Lead ages,reset rubidium-strontium ages and implications for the Archaean crustal evolution of the Diemals area,Central Yilgarn Block,Western Australia     

M.J Bickle  H.J Chapman  L.F Bettenay  D.I Groves  J.R de Laeter 《Geochimica et cosmochimica acta》1983,47(5):907-914

The Pb-Pb whole-rock geochronology of Archaean granitic and gneissic rocks from the Diemals area in the Central Yilgarn granite-greenstone terrain provides important constraints on crustal evolution. The regionally extensive banded gneisses, previously considered as candidates for basement to the greenstones give a Pb-Pb whole-rock age of 2700 ± 97 Ma (2σ errors). This is within error of previously published Rb-Sr and Sm-Nd gneiss ages and also within error of the Sm-Nd ages on the greenstones in the Eastern Goldfields Province. Two synkinematic plutons give Pb-Pb whole-rock ages (2737 ± 62 Ma and 2700 ± 100 Ma) and Pb isotopic compositions consistent with the hypothesis, based on field and geochemical relations, that these plutons were derived by partial melting of the precursors to the banded gneisses. Assuming this, the combined data date the melting event at 2723 ± 25 Ma with a model source μ value of 8.18 ± 0.02. This source μ value is close to the range postulated for mantle values and restricts the crustal history of the precursors to less than ~200 Ma. A post-kinematic pluton with a whole-rock Pb-Pb age of 2685 ± 26 Ma and μ value of 8.26 ± 0.02 puts a younger limit on this relatively short lived crustal accretion-differentiation event.Comparison of Pb-Pb and Rb-Sr whole-rock dates for the plutons suggests that the latter became closed systems up to 200 Ma after the Pb-Pb ages, and that the plutons gained or lost Rb or Sr at this time.  相似文献   

Heathland vegetation,soil moisture and dynamic contributing area     

Angela M. Gurnell 《地球表面变化过程与地形》1981,6(6):553-570

Gurnell (1978) demonstrated the potential of the composition of wet heathland vegetation as an indicator of hydrological processes in a small heathland catchment. The present paper investigates this potential and demonstrates that on a hillslope in the study catchment simple prediction equations for pressure head based entirely on position on the slope can be substantially improved by the inclusion of vegetation related variables. It is suggested that in this context the vegetation composition is largely reflecting soil permeability and that the remaining scatter around the prediction equations results from other factors controlling micro-scale variations in the vegetation pattern.  相似文献   

Machine vision for dimensional measurements in mines     

R. Singh  D. P. Chapman  K. B. Atkinson 《Geotechnical and Geological Engineering》1997,15(3):185-203

Summary Fast growing mechanization and automation in the mining industry has been adopted to increase production, productivity and safety, but it requires quick, precise and automatic measurements. In particular, the measurement of deformations around a coal-mining face has been an extremely difficult task due to the time and space constraints of such sites. In a continuing drive to reduce the inherent risks of danger during working around such difficult areas, much routine inspection work is increasingly being undertaken by remote measuring systems. The advent of digital photogrammetry provides an opportunity for real-time dimensional measurement of such inaccessible areas. In this paper, some examples of reliability testing of automatic measurements using grey scale digital images of mining structures is described. A CCD (charged coupled device) based active triangulation system is combined with image understanding algorithms to provide machine vision capability and for automatic measurement of the textureless and featureless surface of sandstone strata. This paper also presents some results of initial laboratory investigations conducted to test the reliability of basic components of the system.  相似文献   

Human impacts on the Waikato River system, New Zealand   总被引：1，自引：0，他引：1  

M. A. Chapman 《GeoJournal》1996,40(1-2):85-99

The Waikato River drains 13% of the North Island. It rises in the Central Volcanic Plateau; the headwaters, including the Tongariro R., drain into oligotrophic Lake Taupo, important for fishing and holidaying. The river flows north from Taupo for 450 km to the sea near Auckland. Human impacts on the river system have been extensive, primarily dating from European colonisation begun in the 1800s. Most of the catchment below L. Taupo has been altered by agricultural development (mainly sheep and cattle rearing); the original forests and swamps have been lost leading to increased nutrient levels, erosion, light intensities, and water temperatures. There is also extensive use of the water for electricity generation. The Tongarino Power Scheme involves impoundment of water, and the diversion of additional water from the Whanganui River and other catchments with consequent effects on their biota. There are 8 hydro-electric dams on the Waikato River below Taupo causing barriers to migratory animals, downstream effects due to impoundments, and alterations to water flow regimes. Impacts of geothermal power stations, and the water-cooled Huntly Power Station in the lower Waikato are more localised. Eutrophication is enhanced by sewage and stormwater discharges, but all wastes now receive some form of treatment. There are only 340,000 people in the catchment and the major industrial pollution comes from meat and dairy processing and forestry. Some natural pollution results from geothermal inputs. Water abstraction and discharges into the river are now closely regulated. Extensive introductions of exotic biota have been made, notably trout, coarse fish, and macrophytes. The native biota has been little-studied and the biological processes operating in the river are poorly understood. It is not possible to assess the relative importance of eutrophication and habitat change, nor to predict the impacts of future changes.  相似文献   

The effects of agricultural land use and cotton production on tributaries of the Darling River, Australia     

Angela H. Arthington 《GeoJournal》1996,40(1-2):115-125

Intensive agricultural development in the Murray-Darling Basin, Australia, has been achieved at a high cost to the natural environment. This paper assess the hydrological, water quality and ecological changes which have occurred as a result of agricultural land use and particularly, cotton production, in major tributaries of the upper Darling River, using the Namoi Valley, the cradle of the Australian cotton industry, as a case study. Three aspects of cotton production have had detrimental effects in these catchments — extensive vegetation clearing on floodplains and in the riparian zone, water abstraction from regulated and unregulated river flows and intensive chemical use for pest control. The paper outlines the new initiatives in progress to improve the condition of these rivers, including management of pesticide runoff from cotton farms, nutrient reductions in surface waters and restoration of natural patterns of river flow. Constraints on water use off-stream and restrained regional development appear to be inevitable if river health is to be improved.  相似文献   

Thermal effects of intrusion below the Taranaki Basin (New Zealand): evidence from combined apatite fission track age and vitrinite reflectance data   总被引：1，自引：0，他引：1  

P. A. Armstrong  P. J. J. Kamp  R. G. Allis  & D. S. Chapman 《Basin Research》1997,9(2):151-169

A high surface heat-flow anomaly on the northern Taranaki Peninsula in the Taranaki Basin (New Zealand) coincides spatially with Quaternary volcanic edifices, but the temporal aspects of heating of the sedimentary column associated with volcanism and any related plutonism have been unclear. A combined analysis of fission track age and vitrinite reflectance data, in particular comparing data from within the high heat-flow anomaly to calibration wells elsewhere in the Taranaki Basin, provides important new constraints. Within the high heat-flow region, apatite fission track (AFT) ages are older and vitrinite reflectance ( R _o) values are lower than in samples from elsewhere in the basin that have undergone similar burial histories. Modelled AFT ages and R _o values suggest gradual heating to within about 20  °C of maximum temperature followed by rapid heating of sedimentary strata in the last 1 Myr, perhaps as recently as the last 0.1 Myr. The inferred age of this heating event is younger than the age of the volcanic edifice on which it is centred, suggesting that volcanism precedes heating that may be related to plutonism under the northern peninsula. These results suggest that, if the heating is caused by intrusion, then the intrusion is probably in the upper crust.
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A comparison of water-column macroinvertebrate communities in beds of differing submersed aquatic vegetation in the tidal freshwater Potomac River     

Angela G. Thorp  R. Christian Jones  Donald P. Kelso 《Estuaries and Coasts》1997,20(1):86-95

Macroinvertebrates are a major food source for fish species and macrophyte beds are hypothesized to harbor a rich community of these organisms. Macroinvertebrates inhabiting the water column in two macrophyte beds and an adjacent open area were sampled in a small embayment of the tidal freshwater Potomac River. One macrophyte bed consisted of an almost complete monoculture ofHydrilla verticillata, while the second community was a more diverse mixture of plant species. In samples with substantial amounts of submersed aquatic vegetation (SAV), macroinvertebrate density was two orders of magnitude higher than and substantially more taxa were found than at the open water site. Total macroinvertebrate abundance was significantly greater at theH. verticillata site than at the mixed site in July, but no significant difference was observed in August. Taxa richness did not vary between the two vegetated sites in July but was higher in the mixed bed in August. While the two vegetated sites shared similar taxa, they differed in their abundance. TheH. verticillata site harbored more hydrobiid snails, and the mixed site was characterized by more chironomids and hydroptilid caddisflies. Differences between July and August collections were even greater than between sites. Numbers of hydroptilid caddisflies, baetid mayflies, and coenagrionid damselflies were substantially higher in August, while oligochaetes, hydrobiids, and chironomids were reduced. Results support the hypothesis that water-column macroinvertebrates are greatly enhanced in the presence of macrophytes. The ecological significance of the less substantial differences in macroinvertebrates between macrophyte beds requires further study.  相似文献   

Managerial decisions as experiments: an opportunity to determine the ecological impact of boat-generated waves on macrobenthic infauna     

M.J. Bishop  M.G. Chapman 《Estuarine, Coastal and Shelf Science》2004,61(4):613-622

A previous correlative study showed that assemblages of macrobenthic infauna and abundances of common taxa on intertidal mudflats differed between a no-wash zone, where ferries had to minimize production of wash, and places where the production of wash was unrestricted (wash zone). This suggested that boat-generated waves (wash) are important in determining the structure of these assemblages. Causality between wash and the observed patterns could not, however, be unambiguously established, due to the absence of ‘before’ data. Here, a managerial decision to stop ferry services on the upper Parramatta River, Sydney, Australia during the 2000 Olympics was used as the basis for a manipulative experiment to examine the effects of changes in the amount of wash on these fauna. It was hypothesized that if wash is important in structuring infaunal assemblages, assemblages in the wash zone would become more similar to those of the no-wash zone following removal of the disturbing force, i.e. the ferry service. Similarly, if the smaller abundances of capitellids, nereids and spionids in the wash zone are caused by this disturbance, abundances should increase in the wash zone during the stoppage and decrease following the return of services. As hypothesized, assemblages within the wash zone became more similar to those of the no-wash zone following the temporary removal of the ferry services. Following the return of ferries, assemblages changed back towards (although not reaching) their previous state. Abundances of the polychaete families Nereididae, Capitellidae and Spionidae also increased at some sites during the cessation, although this pattern was not found in all sites and there was no general response to the cessation of wash as had been predicted. These results indicate that wash is important in structuring assemblages of macrobenthic infauna, although responses of individual taxa are more idiosyncratic. More importantly, they show that manipulations, resulting from managerial decisions, can be treated as testable hypotheses and utilized by scientists as experiments to test for causal relationships.  相似文献   

Sterols as markers of sewage contamination in a tropical urban estuary (Guanabara Bay, Brazil): space–time variations     

Renato S. Carreira  Angela L. R. Wagener  James W. Readman 《Estuarine, Coastal and Shelf Science》2004,60(4):64

Guanabara Bay, located adjacent to Rio de Janeiro in Brazil, is highly contaminated by substances derived from domestic and industrial effluents as well as from agricultural runoff. In the present work, sedimentary coprostanol and other faecal sterols were used to investigate historical trends in sewage contamination. Sediment cores were collected from eight different (and characterized) locations in the bay and were sectioned into dated segments. Organic carbon was determined by dry combustion and sterols were separated and quantified by GC/MS. The space-distribution of organic carbon and faecal sterol concentrations generally coincided with the presence of known pollution sources. Concentrations of coprostanol as high as 40 μg g⁻¹ were found, indicating areas of severe sewage contamination. Faecal sterol ratios, commonly used as tools to investigate contamination in temperate environments, however, were found to have limited applicability to this tropical estuarine system, probably due to the influence of intensive primary production and microbial processes.  相似文献   

Population biology of the Norway lobster, Nephrops norvegicus (L.) in the Firth of Clyde, Scotland - I: Growth and density     

Tuck  I. D.; Chapman  C. J.; Atkinson  R. J. A. 《ICES Journal of Marine Science》1997,54(1):125-135

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