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华南地区栖霞组“菊花石”假象与海泡石矿成因关系探讨

根据对华南地区二叠系栖霞组内菊花石假象的成因研究,结合对该组内燧石结核,菊花石内正延性玉髓和海泡石形成时代关系的现状关系的观察,认为华南地区栖霞组内的海泡石形成于早期成岩作用过程中,与该组内燧石结核和菊花石假象内的正延性玉髓同期形成,其成因既与高盐度的沉积环境或高盐度的成岩环境条件无关,也与热液活动无关。     

Methodological Problems of Studying the Underwater Relief in the River Delta from Space Images (on the Example of Mapping the Shallows of the Yenisei River Delta)

Water Resources - Based on images from the Sentinel-2 satellite taken in 2017–2019, a map of shallows in the Yenisei delta was compiled. This paper highlighted the methodological problems...     

Development peculiarities of the magmatism synchronous to the formation of the North Atlantic passive margins

Magmatism synchronous to the formation of passive margins of the North Atlantic is discussed. The main features and causes of the geochemical enrichment of the primary magmas at the margins have been established. This paper is based on the published data on the Norwegian-Greenland tectonotype of volcanic margins and the West Iberia-Newfoundland tectonotype of nonvolcanic margins. In the first tectonotype the hot rifting and active magmatism gave rise to the formation of a thick crust at the margin and the adjacent oceanic zone. The second tectonotype is characterized by cold amagmatic rifting and slow initial spreading, which led to the widespread occurrence of ancient continental complexes and serpentinized mantle rocks at the margin, as well as the thin and disturbed oceanic crust nearby. In order to characterize the magmatism and initial oceanic opening, the geological and geochemical data pertaining to the reference sections chosen for each margin were compared in detail. In particular, the geochemical and isotopic data on the flood basalts and suites of parallel dikes related to the pre- and synbreakup magmatic phases were involved for the Norwegian-Greenland region. The predominance of tholeiites enriched in lithophile elements and radiogenic isotopes, as well as a significant contribution of continental material to them, are typical of the volcanic margins. No less than two enriched magma sources for the lower part of the volcanic complex are suggested, whereas a depleted or slightly enriched source is established for the upper part. A more enriched source as compared with the volcanic margins of the Norwegian-Greenland region is suggested for the low-volume magmatic manifestations at the nonvolcanic Iberian margin. The tectonic settings of margins development and their relationships with the effect of deep plumes and the propagation of the extension zone toward the cold Atlantic lithosphere are discussed.     

Long-term variability of active galactic nuclei from the ”Planck” catalog

A complete sample of 104 bright active galactic nuclei (AGNs) from the “Planck” catalog (early results) were observed at 36.8 GHz with the 22-m radio telescope of the Crimean Astrophysical Observatory (CrAO).Variability indices of the sources at this frequency were determined based on data from theWMAP space observatory, theMetsa¨ hovi RadioObservatory (Finland), and the CrimeanAstrophysical Observatory. New observational results confirm that the variability of these AGNs is stronger in the millimeter than at other radio wavelengths. The variability indices probably change as a result of the systematic decrease in the AGN flux densities in the transition to the infrared. Some radio sources demonstrate significant flux-density variations, including decreases, which sometimes cause them to fall out of the analysed sample. The change of the variability index in the millimeter is consistent with the suggestion that this variability is due to intrinsic processes in binary supermassive black holes at an evolutionary stage close to coalescence. All 104 of the sources studied are well known objects that are included in various radio catalogs and have flux densities exceeding 1 Jy at 36.8 GHz.     

A revision of lunar reference points

A selection of 50 points on the lunar surface, considered as appropriate for high accuracy selenodetic measures, is presented.     

Chemical composition of stars in the galactic halo

The chemical compositions of the atmospheres of six metal-poor stars are analyzed. Spectra with signal-to-noise ratios of no less than 100 and a resolution of R≈17 000 were obtained using the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. The abundances of Li, O, α-process elements (Mg, Si, Ca, Ti), Na, K, Sc, iron-peak elements (Cr, Mn, Fe, Ni, Cu, Zn), and s-process elements (Y, Ba) are derived. The star G251-54 ([Fe/H]=?1.55, T _eff=5541 K, logg=3.58) is deficient in some elements compared to both stars with similar metallicities and the Sun. The atmosphere of G251-54 has the following elemental abundances relative to iron: [O/Fe]=+0.47, [α/Fe]≈?0.3, [Na/Fe]=?0.60, [Sc/Fe]=?0.57, [Cr, Ni, Fe]≈0, [Zn/Fe]=+0.16, [Cu/Fe]=?0.66, [Y/Fe]=?0.70, and [Ba/Fe]=?1.35. The remaining five stars have metallicities in the range ?1.6<[Fe/H]相似文献   

Groundwater mixing in a sand-island freshwater lens: density-dependent flow and stratigraphic controls

This paper focuses on a small back-barrier sand-island on the southeast coast of Queensland. The freshwater lens in the study area exhibits anomalously high short-range salinity gradients at shallow depths, which cannot be explained using a standard seawater intrusion model. The island groundwater system consists of two aquifers: a semiconfined aquifer hosting saline to hypersaline groundwater and an overlying unconfined freshwater aquifer. The deeper aquifer is semiconfined within an incised paleovalley, and groundwater flow is restricted to an east – west direction. Tidal response observations show that the tidal signal propagates far more rapidly and is of much higher magnitude in the semiconfined aquifer than the unconfined aquifer. The tidal wave-pulse amplitude is also subject to greater attenuation in the unconfined aquifer. A conceptual hydrogeological model illustrates how upwelling of hypersaline groundwater, induced by density-dependent flow and tidal pumping, has contaminated the shallow groundwater resource. Salinisation at shallow depths is restricted to an area proximal to the paleovalley aquifer. The spatial distribution of lithological heterogeneity is an initial limiting control on the movement of the upwelling saline plume. The extent of shallow groundwater contamination is also limited by the presence of a baroclinic field, resulting from lateral variations in fluid density. Hydrochemical signatures have been used to support the model hypothesis and link the salinisation of fresh groundwater with the semiconfined aquifer as opposed to the surrounding estuarine surface water. The geometry and thickness of the freshwater lens are further controlled by the presence of the largely impermeable bedrock paleosurface between 9 and 12 m depth. The combination of hypersaline groundwater and hydraulically restrictive lithology at shallow depths has produced excessive thinning of the freshwater lens, demonstrating that the application of a model such as the Dupuit – Ghyben – Herzberg relationship would grossly overestimate the available groundwater resource.