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41.
Óscar Pueyo Anchuela Javier Ramajo Cordero Andrés Gil Imaz Guillermo Meléndez Hevia 《International Journal of Earth Sciences》2013,102(4):1131-1149
A combined sedimentological, shape-preferred orientation and anisotropy of magnetic susceptibility (AMS) analysis has been performed at the Arroyofrío Bed (Callovian–Oxfordian boundary level) in the locality of Moneva (Iberian Range, NE Spain). The Arroyofrío bed is a widespread iron-ooid limestone interval forming a condensed sequence. The present study has focused on the analysis of the potential presence of a preferred ooid orientation at the Arroyofrío bed. The obtained data show that ooids were originally ellipsoidal and had an imbricate disposition with respect to the bedding/lamination surface. The main ooid orientation within the bedding plane shows a NNE–SSW trend. Results of AMS analyses show a magnetic foliation parallel or slightly imbricated with respect to bedding and magnetic lineation parallel to the main ooid orientation. Magnetic mineralogy of studied samples shows that AMS is mainly controlled by magnetite with minor contributions of hematite and paramagnetic minerals (that can reach contributions of 35 %). The analyzed ooids show axial ratios between 1.4 and 2.8 (intrinsic anisotropy), while the anisotropy of their distribution shows lower anisotropies (e.g., Rs = 1.15) or very low values of the anisotropic magnetic parameters (e.g., P′ < 1.01). Sedimentary texture, matrix features, bioturbation and fossil content influenced both ooid main orientation and the magnetic fabric. Magnetic lineation and main orientation of long ooid axes are transverse to the inferred coastline in the studied area and parallel to the expected paleocurrent direction with respect to the Ejulve-Maestrazgo paleogeographic high. The direct correlation between AMS magnetic lineation and the ooid analysis permits to demonstrate that the paleocurrent imprint can be recorded by means of AMS despite the highly ferromagnetic context fabric and at coarse deposits. Obtained results support the interest and reliability of AMS to unravel paleocurrent imprints for paleogeographic reconstructions. 相似文献
42.
Juan Porta Jorge Parapar Paula García Gracia Fernández Juan Touriño Ramón Doallo Francisco Ónega Inés Santé Pablo Díaz David Miranda Rafael Crecente 《Earth Science Informatics》2013,6(4):209-226
Land abandonment and stagnation of rural markets in the last few years have become one of the main concerns of rural administrations. The use of Web and GIS (Geographic Information System) technologies can help to mitigate the effects of these problems. This paper pro-poses a novel Web-GIS tool with spatial capabilities for the dynamization of rural land markets by encouraging the transfer of land from owners to farmers through the leasing of plots. The system, based on open source software, offers information about the properties, their environment and their owners. It uses standards for handling the geographic information and for communicating with external data sources. This system was used as the basis for the development of SITEGAL, the tool for the management of the Land Bank of Galicia (www.bantegal.com/sitegal). SITEGAL has been operational since 2007 obtaining benefits for both administration and users (farmers and land owners), and promoting the e-Government. 相似文献
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44.
The influence of penetration electric fields (PEF) on storm-time energetic particles in the inner magnetosphere and on the stability of plasma in the low-latitude ionosphere is widely recognized. We describe two consequences of PEFs, regularly observed during magnetic storms that indicate their persistence throughout the main phases. These are (1) the presence of equatorial plasma bubbles (EPB) across the evening local time sector during main phases and their absence throughout recovery, and (2) detections of low-energy ion precipitation in the dawn sector equatorward of the auroral electron boundary. 相似文献
45.
R. Sigbjörnsson J. Th. Snæbjörnsson S. M. Higgins B. Halldórsson S. Ólafsson 《Bulletin of Earthquake Engineering》2009,7(1):113-126
This preliminary study aims to investigate a M
w
6.3 earthquake that occurred in South Iceland on Thursday 29 May 2008 at 15:45 UTC. The epicentre was in the Olfus District
between the towns of Selfoss and Hveragerdi. This study examines the data recorded and the damage observed immediately after
the event. Horizontal accelerations of up to 80%g were recorded in the epicentral region and there is visual evidence that
the vertical acceleration exceeded 1 g. The PGA data is compared to a ground motion estimation model developed for the South
Iceland earthquakes in June 2000. In general the basic properties of this event are found to be similar to the characteristics
of the South Iceland earthquakes in June 2000. The duration of strong-motion is short and the intensity attenuates rapidly
with increasing distance. The earthquake action resisted by buildings in the near fault area is inspected through evaluation
of elastic as well as inelastic response spectra. The vast majority of structures seemed to withstand the strong-motion fairly
competently and without significant visual damage due firstly to the low-rise, predominantly reinforced concrete or timber,
style of buildings. Secondly, the short duration of strong-motion contributed to the endurance of structures. 相似文献
46.
47.
Yu. N. Pariiskii N. S. Soboleva A. I. Kopylov O. V. Verkhodanov A. V. Temirova O. P. Zhelenkova J. Winn A. Fletcher B. Burke 《Astronomy Letters》2000,26(7):423-427
Based on data from the MIT-GB-VLA 4850-MHz survey, we investigate the radio structure of RC J1148+0455 with a steep radio spectrum (α=?1.04) from the COLD catalog. The radio source consists of two components, each having a complex structure. We analyze an optical identification of the source by using 6-m telescope images. The centroid of the radio source falls on a group of eight galaxies at a 24 m level in R. 相似文献
48.
L. D. Ashwal R. A. Armstrong R. J. Roberts M. D. Schmitz F. Corfu C. J. Hetherington K. Burke M. Gerber 《Contributions to Mineralogy and Petrology》2007,153(4):389-403
Nepheline-bearing gneisses from the 75 km2 Tambani body in the Mozambique Belt of southern Malawi, are miaskitic biotite-nepheline monzodiorites, reflecting an absence
of K-feldspar, alkali amphiboles or pyroxenes, and contain euhedral zircon megacrysts up to 5 cm across. The zircons contain
U = 1–1,860 ppm, Th = 0–2,170 ppm and Y = 400–1,100 ppm, and very low concentrations of all other measured trace elements
except Hf (HfO2 = 0.53–0.92 wt. %). Cathodoluminescence images reveal oscillatory sector growth zoning and no evidence for xenocrystic cores,
indicating that the zircons represent primary magmatic crystallization products that have survived amphibolite grade metamorphism.
U-Pb isotopic analyses (by TIMS) yield an upper intercept age of 730 ± 4 Ma (MSWD = 1.7), which we interpret as the time of
magmatic crystallization of the zircons. This is coincident with 11 SHRIMP spot analyses, which yield a mean age of 729 ±
7 Ma (MSWD = 0.37). Metamorphism, at 522 ± 17 Ma as suggested by monazite, caused partial Pb-loss during local recrystallization
of zircon. Lu-Hf isotopic data for three whole-rock samples of nepheline-bearing gneiss are collinear with those for zircon
megacrysts, and correspond to an age of 584 ± 17 Ma (MSWD = 0.37. We interpret the Lu-Hf array to represent a mixing line
defined by the Hf isotopic signature of primary zircon and that of the rock-forming minerals reset during metamorphic (re-)crystallization;
hence the 584 Ma age is likely geologically meaningless. Given the well-defined association of nepheline syenites (and phonolitic
volcanic equivalents) with continental rifting, we suggest that the Tambani body represents a magmatic product formed at 730 Ma
during the break-up of the Rodinia supercontinent. The 522 Ma age is akin to other Pan-African metamorphic ages that record
collisional suturing events during the final assembly of Gondwana. Zircon-bearing nepheline gneisses thus preserve a record
of intra-continental rifting and of continental collision in southern Malawi. 相似文献
49.
A multi‐proxy study of Holocene environmental change recorded in alluvial deposits along the southern coast of the Pampa region,Argentina
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