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451.
The stratigraphic development of an Upper Jurassic syn‐rift succession exposed at outcrop in the Inner Moray Firth Basin has been investigated using high‐resolution biostratigraphy and sedimentology. A continuous 970 m thick section, exposed in the hangingwall of the Helmsdale Fault was logged in detail. The succession spans 8 Ma and contains eight lithofacies types, which indicate deposition in a deep marine setting. Boulder beds contain large, angular clasts, with bed thicknesses typically >2 m and poor sorting suggesting deposition by debris flows. An inverse clast stratigraphy is observed; the oldest boulder beds contain sandstone clasts of Upper Old Red Sandstone (ORS) with younger debris flows containing clasts of Middle ORS calcareous siltstone. A marked change from siliciclastic to carbonate dominated sedimentation occurred during the Early Tithonian, interpreted primarily as a result of change in lithologies in the footwall catchment from sandstone to calcareous siltstone, which reduced supply of siliciclastic sediment. Secondary factors are identified as increased aridity in the Early Tithonian, which reduced sand supply from the hinterland and a third‐order Early Tithonian eustatic sea‐level rise, which trapped coarser clastic sediment within the hinterland. Biostratigraphy allows calculation of variations in sedimentation rates with recognition of: (1) an early rift phase characterised by sandy turbidite deposition, when sedimentation rates averaged 0.08 m/ky, (2) a rift climax phase from the Early Kimmeridgian where sedimentation rates increased steadily to a maximum of 0.64 m/ky in the Early Tithonian, with strata dominated by boulder scale clast‐supported debris flows and (3) a late stage of rifting from the mid Tithonian, where sedimentation rates decreased to 0.07 m/ky. Overall sedimentation rates are comparable to those of other deep marine rift basins. Unroofing a resistant lithology on the footwall of a rift has important implications for siliciclastic sediment supply in rift basins. 相似文献
452.
Paul Lewis Stewart Fotheringham Adam Winstanley 《International journal of geographical information science》2013,27(5):697-716
GIS elemental unit representations of spatial data are often defined in terms of points, lines and areas. However, another type of spatial data that is becoming frequently captured, but as yet is largely ignored in GIS, is that of video. While digital video recording is a commonly encountered medium in modern society and encompasses many forms, from simple personal camcorders through to sophisticated survey and surveillance systems, its geographical representation in a GIS has not been fully examined or realised. In the majority of cases the video footage is usually captured while the device and/or the objects being viewed are in motion. What is of particular interest is when video streams can be, or have been, associated with spatial data such as location and orientation to create geographically referenced videographic data, which, for simplicity, will be defined as spatial video. Fundamentally, the nature of video is to record space, so when spatial properties can be accurately acquired and associated with this footage, an important geographical element can be considered for integration and analysis within a GIS. Existing spatial video systems, both commercial and research, are predominantly used in survey or LBS roles and are usually bespoke and application specific. These systems do not model spatial video to any recognised standards that is generalised to be both data and platform independent. They do not support GIS integration and/or analysis from a purely spatial content perspective. A video-image/remote-sensing centric approach prevails where usage options range from simple visualisation interfaces to interactive computer vision systems. What has been largely overlooked is a spatial approach where the inherent geographical extent recorded in each video frame can be modelled and used in a geo-spatial analysis context. While this modelling approach has not been fully realised, it does exist in a GIS form based on Open Geospatial Consortium standards, where the spatial context of video is defined in a structure called a ViewCone. However, a ViewCone only defines a 2D model of the geographical extent of each frame and is restricted to a three-or-five sided polygon representation. Thus, this article examines the potential of modelling spatial video through the use of elemental data types within GIS; gives some examples of using this approach; describes some problems in using spatial video within GIS; and then demonstrates how these problems are being solved. This is done in three stages: Firstly, a detailed overview of spatial video in its current GIS role is provided – this is achieved through a complete introduction to the distinct elements of spatial video followed by a review of its use in both commercial and academic application areas. Secondly, a brief theoretical overview of an alternative GIS-constrained ViewCone data structure is given that defines a more flexible spatial video model for both 2D and 3D GIS analysis and visualisation. Thirdly, a selective sample of results is presented based on an implementation of this approach being applied to a constrained spatial video data source in a specific study area. 相似文献
453.
Sarah H. Wallace Samuel Shaw Katherine Morris Joe S. Small Adam J. Fuller Ian T. Burke 《Applied Geochemistry》2012
Strontium-90 is a beta emitting radionuclide produced during nuclear fission, and is a problem contaminant at many nuclear facilities. Transport of 90Sr in groundwaters is primarily controlled by sorption reactions with aquifer sediments. The extent of sorption is controlled by the geochemistry of the groundwater and sediment mineralogy. Here, batch sorption experiments were used to examine the sorption behaviour of 90Sr in sediment–water systems representative of the UK Sellafield nuclear site based on groundwater and contaminant fluid compositions. In experiments with low ionic strength groundwaters (<0.01 mol L−1), pH variation is the main control on sorption. The sorption edge for 90Sr was observed between pH 4 and 6 with maximum sorption occurring (Kd ∼ 103 L kg−1) at pH 6–8. At ionic strengths above 10 mmol L−1, and at pH values between 6 and 8, cation exchange processes reduced 90Sr uptake to the sediment. This exchange process explains the lower 90Sr sorption (Kd ∼ 40 L kg−1) in the presence of artificial Magnox tank liquor (IS = 29 mmol L−1). Strontium K-edge EXAFS spectra collected from sediments incubated with Sr2+ in either HCO3-buffered groundwater or artificial Magnox tank liquor, revealed a coordination environment of ∼9 O atoms at 2.58–2.61 Å after 10 days. This is equivalent to the Sr2+ hydration sphere for the aqueous ion and indicates that Sr occurs primarily in outer sphere sorption complexes. No change was observed in the Sr sorption environment with EXAFS analysis after 365 days incubation. Sequential extractions performed on sediments after 365 days also found that ∼80% of solid associated 90Sr was exchangeable with 1 M MgCl2 in all experiments. These results suggest that over long periods, 90Sr in contaminated sediments will remain primarily in weakly bound surface complexes. Therefore, if groundwater ionic strength increases (e.g. by saline intrusion related to sea level rise or by design during site remediation) then substantial remobilisation of 90Sr is to be expected. 相似文献
454.
Adam Keul 《Geographical review》2014,104(4):506-522
The development of ethnic tourism involves a process of community‐ and individual‐level objectification and commodification. To be attractive to outsiders, planners and tourism professionals often present local lifeways as unique and local while and contrasting them to an external globalized world. Using a political economic approach, this paper shows that this process of self‐commodification may give tourism professionals some control over how ethnic cultures are is presented, but does so within the parameters of state oversight and consumers’ desires. A case study of Louisiana Cajun tourism reveals how a specific narrative of swamp subsistence is deployed by individual tour guides and through the tourism planning process. This “heritage ecology” is used to romanticize a Cajun cultural ecology as “living off of the swamp” despite the fact that swamp commodities have almost always been produced for external markets. Similar to past commodities, swamp tourism still involves the production of Cajun‐swamp culture for outside consumers. This type of tourism paradoxically presents the image of a physically and socially disconnected ethnic group by fostering connections with outsiders while in the swamp. 相似文献
455.
Adam Fisher Patrick Belmont Brendan P. Murphy Lee MacDonald Ken L. Ferrier Kai Hu 《地球表面变化过程与地形》2021,46(8):1610-1628
The watersheds along the north coast of California span a wide range of geologic settings, tectonic uplift rates, and historic timber harvest activity. Known trends in how each of these factors influence erosion rates provides an opportunity to examine their relative importance. We analyzed 71 watersheds within nine larger river basins, investigated the factors influencing suspended sediment rating curves (SRCs), investigated how SRCs varied among our study watersheds, and used Random Forest modeling (RFM) to determine which environmental characteristics and land management metrics influence SRC shapes, vertical offsets, and slopes. While SRCs typically take the form of a power function, they also can exhibit threshold or peak relationships. First, we found both power and threshold relationships for the SRCs within our study watersheds. Second, the SRC offsets and slopes systematically varied with regional tectonic uplift. Third, SRC offsets increased in several watersheds following intensive timber harvest events and SRC slopes decreased due to a greater relative increase in suspended sediment concentration at lower flows than higher flows. Our RFM correctly classified 96% of the SRC shapes using two near-channel metrics; near-channel precipitation-sensitive deep-seated landslide susceptibility and near-channel soil erodibility. Our RFM models also showed that timber harvest activity and near-channel local relief can explain 40% of the variability in SRC offsets, whereas tectonic uplift rates, millennial-scale erosion rates, and precipitation patterns explain 40% of the variability in SRC slopes. 相似文献
456.
Rudy C. Gilmore Aurelien Bouvier Valerie Connaughton Adam Goldstein Nepomuk Otte Joel R. Primack David A. Williams 《Experimental Astronomy》2013,35(3):413-457
Gamma rays at rest frame energies as high as 90 GeV have been reported from gamma-ray bursts (GRBs) by the Fermi Large Area Telescope (LAT). There is considerable hope that a confirmed GRB detection will be possible with the upcoming Cherenkov Telescope Array (CTA), which will have a larger effective area and better low-energy sensitivity than current-generation imaging atmospheric Cherenkov telescopes (IACTs). To estimate the likelihood of such a detection, we have developed a phenomenological model for GRB emission between 1 GeV and 1 TeV that is motivated by the high-energy GRB detections of Fermi-LAT, and allows us to extrapolate the statistics of GRBs seen by lower energy instruments such as the Swift-BAT and BATSE on the Compton Gamma-ray Observatory. We show a number of statistics for detected GRBs, and describe how the detectability of GRBs with CTA could vary based on a number of parameters, such as the typical observation delay between the burst onset and the start of ground observations. We also consider the possibility of using GBM on Fermi as a finder of GRBs for rapid ground follow-up. While the uncertainty of GBM localization is problematic, the small field-of-view for IACTs can potentially be overcome by scanning over the GBM error region. Overall, our results indicate that CTA should be able to detect one GRB every 20–30 months with our baseline instrument model, assuming consistently rapid pursuit of GRB alerts, and provided that spectral breaks below ~100 GeV are not a common feature of the bright GRB population. With a more optimistic instrument model, the detection rate can be as high as 1 to 2 GRBs per year. 相似文献
457.
ValéRie?DauxEmail author Christophe?LéCuyer FréDéRic?Adam Fran?Ois?Martineau Fran?Oise?Vimeux 《Climatic change》2005,70(3):445-464
In order to study climate variations during the last 1700 years in eastern France, fifty-eight oxygen isotope compositions of phosphate were measured in human tooth enamel. The individuals, who lived in Lorraine, are assumed to have drunk local water derived directly from rainfall. According to previous work, drinking water is the main source of oxygen that sets the isotopic composition of phosphatic tissues in humans. The empirical fractionation equation determined from our data combined with those of Longinelli’s one [Geochim. Cosmochim. Acta 48 (1984) 385] was used to calculate the oxygen isotope composition of meteoric waters. The mean air temperature was inferred from these isotope ratios and the Von Grafenstein et al.’s [Geochim. Cosmochim. Acta 60 (1996) 4025] relationship between δ18O and air temperature. Oxygen isotope composition of present-day individuals yields a mean air temperature of 9.9± 1.7 ∘C which is consistent with meteorological data. Application of this method to historical individuals results in mean air temperatures estimates 0 to 3 ∘C higher than present-day air temperature. These warm air temperatures are not realistic during the so-called Little Ice Age for which an air-cooling of about 0.5 to 2 ∘C has been documented. We propose that these relatively high δ18O values of human tooth enamel reflect higher mean δ18O values of meteoric water which can be attributed to an increased proportion of summer rainfall during the “Little Ice Age” time frame in Lorraine. 相似文献
458.
Martin F. Hilfinger IV Henry T. Mullins Adam Burnett Matthew E. Kirby 《Journal of Paleolimnology》2001,26(3):293-305
A series (N = 12) of short (< 1 m) sediment cores were collected from meromictic Green Lake in Fayetteville, New York to investigate potential anthropogenic impacts on the watershed during historic time and environmental change over the past ~ 2,500 years. Stratigraphic data document an abrupt basinwide change during the early 1800's A.D. from brown laminated sediments to grey varved sediments separated by a transition zone rich in aquatic moss. Deforestation of the region by European settlers during the early 1800's A.D. resulted in a flux of nutrients and increased biological productivity followed by a 7fold increase in sediment accumulation rates. Elemental geochemical data document the anthropogenic loading of lead to the to the lake basin via atmospheric fallout. Stable oxygen isotope (18O calcite) data also provide evidence for an abrupt shift in the isotopic composition of lake water ~ 150–200 years ago. This isotopic shift could have been a local phenomenon related to an increased supply of summer enriched precipitation following removal of forest vegetation, or it might have reflected broader scale climatic changes. We hypothesize that the 18O calcite shift was the result of the polar front jet stream migrating from a more southerly prehistoric position to a contracted, northerly configuration ~ 150–200 years ago. Such a shift could have been natural, associated with the end of the Little Ice Age or it may have been anthropogenically forced. 相似文献
459.
Tadeusz Andrzej Przylibski Krystian Mroczkowski Adam Zebrowski Paweł Filbier 《Environmental Geology》2001,40(4-5):429-439
Radon is a significant component of the groundwaters that discharge in the springs of Szczawno Zdrój and are recognized as
medicinal. However, among the five exploited springs adjoining each other, it is only in Marta Spring that radon occurs in
large concentrations (up to 325.6 Bq/dm3). Therefore, the authors have made an attempt to describe and clarify this fact. They found out from their own research and
archival data that 222Rn dissolves in the waters of Marta Spring after acidulous waters of deep circulation have mixed with poorly mineralized shallow
waters in their outflow zone. The genesis of the gas is determined by the content of its parent nuclide, 226Ra, in the sandstones in the vicinity of the intake. The volume of the rocks providing radon to the waters of this intake
has been estimated at several hundred cubic metres. No seasonal fluctuations in radon concentration have been observed and
222Rn concentration changes do not seem to be influenced by changes in the concentration of other chemical components of the
waters or by the discharge of the intake. The process of dissolving 222Rn in the medicinal groundwaters of Marta Spring is the last, the shortest, and the most local of the processes that form
the chemical composition and the physical properties of these waters.
Received: 7 January 2000 · Accepted: 12 August 2000 相似文献
460.
We investigate uncertainties about conventional petroleum resources and substitutes for conventional petroleum, focusing on
the impact of these uncertainties on future greenhouse gas (GHG) emissions. We use examples from the IPCC Special Report on
Emissions Scenarios as a baseline for comparison. The studied uncertainties include, (1) uncertainty in emissions factors
for petroleum substitutes, (2) uncertainties resulting from poor knowledge of the amount of remaining conventional petroleum,
and (3) uncertainties about the amount of production of petroleum substitutes from natural gas and coal feedstocks. We find
that the potential effects of a transition to petroleum substitutes on GHG emissions are significant. A transition to low-quality
and synthetic petroleum resources such as tar sands or coal-to-liquids synfuels could raise upstream GHG emissions by several
gigatonnes of carbon (GtC) per year by mid-century unless mitigation steps are taken. 相似文献