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61.
The concentrations and isotopic compositions of strontium in interstitial waters from several DSDP sites, where sediments consist chiefly of carbonate oozes and chalks, are used as indicators of carbonate diagenesis by reference to a recently-produced curve showing detailed variations in the87Sr/86Sr ratio of seawater with time. Carbonate sediments of the Walvis Ridge show increases in interstitial Sr2+ concentrations in the upper carbonate-ooze sections with the highest concentrations near the ooze-chalk boundary where maximum rates of carbonate recrystallization occur. Below this, in situ production of Sr2+ diminishes and there is a diffusive flux of Sr to an underlying sink, presumably volcanogenic sediments or basalts, leading to Sr isotopic disequilibrium between carbonates and interstitial waters. In some other sites, however, there is no apparent Sr sink at depth and isotopic equilibrium is retained. Overall, diffusive smoothing of profiles exerts an important control on the87Sr/86Sr ratios, although lower ratios than contemporaneous seawater values in the carbonate oozes often correlate with zones of Mg2+ loss and reflect a combination of a flux of Sr2+ from the zone of maximum recrystallization rates together with a contribution from the in situ alteration of volcanic matter. 相似文献
62.
Speleothem stable isotope records interpreted within a multi-proxy framework and implications for New Zealand palaeoclimate reconstruction 总被引:1,自引:0,他引:1
Andrew Lorrey Paul Williams Jim Salinger Tim Martin Jonathan Palmer Anthony Fowler Jian-xin Zhao Helen Neil 《Quaternary International》2008,187(1):52
A primary step in the interpretation of speleothem stable isotope records (18O/16O and 13C/12C) is to conduct a comparison with other local palaeoclimate proxies. Here, two new master speleothem δ18O and δ13C records (one from eastern North Island, and the other from western/southern South Island, New Zealand) are evaluated against independent precipitation and temperature proxy information to assess their palaeoclimate reconstruction potential. This comparison also resulted in a serendipitous opportunity to reconstruct past circulation using climate regime classification [Lorrey, A.M., Fowler, A.M., Salinger, J., 2007a. Regional climate regime classification as a qualitative tool for interpreting multi-proxy palaeoclimate data spatial patterns: a New Zealand case study. Palaeo-3, in press], specifically because these two regional climate districts are hyper-sensitive to westerly circulation changes, and in many cases, exhibit contrasting climate character in response to circulation anomalies.For both the western South Island and the eastern North Island master speleothem δ13C records, variations tracked changes in relative regional precipitation. The δ18O master speleothem record for both regions varied with temperature change. Both records contain strong regional climate signals that suggest they have good value for palaeoclimate reconstruction. The ensuing attempt at a multi-proxy reconstruction of regional climate regimes from the compiled proxies indicates past circulation in the New Zealand sector has varied considerably during the past four millennia. Centennial-scale circulation changes for the past 4000 years are evident, and are analogous to modern Blocking, Zonal and Trough regime types [Kidson J. W., 2000. An analysis of New Zealand synoptic types and their use in defining weather regimes. International Journal of Climatology 20, 299–316] that characterise changes in present-day (prevailing) westerly circulation. This palaeoclimate reconstruction indicates modern regional climate regime classification can be extended at least as far back as the temporal coverage of the records presented here, and it can likely be improved on with better dating control and the addition of new records with higher resolution. It is also anticipated that future work will expand to include more proxy data from across New Zealand to improve the clarity of past climate regime occurrence for the Late Holocene. 相似文献
63.
David C. Palmer Ulrich Bismayer Ekhard K. H. Salje 《Physics and Chemistry of Minerals》1990,17(3):259-265
Hard mode Raman Spectroscopy and optical birefringence studies have been used to evaluate the temperature behaviour of order parameters for the cubictetragonal phase transition in leucite. There is a strong temperature-dependence of Raman line frequencies near 498 cm–1 and 529 cm–1, and the optical birefringence decreases towards zero on heating. Above the transition temperature leucite still shows slight birefringence, which correlates with the persistence of the 200 X-ray reflexion at these temperatures, and is not compatible with the ideal cubic symmetry. Quantitative observations of the temperature evolution of Raman line-frequencies and the birefringence are consistent with an order parameter showing T
1g
symmetry, and a nearly-tricritical phase transition behaviour. The results of earlier X-ray and DSC studies imply the operation of an additional order parameter, with E
g
symmetry; this is observed, but its influence on the transition behaviour is significant only at temperatures close to T
c. The two order parameters are related via linear-quadratic or biquadratic coupling. We develop the form of the Landau Potential for leucite — including both order parameters and their couplings — to discuss the present observations and previous structural data. 相似文献
64.
65.
Variations in dilute-acid (partial digest) metal concentrations in bottom sediments from 49 stations on the Mississippi, Alabama
and Florida continental margin are investigated with the aid of ordination and other multivariate statistical techniques.
Total iron, carbonate content, clay fraction and water depth correlate well with the overall leachable sediment metal values
for pooled station replicates over four sampling periods. Individual metal concentrations also are correlated with these and
other environmental parameters using stepwise multiple linear regression techniques. A weak positive association between Ba,
Cu, Cr, Ni, Pb, and V burdens in the demersal fishSyacium papillosum and the dilute-acid leachable sediment metal TOC and carbonate concentrations is demonstrated. 相似文献
66.
R. A. Glen B. J. Drummond B. R. Goleby D. Palmer K. D. Wake‐Dyster 《Australian Journal of Earth Sciences》2013,60(4):341-352
The Cobar Basin in central western New South Wales is a mineral‐rich Early Devonian basin typical of those that characterize the Siluro‐Devonian history of the Lachlan Orogen of southeastern Australia. One hundred and seventy kilometres of seismic profiling in three lines across the basin have shown it to be asymmetrical in shape with an east‐dipping western margin that is steeper than the moderately west‐dipping eastern margin. Maximum basin thickness is around 6 km, but there are significant thickness changes, especially from south to north, which reflect the effect of synsedimentary faulting. Seismic profiling suggests that the basin deformed by thin‐skinned tectonics; postulated strike‐slip effects were not visible on the sections. The seismic profiling has, for the first time, imaged the western synrift basin margin which is generally not exposed. Strain variations during deformation along this edge were taken up by the formation of a major jog ('dog‐leg') which has propagated into the basin as a tear fault. Intrabasinal tears, as well as thrusts, which link into one or more detachments, provide potential pathways for mineralizing fluids during basin inversion. 相似文献
67.
T. M. Law J. May A. T. Spathis A.T. Du Plessis A. M. Palmer 《Fragblast: International Journal for Blasting and Fragmentation》2001,5(1):1-20
The application of modern bulk emulsion explosive systems at an underground gold mine resulted in a 57% improvement in gold dilution. While this improvement is impressive and could be expected to be achieved at other sites, the work required to assess and demonstrate the benefits is painstaking. Forty-eight rings involving a total of approximately 50 000 tonnes of ore were monitored using various modern surveying instruments over a 6-month period. The geometric data included blasthole locations and deviation, and the cavity monitoring of stopes. Implementation of a bulk emulsion system not only provided logistical benefits but it also has the desirable explosive properties associated with reducing the effects of blast damage and blast dilution. 相似文献
68.
Using a combination of dielectric spectroscopy and atomistic computer simulation techniques, the dynamical behaviour of the
loosely bound (Na+ and K+) channel ions in nepheline has been investigated. The low-frequency dielectric properties of a natural Bancroft nepheline
have been studied from room temperature to 1100 K. At each temperature, the dielectric constant, conductivity and dielectric
loss were determined over a range of frequencies from 100 Hz to 10 MHz. At high temperatures a distinct Debye-type relaxation
in the dielectric loss spectrum was observed; the activation energy for this process was determined to be 1.38 ± 0.02 eV.
Atomistic simulation techniques were used to elucidate the mechanism and energetics of cation migration. A mechanism involving
the hopping of Na+ ions between oval sites and partially occupied hexagonal (K+) sites, via a bottleneck consisting of a distorted sixfold ring of (Al,Si)O4 tetrahedra, was found to give a calculated energy barrier in very good agreement with the experimentally determined activation
energy. These results confirm the nature of the process responsible for the observed dielectric behaviour. Overall, this study
demonstrates the intrinsic, microscopic control of cation diffusion processes in rock-forming minerals. Identifying specific
energy barriers and preferred diffusion pathways is fundamental to the prediction of diffusion energetics.
Received: 8 May 2000 / Accepted: 21 July 2000 相似文献
69.
The occurrence of PMSEs with time of day shows a semi-diurnal variation with minima at 8 and 20 h LT. PMSE layers observed for more than 30 min show an average rate of descent of 2 km h−1. These characteristics suggest the influence of tidal winds. When the observed steady wind and diurnal and semi-diurnal tides at EISCAT are added, the overall magnitude shows a time-variation which matches the occurrence of PMSEs, and the observed rate of descent, approximately 2 km h−1. Atmospheric gravity waves also contribute to the velocity of the neutral wind. When the wave reinforces the background wind, the PMSEs are stronger and descend more rapidly, but when the wave-related velocity opposes the background wind the PMSE is weaker and it descends more slowly. 相似文献
70.
S.L. Donoghue J.A. Gamble A.S. Palmer R.B. Stewart 《Journal of Volcanology and Geothermal Research》1995,68(1-3)
We describe a magma mingling episode from Ruapehu volcano between two andesite magmas, one very much minor in volume relative to the other. The event acted to trigger eruption of the andesitic Pourahu pyroclastic flow which is preserved in a thick sequence of tephras and laharic deposits in the southeastern ring plain of the volcano. The predominant andesite is pale brown coloured and porphyritic containing phenocrysts of plagioclase-clinopyroxene-orthopyroxene-Fe-Ti oxides. Rare clasts of a darker andesite are different texturally, less vesicular, and contain distinctive microphenocrysts of plagioclase and quench olivine. Equally rare clasts, of streaky pumice consisting of interbanded ‘dark’ and ‘light’ andesite attest to mingling between these two andesite components.Chemical analyses of discrete clasts demonstrate that the Pourahu pyroclastic flow andesites span much of the compositional spectrum of Ruapehu andesites. This observation demonstrates heterogeneity in the products of a relatively small eruption. The darker clast analyses and those from associated distal fall deposits lie within the fields defined by the dominant light coloured clasts. Phenocryst and microphenocryst geothermometry suggest slightly higher temperatures in the dark component. However, glasses from groundmass and phenocryst inclusions in the same specimen may differ considerably, leading us to conclude that many phenocrysts are in fact xenocrystic and were incorporated in the melts as they migrated towards the surface.We prefer a model in which a small volume of hot andesite magma injects a vent-feeding magma chamber, triggering vesiculation and eruption. We infer that the process of magma withdrawal extended downward into the magma body causing the dark component to intermingle with the lighter (dominant) component, ‘sucking’ more dark magma into the chamber. Our observations are entirely consistent with the existence of a plexus of small, possibly interlinked magma chambers beneath Ruapehu. 相似文献