Timing of glacial retreat in the Wicklow Mountains,Ireland, conditioned by glacier size and topography          下载免费PDF全文

Matt D. Tomkins  Jason M. Dortch  Philip D. Hughes  Jonny J. Huck  Toby N. Tonkin  Iestyn D. Barr 《第四纪科学杂志》2018,33(6):611-623

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Compositions of three low-FeO ordinary chondrites: Indications of a common origin with the H chondrites     

Julianne Troiano  Mark L. Rivers 《Geochimica et cosmochimica acta》2011,75(21):6511-6519

Burnwell, EET 96031, and LAP 04575 are ordinary chondrites (OC) that possess lower than typical olivine Fa content than has been established for the H chondrites (<∼17 mol%). Mean low-Ca pyroxene Fs contents are typically lower than mean Fa content, with generally ?16 mol% Fs. We have investigated these three low-FeO chondrites by measuring their trace element abundances, oxygen isotopic compositions, and examining their three-dimensional (3D) petrography with synchrotron X-ray microtomography. We compare our results with those established for more common OC. The low FeO chondrites studied here have bulk trace element abundances that are identical to the H chondrites. From bulk oxygen isotopic analysis, we show that Burnwell, EET 96010, and LAP 04757 sampled oxygen reservoirs identical to the H chondrites. Burnwell, EET 96031, and LAP 04575 possess common 3D opaque mineral structures that could be distinct from the H chondrites, as evidenced by X-ray microtomographic analysis, but our comparison suite of H chondrites is small and unrepresentative. Overall, our data suggest a common origin for the low-FeO chondrites Burnwell, EET 96010, and LAP 04757 and the H chondrites. These three samples are simply extreme members of a redox process where a limiting nebular oxidizing agent, probably ice, reacted with material containing slightly higher amounts of metal than typically seen in the H chondrites.  相似文献   

Wyville Thomson Ridge Overflow Water: Spatial and temporal distribution in the Rockall Trough     

Clare Johnson  Toby Sherwin  Denise Smythe-Wright  Tracy Shimmield  William Turrell 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(10):1153-1162

Wyville Thomson Ridge Overflow Water (WTOW), which is the only part of the outflow from the Norwegian Sea not to directly enter the Iceland Basin, is shown to be a significant water mass in the northern Rockall Trough. It is found primarily at intermediate depths (600–1200 m) beneath the northward flowing warm Atlantic waters, and above recirculating Mediterranean influenced waters and Labrador Sea Water (LSW). The bottom of the WTOW layer can be identified by a mid-depth inflexion point in potential temperature–salinity plots. An analysis of historical data reveals that WTOW has been present in all but eight of the last 31 years at 57.5°N in the Rockall Trough. A denser component of WTOW below 1500 m has also been present, although it appears to be less persistent (12 out of the 31 years) and limited to the west of the section. The signature of intermediate WTOW was absent in two periods, the mid-1980s and early 1990s, both of which coincided with a freshening, and probable increase in volume, of LSW in the trough. Potential temperature–salinity diagrams from historical observations indicate that WTOW persists at least as far south as 55°N (and as far west as 20°W in the Iceland Basin) although its signature is quickly lost on leaving the Rockall Trough. We suggest that a transport of WTOW down the western side of the trough exists, with WTOW at intermediate depths entering the eastern trough either via a cyclonic recirculation, or as a result of eddy activity. Further, WTOW is seen on the Rockall–Hatton Plateau and in the deep channels connecting with the Iceland Basin, suggesting additional possible WTOW transport pathways. These suggested transport routes remain to be confirmed by further observational or modelling studies.  相似文献   

Underground measurements of the seismic noise level     

Vít Kárník  Vladimír Tobyáš 《Studia Geophysica et Geodaetica》1961,5(3):231-236

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Magnification control of electromagnetic seismographs with standard a I–IV characteristics     

Vladimír Tobyáš  Reviewer J. Buben 《Studia Geophysica et Geodaetica》1975,19(3):245-260

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Isotopic composition of a large photosymbiotic foraminifer: Evidence for hypersaline environments across the Great Australian Bight during the late Pleistocene     

John M. Rivers  T. Kurt Kyser  Noel P. James 《Sedimentary Geology》2009,213(3-4):113-120

Analysis of carbon and oxygen isotopic compositions of large benthic foraminifera tests (Marginopora vertebralis) that lived in the Great Australian Bight during the late Pleistocene, reveal that the tests are enriched by 1 to 3‰ in both ¹⁸O and ¹³C relative to modern specimens from the same region. The intolerance of M. vertebralis for cool waters negates lower ocean water temperature as an explanation for such high δ¹⁸O values. The oxygen isotopic compositions are thus interpreted to reflect tests secreted in hypersaline waters of up to 56 ppt salinity, concentrated from seawater by evaporation. M. vertebralis thrives today in waters of similar salinity at Shark Bay, Western Australia. The Pleistocene sedimentary assemblage supports an interpretation that environments broadly similar to those in outer modern-day Shark Bay were wide spread across the Great Australian Bight during portions of marine isotope stages 2, 3 and 4. The high δ¹³C values of the Pleistocene M. vertebralis are interpreted to reflect enhanced photosynthetic activity that depletes dissolved carbonate in ¹²C in such shallow, saline settings. These hypersaline environments formed during periods of lower sea-level when shallow-waters (< 20 m depth) extended from the shoreline over ~ 100 km across what is currently a relatively deep shelf. This study indicates that shelf bathymetry was a critical determinant of past environments of deposition across the Great Australian Bight.  相似文献   

Pore size distribution in an uncompacted equilibrated ordinary chondrite     

Jon M. Friedrich  Robert J. Macke  Douglas P. Wignarajah  Mark L. Rivers  Daniel T. Britt  Denton S. Ebel 《Planetary and Space Science》2008,56(7):895-900

The extraordinarily uncompacted nature of the ordinary L chondrite fall Baszkówka gives a unique opportunity to investigate the potentially pre-compaction pore size distribution in an equilibrated ordinary chondrite. Using X-ray microtomography and helium pycnometry on two samples of Baszkówka, we have found that on average, two-thirds of the 19.0% porosity resides in inter- and intra-granular voids with volumes between 3×10⁻⁵ and 3 mm³. We show the cumulative number density of pore volumes observable by X-ray microtomography obeys a power law distribution function in this equilibrated ordinary chondrite. We foresee these data adding to our understanding of the impact processing of chondrites and their parent asteroids, where porosity and pore size play significant roles in the parameterization of impact events.  相似文献   

Pore-scale characteristics of multiphase flow in porous media: A comparison of air–water and oil–water experiments     

K.A. Culligan  D. Wildenschild  B.S.B. Christensen  W.G. Gray  M.L. Rivers 《Advances in water resources》2006

Studies of NAPL dissolution in porous media have demonstrated that measurement of saturation alone is insufficient to describe the rate of dissolution. Quantification of the NAPL–water interfacial area provides a measure of the expected area available for mass transfer and will likely be a primary determinant of NAPL removal efficiency. To measure the interfacial area, we have used a synchrotron-based CMT technique to obtain high-resolution 3D images of flow in a Soltrol–water–glass bead system. The interfacial area is found to increase as the wetting phase saturation decreases, reach a maximum, and then decrease as the wetting phase saturation goes to zero. These results are compared to previous findings for an air–water–glass bead study; The Soltrol–water interfacial areas were found to peak at similar saturations as those measured for the air–water system (20–35% saturation range), however, the peak values were in some cases almost twice as high for the oil-water system. We believe that the observed differences between the air–water and oil–water systems to a large degree can be explained by the differences in interfacial tensions for the two systems.  相似文献   

Solving the housing problem: William Mandel's “Soviet but not Russian”, a book review essay     

Toby Terrar 《GeoJournal》1988,17(1):151-151

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Erratum to “Calculations of neutralino–stau coannihilation channels and the cosmologically relevant region of MSSM parameter space” [Astroparticle Physics 13 (2000) 181–213]     

John Ellis  Toby Falk  Keith A. Olive  Mark Srednicki 《Astroparticle Physics》2001,15(4):413-414

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