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131.
Several hundred hydrothermal vent complexes were formed in the Vøring Basin as a consequence of magmatic sill emplacement in the late Palaeocene. The 6607/12-1 exploration well was drilled through a 220-m-thick sequence of Eocene–Miocene diatomites with carbonate nodules above the apex of one of these vent complexes. Analysed calcites and dolomites from this interval have isotopic signatures typical for methane seep carbonates, with low 13C signatures of –28 to –54 PDB. The data suggest that the vent complex acted as a fluid migration pathway for about 50×106 years after its formation, leading to near-surface microbial activity and seep carbonate formation. 相似文献
132.
Angela Lundberg Pertti Ala‐Aho OleMartin Eklo Björn Klöve Jens Kværner Christine Stumpp 《水文研究》2016,30(8):1230-1250
Vast regions of the northern hemisphere are exposed to snowfall and seasonal frost. This has large effects on spatiotemporal distribution of infiltration and groundwater recharge processes as well as on the fate of pollutants. Therefore, snow and frost need to be central inherent elements of risk assessment and management schemes. However, snow and frost are often neglected or treated summarily or in a simplistic way by groundwater modellers. Snow deposition is uneven, and the snow is likely to sublimate, be redistributed and partly melt during the winter influencing the mass and spatial distribution of snow storage available for infiltration, the presence of ice layers within and under the snowpack and, therefore, also the spatial distribution of depths and permeability of the soil frost. In steep terrain, snowmelt may travel downhill tens of metres in hours along snow layers. The permeability of frozen soil is mainly influenced by soil type, its water and organic matter content, and the timing of the first snow in relation to the timing of sub‐zero temperatures. The aim with this paper is to review the literature on snow and frost processes, modelling approaches with the purpose to visualize and emphasize the need to include these processes when modelling, managing and predicting groundwater recharge for areas exposed to seasonal snow and frost. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
133.
134.
The performance of temperature‐index melt models is particularly affected by the choice of near‐surface lapse rate used to determine the sum of positive daily temperatures at different elevations, and by the choice of factor used to relate this sum to the rate of melting. Data from the Langjökull ice cap are used in this study to quantify the influence of lapse‐rate and degree‐day factor variation on temperature‐index melt simulations. The lapse rate was significantly lower during summer than in spring or autumn, as a result of diabatic cooling, reducing boundary‐layer sensitivity to free‐air temperature change. The summer lapse rate was also significantly lower than the saturated adiabatic lapse rate. A sensitivity of approximately 600 mm water equivalent (w.e.) cumulative June–August melt per 0.1 °C 100 m–1 change in lapse rate was found across a 500‐m altitude range. The sensitivity to a 1‐mm w.e. °C–1 day–1 change in degree‐day factors varied more: from approximately 500 mm w.e. cumulative summer melt at low elevation to approximately 200 mm w.e. at high elevation, reflecting the decline in melt rates associated with the greater persistence of snow with increasing altitude. The determination of a degree‐day factor for snow is complicated by the densification of the ageing snowpack, but the application of a parameterization for near‐surface density on the basis of albedo helped account for the development of snow water equivalence. Lapse rate was parameterized as a function of standardized anomalies in 750 hPa reanalysis temperature and significantly improved the simulation of cumulative summer melt compared with models applying the saturated adiabatic lapse rate. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
135.
The aim of this study is to investigate tide–surge interaction in narrow channels with complex and relatively shallow topography. A high-resolution depth-integrated tidal and storm surge model has been implemented for the Tjeldsund channel which is an important sailing lane in northern Norway. A horizontal grid resolution down to 50 m is applied in order to represent the complex bottom topography and the formation of jets and small-scale eddies. Two typically storm surge events in December 2004 have been examined in detail. The tide–surge interaction is found to influence the generation of higher harmonics and the formation of eddies in the current field. In some cases, the magnitude of storm surge currents may reach the same magnitude as the tidal currents enhancing the formation of jets and eddies. 相似文献
136.
Tamás Mikes Björn Baresel Andreas Kronz Dirk Frei István Dunkl Raimon Tolosana‐Delgado Hilmar Von Eynatten 《地学学报》2009,21(6):495-506
Three independent single‐grain geochronometers applied to detrital minerals from Central Dinaride sediments constrain the timing of felsic magmatism that associated the Jurassic evolution of the Neotethys. The Lower Cretaceous clastic wedge of the Bosnian Flysch, sourced from the Dinaride ophiolitic thrust complex, yields magmatic monazite and zircon grains with dominant age components of 164 ± 3 and 152 ± 10 Ma respectively. A unique tephra horizon within the Adriatic Carbonate Platform was dated at 148 ± 11 Ma by apatite fission track analysis. These consistent results suggest that leucocractic melt generation in the Central Dinaride segment of the Neotethys culminated in Middle to Late Jurassic times, coeval with and slightly post‐dating subophiolitic sole metamorphism. Growth of magmatic monazite and explosive volcanism call for supra‐subduction‐zone processes at the convergent Neotethyan margin. New compilation of geochronological data demonstrates that such Jurassic felsic rocks are widespread in the entire Dinaride–Hellenide orogen. 相似文献
137.
Johan Striberger Svante Björck Ívar Örn Benediktsson Ian Snowball Cintia B. Uvo Ólafur Ingólfsson Kurt H. Kjær 《第四纪科学杂志》2011,26(6):561-565
Surging outlet glaciers are important in draining large ice caps, but the mechanisms controlling surge periodicities are poorly known. We investigated a sediment sequence from the glacier‐fed Lake Lögurinn in eastern Iceland, and our unique annually resolved data, based on sedimentary varves, imply that Eyjabakkajökull, an outlet glacier of Vatnajökull, began surging about 2200 cal a BP (before 1950 AD). Approximately 1700 cal a BP, the glacier started to surge at a uniform 34‐ to 38‐year periodicity that prevailed until the coldest part of the Little Ice Age when the periodicity almost halved to 21–23 years. Since the late 1800 s the surge periodicity of Eyjabakkajökull has returned to a longer period of 35–40 years. We suggest that surge periodicities of Eyjabakkajökull are forced by climatically driven mass balance changes, which may be a common forcing factor for similar surge‐type outlet glaciers. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
138.
Carl Lilja Ewa M. Lind Björn Morén Stefan Wastegård 《Boreas: An International Journal of Quaternary Research》2013,42(3):544-554
Four cores from southwestern Sweden are presented together with their tephra geochemistry. Two cryptotephra horizons were confirmed geochemically in the cores, the Vedde Ash and the Hässeldalen Tephra. The Lateglacial Hässeldalen Tephra (11 360–11 300 cal. a BP) offers great potential as a regional isochrone to add a new degree of certainty to the deglaciation chronology of southern Sweden, including the extent of glacial Lake Bolmen. In addition, the geographical distribution of the Hässeldalen Tephra has recently been extended outside of Sweden, making it an important time‐marker horizon in northern Europe. There are potential difficulties, however. Proper identification of the actual isochrone is complicated by the vertical pattern of shard distribution, which could be the result of several eruptive events, as well as by the fact that shards from the 10‐ka Askja horizon (10 500–10 350 cal. a BP) were found in close stratigraphical proximity. The geochemical data presented are the result of improved EPMA methodology, which significantly reduces sodium mobilization. The results therefore have slightly altered values, which has consequences for classifying new finds when they are compared with previous data for geochemically similar tephras. Finally, potential indications of the Borrobol/Penifiler horizon are presented, although the existence of the horizon could not be confirmed geochemically. This highlights the need to retrieve cores from different locations within a basin based on an analysis of basin morphology if horizons are to be located. 相似文献
139.
Atsushi?KyonoEmail author Stephen?A.?Gramsch Takamitsu?Yamanaka Daijo?Ikuta Muhtar?Ahart Bj?rn?O.?Mysen Ho-kwang?Mao Russell?J.?Hemley 《Physics and Chemistry of Minerals》2012,39(2):131-141
The crystal structure of chromite FeCr2O4 was investigated to 13.7 GPa and ambient temperature with single-crystal X-ray diffraction techniques. The unit-cell parameter
decreases continuously from 8.3832 (5) to 8.2398 (11) Å up to 11.8 GPa. A fit to the Birch–Murnaghan equation of state (EoS)
based on the P–V data gives: K
0 = 209 (13) GPa, K′ = 4.0 (fixed), and V
0 = 588 (1) Å3. The FeO4 tetrahedra and CrO6 octahedra are compressed isotropically with pressure with their Fe–O and Cr–O bond distances decreasing from 1.996 (6) to
1.949 (7) Å and from 1.997 (3) to 1.969 (7) Å, respectively. The tetrahedral site occupied by the Fe2+ cation is more compressible than the octahedral site occupied by the Cr3+ cation. The resulting EoS parameters for the tetrahedral and the octahedral sites are K
0 = 147 (9) GPa, K′ = 4.0 (fixed), V
0 = 4.07 (1) Å3 and K
0 = 275 (24) GPa, K′ = 4.0 (fixed), V
0 = 10.42 (2) Å3, respectively. A discontinuous volume change is observed between 11.8 and 12.6 GPa. This change indicates a phase transition
from a cubic (space group Fd-[`3]{\overline{3}}
m) to a tetragonal structure (space group I41
/amd). At the phase transition boundary, the two Cr–O bonds parallel to the c-axis shorten from 1.969 (7) to 1.922 (17) Å and the other four Cr–O bonds parallel to the ab plane elongate from 1.969 (7) to 1.987 (9) Å. This anisotropic deformation of the octahedra leads to tetragonal compression
of the unit cell along the c-axis. The angular distortion in the octahedron decreases continuously up to 13.7 GPa, whereas the distortion in the tetrahedron
rises dramatically after the phase transition. At the pressure of the phase transition, the tetrahedral bond angles along
the c-axis direction of the unit cell begin decreasing from 109.5° to 106.6 (7)°, which generates a “stretched” tetrahedral geometry.
It is proposed that the Jahn–Teller effect at the tetrahedrally coordinated Fe2+ cation becomes active with compression and gives rise to the tetrahedral angular distortion, which in turn induces the cubic-to-tetragonal
transition. A qualitative molecular orbital model is proposed to explain the origin and nature of the Jahn–Teller effect observed
in this structure and its role in the pressure-induced phase transition. 相似文献
140.
Depositional architecture and evolution of progradationally stacked lobe complexes in the Eocene Central Basin of Spitsbergen 总被引:1,自引:0,他引:1
Sten‐Andreas Grundvåg Erik P. Johannessen William Helland‐Hansen Piret Plink‐Björklund 《Sedimentology》2014,61(2):535-569
The down‐dip portion of submarine fans comprises terminal lobes that consist of various gravity flow deposits, including turbidites and debrites. Within lobe complexes, lobe deposition commonly takes place in topographic lows created between previous lobes, resulting in an architecture characterized by compensational stacking. However, in some deep water turbidite systems, compensational stacking is less prominent and progradation dominates over aggradation and lateral stacking. Combined outcrop and subsurface data from the Eocene Central Basin of Spitsbergen provide a rare example of submarine fans that comprise progradationally stacked lobes and lobe complexes. Evidence for progradation includes basinward offset stacking of successive lobe complexes, a vertical change from distal to proximal lobe environments as recorded by an upward increase in bed amalgamation, and coarsening and thickening upward trends within the lobes. Slope clinoforms occur immediately above the lobe complexes, suggesting that a shelf‐slope system prograded across the basin in concert with deposition of the lobe complexes. Erosive channels are present in proximal axial lobe settings, whereas shallow channels, scours and terminal lobes dominate further basinward. Terminal lobes are classified as amalgamated, non‐amalgamated or thin‐bedded, consistent with turbidite deposition in lobe axis, off‐axis and fringe settings, respectively. Co‐genetic turbidite–debrite beds, interpreted as being deposited from hybrid sediment gravity flows which consisted of both turbulent and laminar flow phases, occur frequently in lobe off‐axis to fringe settings, and are rare and poorly developed in channels and axial lobe environments. This indicates bypass of the laminar flow phase in proximal settings, and deposition in relative distal unconfined settings. Palaeocurrent data indicate sediment dispersal mainly towards the east, and is consistent with slope and lobe complex progradation perpendicular to the NNW–SSE trending basin margin. 相似文献