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11.
Adrian M. Hall John E. Gordon Graeme Whittington Geoffrey A. T. Duller Hendrik Heijnis 《第四纪科学杂志》2002,17(1):51-67
New stratigraphical, palynological and dating evidence is presented for pre‐Late Devensian/Weichselian sediments at Fugla Ness and Sel Ayre, Shetland. The Fugla Ness Peat rests on till and formed during an interglacial that saw the development of maritime heaths, with scattered trees and shrubs, including Pinus and possibly Ilex. A decline into stadial conditions is marked by overlying periglacial breccia and till. The Sel Ayre Organic Sands and Gravels lie between periglacial breccias and beneath till and appear to record a changing interstadial environment in which trees were absent and the vegetation comprised largely heaths, with Bruckenthalia, and grasslands. The Fugla Ness Peat is dated to 110+40/?35 ka by uranium series disequilibrium, suggesting that it formed during the Ipswichian/Eemian Interglacial (Marine Isotope Substage 5e). Luminescence ages of ca. 98–105 ka on intercalated sands within the Sel Ayre Organic Sands and Gravels place these deposits in Marine Isotope Substage 5c (Brørup Interstadial). The two sites provide the first detailed record of Marine Isotope Stage 5 environments on Shetland. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
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Ali M. Bouhifd Alan Whittington Pascal Richet 《Contributions to Mineralogy and Petrology》2001,142(2):235-243
The volumes and expansivities of four hydrous phonolite glasses and liquids have been measured by dilatometry from 300 K up to the glass transition and over a 50 K interval just above the glass transition. The partial molar volume of water is independent of the water content for the glass and liquid phases, with values of about 11.0ǂ.5 and 17.1ǂ.9 cm3/mol at 300 and 800 K, respectively. The partial molar thermal expansivity of water in phonolite glasses is about 8᎒-5 K-1, a result similar to recently published values for different silicate compositions, and about 36.5᎒-5 K-1 in phonolite liquids. The implications for melt density and water dissolution are discussed. 相似文献
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The viscosity of hydrous dacitic liquids: implications for the rheology of evolving silicic magmas 总被引：2，自引：1，他引：1
Alan G. Whittington Bridget M. Hellwig Harald Behrens Bastian Joachim André Stechern Francesco Vetere 《Bulletin of Volcanology》2009,71(2):185-199
The viscosity of a series of six synthetic dacitic liquids, containing up to 5.04 wt% dissolved water, was measured above
the glass transition range by parallel-plate viscometry. The temperature of the 1011 Pa s isokom decreases from 1065 K for the anhydrous liquid, to 864 K and 680 K for water contents of 0.97 and 5.04 wt% H2O. Including additional measurements at high temperatures by concentric-cylinder and falling-sphere viscometry, the viscosity
(η) can be expressed as a function of temperature and water content w according to: where η is in Pa s, T is temperature in K, and w is in weight percent. Within the conditions of measurement, this parameterization reproduces the 76 viscosity data with a
root-mean square deviation (RMSD) of 0.16 log units in viscosity, or 7.8 K in temperature. The measurements show that water
decreases the viscosity of the dacitic liquids more than for andesitic liquids, but less than for rhyolites. At low temperatures
and high water contents, andesitic liquids are more viscous than the dacitic liquids, which are in turn more viscous than
rhyolitic liquids, reversing the trend seen for high temperatures and low water contents. This suggests that the relative
viscosity of different melts depends on temperature and water content as much as on bulk melt composition and structure. At
magmatic temperatures, rhyolites are orders of magnitude more viscous than dacites, which are slightly more viscous than andesites.
During degassing, all three liquids undergo a rapid viscosity increase at low water contents, and both dacitic and andesitic
liquids will degas more efficiently than rhyolitic liquids. During cooling and differentiation, changing melt chemistry, decreasing
temperature and increasing crystal content all lead to increases in the viscosity of magma (melt plus crystals). Under closed
system conditions, where melt water content can increase during crystallization, viscosity increases may be small. Conversely,
viscosity increases are very abrupt during ascent and degassing-induced crystallization. 相似文献
15.
Anne M. Hofmeister Alan G. Whittington Maik Pertermann 《Contributions to Mineralogy and Petrology》2009,158(3):381-400
Thermal diffusivity (D) was measured using laser-flash analysis (LFA) from oriented single-crystal albite and glasses near LiAlSi3O8, NaAlSi3O8, CaAl2Si2O8, LiAlSi2O6 and CaMgSi2O6 compositions. Viscosity measurements of the supercooled liquids, over 2.6 × 108 to 8.9 × 1012 Pa s, confirm strongly non-Arrhenian behavior for CaAl2Si2O8, and CaMgSi2O6, and near-Arrhenian behavior for the others. As T increases, D
glass decreases, approaching a constant near 1,000 K. Upon crossing the glass transition, D decreases rapidly. For feldspars, D for the melt is ~15% below D of the bulk crystal, whereas for pyroxenes, this difference is ~40%. Thermal conductivity (k
lat = ρC
P
D) of crystals decreases with increasing T, but k
lat of glasses increases with T because heat capacity (C
P
) increases with T more strongly than density (ρ) and D decrease. For feldspars, k
lat for the melt is ~10% below that of the bulk crystal or glass, whereas this decrease for pyroxene is ~50%. Therefore, melting
substantially impedes heat transport, providing positive thermal feedback that could promote further melting. 相似文献
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M. Strack J. M. Waddington R. A. Bourbonniere E. L. Buckton K. Shaw P. Whittington J. S. Price 《水文研究》2008,22(17):3373-3385
Peatlands play an important role in the global carbon cycle, and loss of dissolved organic carbon (DOC) has been shown to be important for peatland carbon budgets. The objective of this study was to determine how net production and export of DOC from a northern peatland may be affected by disturbance such as drainage and climate change. The study was conducted at a poor fen containing several pool–ridge complexes: (1) control site–no water table manipulation; (2) experimental site–monitored for one season in a natural state and then subjected to a water table drawdown for 3 years; (3) drained site–subjected to a water table drawdown 9 years prior to monitoring. The DOC concentration was measured in pore water along a microtopographic gradient at each site (hummock, lawn and hollow), in standing water in pools, and in discharge from the experimental and drained sites. The initial water table drawdown released ～3 g of carbon per square metre in the form of DOC, providing a large pulse of DOC to downstream ecosystems. This value, however, represents only 1–9% of ecosystem respiration at this site. Seasonal losses of DOC following drainage were 8–11 g of carbon per square metre, representing ～17% of the total carbon exchange at the experimental study site. Immediately following water table drawdown, DOC concentrations were elevated in pore water and open water pools. In subsequent seasons, DOC concentration in the pool declined, but remained higher than the control site even 11 years after water‐table drawdown. This suggests continued elevated net DOC production under lower water table conditions likely related to an increase in vegetation biomass and larger water table fluctuations at the experimental and drained sites. However, the increase in concentration was limited to initially wet microforms (lawns and hollows) reflecting differences in vegetation community changes, water table and soil subsidence along the microtopographic gradient. Copyright © 2008 John Wiley & Sons, Ltd and Her Majesty the Queen in right of Canada. 相似文献
18.
Recent studies carried out in the Nymphe Bank area of the north Celtic Sea and in the south Irish Sea have prompted a re-assessment of the deposits formerly described as Neogene. Comparison between seismic profiles and borehole results show that the Neogene unit which underlies a boulder clay, correlates with marine sands and gravels and an earlier boulder clay. This, along with other evidence has led us to propose a Pleistocene age for this unit. The approximate extent of these deposits in the south Irish Sea and the north east Celtic Sea is indicated. 相似文献
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Graeme Whittington Paul Buckland Kevin. J. Edwards Malcolm Greenwood Adrian M. Hall Marie Robinson 《第四纪科学杂志》2003,18(2):151-168
Marine erosion at Clettnadal, West Burra island off the west coast of Shetland, caused the drainage of a small water body at Clettnadal, exposing deposits of Late Devensian and Holocene age. Pollen, diatom and invertebrate analyses have provided variable records of environmental change during stratigraphical event GI‐1. Event GS‐1 is revealed by the non‐pollen evidence, especially by Coleoptera, by sediment stratigraphy, and by radiocarbon dating. In contrast, the pollen evidence indicates that an arctic tundra flora, in which dwarf shrubs were prominent, persisted throughout the Late‐glacial. The Holocene brought colonisation by tree birch, but by ca. 9000 14C yr BP the taxon had almost disappeared. This contrasts strongly with other Holocene pollen records for Shetland where both Betula and Corylus avellana‐type survived longer—at some sites, for example, until ca. 2900 yr BP. The extreme westerly and exposed coastal situation of Clettnadal appears to be responsible both for a muted Late‐glacial response in the pollen record of terrestrial vegetation and for the early replacement of woodland by a maritime grassland. The results provoke questions concerning biological stability at times of marked climatic change. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
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