The Balderton Sand and Gravel: Pre-Ipswichian cold stage fluvial deposits near Lincoln,England     

Allan Brandon  Michael G. Sumbler 《第四纪科学杂志》1991,6(2):117-138

The Balderton Terrace marks a former course of the River Trent between Newark and the Lincoln Gap. The principal deposit, the Balderton Sand and Gravel, is interpreted as a braided river sediment. Ice wedge casts truncated by intraformational erosion surfaces at many levels indicate syndepositional permafrost. Remnant cover deposits overlying the Balderton Sand and Gravel include the partly aeolian Whisby Sand. Locally, both the upper part of the Balderton Sand and Gravel and the cover deposits exhibit features indicative of temperate climate pedogenesis. All these deposits are affected by subsequent cryoturbation. On the basis of these features and the geomorphological and topographical relationship to other terrace deposits of the area, the Balderton Sand and Gravel and Whisby Sand are regarded as post-Hoxnian and pre-lpswichian, i.e. Wolstonian. Electron spin resonance age determinations for fossil elephant teeth and amino acid analyses on molluscs from the Balderton Sand and Gravel suggest correlation with Oxygen Isotope Stage 6. The Balderton Sand and Gravel has yielded a cold-climate mammalian fauna dominated by woolly mammoth and woolly rhinoceros, though rarer species suggest periods of milder climate. Silts from channels near the base of the deposit have produced pollen, mollusc, ostracod and beetle assemblages also indicating a cold climate.  相似文献   

The critical inclination problem: A simple treatment     

R. R. Allan 《Celestial Mechanics and Dynamical Astronomy》1970,2(1):121-122

A short analysis is presented in the hope of clarifying the situation.  相似文献   

Distribution of Uranium in the crust of the northwestern canadian shield as shown by lake-sediment analysis     

E.M. Cameron  R.J. Allan 《Journal of Geochemical Exploration》1973,2(3):237-250

In 1972 a reconnaissance geochemical survey was carried out by the Geological Survey of Canada in the northwestern Canadian Shield. Samples of nearshore lake sediment were collected, by helicopter, from 36,000 sq. miles of the Bear and Slave Structural Provinces. Sample density was one per 10 miles. These samples have since been analyzed for 27 elements. This paper is concerned with the distribution of uranium in 1,241 samples from the western third of the survey area. This region mainly comprises the Bear Province, of Proterozoic age.The Bear Province, which is a metallogenic province for uranium, also appears to be a geochemical province for this element. Uranium is four times more abundant in lake sediments from this area (5.3 p.p.m. U) as compared to the eastern part of the Slave Province (1.3 p.p.m. U). The lake-sediment data are in agreement with analyses of composite rock samples from two parts of the survey area.Within the Bear Province the regional distribution of uranium is controlled mainly by the distribution of Proterozoic granitic rocks. Nearly all areas of 5 p.p.m. U or greater in lake sediments are underlain by Proterozoic granites, or are near to these rocks. Within the granite areas, uranium is distributed along two sets of regularly spaced linear trends. The highest contents in lake sediment, which include values up to 300 p.p.m. U, commonly occur near the intersections of the two trends. These trends correspond to a set of northeast and a set of northwest strike-slip faults and lineaments that were produced by east-west compression of the Bear Province during and after the Hudsonian Orogeny (1750 m.y.). Outside the western margin of the survey area, complex epigenetic mineralization is associated with northeasterly-trending faults. Uranium has been produced from veins of this type at Port Radium and at the Rayrock Mine. Since it is associated with faults, this type of mineralization tends to occur in topographic depressions, that often contain lakes and swamps. Lake-sediment analysis is believed to be an excellent means of detecting such mineralization, both within the survey area and possibly elsewhere in the Canadian Shield. The data obtained during 1972 provide a basis for more detailed prospecting in the region.  相似文献   

Regime dependent changes in global precipitation   总被引：1，自引：1，他引：0  

Richard P. Allan 《Climate Dynamics》2012,39(3-4):827-840

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Molecular modelling of rare earth element complexation in subduction zone fluids     

Jelle van Sijl  Neil L. Allan  Wim van Westrenen 《Geochimica et cosmochimica acta》2009,73(13):3934-3947

Complexation of (trace) elements in fluids plays a critical role in determining element mobility in subduction zones, but to date, the atomic-scale processes controlling elemental solubilities are poorly understood. As a first step towards computer simulation of element complexation in subduction zone fluids, a thermodynamic cycle was developed to investigate the hydration environment and energetics of lanthanide complexes using density functional theory. The first solvation shell is explicitly defined and the remaining part of the aqueous fluid is modelled using a polarisable continuum model, which allows extrapolation to a broad pressure and temperature range.We illustrate our method by comparing solvation of lanthanide series elements in H₂O in the presence of fluoride or chloride for conditions relevant to subduction zones. The energetics of lanthanide- and lanthanide-fluoride/chloride hydration complexes were determined computationally. Calculated hydration free energies for trivalent lanthanides with explicit eight- and nine-fold coordinated first hydration shells show good agreement with literature data at room pressure and temperature. The hydration free energy is more negative for smaller complexes (heavy lanthanides) relative to larger complexes (light lanthanides), with the difference between La and Lu in water amounting to 361 kJ mol⁻¹. The hydration free energy of all lanthanide ions becomes less negative with increasing pressure (p) and temperature (T) up to 2.5 GPa and 1000 K (typical conditions in the upper part of subducting slabs). The free energy difference between light- and heavy-lanthanides remains essentially unchanged at elevated (p, T) conditions. There are minor geometrical differences in local hydration environment between light lanthanide-chloride (La-Nd) and heavy lanthanide-chloride (Pm-Lu) hydrated complexes, without a distinguishable energy difference. Complexation with fluoride is energetically more favourable than with chloride by 206 ± 4 kJ mol⁻¹ across the entire lanthanide series. The association of fluoride-water and chloride-water fragments with lanthanide-water complexes is energetically more favourable for aqueous lanthanide complexes surrounded by fewer first hydration shell water molecules.The methods developed in this study, in conjunction with simulation of the energetics of trace element incorporation into minerals, open the possibility to use molecular modelling to constrain elemental behaviour in subduction zones.  相似文献   

Electronic environments in carrollite, CuCo₂S₄, determined by soft X-ray photoelectron and absorption spectroscopy     

Alan N. Buckley  William M. Skinner  Allan Pring 《Geochimica et cosmochimica acta》2009,73(15):4452-4467

Fracture surfaces of a natural carrollite specimen have been characterised by synchrotron and conventional X-ray photoelectron spectroscopy and near-edge X-ray absorption spectroscopy. For the synchrotron X-ray measurements, the mineral surfaces were prepared under clean ultra high vacuum and were unoxidised. The characterisation was undertaken primarily to establish unequivocally the oxidation state of the Cu in the mineral, but also to obtain information on the electronic environments of the Co and S, and on the surface species. Experimental and simulated Cu L_2,3-edge absorption spectra confirmed an oxidation state of Cu^I, while Co 2p photoelectron and Co L_2,3 absorption spectra were largely consistent with the Co^III established previously by nuclear magnetic resonance spectroscopy. S 2p photoelectron spectra provided no evidence for S to be present in the bulk in more than one state, and were consistent with an oxidation state slightly less negative than S^-II. Therefore it was concluded that carrollite can be best represented by Cu^ICo^III₂(S₄)^-VII. The Cu^I oxidation state is in agreement with that expected for Cu tetrahedrally coordinated by S, but is in disagreement with the Cu^II deduced previously from some magnetic, magnetic resonance and Cu L-edge X-ray absorption spectroscopic measurements. A significant concentration of S species with core electron binding energies both lower and higher than the bulk value were formed at fracture surfaces, and these entities were assigned to monomeric and oligomeric surface S species. The density of Cu d states calculated for carrollite differed from that previously reported but was consistent with the observed Cu L₃ X-ray absorption spectrum. The initial oxidation of carrollite in air under ambient conditions was confirmed to be congruent, unlike the incongruent reaction undergone by a number of non-thiospinel sulfide minerals.  相似文献   

Towards molecular-level understanding of geochemical processes in mineral exploration     

Joël Brugger  Allan Pring  Frank Reith  Barbara Etschmann  Weihua Liu 《Journal of Geochemical Exploration》2009

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Properties of hot stars in the Wolf--Rayet galaxy NGC 5253 from ISO-SWS spectroscopy     

Paul A. Crowther  S. C. Beck  Allan J. Willis  Peter S. Conti  Patrick W. Morris  Ralph S. Sutherland 《Monthly notices of the Royal Astronomical Society》1999,304(3):654-668

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Cosmic-ray positrons: are there primary sources?     

Stphane Coutu  Steven W. Barwick  James J. Beatty  Amit Bhattacharyya  Chuck R. Bower  Christopher J. Chaput  Georgia A. de Nolfo  Michael A. DuVernois  Allan Labrador  Shawn P. McKee  Dietrich Müller  James A. Musser  Scott L. Nutter  Eric Schneider  Simon P. Swordy  Gregory Tarl  Andrew D. Tomasch  Eric Torbet 《Astroparticle Physics》1999,11(4):208-435

Galactic cosmic rays consist of primary and secondary particles. Primary cosmic rays are thought to be energized by first order Fermi acceleration processes at supernova shock fronts within our Galaxy. The cosmic rays that eventually reach the Earth from this source are mainly protons and atomic nuclei, but also include electrons. Secondary cosmic rays are created in collisions of primary particles with the diffuse interstellar gas. They are relatively rare but carry important information on the Galactic propagation of the primary particles. The secondary component includes a small fraction of antimatter particles, positrons and antiprotons. In addition, positrons and antiprotons may also come from unusual sources and possibly provide insight into new physics. For instance, the annihilation of heavy supersymmetric dark matter particles within the Galactic halo could lead to positrons or antiprotons with distinctive energy signatures. With the High-Energy Antimatter Telescope (HEAT) balloon-borne instrument, we have measured the abundances of positrons and electrons at energies between 1 and 50 GeV. The data suggest that indeed a small additional antimatter component may be present that cannot be explained by a purely secondary production mechanism. Here we describe the signature of the effect and discuss its possible origin.  相似文献   

A spatially resolved 'inside-out' outburst of IP Pegasi     

N. A. Webb  T. Naylor  Z. Ioannou  W. J. Worraker  J. Stull  A. Allan  R. Fried  N. D. James  D. Strange 《Monthly notices of the Royal Astronomical Society》1999,310(2):407-413

We present a comprehensive photometric data set taken over the entire outburst of the eclipsing dwarf nova IP Peg in 1997 September/October. Analysis of the light curves taken over the long rise to the peak-of-outburst shows conclusively that the outburst started near the centre of the disc and moved outwards. This is the first data set that spatially resolves such an outburst. The data set is consistent with the idea that long rise times are indicative of such 'inside-out' outbursts. We show how the thickness and the radius of the disc, along with the mass transfer rate, change over the whole outburst. In addition, we show evidence of the secondary and the irradiation thereof. We discuss the possibility of spiral shocks in the disc; however, we find no conclusive evidence of their existence in this data set.  相似文献