Long-term impacts of dust storms on transport systems in south-eastern Iran     

Miri  Abbas  Middleton  Nick 《Natural Hazards》2022,114(1):291-312

Natural Hazards - Dust storms are frequent in the Sistan region of south-eastern Iran and cause a wide range of problems, but few studies have assessed their negative impacts. This paper makes an...  相似文献   

Identification of Mineralization in Geochemistry for Grid Sampling Using Generalized Additive Models     

Mikšová  Dominika  Rieser  Christopher  Filzmoser  Peter  Middleton  Maarit  Sutinen  Raimo 《Mathematical Geosciences》2021,53(8):1861-1880

Mathematical Geosciences - The important goals of mineral exploration geochemistry are detection and identification of underlying mineralization. This paper deals with element concentration data...  相似文献   

The 16-day planetary wave in the mesosphere and lower thermosphere   总被引：3，自引：0，他引：3  

N. J. Mitchell  H. R. Middleton  A. G. Beard  P. J. S. Williams  H. G. Muller 《Annales Geophysicae》1999,17(11):1447-1456

A meteor radar located at Sheffield in the UK has been used to measure wind oscillations with periods in the range 10–28 days in the mesosphere/lower-thermosphere region at 53.5°N, 3.9°W from January 1990 to August 1994. The data reveal a motion field in which wave activity occurs over a range of frequencies and in episodes generally lasting for less than two months. A seasonal cycle is apparent in which the largest observed amplitudes are as high as 14 ms⁻¹ and are observed from January to mid-April. A minimum in activity occurs in late June to early July. A second, smaller, maximum follows in late summer/autumn where amplitudes reach up to 7–10 ms⁻¹. Considerable interannual variability is apparent but wave activity is observed in the summers of all the years examined, albeit at very small amplitudes near mid summer. This behaviour suggests that the equatorial winds in the mesopause region do not completely prevent inter-hemispheric ducting of the wave from the winter hemisphere, or that it is generated in situ.  相似文献   

Characteristics and origin of underpressure system in the Shiwu Fault Depression, south-east Songliao Basin, China   总被引：6，自引：0，他引：6  

He  Middleton  & Tang 《Basin Research》2000,12(2):147-158

The vertical characteristics of underpressure, pore fluids and sealing condition in the Shiwu Fault Depression, south‐east Songliao Basin, are investigated. Based on the pore pressure data from drill stem tests collected from 40 wells, the vertical distribution of pore pressure in this depression consists of a shallow hydrostatic pressure system and a deep underpressure system. The observed low pressures range from about 4 to 10 MPa in the depth interval of about 1550–2800 m. The pore water chemistry data document that the ionic evaporite trends of the pore water in the underpressure zone are different from overlying sediments in the hydrostatically pressured section, indicating that the underpressure system is sealed. The study indicates that the depression has undergone rapid deposition in a rift period during the Cretaceous followed by a long‐term slow uplift and erosion in the Tertiary. On the basis of the modelled results of the abnormal pressure evolution in a typical cross‐section using a two‐dimensional numerical flow model, we believe that the predecessor of the underpressure system was an overpressure system. Since the end of the Cretaceous, the observed underpressure system has developed as a result of a geotemperature decrease ranging from 30 to 70 °C, owing to palaeoheat flow reduction and long‐term uplift and erosional cooling. The mudstones below a depth of 1550 m in the deep subnormal pressure system have small measured porosities ranging from 4% to 1.2% with calculated permeability of about 10^?21–10^?24 m². The observed underpressure can be modelled if we assign permeabilities below 10^?20 m² with a linear reduction of geotemperature. The geotemperature decrease, in combination with very low permeability in the Lower Cretaceous mudstones, is therefore a possible origin for the formation of the underpressure system in this depression.  相似文献   

The formation and chronology of the PAT 91501 impact-melt L chondrite with vesicle-metal-sulfide assemblages     

G.K. Benedix  R.A. Ketcham  T.J. McCoy  D.H. Garrison  S. Xue  R. Middleton 《Geochimica et cosmochimica acta》2008,72(9):2417-2428

The L chondrite Patuxent Range (PAT) 91501 is an 8.5-kg unshocked, homogeneous, igneous-textured impact melt that cooled slowly compared to other meteoritic impact melts in a crater floor melt sheet or sub-crater dike [Mittlefehldt D. W. and Lindstrom M. M. (2001) Petrology and geochemistry of Patuxent Range 91501 and Lewis Cliff 88663. Meteoritics Planet. Sci. 36, 439-457]. We conducted mineralogical and tomographic studies of previously unstudied mm- to cm-sized metal-sulfide-vesicle assemblages and chronologic studies of the silicate host. Metal-sulfide clasts constitute about 1 vol.%, comprise zoned taenite, troilite, and pentlandite, and exhibit a consistent orientation between metal and sulfide and of metal-sulfide contacts. Vesicles make up ∼2 vol.% and exhibit a similar orientation of long axes. ³⁹Ar-⁴⁰Ar measurements probably date the time of impact at 4.461 ± 0.008 Gyr B.P. Cosmogenic noble gases and ¹⁰Be and ²⁶Al activities suggest a pre-atmospheric radius of 40-60 cm and a cosmic ray exposure age of 25-29 Myr, similar to ages of a cluster of L chondrites. PAT 91501 dates the oldest known impact on the L chondrite parent body. The dominant vesicle-forming gas was S₂ (∼15-20 ppm), which formed in equilibrium with impact-melted sulfides. The meteorite formed in an impact melt dike beneath a crater, as did other impact melted L chondrites, such as Chico. Cooling and solidification occurred over ∼2 h. During this time, ∼90% of metal and sulfide segregated from the local melt. Remaining metal and sulfide grains oriented themselves in the local gravitational field, a feature nearly unique among meteorites. Many of these metal-sulfide grains adhered to vesicles to form aggregates that may have been close to neutrally buoyant. These aggregates would have been carried upward with the residual melt, inhibiting further buoyancy-driven segregation. Although similar processes operated individually in other chondritic impact melts, their interaction produced the unique assemblage observed in PAT 91501.  相似文献   

Oceanographic controls on shallow‐water temperate carbonate sedimentation: Spencer Gulf,South Australia          下载免费PDF全文

Laura G. O'Connell  Noel P. James  Mark Doubell  John F. Middleton  John Luick  David R. Currie  Yvonne Bone 《Sedimentology》2016,63(1):105-135

Spencer Gulf is a large (ca 22 000 km²), shallow (<60 m water depth) embayment with active heterozoan carbonate sedimentation. Gulf waters are metahaline (salinities 39 to 47‰) and warm‐temperate (ca 12 to ?28°C) with inverse estuarine circulation. The integrated approach of facies analysis paired with high‐resolution, monthly oceanographic data sets is used to pinpoint controls on sedimentation patterns with more confidence than heretofore possible for temperate systems. Biofragments – mainly bivalves, benthic foraminifera, bryozoans, coralline algae and echinoids – accumulate in five benthic environments: luxuriant seagrass meadows, patchy seagrass sand flats, rhodolith pavements, open gravel/sand plains and muddy seafloors. The biotic diversity of Spencer Gulf is remarkably high, considering the elevated seawater salinities. Echinoids and coralline algae (traditionally considered stenohaline organisms) are ubiquitous. Euphotic zone depth is interpreted as the primary control on environmental distribution, whereas seawater salinity, temperature, hydrodynamics and nutrient availability are viewed as secondary controls. Luxuriant seagrass meadows with carbonate muddy sands dominate brightly lit seafloors where waters have relatively low nutrient concentrations (ca 0 to 1 mg Chl‐a m^?3). Low‐diversity bivalve‐dominated deposits occur in meadows with highest seawater salinities and temperatures (43 to 47‰, up to 28°C). Patchy seagrass sand flats cover less‐illuminated seafloors. Open gravel/sand plains contain coarse bivalve–bryozoan sediments, interpreted as subphotic deposits, in waters with near normal marine salinities and moderate trophic resources (0·5 to 1·6 mg Chl‐a m^?3) to support diverse suspension feeders. Rhodolith pavements (coralline algal gravels) form where seagrass growth is arrested, either because of decreased water clarity due to elevated nutrients and associated phytoplankton growth (0·6 to 2 mg Chl‐a m^?3), or bottom waters that are too energetic for seagrasses (currents up to 2 m sec^?1). Muddy seafloors occur in low‐energy areas below the euphotic zone. The relationships between oceanographic influences and depositional patterns outlined in Spencer Gulf are valuable for environmental interpretations of other recent and ancient (particularly Neogene) high‐salinity and temperate carbonate systems worldwide.  相似文献   

Rangeland management and climate hazards in drylands: dust storms,desertification and the overgrazing debate     

Nick Middleton 《Natural Hazards》2018,92(1):57-70

This paper examines the theory and supporting evidence for links between desertification, drought and dust storms with a particular focus on studies undertaken in and around the Gobi Desert. Overgrazing of rangeland by pastoralists has been the most commonly cited cause of desertification in global drylands for more than 30 years, but the evidence supporting this link is not always convincing. Nonetheless, overgrazing, desertification and dust storms are frequently connected, regardless. Drought is another well-known and important driver of vegetation cover change. Distinguishing between vegetation cover adversely affected by drought and that reduced by grazing is imperative for policy makers because identifying the incorrect driver of vegetation change risks the development of inappropriate policy.  相似文献   

RE J1034+396: the origin of the soft X-ray excess and quasi-periodic oscillation     

Matthew Middleton  Chris Done  Martin Ward  Marek Gierli&#;ski  Nick Schurch 《Monthly notices of the Royal Astronomical Society》2009,394(1):250-260

The X-ray quasi-periodic oscillation (QPO) seen in RE J1034+396 is so far unique amongst active galactic nuclei (AGN). Here, we look at another unique feature of RE J1034+396, namely its huge soft X-ray excess, to see if this is related in any way to the detection of the QPO. We show that all potential models considered for the soft energy excess can fit the 0.3–10 keV X-ray spectrum, but the energy dependence of the rapid variability (which is dominated by the QPO) strongly supports a spectral decomposition where the soft excess is from low-temperature Comptonization of the disc emission and remains mostly constant, while the rapid variability is produced by the power-law tail changing in normalization. The presence of the QPO in the tail rather than in the disc is a common feature in black hole binaries (BHBs), but low-temperature Comptonization of the disc spectrum is not generally seen in these systems. The main exception to this is GRS 1915+105, the only BHB which routinely shows super-Eddington luminosities. We speculate that the super-Eddington accretion rates lead to a change in disc structure, and that this also triggers the X-ray QPO.  相似文献   

New physical-statistical methods and models for clutter andreverberation: the KA-distribution and related probability structures     

Middleton  D. 《Oceanic Engineering, IEEE Journal of》1999,24(3):261-284

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A model for the formation of intracratonic sag basins     

M. F. Middleton 《Geophysical Journal International》1989,99(3):665-676

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