Nd isotope mapping of Grenvillian crustal terranes in the vicinity of the Manicouagan Impact Structure     

Stephanie D. Thomson  Alan P. Dickin  John G. Spray 《Precambrian Research》2011,191(3-4):184-193

Over 70 new Nd isotope analyses are presented for the Manicouagan area of the Grenville Province to estimate the crustal age of target rocks involved in the 214 Ma Manicouagan Impact Structure, and to reconstruct the Precambrian geological evolution of this crustal segment. The rocks fall into two main groups: Samples from the Archean-aged Gagnon Terrane to the north and west of the impact give T_DM ages averaging 2.70 Ga. Samples from the Manicouagan Imbricate Zone (MIZ) and other allochthonous lithotectonic domains to the south of the impact yield Paleoproterozoic T_DM ages averaging 2.01 Ga for the MIZ and 1.86 Ga for the southern domains. These Paleoproterozoic terranes are correlated with Makkovik-age crust in Labrador that was heavily reworked by Labradorian magmatism that increased in intensity southwards. The target rocks involved in the impact event would have consisted almost entirely of the MIZ, which formed a layer several kilometres thick, overlying Archean crust at depth.  相似文献   

A model-based evaluation of Marine Protected Areas: the example of eastern Baltic cod (Gadus morhua callarias L.)     

Kraus  Gerd; Pelletier  Dominique; Dubreuil  Julien; Mollmann  Christian; Hinrichsen  Hans-Harald; Bastardie  Francois; Vermard  Youen; Mahevas  Stephanie 《ICES Journal of Marine Science》2009,66(1):109-121

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Transportation geography: The influence of Walter Isard and regional science     

Stephanie E.?ChangEmail author 《Journal of Geographical Systems》2004,6(1):55-69

This paper explores the influence of Walter Isard, his work, and the field of regional science generally on transportation geography. It argues that Isards impact was both subtle and significant. Regional science greatly influenced the emergence of modern transportation geography in the 1950s. Transportation themes and methods from Isards own work provided early building blocks for transportation geography. Moreover, Isard and regional science contributed importantly to the development of the intellectual network of persons, places, and institutions that early on defined the subfield. Regional science and transportation geography have diverged in recent decades, but opportunities exist for renewed interaction.The author thanks Doug Fleming and Dick Morrill for comments on an earlier version of this paper.  相似文献   

Antarctic circumpolar modes in a coupled ocean–atmosphere model     

Simon J.?MarslandEmail author  Mojib?Latif  Stephanie?Legutke 《Ocean Dynamics》2003,53(4):323-331

Eastward-propagating patterns in anomalous potential temperature and salinity of the Southern Ocean are analyzed in the output of a 1000-year simulation of the global coupled atmosphere–ocean GCM ECHO-G. Such features can be associated with the so-called Antarctic Circumpolar Wave (ACW). It is found that time–longitude diagrams that have traditionally been used to aid the visualization of the ACW are strongly influenced by the width of the bandpass time filtering. This is due to the masking of considerable low-frequency variability that occurs over a broad range of time scales. Frequency–wavenumber analysis of the ACW shows that the eastward-propagating waves do have preferred spectral peaks, but that both the period and wavenumber change erratically when comparing different centuries throughout the simulation. The variability of the ACW on a variety of time scales from interannual to centennial suggests that the waiting time for a sufficient observational record to determine the time scale of variability of the real world ACW (and the associated decadal time scale predictability of climate for southern landmasses) will be a very long one.Responsible Editor: Dirk Olbers  相似文献   

Can the nitrogen and carbon stable isotopes of the pygmy mussel,Xenostrobus securis, indicate catchment disturbance for estuaries in northern New South Wales, Australia?     

Stephanie K. Moore  Iain M. Suthers 《Estuaries and Coasts》2005,28(5):714-725

The nitrogen and carbon stable isotope ratios (δ¹⁵N and δ¹³C) of the pygmy mussel,Xenostrobus securis, were determined for three estuaries with varying levels of catchment disturbance in northern New South Wales, Australia. The lower Manning River catchment supported the highest human population densities with 3% residential development and some livestock agriculture (41%); the Wallamba River catchment was mostly livestock agriculture (56%) while the Wallingat River catchment was mostly vegetated (79%). Mussels, estuarine particulate organic matter (POM), and livestock and human-derived waste were collected in two stages during the austral summers of 2001–2002 and 2002–2003 for dual carbon-nitrogen stable isotope analysis. The disturbed Manning and Wallamba River catchment mussels were enriched in¹⁵N by an average of 3.2‰ and 1.5‰, respectively, compared to the vegetated Wallingat River mussels. Mussel δ¹³C values ranged from −24.8‰ to −30.3‰ and showed an estuarine gradient becoming enriched with distance downstream within estuaries, but were unable to distinguish patterns in catchment disturbance between estuaries. The δ¹⁵N and δ¹³C values of POM showed a similar pattern to mussels, indicating a direct link between them within each estuary. A multiple regression model of mussel δ¹⁵N using the fractions of land used for livestock agriculture and residential development within 5 km zones from river networks to a distance equivalent to a tidal ellipse from sites explained 67% of the variation in mussel δ¹⁵N with 95% of the differences lying within 1.6‰ of observed values. Increasing fractions of land used for livestock agriculture depleted mussel δ¹⁵N values estimated by the regression equation, indicating the use of cow manure as a nutrient source with a value of 2.0‰. Increasing fractions of land used for residential development enriched estimated mussel δ¹⁵N, indicating the use of human-derived waste with a value of 20.8‰. Pygmy mussels are a useful long-term bio-indicator for the effects of anthropogenic catchment disturbance and nutrient enrichment in estuaries.  相似文献   

Identifying characteristics of charge transfer transitions in minerals     

Stephanie M. Mattson  George R. Rossman 《Physics and Chemistry of Minerals》1987,14(1):94-99

Criteria used to identify Fe²⁺-Fe³⁺ and Fe²⁺-Ti⁴⁺ intervalence charge transfer absorption bands in electronic spectra are reviewed and compared to the characteristics of unperturbed Fe²⁺ crystal field bands and those that are intensified by interaction with Fe³⁺. Band energy is the least definitive diagnostic criterion. Changes in band intensity with temperature are also of limited value. Large widths are the most reliable characteristic of charge transfer bands. New optical absorption spectra are presented for euclase, as well as 80 K spectra of rockbridgeite, babingtonite and lazulite. Comparison of optical spectra to magnetic susceptibility measurements for rockbridgeite and babingtonite provides support for recent theories regarding the effect of magnetic coupling on the variation of charge transfer intensity with temperature.  相似文献   

Isotopic evidence for the magmatic and tectonic histories of the Carolina terrane: implications for stratigraphy and terrane affiliation     

Stephanie Ingle  Paul A. Mueller  Ann L. Heatherington  Marianne Kozuch 《Tectonophysics》2003,371(1-4):187-211

Establishing the age and crustal nature of exotic terranes and their underlying basements helps to determine their paleogeographic origin and tectonic histories. We present U–Pb ages of zircons and Sm–Nd whole rock isotopic data for volcanic and plutonic rocks of the Carolina terrane, one of several peri-Gondwanan terranes that were accreted to the margins of the circum-Atlantic continents during the Paleozoic. Volcanism in this subduction-related arc culminated in the eruption of the Morrow Mountain rhyolite, at ca. 540 Ma; thus, magmatism in the Carolina terrane ceased at the beginning of the Cambrian. The presence of inherited zircons and non-juvenile depleted mantle model ages of Carolina slate belt rocks favor a basement that is, at least in part, composed of evolved continental crust. Ages of inherited xenocrystic zircons cluster at ca. 1000, 2100 and 2500 Ma. These ages, in addition to volcanism at ca. 618–540 Ma, correlate best with well-known tectonic events in present-day northern South America. Specifically, the Orinoquian-Sunsas, the Trans-Amazonian and the Central Amazonian orogenic zones are likely candidates for potential basement correlatives to the Carolina terrane. Sm–Nd isotopic signatures vary significantly, but permit assimilation of Orinoquian age (1000 Ma) crust by magmas derived from the depleted mantle in a subduction (arc-related) setting. Our findings are also consistent with proposed correlations between the Carolina terrane and Avalonia which is likewise believed to have formed along the northern margin of present-day South America.  相似文献   

The shape of Fraught – urban – rural – the nation-state: tensions and dynamics     

Stephanie Pincetl 《Urban geography》2018,39(9):1431-1434

I argue that the tension between cities and nation states go through the countryside, or rural areas, at least in the U.S. Further, cities are decidedly constrained in their abilities to effectuate many of the changes associated with them: addressing climate change, economic inequality and more. What is missing is the way in which rural alienation from economic prosperity plays out politically.  相似文献   

The effect of tidal forcing on biogeochemical processes in intertidal salt marsh sediments   总被引：1，自引：0，他引：1  

Martial Taillefert  Stephanie Neuhuber  Gwendolyn Bristow 《Geochemical transactions》2007,8(1):6

Background  

Early diagenetic processes involved in natural organic matter (NOM) oxidation in marine sediments have been for the most part characterized after collecting sediment cores and extracting porewaters. These techniques have proven useful for deep-sea sediments where biogeochemical processes are limited to aerobic respiration, denitrification, and manganese reduction and span over several centimeters. In coastal marine sediments, however, the concentration of NOM is so high that the spatial resolution needed to characterize these processes cannot be achieved with conventional sampling techniques. In addition, coastal sediments are influenced by tidal forcing that likely affects the processes involved in carbon oxidation.  相似文献   

Effects of storm-induced salinity changes on submersed aquatic vegetation in Kings Bay, Florida     

Thomas K. Frazer  Sky K. Notestein  Charles A. Jacoby  Chanda Jones Littles  Stephanie R. Keller  Robert A. Swett 《Estuaries and Coasts》2006,29(6):943-953

Hurricanes and other major storms cause acute changes in salinity within Florida's streams and rivers. Winddriven tidal surges that increase salinities may have long-lasting effects on submersed aquatic vegetation (SAV) and the associated fauna. We investigated potential effects of salinity pulses on SAV in Kings Bay, Florida, by subjecting the three most common macrophytes,Vallisneria americana, Myriophyllum spicatum., andHydrilla verticillata, to simulated salinity pulses. In Kings Bay, we documented changes in salinity during three storms in September 2004 and measured biomass and percent cover before and after these storms. During experiments, macrophytes were exposed to salinities of 5‰, 15‰, or 25‰ for 1, 2, or 7 d, with a 28-d recovery period in freshwater. Relative to controls, plants subjected to salinities of 5‰ exhibited few significant decreases in growth and no increase in mortality. All three species exhibited decreased growth in salinities of 15‰ or 25‰.H. verticillata, exhibited 100% mortality at 15‰ and 25‰, irrespective of the duration of exposure.M. spicatum andV. american exhibited increased mortality after 7-d exposures to 15‰ or any exposure to 25‰ Maximum daily salinities in Kings Bay approached or exceeded 15‰ after each of the three storms, with pulses generally lasting less than 2 d. Total aboveground biomass and percent cover of vascular plants, were reduced following the storms.M. spicatum exhibited an 83% decrease in aboveground biomass and an 80% decrease in percent cover.H. verticillata exhibited a 47% and 15% decline in biomass and percent cover, respectively.V. americana, exhibited an 18% increase in aboveground biomass and a 37% increase in percent cover, which suggests greater tolerance of salinity pulses and release from competition with the invasiveH. verticillata andM. spicatum. Our results indicate that rapid, storm-induced pulses of high salinity can have important consequences for submersed aquatic vegetation, restoration efforts, and management of invasive species.  相似文献