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A survey of imposex in Thais orbita (Neogastropoda) along the New South Wales (NSW) coast, Australia, found imposex was still widespread 10 years after a partial ban on tributyltin (TBT) based antifouling paints. Transplant experiments also revealed that imposex was induced in T. orbita over a period of 9 weeks in Sydney Harbour, NSW. A comparison of the imposex data with that collected shortly after the introduction of restrictions on TBT revealed a general decline in imposex frequency occurring at open coast sites, an exception being the site at South West Rocks. Sites located within harbour/bay areas did not display a decline in imposex frequency but a decline in the severity of imposex was apparent. The observed decrease in imposex values in T. orbita may reflect a general decrease of butyltin contamination within the coastal environment. However, the persistence of contamination "hotspots" within harbours and bays remains a concern. 相似文献
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Craig T. Simmons 《Hydrogeology Journal》2005,13(1):116-119
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The Paleoproterozoic Ruttan Cu–Zn volcanogenic massive-sulfide (VMS) deposit is a large, relatively low grade, bimodal-siliciclastic
type deposit in the Rusty Lake volcanic belt of northern Manitoba. The deposit contained over 82.8 million tonnes of massive
sulfide, of which 55.7 million tonnes were mined from 1973 to 2002. The deposit consists of a series of moderately to steeply
dipping, south-facing lenses that extend along strike at the surface for 1.1 km and to a depth of 1.0 km. These lenses occur
within a steeply dipping, bimodal volcanic, volcaniclastic and siliciclastic sequence. In the immediate mine area, transitional
calc-alkalic to high-silica (tholeiitic), felsic, and intermediate volcanic/volcaniclastic rocks of the Mine Sequence are
host to, and intercalated with, the massive-sulfide lenses. Transitional tholeiitic to calc-alkalic basalt and andesite are
present in the footwall sequence, approximately 500 m down-section from the ore horizon. The overlying rocks are predominantly
fine-grained volcaniclastics and siliciclastics, but include polyfragmental agglomerate that contains mafic bombs and scoriaceous
felsic fragments. Syn-depositional felsic and mafic dikes, sills, and apophyses are ubiquitous throughout the Mine Sequence,
including the ore lenses, indicating continued, near-vent magmatism, and volcanism during ore formation. Fabrics in altered
hostrocks have consistent, down-plunge stretching lineations to the SSE that suggest the deposit has been elongated by a factor
of ~1.2–1.5; otherwise, the deposit is remarkably undeformed. Syn- and post-depositional faults in the mine area have relatively
minor displacements up to tens of meters. Proximal (within 200 m) footwall rocks exhibit moderate to strong chloritization,
characterized by the upper greenschist to lower amphibolite facies assemblages that include cordierite–almandine–andalusite–sillimanite–biotite ± staurolite ± anthophyllite ± talc,
and local silicification. The proximal hanging wall rocks are characterized by sericite ± gahnite alteration, which is restricted
to within approximately 75 m of the uppermost lenses. Additional gangue minerals are anhydrite and carbonate minerals (siderite,
dolomite, ankerite, and calcite), as well as chlorite, sericite, biotite, talc, and quartz. Carbonate (excluding siderite),
potassium feldspar, silicification and epidotization are common distal alteration zones in the footwall to the Mine Sequence
several kilometers to the northeast. There are three principal groups of massive sulfide lenses; the East lenses, the West
lenses, and the Western Anomaly lenses to the far west. In general, Cu is relatively enriched at the stratigraphic base and
in the center of the deposit, whereas Zn is enriched upsection and at the outer margins. Some of the Zn-rich ore exhibits
primary mineralogical layering. Parts of the West and Western Anomaly lenses show two layers with Cu-rich bases and Zn-rich
tops. The massive sulfide is typically 10–40-m thick; one area along the margin of the main lenses is over 130-m thick and
may represent deposition adjacent to a syn-depositional fault. The main sulfide phases are pyrite, pyrrhotite, chalcopyrite,
sphalerite, and galena, with tetrahedrite as the most abundant trace phase. Gahnite is ubiquitous in the chlorite-rich assemblages
adjacent to the ore lenses. The average base, precious and trace metal contents estimated from Cu and Zn concentrates, and
from millhead grades and recoveries. Metals easily transported as chloride and bisulfide complexes in hydrothermal fluids
including: Pb, Ag, In, Cu, Cd, Au, and Zn are enriched by 1.5–2.5 orders of magnitude in comparison to the bulk continental
crust. Other elements such as Sn, Mo, and As are at near-crustal concentrations, whereas Mn, Ga, and Co are significantly
depleted in comparison to the crust. Calculated metal concentrations in the average hydrothermal fluid based on the average
metal contents are comparable to, or higher than those measured at sediment covered ridge hydrothermal systems, which precipitate
much of their metal budget in the subsurface. Average rare earth element contents for the sulfide are light rare earth element
enriched (LaN/YbN=22) and range from 0.45 to 0.02x chondritic values, with a moderate negative Eu anomaly (Eu*=0.51). Metal and trace element
contents in the Ruttan exhalite horizon, and in proximal (within 1–2 km) exhalites along strike from the 0.6 million tonne
Dar-2 Cu–Zn deposit 12 km south of Ruttan, have positive Eu anomalies, whereas negative Eu anomalies are present at distance.
The positive Eu anomalies reflect high temperature paleoseafloor hydrothermal venting and precipitation of Eu2+-enriched clays and possibly carbonates, and indicate proximity to base-metal deposits. Silver and lead are also enriched
in the exhalites near the deposits, whereas Mn is enriched at ~1–3 km along strike, but not consistently.
Editorial handling: B. Gemmel
An erratum to this article is available at . 相似文献
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We present data for U and its decay series nuclides 230Th, 226Ra, 231Pa, and 210Po for 14 lavas from Kick’em Jenny (KEJ) submarine volcano to constrain the time-scales and processes of magmatism in the Southern Lesser Antilles, the arc having the globally lowest plate convergence rate. Although these samples are thought to have been erupted in the last century, most have (226Ra)/(210Po) within ±15% of unity. Ten out of 14 samples have significant 226Ra excesses over 230Th, with (226Ra)/(230Th) up to 2.97, while four samples are in 226Ra-230Th equilibrium within error. All KEJ samples have high (231Pa)/(235U), ranging from 1.56 to 2.64 and high 238U excesses (up to 43%), providing a global end-member of high 238U and high 231Pa excesses. Negative correlations between Sr, sensitive to plagioclase fractionation, and Ho/Sm, sensitive to amphibole fractionation, or K/Rb, sensitive to open system behavior, indicate that differentiation at KEJ lavas was dominated by amphibole fractionation and open-system assimilation. While (231Pa)/(235U) does not correlate with differentiation indices such as Ho/Sm, (230Th)/(238U) shows a slight negative correlation, likely due to assimilation of materials with slightly higher (230Th)/(238U). Samples with 226Ra excess have higher Sr/Th and Ba/Th than those in 226Ra-230Th equilibrium, forming rough positive correlations of (226Ra)/(230Th) with Sr/Th and Ba/Th similar to those observed in many arc settings. We interpret these correlations to reflect a time-dependent magma differentiation process at shallow crustal levels and not the process of recent fluid addition at the slab-wedge interface.The high 231Pa excesses require an in-growth melting process operating at low melting rates and small residual porosity; such a model will also produce significant 238U-230Th and 226Ra-230Th disequilibrium in erupted lavas, meaning that signatures of recent fluid addition from the slab are unlikely to be preserved in KEJ lavas. We instead propose that most of the 238U-230Th, 226Ra-230Th, and 235U-231Pa disequilibria in erupted KEJ lavas reflect the in-growth melting process in the mantle wedge (reflecting variations in U/Th, daughter-parent ratios, fO2, and thermal structure), followed by modification by magma differentiation at crustal depths. Such a conclusion reconciles the different temporal implications from different U-series parent-daughter pairs and relaxes the time constraint on mass transfer from slab to eruption occurring in less than a few thousand years imposed by models whereby 226Ra excess is derived from the slab. 相似文献
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J. Stephen Hopkins Paul A. Sandifer M. Richard DeVoe A. Frederick Holland Craig L. Browdy Alvin D. Stokes 《Estuaries and Coasts》1995,18(1):25-42
Shrimp culture technology has resulted in development of a major shrimp farming industry worldwide. Without the shrimp farming industry, increasing demands for shrimp by consumers could not be met, resulting in increased pressure on wild shrimp resources. Unfortunately, there are realized and potential adverse environmental effects on estuarine ecosystems as a result of shrimp farming. The effects can be categorized as wetland destruction for construction of shrimp farms, hypernutrification of estuarine ecosystems by shrim pond effluent, “biological pollution” of native shrimp stocks through escapement of aquaculture stocks, water use and entrainment of estuarine biota, and impacts of shrimp farm chemicals on estuarine systems. While the shrimp farming industry in the United States is small, the United States is effectively addressing all the realized and potential environmental impacts through regulation and research at the federal and state levels. Areas of regulation and research include stringent prohibitions on wetland destruction, regulation of effluents and support of research to eliminate and/or reduce effluents, escapement prevention technology and development of high-health stocks, minimizing entrainment of estuarine biota through water conservation and screening technology, and regulation of chemical use in the shrimp farming industry and support of research on shrimp pathology and environmentally safe disease control. Work is still in progress and not all problems have been resolved to the complete satisfaction of shrimp farmers and estuarine conservationists. However, the situation in the United States should serve as a model of how to encourage sustainable economic development through commercial shrimp farming while abating adverse environmental impacts on estuarine systems. To further improve the situation, the development and adoption of “best management practices” for shrimp aquaculture are recommended. 相似文献
10.
Raphael Neukom David J. Nash Georgina H. Endfield Stefan W. Grab Craig A. Grove Clare Kelso Coleen H. Vogel Jens Zinke 《Climate Dynamics》2014,42(9-10):2713-2726
This study presents the first consolidation of palaeoclimate proxy records from multiple archives to develop statistical rainfall reconstructions for southern Africa covering the last two centuries. State-of-the-art ensemble reconstructions reveal multi-decadal rainfall variability in the summer and winter rainfall zones. A decrease in precipitation amount over time is identified in the summer rainfall zone. No significant change in precipitation amount occurred in the winter rainfall zone, but rainfall variability has increased over time. Generally synchronous rainfall fluctuations between the two zones are identified on decadal scales, with common wet (dry) periods reconstructed around 1890 (1930). A strong relationship between seasonal rainfall and sea surface temperatures (SSTs) in the surrounding oceans is confirmed. Coherence among decadal-scale fluctuations of southern African rainfall, regional SST, SSTs in the Pacific Ocean and rainfall in south-eastern Australia suggest SST-rainfall teleconnections across the southern hemisphere. Temporal breakdowns of the SST-rainfall relationship in the southern African regions and the connection between the two rainfall zones are observed, for example during the 1950s. Our results confirm the complex interplay between large-scale teleconnections, regional SSTs and local effects in modulating multi-decadal southern African rainfall variability over long timescales. 相似文献