A Model of Fluxes of Solar Extreme Ultraviolet Irradiance     

Nusinov  A. A.  Kazachevskaya  T. V.  Katyushina  V. V. 《Geomagnetism and Aeronomy》2019,59(3):265-271

Geomagnetism and Aeronomy - We develop an approach to create a model of the solar extreme ultraviolet spectrum in the wavelength range responsible for dissociation of molecular oxygen...  相似文献   

Are carbonate barrier islands mobile? Insights from a mid to late-Holocene system,Al Ruwais,northern Qatar     

John Rivers  Max Engel  Robert Dalrymple  Ruqaiya Yousif  Christian J. Strohmenger  Ismail Al-Shaikh 《Sedimentology》2020,67(1):534-558

Barrier islands are important landforms in many coastal systems around the globe. Studies of modern barrier island systems are mostly limited to those of siliciclastic realms, where the islands are recognized as mobile features that form on transgressive coastlines and migrate landward as sea-level rises. Barrier islands of the ‘Great Pearl Bank’ along the United Arab Emirates coast are the best-known carbonate examples. These Holocene islands, however, are interpreted to be anchored by older deposits and immobile. The mid-Holocene to late-Holocene depositional system at Al Ruwais, northern Qatar, provides an example of a mobile carbonate barrier island system, perhaps more similar to siliciclastic equivalents. Sedimentological and petrographic analyses, as well as ¹⁴C-dating of shells and biogenic remains from vibracored sediments and surface deposits, show that after 7000 years ago a barrier system with a narrow back-barrier lagoon formed along what is now an exposed coastal zone, while, contemporaneously, a laterally-extensive coral reef was forming immediately offshore. After 1400 years ago the barrier system was forced to step ca 3 km seaward in response to a sea-level fall of less than 2 m, where it re-established itself directly on the mid-Holocene reef. Since that time, the barrier has retreated landward as much as 1000 m to its current position, exposing previously-deposited back-barrier lagoonal sediment at the open-coast shoreline. In modern neritic warm-water carbonate settings mobile barrier island systems are rare. Their construction and migration may be inhibited by reef formation, early cementation, and the relative inefficiency of sourcing beach sediments from open carbonate shelves. Carbonate barrier island systems likely formed more commonly during geological periods when ramps and unrimmed shelves predominated and in calcite seas, when meteoric cementation was minimized as a result of initial calcitic allochem mineralogy. As with their siliciclastic analogues, however, recognition of the influence of these transient landforms in the rock record is challenging.  相似文献   

A shift in eruption mode of Hekla volcano,Iceland, 3000 years ago: two-coloured Hekla tephra series,characteristics, dispersal and age     

GUDRÚN LARSEN  Bryndís G. Róbertsdóttir  Bergrún A. Óladóttir  JÓN EIRÍKSSON 《第四纪科学杂志》2020,35(1-2):143-154

Hekla volcano is a major producer of large, widespread silicic tephras. About 3000 years ago, the dominant eruption mode shifted from infrequent large (>1 km³) to more frequent moderate (<1 km³) eruptions. In the following two millennia ≥20 explosive silicic-to-intermediate eruptions occurred, and six or more basaltic. Three categories can be identified with dacite/andesite to basaltic andesite in the oldest eruptions through basaltic andesite to basalt in the youngest eruptions. Ten tephra layers of the first category have distinct field characteristics: a pale lower unit and a dark upper unit (two coloured or TC-layers). Colour separation is sharp indicating a stratified magma chamber origin. The lower unit is dominantly andesitic (61–63% SiO₂), while the upper unit is basaltic andesite (53–57% SiO₂). Volumes of the eight largest TC-layers range from 0.2 to 0.7 km³ as freshly fallen. Radiocarbon and soil accumulation rate dates constrain the TC-layers to between 3000 and 2200 years ago. Two of these (~2890 and ~2920 b2k) are likely to occur overseas. Low SiO₂ in the last erupted tephra of the TC-layers is comparable to that of historical Hekla lavas, implying a final effusive phase. The Hekla edifice may, consequently, be younger than 3000 years.  相似文献   

Current Levels of Artificial Radioisotopes in Biota from the Arctic Continental Shelf (2013–2018)     

Matishov  G. G.  Ilyin  V. G.  Usyagina  I. S.  Valuyskaya  D. A.  Kirillova  E. E. 《Doklady Earth Sciences》2020,494(1):730-734

Doklady Earth Sciences - This paper analyzes data on the concentration and dynamics of 137Cs and 90Sr in marine organisms on the Arctic shelf under modern conditions (2013–2018). It is shown...  相似文献   

A comparative analysis of time–depth relationships derived from scientific ocean drilling expeditions     

Sauermilch  Isabel  Mateo  Zenon Richard P.  Boaga  Jacopo 《Marine Geophysical Researches》2019,40(4):635-641

Marine Geophysical Research - Time–depth relationships (TDR) are required for correlating geological information from drill sites with seismic reflection profiles. Conventional...  相似文献   

Tsunami hydrodynamic force on a building using a SPH real-scale numerical simulation     

Klapp  Jaime  Areu-Rangel  Omar S.  Cruchaga  Marcela  Aránguiz  Rafael  Bonasia  Rosanna  Godoy  Mauricio J.  Silva-Casarín  Rodolfo 《Natural Hazards》2020,100(1):89-109

Natural Hazards - One of the most important aspects in tsunami studies is the behaviour of the wave when it approaches the coast. Information on physical parameters that characterize waves is often...  相似文献   

Hydrogen fluence in Genesis collectors: Implications for acceleration of solar wind and for solar metallicity     

Gary R. Huss  Elizabeth Koeman‐Shields  Amy J. G. Jurewicz  Donald S. Burnett  Kazuhide Nagashima  Ryan Ogliore  Chad T. Olinger 《Meteoritics & planetary science》2020,55(2):326-351

NASA's Genesis mission was flown to capture samples of the solar wind and return them to the Earth for measurement. The purpose of the mission was to determine the chemical and isotopic composition of the Sun with significantly better precision than known before. Abundance data are now available for noble gases, magnesium, sodium, calcium, potassium, aluminum, chromium, iron, and other elements. Here, we report abundance data for hydrogen in four solar wind regimes collected by the Genesis mission (bulk solar wind, interstream low‐energy wind, coronal hole high‐energy wind, and coronal mass ejections). The mission was not designed to collect hydrogen, and in order to measure it, we had to overcome a variety of technical problems, as described herein. The relative hydrogen fluences among the four regimes should be accurate to better than ±5–6%, and the absolute fluences should be accurate to ±10%. We use the data to investigate elemental fractionations due to the first ionization potential during acceleration of the solar wind. We also use our data, combined with regime data for neon and argon, to estimate the solar neon and argon abundances, elements that cannot be measured spectroscopically in the solar photosphere.  相似文献   

Normal fault growth influenced by basement fabrics: The importance of preferential nucleation from pre‐existing structures     

Luca Collanega  Katherine Siuda  Christopher A.‐L. Jackson  Rebecca E. Bell  Alexander J. Coleman  Antje Lenhart  Craig Magee  Anna Breda 《Basin Research》2019,31(4):659-687

Reactivation of pre‐existing intra‐basement structures can influence the evolution of rift basins, yet the detailed kinematic relationship between these structures and overlying rift‐related faults remains poorly understood. Understanding the kinematic as well as geometric relationship between intra‐basement structures and rift‐related fault networks is important, with the extension direction in many rifted provinces typically thought to lie normal to fault strike. We here investigate this problem using a borehole‐constrained, 3D seismic reflection dataset from the Taranaki Basin, offshore New Zealand. Excellent imaging of intra‐basement structures and a relatively weakly deformed, stratigraphically simple sedimentary cover allow us to: (a) identify a range of interaction styles between intra‐basement structures and overlying, Plio‐Pleistocene rift‐related normal faults; and (b) examine the cover fault kinematics associated with each interaction style. Some of the normal faults parallel and are physically connected to intra‐basement reflections, which are interpreted as mylonitic reverse faults formed during Mesozoic subduction and basement terrane accretion. These geometric relationships indicate pre‐existing intra‐basement structures locally controlled the position and attitude of Plio‐Pleistocene rift‐related normal faults. However, through detailed 3D kinematic analysis of selected normal faults, we show that: (a) normal faults only nucleated above intra‐basement structures that experienced late Miocene compressional reactivation, (b) despite playing an important role during subsequent rifting, intra‐basement structures have not been significantly extensionally reactivated, and (c) preferential nucleation and propagation of normal faults within late Miocene reverse faults and folds appears to be the key genetic relationship between contractionally reactivated intra‐basement structures and rift‐related normal faults. Our analysis shows that km‐scale, intra‐basement structures can control the nucleation and development of newly formed, rift‐related normal faults, most likely due to a local perturbation of the regional stress field. Because of this, simply inverting fault strike for causal extension direction may be incorrect, especially in provinces where pre‐existing, intra‐basement structures occur. We also show that a detailed kinematic analysis is key to deciphering the temporal as well as simply the spatial or geometric relationship between structures developed at multiple structural levels.  相似文献   

Integration of Electrofacies and Hydraulic Flow Units to Delineate Reservoir Quality in Uncored Reservoirs: A Case Study,Nubia Sandstone Reservoir,Gulf of Suez,Egypt     

El Sharawy  Mohamed S.  Nabawy  Bassem S. 《Natural Resources Research》2019,28(4):1587-1608

Natural Resources Research - Recognition of reservoir quality is an important objective in reservoir characterization process. By definition, the quality of a reservoir is described by its...  相似文献   

Assessment of the Accuracy of Calculations Using the International Reference Ionosphere Model IRI-2016: I. Electron Densities     

Lyakhov  A. N.  Kozlov  S. I.  Bekker  S. Z. 《Geomagnetism and Aeronomy》2019,59(1):45-52

Geomagnetism and Aeronomy - The paper quantitatively compares the results of calculations of the electron density Ne by the International Reference Ionosphere model IRI-2016 with experimental data...  相似文献