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31.
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
32.
Macarena Bravo Mª de los ngeles Gallardo Guillermo Luna-Jorquera Paloma Núez Nelson Vsquez Martin Thiel 《Marine pollution bulletin》2009,58(11):1718-1726
Anthropogenic marine debris (AMD) is an ubiquitous problem, which has motivated public participation in activities such as beach surveys and clean-up campaigns. While it is known that beaches in the SE Pacific are also affected by this problem, the quantities and types of AMD remain largely unknown. In the context of an outreach project, volunteers (1500 high-school students) participated in a nation-wide survey of AMD on 43 beaches distributed randomly along the entire Chilean coast (18°S to 53°S). The mean density of AMD was 1.8 items m−2 and the major types were plastics, cigarette butts and glass. Densities in central Chile were lower than in northern and southern Chile, which could be due to different attitudes of beach users or to intense beach cleaning in central regions. We suggest that public participation in surveys and cleaning activities will raise awareness and thereby contribute to an improvement of the situation. 相似文献
33.
Costa Rica is located geographically in the southern part of the Central American Volcanic Front, a zone where interaction between the Mesoamerican and South American cultures occurred in pre-Columbian times. Several volcanoes violently erupted during the Holocene, when the first nomadic human hunters and later settlers were present. Volcanic rocks were the most important geo-resource in making artifacts and as construction materials for pre-Columbian inhabitants. Some pottery products are believed to resemble smoking volcanoes, and the settlements around volcanoes would seem to indicate their influence on daily life. Undoubtedly, volcanic eruptions disrupted the life of early settlers, particularly in the vicinity of Arenal and Irazú volcanoes, where archaeological remains show transient effects and displacement caused by periodical eruptions, but later resilient occupations around the volcanoes. Most native languages are extinct, with the exception of those presently spoken in areas far away from active volcanoes, where no words are related to volcanic phenomena or structures. The preserved legends are ambiguous, suggesting that they were either produced during the early Spanish conquest or were altered following the pre-Columbian period. 相似文献
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35.
The Babcock solar dynamo model and known interactions of the interplanetary magnetic field with the earth's magnetosphere are used to explain the relations found between geomagnetic indices at solar minimum and the sunspot number at the following solar maximum. We augment the work of Kane (1987) by updating his method of analysis, including recent smoothed aa and AP indices. We predict a smoothed maximum sunspot number of 163±40 to peak in October 1990±9 months for solar cycle 22. This value is close to the Schatten and Sofia (1987) predicted value of 170±25, using more direct solar indicators.Now at Dept. of Astronomy, Univ. of Washington 相似文献
36.
The Mexican coast can be regionalized according to the main economic activities performed in it; for the purpose of this work we are considering five regions: North Pacific, Mar de Cortes, outh Pacific, Gulf of Mexico, and Caribbean. According to the national census, the population of the coastal zone in Mexico is increasing at a higher rate than the national average. The main industries located in the coastal and marine zones are oil and gas, fisheries, aquaculture, tourism, maritime transportation and ports, chemical industries, and minerals. Mexico has developed an environmental legal framework based on the Ley General del Equilibrio Ecologico y la Proteccion al Ambiente (LGEEPA), and the coastal management paradigm is strengthened through several other legal tools developed specifically for this purpose. There are three management strategies identified in this work for the coastal zone in Mexico: (1) Agency Leadership, (2) Protected Areas, and (3) Land Ordinance. Each one of these strategies includes stages for eventually developing an Integrated Coastal Zone Management (ICZM) plan that considers vertical and horizontal integration, scientific research of natural resources and ecosystems, and socioeconomic issues. 相似文献
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38.
Commercial whaling is highly contentious, angering animal rights groups and conservation organizations, who threaten boycotts. Proponents of whaling argue that many whale stocks are plentiful enough to support sustainable harvests. In terms of economic efficiency, a nation's decision to engage in whaling depends on rents from the whaling industry, ecological and market linkages, and the potential for boycotts. We analyze the tradeoffs involved in a nation's decision to engage in whaling, whale-watching, and fishing. Scenarios exist in which whaling is economically rational. Indeed, sometimes it makes economic sense to subsidize whaling. In other circumstances, market pressures make commercial whaling inefficient. 相似文献
39.
Guillermo Gonzalez Chris Laws 《Monthly notices of the Royal Astronomical Society》2007,378(3):1141-1152
We present the results of detailed spectroscopic abundance analyses for 18 elements in 31 nearby stars with planets (SWPs). The resulting abundances are combined with other similar studies of nearby SWPs and compared to a sample of nearby stars without detected planets. We find some evidence for abundance differences between these two samples for Al, Si and Ti. Some of our results are in conflict with a recent study of SWPs in the SPOCS data base. We encourage continued study of the abundance patterns of SWPs to resolve these discrepancies. 相似文献
40.
Rodolfo H. Barbá Jesús Maíz Apellániz Enrique Pérez Mónica Rubio Alberto Bolatto Cecilia Fariña Guillermo Bosch Nolan R. Walborn 《Astrophysics and Space Science》2009,324(2-4):309-313
We present the first high-spatial-resolution near-infrared (NIR) imaging of NGC604, obtained with the NICMOS camera onboard the Hubble Space Telescope (HST). These NICMOS broad-band images reveal new NIR point sources, clusters, and diffuse structures. We find an excellent spatial correlation between the 8.4 GHz radio continuum and the 2.2 μm nebular emission. Moreover, massive young stellar object candidates appear aligned with these radio peaks, reinforcing the idea that those areas are star-forming regions. Three different scaled OB associations are recognized in the NICMOS images. The brightest NIR sources in our images have properties that suggest that they are red supergiant stars, of which one was previously known. This preliminary analysis of the NICMOS images shows the complexity of the stellar content of the NGC604 nebula. 相似文献