The weakening role of science in the management of groundfish off the east coast of Canada     

Shelton  Peter A. 《ICES Journal of Marine Science》2007,64(4):723-729

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Dolomitization of the Waulsortian Limestone (Lower Carboniferous) in the Irish Midlands   总被引：1，自引：0，他引：1  

Jay M. Gregg  Kevin L. Shelton  Aaron W. Johnson  Ian D. Somerville  & Wayne R. Wright 《Sedimentology》2001,48(4):745-766

The Waulsortian Limestone (Lower Carboniferous) of the southern Irish Midlands is dolomitized pervasively over a much larger region than previous studies have documented. This study indicates a complex, multistage, multiple fluid history for regional dolomitization. Partially and completely dolomitized sections of Waulsortian Limestones are characterized by finely crystalline (0·01–0·3 mm) planar dolomite. Planar replacive dolomite is commonly followed by coarse (≥0·5 mm) nonplanar replacive dolomite, and pervasive void‐filling saddle dolomite cement is frequently associated with Zn–Pb mineralization. Planar dolomite has average δ¹⁸O and δ¹³C values (‰ PDB) of –4·8 and 3·9 respectively. These are lower oxygen and slightly higher carbon isotope values than averages for marine limestones in the Waulsortian (δ¹⁸O=–2·2, δ¹³C=3·7). Mean C and O isotope values of planar replacive dolomite are also distinct from those of nonplanar and saddle dolomite cement (–7·0 and 3·3; –7·4 and 2·4 respectively). Fluid inclusions indicate a complex history involving at least three chemically and thermally distinct fluids during dolomite cementation. The petrography and geochemistry of planar dolomites are consistent with an early diagenetic origin, possibly in equilibrium with modified Carboniferous sea water. Where the Waulsortian was exposed to hydrothermal fluids (70–280 °C), planar dolomite underwent a neomorphic recrystallization to a coarser crystalline, planar and nonplanar dolomite characterized by lower δ¹⁸O values. Void‐filling dolomite cement is isotopically similar to nonplanar, replacive dolomite and reflects a similar origin from hydrothermal fluids. This history of multiple stages of dolomitization is significantly more complex than earlier models proposed for the Irish Midlands and provides a framework upon which to test competing models of regional vs. localized fluid flow.  相似文献   

Proximity of adult children to their parents in Great Britain     

Shelton N  Grundy E 《International journal of population geography : IJPG》2000,6(3):181-195

Much of the authors' knowledge of kin interaction and exchange in Britain is partial, in that it is based on studies of co-resident groups and excludes consideration of kin "beyond the household". It is known that there have been large declines in intergenerational co-residence, raising fears that family bonds have weakened. It is also commonly assumed that family members are less likely to live in close proximity than in the past. In this paper the authors examine one important aspect of kin relationships--proximity of adult children to their parents--using nationally representative data from 1986, 1995, and 1999. The analyses presented focus on: differences between 1986, 1995, and 1999 in proximity of adults to their parents; sociodemographic characteristics associated with variations in proximity, and temporal differences in the pattern of these variations. The paper concludes with an assessment of some of the policy implications of the findings.  相似文献   

Deformation microstructures in experimentally deformed Maryland diabase     

Andreas K Kronenberg  Glenmore L Shelton 《Journal of Structural Geology》1980,2(3):341-353

Experimentally deformed Maryland diabase has been examined using the transmission electron microscope in order to determine the mechanisms of deformation operative over a range of temperatures and pressures and thereby aid in the interpretation of polyphase flow data. Deformation mechanisms within the plagioclase and clinopyroxene of the diabase have been compared to those within monomineralic aggregates of these phases deformed at the same conditions. Both phases deform by microfracturing, mechanical twinning, and intracrystalline slip.Data for the monomineralic aggregates show that plagioclase is stronger than clinopyroxene at <800°C, but weaker at ≥ 800°C, for a pressure of 15 kbar and strain rate of 10^?6/sec. Observations of the diabase are consistent with this result: at < 800°C, the plagioclase and pyroxene grains are about equally strained, whereas at ≥ 800°C, almost all of the sample strain is accommodated by the plagioclase, the more continuous phase.  相似文献   

Uncertainty in modelling of faecal coliform overland transport associated with manure application in Maryland     

A. K. Guber  Y. A. Pachepsky  A. M. Yakirevich  D. R. Shelton  A. M. Sadeghi  D. C. Goodrich  C. L. Unkrich 《水文研究》2011,25(15):2393-2404

Concerns for microbial safety of surface water facilitate development of predictive models that estimate concentrations and total numbers of pathogen and indicator organisms leaving manure‐fertilized fields in overland flow during runoff events. Spatial variability of bacterial concentrations in applied manure introduces high uncertainty in the model predictions. The objective of this work was to evaluate the uncertainty in model predictions of the manure‐borne bacteria overland transport caused by limited information on the spatial distribution of bacteria in surface‐applied manure. Experiments were carried out at the ARS Beltsville experimental watershed site (OPE3) in Maryland. Dairy bovine manure was applied at a 59·3 t/ha rate on the 3·55 hectare experimental field. Faecal coliform (FC) concentrations in manure measured in 2004, 2005, 2007, and 2009 varied by 4 orders of magnitude each year. Both runoff volume and FC concentrations in runoff water were monitored using a runoff flume equipped with a refrigerated pump sampler. Two runoff events occurred before the manure was incorporated into the soil. A bacteria transport add‐on module simulator of transport with infiltration and runoff (STWIR) was linked with the event‐based kinematic runoff and erosion model (KINEROS2) to simulate convective‐dispersive overland transport, bacteria release from manure, reversible attachment–detachment to soil, and surface straining of infiltrating bacteria. The model was successfully calibrated with the field experiment data. Monte Carlo simulations were carried out to account for the spatial variation in FC in applied manure and uncertainty in the FC distribution in manure caused by the small number of samples. A tenfold and twofold variation in FC concentrations in the runoff were obtained within the 90% probability interval when initial FC spatial distributions in the manure were represented by 5 and 29 samples, respectively. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Transport of anchovy, Engraulis capensis Gilchrist, eggs and early larvae by a frontal jet current     

Shelton  P. A.; Hutchings  L. 《ICES Journal of Marine Science》1982,40(2):185-198

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Influence of microstructure of loess on triaxial shear strength     

R.V. Matalucci  M. Abdel-hady  J.W. Shelton 《Engineering Geology》1970,4(4):341-351

Vicksburg loess is characterized by preferred orientation of constituent grains, which on the average dip 4° toward the west (N 80–85°W). This investigation was undertaken to study, quantitatively, the relationship between natural fabric anisotropies of Vicksburg loess and the orientation of applied stress distribution Results of the study indicate the fabric anisotropies in Vicksburg loess are reflected by definite variation in triaxial shear strength of dry and moist specimens.

In two series of triaxial tests, ultimate strength of the loess is maximum where σ₁ is perpendicular to grain orientation, and it is reduced where the principal stresses are 45° to the fabric plane. In this respect, Vicksburg loess may serve as a structural model for granular earth materials in illustrating the influence of fabric on ultimate strength. Moreover, the Mohr-Coulomb fracture line consists of two line segments, with an increase in slope at higher confining pressure. This characteristic suggests that poorly-cemented sands, or sandstones, and silts, or siltstones, may undergo two failures: one at small strains where cement bonds are disrupted and the other at larger strains where internal shearing resistance of granular components is exceeded.  相似文献   

Evolution of a Carboniferous carbonate-hosted sphalerite breccia deposit,Isle of Man     

Kevin L. Shelton  Justin M. Beasley  Jay M. Gregg  Martin S. Appold  Stephen F. Crowley  James P. Hendry  Ian D. Somerville 《Mineralium Deposita》2011,46(8):859-880

A newly discovered, extensive sphalerite-bearing breccia (~7.5 wt.% Zn) is hosted in dolomitised Carboniferous limestones overlying Ordovician–Silurian metasedimentary rocks on the Isle of Man. Although base metal sulphide deposits have been mined historically on the island, they are nearly all quartz vein deposits in the metamorphic basement. This study investigates the origin of the unusual sphalerite breccia and its relationship to basement-hosted deposits, through a combination of petrographic, cathodoluminescence, fluid inclusion, stable isotope and hydrogeologic modelling techniques. Breccia mineralisation comprises four stages, marked by episodes of structural deformation and abrupt changes in fluid temperature and chemistry. In stage I, high-temperature (T _h > 300°C), high-salinity (20–45 wt.% equiv. NaCl) fluid of likely basement origin deposited a discontinuous quartz vein. This vein was subsequently dismembered during a major brecciation event. Stages II–IV are dominated by open-space filling sphalerite, quartz and dolomite, respectively. Fluid inclusions in these minerals record temperatures of ~105–180°C and salinities of ~15–20 wt.% equiv. NaCl. The δ³⁴S values of sphalerite (6.5–6.9‰ Vienna-Canyon Diablo troilite) are nearly identical to those of ore sulphides from mines in the Lower Palaeozoic metamorphic rocks. The δ¹⁸O values for quartz and dolomite indicate two main fluid sources in the breccia’s hydrothermal system, local Carboniferous-hosted brines (~0.5–6.0‰ Vienna standard mean ocean water) and basement-involved fluids (~5.5–11.5‰). Ore sulphide deposition in the breccia is compatible with the introduction and cooling of a hot, basement-derived fluid that interacted with local sedimentary brines.  相似文献   

Sulfur isotope evidence for penetration of MVT fluids into igneous basement rocks,southeast Missouri,USA     

K. L. Shelton  I. B. Burstein  R. D. Hagni  C. B. Vierrether  S. K. Grant  Q. T. Hennigh  M. F. Bradley  R. T. Brandom 《Mineralium Deposita》1995,30(5):339-350

Previous studies of galena and sphalerite from Paleozoic MVT deposits in the Viburnum Trend, southeast Missouri documented large variations in ³⁴S values throughout the ore-forming event. The present study of Cu-Fe-sulfides reveals a similar ³⁴S variation that reflects two end-member sulfur reservoirs whose relative importance varied both temporally and spatially. More ³⁴S-enriched sulfides (³⁴S approaching 25) indicate introduction of sulfur from basinal sedimentary sources, whereas more ³²S-enriched sulfides (³⁴S < 5) may reflect fluids moving through underlying granitic basement. Two areas containing Precambrian, igneous-hosted FeCu mineralization in southeast Missouri (West and Central Domes of Boss-Bixby) were investigated to elucidate their relationship to Cu-rich MVT orebodies hosted nearby within the overlying Cambrian Bonneterre Dolomite. Mineralization at Boss-Bixby is composed of an early phase of iron oxide deposition followed by Cu-Fe-sulfides. The Central Dome is faulted and its mineralization is more fracture-controlled than the typically podiform ores of the West Dome. The ³⁴S values of West Dome sulfides are 0.9 to 6.5 and pyrite-chalcopyrite indicate a temperature of 525° ± 50 °C. These data indicate an igneous source of sulfur during Precambrian ore deposition. In contrast, ³⁴S values of Central Dome sulfides are 9.4 to 20.0 and pyrite-chalcopyrite indicate temperatures of 275° ± 50 °C. Similar ³⁴S values are obtained for chalcopyrite from the overlying MVT deposits. We speculate that deeply circulating, basin-derived MVT fluids mobilized sulfur and copper from the underlying igneous basement and redeposited them in overlying Curich MVT orebodies, as well as overprinting earlier Precambrian sulfides of the Central Dome with a later, Paleozoic MVT sulfur isotope signature. Many models for MVT fluid circulation in the Midcontinent region of North America assume that igneous basement rocks are an impermeable boundary, but in southeast Missouri, evidence exists for structurally controlled MVT fluid movement > 600 m vertically through underlying Precambrian igneous rocks. Such basement involvement has been suggested for other carbonate-hosted base-metal districts (e.g. Irish base metal deposits) and should be considered an integral part of the ore-forming process in southeast Missouri.  相似文献   

Interpreting catch per unit effort data to assess the status of individual stocks and communities   总被引：3，自引：0，他引：3  

Maunder  Mark N.; Sibert  John R.; Fonteneau  Alain; Hampton  John; Kleiber  Pierre; Harley  Shelton J. 《ICES Journal of Marine Science》2006,63(8):1373-1385

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