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1.
Thermoluminescence dating of sediments in the Warsaw laboratory is based on blue-to-green emission. The ‘partial bleach + regeneration’ method is proposed for dating sediments which have not been completely bleached at the time of burial. Correct TL ages are reported for sediments covering organic deposits of the Eemian Interglacial and also for glacial sediments of Würm and Riss age. We obtained good results for dating till using the partial bleach + regeneration method. The TL zeroing in till is explained by the ‘rubbing’ or compression of grains beneath the glacier and by the freeze-thaw activity occurring during glacial transport and deglaciation.  相似文献   

2.
A review of current research on TL dating of loess   总被引：1，自引：0，他引：1  
The thick loess deposits of China, Central Europe and North America are particularly suitable for the application of the thermoluminescence (TL) dating method because individual grains are likely to have travelled large distances and thus been well exposed to light before deposition. Wind-blown silt grains collected close to glacial rivers in Alaska have been shown to give a ‘zero age’ of not more than 2 ka, demonstrating the efficiency of the zeroing mechanism.Differences in laboratory procedures can cause differences in the TL ages reported, particularly for loess over 100 ka. TL ages for interstadial soils in Europe are in agreement with the very few radiocarbon dates on reliable material, such as charcoal. On the other hand TL dates from sites in Belgium and north-western Germany indicate that the previously accepted chronology, which was based on two radiocarbon dates on humic-rich sediments, is incorrect.The use of the ‘last interglacial’ palaeosol for assessing the TL dates on loess above and below it is limited by the uncertainty in the timing of termination of soil-forming processes; 107 and 71 ka are the limits suggested by the astronomically-derived time scale. Results on deposits from China, North America, Alaska and Europe are discussed in this context.  相似文献   

3.
Based on an environmental geochemistry case study carried out in the neighbourhood of a W–Sn abandoned mine, the pollution in stream sediments was modelled through a Global Contamination Index. Such an index permits one to summarize the combination of deleterious elements in a single variable, obtained by the projection of samples onto the first axis of a PCASD (Principal Components Analysis of Standardized Data) applied to the entire n × p matrix containing the available concentrations of p = 16 elements in the set of n = 220 collected samples.In order to provide a sound basis for a coherent planning of the remediation process which will be put in operation in the affected area, it is necessary to balance the costs of reclaiming with the probabilities of exceeding the upper limits accepted for concentrations of environmentally harmful elements in sediments. Given these limits, they are back-transformed in the index values, providing a practical threshold between ‘clean’ and ‘contaminated’ samples. On the other hand, the minimum dimension of the cell to be reclaimed is restrained by the selected remediation process to be applied in the affected area. Hence, to meet the constraints of such a remediation process, it is required to estimate the probabilities of exceeding the index threshold in technologically meaningful sub-areas. For this end, the Indicator Block Kriging technique was applied, producing a series of maps where sub-areas to be reclaimed can be spotted for different probability levels. These maps, on which the decision making remediation agency can rely for its cost-benefit analysis, take into account both the spatial structure of ‘clean’ vs. ‘contaminated’ samples and the constraints of the reclaiming process.  相似文献   

4.
In the mining district of Plombières-La Calamine (East Belgium), extensive Pb–Zn mining activities resulted in an important contamination of overbank sediments along the Geul river. Moreover, a huge amount of heavy metals is stored in a dredged mine pond tailing, which is located along the river. In the dredged mine pond tailing sediments, Pb–Zn minerals control the solubility of Zn, Pb and Cd. Although Pb, Zn and Cd display a lower solubility in overbank sediments compared to the mine tailing pond sediments, elevated concentrations of Pb, Zn and Cd are still found in the porewater of the overbank sediments. The considerable ‘actual’ and ‘potential’ mobility of Zn, Pb and Cd indicates that the mine pond tailing sediments and the overbank sediments downstream from the mine pond tailing represent a considerable threat for the environment. Besides the chemical remobilisation of metals from the sediments, the erosion of overbank sediments and the reworking of riverbed sediments act as a secondary source of pollution.  相似文献   

5.
During the Albian and Cenomanian, the Pieniny Klippen Belt Basin, a part of the Carpathian geosynclinal domain, showed a clear differentiation into an axial deepest part represented by the Pieniny and Branisko successions and two marginal zones, a southern (Nizna and Haligovce successions, in Slovakia) and a northern zone (in Poland and Slovakia) represented by the Niedzica, Czertezik and Czorsztyn successions, becoming progressively more shallow towards the north. Five palaeobathymetric foraminiferal associations have been distinguished in the axial and northern marginal zone sediments of the Klippen Basin, corresponding to: ‘A’ shelf and upper slope: relatively large proportion of nodosariids and miliolids (Czorsztyn succession); ‘B1’ middle part of slope; oligotaxic planktonic assemblage dominant (Niedzica through Branisko successions and northern part of the Pieniny succession); ‘B2’ middle part of slope: larger proportion of agglutinated foraminifers, association characteristic of sediments influenced by turbidites (submarine flyschoid channels in the Branisko succession); ‘Cl’ middle and lower parts of slope: scarce microfauna, Hedbergella and textularids dominant (Pieniny succession, middle part); ‘C2’ slope/abyssal plain transition, close to foraminiferal lysocline (probably about 3500m below sea level): scarce specimens corroded and slightly dissolved (Pieniny succession, southern part).  相似文献   

6.
A.K. Mahajan   《Engineering Geology》2009,104(3-4):232-240
Shear wave velocity of the near surface soil at nearly 50 sites in the sub Himalayan mountain exit covering Doon fan deposits, was determined using Multi-channel Analysis of Surface Waves (MASW), a seismic reflection technique. Based on the average shear wave velocity of the upper 30 m soil column, sites in the Dehradun fan are predominantly classified as class ‘D’ (180–360 m/s). Similarly, sites located on the northwestern, eastern and southeastern sides of the fan deposit have shear wave velocities (in the upper 30 m soil) greater than 360 m/s, thereby classifying them as class ‘C’ (360–760 m/s) in accordance with NEHRP provisions. Some of the sites towards the southwestern side of the fan deposits had average shear wave velocities less than 180 m/s and could be classified as soil class ‘E’. One dimensional site effects, including amplification and dynamic period were calculated for the majority of the sites. However, some of the representative suite of sites across the north–south profile of Dehradun fan has been discussed here. Although the attenuation is greater on the southwestern side of the Dehradun fan deposits (i.e. thicker, low velocity sediments) and the sites had been classified as class ‘D’ and ‘E’ but the site amplification tends to be greater in the northern and northwestern part of the city due to large impedance contrast with in the near surface soils.  相似文献   

7.
Analysis of hydraulic heads and chemical compositions of Devonian formation waters in the west central part of the Alberta Basin, Canada, characterizes the origin of formation waters and migration of brines. The Devonian succession in the study area lies 2000–5000 m below the ground surface, and has an approximate total thickness of 1000 m and an average slope of 15 m/km. Four Devonian aquifers are present in the study area, which form two aquifer systems [i.e., a Middle–Upper Devonian aquifer system (MUDAS) consisting of the Elk Point and Woodbend–Beaverhill Lake aquifers, and an Upper Devonian aquifer system (UDAS) consisting of the Winterburn and Wabamun aquifers]. The Ireton is an effective aquitard between these two systems in the eastern parts of the study area. The entire Devonian succession is confined below by efficient aquitards of the underlying Cambrian shales and/or the Precambrian basement, and above by overlying Carboniferous shales of the Exshaw and Lower Banff Formations.The formation water chemistry shows that the Devonian succession contains two distinct brine types: a ‘heavy brine,’ located updip, defined approximately by TDS >200 g/l, and a ‘light brine’ with TDS <200 g/l. Hydraulic head distributions suggest that, presently, the ‘light brine’ attempts to flow updip, thereby pushing the ‘heavy brine’ ahead. The interface between the two brines is lobate and forms large-scale tongues that are due to channeled flow along high-permeability pathways. Geological and hydrogeochemical data suggest that the following processes determined the present composition of the ‘light’ and ‘heavy’ brines: original seawater, evaporation beyond gypsum but below halite saturation, dolomitization, clay dehydration, gypsum dewatering, thermochemical sulfate reduction (TSR), and halite dissolution. The influx of meteoric (from the south) and metamorphic (from the west) waters can be recognized only in the ‘light brine.’ Albitization can be unequivocally identified only in the ‘heavy brine.’ The ‘heavy brine’ may be residual Middle Devonian evaporitic brine from the Williston Basin or the Elk Point Basin, or it may have originated from partial dissolution of thick, laterally extensive Middle Devonian evaporite deposits to the east of the study area. The ‘light brine’ most probably originated from dilution of ‘heavy brine’ in post-Laramide times.  相似文献   

8.
The paper addresses cultural assumptions about ‘nativeness’ and ‘belonging’ to place as they are implicated in notions of ‘ecological restoration’. Given the centrality of complex notions of ‘indigeneity’ to the issue of what ecological ‘restoration’ means in Australia, this is a rich area for cultural and historical analysis. Case materials illustrate the negotiated and ambiguous nature of Australian ideas about what ‘belongs’ ecologically and culturally across the broad continent of this relatively young post-Settler nation. We seek to foreground these issues through consideration of what ‘restoring’ nature might mean in the context of debates about native plants, the re-introduction of an iconic species of ground dwelling bird, the removal of cane toads that are demonised as highly ‘alien’, and the multiple ways in which the dingo is regarded ambiguously as both native and a ‘pest’ that needs to be controlled and culled. By showing how ‘restoration’ can be understood and mobilised in a variety of ways – in terms of the ‘re-naturing’, ‘re-valuing’ and/or ‘repatriating’ of indigenous species, as well as impassioned rejection of ‘exotics’ – we emphasise the importance of social science for building a well-grounded sense of how environmental management priorities and approaches are informed by a wider set of cultural assumptions.  相似文献   

9.
Using a new approach to classifying migrant group concentrations, we test for evidence of the effects of globalisation, associated by some with ‘protopostmodernity’, on two Australian cities. Sydney is characterised as an emergent world city and a focus of ‘new economy’ activities. Melbourne is associated with ‘old economy’ activities, dominated by manufacturing. In the Australian context, the onset of globalisation also coincided with significant changes to immigration policy: the end of a ‘white Australia’ policy in the early 1970s in favour of a skills-based policy, regardless of race or ethnicity. We argue that the evidence of the spatial behaviour of ethnic groups for these two cities highlights the essential continuity of ethnic segregation and spatial assimilation processes in two cities where segregation levels and experience are fundamentally different from many overseas examples. We further argue for a need to recognise that context, and the ethnic experience, are everywhere different, both intra- and internationally.  相似文献   

10.
At Pedregal, more than 40 m of sediments are exposed within a ‘fan complex’ formed between lateral moraines of the adjacent Mucuchache and El Caballo valleys. Early and late Mérida (Wisconsinan) glaciations are represented by till and till plus proglacial sediments, respectively. A middle Wisconsinan interstadial event, here termed the Pedregal interstade, began at the end of the Early Mérida glaciation at approximately 60 ka BP. Following the retreat of ice from the small Pedregal Basin, a lake formed when the local drainage was blocked due to movement of the Mesa de Caballo along the Boconó Fault. Shallow lake or no-lake phases lasted approximately a few hundred to, at most, 2000 years, and each lake phase was marked by peat accumulation. Four of seven peats identified formed during sufficiently long intervals for soil profiles (incipient to mature Spodosols) also to develop. The Spodosol with the strongest development (Eb/Bsb/Coxb/Cub horizons) is found adjacent to the lowest peat and reflects ongoing early Mérida stadial (MIS 3) conditions; the youngest peats, associated with weak podzolic soils (Eb/Bsb horizons), formed under slightly warmer interstadial conditions, presumably with less soil water. Cyclic lacustrine deposition is related to lake level and relative depth fluctuations, due in part to variable shoreline/delta progradation and shallowing as the lake deepened in general. Whereas final drainage of the lake is related to movement of the Boconó Fault and breach of the moraines that form the Mesa de Caballo, earlier lake level fluctuations appear related to climate change. Radiocarbon dating of the peats suggests they are related to warmer periods and may tentatively correlate with small ‘interstadials’ or ‘D-O events’ detected in the oxygen-isotope record of Greenland ice cores and North Atlantic marine sediments.  相似文献   

11.
‘New regionalism’ has become a buzzword in current debates on regions and regional governance. Much of this discussion revolves around the ‘right’ scale and structure of regional governance, implying changes to the ways in which the conventional main variables institutions, hierarchy and territoriality interact to circumscribe ‘regions’. The main difference between ‘old’ and ‘new’ regionalism is the degree of variability and responsiveness to locational strategies by businesses, i.e. essentially relative regional competitiveness, and thus by implication the question of territoriality and boundedness. Evidence ‘on the ground’ among policy makers, however, suggests that the changes may go further than theoretical arguments with their emphasis on territory and scale (Brenner, 2000, 2003) are suggesting. Much of the difference revolves around the distinction between technocratic, planning focused and firmly institutionalised understandings of territorially fixed regions within a government structure on the one hand, and more purpose driven, flexible, and inherently temporary and variable arrangements outside fixed government structures, whose territoriality is composed of the varying spatial background of the participating actors. Here, regional territoriality is an incidental rather than determining factor. The cleavage between ‘old’ and ‘new’ regionalism has become particularly obvious in post-socialist eastern Germany, where staid forms of traditional institutionalism and territorial governance had been transferred from ‘west’ to ‘east’. Increasingly, these arrangements appeared inadequate to respond to the vast and spatially widely varying challenges of post-socialist restructuring. The result has been a tentative emergence of new forms of regionalisation in between, and in addition to, the established ‘old regionalist’ approaches. Evidence from eastern Germany suggests that ‘new’ is not necessarily replacing ‘old’ regionalism’ in the wake of a shift in paradigm, but rather that the two coexist, with new forms of regionalisation sitting within established conventional territorial-administrative arrangements. This points to the emergence of a dual track approach to regionalisation, sometimes covering the same territory, more often relating to variably sized areas that overlap. Both forms of regionalisation aim at an internal and external audience, using varying images and employing different sets of actors when dealing with the two main sources/directions of consumption: internal (local) and external (corporate, competitive). By their very nature, however, these processes are varied and differ between places, rooted in particular local-regional constellations of policy-making pressures, actor personalities and established ways of doing things. This paper examines such processes for two regions in eastern Germany, both with distinctly different economic traditions and geographical contexts, aiming to illustrate the multi-layered process of regionalisation and region making. Inevitably, within the scope of this paper, the study cannot cover all possible models and regionalisation approaches across eastern Germany, because they not only differ between places, but also over time.  相似文献   

12.
Commodity geographies are politically weak. Geographical pedagogy isn’t particularly engaging. Radical geography should make connections. But it rarely leaves room for interpretation. Too much seems to be too didactic. And to preach to the converted. That’s a problem that needs attention. So, is it possible to develop a radical, less didactic, geography? With research funding, publication and teaching the way they are? To engage more students, more heartily, in the issues studied? To promote social justice, critical citizenship, and participatory democracy? But not by setting out the right ways to think, be, or act. Some film-makers, artists and writers have been able to do this. It seems. Subtly and cleverly. Through projects attempting to de-fetishise commodities. But their politics have been placed largely in the background, between the lines of, or separated out from, the presentation of scenes, things, relations, bodies, lives and voices. Seen and unseen elements of their audiences’ lives. Re-connected. Perhaps. Through communication strategies giving audiences something to think about and to think with, to argue about and to argue with. Putting themselves in the picture, in the process. These less didactic materials may be difficult to master for an exam or an essay. They may not make it clear who or what’s right or wrong or what audiences are supposed to do. But they could engage them in less direct ways. When they’re shopping for petrol or fish, or when they’re doing or thinking about completely different things. Things that may not even come under the heading of ‘production’ or ‘consumption’. This approach might be labelled as ‘weak’, ‘relativist’, a bit too ‘cultural’ ‘post-modern’, or ‘defunct’. But it’s an approach that may be radical in effect because its ‘politics’ aren’t so straightforward or ‘up front’. This paper is about changing relationships between research, writing, teaching, learning and assessment; expanding fields of commodity geographies to include classrooms as sites not only of ‘instruction’, but also of learning, for researchers and their students1; showing how such learning might usefully shape research and writing elsewhere in these fields for those engaged in this defetishising project.  相似文献   

13.
A combination of ‘bomb spike’ calibration and conventional calibration of AMS 14C dating has been used to determine a detailed age-depth model for a 1-m sediment section collected from a salt marsh in Poole Harbour, southern England. These data were compared with the chronology obtained from 210Pb analysis and 137Cs age markers. We report post bomb values of over 1.46 F14C (> 146% modern 14C), and both the rising and falling limbs of the atmospheric ‘bomb spike’ are identified. Five pre-bomb samples were analysed using multi-target high-precision 2‰ AMS analysis, and after the replicates were combined the one-sigma uncertainty was as low as ± 9 14C yr on some ages. These data, and an additional three normal-precision pre-bomb 14C samples, were calibrated using CALIB 5.0 and the chronology constrained using the ‘prior knowledge’ of independent age markers obtained from the analysis of pollen and spheroidal carbonaceous particle (SCPs). No agreement was found between the 14C ‘bomb spike’ dates and the CRS 210Pb chronology modelled for this sequence. In addition, poor agreement was found between the signal of the 1960s weapons test fallout indicated by the 14C ‘bomb spike’ dates and the timing suggested by the 137Cs data. This disagreement is attributed to the influence of the local discharge of 137Cs from the former UKAEA site at Winfrith. We use our new chronology to confirm the existence of an acceleration in sedimentation rates in Poole Harbour during the last 100 yr previously reported for this site by Long et al. (Long, A.J., Scaife, R.G., Edwards, R.J. 1999. Pine Pollen in intertidal sediments from Poole Harbour, UK; implications for late-Holocene sediment accretion rates and sea-level rise. Quaternary International, 55, 3–16.), and conclude that ‘bomb spike’ 14C calibration dating may offer a more robust alternative to the use of 210Pb chronologies for dating sediment deposition in salt-marsh environments. In addition, we demonstrate how the use of high-precision AMS analysis has the potential for reducing some of the uncertainties involved in the high-resolution dating of recent salt-marsh sediments.  相似文献   

14.
Many of the estuaries of the Pacific Northwest of the U.S.A. and Canada contain stratigraphic sequences typified by alternating peat-mud couplets. Recent studies in this region interpret such couplets as the product of repeated large (magnitude S or 9) earthquakes on the Cascadia subduction zone. The resultant pattern of land-level movements is described by a model, the ‘earthquake deformation cycle’, of coseismic land subsidence followed by land uplift during interseismic strain accumulation. However, peat-mud couplets similar to those recorded in the Pacific Northwest are found on other less tectonically active temperate-latitude coasts, such as northwest Europe and the Atlantic coast of the U.S.A., where they have been interpreted as the product of non-seismic coastal processes. In this paper we apply the methods and scientific framework common to sea-level investigations in northwest Europe to a sequence of peat-mud couplets recorded in the lower Johns River, an estuary in southern Washington, to provide a test of the ‘earthquake deformation cycle’.Stratigraphic investigations of the intertidal sediments along the lower Johns River, using lithological, pollen, diatom and foraminiferal data, show evidence for eight coastal submergence events during the last 5000 years. To evaluate the ‘earthquake deformation cycle’ we assess the lateral extent of peat-mud couplets, the synchroneity of submergence, the presence of tsunami deposits accompanying submergence, and the suddenness and amount of submergence. Each submergence is shown to be accompanied by changes in coastal sedimentation broadly commensurate with those predicted by the ‘earthquake deformation cycle’, demonstrating the continued intermittent seismic activity of the Cascadia subduction zone throughout the mid and late-Holocene.Quantitative analyses of contemporary and fossil biostratigraphic data, using TWINSPAN and Detrended Correspondence Analysis, enable us to estimate the magnitude of submergence accompanying each peat-mud couplet. One event was accompanied by submergence of about 1.5 m or more, four events by intermediate submergence of about 1±0.5 m, and a further three events by submergence of <0.5 m. There is evidence for non-seismic relative sea-level rise prior to two of the eight submergence events, but for at least the last 3500 years the magnitude of relative sea-level rise has been less than the combined influence of sediment accretion following submergence and interseismic land uplift.  相似文献   

15.
Dating of speleothems by TL and ESR is seriously complicated by radioactive disequilibria in the uranium series. This paper presents a simple method which takes into consideration the U-series disequilibria in the case where the annual dose is determined by gamma scintillation spectrometry. The method described is based on the concept of an appropriately defined ‘laboratory age’ and enables direct reading of the age of a sample from the curve (the GH plot) independently of the results of measurements.  相似文献   

16.
Since the late 1970s, the UK has experienced a series of changes in the mechanisms of governing local economic development. This paper considers the methodological consequences of these recent changes. Drawing on two local elite-based case studies, involving semi-structured interviews, we reflect on our acquired ‘situated knowledge’ and argue that this is related to the contingent nature of our respective research access. We advocate that an approach sensitive to ‘research situatedness’ (with respect to the politics of time as a ‘research moment’) is essential to avoid over generalising from our experiences. To address this concern, the paper offers two concepts for debate – political-temporal contingency and the mode of entry.  相似文献   

17.
Jianfa Shen 《Geoforum》1995,26(4):395-409
Economic reforms since the late 1970s have brought about significant changes in rural China. A large number of surplus rural labourers have been released from the agricultural sector and there has been a massive transition of rural residents from agricultural to non-agricultural employment. These changes will be analyzed by examining the changes in the employment structure of rural residents. Rural to urban migration is another important option for many rural labourers. The size of China's urban population and the scale of rural to urban migration continue to be an ‘enigma’ due to several changes in the definition of the urban population. Several data sources will be used to provide more realistic estimates of rural to urban migrations on a set of comparable though different bases. Data on the new entries into urban employment and the urban ‘non-agricultural population’ will be used to illustrate the scale of migration by rural residents to the formal urban sector. This may only record those migrants who have changed their registration status from ‘agricultural population’ to ‘non-agricultural population’ which is tightly controlled by the government. The 1990 Census data provide some evidence on the rural to urban migration by the registered ‘agricultural population’. The 1987 1% population sampling data will be used to analyze the actual migrations among cities, towns and counties over the period 1982–1987. It is found that town and county populations tended to move to towns at the intra-provincial level, but to cities at the inter-provincial level. Out-migrants from cities tended to move to cities at both the intra- and inter-provincial levels.  相似文献   

18.
Auto-regenerative dating of zircon grains from fired materials has been shown to be a very powerful technique. The high internal dose rate in zircon gives a measurable auto-regenerated TL signal a few months after the natural TL measurement, allowing the determination of age without dosimetry. The technique has been extended to zircon grains from sediments, using optically stimulated luminescence (OSL) techniques to measure the natural signal. The auto-regenerated signal is only a few hundred photons and cannot be measured above background using present OSL techniques, so it is counted using the highly sensitive TL reader developed for fired zircon grains. Preliminary measurements on fired zircons are in good accord with TL dating and the known ages, but precision becomes poor for samples <1 ka in age. Possible improvements using auto-regenerative phototransfer TL dating are discussed.  相似文献   

19.
第四纪沉积物光释光测年中等效剂量测定方法的对比研究   总被引：12，自引：0，他引：12  
陈杰  魏兰英 《地球化学》1999,28(5):443-452
准确地测定碎屑矿物沉积后吸收的等效剂量第四纪沉积物释光测年中最关键的一环。用光释光测年技术对几年全新世坡积物,古土地和黄土等样品中的石英,长石等碎屑矿物进行了测定等效剂量的对比研究。  相似文献   

20.
Matt Lobley  Clive Potter 《Geoforum》1998,29(4):413-432
Research into the adoption of Environmental Land Management Schemes (ELMS) has typically sought to identify the defining characteristics of participants and the ‘barriers to entry’ that dissuade others from joining. More recently, attention has focused on the motivation of participants and non-participants in helping to understand patterns of participation. This paper compares the pattern of participation in two distinct schemes operating in South East England. Indirect evidence suggests that scheme design and implementation is influencing the type of farmer joining and their motivation for doing so. Results from a survey of farmers also support the idea that the schemes are recruiting from different sections of the farming community. ESA farmers are largely motivated by financial gain, whereas those enrolling land in the Countryside Stewardship Scheme have more clearly defined conservation motives. Although there is also a ‘core’ of resistant non-participants, further changes to the design and delivery of policy could encourage a large number of ‘potential enrolers’ to join.  相似文献   

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