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181.
182.
Peter Jenniskens Jason Utas Qing‐Zhu Yin Robert D. Matson Marc Fries J. Andreas Howell Dwayne Free Jim Albers Hadrien Devillepoix Phil Bland Aaron Miller Robert Verish Laurence A. J. Garvie Michael E. Zolensky Karen Ziegler Matthew E. Sanborn Kenneth L. Verosub Douglas J. Rowland Daniel R. Ostrowski Kathryn Bryson Matthias Laubenstein Qin Zhou Qiu‐Li Li Xian‐Hua Li Yu Liu Guo‐Qiang Tang Kees Welten Marc W. Caffee Matthias M. M. Meier Amy A. Plant Colin Maden Henner Busemann Mikael Granvik 《Meteoritics & planetary science》2019,54(4):699-720
It has been proposed that all L chondrites resulted from an ongoing collisional cascade of fragments that originated from the formation of the ~500 Ma old asteroid family Gefion, located near the 5:2 mean‐motion resonance with Jupiter in the middle Main Belt. If so, L chondrite pre‐atmospheric orbits should be distributed as expected for that source region. Here, we present contradictory results from the orbit and collisional history of the October 24, 2015, L6 ordinary chondrite fall at Creston, CA (here reclassified to L5/6). Creston's short 1.30 ± 0.02 AU semimajor axis orbit would imply a long dynamical evolution if it originated from the middle Main Belt. Indeed, Creston has a high cosmic ray exposure age of 40–50 Ma. However, Creston's small meteoroid size and low 4.23 ± 0.07° inclination indicate a short dynamical lifetime against collisions. This suggests, instead, that Creston originated most likely in the inner asteroid belt and was delivered via the ν6 resonance. The U‐Pb systematics of Creston apatite reveals a Pb‐Pb age of 4,497.1 ± 3.7 Ma, and an upper intercept U‐Pb age of 4,496.7 ± 5.8 Ma (2σ), circa 70 Ma after formation of CAI, as found for other L chondrites. The K‐Ar (age ~4.3 Ga) and U,Th‐He (age ~1 Ga) chronometers were not reset at ~500 Ma, while the lower intercept U‐Pb age is poorly defined as 770 ± 320 Ma. So far, the three known L chondrites that impacted on orbits with semimajor axes a <2.0 AU all have high (>3 Ga) K‐Ar ages. This argues for a source of some of our L chondrites in the inner Main Belt. Not all L chondrites originate in a continuous population of Gefion family debris stretching across the 3:1 mean‐motion resonance. 相似文献
183.
184.
Dispersant Use and a Bioremediation Strategy as Alternate Means of Reducing Impacts of Large Oil Spills on Mangroves: The Gladstone Field Trials 总被引:2,自引:0,他引:2
Norman C Duke Kathryn A Burns Richard P.J Swannell Otto Dalhaus Roland J Rupp 《Marine pollution bulletin》2000,41(7-12):403-412
Over a three-year period (1995–1998), we studied short-term effects of dispersant use and a bioremediation strategy in two consecutive field trials in sub-tropical Australian mangroves. In each case, weathered oil was applied, and a large spill simulated, in mature Rhizophora stylosa trees around 4–9 m tall. In the first trial, we used Gippsland light crude oil with or without dispersant, Corexit 9527. In the second, a bioremediation strategy followed application of Gippsland oil or Bunker C fuel oil. Bioremediation involved forced aeration with supplemental application of nutrients. Dispersant use had an overall positive benefit shown as reduced tree mortality. By contrast, there was no apparent reduction in mortality of trees with bioremediation. However, one year after oiling, leaf densities of surviving trees were greater in bioremediation plots than in controls, and less in oil-only plots. These and other results have been incorporated into spill response management strategies in Australia. 相似文献
185.
The Burrum River estuary: identifying reference sites for Australian sub-tropical estuarine systems using paleolimnological methods 总被引:1,自引:0,他引:1
There is a pressing need to obtain historical information on estuaries so that levels of natural variability and ecosystem
thresholds can be identified. Once these factors are known, estuaries that exhibit high conservation value and minimal impact
from anthropogenic activity can be acknowledged and protected. In order to understand and quantify the level of change that
may have occurred due to human impact, near pristine estuaries that have the potential to act as reference sites need to be
identified. However, this is often difficult due to a lack of documented knowledge of estuary variability. This paper retrospectively
assesses environmental conditions in the Burrum River, a sub-tropical east Australian estuary on the coast of Queensland,
using diatom and stable isotope analyses. These techniques were combined with AMS 14C dating methods to determine if this system has undergone any natural or anthropogenically induced change. Diatom assemblages
have shown very little variation over the past 5,000 years, indicating minimal changes to water quality. Upper and lower limits
for δ13C and δ15N stable isotope results also infer that the sources of carbon and nitrogen to the Burrum River estuary have remained constant
over this time period. Carbon inputs have been dominated by marine autotrophic production, whilst nitrogen inputs are indicative
of terrestrial sources. Hence, the Burrum River has not been altered by anthropogenic activities and is a suitable reference
site for benchmarking impacted sub-tropical estuaries. This paper demonstrates that paleolimnological techniques can be applied
successfully to identify estuaries that are suitable as reference sites. 相似文献
186.
Michel L. Schlegel Kathryn. L. Nagy Paul Fenter Neil C. Sturchio 《Geochimica et cosmochimica acta》2006,70(14):3549-3565
The structure and mechanism of cation sorption at the (0 0 1) muscovite-water interface were investigated in 0.01 and 0.5 m KCl, CsCl, and CaCl2 and 0.01 m BaCl2 solutions at slightly acidic pH by high-resolution X-ray reflectivity. Structural relaxations of atom positions in the 2M1 muscovite were small (?0.07 Å) and occurred over a distance of 30 to 40 Å perpendicular to the interface. Cations in all solutions were sorbed dominantly in the first and second solution layers adjacent to the mineral surface. The derived heights of the first solution layer in KCl and CsCl solutions, 1.67(6)-1.77(7) and 2.15(9)-2.16(2) Å, respectively, differ in magnitude by the approximate difference in crystallographic radii between K and Cs, and correspond closely to the interlayer cation positions in bulk K- and Cs-mica structures. The first solution layer heights in CaCl2 and BaCl2 solutions, 2.46(5)-2.56(11) and 2.02(5) Å, respectively, differ in a sense opposite to that expected based on crystallographic or hydrated radii of the divalent cations. The derived ion heights in all solutions imply that there is no intercalated water layer between the first solution layer and the muscovite surface. Molecular compositions were assigned to the first two solution layers in the electron density profiles using models that constrain the number density of sorbed cations, water molecules, and anions by considering the permanent negative charge of the muscovite and average solution density. The models result in partial charge balance (at least 50%) by cations sorbed in the first two layers in the 0.01 m solutions and approximately full charge balance in the 0.5 m solutions. Damped oscillations of model water density away from the first two solution layers agree with previous X-ray reflectivity results on the muscovite (0 0 1) surface in pure water. 相似文献
187.
Supply limited sediment transport in a high-discharge event of the tropical Burdekin River, North Queensland, Australia 总被引:1,自引:0,他引:1
Kathryn J. Amos Jan Alexander Anthony Horn† Geoff D. Pocock‡ Chris R. Fielding§ 《Sedimentology》2004,51(1):145-162
Interactions between catchment variables and sediment transport processes in rivers are complex, and sediment transport behaviour during high‐flow events is not well documented. This paper presents an investigation into sediment transport processes in a short‐duration, high‐discharge event in the Burdekin River, a large sand‐ and gravel‐bed river in the monsoon‐ and cyclone‐influenced, semi‐arid tropics of north Queensland. The Burdekin's discharge is highly variable and strongly seasonal, with a recorded maximum of 40 400 m3 s?1. Sediment was sampled systematically across an 800 m wide, 12 m deep and straight reach using Helley‐Smith bedload and US P‐61 suspended sediment samplers over 16 days of a 29‐day discharge event in February and March 2000 (peak 11 155 m3 s?1). About 3·7 × 106 tonnes of suspended sediment and 3 × 105 tonnes of bedload are estimated to have been transported past the sample site during the flow event. The sediment load was predominantly supply limited. Wash load included clay, silt and very fine sand. The concentration of suspended bed material (including very coarse sand) varied with bedload transport rate, discharge and height above the bed. Bedload transport rate and changes in channel shape were greatest several days after peak discharge. Comparison between these data and sparse published data from other events on this river shows that the control on sediment load varies between supply limited and hydraulically limited transport, and that antecedent weather is an important control on suspended sediment concentration. Neither the empirical relationships widely used to estimate suspended sediment concentrations and bedload (e.g. Ackers & White, 1973) nor observations of sediment transport characteristics in ephemeral streams (e.g. Reid & Frostick, 1987) are directly applicable to this river. 相似文献
188.
Timo?M.?Kirchner Kathryn?M.?GillisEmail author 《Contributions to Mineralogy and Petrology》2012,164(1):123-141
Tectonic exposures of upper plutonics (>800 m) that are part of a contiguous section of young East Pacific Rise (EPR) crust
at the Hess Deep Rift provide the first regional-scale constraints on hydrothermal processes in the upper plutonic crust formed
at a fast-spreading ridge. Submersible-collected samples recovered over a 4-km-wide region show that the sheeted dike complex
is largely underlain by a 150- to 200-m-thick gabbro unit, followed by a more primitive gabbronorite unit. Gabbroic samples
are variably altered by pervasive fluid flow along fracture networks to amphibole-dominated assemblages. The gabbroic rocks
are significantly less altered (average 11% hydrous phases) than the overlying sheeted dike complex (average 24%), and the
percentage of hydrous alteration diminishes with depth. Incipient, pervasive fluid flow occurred at amphibolite facies conditions
(average 720°C), with slightly higher temperatures in the lower 500 m of the section. The extent of subsequent lower-temperature
alteration is generally low and regionally variable. The gabbroic samples are slightly elevated in 87Sr/86Sr relative to fresh rock values (0.7024) and less enriched than the overlying sheeted dike complex. 87Sr/86Sr for the pervasively altered gabbroic samples ranges from 0.70244 to 0.70273 (mean 0.70257), tonalites is 0.7038, and pyroxene
hornfels ranges from 0.70259 to 0.70271. 87Sr/86Sr does not vary with depth, and there is a strong positive correlation with the percentage of hydrous phases. Strontium contents
of igneous and hydrothermal minerals, combined with bulk rock 87Sr/86Sr, indicate that Sr-isotopic exchange is largely controlled by the uptake of fluid 87Sr/86Sr in hydrous minerals and does not require Sr gain or loss. The minimum, time-integrated fluid–rock ratio for the sheeted
dike complex and upper plutonics is 0.55–0.66, and the fluid flux calculated by mass balance is ~2.1 to 2.5 × 106 kg m−2, 30–60% higher than fluid fluxes calculated in the same manner for sheeted dike complexes on their own at Hess and Pito Deeps,
and Ocean Drilling Program Hole 504B. Alteration patterns within the upper plutonics evolved in response to axial magma chamber
(AMC) dynamics at the EPR, such that magma replenishment led to assimilation and thermal metamorphism of the country rock,
and the position of the hydrothermal root-zone tracked the vertical migration of the AMC. The freshness of the lowermost gabbroic
rocks suggests that pervasive fluid flow does not lead to significant fluid and heat fluxes at and near fast-spreading ridges. 相似文献
189.
The effects of soil minerals on chromate (CrVIO4
2-, noted as Cr(VI)) reduction by sulfide were investigated in the pH range of 7.67 to 9.07 under the anoxic condition. The
examined minerals included montmorillonite (Swy-2), illite (IMt-2), kaolinite (KGa-2), aluminum oxide (γ-Al2O3), titanium oxide (TiO2, P-25, primarily anatase), and silica (SiO2). Based on their effects on Cr(VI) reduction, these minerals were categorized into three groups: (i) minerals catalyzing
Cr(VI) reduction – illite; (ii) minerals with no effect – Al2O3; and (iii) minerals inhibiting Cr(VI) reduction- kaolinite, montmorillonite, SiO2 and TiO2 . The catalysis of illite was attributed primarily to the low concentration of iron solubilized from the mineral, which could
accelerate Cr(VI) reduction by shuttling electrons from sulfide to Cr(VI). Additionally, elemental sulfur produced as the
primary product of sulfide oxidation could further catalyze Cr(VI) reduction in the heterogeneous system. Previous studies
have shown that adsorption of sulfide onto elemental sulfur nanoparticles could greatly increase sulfide reactivity towards
Cr(VI) reduction. Consequently, the observed rate constant, k
obs, increased with increasing amounts of both iron solubilized from illite and elemental sulfur produced during the reaction.
The catalysis of iron, however, was found to be blocked by phenanthroline, a strong complexing agent for ferrous iron. In
this case, the overall reaction rate at the initial stage of reaction was pseudo first order with respect to Cr(VI), i.e.,
the reaction kinetics was similar to that in the homogeneous system, because elemental sulfur exerted no effect at the initial
stage prior to accumulation of elemental sulfur nanoparticles. In the suspension of kaolinite, which belonged to group (iii),
an inhibitive effect to Cr(VI) reduction was observed and subsequently examined in more details. The inhibition was due to
the sorption of elemental sulfur onto kaolinite, which reduced or completely eliminated the catalytic effect of elemental
sulfur, depending on kaolinite concentration. This was consistent with the observation that the catalysis of externally added
elemental sulfur (50 μM) on Cr(VI) reduction would disappear with a kaolinite concentration of more than 5.0 g/L. In kaolinite
suspension, the overall reaction rate law was:
相似文献
190.
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