Stochastic Representation of Sedimentary Geology     

M. K. Elmouttie  G. Krähenbühl  G. V. Poropat  I. Kelso 《Rock Mechanics and Rock Engineering》2014,47(2):507-518

Discrete fracture network representations of discontinuities in rock masses have been shown to be useful in capturing heterogeneity in rock mass properties. Providing computational efficiency in the resulting simulations and analyses is attained, these fracture representations can be combined with structural modelling and sampling algorithms. Multiple fracture network realisations can be generated and the resulting rock mass properties interrogated. Statistical analyses based on fracture connectivity, block size distribution and slope stability can be performed and provide results defined in terms of confidence intervals. For sedimentary geology consisting of dense bedding, equivalent medium continuum methods have traditionally been used in preference to discrete fracture representations due to the large numbers of structures involved and resulting computational complexity. In this paper, it is shown that stochastic representation of these layers can be employed. An analytical solution to accommodate bedding given an assumed block size distribution has been derived. Using this formulation, polyhedral modelling has been used to investigate the influence of bedding on block formation and block size distributions using field data. It is shown that the analysis is both computationally efficient and can capture truncation of size distribution by such layers without numerical methods.  相似文献   

On the role of tides and strong wind events in promoting summer primary production in the Barents Sea     

Vincent Le Fouest  Clare PostlethwaiteMiguel Angel Morales Maqueda  Simon BélangerMarcel Babin 《Continental Shelf Research》2011,31(17):1869-1879

Tides and wind-driven mixing play a major role in promoting post-bloom productivity in subarctic shelf seas. Whether this is also true in the high Arctic remains unknown. This question is particularly relevant in a context of increasing Arctic Ocean stratification in response to global climatic change. We have used a three-dimensional ocean-sea ice-plankton ecosystem model to assess the contribution of tides and strong wind events to summer (June-August 2001) primary production in the Barents Sea. Tides are responsible for 20% (60% locally) of the post-bloom primary production above Svalbard Bank and east of the Kola Peninsula. By contrast, more than 9% of the primary production is due to winds faster than 8 m s⁻¹ in the central Barents Sea. Locally, this contribution reaches 25%. In the marginal ice zone, both tides and wind events have only a limited effect on primary production (<2%). Removing tides or winds faster than 8 m s⁻¹ promotes a regime more sustained by regenerated production with a f-ratio (i.e. the proportion of nitrate-based “new” primary production in the total primary production) that decreases by up to 26% (east of the Kola Peninsula) or 35% (central Barents Sea), respectively. When integrated over all Barents Sea sub-regions, tides and strong wind events account, respectively, for 6.8% (1.55 Tg C; 1 Tg C=10¹² g C) and 4.1% (0.93 Tg C) of the post-bloom primary production (22.6 Tg C). To put this in context, this contribution to summer primary production is equivalent to the spring bloom integrated over the Svalbard area. Tides and winds are significant drivers of summer plankton productivity in the Barents Sea.  相似文献   

Quantifying large‐scale historical formation of accommodation in the Mississippi Delta     

Robert A. Morton  Julie C. Bernier  Kyle W. Kelso  John A. Barras 《地球表面变化过程与地形》2010,35(14):1625-1641

Large volumes of new accommodation have formed within the Mississippi Delta plain since the mid‐1950s in association with rapid conversion of coastal wetlands to open water. The three‐dimensional aspects and processes responsible for accommodation formation were quantified by comparing surface elevations, water depths, and vertical displacements of stratigraphic contacts that were correlated between short sediment cores. Integration of data from remotely sensed images, sediment cores, and water‐depth surveys at 10 geologically diverse areas in the delta plain provided a basis for estimating the total volume of accommodation formed by interior‐wetland subsidence and subsequent erosion. Results indicate that at most of the study areas subsidence was a greater contributor than erosion to the formation of accommodation associated with wetland loss. Tens of millions of cubic meters of accommodation formed rapidly at each of the large open‐water bodies that were formerly continuous interior delta‐plain marsh. Together the individual study areas account for more than 440 × 10⁶ × m³ of new accommodation that formed as holes in the Mississippi River delta‐plain fabric between 1956 and 2004. This large volume provides an estimate of the new sediment that would be needed just at the study areas to restore the delta‐plain wetlands to their pre‐1956 areal extent and elevations. Published 2010. This article is a US Government work and is in the public domain in the USA.  相似文献   

Rethinking responsibility and care for a postcolonial world     

Parvati Raghuram  Clare Madge 《Geoforum》2009,40(1):5-13

Both responsibility and care have much to offer in thinking through the relationalities that make up a postcolonial world. Although contemporary political systems often posit responsibility and care within the context of individuated and autonomous selves, geographers have done much to relocate responsibility and care within narratives of interdependency - spatially and temporally. They have argued that both terms offer a route for thinking about ethical geographical relations between myriad places. In this article we take this project further, by looking at how the nature and shape of these relationships might be construed in a postcolonial world. We suggest that, through a more critical engagement with postcolonial thinking, any exploration of existing practices of responsibility and care will not only reveal the enormous potential of imagining these geographies as forms of existing and evolving relationalities, but will also lead us to interrogate the deployments of these terms in the context of past and present inequalities. We show that routing care and responsibility through postcolonial geographies moves us towards a more pragmatic responsiveness, one that involves a ‘care-full’ recognition of postcolonial interaction.  相似文献   

A new method for the separation of paramagnetic and ferromagnetic susceptibility anisotropy using low field and high field methods     

Paul R. Kelso  Basil Tikoff  Mike Jackson  W. Sun 《Geophysical Journal International》2002,151(2):345-359

  相似文献   

The effect of salinity on the development ofLoxothylacus panopaei larvae (Crustacea: Cirripedia: Rhizocephala)     

Graham Walker  Anthony S. Clare 《Estuaries and Coasts》1994,17(1):276-282

The rhizocephalan barnacleLoxothylacus panopaei, which parasitizes the mud crabRhithropanopeus harrisii, releases its larvae as nauplii. The nauplii develop through four stages to the cypris stage; both larval forms are lecithotrophs. Parasitized crabs were acclimated in 10‰, 15‰, and 20‰ water during August and the development of releasedL. panopaei larvae was monitored in a range of salinities. After 48–60 h, the nauplii and cyprids in each experimental salinity were counted and the numbers used to calculate a developmental index. The range of salinities in which successful development to cyprids occurred (developmental index >70%) could be shifted as a consequence of the acclimating salinity.L. panopaei larvae can develop successfully over a 10–30‰ salinity range, indicating that settlement onto host crabs and virgin externae is likely to take place in nature within this range.  相似文献   

Benthic Oxygen Consumption and Organic Matter Turnover in Organic-poor, Permeable Shelf Sands     

Antje Rusch  Markus Huettel  Christian Wild  Clare E. Reimers 《Aquatic Geochemistry》2006,12(1):1-19

The high permeability of sediments and strong near-bottom currents cause seawater to infiltrate the surface layers of Middle Atlantic Bight shelf deposits. In this study, sandy sediment cores from 11 to 12 m water depth were percolated with filtered seawater on shipboard. Sedimentary oxygen consumption (SOC) increased non-linearly with pore water flow, approaching maximum rates of 120 mmol m⁻² d⁻¹ (May 2001) or 75 mmol m⁻² d⁻¹(July 2001). The addition of acetate to the inflowing water promptly enhanced the release of dissolved inorganic carbon (DIC) from the cores. DIC production rates were a linear function of acetate concentration, ranging from 100 to 300 mmol m⁻² d⁻¹ without substrate addition to 572 mmol m⁻² d⁻¹ with 100 mM acetate. The sediments also hydrolyzed a glucose pseudopolymer, and the liberated glucose prompted an increase of SOC. Our results suggest that decomposition rates of organic matter in permeable sands can exceed those of fine-grained, organic-rich deposits, when water currents cause advective interstitial flow, supplying the subsurface microbial community with degradable material and electron acceptors. We conclude that the highly permeable sand beds of the Middle Atlantic Bight are responsive within minutes to hours and efficiently operate as biocatalytical filters.  相似文献   

Climate forcing due to the 8200 cal yr BP event observed at Early Neolithic sites in the eastern Mediterranean     

Bernhard Weninger  Eva Alram-Stern  Eva Bauer  Lee Clare  Uwe Danzeglocke  Olaf Jris  Claudia Kubatzki  Gary Rollefson  Henrieta Todorova  Tjeerd van Andel 《Quaternary Research》2006,66(3):401-420

We explore the hypothesis that the abrupt drainage of Laurentide lakes and associated rapid switch of the North Atlantic thermohaline circulation 8200 yr ago had a catastrophic influence on Neolithic civilisation in large parts of southeastern Europe, Anatolia, Cyprus, and the Near East. The event at 8200 cal yr BP is observed in a large number of high-resolution climate proxies in the Northern Hemisphere, and in many cases corresponds to markedly cold and arid conditions. We identify the relevant archaeological levels of major Neolithic settlements in Central Anatolia, Cyprus, Greece and Bulgaria, and examine published stratigraphic, architectural, cultural and geoarchaeological studies for these sites. The specific archaeological events and processes we observe at a number of these sites during the study interval 8400–8000 cal yr BP lead us to refine some previously established Neolithisation models. The introduction of farming to South-East Europe occurs in all study regions (Thrace, Macedonia, Thessaly, Bulgaria) near 8200 cal yr BP. We observe major disruptions of Neolithic cultures in the Levant, North Syria, South-East Anatolia, Central Anatolia and Cyprus, at the same time. We conclude that the 8200 cal yr BP aridity event triggered the spread of early farmers, by different routes, out of West Asia and the Near East into Greece and Bulgaria.  相似文献   

Unstable Asia: active deformation of Siberia revealed by drainage shifts     

Mark B. Allen  Clare E. Davies†  ‡ 《Basin Research》2007,19(3):379-392

Regional incision and lateral shifts of rivers in the West Siberian Basin and surrounding areas show the action of long wavelength surface tilting, directed away from the Urals and Central Asian mountains and towards the Siberian Craton. In the north of the basin, surface uplift of individual folds is recorded by local lateral drainage migration. Lateral slopes of river valleys vary in gradient from 0.001 to 0.0001, generally decreasing with increasing river discharge. As a result of this surface deformation significant drainage shifts are taking place in three of the longest and highest discharge river systems on Earth: the Yenisei, Ob' and Irtysh. The deformation is most plausibly caused by subtle faulting at depth, below the thick basin fill of Mesozoic and Lower Cenozoic sediments. Active deformation of western Siberia appears to represent a previously unrecognised, far-field effect of the India–Eurasia collision, up to ∼1500 km north of the limit of major seismicity and mountain building. It adds ∼2.5 × 10⁶ km² to the region deformed by the collision, which is an area greater than the Himalayas and Tibet combined. It is also an analogue for the formation of low-angle unconformities in terrestrial sedimentary basins on the periphery of other orogenic belts.  相似文献   

SPATIAL DISTRIBUTION OF PRIMARY INDIVIDUALS     

Clare M. Stapleton Concord 《The Professional geographer》1982,34(2):167-177

Primary individuals and the households that they head now compose a significant proportion of US households. This paper examines the regional and intraurban distribution of primary households. Macro-scale data from the 1960 and 1970 Censuses are used to examine the evolving regional patterns of primary individuals and households. Using intraurban data for the 1970's, the paper also examines the impact of recent rapid growth in the number of primary individuals on the spatial distribution of primary households within urban areas. Inferences are drawn with respect to the macro- and micro-scale distributions of primary individuals and households and the impact of continued growth of this subpopulation on urban form and population distribution.  相似文献