Character and distribution of hybrid sediment gravity flow deposits from the outer Forties Fan, Palaeocene Central North Sea, UKCS   总被引：1，自引：0，他引：1  

Christopher Davis  Peter Haughton  William McCaffrey  Erik Scott  Nicholas Hogg  David Kitching 《Marine and Petroleum Geology》2009,26(10):1919

Seven categories of event bed (1–7) are recognised in cores from hydrocarbon fields in the outer part of the Palaeocene Forties Fan, a large mixed sand-mud, deep-water fan system in the UK and Norwegian Central North Sea. Bed Types 1, 6 and 7 resemble conventional high-density turbidite, debrite and low-density turbidite, respectively. However the cores are dominated by distinctive hybrid event beds (Types 2–5; 81% by thickness) that comprise an erosively-based graded and structureless and/or banded sandstone overlain by an argillaceous sandstone or sandy-mudstone unit containing mudstone-clasts and common carbonaceous fragments. Many of the hybrid beds are capped by a thin laminated sandstone–mudstone couplet (the deposit of a dilute wake behind the head of the turbidity current). Different types of hybrid event bed Types are defined on the basis of the ratio of sandier lower part to upper argillaceous part of the bed, and the internal structure, particularly the presence of banding. Although the argillaceous and clast-rich upper divisions could reflect post-depositional mixing, sand injection or substrate deformation, they can be shown to be dominantly primary depositional features and record both a temporal (and by implication) spatial change from turbidite to debrite deposition beneath rheologically complex hybrid flows. Where banding occurs between lower sandy and upper argillaceous divisions, the flow may have passed through a transitional flow regime. Significantly, the often soft-sediment sheared and partly sand-injected argillaceous divisions are present in cores both close to and remote from salt diapirs and hence are not a local product of remobilisation around salt-cored topography. Lateral correlations between wells establish that sandy hybrid beds (Types 2, 3S) pass down-dip and laterally into packages dominated by muddier hybrid beds (Types 3M, 4) over relatively short distances (several km). Type 5 beds have minimal or no lower sandier divisions, implying that the debritic component outran the sandier component of the flow. The Forties hybrid beds are thought to record flow transformations affecting fluidal flows following erosion and bulking with mudstone clasts and clays that suppressed near-bed turbulence and induced a change to plastic flow. Hybrid beds dominate the muddier parts of sandying-upward, muddying-upward and sandying to muddying-upward successions, interpreted to record splay growth and abandonment, overall fan progradation, and local non-uniformity effects that either delayed or promoted the onset of flow transformations. The dominance of hybrid event beds in the outer Forties Fan may reflect very rapid delivery of sand to the basin, an uneven substrate that promoted flow non-uniformity, tilting as a consequence of source area uplift and extensive inner-fan erosion to create deep fan valleys. This combination of factors could have promoted erosion and bulking, and hence transformations leading to the predominance of hybrid beds in the outer parts of the fan.  相似文献   

Nutrient transport from an artificial upwelling of deep sea water     

Nicholas Williamson  Atsuki Komiya  Shigenao Maruyama  Masud Behnia  Steve W. Armfield 《Journal of Oceanography》2009,65(3):349-359

The transport of nutrient-rich, deep sea water from an artificial upwelling pipe has been simulated. A numerical model has been built within a commercial Computational Fluid Dynamics (CFD) package. The model considers the flow of the deep sea water after it is ejected from the pipe outlet in a negatively buoyant plume (densimetric Froude number = −2.6), within a stably stratified ocean environment subject to strong ocean current cross flow. Two cross-flow profiles were tested with momentum flux ratios equal to 0.92 and 3.7. The standard k-ε turbulence model has been employed and a range of turbulent Schmidt and Prandtl numbers tested. In all cases the results show that the rapid diffusion of heat and salinity at the pipe outlet causes the plume to attain neutral buoyancy very rapidly, preventing strong fountain-like behavior. At the higher momentum flux ratio fountain-like behavior is more pronounced close to the pipe outlet. The strong cross-current makes horizontal advection the dominant transport process downstream. The nutrient plume trajectory remains largely within one relatively thin stratified layer, making any ocean cross-flow profile less important. Very little unsteady behavior was observed. The results show that the nutrient is reduced to less than 2% of its inlet concentration 10 meters downstream of the inlet and this result is largely independent of turbulent Prandtl or Schmidt number. Initial results would suggest that if such an artificial upwelling were to be viable for an ocean farming project, a large number of upwelling pipes would be necessary. Further work will have to determine the minimum nutrient concentration required to sustain a viable phytoplankton population and the required spacing between upwelling pipes.  相似文献   

Correction to: An integrated framework of coastal flood modelling under the failures of sea dikes: a case study in Shanghai     

Ke  Qian  Yin  Jiangshan  Bricker  Jeremy D.  Savage  Nicholas  Buonomo  Erasmo  Ye  Qinghua  Visser  Paul  Dong  Guangtao  Wang  Shuai  Tian  Zhan  Sun  Laixiang  Toumi  Ralf  Jonkman  Sebastiaan N. 《Natural Hazards》2021,109(1):705-706

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The California water model: Resilience through failure     

Nicholas Pinter  Jay Lund  Peter Moyle 《水文研究》2019,33(12):1775-1779

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Patagonian ash on sub‐Antarctic South Georgia: expanding the tephrostratigraphy of southern South America into the Atlantic sector of the Southern Ocean          下载免费PDF全文

Lea Toska Oppedal  Willem G. M. van der Bilt  Nicholas L. Balascio  Jostein Bakke 《第四纪科学杂志》2018,33(5):482-486

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Internal structure and significance of ice‐marginal moraine in the Kebnekaise Mountains,northern Sweden     

Toby N. Tonkin  Nicholas G. Midgley  David J. Graham  Jillian C. Labadz 《Boreas: An International Journal of Quaternary Research》2017,46(2):199-211

Despite a long history of glaciological research, the palaeo‐environmental significance of moraine systems in the Kebnekaise Mountains, Sweden, has remained uncertain. These landforms offer the potential to elucidate glacier response prior to the period of direct monitoring and provide an insight into the ice‐marginal processes operating at polythermal valley glaciers. This study set out to test existing interpretations of Scandinavian ice‐marginal moraines, which invoke ice stagnation, pushing, stacking/dumping and push‐deformation as important moraine forming processes. Moraines at Isfallsglaciären were investigated using ground‐penetrating radar to document the internal structural characteristics of the landform assemblage. Radar surveys revealed a range of substrate composition and reflectors, indicating a debris‐ice interface and bounding surfaces within the moraine. The moraine is demonstrated to contain both ice‐rich and debris‐rich zones, reflecting a complex depositional history and a polygenetic origin. As a consequence of glacier overriding, the morphology of these landforms provides a misleading indicator of glacial history. Traditional geochronological methods are unlikely to be effective on this type of landform as the fresh surface may post‐date the formation of the landform following reoccupation of the moraine rampart by the glacier. This research highlights that the interpretation of geochronological data sets from similar moraine systems should be undertaken with caution.  相似文献   

The role of land surface versus drainage network characteristics in controlling water quality and quantity in a small urban watershed          下载免费PDF全文

Katherine L. Meierdiercks  Mary Beth Kolozsvary  Kevin P. Rhoads  Michele Golden  Nicholas F. McCloskey 《水文研究》2017,31(24):4384-4397

The processes that control run‐off quantity and quality in urban watersheds are complex and not well understood. Although impervious surface coverage has traditionally been used to examine altered hydrologic response in urban watersheds, several studies suggest that other elements of the urban landscape, particularly those associated with urban infrastructure and the drainage system, play an equally important role. The relative importance of impervious surfaces, stormwater ponds, expansion of the drainage network, and drainage network structures in controlling hydrologic response was examined in the subwatersheds of the Kromma Kill, an urban watershed located in Albany County, NY. In this study, geographic information systems was used to compute geospatial land surface and drainage network properties of 5 Kromma Kill subwatersheds. In these same subwatersheds, water quantity (rainfall and run‐off) and quality (macroinvertebrates, nitrate, total nitrogen, dissolved oxygen, total dissolved solids, and nonpurgable organic carbon) parameters were measured. Strong and significant correlations were identified between land surface and drainage network properties and field observations. Causal relationships were then tested using the Environmental Protection Agency's Stormwater Management Model. Field and model analyses suggest that whereas percent imperviousness is a dominant control on water quality, drainage density and slope are equally important. However, for water quantity, whereas imperviousness is positively correlated with increased run‐off volumes, drainage network properties and slope are the dominant controls on run‐off volumes. Results have important implications for stormwater management plans, especially those aimed at reducing the effective impervious surface coverage of urban watersheds. Reducing the percentage of effective imperviousness in a watershed is not a “one size fits all” solution and can help to meet some management objectives, such as reducing nitrogen concentrations and improving water quality, but may not serve as the most effective, and therefore economical, solution for every management objective including reducing run‐off volumes.  相似文献   

Suspended sediment monitoring in alluvial gullies: A laboratory and field evaluation of available measurement techniques     

Nicholas J. C. Doriean  Andrew P. Brooks  Peter R. Teasdale  David T. Welsh  William W. Bennett 《水文研究》2020,34(16):3426-3438

Gully erosion is a significant source of fine suspended sediment (<63 μm) and associated nutrient pollution to freshwater and marine waterways. Researchers, government agencies, and monitoring groups are currently using monitoring methods designed for streams and rivers (e.g., autosamplers, rising stage samplers, and turbidity loggers) to evaluate suspended sediment in gullies. This is potentially problematic because gullies have several hydrological features and monitoring operational challenges that differ to those of continually flowing streams and rivers (e.g., short and intense flows, high suspended sediment concentrations, and rapid scouring and aggradation). Here we present a laboratory and field-based assessment of the performance of common suspended sediment monitoring techniques applied to gullies. We also evaluate a recently-described method; the pumped active suspended sediment (PASS) sampler, which has been modified for monitoring suspended sediment in gully systems. Discrete autosampling provided data at high temporal resolution, however, it had poor collection efficiency (25 ± 10%) of coarser sediment particles (i.e., sand). Rising stage sampling, while robust and cost-effective, suffered from large amounts of condensation under field conditions (25–35% of sampler volume), due to harsh climatic conditions creating large diurnal temperature differences at the field site, thereby diluting sample concentrations and introducing additional measurement uncertainty. The turbidity logger exhibited a highly variable response when calibrated at each site with physically collected suspended sediment samples (R² = 0.17–0.83), highlighting that this approach should be used with caution. The modified PASS sampler proved to be a reliable and representative measurement method for gully sediment water quality, however, the time-integrated nature of the method limits its temporal resolution compared to the other monitoring methods. We recommend monitoring suspended sediment in alluvial gully systems using a combination of complementary techniques (e.g., PASS and RS samplers) to account for the limitations associated with individual methods.  相似文献   

Rupture complexity of a moderate intraplate earthquake in the Alps: the 1996 M5 Epagny–Annecy earthquake     

Françoise Courboulex  Nicholas Deichmann  & Jean-Christophe Gariel 《Geophysical Journal International》1999,139(1):152-160

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An individual-component approximation to quadratic stress for flow-decomposition analysis     

Adele Militello  Nicholas C. Kraus 《Ocean Engineering》1999,26(11):1039

An individual-component approximation (ICA) to the one-dimensional quadratic stress is presented for analysis of hydrodynamic systems that contain multiple-frequency fluid motion such as tidal current and nearshore currents. Criteria governing development of the approximation are accuracy, symmetry, and preservation of contributions (magnitude and direction) of individual and coupled velocity components. Preservation of directionality is required to isolate functioning of individual terms for flow-decomposition analysis. The ICA is compared with the small-amplitude approximation analytically and through numerical examination for two velocity components. The two approximations differ at second order within the range of validity of the small-amplitude approximation. The ICA is exact in the limits of components with large magnitudes and components of equal magnitudes. Based on calculations comparing the exact numerical solution for velocity components with a wide range of relative magnitudes, relative periods, and phase differences, the ICA is accurate except in restricted regions of small-magnitude quadratic velocity. The ICA is generalized to multiple components without restriction on magnitude, period, or phase, and example calculations are given for flows comprised of three components and six components. The method is applied to velocity tidal constituents for Galveston Bay, Texas, and Tampa Bay, Florida.  相似文献