An igneous fragment from cluster IDP L2011#21: An analog for the source of pyrrhotite and taenite in comet 81P/Wild 2 captured in Stardust aerogel     

Frans J. M. Rietmeijer 《Meteoritics & planetary science》2013,48(8):1427-1439

The silica glass extracted from the bulbous parts of Stardust tracks is riddled by electron‐opaque nanograins with compositions that are mostly between pyrrhotite and metallic iron with many fewer nanograins having a Fe‐Ni‐S composition. Pure taenite nanograins are extremely rare, but exist among the terminal particles. Assuming that these Fe‐Ni‐S compositions are due to mixing of pyrrhotite and taenite melt droplets, it is remarkable that the taenite melt grains had discrete Fe/Ni ratios. This paper presents the data from an igneous pyrrhotite/taenite fragment of cluster IDP L2011#21, wherein the taenite compositions have the same discrete Fe/Ni clusters as those inferred for the Stardust nanograins. These Fe/Ni clusters are a subsolidus feature with compositions that are constrained by the Fe‐Ni phase diagram. They formed during cooling of the parent body of this cluster IDP fragment. These specific Fe/Ni ratios, 12.5, 24, 40, and 53 atom% Ni, were preserved in asteroidal taenite that survived radially outward transport to the Kuiper Belt where it accreted into the (future) comet Wild 2 nucleus.  相似文献   

基于SoftGIS的土地利用地域性认同测度研究——以荷兰为例     

彭建超  钱畅  吴群  Dirk Strijker  Frans Sijtsma 《地理科学》2016,36(3):401-409

在剖析地域性认同双重内涵及其与土地利用关系的基础上,结合SoftGIS技术,研究构建土地利用地域性认同测度方法,并以荷兰为例进行实证分析。数据分析显示,传统GIS数据可与土地利用认知数据相融合,基于核密度修正法构建的土地利用地域性认同指数可测度地域性认同的空间差异,应用于土地利用评价或规划决策。结论表明,测度平台在问卷设计和调查空间尺度上具有灵活性,数据收集快捷,通过平台的高清卫星地图定位,调查对象可反馈空间准确、情景真实的土地利用地域性认同信息。  相似文献   

Demise of the Diamantina Dent     

Joseph R. Curray  Frans J. Emmel 《Marine Geology》1981,40(3-4):M69-M72

A new satellite-navigated survey line has shown that the most pronounced indentation in the outline of the western Sunda Trench off Sumatra, frequently the subject of tectonic speculation, was only an artifact of a single pre-satellite navigation survey line. This note is intended as a reminder that tectonic patterns can be no better than the data on which they are based.  相似文献   

The Bengal Fan: morphology, geometry, stratigraphy, history and processes   总被引：2，自引：0，他引：2  

Joseph R. Curray  Frans J. Emmel  David G. Moore 《Marine and Petroleum Geology》2002,19(10)

The Bengal Fan is the largest submarine fan in the world, with a length of about 3000 km, a width of about 1000 km and a maximum thickness of 16.5 km. It has been formed as a direct result of the India–Asia collision and uplift of the Himalayas and the Tibetan Plateau. It is currently supplied mainly by the confluent Ganges and Brahmaputra Rivers, with smaller contributions of sediment from several other large rivers in Bangladesh and India.The sedimentary section of the fan is subdivided by seismic stratigraphy by two unconformities which have been tentatively dated as upper Miocene and lower Eocene by long correlations from DSDP Leg 22 and ODP Legs 116 and 121. The upper Miocene unconformity is the time of onset of the diffuse plate edge or intraplate deformation in the southern or lower fan. The lower Eocene unconformity, a hiatus which increases in duration down the fan, is postulated to be the time of first deposition of the fan, starting at the base of the Bangladesh slope shortly after the initial India–Asia collision.The Quaternary of the upper fan comprises a section of enormous channel-levee complexes which were built on top of the preexisting fan surface during lowered sea level by very large turbidity currents. The Quaternary section of the upper fan can be subdivided by seismic stratigraphy into four subfans, which show lateral shifting as a function of the location of the submarine canyon supplying the turbidity currents and sediments. There was probably more than one active canyon at times during the Quaternary, but each one had only one active fan valley system and subfan at any given time. The fan currently has one submarine canyon source and one active fan valley system which extends the length of the active subfan. Since the Holocene rise in sea level, however, the head of the submarine canyon lies in a mid-shelf location, and the supply of sediment to the canyon and fan valley is greatly reduced from the huge supply which had existed during Pleistocene lowered sea level. Holocene turbidity currents are small and infrequent, and the active channel is partially filled in about the middle of the fan by deposition from these small turbidity currents.Channel migration within the fan valley system occurs by avulsion only in the upper fan and in the upper middle fan in the area of highest rates of deposition. Abandoned fan valleys are filled rapidly in the upper fan, but many open abandoned fan valleys are found on the lower fan. A sequence of time of activity of the important open channels is proposed, culminating with formation of the one currently active channel at about 12,000 years BP.  相似文献   

Dynamic events near the upper and mid-fan boundary of the Bengal Fan     

Emmel  Frans J.  Curray  Joseph R. 《Geo-Marine Letters》1981,1(3-4):201-205

Bathymetric sections across the most recent valley just above and below the transition of upper to middle fan show a northward shift of the thalweg between the confines of the levees. This small-scale migration was followed by a levec break on the higher north side. Part of the bottom currents, which normally would have been contained within the levees, spilled over and spread laterally in a northward direction. This levee break caused a canyonward shift of the boundary between the upper and mid fan, and the diverted flow croded smaller valleys in the western part of the fan.  相似文献   

Leonid MAC Workshop 1999, April 12–15     

Frans J. M. Rietmeijer 《Meteoritics & planetary science》1999,34(4):495-495

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The smallest comet 81P/Wild 2 dust dances around the CI composition          下载免费PDF全文

Frans J. M. Rietmeijer 《Meteoritics & planetary science》2015,50(10):1767-1789

The bulbous Stardust track #80 (C2092,3,80,0,0) is a huge cavity. Allocations C2092,2,80,46,1 nearest the entry hole and C2092,2,80,47,6 about 0.8 mm beneath the entry hole provide evidence of highly chaotic conditions during capture. They are dominated by nonvesicular low‐Mg silica glass instead of highly vesicular glass found deeper into this track which is consistent with the escape of magnesiosilica vapors generated from the smallest comet grains. The survival of delicate (Mg,Al,Ca)‐bearing silica glass structures is unique to the entry hole. Both allocations show a dearth of surviving comet dust except for a small enstatite, a low‐Ca hypersthene grain, and a Ti‐oxide fragment. Finding scattered TiO₂ fragments in the silica glass could support, but not prove, TiO₂ grain fragmentation during hypervelocity capture. The here reported dearth in mineral species is in marked contrast to the wealth of surviving silicate and oxide minerals deeper into the bulb. Both allocations show Fe‐Ni‐S nanograins dispersed throughout the low‐Mg silica glass matrix. It is noted that neither comet Halley nor Wild 2 had a CI bulk composition for the smallest grains. Using the analogs of interplanetary dust particles (IDPs) and cluster IDPs it is argued that a CI chondritic composition requires the mixing of nonchondritic components in the appropriate proportions. So far, the fine‐grained Wild 2 dust is biased toward nonchondritic ferromagnesiosilica materials and lacking contributions of nonchondritic components with Mg‐Fe‐Ni‐S[Si‐O] compositions. To be specific, “Where are the GEMS”? The GEMS look‐alike found in this study suggests that evidence of GEMS in comet Wild 2 may still be found in the Stardust glass.  相似文献   

Stardust glass: Indigenous and modified comet Wild 2 particles     

Frans J. M. Rietmeijer 《Meteoritics & planetary science》2009,44(11):1707-1715

Abstract— Does comet 81P/Wild 2 have indigenous glass? Glass is used here to include all types of amorphous materials that could be either indigenous or modified comet Wild 2 grains, and all amorphous phases in chondritic aggregate interplanetary dust particles (IDPs). The answer is that it probably does, but very little is known of their compositions to allow a definitive answer to be given. There is no evidence among the collected comet dust for interstellar glass with embedded metals and sulfides. There is, however, ample evidence for melting of the smallest, sub‐micrometer comet particles of nanometer‐scale grains similar to those in the matrix of chondritic aggregate IDPs, including pyrrhotite. Massive patches of Mg‐SiO, Al‐SiO, or Ca‐Si‐O glass are incorporated in the familiar, vesicular Si‐rich glass are melted Wild 2 silicates. Magnesiosilica glass has a deep metastable eutectic smectite‐dehydroxylate composition. It indicates that very high temperatures well above the liquidus temperatures of forsterite were achieved very rapidly and were followed but ultra‐rapid quenching. This predictable and systematic response is not limited to Mg‐silicates, and recognizing this phenomenon among massive glass will provide a means to complete the reconstruction of this comet's original minerals, as well as constrain the physiochemical environment created during aerogel melting and evaporation.  相似文献   

Navigating the dilemmas of climate policy in Europe: evidence from policy evaluation studies     

Constanze Haug  Tim Rayner  Andrew Jordan  Roger Hildingsson  Johannes Stripple  Suvi Monni  Dave Huitema  Eric Massey  Harro van Asselt  Frans Berkhout 《Climatic change》2010,101(3-4):427-445

Climate change is widely recognised as a ‘wicked’ policy problem. Agreeing and implementing governance responses is proving extremely difficult. Policy makers in many jurisdictions now emphasise their ambition to govern using the best available evidence. One obvious source of such evidence is the evaluations of the performance of existing policies. But to what extent do these evaluations provide insights into the difficult dilemmas that governors typically encounter? We address this question by reviewing the content of 262 evaluation studies of European climate policies in the light of six kinds of dilemma found in the governance literature. We are interested in what these studies say about the performance of European climate policies and in their capacity to inform evidence-based policy-making. We find that the evaluations do arrive at common findings: that climate change is framed as a problem of market and/or state failure; that voluntary measures tend to be ineffective; that market-based instruments tend to be regressive; that EU-level policies have driven climate policies in the latecomer EU Member States; and that lack of monitoring and weak enforcement are major obstacles to effective policy implementation. However, we also conclude that the evidence base these studies represent is surprisingly weak for such a high profile area. There is too little systematic climate policy evaluation work in the EU to support systematic evidence-based policy making. This reduces the scope for sound policy making in the short run and is a constraint to policy learning in the longer term.  相似文献   

Distribution patterns of living benthic foraminifera from Cap Breton canyon,Bay of Biscay: Faunal response to sediment instability     

Silvia Hess  Frans J. Jorissen 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(9):1555-1578

Analysis of living (Rose Bengal-stained) benthic foraminifera in 13 multicorer samples taken along the Cap Breton canyon (Bay of Biscay) revealed that the combination of organic-rich material and sediment instability provides very specific benthic ecosystem conditions. The active canyon hosts different foraminiferal assemblages that appear to be determined by different types and frequencies of environmental disturbance at the sites. Most of them are strongly dominated by shallow-infaunal living taxa that combine a tolerance for low-quality organic matter with a high reproductive potential. Foraminiferal assemblages characterized by high densities, very superficially living taxa and strong dominance of bolivinids and buliminids, follow a poor pioneer fauna dominated by Technitella melo. These assemblages are observed in the narrow canyon axis, where frequent sediment resuspension occurs and affects habitat stability. Assemblages studied from sites outside the canyon axis are still dominated by shallow-infaunal species but show lower foraminiferal densities and higher diversities. Deep-infaunal taxa are only present in some inner meanders and more distal stations. These assemblages are typical for ecological niches that are relatively stable and unaffected by re-sedimentation processes. They have attained a more advanced stage of ecosystem stability. They are influenced by neither lateral sediment nor enriched organic matter input.  相似文献