where T is temperature in degrees Celsius, δarag is the δ18O value of aragonite normalized to VPDB, and δsw is the δ18O value of water normalized to VSMOW. This calibration improves accuracy and precision of Caribbean sclerosponges for reconstructions of temperature as well as δ18O values of seawater.  相似文献   

18.
Geochemistry of hydroxy acids in sediments—I. Some freshwater and brackish water lakes in Japan     
Kazuo Fukushima  Hiroshi Kondo  Susumu Sakata 《Organic Geochemistry》1992,18(6)
Series of α, β, ω and (ω-1) hydroxy fatty acids (FAOHs) were determined in several freshwater and brackish water lacustrine sediments in Japan. Analytical procedure used was digestion of the solvent-extracted sediment with HF/HCl followed by solvent and saponification extraction of the residue. Abundances of α/β and ω-FAOH determined by this procedure were 2–3 times higher than those obtained by single alkaline saponification and of the same order with those provided by HCl hydrolysis. Major portion of α/β-FAOH was obtained by solvent extraction of the acid-treated sediments, while subsequent alkaline saponification was needed for the majority of ω-FAOH to be recovered. Thus determined FAOHs comprised 33–61% (Av. = 42%) of the “bound” acid constituents in the lacustrine surface sediments. The α/β and ω-FAOH composition was principally the same among the samples examined, except for relative proportions of the iso to anteiso C15 and C17 ß(α)-FAOH, which showed significant variations in the ranges of 0.30–1.1 and 0.46–1.5, respectively. In the holomictic lakes, the ratios together with the same ratios of the “bound” branched monocarboxylic acids tended to decrease with increasing water depth of the lakes, suggesting that the ratios may indicate an extent of the early diagenetic alteration of the bacteria-derived lipids either in water column or in surface sediment.  相似文献   

19.
Sigioite : The oxidation mechanism in [M 2 3 + (PO4)2(OH)2(H2O)2]2 - structures     
Dr. Frank C. Hawthorne 《Mineralogy and Petrology》1988,38(3):201-211
Summary The crystal structure of sigloite, Fe3 [(H2O)3OH] [Al2(PO4)2(OH)2(H2O)2]- 2 H2O, triclinic, a 5.190 (2), b 10.419 (4), c 7.033 (3) Å, 105.00 (3), 111.31(3), 70.87 (3)°, V 330.5 (2) Å3, Z = 1, space group P , has been refined to anR index of 5.3% using 1713 observed (I > 2.5 1) reflections collected with graphite-monochromated MoK X-rays. Sigloite is isostructural with the laueite-group minerals. Corner-linked [A15] chains (: unspecified ligand) are cross-linked by (PO4) tetrahedra to form a mixed corner-linked tetrahedral-octahedral sheet of composition [A12(PO4)2(OH)2(H2O)2]2-. These sheets are linked by (Fe3+O2(OH, H2O)4) octahedra and two (H2O) groups that participate in a hydrogen-bonding network. Sigloite is the oxidized equivalent of paravauxite, Fe2+(H2O)4[Al2(PO4)2(OH)2(H2O)2]-2 H2O, and detailed comparison of the two structures shows that the oxidation mechanism involves loss of hydrogen from one of the (H2O) groups coordinating the Fe3+, and positional disorder of both the Fe3+ and (OH) and (H2O) ligands.
Siggloit: Der Oxidationsmechanismus in (M 2 3 + (PO4)2(OH)2(H2O)2]2- Strukturen
Zusammenfassung Die Kristallstruktur von Sigloit, Fe3+ [(H2O)3OH] [Al2(PO4)2(OH)2(H2O)2].2 H2O, triklin, a 5,190 (2), b 10,419 (4), c 7,033 (3) Å, 105,00 (3), 111,31 (3), 70,87 (3)°, V 330,5 (2) Å3,Z = 1, Raumgruppe P , wurdefür 1713 beobachtete Reflexe (I > 2,5 I), die mit MoKa-Röntgenstrahlung (Graphit-Monochromator) gesammelt wurden, auf einen R-Wert von 5,3% verfeinert. Sigloit ist isotyp mit den Mineralen deer Laueit-Gruppe. Über Ecken verknüpfte [A15]-Ketten (: nicht spezifizierter Ligand) werden über (P04)-Tetraeder zu ebenfalls über Ecken verknüpfte Tetraeder-OktaederSchichten der Zusammensetzung [A12(PO4)2(OH)2(H2O)2]2- verbunden. Diese Schichten werden über (Fe3+O2(OH, H2O)4)-Oktaeder und zwei (H2O)-Gruppen, die amWasserstoffbrücken-Netzwerk beteiligt sind, verbunden. Sigloit ist das oxidierte Analogon zu Paravauxit, Fe2+(H2O)4[A12(PO4)2(OH)2(H2O)2] - 2 H2O; ein detaillierter Vergleich dieser beiden Strukturen zeigt, daß der Oxidationsmechanismus sowohl den Verlust eines Wasserstoffatoms (H2O)-Gruppe, welche ein Fe3+-Atom koordiniert, als auch eine Fehlordnung der Punktlagen von Fe3+ und von den (OH) und (H2O) Liganden bedingt.
  相似文献   

20.
The crystal structure of Ca5(PO4)2SiO4 (Silico-Carnotite)     
Dr. B. Dickens  Dr. W. E. Brown 《Mineralogy and Petrology》1971,16(1-2):1-27
Summary The crystal structure of Ca5(PO4)2SiO4 (silico-carnotite) has been determined from 3358 x-ray diffraction data collected by a counter method and has been refined toR w =0.038,R=0.045, in space group Pnma. The unit cell parameters area=6.737 (1) Å,b=15.508 (2) Å andc=10.132 (1) Å at 24°C;Z=4. The observed density is 3.06 and the calculated density is 3.03 g · cm–3. The crystal contains about 2.5% V2O5 as an impurity. The bond lengths within the tetrahedral anions suggest that substitution or disorder of PO4 3–, SiO4 4– and possibly VO4 3– occurs among the anion sites. The structure has some relationship to that of Ca5(PO4)3OH, the predominant inorganic phase in the human body, but suggests that the Ca5(PO4)3OH type structure may not be stable without some of the OH positions being filled. Ca5(PO4)2SiO4 is more closely related to K3Na(SO4)2 (glaserite) if it is considered that there are systematic cation vacancies in Ca5(PO4)2SiO4.This type of structure is consistent with the view that cation vacancies in the glaserite-type structure account for solid solutions between Ca2SiO4 and Ca3(PO4)2 and between Ca3(PO4)2 and CaNaPO4.
Die Kristallstruktur vonCa 5(PO 4)2 SiO 4 (Silicocarnotit)
Zusammenfassung Die Kristallstruktur von Ca5(PO4)2SiO4 (Silicocarnotit) wurde aus 3358 Röntgendiffraktometer-Daten bestimmt und in Raumgruppe Pnma aufR w =0,038,R=0,045 verfeinert. Die Gitterkonstanten (bei 24° C) sind:a=6,737 (1) Å,b=15,508 (2) Å undc=10,132 (1) Å,Z=4; Dobs.=3,06 g · cm–3, Dexp.=3,03 g · cm–3. Der Kristall enthält etwa 2,5% V2O5 als Verunreinigung. Die Bindungslängen in den tetraedrischen Anionen legen nahe, daß unter den Anionenplätzen gegenseitige Vertretung oder Unordnung von PO4 3–, SiO4 4– und möglicherweise VO4 3– auftritt. Die Struktur zeigt einige Verwandtschaft zu der von Ca5(PO4)3OH, der wichtigsten anorganischen Substanz im menschlichen Körper, weist aber darauf hin, daß eine Struktur vom Ca5(PO4)3OH-Typ ohne Besetzung eines Teiles der OH-Position nicht stabil ist. Ca5(PO4)2SiO4 zeigt engere Beziehungen zu K3Na(SO4)2 (Glaserit), wenn man berücksichtigt, daß in Ca5(PO4)3SiO4 systematische Kationen-Leerstellen sind. Dieser Strukturtyp ist mit derAuffassung in Übereinstimmung, daß Kationenleerstellen für die festen Lösungen zwischen Ca2SiO4 und Ca3(PO4)2 und zwischen Ca3(PO4)2 und CaNaPO4 verantwortlich sind.

With 9 Figures  相似文献   

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1.
The thermodynamic stability of selected alkylated, dealkylated and rearranged 17α- and 17β-hopane isomers in the C27, C28, C29, C30 and C31 families were calculated using molecular mechanics (MM2) methods and, where possible, calculated equilibrium ratios of certain isomers were compared with observed ratios of isomers in thermally mature crude oil samples. Those calculated and observed ratios having similar values include: (1) the relative distributions among 17β(H)/17α(H) and 21β(H)/21α(H)-hopanes including the absence of the 17β(H),21β(H)- and 17α(H),21α(H)-hopanes; (2) the 22R/22S ratios in 30-methyl-17α-hopane and 30-methyl-17β-moretane; (3) the relative distributions among 17α(H)/17β(H)- and 21α(H)/21β(H)-28,30-bisnorhopanes and among 25,28,30-trisnorhopanes, including the relatively greater stability of 17β(H) isomers in contrast to the regular hopane series; and (4) the ratios of 28(18−17S)abeo hopanes with respect to their unrearranged counterparts including the C27 compounds, Ts/Tm.  相似文献   

2.
A tetradeuteriated cholestane was heated with kerogen isolated from the Messel oil shale at 350 °C for 25 different time periods (ranging from 0.5 to 80 h) in borosilicate vessels. Three isomers of tetradeuteriated dimethylperhydrophenanthrene were formed and one of these was the major saturated hydrocarbon product under most conditions. The stereochemistry for these isomers was unknown but if the stable 5α,8β,9α(H),10β(CH3) sterane configuration is inherited from the cholestane then there are four possible isomers namely: I and II [13β(H) and 13α(H) diastereomers, respectively, of 10,13-dimethylperhydrophenanthrene] as well as III and IV [14β(H) and 14α(H) diastereomers, respectively, of 10,14-dimethylperhydrophenanthrene]. Molecular mechanics revealed that I is the most stable form and therefore is the component that dominated the saturated hydrocarbon degradation products. The identification of only three isomers of deuteriated dimethylperhydrophenanthrene in the pyrolysis experiments is supported by the calculated stabilities (ΔΔG) as isomer IV is considerably more unstable (by 1.7 kcal/mol) than II which is the least stable of I, II and III. If these compounds can be detected in crude oils their distributions may be useful maturity indicators in oils that have been generated at high thermal maturity.  相似文献   

3.
The extent of sterane isomerisation reactions and the moretane/hopane ratios of 234 crude oils, taken world wide, from a wide variety of source rocks of differing geological ages, have been measured.This data indicates that in 78 crude oils derived from Tertiary source rocks, sterane isomerisation reactions as determined by the 20S/(20S + 20R) ration of the C29 5α(H), 14α(H), 17α(H) normal-steranes and the C29 iso/(iso + normal) ratio [iso = 5α (H), 14β(H), 17β(H)] are mainly incomplete and sometimes considerably so. In addition, the same crude oils have 17β(H), 21α(H)-moretane/17α(H), 21β(H)-hopane ratios which are significantly greater (predominantly in the range 0.10–0.30) than those of crude oils derived from older, mature source rocks (mainly less than 0.1).This data, for crude oils, lends support to the hypothesis, proposed by Mackenzie and McKenzie (1983) for source rock extracts, that the time/temperature constraints of sterane isomerisation reactions are such that the time available for isomerisation in Tertiary sediments is generally insufficient, despite generation of crude oil at relatively high temperatures.An alternative hypothesis is that the incomplete sterane isomerisation of Tertiary crude oils may be due to generation of these crude oils from their deltaic, land plant-containing source rocks under low heating conditions.A third hypothesis proposes that the Tertiary crude oils may have picked up the incompletely isomerised steranes from immature sediments during migration. Although possible in particular instances, such a mechanism does not appear to be generally applicable since, in that case, the phenomenon would then appear to be restricted to the Tertiary.The higher moretane/hopane ratios of the Tertiary crude oils could suggest that constraints, similar to those applying in sterane isomerisation, also operate in the conversion of moretane to 17α(H)-hopane.  相似文献   

4.
The major steranes of the non-asphaltene fraction of Nigerian tar sand bitumen (maltene) are the c27-c29 diasteranes [13β(H),17α(H); 20R + S] and C28-C29 regular steranes [14β (H),17β (H); 20S]. The reducing metal reaction products of the corresponding asphaltenes (maltene-I) contain mainly C27-C29 regular steranes with the 14β(H),17β(H); 20R + S and 14α(H),17α(H); 20R + S configurations as well as the corresponding diasteranes having the 13β(H),17α(H); 20R + S configuration. These sterane distributions suggest that maltene-I corresponds to an unaltered oil whilst the maltene is equivalent to the product of severe biodegradation of maltene-I. This is consistent with maltene-I being the remnant of “original oil” trapped within the asphaltene matrix and protected from the effect of in-reservior biodégradation.Degradation of Nigerian asphaltenes by refluxing with ferric chloride-acetic anhydride or methanolic potassium hydroxide also releases soluble reaction products having the characteristics of unaltered oil such as the presence of n-alkanes having an unbiased distribution. These methods appear to be milder and more suitable than reducing metal reactions for releasing hydrocarbons occluded by asphaltenes.  相似文献   

5.
A novel series of 3-alkyl and 3-carboxyalkyl-5β(H)-steranes 7–10 along with a full homologous series of carboxyalkyl-sterane (C1 to C6) 4–6 with 3α(H)5α(H) configuration have been identified in marine-evaporitic oils from Fazenda Belém, Potiguar Basin (Brazil) on the basis of mass spectral interpretation. The synthesis of enantiomerically pure 3α-alkyl-5β(H)-cholestane and 3β-alkyl-5α(H)-cholestane standards and their coinjection with petroleum fractions confirmed the structural assignments.  相似文献   

6.
The distributions of polycyclic alkanes were monitored in a Neocomian sequence (well 1-ESS-34) from the Espirito Santo Basin, southeast Brazil. The profiles included, apart from regular hopanes, significant concentrations of 18α(H), 28,30-bisnorhopane and subordinate amounts of gammacerane. Sterane concentrations, normally with hopane/sterane <5, were compatible with other geochemical data indicating a predominantly planktonic/microbial source of the deposited organic matter. Sample maturities ranged from very immature to the onset of oil generation, allowing biomarker distributions to be followed along a broad maturation range. The ability of certain molecular ratios (e.g. C27 17α(H)/17β(H)hopanes) to reflect a maturity sequence with depth in the closely-spaced strata of the immature upper levels (Jiquiá Stage) showed the value of molecular techniques over classical geochemical methods (e.g. vitrinite reflectance) for the study of immature sequences. The presence in the oils of southern Espirito Santo of 28,30-bisnorhopane, gammacerane and methyl steranes in similar concentrations as in extracts of the deepest levels of the 1-ESS-34 well qualify the Jiquia Stage as the probable source rock of oils accumulated in the basin.  相似文献   

7.
Twenty-seven heavy crude oils of diverse origin were geochemically assessed with respect to both bulk and mlecular composition for the purpose of identifying and quanttfying valid biomarker parameters for low maturity oils. The low thermal maturity level of many of these oils is evident from the bulk and alipathic chromatographic data, and oil sourced from both marine and terrigenous organic matter are represented. Selective metastable ion monitoring (SMIM) was employed to measure separately the distribution of C27, C28, and C29 sterane isomers. The useful maturity indicators include the C29 5α(H) 20S/20R ratio, the relative quantity of the biological sterane configuration in each of the total normal C27, C28, and C29 steranes, and the rearranged to normal sterane ratio. In addition, C27 rearranged steran es appear to form at a faster rate than C28 or C29 rearranged steranes. However, the isomerization of the C27 biological component appears to occur at a slower rate than the C29 counterpart suggesting that the former may be used as a maturity parameter at higher levels of thermal maturation. In the triterpane distributions, the C27 trisnorhopane isomers and the moretane to hopane ratios appear to be both source and maturity related and cannot be used as successful maturity parameters in oils unless they share a common source. The C31+ hopane 22S/22R equilibrium ratio appears to increase with increasing molecular weight (C31–C34).  相似文献   

8.
Biomarker ratios, together with stable carbon (δ13C) and hydrogen (δD) isotopic compositions of individual hydrocarbons have been determined in a suite of crude oils (n = 24) from the East Sirte Basin to delineate their sources and respective thermal maturity. The crude oil samples are divided into two main families (A and B) based on differences in source inputs and thermal maturity. Using source specific parameters including pristane/phytane (Pr/Ph), hopane/sterane, dibenzothiophene/phenanthrene (DBT/P), Pr/n-C17 and Ph/n-Cl8 ratios and the distributions of tricyclic and tetracyclic terpanes, family B oils are ascribed a marine source rock deposited under sub-oxic conditions, while family A oils have a more terrigenous source affinity. This genetic classification is supported by the stable carbon isotopic compositions (δ13C) of the n-alkanes. Using biomarker maturity parameters such as the abundance of Pr and Ph relative to n-alkanes and the distribution of sterane and hopane isomers, family A oils are shown to be more thermally mature than family B oils. The contrasting maturity of the two families is supported by differences between the stable hydrogen isotopic compositions (δD) of Pr and Ph and the n-alkanes, as well as the δ13C values of n-alkanes in their respective oils.  相似文献   

9.
Cinnabar (α-HgS) and metacinnabar (β-HgS) dissolved at environmentally significant rates in oxygenated slurry experiments simulating a low-flow fluvial system. Based on SO42− production, cinnabar dissolution rates were 2.64 to 6.16 μmol (SO42−) m− 2 day− 1, and metacinnabar dissolution rates were 1.20 to 1.90 μmol (SO42−) m− 2 day− 1. Monodentate-bound thiosulfate (S2O32−) was identified as an oxidation product on the HgS surface by ATR-IR spectroscopy based on strong infrared absorption bands in the 1140–1145 cm− 1 and 1006–1014 cm− 1 regions. The presence of sulfide oxidation intermediates on the HgS surface indicates that SO42− concentration underestimates α-HgS and β-HgS dissolution in this setting. Mercury release rates during dissolution were more than two orders of magnitude less than SO42− production, but were significant: 0.47 mg (Hg) m− 2 y− 1 from cinnabar [6.45 nmol (Hg) m− 2 day− 1], and 0.17 mg (Hg) m− 2 y− 1 from metacinnabar [2.29 nmol (Hg) m− 2 day− 1]. The Hg mobilized during α-HgS and β-HgS dissolution is sufficient to form natural Au–Hg amalgam in downstream placer settings. The proportion of mercury that is not remobilized during α-HgS and β-HgS dissolution likely adsorbs to the dissolving mercuric sulfide. Adsorption of Hg2+ to cinnabar was detected in situ by anodic stripping voltammetry using a cinnabar-modified carbon paste electrode following accumulation of Hg2+ on the electrode at open circuit potential.  相似文献   

10.
A series of tricyclic terpenoid carboxylic acids (C20–C40) was found in the acidic fraction of Tasmanian tasmanite bitumen, occurring as a mixture of stereoisomers with mainly the 13β(H), 14α(H)-and 13α(H),14α(H)-configurations. These dominant acidic tricyclic constituents have the same carbon skeleton as the ubiquitous tricyclic terpane biomarkers. A novel series of ring-C monoaromatic tricyclic terpenoid carboxylic acids was also characterized. The series ranges from C19 to C39 and is the acidic counterpart of the recently described series of monoaromatic tricyclic terpanes.  相似文献   

11.
The crystal structure of a new compound, [(H5O2)(H3O)(H2O)][(UO2)(SeO4)2] (monoclinic, P21/n a = 8.3105(15), b = 11.0799(14), c = 13.227(2) Å, β = 103.880(13)°, V = 1182.4(3) Å3), has been solved by direct methods and refined to R 1 = 0.036. The structure is based on [(UO2)(SeO4)2]2? sheet complexes formed by corner-shared UO7 pentagonal bipyramids and SeO4 tetrahedrons. The sheets are parallel to the ( $ \bar 1 The crystal structure of a new compound, [(H5O2)(H3O)(H2O)][(UO2)(SeO4)2] (monoclinic, P21/n a = 8.3105(15), b = 11.0799(14), c = 13.227(2) ?, β = 103.880(13)°, V = 1182.4(3) ?3), has been solved by direct methods and refined to R 1 = 0.036. The structure is based on [(UO2)(SeO4)2]2− sheet complexes formed by corner-shared UO7 pentagonal bipyramids and SeO4 tetrahedrons. The sheets are parallel to the (01) plane. Oxonium ions and water molecules forming [(H3O)·(H2O)·(H5O2)]2+ complexes are interlayer. Among minerals, the existence of (H5O2)+ has been unambiguously confirmed only in rhomboclase, (H5O2)+[Fe2(SO4)2(H2O)2]. Original Russian Text ? S.V. Krivovichev, 2008, published in Zapiski Rossiiskogo Mineralogicheskogo Obshchestva, 2008, No. 2, pp. 123–130.  相似文献   

12.
Variations in the carbon isotopic composition (δ13C) of pristane, phytane, n-heptadecane (n-C17), C29 ααα 20R sterane, and aryl isoprenoids provide evidence for a diverse community of algal and bacterial organisms in organic matter of the Upper Ordovician Maquoketa Group of the Illinois Basin. Carbon isotopic compositions of pristane and phytane from the Maquoketa are positively covariant (r = 0.964), suggesting that these compounds were derived from a common source inferred to be primary producers (algae) from the oxygenated photic zone. A variation of 3‰ in δ13C values (−31 to −34‰) for pristane and phytane indicates that primary producers utilized variable sources of inorganic carbon. Average isotopic compositions of n-C17 (−32‰) and C29 ααα 20R sterane (−31‰) are enriched in 13C relative to pristane and phytane (−33‰) suggesting that these compounds were derived from a subordinate group of primary producers, most likely eukaryotic algae. In addition, a substantial enrichment of 13C in aryl isoprenoids (−14 to −18‰) and the identification of tetramethylbenzene in pyrolytic products of Maquoketa kerogen indicate a contribution from photosynthetic green sulfur bacteria to the organic matter. The presence of anaerobic, photosynthetic green sulfur bacteria in organic matter of the Maquoketa indicates that anoxic conditions extended into the photic zone.The δ13C of n-alkanes and the identification of an unusual suite of straight-chain n-alkylarenes in the m/z 133 fragmentograms of Ordovician rocks rich in Gloeocapsomorpha prisca (G. prisca) indicate that G. prisca did not contribute to the organic matter of the Maquoketa Group.  相似文献   

13.
Summary The crystal structure of liebigite, previously only incompletely known from a short note, has been determined from X-ray 4-circle diffractometer data and refined toR=0.030 for 3005 observed reflections. Liebigite from Joachimsthal, Böhmen, was used. It was found to crystallize in the polar orthorhombic space groupBba2–C 2v 17 witha=16.699(3),b=17.557(3),c=13.697(3) Å,V=4016 Å3 and a cell content of 8 Ca2UO2(CO3)3·11H2O. The structure contains UO2(CO3)3 units which are linked by two kinds of CaO4(H2O)4 polyhedra and one kind of CaO3(H2O)4 polyhedron to form puckered Ca2UO2(CO3)3·8H2O layers parallel to (010). These layers are interconnected only by hydrogen bonds, both directly as well as via three additional interlayer H2O molecules, two of which show positional disorder.
Die Kristallstruktur des Liebigits, Ca2UO2(CO3)3·11H2O
Zusammenfassung Die Kristallstruktur des Minerals Liebigit, die bis jetzt nur unzureichend bekannt war, wurde mit Röntgen-Vierkreisdiffraktometer-Daten bestimmt und für 3005 beobachtete Reflexe aufR=0,030 verfeinert. Der untersuchte, von Joachimsthal, Böhmen, stammende Liebigit kristallisiert in der polaren rhombischen RaumgruppeBba2–C 2v 17 mita=16,699(3),b=17,557(3),c=13,697(3) Å,V=4016 Å3 und einem Zellinhalt von 8 Ca2UO2(CO3)3·11H2O. Die Struktur enthält UO2(CO3)3-Gruppen, die durch zwei Arten von CaO4(H2O)4-Polyedern und eine Art von CaO3(H2O)4-Polyedern zu buckeligen Ca2UO2(CO3)3·8H2O-Schichten parallel (010) verknüpft sind. Diese Schichten sind nur durch Wasserstoffbrücken verbunden, und zwar sowohl direkt als auch mittels dreier zusätzlicher freier Wassermoleküle, von denen zwei eine Lagenfehlordnung aufweisen.

With 3 Figures  相似文献   

14.
Lake Kinneret, a relict lake from the Neogene, is characterised by the dominance among its phytoplankton of the dinoflagellate Peridinium cinctum. The lipid geochemistry of Lake Kinneret is discussed herein in terms of the biology, chemistry and hydrology of the lake. Lipids isolated from two sediment sections (surface and 15 cm deep), obtained from the deepest point of Lake Kinneret, include: (1) 4α-methyl-5α (H)-stanols and related derivatives characteristic of P. cinctum, the novel sterol 4a-methylgorgosterol, and peridinosterol and 4α-methylgorgostanol, not previously reported to occur in lacustrine sediments; (2) C30 and C32 alkane-1,15-diols, not previously reported to occur in contemporary lacustrine deposits, and (3) products of early diagenesis. Many similarities were observed with the more widely studied marine dinoflagellates and marine sediments with dinoflagellate input.  相似文献   

15.
Mixtures of hopane diastereomers obtained by fractionation of the organic extract from an immature oil shale have been heated in the presence of clay-containing substrates. In experiments conducted at 250°C with an extracted source rock as the substrate, the relative amounts of 17β(H),21β (H)-hopanes were found to decrease with respect to the moretanes and 17α(H),21β(H)-hopanes in a manner parallelling that observed with increasing maturity in sediments. In this case however, the change was shown to be due to the selective removal of the 17β(H),21β(H)-hopanes, rather than conversion of these compounds into the other diastereomers. In order to assess whether the use of elevated temperatures was enhancing processes other than those which operate in natural systems, a second experiment was conducted in which the sample of immature hopanes was heated at 75°C with the very catalytically active substrate aluminum montmorillonite. In this experiment also, the changes in hopane composition was shown to be due to selective removal of 17β(H),21β(H)-hopanes rather than conversion into the corresponding compounds in the other two series of diastereomers. These results suggest that the observed relative depletion of 17β(H),21β(H)-hopanes in sedimentary rocks of increasing maturity may similarly be due to removal by selective catalytic processes, and not to interconversion processes associated with isomerisation at C-17 and C-21 as had previously been believed.  相似文献   

16.
Zusammenfassung Die Kristallstruktur des Johannits wurde anhand eines verzwillingten Kristalls von Joachimsthal, Böhmen, mit dreidimensionalen Röntgendaten bestimmt und für 2005 unabhängige Reflexe aufR=0,039 verfeinert. Johannit kristallisiert triklin, RaumgruppeP1, mita=8,903 (2),b=9,499 (2),c=6,812 (2) Å, =109,87 (1) =112,01 (1), =100,40 (1)° undV=469,9 Å3. Chemische Formel und Zellinhalt lauten Cu(UO2)2(OH)2(SO4)2·8H2O, das ist um zwei H2O-Moleküle mehr als bisher angenommen. In der Struktur sind pentagonal dipyramidale (UO2)(OH)2O3-Polyeder paarweise über eine von zwei OH-Gruppen gebildete Kante zu Doppelpolyedern und diese wiederum durch SO4-Gruppen zu (UO2)2(OH)2(SO4)2-Schichten parallel (100) verknüpft. Die Schichten sind parallel über gestreckte Cu(H2O)4O2-Oktaeder und Wassermoleküle miteinander verbunden. Folgende Bindungslängen wurden gefunden: U–O=1,78 Å (2x) und 2,34–2,39 Å (5x); Cu–O=1,97 Å (4x) und 2,40 Å (2x); =1,47 Å; O–O in Wasserstoffbrücken 2,71–2,91 Å (8x) und 3,30 Å.
The crystal structure of johannite, Cu(UO2)2(OH)2(SO4)2·8H2O
Summary The crystal structure of johannite has been determined from threedimensional X-ray data measured on a twinned crystal from Joachimsthal, Böhmen, and has been refined toR=0.039 for 2005 independent reflections. Johannite crystallizes triclinic, space groupP1, witha=8.903 (2),b=9.499 (2),c=6.812 (2) Å, =109.87(1), =112.01(1), =100.40 (1)° andV=469.9 Å3. Chemical formula and cell content are Cu(UO2)2(OH)2(SO4)2·8H2O, by two H2O molecules more than previously assumed. Pairs of pentagonal dipyramidal (UO2) (OH)2O3 polyhedra form double polyhedra by edgesharing via two OH groups. The double polyhedra are linked by the SO4 tetrahedra to form layers (UO2)2(OH)2(SO4)2 parallel zu (100). These layers are interconnected parallel toa by elongated Cu(H2O)4O2 octahedra and water molecules. Following bond lengths have been observed: U–O=1.78 Å (2x) and 2.34–2.39 Å (5x); Cu–O=1.97 Å (4x) and 2.40 Å (2x); =1.47 Å; O–O for hydrogen bonds 2.71–2.91 Å (8x) and 3.30 Å.

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17.
A revised calibration is presented relating the oxygen isotope composition of the aragonite-secreting sclerosponge Ceratoporella nicholsoni, oxygen isotope composition of seawater, and ambient water temperature. This new relationship has been obtained using high-resolution δ18O data measured in sclerosponges from the Bahamas and Jamaica compared to ambient temperature measurements and δ18O values of seawater from the two locations, both measured and published. New data improve an existing calibration which was determined using measurements of salinity rather than directly measured δ18O values of the seawater and was composed of measurements from different species of sclerosponge and other aragonite-secreting organisms. The updated calibration (n = 12, r2 = 0.95) is:
T(°C)=16.1(±3.1)-[6.5(±1.1)](δarag-δsw),
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