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111.
The Eocene La Meseta Formation is the youngest exposed unit of the back-arc James Ross Basin, Antarctic Peninsula, cropping out in Seymour (Marambio) Island. The formation comprises 720 m of clastic sedimentary rocks of deltaic, estuarine and shallow marine origin. It was subdivided into six unconformity-based units (Valle de Las Focas, Acantilados, Campamento, Cucullaea I, Cucullaea II and Submeseta Allomembers) grouped into three main facies associations. Facies association I represents valley-confined deposition in a progradational/aggradational tide-dominated and wave-influenced delta front/delta plain environment. Facies association II includes tidal channels, mixed tidal flats, tidal inlets and deltas, washover and beach environments. Facies association III represents nonconfined tide- and storm-influenced nearshore environments. La Meseta Formation sandstones are quartzofeldspathic with some hybrid arenites (glauconite and carbonate bioclasts-rich). Sandstone detrital modes are subdivided into two distinctive petrofacies: the low quartz petrofacies (petrofacies I, Q<55% and L>12%), interpreted to retain the original provenance signal, and the high quartz petrofacies (petrofacies II, Q>55% and L<12%), representing the reworking product of the former after selective elimination of the more labile components. Petrofacies I sandstone framework grains were mainly derived from a dissected magmatic arc and an associated metamorphic belt. Textural evidence for recycling of some grains (e.g. garnet) from older sedimentary units during valley incision is not conclusive. Changes in the relative participation of source areas during the evolution of the incised-valley system are evaluated from the relative proportions of lithic fragments and monomineralic clasts derived from each rock type. Two lithic assemblages were recognized. The mixed lithic assemblage (Rv/Rm+Rp<1.4) shows participation of all rock types; it represented valley-confined environments, either during the initial stage of valley development, or after main episodes of incision. The volcanic lithic assemblage (Rv/Rm+Rp>1.4) is clearly dominated by volcanic-derived clasts; it developed at times of high sea level and/or during later stages of the valley fill, when an “energy fence” at the shoreline prevented delivery of sediment from the Antarctic Peninsula, thus enhancing the relative participation of local volcanic sources. 相似文献
112.
Roberto Oyarzun Alvaro Márquez Javier Lillo Ivan López Sergio Rivera 《Mineralium Deposita》2002,37(8):795-799
113.
RC structures cyclic behavior simulation with a model integrating plasticity,damage, and bond‐slip
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Bashar Alfarah Juan Murcia‐Delso Francisco López‐Almansa Sergio Oller 《地震工程与结构动力学》2018,47(2):460-478
The behavior of reinforced concrete structures under severe demands, as strong ground motions, is highly complex; this is mainly due to the complexity of concrete behavior and to the strong interaction between concrete and steel, with several coupled failure modes. On the other hand, given the increasing awareness and concern on the worldwide seismic risk, new developments have arisen in earthquake engineering; nonetheless, some developments are mainly based on simple analytical tools that are widely used, given their moderate computational cost. This research aims to provide a solid basis for validation and calibration of such developments by using computationally efficient continuum mechanics‐based tools. Within this context, this paper presents a model for 3D simulation of cyclic behavior of RC structures. The model integrates a bond‐slip model developed by one of the authors and the damage variable evolution methodology for concrete damage plastic model developed by some authors. In the integrated model, a new technique is derived for efficient 3D analysis of bond‐slip of 2 or more crossing reinforcing bars in beam‐column joints, slabs, footings, pile caps, and other similar members. The analysis is performed by implementing the bond‐slip model in a user element subroutine of Abaqus and the damage variable evolution methodology in the original concrete damage plastic model in the package. Two laboratory experiments consisting of a column and a frame subjected to cyclic displacements up to failure are simulated with the proposed formulation. 相似文献
114.
Deville Diego Sanchez Gustavo Barahona Sergio Yamashiro Carmen Oré-Chávez Daniel Bazán Roger Quiroz Umino Tetsuya 《Ocean Science Journal》2020,55(1):33-48
Ocean Science Journal - We evaluated the influence of areas with dissimilar upwelling intensity along the Humboldt Current System on the morphological variation of the economically important sea... 相似文献
115.
116.
Louise K. Harra Nancy U. Crooker Cristina H. Mandrini Lidia van Driel-Gesztelyi Sergio Dasso Jingxiu Wang Heather Elliott Gemma Attrill Bernard V. Jackson Mario M. Bisi 《Solar physics》2007,244(1-2):95-114
We describe the interplanetary coronal mass ejections (ICMEs) that occurred as a result of a series of solar flares and eruptions
from 4 to 8 November 2004. Two ICMEs/magnetic clouds occurring from these events had opposite magnetic orientations. This
was despite the fact that the major flares related to these events occurred within the same active region that maintained
the same magnetic configuration. The solar events include a wide array of activities: flares, trans-equatorial coronal loop
disappearance and reformation, trans-equatorial filament eruption, and coronal hole interaction. The first major ICME/magnetic
cloud was predominantly related to the active region 10696 eruption. The second major ICME/magnetic cloud was found to be
consistent with the magnetic orientation of an erupting trans-equatorial filament or else a rotation of 160° of a flux rope
in the active region. We discuss these possibilities and emphasize the importance of understanding the magnetic evolution
of the solar source region before we can begin to predict geoeffective events with any accuracy. 相似文献
117.
118.
This paper analyses the role played by the North Atlantic Oscillation (NAO) in the creation of drought conditions in a semi-arid
region of north-east Spain (the middle Ebro valley), from 1600 to the year 2000. The study used documents from ecclesiastical
archives for the seventeenth, eighteenth and nineteenth centuries. For the twentieth century, instrumental precipitation records
were used as well. A December–August drought index from 1600 to 1900 was compiled from the historical documentary sources
(rogation ceremonies). The index was validated by means of precipitation records between 1858 and 1900 and independent precipitation
data from 1600 reconstructed by means of dendrochronological records. Using instrumental data a drought index was also calculated
(Standardized Precipitation Index, SPI) for the 1958–2000 period. We found that the NAO was important in explaining the droughts
identified in the study area from documents and instrumental data. Positive values of the winter NAO index are prone to cause
droughts in the middle Ebro valley. This finding has been verified since 1600 by means of two independent reconstructions
of the winter NAO index. The same behaviour has been observed during the nineteenth and twentieth centuries by means of instrumental
records. The climatic and geographic factors that explain the high influence of North Atlantic Oscillation on droughts in
this region are discussed in depth. 相似文献
119.
Giant versus small porphyry copper deposits of Cenozoic age in northern Chile: adakitic versus normal calc-alkaline magmatism 总被引:63,自引:0,他引:63
Roberto Oyarzun Alvaro Márquez Javier Lillo Ivan López Sergio Rivera 《Mineralium Deposita》2001,36(8):794-798
Cenozoic magmatic activity in northern Chile led to the formation of two contrasting porphyry copper belts: (1) a Paleocene-Early Eocene belt comprising small porphyry copper deposits (e.g., Lomas Bayas) of normal calc-alkaline affinity; and (2) a Late Eocene-Early Oligocene belt hosting huge porphyry copper deposits (e.g., Chuquicamata) of adakitic affinity. Although the first belt comprises both volcanic and plutonic rocks (andesitic-basaltic and rhyolitic lavas and tuffs, and associated sub-volcanic porphyries and felsic stocks), the latter only includes intrusions (mostly granodioritic types, including porphyry copper deposits). We suggest that the Late Eocene-Early Oligocene belt formed when fast and oblique convergence between the South America and Farallon plates led to flat subduction and direct melting of the subducting plate, hence giving rise to plutonic rocks of adakitic affinity. The absence of volcanism, under prevailing compressional conditions, prevented the escape of SO2 from the adakitic, sulfur-rich, highly oxidized magmas ("closed porphyry system"), which allowed formation of huge mineral deposits. On the contrary, coeval volcanic activity during formation of the Paleocene-Early Eocene calc-alkaline porphyries allowed development of "open systems", hence to outgassing, and therefore, to small mineral deposits. 相似文献
120.
José F. Gómez Joaquín Trapero Sergio Pascual Nimesh Patel Carmen Morales José M. Torrelles 《Monthly notices of the Royal Astronomical Society》2000,314(4):743-746
We present NH3 (1,1) and (2,2) observations of MBM 12, the closest known molecular cloud (65-pc distance), aimed at finding evidence for on-going star formation processes. No local temperature (with a T rot upper limit of 12 K) or linewidth enhancement is found, which suggests that the area of the cloud that we have mapped (15-arcmin size) is not currently forming stars. Therefore this nearby 'starless' molecular gas region is an ideal laboratory to study the physical conditions preceding new star formation.
A radio continuum source has been found in Very Large Array archive data, close to but outside the NH3 emission. This source is likely to be a background object. 相似文献
A radio continuum source has been found in Very Large Array archive data, close to but outside the NH