Controls on fluvial sedimentary architecture and sediment‐fill state in salt‐walled mini‐basins: Triassic Moenkopi Formation,Salt Anticline Region,SE Utah,USA     

Steven G. Banham  Nigel P. Mountney 《Basin Research》2013,25(6):709-737

The Triassic Moenkopi Formation in the Salt Anticline Region, SE Utah, represents the preserved record of a low‐relief ephemeral fluvial system that accumulated in a series of actively subsiding salt‐walled mini‐basins. Development and evolution of the fluvial system and its resultant preserved architecture was controlled by the following: (1) the inherited state of the basin geometry at the time of commencement of sedimentation; (2) the rate of sediment delivery to the developing basins; (3) the orientation of fluvial pathways relative to the salt walls that bounded the basins; (4) spatially and temporally variable rates and styles of mini‐basin subsidence and associated salt‐wall uplift; and (5) temporal changes in regional climate. Detailed outcrop‐based tectono‐stratigraphic analyses demonstrate how three coevally developing mini‐basins and their intervening salt walls evolved in response to progressive sediment loading of a succession of Pennsylvanian salt (the Paradox Formation) by the younger Moenkopi Formation, deposits of which record a dryland fluvial system in which flow was primarily directed parallel to a series of elongate salt walls. In some mini‐basins, fluvial channel elements are stacked vertically within and along the central basin axes, in response to preferential salt withdrawal and resulting subsidence. In other basins, rim synclines have developed adjacent to bounding salt walls and these served as loci for accumulation of stacked fluvial channel complexes. Neighbouring mini‐basins exhibit different styles of infill at equivalent stratigraphic levels: sand‐poor basins dominated by fine‐grained, sheet‐like sandstone fluvial elements, which are representative of nonchannelised flow processes, apparently developed synchronously with neighbouring sand‐prone basins dominated by major fluvial channel‐belts, demonstrating effective partitioning of sediment route‐ways by surface topography generated by uplifting salt walls. Reworked gypsum clasts present in parts of the stratigraphy demonstrate the subaerial exposure of some salt walls, and their partial erosion and reworking into the fill of adjoining mini‐basins during accumulation of the Moenkopi Formation. Complex spatial changes in preserved stratigraphic thickness of four members in the Moenkopi Formation, both within and between mini‐basins, demonstrates a complex relationship between the location and timing of subsidence and the infill of the generated accommodation by fluvial processes.  相似文献   

How much physical complexity is needed to model flood inundation?     

Jeffrey Neal  Ignacio Villanueva  Nigel Wright  Thomas Willis  Timothy Fewtrell  Paul Bates 《水文研究》2012,26(15):2264-2282

Two‐dimensional flood inundation models are widely used tools for flood hazard mapping and an essential component of statutory flood risk management guidelines in many countries. Yet, we still do not know how much physical complexity a flood inundation model needs for a given problem. Here, three two‐dimensional explicit hydraulic models, which can be broadly defined as simulating diffusive, inertial or shallow water waves, have been benchmarked using test cases from a recent Environment Agency for England and Wales study, where results from industry models are also available. To ensure consistency, the three models were written in the same code and share subroutines for all but the momentum (flow) and time‐stepping calculations. The diffusive type model required much longer simulation times than the other models, whilst the inertia model was the quickest. For flows that vary gradually in time, differences in simulated velocities and depths due to physical complexity were within 10% of the simulations from a range of industry models. Therefore, for flows that vary gradually in time, it appears unnecessary to solve the full two‐dimensional shallow water equations. As expected, however, the simpler models were unable to simulate supercritical flows accurately. Finally, implications of the results for future model benchmarking studies are discussed in light of a number of subtle factors that were found to cause significant differences in simulations relative to the choice of model. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Smoothing of digital elevation models and the alteration of overland flow path length distributions     

Nigel Van Nieuwenhuizen  John B. Lindsay  Ben DeVries 《水文研究》2021,35(7):e14271

DEM smoothing is a common pre-processing technique used to remove undesirable roughness from a DEM. However, it is hypothesized that smoothing straightens and reduces the length of overland flow paths, which is an important factor controlling modelled time-to-peak flow. Currently, there is a lack of research comparing how different smoothing techniques alter the distribution of overland flow path length. Four low-pass filtering techniques were applied to three fine-resolution LiDAR DEMs of varying relief: the mean filter, the median filter, the Gaussian filter, and the feature-preserving DEM smoothing (FPDEMS) filter, each with different degrees of smoothing. Downslope-distance-to-stream distributions were then derived using D8 and D∞ flow directions and statistically compared to distributions derived from the unsmoothed DEM for each study site. The results indicate that the alteration of flow path length distributions as a result of smoothing is complex. Mean flow path lengths may decrease or increase in response to smoothing, depending on landscape relief and the derivation of flow directions, and generalized flow paths may become longer. The largest increase in mean flow path lengths was 19.2 m using the 21 × 21 median filter and D8 flow directions in the high-relief study site, relative to an unsmoothed mean length of 138.6 m in this site. The largest decrease in mean flow path length was 48.9 m using the 21 × 21 mean filter and D∞ flow directions in the low-relief study site, relative to an unsmoothed mean length of 290.9 m in this site. Furthermore, minimal flow path length alterations were achieved with the Gaussian filter when gentle smoothing is required, and with the FPDEMS filter when moderate to aggressive smoothing is required. These results suggest that an appropriate smoothing method should be chosen based on the relief of the landscape and the degree of smoothing required.  相似文献   

Oxygen stable isotope ratios from British oak tree-rings provide a strong and consistent record of past changes in summer rainfall     

Giles H. F. Young  Neil J. Loader  Danny McCarroll  Roderick J. Bale  Joanne C. Demmler  Daniel Miles  Nigel T. Nayling  Katja T. Rinne  Iain Robertson  Camilla Watts  Matthew Whitney 《Climate Dynamics》2015,45(11-12):3609-3622

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Simulating the Carbon Cycling of Northern Peatlands Using a Land Surface Scheme Coupled to a Wetland Carbon Model (CLASS3W-MWM)     

Jianghua Wu  Nigel T. Roulet  Mats Nilsson  Peter Lafleur  Elyn Humphreys 《大气与海洋》2013,51(4):487-506

Northern peatlands store approximately one-third of the terrestrial soil carbon (C), although they cover only 3% of the global land mass. Northern peatlands can be subdivided into bogs and fens based on their hydrology and biogeochemistry. Peatland hydrology and biogeochemistry are tightly coupled to climate and, therefore, may be very sensitive to climate variability and change. To address the fate of the large peatland soil C storage under a future changed climate, a peatland C model, the McGill Wetland Model (MWM), was coupled to a land surface climate model (the wetland version of the Canadian Land Surface Scheme, CLASS3W), referred as CLASS3W-MWM. We evaluated the CLASS3W-MWM for a bog (Mer Bleue, located at 45.41°N, 75.48°W, in eastern Canada) and a poor fen (Degerö Stormyr, located at 64°11′N, 19°33′E, in northern Sweden).

CLASS3W-MWM captured the magnitude and direction of the present day C cycling very well for both bogs and fens. Moreover, the seasonal and interannual variability were reproduced reasonably well. Root mean square errors (RMSE) were <0.65 and the degree of agreements (d*) were >0.8 for the components of net ecosystem production (NEP) for both the Mer Bleue bog and the Degerö Stormyr fen. The performance of the coupled model for both bog and fen is similar to that of the stand-alone MWM driven by observed weather rather than simulated surface and soil climate. This modelling study suggests that northern peatlands are hydrologically and thermally conservative ecosystems. It was also shown that C cycling for bogs and fens was more sensitive to changes in air temperature than precipitation. Changes in temperature within the Intergovernmental Panel on Climate Change (IPCC) projected range switch the peatlands from a present-day C sink to a source, but projected changes in precipitation still maintain the peatlands as a C sink, although to a somewhat lesser degree. Increase in atmospheric CO₂ concentration enhances C sequestration for both bogs and fens. Our sensitivity analysis suggests that northern peatlands respond to changes in temperature, precipitation and doubled CO₂ concentration in a highly non-linear way. The sensitivity of C cycling in northern peatlands with respect to changes in air temperature, precipitation and the concentration of atmospheric CO₂ together is not a simple addition or subtraction of the sensitivity of the individual changes. Therefore, the sensitivity of a combination of changes in temperature, precipitation and doubled CO₂ concentration is very different from the sensitivity of peatlands to each environmental variable on their own. Our sensitivity analysis suggests that fens have a narrower tolerance to climate changes than bogs.

RÉSUMÉ [Traduit par la rédaction] Les tourbières du Nord renferment approximativement le tiers du carbone se trouvant dans le sol terrestre, même si elles ne couvrent que 3% des terres du globe. On peut subdiviser les tourbières du Nord en tourbières hautes et en tourbières basses selon leur hydrologie et leur biogéochimie. L'hydrologie et la biogéochimie des tourbières sont intimement liées au climat et peuvent donc être très sensibles à la variabilité et au changement climatique. Pour étudier comment évoluera le stockage du carbone dans les grands terrains tourbeux sous un climat futur modifié, nous avons couplé un modèle de carbone de tourbière, le McGill Wetland Model (MWM), à un modèle climatique de surface terrestre (la version terres humides du CLASS3W canadien), c'est-à-dire le CLASS3W–MWM. Nous avons évalué le CLASS3W–MWM pour une tourbière haute (Mer Bleue, situé à 45,41°N, 75,48°O, dans l'est du Canada) et pour une tourbière basse ombrotrophe (Degerö Stormyr, situé à 64°11′N, 19°33′E, dans le nord de la Suède).

Le CLASS3W–MWM a très bien capturé la grandeur et la direction du recyclage actuel du carbone, tant pour les tourbières hautes que pour les tourbières basses. De plus, la variabilité saisonnière et interannuelle a été raisonnablement bien reproduire. Les écarts-types étaient <0,65 et les degrés de concordance (d*) étaient >0,8 pour les composantes de la production nette de l’écosystème tant pour la tourbière haute Mer Bleue que pour la tourbière basse Degerö Stormyr. La performance du modèle couplé pour la tourbière haute et la tourbière basse est semblable à celle du MWM autonome piloté par des conditions observées plutôt que par un climat simulé de la surface et du sol. Cette étude par modèle suggère que les tourbières du Nord sont des écosystèmes hydrologiquement et thermiquement conservatifs. Il a aussi été démontré que le recyclage du carbone pour les tourbières hautes et basses était plus sensible aux changements dans la température de l'air que dans les précipitations. Des changements de température de l'ordre de ceux projetés par le Groupe d'experts intergouvernemental sur l’évolution du climat (GIEC) font que les actuels puits de carbone que constituent les tourbières se transforment en sources, mais les changements projetés dans les précipitations maintiennent encore les tourbières comme des puits de carbone, quoique dans une moindre mesure. L'accroissement de la concentration du CO₂ atmosphérique améliore la séquestration du carbone à la fois pour les tourbières hautes et les tourbières basses. Notre analyse de sensibilité suggère que les tourbières du Nord réagissent aux changements dans la température et les précipitations et à une concentration doublée de CO₂ d'une façon fort peu linéaire. La sensibilité du recyclage du carbone dans les tourbières du Nord par rapport aux changements dans la température de l'air, les précipitations et la concentration du CO₂ atmosphérique ensemble n'est pas une simple addition ou soustraction de la sensibilité aux changements individuels. Par conséquent, la sensibilité à une combinaison de changements dans la température et les précipitations et à une concentration doublée de CO₂ est très différente de la sensibilité des tourbières à chaque variable environnementale prise seule. Notre analyse de sensibilité suggère que les tourbières basses ont une plus faible tolérance aux changements climatiques que les tourbières hautes.  相似文献   

The global-scale impacts of climate change on water resources and flooding under new climate and socio-economic scenarios   总被引：4，自引：3，他引：1  

Nigel W. Arnell  Ben Lloyd-Hughes 《Climatic change》2014,122(1-2):127-140

This paper presents a preliminary assessment of the relative effects of rate of climate change (four Representative Concentration Pathways - RCPs), assumed future population (five Shared Socio-economic Pathways - SSPs), and pattern of climate change (19 CMIP5 climate models) on regional and global exposure to water resources stress and river flooding. Uncertainty in projected future impacts of climate change on exposure to water stress and river flooding is dominated by uncertainty in the projected spatial and seasonal pattern of change in climate. There is little clear difference in impact between RCP2.6, RCP4.5 and RCP6.0 in 2050, and between RCP4.5 and RCP6.0 in 2080. Impacts under RCP8.5 are greater than under the other RCPs in 2050 and 2080. For a given RCP, there is a difference in the absolute numbers of people exposed to increased water resources stress or increased river flood frequency between the five SSPs. With the ‘middle-of-the-road’ SSP2, climate change by 2050 would increase exposure to water resources stress for between approximately 920 and 3,400 million people under the highest RCP, and increase exposure to river flood risk for between 100 and 580 million people. Under RCP2.6, exposure to increased water scarcity would be reduced in 2050 by 22-24 %, compared to impacts under the RCP8.5, and exposure to increased flood frequency would be reduced by around 16 %. The implications of climate change for actual future losses and adaptation depend not only on the numbers of people exposed to changes in risk, but also on the qualitative characteristics of future worlds as described in the different SSPs. The difference in ‘actual’ impact between SSPs will therefore be greater than the differences in numbers of people exposed to impact.  相似文献   

12th Quadrennial Symposium of the International Association on the Genesis of Ore Deposits （IAGOD）Moscow, Russia, August 20-24, 2006     

Sergei Cherkasov Nigel Cook Reimar Seltmann 《《幕》》2006,29(4):289-290

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Feature: The sedimentary signature of deserts and their response to environmental change     

Nigel P. Mountney 《Geology Today》2004,20(3):101-106

Desert sedimentary systems comprise a variety of related sub-environments including aeolian dunes, intervening interdunes, sandsheets, salt flats, playa lakes, ephemeral fluvial systems and alluvial fans. These are highly sensitive, and undergo subtle but systematic morphological and sedimentary adjustments in response to externally-imposed environmental change. This article presents a dynamic model explaining how desert successions – particularly aeolian dune and interdune environments – are determined both by intrinsic sedimentary behaviour, such as dune migration, and by the imposition of externally-forced changes such as climate change.  相似文献   

A palaeomagnetic study of the Builth Wells-Llandrindod Wells Ordovician Inlier, Wales: palaeogeographic and structural implications     

Allan Trench  Trond H. Torsvik  Mark A. Smethurst  Nigel H. Woodcock  Richard Metcalfe 《Geophysical Journal International》1991,105(2):477-489

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