Strontium in coral aragonite: 2. Sr coordination and the long-term stability of coral environmental records     

Adrian A. Finch  Nicola Allison 《Geochimica et cosmochimica acta》2003,67(23):4519-4527

We have used X-ray Diffraction (XRD) and Sr K-edge Extended X-ray Absorption Fine Structure (EXAFS) to determine the structural state of Sr in a suite of coral aragonite samples. Our samples encompassed a selection of coral species (Porites lobata, Porites lutea, Pocillopora eydouxi, Montastrea annularis, Pavona gigantea and Pavona clavus) including some commonly used for palaeoenvironmental reconstruction. Aragonite was the only carbonate observed by XRD. We refined the isolated EXAFS against structural models for Sr in aragonite and two-phase strontianite/aragonite mixes. Our data are indistinguishable from Sr ideally substituted in aragonite and strontianite was present below detection levels (estimated at <5% of Sr present). Comparisons of recent and ancient coral aragonite show no sign of exsolution, either by spinodal decomposition or by the direct nucleation of strontianite domains. Published diffusion rates of Sr in ionic solids support the view that exsolution would occur prohibitively slowly. Coral aragonites are metastable materials with slow diffusion kinetics that have the potential to encode environments over timescales of millions of years.  相似文献   

Monitoring and modelling of pore water pressure changes and riverbank stability during flow events   总被引：1，自引：0，他引：1  

Massimo Rinaldi  Nicola Casagli  Stefano Dapporto  Alessandro Gargini 《地球表面变化过程与地形》2004,29(2):237-254

Pore water pressures (positive and negative) were monitored for four years (1996–1999) using a series of tensiometer‐piezometers at increasing depths in a riverbank of the Sieve River, Tuscany (central Italy), with the overall objective of investigating pore pressure changes in response to ?ow events and their effects on bank stability. The saturated/unsaturated ?ow was modelled using a ?nite element seepage analysis, for the main ?ow events occurring during the four‐year monitoring period. Modelling results were validated by comparing measured with computed pore water pressure values for a series of representative events. Riverbank stability analysis was conducted by applying the limit equilibrium method (Morgenstern‐Price), using pore water pressure distributions obtained by the seepage analysis. The simulation of the 14 December 1996 event, during which a bank failure occurred, is reported in detail to illustrate the relations between the water table and river stage during the various phases of the hydrograph and their effects on bank stability. The simulation, according to monitored data, shows that the failure occurred three hours after the peak stage, during the inversion of ?ow (from the bank towards the river). A relatively limited development of positive pore pressures, reducing the effective stress and annulling the shear strength term due to the matric suction, and the sudden loss of the con?ning pressure of the river during the initial drawdown were responsible for triggering the mass failure. Results deriving from the seepage and stability analysis of nine selected ?ow events were then used to investigate the role of the ?ow event characteristics (in terms of peak stages and hydrograph characteristics) and of changes in bank geometry. Besides the peak river stage, which mainly controls the occurrence of conditions of instability, an important role is played by the hydrograph characteristics, in particular by the presence of one or more minor peaks in the river stage preceding the main one. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Beryllium-10 in Australasian tektites: Constraints on the location of the source crater     

P. Ma  K. Aggrey  C. Tonzola  C. Schnabel  P. de Nicola  J.T. Wasson  L. Brown  R. Middleton 《Geochimica et cosmochimica acta》2004,68(19):3883-3896

By using accelerator mass spectrometry we have measured the ¹⁰Be concentrations of 86 Australasian tektites. Corrected to the time of tektite production ∼0.8 My ago, the ¹⁰Be concentrations (10⁶ atom/g) range from 59 for a layered tektite from Huai Sai, Thailand, to 280 for an australite from New South Wales, Australia. The average value is 143 ± 50. When tektites are sorted by country, their average measured ¹⁰Be concentrations increase slowly with increasing distance from Southeast Asia, the probable location of the tektite producing event, from 59 ± 9 for 6 layered tektites from Laos to 136 ± 20 for 20 splash-form tektites from Australia. The lowest ¹⁰Be concentrations for tektites fall on or within a contour centered off the shore of Vietnam, south of the Gulf of Tonkin (107°E; 17°N), but also encompassing two other locations in the area of northeastern Thailand previously proposed for the site of a single tektite-producing impact. The ¹⁰Be concentrations of layered tektites show only a weak anticorrelation (R ∼ −0.3) with the numbers of relict crystalline inclusions.Loosely consolidated, fine-grained terrestrial sediments or recently consolidated sedimentary rocks are the most likely precursor materials. Dilution of sediments with other kinds of rock raises problems in mixing and is not supported by petrographic data. Sedimentary columns that have the right range of ¹⁰Be concentrations occur off the coasts of places where sedimentation rates are high relative to those in the deep sea. A single impact into such a region, 15 to 300 m thick, could have propelled near-surface, high-¹⁰Be material farthest—to Australia—while keeping the deeper-lying, low-¹⁰Be layers closer to home. We do not rule out, however, other proposed mechanisms for tektite formation.  相似文献   

6: Classification of VMS deposits: Lessons from the South Uralides     

Richard Herrington  Valeriy Maslennikov  Victor Zaykov  Igor Seravkin  Alexander Kosarev  Bernd Buschmann  Jean-Jacques Orgeval  Nicola Holland  Svetlana Tesalina  Paolo Nimis  Robin Armstrong 《Ore Geology Reviews》2005,27(1-4):203

VMS deposits of the South Urals developed within the evolving Urals palaeo-ocean between Silurian and Late Devonian times. Arc-continent collision between Baltica and the Magnitogorsk Zone (arc) in the south-western Urals effectively terminated submarine volcanism in the Magnitogorsk Zone with which the bulk of the VMS deposits are associated. The majority of the Urals VMS deposits formed within volcanic-dominated sequences in deep seawater settings. Preservation of macro and micro vent fauna in the sulphide bodies is both testament to the seafloor setting for much of the sulphides but also the exceptional degree of preservation and lack of metamorphic overprint of the deposits and host rocks. The deposits in the Urals have previously been classified in terms of tectonic setting, host rock associations and metal ratios in line with recent tectono-stratigraphic classifications. In addition to these broad classes, it is clear that in a number of the Urals settings, an evolution of the host volcanic stratigraphy is accompanied by an associated change in the metal ratios of the VMS deposits, a situation previously discussed, for example, in the Noranda district of Canada.Two key structural settings are implicated in the South Urals. The first is seen in a preserved marginal allochthon west of the Main Urals Fault where early arc tholeiites host Cu–Zn mineralization in deposits including Yaman Kasy, which is host to the oldest macro vent fauna assembly known to science. The second tectonic setting for the South Urals VMS is the Magnitogorsk arc where study has highlighted the presence of a preserved early forearc assemblage, arc tholeiite to calc-alkaline sequences and rifted arc bimodal tholeiite sequences. The boninitc rocks of the forearc host Cu–(Zn) and Cu–Co VMS deposits, the latter hosted in fragments within the Main Urals Fault Zone (MUFZ) which marks the line of arc-continent collision in Late Devonian times. The arc tholeiites host Cu–Zn deposits with an evolution to more calc-alkaline felsic volcanic sequences matched with a change to Zn–Pb–Cu polymetallic deposits, often gold-rich. Large rifts in the arc sequence are filled by thick bimodal tholeiite sequences, themselves often showing an evolution to a more calc-alkaline nature. These thick bimodal sequences are host to the largest of the Cu–Zn VMS deposits.The exceptional degree of preservation in the Urals has permitted the identification of early seafloor clastic and hydrolytic modification (here termed halmyrolysis sensu lato) to the sulphide assemblages prior to diagenesis and this results in large-scale modification to the primary VMS body, resulting in distinctive morphological and mineralogical sub-types of sulphide body superimposed upon the tectonic association classification.It is proposed that a better classification of seafloor VMS systems is thus achievable using a three stage classification based on (a) tectonic (hence bulk volcanic chemistry) association, (b) local volcanic chemical evolution within a single edifice and (c) seafloor reworking and halmyrolysis.  相似文献   

Geological mapping reveals the role of Early Jurassic rift architecture in the dispersal of calciturbidites: New insights from the Central and Northern Apennines     

Angelo Cipriani  Martina Caratelli  Massimo Santantonio 《Basin Research》2020,32(6):1485-1509

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Deep uncertainty in long-term hurricane risk: Scenario generation and implications for future climate experiments     

Nicola Ranger  Falk Niehörster 《Global Environmental Change》2012,22(3):703-712

Current projections of long-term trends in Atlantic hurricane activity due to climate change are deeply uncertain, both in magnitude and sign. This creates challenges for adaptation planning in exposed coastal communities. We present a framework to support the interpretation of current long-term tropical cyclone projections, which accommodates the nature of the uncertainty and aims to facilitate robust decision making using the information that is available today. The framework is populated with projections taken from the recent literature to develop a set of scenarios of long-term hurricane hazard. Hazard scenarios are then used to generate risk scenarios for Florida using a coupled climate–catastrophe modeling approach. The scenarios represent a broad range of plausible futures; from wind-related hurricane losses in Florida halving by the end of the century to more than a four-fold increase due to climate change alone. We suggest that it is not possible, based on current evidence, to meaningfully quantify the relative confidence of each scenario. The analyses also suggest that natural variability is likely to be the dominant driver of the level and volatility of wind-related risk over the coming decade; however, under the highest scenario, the superposition of this natural variability and anthropogenic climate change could mean notably increased levels of risk within the decade. Finally, we present a series of analyses to better understand the relative adequacy of the different models that underpin the scenarios and draw conclusions for the design of future climate science and modeling experiments to be most informative for adaptation.  相似文献   

In situ high-temperature X-ray diffraction and spectroscopic study of fibroferrite,FeOH(SO<Subscript>4</Subscript>)·5H<Subscript>2</Subscript>O     

Gennaro Ventruti  Giancarlo Della Ventura  Nicola Corriero  Daniele Malferrari  Alessandro F. Gualtieri  Umberto Susta  Maria Lacalamita  Emanuela Schingaro 《Physics and Chemistry of Minerals》2016,43(8):587-595

The thermal dehydration process of fibroferrite, FeOH(SO₄)·5H₂O, a secondary iron-bearing hydrous sulfate, was investigated by in situ high-temperature synchrotron X-ray powder diffraction (HT-XRPD), in situ high-temperature Fourier transform infrared spectroscopy (HT-FTIR) and thermal analysis (TGA-DTA) combined with evolved gas mass spectrometry. The data analysis allowed the determination of the stability fields and the reaction paths for this mineral as well as characterization of its high-temperature products. Five main endothermic peaks are observed in the DTA curve collected from room T up to 800 °C. Mass spectrometry of gases evolved during thermogravimetric analysis confirms that the first four mass loss steps are due to water emission, while the fifth is due to a dehydroxylation process; the final step is due to the decomposition of the remaining sulfate ion. The temperature behavior of the different phases occurring during the heating process was analyzed, and the induced structural changes are discussed. In particular, the crystal structure of a new phase, FeOH(SO₄)·4H₂O, appearing at about 80 °C due to release of one interstitial H₂O molecule, was solved by ab initio real-space and reciprocal-space methods. This study contributes to further understanding of the dehydration mechanism and thermal stability of secondary sulfate minerals.  相似文献   

A statistical-based approach for determining the intensity of unrest phases at Stromboli volcano (Southern Italy) using one-step-ahead forecasts of displacement time series   总被引：1，自引：0，他引：1  

Tommaso Carlà  Emanuele Intrieri  Federico Di Traglia  Nicola Casagli 《Natural Hazards》2016,84(1):669-683

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Satellite radar data for back-analyzing a landslide event: the Ponzano (Central Italy) case study     

Lorenzo Solari  Federico Raspini  Matteo Del Soldato  Silvia Bianchini  Andrea Ciampalini  Federica Ferrigno  Stefano Tucci  Nicola Casagli 《Landslides》2018,15(4):773-782

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Establishment of ICL Italian network   总被引：1，自引：1，他引：0  

Nicola Casagli  Veronica Tofani 《Landslides》2018,15(10):1907-1908

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