We report on the microscopic impactor debris around Kamil crater (45 m in diameter, Egypt) collected during our 2010 geophysical expedition. The hypervelocity impact of Gebel Kamil (Ni‐rich ataxite) on a sandstone target produced a downrange ejecta curtain of microscopic impactor debris due SE–SW of the crater (extending ~300,000 m2, up to ~400 m from the crater), in agreement with previous determination of the impactor trajectory. The microscopic impactor debris include vesicular masses, spherules, and coatings of dark impact melt glass which is a mixture of impactor and target materials (Si‐, Fe‐, and Al‐rich glass), plus Fe‐Ni oxide spherules and mini shrapnel, documenting that these products can be found in craters as small as few tens of meters in diameter. The estimated mass of the microscopic impactor debris (<290 kg) derived from Ni concentrations in the soil is a small fraction of the total impactor mass (~10 t) in the form of macroscopic shrapnel. That Kamil crater was generated by a relatively small impactor is consistent with literature estimates of its pre‐atmospheric mass (>20 t, likely 50–60 t). 相似文献
It is often assumed that the terrestrial worlds have experienced identical impact regimes over the course of their formation and evolution, and, as a result, would have started life with identical volatile budgets. In this work, through illustrative dynamical simulations of the impact flux on Venus, the Earth, and Mars, we show that these planets can actually experience greatly different rates of impact from objects injected from different reservoirs. For example, we show scenarios in which Mars experiences far more asteroidal impacts, per cometary impactor, than Venus, with the Earth being intermediate in value between the two. This difference is significant, and is apparent in simulations of both quiescent and highly stirred asteroid belts (such as could be produced by a mutual mean-motion resonance crossing between Jupiter and Saturn, as proposed in the Nice model of the Late Heavy Bombardment). We consider the effects; such differences would have on the initial volatilisation of the terrestrial planets in a variety of scenarios of both endogenous and exogenous hydration, with particular focus on the key question of the initial level of deuteration in each planet's water budget. We conclude that each of the terrestrial worlds will have experienced a significantly different distribution of impactors from various reservoirs, and that the assumption that each planet has the same initial volatile budget is, at the very least, a gross over-simplification. 相似文献
An In Situ Ultraviolet Spectrophotometer (ISUS) was coupled to a benthic chamber to characterize the bisulfide flux emanating from a warm spring at the Extrovert Cliff locality within Monterey Bay, California. The chamber was periodically flushed with bottom seawater to reset chemical concentrations, which enabled deployments over multiple days. Data from several deployments, each lasting at least 10 days, were used to calculate flow rates, fluid concentrations, and fluxes over time. The bisulfide concentration of the fluid entering the chamber varied from 75 to 4500 μmol l?1. Positive temperature anomalies up to 3.5° were associated with these elevated concentrations. Linear flow rates ranged from 2 to >17 m day?1, while the bisulfide fluxes varied from 0.2 to 80 mol m?2 day?1. The bisulfide originated at depth and was not produced in the surface sediments via an anaerobic oxidation of methane coupled to sulfate reduction. Tides modulated the flow as well as the composition of the fluid entering the chamber. It appeared that a deep sourced fluid, which supplied the bisulfide, was mixed with a second, ambient seawater-like fluid before entering the flux chamber. At low tides, flow rates were at their highest and the contribution of the deep sourced fluid to the fluid entering the chamber was at a maximum. 相似文献
Raman spectra of Mg2GeO4-olivine were obtained from ambient pressure up to 34 GPa at ambient temperature. Under quasi-hydrostatic pressure conditions, the following modifications in the Raman spectra occur as pressure increases: 1) near 11 GPa, two sharp extra bands appear in the 600–700 cm?1 frequency range, and increase in intensity with respect to the olivine bands; 2) above 22 GPa, these two bands become very intense, and the number, position and relative intensity of the other vibrational bands drastically change; 3) the intensity of sharp bands progressively decreases above 25 GPa. The transformation occurs at lower pressures under non-hydrostatic conditions. During decompression to atmospheric pressure, the high-pressure phase partially reverts to olivine. These observations can be interpreted as the progressive metastable transformation from the olivine structure to a crystalline phase with four-fold coordinated Ge, in which the GeO4 tetrahedra are polymerized. We propose that the metastable high-pressure phase is a structurally disordered spinelloid close to the hypothethical ω- or ?*-phase, and forms by a shear mechanism assisted by the development of a dynamical instability in the olivine structure. Implications for the transformations undergone by olivines under far-from-equilibrium conditions (e.g. in subducting lithospheric slabs and in shocks) are discussed. 相似文献
Flume experiments were conducted using four different gravel beds (D50 + 12–39 mm) and a range of marked particles (10–65 mm). The shear stresses were evaluated from friction velocities, when initial movement of marked particles occurred. Two kinds of equations were produced: first for the threshold of initial movement, and second for generalized movement. Equations of the type 0c + a(Di/D50)b, as proposed by Andrews (1983) are applicable even if the material is relatively well sorted. However, the values of a and b are lower (respectively 0·050 and -0·70) for initial movement. Generalized movement requires a higher shear stress (a + 0·068 and b + -0·80). D90 of the bed material and y0 (the bed roughness parameter) were also used as reference values in place of D50. They produced lower values than in natural streams, mainly owing to the fact that the material used in the flume is better sorted: clusters are less well developed and the bed roughness is lower. 相似文献
A chemical product tanker, The Ievoli Sun, was abandoned and later sank approximately 11 miles NW of Alderney in the English Channel in October 2000. The vessel carried a mixed cargo comprising 4000 tonnes of styrene, and 1000 tonnes each of methyl ethyl ketone and isopropyl alcohol. These chemicals are of low to moderate toxicity to aquatic life, are not persistent and have a low potential for bio-accumulation. Both of the solvents are miscible in water, whilst styrene is practically insoluble and, following release, it will rise to the sea surface and rapidly evaporate. More than 1000 tonnes of styrene are believed to have been lost to sea during the incident, resulting in an aerial plume of vapour which crossed Alderney and episodic contamination of air and water in the immediate vicinity of the wreck site. Analysis of edible tissues using coupled gas chromatography/mass spectrometry demonstrated low-level styrene contamination of crabs recovered from pots laid very close to the wreck site prior to the incident. These concentrations posed no risks to human consumers, and no fishery controls were implemented. The remainder of the styrene and the ship's main bunker fuel were recovered from the wreck on the seabed, whilst the two chemical solvents were released to the water column in a slow, controlled manner. 相似文献
The waters of the Seine river estuary, located in a highly anthropogenicized area in the northern part of France, are of poor
microbiological quality; the concentrations of faecal bacteria usually exceed the European Union bathing and recreational
water directives. The aim of the present study was to identify the main sources of the faecal pollution of the Seine estuary
in order to help define priorities for management and sanitation efforts. Budgets of faecal coliform (FC) inputs to the estuary
were established for various hydrological conditions. Main sources of FC were the outfalls of the treated effluents of the
wastewater treatment plants (WWTPs) located along the estuary, the faecal bacteria brought in through the tributaries of the
Seine estuary, and the faecal bacteria transported by the Seine river flow at the estuary entrance at Poses dam. In order
to quantify these inputs, FC were enumerated during sampling campaigns conducted for various hydrological conditions in the
Seine at the entrance of the estuary, in the tributaries close to their confluence with the estuary, and in the effluents
of some WWTPs located along the estuary. The importance of the flux of FC transported by the Seine river flow at the estuary
entrance at Poses dam decreased from 92% of the total FC input when the flow rate was high (717 m3 s−1) to 5% when flow rate was low (143 m3 s−1). The release of the domestic wastewaters of the large city of Paris located 120 km upstream from the entrance of the estuary
was mainly responsible for this microbiological pollution. At low flow rates, the tributaries represent the most important
source of FC (64–76% for flow rates of the Seine at Poses at approximately 150 m3 s−1), mainly from the Robec and Eure rivers. The treated wastewater of the WWTPs located along the estuary was the second source
of FC for low flow conditions (19–30%); it was less important for high to intermediate flow rate conditions. 相似文献
Meteoric smoke particles (MSPs) form through the vaporization of meteoroids and the subsequent re-condensation of metallic species in the mesosphere. Recently, iridium and platinum enrichments have been identified in Greenland ice layers and attributed to the fallout of MSPs supplying polar latitudes with cosmic matter during the Holocene. However, the MSP fallout to Antarctica during the Earth's climatic history remains essentially unknown.
We have determined iridium and platinum in deep Antarctic ice from Dome C and Vostok dated back to 240 kyrs BP. We find high super-chondritic fluxes during warm periods and low meteoric accretion during glacial times, a pattern that is opposite to any known climatic variation in dust fallout to polar regions. The proposed explanation of this accretion regime is a weaker polar vortex during warm periods, allowing peripheral air masses enriched in volcanic iridium and platinum to penetrate inland to Antarctica. The MSP signal emerges only during cold phases and is four times lower than in the Greenland ice cap where more snow accumulates. This suggests that wet deposition is an important route of cosmic material to the Earth's surface. 相似文献
This paper presents the first remote measurements of La Soufrière gas emissions since the fumarolic and seismic reactivation in 1992. The chemical composition of the plumes has been measured from May 2003 to September 2004 using an Open Path Fourier Transform InfraRed (OP-FTIR) spectrometer, up to 15 m downwind the South Crater. HCl is clearly detected (concentration between 2.4 and 12 ppmv) whereas SO2 and H2S generally remain below the detection limit of the OP-FTIR. Direct measurements of SO2 and H2S near the South Crater with a Lancom III analyzer show a fast decrease of their concentrations with the distance. Calculated Cl / S mass ratios are high: from 9.4 ± 1.7 at 15 m from the vent to 2.8 ± 0.6 at 140 m. The enrichment in HCl of the gas emitted at La Soufrière, observed since 1998, corresponds to the degassing of a magma enriched in Cl and depleted in S. This result agrees with isotopic measurements which suggest a magmatic origin of the gases. Readjustments inside the volcanic system may have taken place during the seismic activity beginning in 1992 and enhance the transfer of magmatic gases to the summit. 相似文献