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11.
The Fourier transform infrared spectra of individual conodonts with various CAI values indicate definite changes in conodont francolite during diagenesis. Steady decarbonation can be observed in the increasing intensity of the band with the wavenumber 2340 an-1 , which is assigned to trapped molecular CO2 . Carbon dioxide originates from decomposing CO2- 3 -ions occupying the B-site in francolite. Furthermore, the intensity of the water-deformation band at 1644 cm-1 decreases with higher CAI values. These changes of intensity can be quantified by calculating the maximum extinction (Emax ) for the corresponding absorption maxima and correlated with the CAI. Unaltered conodonts have a relative variable water 'content' and very little CO2 . Up to a CAI value of 4 conodont francolite continuously expells water and carbon dioxide is trapped. Conodonts with CAI = 5 have similar water 'contents' to CAI = 4 conodonts, but decarbonation continues to take place during this stage of diagenesis. 相似文献
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Towards a better understanding of magnesium-isotope ratios from marine skeletal carbonates 总被引:2,自引:0,他引:2
Dorothee Hippler Dieter Buhl Detlev K. Richter 《Geochimica et cosmochimica acta》2009,73(20):6134-2836
This study presents magnesium stable-isotope compositions of various biogenic carbonates of several marine calcifying organisms and an algae species, seawater samples collected from the western Dutch Wadden Sea, and reference materials. The aim of this study is to explore the influence of mineralogy, taxonomy and environmental factors (e.g., seawater isotopic composition, temperature, salinity) on magnesium-isotopic (δ26Mg) ratios of skeletal carbonates. Using high-precision multi-collector inductively coupled plasma mass spectrometry, we observed that the magnesium-isotopic composition of seawater from the semi-enclosed Dutch Wadden Sea is identical to that of open marine seawater. We further found that a considerable component of the observed variability in δ26Mg values of marine skeletal carbonates can be attributed to differences in mineralogy. Furthermore, magnesium-isotope fractionation is species-dependent, with all skeletal carbonates being isotopically lighter than seawater. While δ26Mg values of skeletal aragonite and high-magnesium calcite of coralline red algae indicate the absence or negligibility of metabolic influences, the δ26Mg values of echinoids, brachiopods and bivalves likely result from a taxon-specific level of control on Mg-isotope incorporation during biocalcification. Moreover, no resolvable salinity and temperature effect were observed for coralline red algae and echinoids. In contrast, Mg-isotope data of bivalves yield ambiguous results, which require further validation. The data presented here, point to a limited use of Mg isotopes as temperature proxy, but highlight the method’s potential as tracer of seawater chemistry through Earth’s history. 相似文献
14.
Hartmut H. Hellmer Monika Rhein Günther Heinemann Janna Abalichin Wafa Abouchami Oliver Baars Ulrich Cubasch Klaus Dethloff Lars Ebner Eberhard Fahrbach Martin Frank Gereon Gollan Richard J. Greatbatch Jens Grieger Vladimir M. Gryanik Micha Gryschka Judith Hauck Mario Hoppema Oliver Huhn Torsten Kanzow Boris P. Koch Gert König-Langlo Ulrike Langematz Gregor C. Leckebusch Christof Lüpkes Stephan Paul Annette Rinke Bjoern Rost Michiel Rutgers van der Loeff Michael Schröder Gunther Seckmeyer Torben Stichel Volker Strass Ralph Timmermann Scarlett Trimborn Uwe Ulbrich Celia Venchiarutti Ulrike Wacker Sascha Willmes Dieter Wolf-Gladrow 《Ocean Dynamics》2016,66(11):1379-1413
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S. Heinemann T. G. Sharp F. Seifert D. C. Rubie 《Physics and Chemistry of Minerals》1997,24(3):206-221
Garnets along the join Mg4Si4O12 (majorite end member) – Mg3Al2Si3O12 (pyrope) synthesized at 2000 °C, 19 GPa are, after quench, tetragonal in the compositional range up to 20 mol% pyrope, but
cubic at higher Al contents. Lattice constants a
tet and a
tet in the tetragonal compositional range converge with increasing pyrope contents towards the lattice constant of the cubic
garnets. The elastic strain and the intensity of the (222) reflection as a function of composition indicate a second-order
phase transition near 20 mol% pyrope. From the wedge-like shape of pseudomerohedral twins and their interaction near 90° twin-boundary
corners, as well as from the absence of growth-induced dislocations, it is concluded that the Al-poor garnets are also cubic
at synthesis conditions but invert by (Mg,Si) ordering on the octahedral sites into tetragonal phases of space group I41/a upon quench. This implies that the cubic-to-tetragonal phase transition in Mg4Si4O12 garnet occurs below 2000 °C at 19 GPa and at even lower temperatures in more aluminous compositions. A composition-dependent
Landau model is consistent with a direct transformation from Ia3d to I41/a. Comparison of the T-X stability field of majorite-pyrope garnets with the chemistry of majorite-rich garnets expected to occur in the Earth's transition
zone shows that the latter will be cubic under all conditions. Softening of elastic constants, which commonly accompanies
ferroelastic phase transitions, may affect the seismic velocities of garnets in the deeper transition zone where majorite
contents are highest.
Received July 5, 1996 / Revised, accepted September 24, 1996 相似文献
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North Sea near-surface wind climate and its relation to the large-scale circulation patterns 总被引:1,自引:0,他引:1
The North Sea 10-m wind speed (WS10) climate is compared and related to circulation patterns based on the sea level pressure (SLP) extracted from three reanalysis and one high-resolution model dataset. The mean magnitude and the trends of WS10 depend considerably on the selected reanalysis. The variability of WS10 among the three reanalysis datasets is highly correlated in the recent period (1980–2000) but less so in the past period (1960–1980). The WS10 over the North Sea is well represented by the relatively low reanalysis resolution when compared to the high-resolution WS10 model data partially owing to the high spatial correlation of WS10. Exceptions are observed only at the coastal areas. The dominant mode of WS10 explains coherent variability of WS10 over the North Sea and is related to a SLP pattern similar to the North Atlantic oscillation (NAO). The increase of the magnitude of the dominant WS10 pattern is related to the increase of the magnitude of the NAO-like SLP pattern from 1960s to mid-1990s. The second dominant WS10 pattern—a dipole in WS10 to the north and south of Great Britain—is related to the differences in SLP between Scandinavia and Iceland. The relation between the second WS10 and SLP patterns is more prominent in the recent period. The extreme WS10 in the German Bight is related to the low SLP over Scandinavia. The extreme WS10 is strongly increasing from the early 1980s to the beginning of 1990s, which is not observed in the corresponding SLP time series over Scandinavia. 相似文献
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Mn-activated cathodoluminescence can be used in several fields of carbonate petrography. It may, for instance, be possible to recognize
- cement sequences and their correlation (Tab. 1, Figs. 1, 2, 4; Tab. 2, Fig. 1)
- growth fabrics of skeletons (Tab. 2, Figs. 2, 3, 4; Tab. 3, Figs. 1, 2)
- dolomitisation processes and problems (Tab. 1, Figs. 1, 2; Tab. 4, Fig. 2)
- transformation paths from Mg-calcite to calcite and from aragonite to calcite (Tab. 2, Fig. 1; Tab. 3, Figs. 3, 4; Tab. 4, Fig. 1)
- growth structures in certain types of ooids (Tab. 1, Fig. 4; Tab. 3, Fig. 3; Tab. 4, Fig. 1)
- reworked skeletal particles (Tab. 3, Fig. 4)
- phantom grains and fossil-outlines in a micro- or macrocrystalline groundmass (Tab. 4, Figs. 2, 3)
- healed fissures crossing micro- or macrocrystalline carbonate rocks (Tab. 4, Fig. 4).