Shoreface translation and the Holocene stratigraphic record: Examples from Nova Scotia, the Mississippi Delta and eastern Australia     

Ron Boyd  Shea Penland 《Marine Geology》1984,60(1-4):391-412

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Species, tissue and gender-related organochlorine bioaccumulation in white-sided dolphins, pilot whales and their common prey in the northwest Atlantic   总被引：5，自引：0，他引：5  

Weisbrod AV  Shea D  Moore MJ  Stegeman JJ 《Marine environmental research》2001,51(1):29-50

Organochlorine concentrations were measured in white-sided dolphins, pilot whales, and their prey from the Gulf of Maine and used to identify species, tissue, and gender differences, and trophic transfer trends, in bioaccumulation. Polychlorinated biphenyl concentrations ([PCB]) in dolphin blubber (13 +/- 7.1 micrograms/g fresh wt.) were twice those in pilot whales, but pesticide concentrations (20 +/- 13 micrograms/g fresh) were similar between species. 4,4'-DDE, trans-non-achlor, Cl6(153) and Cl6(138) concentrations were highest. Skin tissues had more recalcitrant organochlorines than the internal organs. Male dolphins bioaccumulated higher concentrations of nonmetabolizable PCBs and hexachlorocyclohexane (HCH) isomers, whereas pilot whales had no gender-related differences in bioaccumulation. Pilot whales, mackerel, and herring had proportionately higher concentrations of DDTs, whereas [PCB] were higher in dolphins and squid. Although these odontocetes feed at the same trophic level and store a similar suite of contaminants, dolphins bioaccumulated higher and potentially hazardous 4,4'-DDE and PCB concentrations from food in their more geographically restricted range.  相似文献   

The regional geology of the Poços de Caldas alkaline complex: mineralogy and geochemistry of selected nepheline syenites and phonolites     

H.D. Schorscher  M.E. Shea 《Journal of Geochemical Exploration》1992,45(1-3)

The Mesozoic Poços de Caldas alkaline complex, the largest known in South America, is circular-shaped with a mean diameter of about 33 km, and developed during continental break-up and drift. It comprises a suite of alkaline volcanic and plutonic rocks (mainly phonolites and nepheline syenites) with average amounts of U, Th and rare-earth elements (REEs). The evolutionary history began with major early volcanism involving ankaratrites, phonolite lavas and volcanoclastics, followed by caldera subsidence and nepheline syenite intrusions forming minor ring dykes, various intrusive bodies and circular structures. Finally, the addition or concentration of strongly incompatible elements led to the formation of eudialyte nepheline syenites and phonolites.Magmatic evolution included deuteric processes indicating a volatile-rich parent magma of upper mantle origin, without appreciable crustal contamination. These processes extended over a large temperature range and resulted in the formation of pegmatitic veins and comprised mineral assemblages including rare metal silicates such as giannettite, incipient alkali exchange reactions of feldspars, various zeolites, fluorite and hematite. Geochemically, the resulting rocks are enriched in potassium when compared to global nepheline syenites and phonolites. Mobilization and concentration of U, Th and REEs did not apparently occur at this stage.At one place (Morro do Ferro) the intermediate nephelinic suite was affected by a possible carbonatite intrusion and the formation of a stockwork of magnetite veins.Very intensive hydrothermal K- and S-rich alteration, associated with contemporaneous volcanic breccias, occurred locally. These processes led to the formation of several important radioactive and REE-rich anomalies. Two of these, the Th-REE occurrence of Morro do Ferro and the U-Zr-REE-Th occurrence of the Osamu Utsumi uranium mine, comprise the study sites of the Poços de Caldas Analogue Project.Later major stages in the evolution of the Poços de Caldas complex involved the emplacement of mafic-ultramafic dyke rocks and the onset of lateritic and allitic weathering, resulting (at the uranium mine) in supergene geochemical redistribution and the formation of redox fronts sometimes related to uranium enrichments. The end of the magmatic and hydrothermal-mineralizing events is likely fixed by the Ar-Ar dating of a lamprophyre dyke at the uranium mine (76 Ma).This study was focused towards the major rock types of the regional nephelinic suite relative to those experiencing more local hydrothermal and final weathering-related alteration. In the studied intrusive, subvolcanic and volcanic nepheline syenites and phonolites, very little variation was observed. This lack of differentiation may be seen as an argument for a short emplacement history of these rock bodies. Present radiometric age measurements suggest a time span of about 10 Ma for igneous activity at the caldera.  相似文献   

Present and Future Observing Trends in Atmospheric Magnetoseismology     

D. Banerjee  R. Erdélyi  R. Oliver  E. O’Shea 《Solar physics》2007,246(1):3-29

With modern imaging and spectral instruments observing in the visible, EUV, X-ray, and radio wavelengths, the detection of oscillations in the solar outer atmosphere has become a routine event. These oscillations are considered to be the signatures of a wave phenomenon and are generally interpreted in terms of magnetohydrodynamic (MHD) waves. With multiwavelength observations from ground- and space-based instruments, it has been possible to detect waves in a number of different wavelengths simultaneously and, consequently, to study their propagation properties. Observed MHD waves propagating from the lower solar atmosphere into the higher regions of the magnetized corona have the potential to provide excellent insight into the physical processes at work at the coupling point between these different regions of the Sun. High-resolution wave observations combined with forward MHD modeling can give an unprecedented insight into the connectivity of the magnetized solar atmosphere, which further provides us with a realistic chance to reconstruct the structure of the magnetic field in the solar atmosphere. This type of solar exploration has been termed atmospheric magnetoseismology. In this review we will summarize some new trends in the observational study of waves and oscillations, discussing their origin and their propagation through the atmosphere. In particular, we will focus on waves and oscillations in open magnetic structures (e.g., solar plumes) and closed magnetic structures (e.g., loops and prominences), where there have been a number of observational highlights in the past few years. Furthermore, we will address observations of waves in filament fibrils allied with a better characterization of their propagating and damping properties, the detection of prominence oscillations in UV lines, and the renewed interest in large-amplitude, quickly attenuated, prominence oscillations, caused by flare or explosive phenomena.  相似文献   

A summary of major solar proton events   总被引：9，自引：0，他引：9  

M. A. Shea  D. F. Smart 《Solar physics》1990,127(2):297-320

Solar proton events have been routinely detected by satellites since the 20th solar cycle; however, before that time only very major proton events were detected at the Earth. Even though the detection thresholds differed between the 19th and more recent cycles, more than 200 solar proton events with a flux of over 10 particles (cm² s ster)^–1 above 10 MeV have been recorded at the Earth in the last three solar cycles. At least 15% of these events had protons with energies greater than 450 MeV detected at the Earth. Other than an increase in solar proton event occurrence with increasing solar cycle, no recognizable pattern could be identified between the occurrence of solar proton events and the solar cycle. The knowledge we have gained from the data acquired over the past 40 years illustrates the difficulty in extrapolating back in time to infer the number and intensity of major solar proton events at the Earth.The U.S. Government retains a nonexclusive, royalty-free license to publish or reproduce the published form of this contribution, or allow others to do so, for U.S. Government purposes.  相似文献   

Artifact abrasion,fluvial processes,and “living floors” from the Early Paleolithic site of ’Ubeidiya (Jordan Valley,Israel)     

John J. Shea 《Geoarchaeology》1999,14(2):191-207

Early Acheulian assemblages in fluviolacustrine contexts at the Early Pleistocene site of ‘Ubeidiya (Jordan Valley, Israel) have been described as “living floors.” A study of variation in the surface abrasion of stone tools from several such “living floors” suggest a mixture of cultural and geological factors were involved in the formation of these assemblages. © 1999 John Wiley & Sons, Inc.  相似文献   

Discovery of a trachyte ignimbrite sequence at Hualālai,Hawaii     

Thomas Shea  Jacqueline Owen 《Bulletin of Volcanology》2016,78(5):34

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Increasing the usability and accessibility of geodynamic modelling tools to the geoscience community: UnderworldGUI     

Shea Goyette  Masa Takatsuka  Stuart Clark  R. Dietmar Müller  Patrice Rey  Dave R. Stegman 《Visual Geosciences》2008,13(1):25-36

Geoscientists are faced with a number of complexities that represent obstacles to the development of realistic simulation of deep earth processes. Realistic 4D thermo-mechanical simulation using software packages like Underworld and Gale, when combined appropriately with geoscientific expertise, can lead to novel insights into the deformation of geological structures at a wide range of time and spatial scales. The challenge for end-user geoscientists lies in applying their knowledge within the framework of the software’s input specification, including initial, internal, and boundary conditions and output visualization parameters. We have built a Graphical User Interface (GUI) to remove many of the difficulties related to editing the Extensible Markup Language (XML) encoded input files of Underworld/Gale geomodels and therefore, to greatly broaden the user base of these software packages. By helping Underworld/Gale to meet a large audience, we provide a tool to the geoscience community that helps to move from untested conceptual models to physically valid, properly scaled modelling. Furthermore, the UnderworldGUI offers a mechanism for storing and retrieving experimental models in a centralised database, thus providing the geoscience community with a means to share the outcomes of its experimental research. Further details of the UnderworldGUI are available at the web site .

Shea GoyetteEmail:

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Near-field high temperature transport: evidence from the genesis of the Osamu Utsumi uranium mine, Poços de Caldas alkaline complex, Brazil     

L.M. Cathles  Michael E. Shea 《Journal of Geochemical Exploration》1992,45(1-3)

The chemical, isotopic and mineralogical alteration which occurred during primary uranium ore deposition at the breccia pipe-hosted Osamu Utsumi mine, Poços de Caldas, Brazil was studied as a natural analogue for near field radionuclide migration. Chemical and isotopic alteration models were combined with finite difference models of the convective cooling of caldera intrusives. The modeling indicates that the intense chemical, isotopic, and mineralogical alteration of the Osamu Utsumi breccia pipe requires the circulation of > 10⁵ kg/cm² of boiling hydrothermal fluid > 200°C through each square centimeter cross-section of the pipe. This circulation could be driven by heat from a 6 km diameter intrusive extending to 10 km depth. Even with this large amount of circulation concentrated in the permeable breccia pipe, uranium solubilities must be orders of magnitude greater than indicated in the most recent experiments (and more in line with previous estimates) to produce the primary uranium mineralization at the Osamu Utsumi mine.The same models applied to a hypothetical high temperature waste repository show that heat from radioactive decay will produce a hydrothermal circulation system remarkably similar to that studied at the natural analogue site at Poços de Caldas. The depth of fluid convection induced by the hypothetical repository would be 5 to 10 km, the maximum temperature would be 300°C, the lifetime of the high temperature phase would be a few thousand years, and boiling would occur and cause most of the alteration within the hypothetical waste repository. This physical analysis emphasizes the importance of permeability on a 10 × 10 × 10 km scale in controlling the potential amount of circulation through the hypothetical repository.Application of the chemical models successfully used to interpret mineralization and alteration at the Poços de Caldas Osamu Utsumi mine to the hypothetical waste repository shows that even in a worst case scenario (waste implaced in a permeable host rock with no measures taken to inhibit flow though the repository) the amount of hydrothermal alteration in the hypothetical repository will be 0.1% of that in the breccia pipe at Osamu Utsumi. Assuming no barriers to uranium mobility, uranium precipitation above the hypothetical repository would be 0.04 ppm (rather than 40 ppm), hydrothermal alteration 0.03 wt% (rather than 30 wt%), etc.Our analysis indicates that modeled mineralogical alteration is sensitive to the thermodynamic data base used. Prediction of mineralogical alteration (which may be necessary to predict the migration of radionuclides other than uranium, for example) probably cannot be based directly on even very carefully collected laboratory thermodynamic data. Mineralogical complexities of the system, as well as data base uncertainties will require calibration of the thermodynamic framework against mineralogical alteration observed in the laboratory or field.  相似文献   

Hurricane impact and recovery shoreline change analysis of the Chandeleur Islands,Louisiana, USA: 1855 to 2005   总被引：1，自引：0，他引：1  

Sarah Mary Fearnley  Michael D. Miner  Mark Kulp  Carl Bohling  Shea Penland 《Geo-Marine Letters》2009,29(6):455-466

Results from historical (1855–2005) shoreline change analysis conducted along the Chandeleur Islands, Louisiana demonstrate that tropical cyclone frequency dominates the long-term evolution of this barrier island chain. Island area decreased at a rate of −0.16 km²/year for the relatively quiescent time period up until 1996, when an increase in tropical cyclone frequency accelerated this island area reduction to a rate of −1.01 km²/year. More frequent hurricanes also affected shoreline retreat rates, which increased from −11.4 m/year between 1922 and 1996 to −41.9 m/year between 1982 and 2005. The erosional impact caused by the passage of Hurricane Katrina in 2005 was unprecedented. Between 2004 and 2005, the shoreline of the northern islands retreated −201.5 m/year, compared with an average retreat rate of −38.4 m/year between 1922 and 2004. A linear regression analysis of shoreline change predicts that, as early as 2013, the backbarrier marsh that serves to stabilize the barrier island chain will be completely destroyed if storm frequency observed during the past decade persists. If storm frequency decreases to pre-1996 recurrence intervals, the backbarrier marsh is predicted to remain until 2037. Southern portions of the barrier island chain where backbarrier marsh is now absent behave as ephemeral islands that are destroyed after storm impacts and reemerge during extended periods of calm weather, a coastal behavior that will eventually characterize the entire island chain.  相似文献