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881.
Magaia Luís André Koike Katsuaki Goto Tada-nori Masoud Alaa Ahmed 《Natural Resources Research》2019,28(3):1197-1215
Natural Resources Research - Unlike in coastal and sedimentary basins, regional-scale exploration of groundwater resources using only geophysical methods is costlier in consolidated rocks such as... 相似文献
882.
Zakia MOKRANE Mustapha BOUDJENAH Yasmina BELKACEM EL Hadi MORSLI Ahmed INAL Fahima BOUARAB 《资源与生态学报(英文版)》2019,10(4):432-440
The phytoplankton group’s composition is an excellent indicator of the state of coastal waters. The aim of this study is to explore spatial variability of phytoplankton in shallow coastal areas from different regions (East, Center and West) of the Algerian coast. The quantitative and qualitative study of the phytoplankton population was conducted on samples taken during the 2012-2013 period by the research vessel GRINE BELKACEM. The qualitative results show a significant diversity of diatoms and dinoflagellates, which rank first and second in the total flora (Fr > 50%). This finding is also confirmed quantitatively by the abundance values in both 2013 and 2012 samples which largely exceeds the average value in most other areas of the western region (56%) and slightly exceeding 52% in all central areas which represent an equi-distribution between diatoms and dinoflagellates. The Dinoflagellates contribute significantly to the quantitative richness in the eastern region (>60%). The minimum value of Dia/Dino index, recorded in the eastern region confirms the dominance of the dinoflagellates especially in Skikda (0.31) (Skikda).However, our results reveal the presence, in smaller proportion, of other groups such as the cocolithophoridae and euglenophyceae. 相似文献
883.
Feki-Sahnoun Wafa Njah Hasna Hamza Asma Barraj Nouha Mahfoudi Mabrouka Rebai Ahmed Bel Hassen Malika 《Ocean Dynamics》2020,70(7):897-911
Ocean Dynamics - The blooms of the toxic dinoflagellate Karenia selliformis can be predicted with accuracy derived from knowledge of the main forcing variables. A naive Bayes classifier modeling... 相似文献
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885.
VARIATIONS IN KAMILA AMPHIBOLITES FROM SOUTHEASTERN PART OF THE KOHISTAN ISLAND-ARC TERRANE,PAKISTAN
VARIATIONS IN KAMILA AMPHIBOLITES FROM SOUTHEASTERN PART OF THE KOHISTAN ISLAND-ARC TERRANE,PAKISTAN 相似文献
886.
Astronomy Letters - Globular clusters $$(GCs)$$ are among the oldest stellar systems in the early universe. We present galaxies formed with two different stellar populations, which depend on the... 相似文献
887.
888.
Chert nodules of the Drunka Formation (Lower Eocene) are mostly spherical, have diameters from 40 to 120 cm, are quasi-uniformly spaced 2–3 m apart in the plane of bedding, have concentric internal structure and, except for rare small (<6 cm) solid chert nodules, are less than 85% chertified. Nodules formed after moderate alteration of limestone by meteoric water (δ18Ocalcite = –4 to –8‰) at shallow (<100 m) burial depths; more extensive alteration of limestone (δ18O = –10 to –16‰) by meteoric water followed nodule growth. Chertification was by low-temperature meteoric water (δ18Oquartz = +18‰ in margins to +22‰ in nuclei) at shallow burial depths. Meteoric water may have invaded the Drunka Formation in association with shelf progradation during the Early Eocene, or during the development of a Middle Eocene unconformity. Replacement of carbonate mud by microcrystalline quartz was the dominant chertification process, but fossils were replaced in part by fine-grained equant megaquartz, quartzine and chalcedony; the last of these occurs in places as beekite. Opal A-secreting marine organisms are the inferred source of silica, but none are preserved. There is no compelling evidence of an opal-CT precursor, so quartz may have formed by direct precipitation. Self-organization processes of enigmatic character established the spacing pattern of the nodules and also the Liesegang-banded internal structure of the chert nodules. Nodules grew chiefly by diffusive supply of silica, although one locality has elongate nodules that grew when there was some porewater advection. Chertification patterns and δ18O values of both calcite and quartz indicate that nodule growth was complex and variable. Some nodules probably grew from the centre outwards. Many nodules, however, initially grew simultaneously across the entire nodule, but late-stage growth was predominantly at the outer margins or at selective internal sites. 相似文献
889.
The analysis of Stoneley wave propagation in a fracture is essential for the identification and evaluation of fracture parameters from the borehole Stoneley wave. Also, it is important for many geophysics considerations, e.g. for tremor and long-period events observed in volcanoes and geothermal areas. In this paper, we investigate the guided waves propagation in a fluid layer lying between two viscoelastic vertically transversely isotropic media. The viscoelastic mechanism models the attenuation due to the presence of fluid saturation in the rock. A model based on the superposition of three inhomogeneous partial plane waves: one in the fluid and two heterogeneous waves in the solid is developed. The dispersion equation is obtained for this case. A numerical solution is carried out to obtain the guided wave velocity and attenuation coefficient. The results of this investigation show that there is a strong correlation between the velocity dispersion and attenuation of Stoneley wave and the anisotropic parameters of the medium especially in a sandstone (fast) medium. 相似文献
890.