Elm bark beetle in Holocene peat deposits and the northwest European elm decline     

Sarah H. E. Clark  Kevin J. Edwards 《第四纪科学杂志》2004,19(6):525-528

The elm decline of 5000 ¹⁴C yr ago has been the most widely discussed phenomenon in post‐glacial vegetation history. This pan‐European reduction of elm populations, echoed in the decimation of elmwoods in Europe during the twentieth century, has attracted a series of interrelated hypotheses involving climate change, human activity, disease and soil deterioration. The elm bark beetle (Scolytus scolytus L.) is an essential component of disease explanations. We present evidence for the presence of the beetle over a prolonged period (ca. 7950–4910 yr BP [8800–5660 cal. yr BP]) from a lowland raised mire deposit in northeast Scotland, with its final appearance at this site, and the first and only appearance in another mire of a single scolytid find, around the time of the elm decline. The subfossil S. scolytus finds are not only the first from Scotland, but they also represent the most comprehensive sequence of finds anywhere. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Step-wise and continuous thermal demagnetization and theories of thermoremanence     

P. W. Schmidt  D. A. Clark 《Geophysical Journal International》1985,83(3):731-751

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Constraints on a planetary origin for the gap in the protoplanetary disc of GM Aurigae   总被引：1，自引：0，他引：1  

W. K. M. Rice  Kenneth Wood  P. J. Armitage  B. A. Whitney  J. E. Bjorkman 《Monthly notices of the Royal Astronomical Society》2003,342(1):79-85

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The D-CIXS X-ray mapping spectrometer on SMART-1     

M Grande  R BrowningN Waltham  D ParkerS.K Dunkin  B KentB Kellett  C.H PerryB Swinyard  A PerryJ Feraday  C HoweG McBride  K PhillipsJ Huovelin  P MuhliP.J Hakala  O VilhuJ Laukkanen  N ThomasD Hughes  H AlleyneM Grady  R LundinS Barabash  D BakerP.E Clark  C.D MurrayJ Guest  I CasanovaL.C d'Uston  S MauriceB Foing  D.J Heather  V FernandesK Muinonen  S.S RussellA Christou  C OwenP Charles  H KoskinenM Kato  K SipilaS Nenonen  M HolmstromN Bhandari  R ElphicD Lawrence 《Planetary and Space Science》2003,51(6):427-433

The D-CIXS Compact X-ray Spectrometer will provide high quality spectroscopic mapping of the Moon, the primary science target of the ESA SMART-1 mission. D-CIXS consists of a high throughput spectrometer, which will perform spatially localised X-ray fluorescence spectroscopy. It will also carry a solar monitor, to provide the direct calibration needed to produce a global map of absolute lunar elemental abundances, the first time this has been done. Thus it will achieve ground breaking science within a resource envelope far smaller than previously thought possible for this type of instrument, by exploiting two new technologies, swept charge devices and micro-structure collimators. The new technology does not require cold running, with its associated overheads to the spacecraft. At the same time it will demonstrate a radically novel approach to building a type of instrument essential for the BepiColombo mission and potential future planetary science targets.  相似文献   

Palaeo-ice streams: an introduction     

Chris D. Clark  David J. A. Evans  Jan A. Piotrowski 《Boreas: An International Journal of Quaternary Research》2003,32(1):1-3

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S-type asteroids,ordinary chondrites,and space weathering: The evidence from Galileo's fly-bys of Gaspra and Ida     

Clark R. CHAPMAN 《Meteoritics & planetary science》1996,31(6):699-725

Abstract— New observations of the S-type asteroids Gaspra and Ida, especially, by the Galileo spacecraft demonstrate that a “space weathering” process operates, which modifies the reflectance spectra of fresh material to be redder, straighter, and have shallower absorption bands. The weathering process appears similar to but less potent than that observed on the Moon. It operates in the sense that it would tend to convert spectra of ordinary chondrites (OC) to having the spectral traits of S-type asteroids. These results appear to resolve the major obstacles of the long standing “S-type conundrum” about the provenance of ordinary chondrite meteorites. A wide body of recent research, which is reviewed here, builds on previous meteoritical evidence to support a new, developing consensus that the larger S-type asteroids are a diverse assortment of silicaceous assemblages, which includes the ordinary chrondite parent bodies. Recent fairly realistic laboratory simulations of space weathering processes have changed OC spectra to resemble S-type spectra. J. F. Bell's highly regarded earlier paradigm that OC parent bodies would be found only among sub-10 km main-belt asteroids has been tested by an extensive observational survey by R. Binzel and his proteges; the result is that no small, main-belt analog for the OCs has been found, not even the somewhat OC-like object Boznemcová. This article reviews the history of the S-type conundrum, which set the stage for Galileo's historic flybys. I review the findings about Gaspra and Ida, including results about their geology, their geophysical structure and probable origins, and about Ida's small moonlet, Dactyl. Density constraints on Ida set by Dactyl's orbit rule out (for Ida, at least) the classic view of S-types as metallic, stripped cores of differentiated precursor asteroids. New analysis of the Galileo spectral images of Ida is presented that provides strong evidence that space weathering occurs on Ida, and that Ida, and the Koronis family asteroids in general, are plausibly OC-like in composition. After reviewing 1990s developments on the S-type conundrum, I advocate a new perspective that the ordinary chondrite parent bodies are among the S-type asteroids, a diverse grouping that also contains other silicaceous and silicate/metal assemblages, presumably including various stony-irons and primitive achondrites represented in meteorite collections; Gaspra may be such a metal-rich assemblage.  相似文献   

The origin of selected lunar geochemical anomalies: Implications for early volcanism and the formation of light plains     

Bernard Ray Hawke  Paul D. Spudis  P. E. Clark 《Earth, Moon, and Planets》1985,32(3):257-273

The Apollo orbital geochemistry, photogeologic, and other remote sensing data sets were used to identify and characterize geochemical anomalies on the eastern limb and farside of the Moon and to investigate the processes responsible for their formation. The anomalies are located in the following regions: (1) Balmer basin, (2) terrain northeast of Mare Smythii, (3) near Langemak crater, (4) Pasteur crater, (5) terrain northwest of Milne basin, (6) northeast of Mendeleev basin, (7) north and northeast of Korolev basin, (8) terrain north of Taruntius crater, and (9) terrain north of Orientale basin. The anomalies are commonly associated with Imbrian- or Nectarian-aged light plains units which exhibit dark-haloed impact craters. The results of recent spectral reflectance studies of dark-haloed impact craters plus consideration of the surface chemistry of the anomalies strongly indicate that those geochemical anomalies associated with light plains deposits which display dark-haloed impact craters result from the presence of basaltic units that are either covered by varying thickness of highland debris or have a surface contaminated with significant amounts of highlands material. The burial or contamination of ancient volcanic surfaces by varying amounts of highland material appears to have been an important (though not the dominant) process in the formation of lunar light plains. Basaltic volcanism on the eastern limb and farside of the Moon was more extensive in both space and time than has been accepted.  相似文献   

Coulometric TCO2 analyses for marine studies; an introduction     

Kenneth M Johnson  Arthur E King  John McN Sieburth 《Marine Chemistry》1985,16(1):61-82

Progress in the introduction of coulometry for the analysis of total carbon dioxide (TCO₂) in marine waters is described. An extractor—stripper removes CO₂ that is measured coulometrically by the quantity of electricity (coulombs) used to electrogenerate OH^? ions for the titration of the acid formed by the reaction of CO₂ and ethanolamine. The equivalence point is detected photometrically with thymolphthalein as the indicator, and Faraday's Law relates coulombs to equivalents of titrant generated and CO₂ determined so that there are no standard curves needed or titrants to standardize or store. Accuracy was determined by adding gelatin capsules containing 100–1500 μg C of pure CaCO₃ into the stripper, and accuracies of better than ± 1 μg C were achieved. The best precision for natural seawater (± 1 standard error) of ± 0.5 μmol l^?1 was found for 17 samples of Bermuda coastal waters having a mean TCO₂ of 2007.2 μmol l^?1 (0.05% CV). Sources of error and precautions are discussed. This method, which has been used successfully at sea, can be used to study a variety of marine phenomena involving TCO₂.  相似文献   

Aquitard Distribution In A Northern Reach Of The Miami Valley Aquifer,Ohio, USA: Part 1. Three-Dimensional Geostatistical Evaluation Of Physical Heterogeneity     

Robert W. Ritzi  David F. Dominic  Kenneth W. Kausch 《Hydrogeology Journal》1996,4(2):12-24

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Deformation styles as a key for interpreting glacial depositional environments     

Danny McCarroll  Kenneth F. Rijsdijk 《第四纪科学杂志》2003,18(6):473-489

Lithostratigraphical and lithofacies approaches used to interpret glacial sediments often ignore deformation structures that can provide the key to environment of formation. We propose a classification of deformation styles based on the geometry of structures rather than inferred environment of formation. Five styles are recognised: pure shear (P), simple shear (S), compressional (C), vertical (V) and undeformed (U). These dictate the first letter of the codes; the remaining letters conveying the evidence. This information can be used to reconstruct palaeostress fields and to infer physical properties of sediments when they deformed. Individual structures are not diagnostic of particular environments but the suite of structures, their relative scale, stratigraphical relationships, and orientation relative to palaeoslopes and to palaeoice‐flow directions can be used to infer the environment in which they formed. This scheme is applied at five sites in west Wales. The typical succession is interpreted as subglacial sediments overlain by meltout tills, flow tills and sediment flows. Paraglacial redistribution of glacial sediments is widespread. Large‐scale compressional deformation is restricted to sites where glaciers readvanced. Large‐scale vertical deformation occurs where water was locally ponded near the ice margin. There is no evidence for glaciomarine conditions. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献