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51.
Amélie Bordage Etienne Balan Johan P. R. de Villiers Robert Cromarty Amélie Juhin Claire Carvallo Georges Calas P. V. Sunder Raju Pieter Glatzel 《Physics and Chemistry of Minerals》2011,38(6):449-458
The oxidation state of vanadium in natural and synthetic Fe–Ti oxides is determined using high-energy resolution fluorescence-detected
X-ray absorption spectroscopy (HERFD-XAS). Eleven natural magnetite-bearing samples from a borehole of the Main Magnetite
Layer of the Bushveld Complex (South Africa), five synthetic Fe oxide samples, and three natural hematite-bearing samples
from Dharwar supergroup (India) are investigated. V K edge spectra were recorded on the ID26 beamline at the European Synchrotron Radiation Facility (Grenoble, France), and the
pre-edge features were used to determine the local environment and oxidation state of vanadium. In the case of the magnetite
samples (natural and synthetic), we show that vanadium is incorporated in the octahedral site of the spinel structure under
two oxidation states: +III and +IV. The variations of the pre-edge area are interpreted as various proportions in V3+ and V4+ (between 9.5 and 16.3% of V4+), V3+ being the main oxidation state. In particular, the variations of the V4+/V3+ ratio along the profile of the Main Magnetite Layer seem to follow the crystallization sequence of the layer. In the case
of the hematite samples from India, the pre-edge features indicate that vanadium is substituted to Fe and mainly incorporated
as V4+ (between 40 and 72% of V4+). We also demonstrate the potentiality of HERFD-XAS for mineralogical studies, since it can filter out the unwanted fluorescence
and give better resolved spectra than conventional XAS. 相似文献
52.
Catherine Jeandel Celia Venchiarutti Michael Bourquin Catherine Pradoux François Lacan Pieter van Beek Jean Riotte 《Geostandards and Geoanalytical Research》2011,35(4):449-459
A new procedure allowing the sequential extraction of Ra, Nd, Th, Pa and U from the same initial natural sample (sea or river waters, particles, sediments, rocks) is proposed. Extraction recoveries were better than 90%. Procedural blanks ranged from 80 pg (for Nd) to below 1 fg, the detection limit of the MC‐ICP‐MS used (for Pa); all were negligible compared with the amounts of elements currently determined. Based on classical anionic resins attached to a peristaltic pump allowing precise flow rate control, this procedure allowed a consequent reduction of the sample size, which improved the sampling resolution and reduced the sampling cost. It also ensured a better consistency of the samples for the five tracers. 相似文献
53.
Pieter H. Fourie Udo Zimmermann Nicolas J. Beukes Thanusha Naidoo Katsuro Kobayashi Jan Kosler Eizo Nakamura Jenny Tait Johannes N. Theron 《International Journal of Earth Sciences》2011,100(2-3):527-541
In order to facilitate the understanding of the geological evolution of the Kalahari Craton and its relation to South America, the provenance of the first large-scale cratonic cover sequence of the craton, namely the Ordovician to Carboniferous Cape Supergroup was studied through geochemical analyses of the siliciclastics, and age determinations of detrital zircon. The Cape Supergroup comprises mainly quartz-arenites and a Hirnantian tillite in the basal Table Mountain Group, subgreywackes and mudrocks in the overlying Bokkeveld Group, while siltstones, interbedded shales and quartz-arenites are typical for the Witteberg Group at the top of the Cape Supergroup. Palaeocurrent analyses indicate transport of sediment mainly from northerly directions, off the interior of the Kalahari Craton with subordinate transport from a westerly source in the southwestern part of the basin near Cape Town. Geochemical provenance data suggest mainly sources from passive to active continental margin settings. The reconnaissance study of detrital zircons reveals a major contribution of Mesoproterozoic sources throughout the basin, reflecting the dominance of the Namaqua-Natal Metamorphic Belt, situated immediately north of the preserved strata of Cape Supergroup, as a source with Archaean-aged zircons being extremely rare. We interpret the Namaqua-Natal Metamorphic Belt to have been a large morphological divide at the time of deposition of the Cape Supergroup that prevented input of detrital zircons from the interior early Archaean Kaapvaal cratonic block of the Kalahari Craton. Neoproterozoic and Cambrian zircons are abundant and reflect the basement geology of the outcrops of Cape strata. Exposures close to Cape Town must have received sediment from a cratonic fragment that was situated off the Kalahari Craton to the west and that has subsequently drifted away. This cratonic fragment predominantly supplied Meso- to Neoproterozoic, and Cambrian-aged zircon grains in addition to minor Silurian to Lower Devonian zircons and very rare Archaean (2.5?Ga) and late Palaeoproterozoic (1.8-2.0?Ga) ones. No Siluro-Devonian source has yet been identified on the Kalahari Craton, but there are indications for such a source in southern Patagonia. Palaeozoic successions in eastern Argentina carry a similar detrital zircon population to that found here, including evidence of a Silurian to Lower Devonian magmatic event. The Kalahari and Río de la Plata Cratons were thus in all likelihood in close proximity until at least the Carboniferous. 相似文献
54.
55.
Isoplot R: A free and open toolbox for geochronology 总被引:1,自引:0,他引:1
Pieter Vermeesch 《地学前缘(英文版)》2018,9(5):1479-1493
56.
AbstractA new structured approach is presented to derive groundwater baseline conditions, in this case for a dolomitic limestone aquifer suffering from salinization and other anthropogenic impacts. It builds on the HydroChemical System Analysis (HCSA) to map different groundwater bodies (hydrosomes) and hydrochemical zones within them, each of which show significant differences in baseline conditions. It also comprises a rigorous elimination scheme for samples affected by bias or pollution. The method is applied to the Damour coastal aquifer system, south of Beirut (Lebanon). Concentrations of Cl, Cl/Br, 2H, 18O and Ca/Sr were used to discern five hydrosomes and to determine mixing ratios. The dominant hydrochemical facies was (sub)oxic, calcareous and salinized, indicating a very low reduction capacity of the aquifer system, strong dissolution of dolomitic limestone and clear traces of seawater encroachment. The method proposed was capable of filtering out baseline conditions for 16 main constituents, 64 trace elements and two isotopes. 相似文献
57.
Mehdi F. Harandi Shantia Yarahmadian Mohammad Sepehrifar Pieter H. A. J. M. van Gelder 《Stochastic Environmental Research and Risk Assessment (SERRA)》2014,28(7):1889-1896
We use the Dichotomous Markov Noise model with constant transition rates to describe the dynamics of fluctuations in the water level as a stochastic process, which is imposed on river discharge changes. By applying this model, two different regimes are determined for the long-term behaviour of the river. Based on these regimes, we define two nonparametric classes of the overall increasing/decreasing nature of the water level in the long-term behaviour, which are separated by an exponential steady state regime. In this paper, we develop a nonparametric testing procedure to test exponentially (steady state regime) against an alternative overall decreasing level distribution. The proposed test predicts the long-term regime behaviour of the river. The mathematical tools introduced to handle the problem should be of general use and the testing procedure can be considered as a new mathematical tool in the study of water level dynamics. Under conditions of data austerity and as a case of study, we examine the stochastic characteristics of the Zayandeh Rud (Zāyandé-Rūd or Zāyanderūd, also spelled as Zayandeh-Rood or Zayanderood) River (Isfahan, Iran) water level. 相似文献
58.
59.
Patterns in groundwater chemistry resulting from groundwater flow 总被引:18,自引:7,他引:11
Pieter J. Stuyfzand 《Hydrogeology Journal》1999,7(1):15-27
Groundwater flow influences hydrochemical patterns because flow reduces mixing by diffusion, carries the chemical imprints
of biological and anthropogenic changes in the recharge area, and leaches the aquifer system. Global patterns are mainly dictated
by differences in the flux of meteoric water passing through the subsoil. Within individual hydrosomes (water bodies with
a specific origin), the following prograde evolution lines (facies sequence) normally develop in the direction of groundwater
flow: from strong to no fluctuations in water quality, from polluted to unpolluted, from acidic to basic, from oxic to anoxic–methanogenic,
from no to significant base exchange, and from fresh to brackish. This is demonstrated for fresh coastal-dune groundwater
in the Netherlands. In this hydrosome, the leaching of calcium carbonate as much as 15 m and of adsorbed marine cations (Na+, K+, and Mg2+) as much as 2500 m in the flow direction is shown to correspond with about 5000 yr of flushing since the beach barrier with
dunes developed. Recharge focus areas in the dunes are evidenced by groundwater displaying a lower prograde quality evolution
than the surrounding dune groundwater. Artificially recharged Rhine River water in the dunes provides distinct hydrochemical
patterns, which display groundwater flow, mixing, and groundwater ages.
Received, May 1998 · Revised, August 1998 · Accepted, October 1998 相似文献
60.
Physical controls on sand composition and relative durability of detrital minerals during ultra‐long distance littoral and aeolian transport (Namibia and southern Angola)
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Eduardo Garzanti Alberto Resentini Sergio Andò Giovanni Vezzoli Alcides Pereira Pieter Vermeesch 《Sedimentology》2015,62(4):971-996
Sediment in coastal Namibia to southern Angola is supplied dominantly from the Orange River with minor additional fluvial input and negligible modifications by chemical processes, which makes this a great test case for investigating physical controls on sand texture and composition. This study monitored textural, mineralogical and geochemical variability in beach and aeolian‐dune sands along a ca 1750 km stretch of the Atlantic coast of southern Africa by using an integrated set of techniques, including image analysis, laser granulometry, optical microscopy, Raman spectroscopy and bulk‐sediment geochemistry. These results contrast with previous reports that feldspars and volcanic detritus break down during transport, that sand grains are rounded rapidly in shallow‐marine environments, and that quartzose sands may be produced by physical processes. Mechanical wear is unable to modify the relative abundance of detrital components, including pyroxene and mafic volcanic rock fragments traditionally believed to be destroyed rapidly. The sole exceptions are poorly lithified or cleaved sedimentary/metasedimentary rock fragments, readily lost at the transition to the marine environment, and slow‐settling flaky micas, winnowed and deposited offshore. Coastal sediments tend to be depleted in relatively mobile amphibole, preferentially entrained offshore or re‐deposited in sheltered beaches, while less mobile garnet is retained onshore. No detrital mineral displays a significant increase in grain roundness after 300 to 350 km of longshore transport in high‐energy littoral environments from the Orange mouth to south of the Namib Erg, but all minerals get rapidly rounded after passing into the dunefield. Pyroxene and opaques get rounded faster than harder quartz and garnet, but sand mineralogy remains unchanged. Excepting strong transient selective‐entrainment effects, physical processes are unable to modify sand composition significantly. Selective mechanical breakdown can be largely neglected in quantitative provenance analysis of sand and sandstone even in the case of ultra‐long‐distance transport in high‐energy environments dominated by strong persistent winds and waves. 相似文献