Depositional environment of a Kimmeridgian carbonate 'black band' (Akkuyu Formation, south-western Turkey)     

François Baudin  Nicolas Tribovillard  Fatima Laggoun-Défarge  Eric Lichtfouse  Olivier Monod  & Silvia Gardin 《Sedimentology》1999,46(4):589-602

The Upper Jurassic Akkuyu Formation of south-western Turkey consists of pale-coloured carbonate facies, but includes a peculiar ‘black band’ at its base. In order to characterize the depositional environment of this level, a sedimentological, organic and inorganic geochemical study was performed on 30 samples. Three units are distinguished. Unit 1 consists of black marlstones, very rich in organic carbon (22–30%) with HI (hydrogen index) values around 600. The organic matter is an amorphous homogeneous material even at nanoscopic scale. This unit is also characterized by a very high concentration of V ( >1000 p.p.m.) and a δ¹³C_org value around ?26·5‰. Unit 2 shows thin-bedded black limestones with chert layers. Its organic content varies from 2% to 6%. As in unit 1, the HI values are uniformly high (600), and gas chromatography shows a high quantity of hopanes. The V concentration is also high (≈400 p.p.m.). The unit has a high Sr/Ca ratio, an organic carbon isotopic ratio close to ?28·7‰ and diffuse, nanoscopically amorphous organic material that is closely associated with pyrite. Unit 3 corresponds to the white limestones overlying the ‘black band’. This calcitic facies is almost devoid of organic carbon (<0·1%). The δ¹³C_org values are similar to those of unit 1 (?25·5‰ to ?26‰). Deposition occurred in a basinal environment surrounded by a carbonate platform. Primary productivity was high but not exceptional; terrestrial organic inputs were scarce. Bottom waters were probably euxinic during the deposition of unit 1. The presence of both hopane-rich and sulphur-rich nanoscopically amorphous organic matter may be the result of strong sulphate-reducing bacterial activity. Coupled with low amounts of iron, this led to intense vulcanization of the organic matter and thus good preservation. With the onset of unit 2 deposition, environmental conditions became less extreme, perhaps because of cooler water temperatures. Finally, the depositional conditions became oxic, leading to the accumulation of pale-coloured organic-poor limestones of unit 3.  相似文献   

铁—磺基水杨酸—二甲氧基羟基苯基荧光酮—TritonX—100体系的光度研究 …   总被引：3，自引：1，他引：2       下载免费PDF全文

刘少民  潘教麦 《岩矿测试》1999,20(2):120-123

研究了在表面活性剂存在下,铁与新显色剂二甲氧基羟基苯基荧光酮（ＤＭＨＰＦ）的显色反应。在ｐＨ９．０～１０．５的氨性介质中,有磺基水杨酸（Ｓａｌ）存在下,形成Ｆｅ３＋ＳａｌＤＭＨＰＦＴｒｉｔｏｎＸ１００四元混配配合物,其最大吸收峰在５９０ｎｍ,测定波长选择６１０ｎｍ,表观摩尔吸光系数分别为１．３×１０５Ｌ·ｍｏｌ－１·ｃｍ－１和９．４×１０４Ｌ·ｍｏｌ－１·ｃｍ－１。配合物组成比ｎＦｅ３＋∶ｎＤＭＨＰＦ＝１∶２,Ｆｅ３＋的质量浓度为０～６００μｇ／Ｌ时符合比尔定律。以直接光度法测定工业硅和石灰石样品中微量铁,结果与标准值相符,５次测定的ＲＳＤ在０．６４％～２．４１％。  相似文献   

Boron isotopic composition of subduction-zone metamorphic rocks   总被引：1，自引：0，他引：1  

Simon M. Peacock  Richard L. Hervig   《Chemical Geology》1999,160(4):51-290

Many arc lavas contain material derived from subducted oceanic crust and sediments, but it remains unresolved whether this distinctive geochemical signature is transferred from the subducting slab by aqueous fluids, silicate melts, or both. Boron isotopic measurements have the potential to distinguish between slab transfer mechanisms because ¹¹B fractionates preferentially into aqueous fluids whereas little fractionation may occur during partial melting. Previous studies have shown that δ¹¹B values of island arc lavas (−6 to +7) overlap the range of δ¹¹B values for altered oceanic crust (−5 to +25) and pelagic sediments and turbidites (−7 to +11). Secondary ion mass spectrometry (SIMS) analyses of minerals in subduction-zone metamorphic rocks yield δ¹¹B=−11 to −3 suggesting that slab dehydration reactions significantly lower the δ¹¹B values of subducted oceanic crust and sediments. In order to explain the higher δ¹¹B values reported for arc lavas as compared to subduction-zone metamorphic rocks, the B-bearing component derived from the metamorphosed slab must be enriched in ¹¹B relative to the slab, favoring an aqueous fluid as the slab transfer mechanism.  相似文献   

Seasonal variation in the biogeochemical cycling of seston in Grand Traverse Bay, Lake Michigan     

Eileen M. McCusker  Peggy H. Ostrom  Nathaniel E. Ostrom  Jeffery D. Jeremiason  Joel E. Baker 《Organic Geochemistry》1999,30(12):687

This study describes the biogeochemical cycling of seston in Grand Traverse Bay, Lake Michigan. Seston was characterized by carbon and nitrogen elemental and isotopic abundances. Fluorescence, temperature, light transmittance, and concentrations of dissolved inorganic nitrogen were also determined. PCBs were analyzed from surface (10 m) seston and ΣPCB was calculated by summing all of the congeners quantified in each sample. The vertical and seasonal trends in the δ¹³C values of seston exhibited a broad range from −30.7 to −23.9‰. Low δ¹³C values that occur concurrently with a peak in fluorescence below the thermocline reflect uptake of ¹³C depleted respiratory CO₂ and/or the accumulation of ¹³C depleted lipids by phytoplankton. High δ¹³C values late in the season likely result from a reduction in photosynthetic fractionation associated with a decrease in the CO₂ pool. Seasonal δ¹⁵N values of seston were high in the spring and declined through August. The δ¹⁵N values of seston reflect a balance between fractionation during assimilation of NH₄⁺ or NO₃⁻ and degradative processes. The seston ΣPCB and fluorescence were both high in the spring and subsequently declined, suggesting that the concentrations of PCBs in seston were associated with labile material derived from primary productivity. The strong seasonal trends in the organic geochemical characteristics of seston and concentrations of PCBs emphasize the complex nature of particle cycling in aquatic environments.  相似文献   

Detection of petroleum contamination in river sediments from Quebec City region using GC–IRMS     

K. M. Rogers  M. M. Savard 《Organic Geochemistry》1999,30(12):8399

Isotopic analysis by compound specific gas chromatography–isotope ratio mass spectrometry (GC–IRMS) is used to detect and characterize petroleum pollution in surficial sediments along the St Lawrence River, near Quebec City. Unusually mature n-alkane distributions have been found in some recent intertidal sediments in the region. GC–IRMS results suggest that the n-alkanes are not derived from indigenous organic sources because they carry δ¹³C values between −30.0 and −27.0‰, as well as very small isotopic differences between odd and even numbered n-alkanes, which are both typically associated with petroleum products. Comparison of these sediments with bunker fuel, an oil used in the shipping industry, has shown a close isotopic correlation in some sites, which is further supported by biomarkers. Overall, the contamination has been dispersed along the river but is generally localized around the industrial region where hydrocarbon transfer from shore storage to ships takes place. This study illustrates how GC–IRMS can be used effectively in the detection and characterization of petroleum pollutants in sediments.  相似文献   

Organic carbon isotopes of the Sinian and Early Cambrian black shales on Yangtze Platform, China   总被引：5，自引：0，他引：5  

Renwei Li  Jialan Lu  Shukun Zhang  Jiajin Lei 《中国科学D辑(英文版)》1999,42(6):595-603

Organic matter of the Sinian and early Cambrian black shales on the Yangtze Platform belongs to the light carhon group of isotopes with the δ¹³C values from - 27% to - 35 %, which are lower than those of the contempomneously deposited carbonates and phosphorites. A carbon isotope-stratified paleooceanographic model caused by upwelling is proposed, which can be used not only to interpret the characteristies of organic carbon isotopic compositions of the black shales, but also to interpret the paleogeographic difference in the organic carbon isotope compositions of various types of sedimentary rocks. Project supported by the National Natural Science Foundation of China (Grant No. 49472114) and the Open Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences.  相似文献   

热液脉型铅-锌-银矿床富铁闪锌矿中硫化物包裹体成因探讨   总被引：12，自引：3，他引：9       下载免费PDF全文

黄典豪 《矿床地质》1999,18(3):244-252

通过对热液脉型的铅－锌－银矿床（３个）和银矿床（１个）和闪锌矿中硫化物包囊体的特征研究表明,石英－硫化物阶段富铁闪锌矿（主矿物）的硫化物包裹体十分发育：沿生长带产出的乳滴状黄铜矿与主矿物为共同沉淀成因;沿穿切主矿物的黄铜矿或石英细脉两侧,和受粗粒黄铜矿溶蚀的富铁闪锌矿近接触部位发育的乳滴状黄铜矿为渗透－交代产物;沿解理（裂隙）或粒间、粒内产出的各种形态磁黄铁矿是充填－交代的结果;沿解理分布的脉状毒  相似文献   

新疆罗布泊盐湖氢氧锶硫同位素地球化学及钾矿成矿物质来源   总被引：33，自引：9，他引：24       下载免费PDF全文

刘成林  王弭力  焦鹏程 《矿床地质》1999,18(3):268-275

罗布泊罗北凹地第四系上部盐层中蕴藏丰富的卤水,卤水中则富含钾（ＫＣｌ平均品位为１．４０％）。文章通过对罗布泊卤水氢、氧、锶及硫同位素等分析及与塔里木盆地（河流）、柴达木盆地等地区对比研究,确定了罗布泊富钾卤水源于地表水,可能主要是塔里木盆地南北缘河流水;卤水中的硫钾等物质组分主要来源于南天山、塔里木盆地西北、西南部中新生代石膏钙芒硝石盐矿床或地层及其古代地层卤水。由于第四纪期间塔里木盆地西部抬升。  相似文献   

赣中变质岩带的Sm—Nd,Rb—Sr同位素年代研究   总被引：1，自引：1，他引：0  

胡恭任  章邦桐  于瑞莲 《地质论评》1999,45(2):129-134

赣中变质岩带主要由斜长(云母)变粒岩、十字石榴云母片岩、云母石英片岩夹斜长角闪岩组成。斜长角闪岩Sm-Nd全岩等时线年龄为1113±19Ma,相当于该变质岩带的原岩形成年龄。ε_(Nd)(t)值为2.4±0.1,说明岩浆起源于亏损程度较低的地幔源区:726.6±1.1Ma、403.1±6.4Ma的Rb-Sr等时线年龄表明赣中地区在新元古代末期、加里东期经历了一次强烈的构造变质热作用,其地质、地球化学特征及时代可与浙闽地区陈蔡群、建瓯群进行对比。因此赣中变质岩带并非长期公认的华南加里东褶皱带,应是华夏地块的一部分,这一事实对华南大地构造单元的划分及构造演化具有重要意义。  相似文献   

Pathways and distances of fluid flow during low-grade metamorphism: evidence from pyrite deposits of the Cameros Basin, Spain   总被引：1，自引：0，他引：1  

Alonso-Azcárate  Rodas  Bottrell  Raiswell  Velasco  & Mas 《Journal of Metamorphic Geology》1999,17(4):339-348

New geochemical and sulphur isotopic data are presented for a number of pyrite deposits from the Late Jurassic–Early Cretaceous Cameros Basin, Spain. The deposits were formed at, or close to, the peak of metamorphism and are always related to sandstone units in the mainly metapelite sequence. Iron remained immobile and conservative, pyrite iron being derived by sulphidation of chlorite in the host metapelites. Reduced sulphur, however, was supplied from two external sources: thermochemical reduction of sulphate and release of S during metamorphism of sedimentary sulphides. These sources provided isotopically heavy and light S, respectively, with variation in pyrite isotopic composition between different deposits resulting from differences in their relative importance at each site. During metamorphism, the sandstone units acted as aquifers, carrying the sulphidic pore waters to locations where permeability provided by syn-depositional fractures on a scale of 0.5–5  m allowed its interaction with the metapelites. Transport distances for sulphide during metamorphism were of the order of hundreds of metres.  相似文献