K-feldspar rich shales from Jurassic bedded cherts in southeastern Slovenia     

Simona Skobe  Špela Goričan  Dragomir Skaberne  Tomaž Verbič  Miha Mišič  Nina Zupančič 《Swiss Journal of Geoscience》2013,106(3):491-504

The study area in southeastern Slovenia is part of the transitional zone between the internal and the external Dinarides. Within Jurassic bedded cherts there are up to 2 cm thick shale intercalations, consisting of laminated, soft, fine-grained, green to brown material whose origin has been in question. In the majority of Tethyan cherts, the interbedded material is reported to be volcanogenic and/or terrigenous, although a detailed mineralogical analysis of the material is lacking. An XRD analysis confirmed the presence of quartz, illite, chlorite and K-feldspar, which is the prevailing component in some samples. Major and trace element data exclude both a volcanogenic and an hydrothermal origin. Several discrimination diagrams indicate the upper crustal terrigenous nature of shales and a biogenic silica source. The source material was probably from a Variscan crust, which at the time of deposition had already been weathered to kaolinite, and some sporadic muscovite. The MnO/Al₂O₃ ratio suggests a slow sedimentation rate of cherts and a faster one for shales, which probably settled from distal turbidity currents. The negative Ce anomaly indicates prolonged contact with ocean water. Sediments were deposited on a Tethyan passive margin, originally as silica-rich carbonate beds intercalated with mud. During late diagenesis, the mixing of marine and meteoric waters caused the further silicification of limestone and simultaneous potassium enrichment of shale which led to their alteration into illite or chlorite and, in sediments already rich in K-minerals, into K-feldspar.  相似文献   

Redox-active phases and radionuclide equilibrium valence state in subsurface environments – New insights from 6th EC FP IP FUNMIG     

C. Bruggeman  N. Maes  B.C. Christiansen  S.L.S. Stipp  E. Breynaert  A. Maes  S. Regenspurg  M.E. Malström  X. Liu  B. Grambow  Th. Schäfer 《Applied Geochemistry》2012

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Formation and significance of laurionite in geothermal brine     

Simona Regenspurg  Dejene Legesse Driba  Carolin Zorn 《Environmental Earth Sciences》2016,75(10):865

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A search for large meteoroids in the Perseid stream     

Martin BEECH  Simona NIKOLOVA 《Meteoritics & planetary science》1999,34(6):849-852

Abstract— We report on two surveys conducted during the times of Perseid shower maximum in 1997 and 1998. The first survey entailed the video monitoring of the Moon's disk with the intent of recording the optical flashes that should result when large meteoroids strike the lunar surface. The second survey consisted of a combination video camera and very low frequency (VLF) radiowave receiver system capable of detecting electrophonic meteors during their ablation in the Earth's atmosphere. Using standard ablation theory, we find that for a Perseid meteoroid to be capable of generating electrophonic sounds, it must have an initial mass in excess of 495 kg. We also find, as a result of the surveys, an upper limit of 2 × 10^?17 m^?2 s^?1 to the flux of electrophonic Perseid meteors entering the Earth's atmosphere. Although our study indicates that large, meter-sized meteoroids must, at best, be sparsely distributed within the Perseid stream, we briefly discuss some tantalizing lines of evidence, found from within the astronomical literature, that hint at their true existence.  相似文献   

A systematic analysis of the XMM-Newton background: III. Impact of the magnetospheric environment     

Simona Ghizzardi  Martino Marelli  David Salvetti  Fabio Gastaldello  Silvano Molendi  Andrea De Luca  Alberto Moretti  Mariachiara Rossetti  Andrea Tiengo 《Experimental Astronomy》2017,44(3):273-285

A detailed characterization of the particle induced background is fundamental for many of the scientific objectives of the Athena X-ray telescope, thus an adequate knowledge of the background that will be encountered by Athena is desirable. Current X-ray telescopes have shown that the intensity of the particle induced background can be highly variable. Different regions of the magnetosphere can have very different environmental conditions, which can, in principle, differently affect the particle induced background detected by the instruments. We present results concerning the influence of the magnetospheric environment on the background detected by EPIC instrument onboard XMM-Newton through the estimate of the variation of the in-Field-of-View background excess along the XMM-Newton orbit. An important contribution to the XMM background, which may affect the Athena background as well, comes from soft proton flares. Along with the flaring component a low-intensity component is also present. We find that both show modest variations in the different magnetozones and that the soft proton component shows a strong trend with the distance from Earth.  相似文献   

Petrographic evidence of the past occurrence of gas hydrates in the Tertiary Piedmont Basin (NW Italy)     

Luca Martire  Marcello Natalicchio  Catalin Costel Petrea  Simona Cavagna  Pierangelo Clari  Francesco Dela Pierre 《Geo-Marine Letters》2010,30(3-4):461-476

Methane-derived rocks in Monferrato and the Tertiary Piedmont Basin (NW Italy) consist of seep carbonates, formed by gas seepage at the seafloor, and macroconcretions resulting from the cementation of buried sediments crossed by gas-rich fluids. These rocks are characterized by both negative δ¹³C values and a marked enrichment in δ¹⁸O. Petrographic features not commonly described and that point to enigmatic depositional and diagenetic conditions have been observed in both types of rocks: inhomogeneous distribution of cements within cavities; dolomite crystals floating within cavity-filling calcite spar; non-gravitational fabrics of internal sediments plastering cavity walls; open framework within microbial crusts. These features suggest the former presence of gas hydrates in sediments. During their dissociation, new space was formed and filled with authigenic carbonates or injected sediments. Analogous mechanisms of clathrate freeze-and-thaw processes have been inferred for the genesis of zebra and stromatactis structures and particular kinds of carbonate breccias. The term melt-seal structure is proposed for this kind of diagenetic structure. The fabrics of gas hydrates and the geochemical conditions of sediments, in turn depending on the relative rates of supply of methane-rich fluids and normal seawater, conditioned the final aspect of the rocks.  相似文献