新突破。矿体呈层状、似层状产于碑坝隆起翼部震旦系灯影组角砾状白云岩层间构造带中,围岩蚀变很弱。矿石中硫化物以闪锌矿、方铅矿为主,中粗粒晶质结构,充填于白云岩角砾间。闪锌矿富集Cd、Ge、Ag,贫In、Tl、Se,Ga/In为6~132,Ge/In多1000,成矿温度以中-低温为主。金属硫化物ε~(34)S值相对集中,为12.9‰~19.4‰,平均为17.4‰,来自于海相硫酸盐的还原。铅同位素组成稳定,~(206)Pb/~(204)Pb为17.858~17.918:~(207)Pb/~(204)Pb为15.603~15.694;~(208)Pb/~(204)Pb为37.756~38.046,具有造山带和上地壳铅的特征,震旦系可能提供了金属成矿物质。闪锌矿中流体包裹体的~3He/~4He为0.03Ra~1.05Ra,~(40)Ar/~(36)Ar为326.1~765.1,~(38)Ar/~(36)Ar为0.183~0.204,表明成矿流体主要为地壳流体和饱和大气水(大气降水或海水)的混合。闪锌矿内流体包裹体挥发分δ~(13)C_(CH_4)值为-36.01‰~-28.80‰,δ~(13)C_(C_2H_6)值为-27.72‰~-22.44‰,δ~(13)C_(CO_2)值为-23.24‰~-9.68‰,表明有机流体参与了成矿作用。石英、方解石的H-O同位素结果表明具有海水和有机水混合的特征。可见,成矿流体具有两种流体混合的特征,一为蒸发海水与围岩反应所形成的盆地卤水,二为有机流体。推测矿区可能存在一个古油气藏,由于TSR生成一高硫气藏,为区内还原性有机流体的主要来源。当富含Pb、Zn等成矿物质的成矿流体运移至富含CH_4和H_2S的还原性流体的矿区角砾岩带时,两种流体混合,Pb、Zn等遇到H_2S发生反应而沉淀成矿,并伴生热液白云石等,形成了马元铅锌矿床。综上所述,我们认为马元矿床属MVT型铅锌矿床。 相似文献
16.
Delivery of Trace Metals (Al,Fe, Mn,V, Co,Ni, Cu,Cd, Ag,Pb) from the Trinity River Watershed Towards the Ocean 总被引：2，自引：0，他引：2
The Trinity River (Texas, USA) contains in its watershed 23 different reservoir lakes, the largest one being Lake Livingston
situated in the lower Trinity River watershed and two potentially polluting metroplexes, Dallas and Houston. In order to determine
fluxes of nutrients and trace metals to Galveston Bay, a survey that included 24 discreet samples collected over a year and
at various stages of discharge was carried out during 2000–2001. Geochemical (i.e., sorption by Fe oxyhydroxides), biological
(i.e., seasonal uptake by sinking algae in Lake Livingston), and hydrological (i.e., dilution effects by increasing flow rates)
controls were found to be mainly responsible for variations in dissolved trace metal concentrations rather than pollution
sources. The Trinity River loads of suspended sediments and pollutant trace metals entering Galveston Bay at Anahuac were
<20% of those reaching Lake Livingston, and only a few percent of the total upstream trace metal load is entering the Gulf
of Mexico. Thus, during the transit through the 23 man-made lakes and an estuary, >96% of the pollutant trace metal load is
lost to sediments. 相似文献
17.
18.
V. Yu. Prokof’ev L. D. Zorina V. A. Kovalenker N. N. Akinfiev I. A. Baksheev A. N. Krasnov G. A. Yurgenson N. V. Trubkin 《Geology of Ore Deposits》2007,49(1):31-68
The mineral composition of the Talatui gold deposit has been studied with modern methods. Previously unknown minerals (ilmenite, siegenite, glaucodot, wittichenite, matildite, hessite, pilsenite, zircon, tremolite, cummingtonite, hercynite, and goethite) have been identified in the ore. A high Re content has been detected in molybdenite. The spatiotemporal separation of Au and Ag is caused by different mineral species of these elements and their diachronous precipitation during the ore-forming process. Gold crystallized along with early mineral assemblages, beginning from virtually pure gold (the fineness is 996). Silver precipitated largely at the end of the process as hessite (Ag2Te) and matildite (AgBiS2). The temperature of ore deposition varied from 610 to 145°C, the pressure was 3370–110 bar, and the salt concentration ranged from 56.3 to 0.4 wt % NaCl equiv. The heterogeneous state (boiling) of fluid at the early stages has been documented. The chemical and isotopic compositions of the fluid testify to its magmatic nature and the participation of meteoric water at late stages in the ore-forming process. Thermodynamic modeling reproduces the main specific features of ore formation, including separation of Au and Ag. A physicochemical model of the gold mineralization in the Darasun ore district has been proposed. On the basis of several attributes, the Talatui deposit has been referred to the prophyry gold-copper economic type. 相似文献
19.
山西五台山区滹沱群变质玄武岩岩石学、地球化学特征及其成因意义 总被引：10，自引：0，他引：10
在野外地质调查的基础上,选取滹沱群豆村亚群底部四集庄组玄武岩、顶部青石村组玄武岩和东冶亚群中下部河边村组玄武岩,进行岩石学和地球化学研究。分析结果表明：玄武岩主量元素高TiO2、TFeO,低MgO,具有演化的基性岩浆的特征。稀土元素含量相对较高,具有弱—中等程度的轻稀土元素富集,中等程度的轻重稀土元素分异,轻微的Eu异常;玄武岩中Cr、Ni含量变化较大,但与Mg#具有很好的正相关性。微量元素配分图解中具有明显的Sr负异常,部分样品具有Nb、Ta和Ti负异常,无Zr、Hf负异常,与岛弧火山岩不同;同时Nb、Ta无分异,Zr/Hf值较高,具有板内玄武岩浆的特征。综合分析认为,滹沱群玄武岩可能形成于板内裂谷环境。在岩浆上升过程中发生橄榄石与尖晶石的分离结晶作用,同时不同程度地受到地壳的混染。 相似文献