Detrital zircon U–Pb provenance and palaeogeography of Triassic rift basins in the Marrakech High Atlas          下载免费PDF全文

Mireia Domènech  Daniel F. Stockli  Antonio Teixell 《地学学报》2018,30(4):310-318

The Marrakech High Atlas contains some of the best exposures of the Triassic early‐rift strata related to Atlantic opening in NW Africa. We present the first detrital zircon U–Pb data of five Triassic redbed samples from the Tizi n'Test basin to quantify sediment provenance, transport and dispersal patterns during early rifting. These U–Pb ages document dominant sediment sourcing from the south, the Anti‐Atlas domain, with very limited to absent input from the Variscan Meseta domain to the north. This combined with stratigraphic and thermochronologic information points to a highly asymmetric palaeogeography during Triassic rifting. Furthermore, the occurrence of Archaean detrital zircon grains in Triassic sandstone, likely recycled from the Reguibat shield, suggests the presence of a fully developed regional drainage system with rivers and catchments reaching hundreds of kilometres into the hinterland of the rift flank.  相似文献   

On the devil's tracks: unexpected news from the Foresta ichnosite (Roccamonfina volcano,central Italy)     

Adolfo Panarello  Maria Rita Palombo  Italo Biddittu  Mauro Antonio Di Vito  Gennaro Farinaro  Paolo Mietto 《第四纪科学杂志》2020,35(3):444-456

The Foresta ichnosite is well known for preserving some of the oldest human fossil footprints recorded in Europe so far. This research aims to: i) describe new footprints that are larger than those already reported, some of which form a new trackway that moves in the opposite direction to all the others; ii) announce the discovery of some stone tools also in the surroundings of the Foresta ichnosite. The new results increase the total number of human fossil footprints to at least 81, specify the direction and the number of footprints of Trackway C, and identify three new directions of walking at the site. More compelling and complete estimates of the dimensional range of all ichnological evidence enables us, furthermore, to estimate the number of trackmakers walking on the trampled surface as a minimum of five, one of them likely being an adult male. The general shape of all the recorded footprints suggests that the Foresta trackmakers share some similarities with those at Sima de los Huesos, and belong to the same taxonomical group as the Ceprano skull. All the new evidence enables us to better understand the presence of hominin populations in the Roccamonfina volcano area during the Middle Pleistocene. © 2020 John Wiley & Sons, Ltd.  相似文献   

Isotopic composition of precipitation during strong El Niño–Southern Oscillation events in the Southeast Region of Brazil     

Vinícius dos Santos  Marcelo Dias de Oliveira  Jan Boll  Ricardo Snchez‐Murillo  Amauri Antonio Menegrio  Luiz Felippe Gozzo  Didier Gastmans 《水文研究》2019,33(4):647-660

Equatorial Pacific sea surface temperature variations interact with processes of atmospheric circulation, creating conditions for the occurrence of El Niño–Southern Oscillation (ENSO). ENSO events represent the most important interannual phenomena affecting climate patterns worldwide and causing significant socio‐economic impacts. In the Brazilian territory, ENSO leads to an increase in drought episodes in the north‐eastern region and an increase in precipitation in the southern region, whereas the effects over the south‐east region are yet not well understood. The main goal of this study is to compare variations of isotopic composition in precipitation across the south‐east portion of the Brazilian territory during two very strong ENSO events: 1997–1998 (ENSO 1) and 2014–2016 (ENSO 2). Daily isotopic records, available from the Global Network of Isotopes in Precipitation database for ENSO 1, and samples collected during ENSO 2 were used to compare the influence of both events on the isotopic composition of precipitation. Seasonal variations indicated more depleted precipitation during the wet seasons (δ¹⁸O = ?5.4 ± 4.0‰) and enriched precipitation during the dry seasons (δ¹⁸O = ?2.8 ± 2.3‰). Observed rainfall variations were associated with atmospheric large‐scale processes and moisture transport from the Amazon region, whereas extreme values (enriched or depleted) appear to be associated with particular convective and stratiform precipitation events. Overall, more depleted isotopic composition of precipitation (δ¹⁸O = ?4.60‰) and higher d‐excess (up to +15‰) were observed during the dry season of ENSO 1 when compared with ENSO 2 dry season (δ¹⁸O‰ = ?2.80‰, d‐excess lower than +14‰). The latter is explained by greater atmospheric moisture content, particularly associated with recycling of transpiration fluxes from the Amazon region, during dry season of ENSO 1. No significant differences for δ¹⁸O and δ²H were observed during the wet season; however, d‐excess from ENSO 2 was greater than ENSO 1, due to the slightly greater atmospheric moisture content and very strong upward motion observed. Our findings highlight the opportunity that environmental isotopes offer towards understanding hydrometeorological processes, particularly, the evolution of extreme climatic events of global resonance such as ENSO.  相似文献   

Non-expanding universe: a cosmological system of units     

Antonio Alfonso-Faus 《Astrophysics and Space Science》2010,326(2):159-162

The product of two empirical constants, the dimensionless fine-structure constant (α) and the von Klitzing constant (R _k, an electrical resistance), turns out to be an exact dimensionless number. Then the accuracy and cosmological time variation (if any) of these two constants can be tied together. Also this product defines a natural unit of the electrical resistance, the inverse of a quantum of conductance. When the speed of light c is taken away from α, as has been shown elsewhere, the constancy of α implies the constancy of the ratio e ²/h (the inverse of the von Klitzing constant), e being the charge of the electron and h the Planck constant. This forces the charge of the electron e to be constant as long as the action h (an angular momentum) is a true constant too. From the constancy of the Rydberg constant the Compton wavelength, h/mc, is then a true constant and consequently there is no expansion at the quantum mechanical level. The momentum mc is also a true constant and then general relativity predicts that the universe is not expanding, as shown elsewhere. The time variation of the speed of light explains the observed Hubble red shift. And there is a mass-boom effect. From this a coherent cosmological system of constant units can be defined.  相似文献   

Formation of the extreme Kuiper-belt binary 2001 QW<Subscript>322</Subscript> through adiabatic switching of orbital elements     

Antonio Gamboa Suárez  Daniel Hestroffer  David Farrelly 《Celestial Mechanics and Dynamical Astronomy》2010,106(3):245-259

Binaries in the Kuiper-belt are unlike all other known binaries in the Solar System. Both their physical and orbital properties are highly unusual and, because these objects are thought to be relics dating back to the earliest days of the Solar System, understanding how they formed may provide valuable insight into the conditions which then prevailed. A number of different mechanisms for the formation of Kuiper-belt binaries (KBBs) have been proposed including; two-body collisions inside the Hill sphere of a larger body; strong dynamical friction; exchange reactions; and chaos assisted capture. So far, no clear consensus has emerged as to which of these mechanisms (if any) can best explain the observed population of KBBs. Indeed, the recent characterization of the mutual orbit of the symmetric (i.e., roughly equal mass) KBB 2001 QW₃₂₂ has only served to complicate the picture because its orbit does not seem readily explicable by any of the available models. The binary 2001 QW₃₂₂ stands out even among the already unusual population of KBBs for the following reasons: its mutual orbit is extremely large (≈10⁵ km or about 30% of the Hill sphere radius), retrograde, it is inclined ≈120^° from the ecliptic and has very low eccentricity, i.e., e ≤ 0.4 (and possibly e ≤ 0.05). Here we propose a hybrid formation mechanism for this object which combines aspects of several of the mechanisms already proposed. Initially two objects are temporarily trapped in a long-living chaotic orbit that lies close to a retrograde periodic orbit in the three-dimensional Hill problem. This is followed by capture through gravitational scattering with a small intruder object. Finally, weak dynamical friction gradually switches the original orbit “adiabatically” into a large, almost circular, retrograde orbit similar to that actually observed.  相似文献   

Gravitational waves from compact objects     

José Antonio de Freitas Pacheco 《中国天文和天体物理学报》2010,10(11)

Large ground-based laser beam interferometers are presently in operation both in the USA(LIGO) and in Europe(VIRGO) and potential sources that might be detected by these instruments are revisited.The present generation of detectors does not have a sensitivity high enough to probe a significant volume of the universe and,consequently,predicted event rates are very low.The planned advanced generation of interferometers will probably be able to detect,for the first time,a gravitational signal.Advanced LIGO and...  相似文献   

The integration of PESETA sectoral economic impacts into the GEM-E3 Europe model: methodology and results     

Juan-Carlos Ciscar  László Szabó  Denise van Regemorter  Antonio Soria 《Climatic change》2012,112(1):127-142

The PESETA project has estimated the physical effects of climate change in Europe for the following impact categories with a market valuation: agriculture, river floods, coastal systems and tourism. Four alternative scenarios of future climate change have been considered. The computable general equilibrium (CGE) GEM-E3 model for Europe has been used to integrate the PESETA damages under a consistent economic framework. The approach followed has been to assess the effects of future climate (as of 2080s) on today’s economy. This article details the way each sectoral impact has been integrated into the CGE model. The EU welfare loss is estimated to be in a range of 0.2% to 1%, depending on the climate future and the projected sea level rise. Results show that the Southern Europe region appears as the most vulnerable area to climate change. Impacts in coastal systems, agriculture and river floods determine the overall and regional pattern of impacts within Europe.  相似文献   

Holocene environmental change in southern Spain deduced from the isotopic record of a high-elevation wetland in Sierra Nevada     

Antonio García-Alix  Gonzalo Jiménez-Moreno  R. Scott Anderson  Francisco J. Jiménez Espejo  Antonio Delgado Huertas 《Journal of Paleolimnology》2012,48(3):471-484

Small lakes and wetlands from high elevation within the Sierra Nevada Range (southern Spain) preserve a complete post-glacial Holocene record. Isotopic, TOC and C/N analyses, carried out on a sediment core, show various stages in the evolution of the Borreguiles de la Virgen, which today constitute a small bog at about 2,950?m above sea level. Glacial erosion generated a cirque depression, which became a small lake during the first phase of infilling (from?8,200 to 5,100?cal?yr BP), as suggested by sedimentary evidence, including an atomic C/N ratio generally below 20, low TOC values and the highest ??¹³C and ??¹⁵N values of the record. These results imply significant algal productivity, which is confirmed by the microscopic algal remains. Drier conditions became established progressively in this area from?5,100 to 3,700?cal?yr BP. Subsequently, the lake evolved into a bog as shown by geochemical evidence (C/N ratios above 20, high TOC content and low ??¹³C values). Unstable conditions prevailed from?3,600 to 700?cal?yr BP; an extremely low sedimentation rate and scarcity of data from this period do not allow us to make a coherent interpretation. Fluctuating conditions were recorded during the last?~700?cal?yr BP, with wetter conditions prevailing during the first part of the interval (with C/N rate below 20) up to 350?years ago. In general, a gradual trend toward more arid conditions occurred since?~6,900?cal?yr BP, with a further increase in aridity since?~5,100?cal?yr BP. This evidence is consistent with other contemporaneous peri-Mediterranean records.  相似文献   

Novel narrow filters for imaging in the 50–150 nm VUV range     

Mónica Fernández-Perea  Manuela Vidal-Dasilva  Juan Ignacio Larruquert  José Antonio Méndez  José Antonio Aznárez 《Astrophysics and Space Science》2009,320(1-3):243-246

GOLD (Grupo de Óptica de Láminas Delgadas) is devoted to the development of novel coatings with challenging performance in the far and the extreme ultraviolet (FUV-EUV, 50–200 nm). One of the main goals of this research is to provide the communities of astronomy, solar physics and atmospheric physics with coatings with high reflectance or transmittance at a target wavelength or band, and high rejection of the out-of-band at this complicated spectral range. Above the transparency cutoff of MgF₂ (115 nm), transmittance filters based on Al/MgF₂ multilayers have been developed peaked at wavelengths as short as 124 nm, with a peak transmittance of 27% and a FWHM of 12 nm for a non-aged coating. Below 115 nm, a research on reflectance filters has recently started with very promising results on filters peaked at the 83.4 nm OII spectral line. Fresh filters with 27% peak reflectance at normal incidence and a FWHM of 14 nm have been obtained. Furthermore, the peak reflectance wavelength of these filters can be tuned by rotation. A filter peaked at 83 nm at normal incidence will shift to ～73 nm at 30 deg from the normal and to ～58 nm at 45 deg. These novel reflective filters based on Al, Yb and SiO must still demonstrate stability over time.  相似文献   

Kolmogorov and Nekhoroshev theory for the problem of three bodies     

Antonio Giorgilli  Ugo Locatelli  Marco Sansottera 《Celestial Mechanics and Dynamical Astronomy》2009,104(1-2):159-173

We investigate the long time stability in Nekhoroshev’s sense for the Sun– Jupiter–Saturn problem in the framework of the problem of three bodies. Using computer algebra in order to perform huge perturbation expansions we show that the stability for a time comparable with the age of the universe is actually reached, but with some strong truncations on the perturbation expansion of the Hamiltonian at some stage. An improvement of such results is currently under investigation.  相似文献