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991.
Moshood Niyi Tijani Matthew Essien Nton Ryuji Kitagawa 《Comptes Rendus Geoscience》2010,342(2):136-150
This study presents the mineralogical, textural and geochemical characteristics of the regional Maastrichtian Ajali Sandstone in Anambra Basin, SE Nigeria. The intent is to highlight possible constraints on the chemical weathering conditions of the source materials on one hand, and to infer the provenance on the other hand. The investigation approach involved field studies and collection of samples from 12 different outcrop locations, followed by laboratory studies involving grain-size analysis (GSA), major and trace elements analyses using the X-ray fluorescence (XRF) method as well as thin section petrography. Field studies show that the sandstones are friable at all locations and range in color from white in freshly cut stone, to reddish brown on weathering. In addition, the sandstone units are cross-bedded and show graded bedding exemplified by fining upward sequence. Textural examination indicates that the sandstones range from fine to medium sands, constituting about 76 to 99% sand fraction, with graphic mean grain size of 0.23 to 0.53 mm. Standard deviation (sorting) ranges from 0.56 to 1.24 Ø and implies moderately well sorted sediments. Inferred from the textural indices, the depo-environmental discrimination of the Ajali Sandstone revealed a fluvial/river system-dominated sedimentary process. The sandstones are quartz arenite with quartz greater than 90% and less than 5% K-feldspar which indicate a predominant basement source as also revealed by the heavy mineral assemblages. In addition, major elemental oxides shows SiO2 content greater than 96% for the fresh Ajali Sandstone samples with extreme depletion of mobile oxides such as Na2O, CaO and the ferromagnesian minerals through weathering and sedimentary processes. Provenance and tectonic setting discrimination using geochemical data and compositional maturity revealed typical felsic igneous-dominated cratonic environment while inter-elemental ratios (such as Zr/Cr, Y/Ni, Th/Sc, La/Sc and La/Co) and ternary plots (e.g. Th–Sc–Zr; La-Th–Sc and Th-Co-Zr) reflect passive continental margin setting for the Ajali Sandstone. Consequently, the source area is constrained to the Precambrian basement rock units of Adamawa-Oban massif areas to the east of the Anambra Basin and the adjacent Abakaliki Anticlinorium. 相似文献
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Martin C. Smith Gregory R. Ruchti Amina Helmi Rosemary F. G. Wyse J. P. Fulbright K. C. Freeman J. F. Navarro G. M. Seabroke M. Steinmetz M. Williams O. Bienaymé J. Binney J. Bland-Hawthorn W. Dehnen B. K. Gibson G. Gilmore E. K. Grebel U. Munari Q. A. Parker R.-D. Scholz A. Siebert F. G. Watson T. Zwitter 《Monthly notices of the Royal Astronomical Society》2007,379(2):755-772
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999.
X. Hernandez Changbom Park B. Cervantes-Sodi Yun-Young Choi 《Monthly notices of the Royal Astronomical Society》2007,375(1):163-170
Using simple dimensional arguments for both spiral and elliptical galaxies, we present formulae to derive an estimate of the halo spin parameter λ for any real galaxy, in terms of common observational parameters. This allows a rough estimate of λ, which we apply to a large volume-limited sample of galaxies taken from the Sloan Digital Sky Survey data base. The large numbers involved (11 597) allow the derivation of reliable λ distributions, as signal adds up significantly in spite of the errors in the inferences for particular galaxies. We find that if the observed distribution of λ is modelled with a lognormal function, as often done for this distribution in dark matter haloes that appear in cosmological simulations, we obtain parameters λ0 = 0.04 ± 0.005 and σλ = 0.51 ± 0.05 , interestingly consistent with values derived from simulations. For spirals, we find a good correlation between empirical values of λ and visually assigned Hubble types, highlighting the potential of this physical parameter as an objective classification tool. 相似文献
1000.
Geochemical Characteristics of a Veinlet Kupferschiefer Profile from the Lubin Mine, Southwestern Poland 总被引:3,自引:0,他引:3
Previous studies have shown that the ascending, oxidizing brines play a very important role in Kupferschiefer mineralization. Fractures could be the pathway of the brines. In order to clarify the influences of the brines on bulk organic matter, aromatic hydrocarbons and Kupferschiefer mineralization, one veinlet Kupferschiefer profile from the Lubin mine, southwestern Poland was studied with the microscopic, geochemical and Rock-Eval methods. The microscopic results indicate that organic matter of the veinlet sample consists dominantly of bitumen. Its extract content is higher than in other samples. The dominant aromatic compounds are naphthalene and alkylated naphthalenes (Na-PAH), which have migrated into the veinlet sample from other sediments. The content of phenanthrene and its methylated derivatives (Ph-PAH) is much lower than in other samples. The reason may be due to their heavier mass than Na-PAH. It is more difficult for Ph-PAH to migrate. The Na-PAH was probably removed from the shale by dist 相似文献