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1.
The major and minor element compositions of a suite of abyssal sea-floor ferromanganese nodules and associated sediments from the eastern central Pacific have been used to examine inter-element relationships and the mineralogy of the nodules, the relationship between the composition of nodules and their associated sediments and regional variations in composition with respect to likely modes of formation of such deposits. Apart from Mn and Fe, significant proportions of the total Ti, Ca, Mg, K, Ba, Sr, Th and Y and almost all the P, As, Ce, Co, Cu, Mo, Ni, Pb, Zn and Zr are present in the oxide fractions of the nodules. The Mg, Ba, Cu, Mo, Ni and Zn contents are significantly correlated with the Mn content, while Ti, P, As, Pb, Sr, Y and Zr are similarly correlated with the total Fe content.Nodules from the northeastern tropical Pacific have Mn/Fe ratios higher than those in the oxide fractions of their associated sediments, todorokite as the principal Mn phase and relatively high concentrations of minor elements associated with Mn. Nodules from the south central Pacific have Mn/Fe ratios similar to those in the oxide fractions of the associated sediments, δ-MnO2 as the only Mn-phase, and relatively high concentrations of minor elements associated with Fe. There appears to be a smooth gradation in composition in the tropical Pacific between these two end members.The regional compositional variation is interpreted as a reflection of different sources of metals for, and different growth mechanisms of, sea-floor nodules. The oxide precipitate from sea water consists of δ-MnO2, has a relatively low Mn/Fe ratio and minor element contents related to the total Fe and Mn(δ-MnO2) content. The oxide precipitate forming in areas of very low sedimentation as a result of diagenetic remobilisation in the surface sediment consists of todorokite, and has a high Mn/Fe ratio and enhanced metal content in the Mn-(todorokite)phase. Available information on the morphology and compositional variation of individual nodules from the tropical Pacific corroborates these contrasting metal sources and suggests that they can be resolved on the scale of an individual oxide concretion. 相似文献
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Tingting Yao Craig Calvert Tom Jones Glen Bishop Yuan Ma Lincoln Foreman 《Mathematical Geology》2006,38(1):51-62
Spectral simulation has gained application in building geologic models due to the advantage of better honoring the spatial continuity of petrophysical properties, such as reservoir porosity and shale volume. Distinct from sequential simulation methods, spectral simulation is a global algorithm in the sense that a global density spectrum is calculated once and the inverse Fourier transform is performed on the Fourier coefficient also only once to generate a simulation realization. The generated realizations honor the spatial continuity structure globally over the whole field instead of only within a search neighborhood, as with sequential simulation algorithms. However, the disadvantage of global spectral simulation is that it traditionally cannot account for the local information such as the local continuity trends, which are often observed in reservoirs and hence are important to be accounted for in geologic models. This disadvantage has limited wider application of spectral simulation in building geologic models. In this paper, we present ways of conditioning geologic models to the relevant local information. To account for the local continuity trends, we first scale different frequency components of the original model with local-amplitude spectrum ratios that are specific to the local trend. The sum of these scaled frequency components renders a new model that displays the desired local continuity trend. The implementation details of this new method are discussed and examples are provided to illustrate the algorithm. 相似文献
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L. Fedele D. D. Insinga A. T. Calvert V. Morra A. Perrotta C. Scarpati 《Bulletin of Volcanology》2011,73(9):1323-1336
The Campi Flegrei hosts numerous monogenetic vents inferred to be younger than the 15 ka Neapolitan Yellow Tuff. Sanidine
crystals from the three young Campi Flegrei vents of Fondi di Baia, Bacoli and Nisida were dated using 40Ar/39Ar geochronology. These vents, together with several other young edifices, occur roughly along the inner border of the Campi
Flegrei caldera, suggesting that the volcanic conduits are controlled by caldera-bounding faults. Plateau ages of ∼9.6 ka
(Fondi di Baia), ∼8.6 ka (Bacoli) and ∼3.9 ka (Nisida) indicate eruptive activity during intervals previously interpreted
as quiescent. A critical revision, involving calendar age correction of literature 14C data and available 40Ar/39Ar age data, is presented. A new reference chronostratigraphic framework for Holocene Phlegrean activity, which significantly
differs from the previously adopted ones, is proposed. This has important implications for understanding the Campi Flegrei
eruptive history and, ultimately, for the evaluation of related volcanic risk and hazard, for which the inferred history of
its recent activity is generally taken into account. 相似文献
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Age spectra from 40Ar/39Ar incremental heating experiments yield ages of 298 ± 25 ka and 310 ± 31 ka for transitional composition lavas from two cones
on submarine Mahukona Volcano, Hawaii. These ages are younger than the inferred end of the tholeiitic shield stage and indicate
that the volcano had entered the postshield alkalic stage before going extinct. Previously reported elevated helium isotopic
ratios of lavas from one of these cones were incorrectly interpreted to indicate eruption during a preshield alkalic stage.
Consequently, high helium isotopic ratios are a poor indicator of eruptive stage, as they occur in preshield, shield, and
postshield stage lavas. Loihi Seamount and Kilauea are the only known Hawaiian volcanoes where the volume of preshield alkalic
stage lavas can be estimated.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
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Anthony H. McDaniel Chris A. Cantrell James A. Davidson Richard E. Shetter Jack G. Calvert 《Journal of Atmospheric Chemistry》1991,12(3):211-227
The infrared absorption cross-sections for eight commonly used halogenated methanes and ethanes have been measured as a function of temperature from 203 to 293 K. High resolution spectra (0.03 cm-1) have been used to derive integrated band strengths and peak cross-sections associated with the spectral features in the infrared region from 600 to 1500 cm-2. The values obtained in this study are compared to those from previous reports, and recommendations are made for uses in atmospheric sensing and radiative energy transfer models. The observed temperature dependence in the spectral features is also discussed. 相似文献
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New constraints on the pyroclastic eruptive history of the Campanian volcanic Plain (Italy) 总被引:2,自引:0,他引:2
B. De Vivo G. Rolandi P. B. Gans A. Calvert W. A. Bohrson F. J. Spera H. E. Belkin 《Mineralogy and Petrology》2001,73(1-3):47-65
Summary The ∼ 150 km3 (DRE) trachytic Campanian Ignimbrite, which is situated north-west of Naples, Italy, is one of the largest eruptions in the
Mediterranean region in the last 200 ky. Despite centuries of investigation, the age and eruptive history of the Campanian
Ignimbrite is still debated, as is the chronology of other significant volcanic events of the Campanian Plain within the last
200–300 ky. New 40Ar/39Ar geochronology defines the age of the Campanian Ignimbrite at 39.28 ± 0.11 ka, about 2 ky older than the previous best estimate.
Based on the distribution of the Campanian Ignimbrite and associated uppermost proximal lithic and polyclastic breccias, we
suggest that the Campanian Ignimbrite magma was emitted from fissures activated along neotectonic Apennine faults rather than
from ring fractures defining a Campi Flegrei caldera. Significantly, new volcanological, geochronological, and geochemical
data distinguish previously unrecognized ignimbrite deposits in the Campanian Plain, accurately dated between 157 and 205 ka.
These ages, coupled with a xenocrystic sanidine component > 315 ka, extend the volcanic history of this region by over 200 ky.
Recent work also identifies a pyroclastic deposit, dated at 18.0 ka, outside of the topographic Campi Flegrei basin, expanding
the spatial distribution of post-Campanian Ignimbrite deposits. These new discoveries emphasize the importance of continued
investigation of the ages, distribution, volumes, and eruption dynamics of volcanic events associated with the Campanian Plain.
Such information is critical for accurate assessment of the volcanic hazards associated with potentially large-volume explosive
eruptions in close proximity to the densely populated Neapolitan region.
Received August 1, 2000; accepted November 2, 2000 相似文献
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Surface sediments from the South West Africa shelf and the Gulf of California have been analysed for iodine and organic carbon. The iodine contents range from 96 to 1990 ppm. While iodine and organic carbon show certain anomalies on the South West Africa shelf, the trend of the ratios is smooth and decreases from the shelf edge, an area of oxidising surface sediment, shorewards to reducing sediments, formed as a result of intense water upwelling. In the Gulf of California, a similar distribution of ratios with surface sediment type occurs; lowest values occur in the reduced sediments and highest in oxidised sediments. Values of the ratio of the oxidised sediments (~250) are more than an order of magnitude higher than in reduced sediments, and are similar to some other surface oxidised sediments.The high I content of oxidised sediments is mostly due to uptake of I on to plankton seston on the seabed. In reduced sediments, I contained in planktonic matter originating in surface waters forms the bulk of iodine in the sediment.With sediment burial, oxidised sediments lose most of the iodine through degradation of unspecified organic constituents. This does not happen to the same extent in reduced sediments. The geological implications of these reactions are briefly discussed. 相似文献