The fusion crusts of stony meteorites: Implications for the atmospheric reprocessing of extraterrestrial materials     

Matthew J. GENGE  Monica M. GRADY 《Meteoritics & planetary science》1999,34(3):341-356

Abstract— Fusion crusts develop on all meteorites during their passage through the atmosphere but have been little studied. We have characterized the textures and compositions of the fusion crusts of 73 stony meteorites to identify the nature of meteorite ablation spheres (MAS) and constrain the processes operating during the entry heating. Most chondrite fusion crusts are porphyritic and are dominated by olivine, glass, and accessory magnetite; whereas those of the achondrites are mainly glassy. Chondrite fusion crusts contain sulphide droplets with high-Ni contents (>55 wt%). The partially melted substrate of ordinary chondrites (underlying the outer melted crusts) are dominated by silicate glass and composite metal, sulphide, and Cr-bearing Fe-oxide droplets that form as coexisting immiscible liquids. Enstatite chondrite substrates contain Cr- and Mn- bearing sulphides. The substrates of the carbonaceous chondrites comprise a sulphide-enriched layer of matrix. The compositions of melted crusts are similar to those of the bulk meteorite. However, differences from whole rock suggest that three main processes control their chemical evolution: (1) the loss and reaction of immiscible Fe-rich liquids, (2) mixing between substrate partial melts and bulk melts of the melted crust, and (3) the loss of volatile components by evaporation and degassing. Data from fusion crusts suggest that MAS produced at low altitude have compositions within the range of those of silicate-dominated cosmic spherules that are formed by the melting dust particles. Meteorite ablation spheres produced at high altitude probably have compositions very different from bulk meteorite and will resemble cosmic spherules derived from coarse-grained precursors.  相似文献   

Assessing water contamination risk from vegetation fires: Challenges,opportunities and a framework for progress          下载免费PDF全文

Joao P. Nunes  Stefan H. Doerr  Gary Sheridan  Jonay Neris  Cristina Santín  Monica B. Emelko  Uldis Silins  Peter R. Robichaud  William J. Elliot  Jacob Keizer 《水文研究》2018,32(5):687-694

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The Emergence of Digital Twins in Remediation: How Platform Synchrony Will Change the Model for Delivery     

John Horst  Nick Welty  Allison Yanites  Francois Appere  Monica Dupre  Shahansha Shaik 《Ground Water Monitoring & Remediation》2020,40(3):14-20

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Impact of a harbour construction on the benthic community of two shallow marine caves     

Ettore Nepote  Carlo Nike Bianchi  Carla Morri  Marco Ferrari  Monica Montefalcone 《Marine pollution bulletin》2017,114(1):35-45

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Observational information on a temperate reef community helps understanding the marine climate and ecosystem shift of the 1980–90s     

Giulia Gatti  Carlo Nike Bianchi  Monica Montefalcone  Sara Venturini  Giovanni Diviacco  Carla Morri 《Marine pollution bulletin》2017,114(1):528-538

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Phylogeography of the rocky intertidal periwinkle Echinolittorina paytensis through a biogeographic transition zone in the Southeastern Pacific     

Sergio P. Barahona  Ximena Vlez‐Zuazo  Monica Santa‐Maria  Aldo S. Pacheco 《Marine Ecology》2019,40(4)

Barriers to dispersal are recognized to play an important role in the differentiation of populations and ultimately in speciation. In the southeast Pacific, on the northern coast of Peru, a transition zone between the Peruvian and Panamic marine biogeographic provinces exists. Here, the convergence between two contrasting surface currents could generate a barrier effect for the larval dispersal of meroplanktonic invertebrates, which could in turn generate differentiated populations or genetic lineages on both sides of the transition zone. To address this, we studied to Echinolittorina paytensis, an abundant rocky intertidal periwinkle that spans both biogeographic provinces. A total of 95 individuals from Ecuador (2°19′S) to central Peru (7°31′S), covering the Panamic Province, the Peruvian Province, and the transition zone between, were collected. The mitochondrial markers cytochrome c oxidase I and 16SrRNA were sequenced in order to investigate phylogeography and genetic structuring. In general, no genetic structuring was found across the transition zone, suggesting this biogeographic boundary would not be acting as a barrier in this species. Factors such as a high larval dispersal capability and the occurrence of El Niño–Southern Oscillation events such as El Niño are discussed.  相似文献   

The influence of coastal dynamics on the upper limit of the Posidonia oceanica meadow     

Matteo Vacchi  Monica Montefalcone  Carlo Nike Bianchi  Carla Morri  Marco Ferrari 《Marine Ecology》2010,31(4):546-554

The recognized ecological importance of Posidonia oceanica, the most important seagrass of the Mediterranean Sea, makes it crucial to assess the state of health of its meadows, discriminating natural from anthropogenic impacts. In this paper, the hydrodynamic conditions at the upper limit of P. oceanica meadows along the Ligurian coast (NW Mediterranean Sea) were investigated. A relationship between the distance of the upper limit of the meadow from the shoreline and the morphodynamic domain of the beach (i.e. distinctive types of beach produced by the topography, wave climate and sediment composition) was found. A zonation of the state of the shallow portions of the meadows down the submerged beach profile was identified. Zone a, from the shoreline to the breaking limit, is naturally critical for the development of the meadow. Zone b, from the breaking limit to the closure depth, is subjected to natural and human impacts. Zone c, below the closure depth, is little influenced by coastal dynamics. This study quantifies for the first time how much the status of the shallow portions of P. oceanica meadows is dependent on coastal dynamics, which is important for their proper management.  相似文献   

Dantu's mineralogical properties – A view into the composition of Ceres' crust          下载免费PDF全文

K. Stephan  R. Jaumann  R. Wagner  M. C. De Sanctis  E. Palomba  A. Longobardo  D. A. Williams  K. Krohn  F. Tosi  L. A. McFadden  F. G. Carrozzo  F. Zambon  E. Ammannito  J.‐P. Combe  K.‐D. Matz  F. Schulzeck  I. von der Gathen  T. Roatsch  C. A. Raymond  C. T. Russell 《Meteoritics & planetary science》2018,53(9):1866-1883

Impact crater Dantu not only exhibits a very complex geological history but also shows an exceptional heterogeneity of its surface composition. Because of its location within a low‐lying region named Vendimia Planitia, which has been proposed to represent an ancient impact basin, Dantu possibly offers a window into the composition of Ceres’s deeper crust, which apparently is enriched in ammonia. Local concentration of carbonates within Dantu or its ejecta blanket may be either exposed or their emplacement induced by the Dantu impact event. Because carbonates can be seen along Dantu's crater walls, exposed due to recent slumping, but also as fresh spots or clusters of spots scattered across the surface, the deposition/formation of carbonates took place over a long time period. The association of several bright spots enriched in carbonates with sets of fractures on Dantu's floor might be accidental. Nevertheless, its morphological and compositional similarity to the faculae in Ceres’s prominent impact crater Occator including its hydrated state does not exclude a cryo‐volcanic origin, i.e., upwelling of carbonate‐enriched brines influenced by H₂O ice in the subsurface. Indeed, an isolated H₂O ice spot can be identified near Dantu, which shows that ice still exists in Ceres’s subsurface at midlatitudes and that it can exist on the surface for a longer period of time.  相似文献   

Holocene settlement in the rio de la plata littoral (argentina): A methodological approach     

Monica Salemme  Laura Miotti  Marina Aquirre 《Geoarchaeology》1989,4(1):69-80

Cultural and faunal remains from archaeological sites of the Rio de La Plata littoral, Argentina, have been studied, attempting to verify their primary associations and occupations during the Holocene. the sites were localized within shell beach ridges more or less parallel to the present shore and are composed of bivalves, gastropods, scarce barnacles, and sandy sediments. the thanatocoenosis found could be equivalent to a transitional area between fluviomarine (mixohaline) and oceanic (polyeuhaline) gradients, i.e., an environment with greater salinity conditions than that of the adjacent coast in the present estuary. These deposits correspond to the Las Escobas Formation (Holocene). Archaeological remains were found from the base of the shell ridge up into the overlying sediments. the hypothesis proposed here is that the human occupation is not contemporaneous with the formation of the shell ridge. the cultural sequence in this kind of site can be altered by disturbances of the stratigraphy as a consequence of environmental and geological events.  相似文献   

Shell layer variation in trace element concentration for the freshwater bivalve Elliptio complanata     

Monica Carroll  Christopher S. Romanek 《Geo-Marine Letters》2008,28(5-6):369-381

While the elemental chemistry of marine mollusk shells contains valuable environmental information, extending these interpretations to freshwater bivalve shells may be problematic, given the wide range of aqueous chemistries that exist in freshwater environments. To better understand the significance of these records, 20 bivalves were collected from four freshwater streams to determine the geochemical relationships that exist between the bivalve shell and their sources streams. The concentrations of manganese (Mn), copper (Cu), strontium (Sr), barium (Ba), and calcium (Ca) were analyzed by laser ablation inductively coupled plasma mass spectrometry across the inner (INL) and outer nacreous layer (ONL) of each shell for comparison to stream data collected over the period of shell growth. Within an individual shell, the content of Mn, Sr, and Ba were significantly higher in the INL than the ONL, while Cu concentrations were similar. Strontium and Ba concentrations co-varied between the two layers in 1:1 relationships, while Mn displayed a preferential enrichment in the INL that increased from 2:1 to 5:1 as the Mn content of the shell decreased. Each elemental profile can be correlated between shell layers, except for the trace element Cu, which appeared to be more closely related to the organic content of the shell. These results suggest that the major element geochemistry of the shell layers differentially reflect the aqueous chemistry of the water in which a bivalve lived, but that these records are most likely overprinted by physiological processes specific to the mantle tissue from which a particular shell layer is secreted. Distribution coefficients (shell _{M /Ca}:water _{M /Ca}, where M?=?trace element of interest) were calculated using the median molar elemental concentration for each shell (by layer), and the appropriate water concentration. Bivalves from a contaminated site were excluded from this analysis because their shells were anomalous in size and color. For the remaining 15 shells, distribution coefficients (INL and ONL) were: Mn (0.50 and 0.21), Sr (0.26 and 0.17), and Ba (0.05: INL only). Inner nacreous layer values were comparable to the upper end of published estimates for freshwater bivalves and fish otoliths, while the ONL values were comparable to the lower range of values. Inclusion of shells from the contaminated site resulted in the calculation of distribution coefficients that fell outside the range of published estimates. These results suggest that exposure to pollutants may have a bearing on the biological factors that control the elemental concentration of bivalve shells in freshwater environments. While researchers generally avoid sampling shell material from the INL because of the potential for shell dissolution, the similarity in elemental profile trends observed here suggests that both the INL and ONL record accurate geochemical information, but in distinct forms. An obvious advantage of INL analysis is the relative increase in elemental concentration, but this is afforded at the expense of spatial resolution. Considered collectively, these results suggest that valuable information can be gleaned from the elemental concentration of freshwater bivalve shells when care is taken in the choice of material from which these records are extracted.  相似文献