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  • Articles  (210)
  • 1995-1999  (210)
  • Geosciences  (210)
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  • Articles  (210)
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  • 1
    Publication Date: 1998-09-01
    Print ISSN: 1070-485X
    Electronic ISSN: 1938-3789
    Topics: Geosciences
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Terra nova 9 (1997), S. 0 
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: General Circulation Models (GCMs) are currently used to predict future global change. However, the robustness of GCMs can, and should, be evaluated by their ability to simulate past climate regimes. Their success in ‘retrodiction’ can then be assessed by reference to the testimony of the geological record. Geological evidence provides a database which can be used in the estimation of sea surface temperatures and other proxy data useful in palaeoclimatic studies. These data can then be used to refine the prescribed boundary conditions for running GCMs themselves. Results of modelling experiments confirm a generally warmer Mesozoic earth with arid tropics and convective rainfall higher over the oceans than at present. Circum-polar wetlands are also indicated. Modelled cloudiness is also higher in the Mesozoic, contributing to greenhouse conditions and possibly influencing terrestrial biomes and marine ecosystems.
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 34 (1996), S. 0 
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Detailed hydrologic and water-chemistry data were collected that document the movement of bank-storage water during March 7-April 17, 1990, in an alluvial aquifer adjacent to the Cedar River, Iowa. Hydrologic data included 745 daily ground-water-level measurements from 27 observation wells. Water-chemistry data indicate that bank-storage water had smaller specific conductance and larger concentration of atrazine than ambient ground water. To quantify the movement of the bank-storage water, a two-dimensional ground-water flow model was constructed, and the resulting calibrated model accurately simulated observed conditions. Analysis of water chemistry and model results indicate that a 2-meter rise in the river stage caused bank-storage water to move horizontally at least 30 meters into the aquifer and vertically about 4 meters below the river bottom, whereas the remaining 30 percent moved laterally through the riverbank. The model also showed that bank storage caused the ground-water flux to the river to increase by a factor of five during the first three weeks of base flow after runoff and that it required about five weeks for bank-storage water to discharge from the alluvial aquifer after the peak river stage. These results quantitatively demonstrate the importance of bank storage as a source of recharge to the alluvial aquifer and as a source of water to the river during early base-flow conditions.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Sedimentology 43 (1996), S. 0 
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Coeval stratigraphic units of similar petrology occur throughout the northern Bahamas islands. The petrographic composition of these limestones provides clues about regional sea level and climate changes during the late Quaternary. At least eight fossil shoreline units, which are linked to transgressive episodes between the middle Pleistocene and the late Holocene, are recognized in the Bahamas. The petrographic composition of these units is either dominated by ooids and peloids or by bioclasts. Sedimentological observations demonstrate that oolitic-peloidal units were formed when sea level was higher than today, whereas skeletal units were deposited at or below modern ordnance datum. Skeletal units may reflect times of partial, or modest platform flooding, when the bulk of sediments brought to islands originates from bank-margin reefs. In contrast, oolitic-peloidal units correspond to major flooding events and active water circulation on the bank top. Cement fabrics further show that the early diagenesis of oolitic units took place during warm and humid climatic conditions, whereas skeletal rock bodies underwent subaerial diagenesis during drier climatic conditions characterized by marked seasonal changes. This example from the Bahamas suggests that compositional analysis of limestone from fossil carbonate platforms could be used for resolving ancient climate and sea-level changes.
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  • 5
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: To date, discussion of changes in alluvial style and in the character of palaeosols in relation to changes in accommodation and sediment supply on floodplains has primarily been from a conceptual standpoint: few case studies are available against which to test ideas. One hundred and thirty metres of non-marine strata of the Dunvegan Formation were examined in 14 closely spaced sections in the canyon of the Kiskatinaw River, NE British Columbia, Canada. This site was located about 120 km inland from the transgressive limit of the contemporary marine shoreline and represents almost exclusively freshwater environments. Fluvial channels in the Kiskatinaw River section are of two types. Small, single-storey, very fine- to fine-grained sandstone ribbons with W/T ratios 〈30, encased in fine-grained floodplain sediments are interpreted as anastomosed channels. Fine- to medium-grained, laterally accreted point-bar deposits forming multistorey sand bodies with individual W/T ratios 〉30 are interpreted as the deposits of meandering rivers filling incised valleys. Interchannel facies include the deposits of crevasse channels and splays, lakes, floodplains and palaeosols. Floodplain palaeosols consist of laterally heterogeneous, simple palaeosol profiles and pedocomplexes similar to modern Entisols, Inceptisols and hydromorphic soils. Interfluve, sequence-bounding palaeosols adjacent to incised valleys are laterally continuous, up to 3 m thick and can be reliably identified using a combination of (1) stratigraphic position; (2) field observations, such as thickness, structure, colour, degree of rooting; and (3) micromorphological features, such as evidence of bioturbation, clay coatings, ferruginous features and sphaerosiderite. Interfluve palaeosols are similar to modern Alfisols and Ultisols. Correlation of the local stratigraphic succession with the regional sequence stratigraphic framework, based on 2340 well logs and 60 outcrop sections, shows that the vertical changes in coastal plain character (more coals and lakes vs. more pedogenesis) can be related to relatively high-frequency base level cycles (eustatic?) that are expressed as transgressive–regressive marine cycles in downdip areas. Regional isopach maps show that these cycles were progressively overprinted and modified by an increasing rate of tectonic subsidence in the north and west. The character of palaeosols developed on aggrading floodplains primarily reflects local sediment supply and drainage. In contrast, well-developed interfluve palaeosols record pedogenesis during periods of reduced or negative accommodation (base level fall). Vertical changes in floodplain palaeoenvironments and palaeosol types reflect changes in accommodation rate. The detailed micromorphological analysis of interfluve palaeosols represents a powerful application of an under-used technique for the recognition of key surfaces in the geological record. This has broad implications for non-marine sequence stratigraphy.
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  • 6
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The Lower Cretaceous (Albian) upper Blairmore Group is part of a thick clastic wedge that formed adjacent to the rising Cordillera in south-western Alberta. Regional transgressive intervals are superimposed on the overall regressive succession. Alluvial conglomerates, sandstones and mudstones were deposited in east-north-eastward draining fluvial systems, orientated transverse to the basin axis. Five facies associations have been identified: igneous pebble conglomerate, thick sandstone, interbedded lenticular sandstone and mudstone, thick mudstone with thin sandstone interlayers, and fossiliferous sandstone and mudstone. The facies associations are interpreted as gravelly fluvial channels, sandy fluvial channels, sand-dominated floodplains, mud-dominated floodplains, and marine shoreline deposits, respectively.Five types of palaeosols are recognized in the upper Blairmore Group based on lithology, the presence of pedogenic features (clay coatings, root traces, ferruginous nodules, slickensides, carbonate nodules) and degree of horizonization. The regional distribution of the various types of palaeosols enables a refinement of the palaeoenvironmental reconstruction permitting an assessment of the controls on floodplain evolution. In source-proximal areas, palaeosol development was inhibited by high rates of sedimentation. In source-distal locations, poor drainage resulting from high watertables, low topography and lower rates of sedimentation also inhibited palaeosol development. The best-developed palaeosols (containing Bt horizons) occur in intermediate alluvial plain positions (tectonic hinge zone) where the floodplains were most stable due to a balance between sedimentation, erosion and subsidence rates. Extrapolating from the upper Blairmore Group suggests that the tectonic hinge zone of continental foreland basins can be established by palaeosol analysis. At the hinge zone, soil development is controlled primarily by climate and tectonics and their effect on sediment supply, whereas closer to the palaeoshoreline, relative sea level fluctuations, resulting in poor drainage, may have a more significant influence.
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Ground water monitoring & remediation 19 (1999), S. 0 
    ISSN: 1745-6592
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Water samples collected for the determination of volatile organic compounds (VOCs) are often preserved with hydrochloric acid (HCl) to inhibit the biotransformation of the analytes of interest until the chemical analyses can he performed. However, it is theoretically possible that residual free chlorine in the HCl can react with dissolved organic carbon (DOC) to form chloroform via the haloform reaction. Analyses of 1501 ground water samples preserved with HCl from the U.S. Geological Survey's National Water-Quality Assessment Program indicate that chloroform was the most commonly detected VOC among 60 VOCs monitored. The DOC concentrations were not significantly larger in samples with detectable chloroform than in those with no delectable chloroform, nor was there any correlation between the concentrations of chloroform and DOC. Furthermore, chloroform was detected more frequently in shallow ground water in urban areas (28.5% of the wells sampled) than in agricultural areas (1.6% of the wells sampled), which indicates that its detection was more related to urban land-use activities than to sample acidification. These data provide strong evidence that acidification with HCl does not lead to the production of significant amounts of chloroform in ground water samples. To verify these results, an acidification study was designed to measure the concentrations of all trihalomethanes (THMs) that can form as a result of HCl preservation in ground water samples and to determine if ascorbic acid (C6H8O6) could inhibit this reaction if it did occur. This study showed that no THMs were formed as a result of HCl acidification, and that ascorbic acid had no discernible effect on the concentrations of THMs measured.
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  • 8
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Because of its intrinsic lability, wild-type plasminogen activator inhibitor 1 (PAI-1) cannot be crystallized in its active conformation. Therefore, a stable variant of PAI-1 was used to retain the active conformation during crystallization. Four different crystallization conditions were evaluated in detail and two major types of crystals were detected. Whereas solutions consisting of either (i) cacodylate and sodium acetate, (ii) lithium sulfate and polyethylene glycol 4K, or (iii) imidazole, sodium chloride and sodium potassium phosphate buffer revealed thin platelet crystals, a solution (iv) containing ammonium acetate, citrate and polyethylene glycol 4K appeared to enhance the formation of clustered brush-like crystals. Crystals grown under condition (iii) were found to be suitable for X-ray data collection and consequent structural investigation. Data collection was 79.8% complete with a maximum resolution of 2.92 Å. Importantly, PAI-1 retained its functional properties under all conditions.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Bulletin of volcanology 59 (1998), S. 327-344 
    ISSN: 1432-0819
    Keywords: Key words Kilauea ; Volcanic processes ; Basalt ; Volatiles ; Degassing ; Mantle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  Lava drainback has been observed during many eruptions at Kilauea Volcano: magma erupts, degasses in lava fountains, collects in surface ponds, and then drains back beneath the surface. Time series data for melt inclusions from the 1959 Kilauea Iki picrite provide important evidence concerning the effects of drainback on the H2O contents of basaltic magmas at Kilauea. Melt inclusions in olivine from the first eruptive episode, before any drainback occurred, have an average H2O content of 0.7±0.2 wt.%. In contrast, many inclusions from the later episodes, erupted after substantial amounts of surface degassed lava had drained back down the vent, have H2O contents that are much lower (≥0.24 wt.% H2O). Water contents in melt inclusions from magmas erupted at Pu'u 'O'o on the east rift zone vary from 0.39–0.51 wt.% H2O in tephra from high fountains to 0.10–0.28 wt.% H2O in spatter from low fountains. The low H2O contents of many melt inclusions from Pu'u 'O'o and post-drainback episodes of Kilauea Iki reveal that prior to crystallization of the enclosing olivine host, the melts must have exsolved H2O at pressures substantially less than those in Kilauea's summit magma reservoir. Such low-pressure H2O exsolution probably occurred as surface degassed magma was recycled by drainback and mixing with less degassed magma at depth. Recognition of the effects of low-pressure degassing and drainback leads to an estimate of 0.7 wt.% H2O for differentiated tholeiitic magma in Kilauea's summit magma storage reservoir. Data for MgO-rich submarine glasses (Clague et al. 1995) and melt inclusions from Kilauea Iki demonstrate that primary Kilauean tholeiitic magma has an H2O/K2O mass ratio of ∼1.3. At transition zone and upper mantle depths in the Hawaiian plume source, H2O probably resides partly in a small amount of hydrous silicate melt.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Climate dynamics 12 (1996), S. 497-511 
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A range of diagnostics from two GCM simulations, one of the present-day climate and one of the last glacial maximum (LGM) is used to gain insight into their different temperature structures and eddy dynamics. There are large local increases in baroclinicity at the LGM, especially in the Atlantic storm track, with large accompanying increases in the low level transient eddy heat flux. However, the differences in the zonal mean are much smaller, and the increases in both baroclinicity and heat flux are confined to low levels. Supplementary experiments with baroclinic wave lifecycles confirm the marked contrast between local and zonal mean behaviour, but do not adequately explain the differences between the zonal mean climates. The total flux of energy across latitude circles in the Northern Hemisphere does not change much during DJF, although its transient component is actually reduced at the LGM (during JJA the transient component is increased). Calculations of total linear eddy diffusivity reveal that changes in the time mean stationary waves are chiefly responsible for the seasonal range of this quantity at the LGM, while they only account for half the seasonal range at the present-day.
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