Pockmarks on either side of the Strait of Gibraltar: formation from overpressured shallow contourite gas reservoirs and internal wave action during the last glacial sea-level lowstand?     

Ricardo León  Luis Somoza  Teresa Medialdea  Francisco Javier González  Carmen Julia Gimenez-Moreno  Raúl Pérez-López 《Geo-Marine Letters》2014,34(2-3):131-151

Integrating novel and published swath bathymetry (3,980 km²), as well as chirp and high-resolution 2D seismic reflection profiles (2,190 km), this study presents the mapping of 436 pockmarks at water depths varying widely between 370 and 1,020 m on either side of the Strait of Gibraltar. On the Atlantic side in the south-eastern Gulf of Cádiz near the Camarinal Sill, 198 newly discovered pockmarks occur in three well localized and separated fields: on the upper slope (n=14), in the main channel of the Mediterranean outflow water (MOW, n=160), and on the huge contourite levee of the MOW main channel (n=24) near the well-known TASYO field. These pockmarks vary in diameter from 60 to 919 m, and are sub-circular to irregularly elongated or lobate in shape. Their slope angles on average range from 3° to 25°. On the Mediterranean side of the strait on the Ceuta Drift of the western Alborán Basin, where pockmarks were already known to occur, 238 pockmarks were identified and grouped into three interconnected fields, i.e. a northern (n=34), a central (n=61) and a southern field (n=143). In the latter two fields the pockmarks are mainly sub-circular, ranging from 130 to 400 m in diameter with slope angles averaging 1.5° to 15°. In the northern sector, by contrast, they are elongated up to 1,430 m, probably reflecting MOW activity. Based on seismo-stratigraphic interpretation, it is inferred that most pockmarks formed during and shortly after the last glacial sea-level lowstand, as they are related to the final erosional discontinuity sealed by Holocene transgressive deposits. Combining these findings with other existing knowledge, it is proposed that pockmark formation on either side of the Strait of Gibraltar resulted from gas and/or sediment pore-water venting from overpressured shallow gas reservoirs entrapped in coarse-grained contourites of levee deposits and Pleistocene palaeochannel infillings. Venting was either triggered or promoted by hydraulic pumping associated with topographically forced internal waves. This mechanism is analogous to the long-known effect of tidal pumping on the dynamics of unit pockmarks observed along the Norwegian continental margin.  相似文献   

Scales and causes of heterogeneity in bars in a large multi‐channel river: Río Paraná, Argentina     

Arnold J. H. Reesink  Philip J. Ashworth  Gregory H. Sambrook Smith  James L. Best  Daniel R. Parsons  Mario L. Amsler  Richard J. Hardy  Stuart N. Lane  Andrew P. Nicholas  Oscar Orfeo  Steven D. Sandbach  Christopher J. Simpson  Ricardo N. Szupiany 《Sedimentology》2014,61(4):1055-1085

To date, published studies of alluvial bar architecture in large rivers have been restricted mostly to case studies of individual bars and single locations. Relatively little is known about how the depositional processes and sedimentary architecture of kilometre‐scale bars vary within a multi‐kilometre reach or over several hundreds of kilometres downstream. This study presents Ground Penetrating Radar and core data from 11, kilometre‐scale bars from the Río Paraná, Argentina. The investigated bars are located between 30 km upstream and 540 km downstream of the Río Paraná – Río Paraguay confluence, where a significant volume of fine‐grained suspended sediment is introduced into the network. Bar‐scale cross‐stratified sets, with lengths and widths up to 600 m and thicknesses up to 12 m, enable the distinction of large river deposits from stacked deposits of smaller rivers, but are only present in half the surface area of the bars. Up to 90% of bar‐scale sets are found on top of finer‐grained ripple‐laminated bar‐trough deposits. Bar‐scale sets make up as much as 58% of the volume of the deposits in small, incipient mid‐channel bars, but this proportion decreases significantly with increasing age and size of the bars. Contrary to what might be expected, a significant proportion of the sedimentary structures found in the Río Paraná is similar in scale to those found in much smaller rivers. In other words, large river deposits are not always characterized by big structures that allow a simple interpretation of river scale. However, the large scale of the depositional units in big rivers causes small‐scale structures, such as ripple sets, to be grouped into thicker cosets, which indicate river scale even when no obvious large‐scale sets are present. The results also show that the composition of bars differs between the studied reaches upstream and downstream of the confluence with the Río Paraguay. Relative to other controls on downstream fining, the tributary input of fine‐grained suspended material from the Río Paraguay causes a marked change in the composition of the bar deposits. Compared to the upstream reaches, the sedimentary architecture of the downstream reaches in the top ca 5 m of mid‐channel bars shows: (i) an increase in the abundance and thickness (up to metre‐scale) of laterally extensive (hundreds of metres) fine‐grained layers; (ii) an increase in the percentage of deposits comprised of ripple sets (to >40% in the upper bar deposits); and (iii) an increase in bar‐trough deposits and a corresponding decrease in bar‐scale cross‐strata (<10%). The thalweg deposits of the Río Paraná are composed of dune sets, even directly downstream from the Río Paraguay where the upper channel deposits are dominantly fine‐grained. Thus, the change in sedimentary facies due to a tributary point‐source of fine‐grained sediment is primarily expressed in the composition of the upper bar deposits.  相似文献   

In situ U/Pb dating of impact‐produced zircons from the Vargeão Dome (Southern Brazil)     

Anne Nédélec  Jean‐Louis Paquette  Elder Yokoyama  Ricardo I. F. Trindade  Thierry Aigouy  David Baratoux 《Meteoritics & planetary science》2013,48(3):420-431

The Vargeão impact structure was formed in the Serra Geral basaltic and rhyodacitic to rhyolitic lava flows of southern Brazil, that belong to the Paraná‐Etendeka large igneous province. The Chapecó‐type rhyodacites contain small baddeleyite crystals recently dated at 134.3 (±0.8) Ma, which is regarded as the age of this acid volcanism coeval to the flood basalt eruption. Inside the impact structure, a brecciated rhyodacitic sample displays fine veinlets containing numerous lithic fragments in a former melt. This impact breccia contains newly formed zircons, either in the veins or at the contact between a vein and the volcanic matrix. The zircons are 10–50 μm in length, clear and nearly unzoned. In situ laser‐ablation dating of the zircons provides a concordant Early Aptian age of 123.0 ± 1.4 Ma that is regarded as the age of the impact event. As in situ age determination ensures the best possible selection of the analyzed mineral grains, the methodology employed in this study also represents a promising method for dating other impact structures.  相似文献   

A Very Small Array search for the extended Sunyaev–Zel''dovich effect in the Corona Borealis supercluster     

Ricardo Génova-Santos  José Alberto Rubiño-Martín  Rafael Rebolo †  Kieran Cleary ‡  Rod D. Davies  Richard J. Davis  Clive Dickinson §  Nelson Falcón ‡‡  Keith Grainge  Carlos M. Gutiérrez  Michael P. Hobson  Michael E. Jones ¶  Rüdiger Kneissl &#;  Katy Lancaster  Carmen P. Padilla-Torres  Richard D. E. Saunders  Paul F. Scott  Angela C. Taylor ¶  Robert A. Watson †† 《Monthly notices of the Royal Astronomical Society》2005,363(1):79-92

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Identification of Possible Intense Historical Solar Storms During the Years 1781–1788 Inferred from Aurorae and Geomagnetic Observations in Rio De Janeiro     

José M. Vaquero  Ricardo M. Trigo 《Solar physics》2006,235(1-2):419-432

The reconstruction of solar activity during the late 18th century is a puzzle for researchers due to the scarcity of sunspot observations in that epoch. In this work, we analyse some details of the solar activity during the years 1781–1788, inferred from geomagnetic measurements and visual observations of aurorae performed by the Portuguese scientist Bento Sanches Dorta from Rio de Janeiro. We describe in greater detail four large solar storms that induced large changes in daily values of geomagnetic declination and, simultaneously, correspond to visual observations of aurorae described by Sanches Dorta.  相似文献   

Instruments, Detectors and the Future of Astronomy with Large Ground Based Telescopes     

Douglas A. Simons  Paola Amico  Dietrich Baade  Sam Barden  Randall Campbell  Gert Finger  Kirk Gilmore  Roland Gredel  Paul Hickson  Steve Howell  Norbert Hubin  Andreas Kaufer  Ralf Kohley  Philip MacQueen  Sergej Markelov  Mike Merrill  Satoshi Miyazaki  Hidehiko Nakaya  Darragh O'Donoghue  Tino Oliva  Andrea Richichi  Derrick Salmon  Ricardo Schmidt  Hongjun Su  Simon Tulloch  Maria Luisa García Vargas  R. Mark Wagner  Olivier Wiecha  Binxun Ye 《Experimental Astronomy》2005,19(1-3):15-44

Results of a survey of instrumentation and detector systems, either currently deployed or planned for use at telescopes larger than 3.5 m, in ground based observatories world-wide, are presented. This survey revealed a number of instrumentation design trends at optical, near, and mid-infrared wavelengths. Some of the most prominent trends include the development of vastly larger optical detector systems (> 10⁹ pixels) than anything built to date, and the frequent use of mosaics of near-infrared detectors – something that was quite rare only a decade ago in astronomy. Some future science applications for detectors are then explored, in an attempt to build a bridge between current detectors and what will be needed to support the research ambitions of astronomers in the future.  相似文献   

A three-dimensional model of moist convection for the giant planets II: Saturn's water and ammonia moist convective storms     

Ricardo Hueso  Agustín Sánchez-Lavega 《Icarus》2004,172(1):255-271

Moist convective storms constitute a key aspect in the global energy budget of the atmospheres of the giant planets. Among them, Saturn is known to develop the largest scale convective storms in the Solar System, the Great White Spots (GWS) which occur rarely and have been detected once every 30 years approximately. On the average, Saturn seems to show much less convective storms than Jupiter with smaller size and reduced frequency and intensity. Here we present detailed simulations of the onset and development of storms at the Equator and mid-latitudes of Saturn. These are the regions where most of the recent convective activity of the planet has been observed. We use a 3D anelastic model with parameterized microphysics (Hueso and Sánchez-Lavega, 2001, Icarus 151, 257) studying the onset and evolution of water and ammonia moist convective storms up to sizes of a few hundred km. Water storms, while more difficult to initiate than in Jupiter, can be very energetic, arriving to the 150 mbar level and developing vertical velocities on the order of 150 m s⁻¹. Ammonia storms develop easier but with a much smaller intensity unless very large abundances of ammonia (10 times solar) are present in Saturn's atmosphere. The Coriolis forces play a major role in the morphology and properties of water based storms.  相似文献   

A late Neoproterozoic paleomagnetic pole for the Congo craton: Tectonic setting, paleomagnetism and geochronology of the Nola dike swarm (Central African Republic)     

Gatan R. Moloto-A-Kenguemba  Ricardo I.F. Trindade  Patrick Moni  Anne Ndlec  Roberto Siqueira 《Precambrian Research》2008,164(3-4):214-226

New structural, geochronological and paleomagnetic data were obtained on dolerite dikes of the Nola region (Central African Republic) at the northern border of the Congo craton. In this region, metavolcanic successions were thrust southward onto the craton during the Panafrican orogenic events. Our structural data reveal at least two structural klippes south of the present-day limits of the Panafrican nappe suggesting that it has once covered the whole Nola region, promoting the pervasive hydrothermal greenschist metamorphism observed in the underlying cratonic basement and also in the intrusive dolerite dikes. Paleomagnetic measurements revealed a stable dual-polarity low-inclination magnetization component in nine dikes (47 samples), carried by pyrrhotite and magnetite. This component corresponds to a paleopole at 304.8°E and 61.8°S (dp = 5.4, dm = 10.7) graded at Q = 6. Both metamorphism and magnetic resetting were dated by the ⁴⁰Ar/³⁹Ar method on amphibole grains separated from the dikes at 571 ± 6 Ma. The Nola pole is the first well-dated paleomagnetic pole for the Congo craton between 580 and 550 Ma. It marks a sudden change in direction of the Congo craton apparent polar wander path at the waning stages of the Panafrican orogenic events.  相似文献   

Another Year of Record Heat for the Oceans     

Lijing CHENG  John ABRAHAM  Kevin E.TRENBERTH  John FASULLO  Tim BOYER  Michael E.MANN  Jiang ZHU  Fan WANG  Ricardo LOCARNINI  Yuanlong LI  Bin ZHANG  Fujiang YU  Liying WAN  Xingrong CHEN  Licheng Feng  Xiangzhou SONG  Yulong LIU  Franco RESEGHETTI  Simona SIMONCELLI  Viktor GOURETSKI  Gengxin CHEN  Alexey MISHONOV  Jim REAGAN  Guancheng LI 《大气科学进展》2023,40(6):963-974

Changes in ocean heat content(OHC), salinity, and stratification provide critical indicators for changes in Earth’s energy and water cycles. These cycles have been profoundly altered due to the emission of greenhouse gasses and other anthropogenic substances by human activities, driving pervasive changes in Earth’s climate system. In 2022, the world’s oceans, as given by OHC, were again the hottest in the historical record and exceeded the previous 2021 record maximum.According to IAP/CAS data, ...  相似文献   

The Westerly Index as complementary indicator of the North Atlantic oscillation in explaining drought variability across Europe   总被引：1，自引：0，他引：1  

Sergio M. Vicente-Serrano  Ricardo García-Herrera  David Barriopedro  Cesar Azorin-Molina  Juan I. López-Moreno  Natalia Martín-Hernández  Miquel Tomás-Burguera  Luis Gimeno  Raquel Nieto 《Climate Dynamics》2016,47(3-4):845-863

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