Bulk mineralogy,water abundance,and hydrogen isotope composition of unequilibrated ordinary chondrites     

Helen Grant  Romain Tartèse  Rhian Jones  Laurette Piani  Yves Marrocchi  Ashley King  Thomas Rigaudier 《Meteoritics & planetary science》2023,58(9):1365-1381

The origin and transport of water in the early Solar System is an important topic in both astrophysics and planetary science, with applications to protosolar disk evolution, planetary formation, and astrobiology. Of particular interest for understanding primordial water transport are the unequilibrated ordinary chondrites (UOCs), which have been affected by very limited alteration since their formation. Using X-ray diffraction and isotope ratio mass spectrometry, we determined the bulk mineralogy, H₂O content, and D/H ratios of 21 UOCs spanning from petrologic subtypes 3.00–3.9. The studied UOC falls of the lowest subtypes contain approximately 1 wt% H₂O, and water abundance globally decreases with increasing thermal metamorphism. In addition, UOC falls of the lowest subtypes have elevated D/H ratios as high as those determined for some outer Solar System comets. This does not easily fit with existing models of water in the protoplanetary disk, which suggest D/H ratios were low in the warm inner Solar System and increased radially. These new analyses confirm that OC parent bodies accreted a D-rich component, possibly originating from either the outer protosolar nebula or from injection of molecular cloud streamers. The sharp decrease of D/H ratios with increasing metamorphism suggests that the phase(s) hosting this D-rich component is readily destroyed through thermal alteration.  相似文献   

Provenance of altered carbon phases and impact history of the Stac Fada Member,NW Scotland     

Arthur Goodwin  Romain Tartèse  Russell J. Garwood  Rhodri Jerrett  Katherine H. Joy 《Meteoritics & planetary science》2023,58(8):1099-1116

The Stac Fada Member (Stoer Group) is a ~1.2 Ga melt-rich impact breccia preserved and intermittently exposed along the NW coast of Scotland. Using a combination of x-ray diffraction and micro-Raman spectroscopy, we identify potential coesite that is spatially associated with micron-sized diamonds, as well as disordered carbon phases. Comparing the graphite G-band of disordered carbon phases in the impact breccia to samples from underlying units indicates that most of the carbon in the Stoer Group was ultimately derived from the underlying Lewisian basement. Disordered carbon phases within the Stac Fada Member have been modified by mild heating within a hot ejecta blanket rather than shock pressure. We also report the first evidence for impact diamonds discovered within the Stac Fada Member. These diamonds have an average Raman shift of 1328.5 cm⁻¹ and are present within both the impact breccia and the shocked gneiss clasts that are present in sandstones directly underlying the Stac Fada Member contact, and within sandstone rafts entrapped in the unit. These findings have implications for the timing of deposition of the Stac Fada Member, which must have occurred after ballistic ejection of Lewisian basement clasts during the impact event.  相似文献   

Spatial structure analysis of a reptile community with airborne LiDAR data     

N. Sillero  Luís Gonçalves-Seco 《International journal of geographical information science》2014,28(8):1709-1722

The analysis of the spatial structure of animal communities requires spatial data to determine the distribution of individuals and their limiting factors. New technologies like very precise GPS as well as satellite imagery and aerial photographs of very high spatial resolution are now available. Data from airborne LiDAR (Light Detection and Ranging) sensors can provide digital models of ground and vegetation surfaces with pixel sizes of less than 1 m. We present the first study in terrestrial herpetology using LiDAR data. We aim to identify the spatial patterns of a community of four species of lizards (Lacerta schreiberi, Timon lepidus, Podarcis bocagei, and P. hispanica), and to determine how the habitat is influencing the distribution of the species spatially. The study area is located in Northern Portugal. The position of each lizard was recorded during 16 surveys of 1 h with a very precise GPS (error < 1 m). LiDAR data provided digital models of surface, terrain, and normalised height. From these data, we derived slope, ruggedness, orientation, and hill-shading variables. We applied spatial statistics to determine the spatial structure of the community. We computed Maxent ecological niche models to determine the importance of environmental variables. The community and its species presented a clustered distribution. We identified 14 clusters, composed of 1–3 species. Species records showed two distribution patterns, with clusters associated with steep and flat areas. Cluster outliers had the same patterns. Juveniles and subadults were associated with areas of low quality, while sexes used space in similar ways. Maxent models identified suitable habitats across the study area for two species and in the flat areas for the other two species. LiDAR allowed us to understand the local distributions of a lizard community. Remotely sensed data and LiDAR are giving new insights into the study of species ecology. Images of higher spatial resolutions are necessary to map important factors such as refuges.  相似文献   

Dynamics of water vapor flux and water separation processes during evaporation from a salty dry soil     

Meritxell Gran  Jesús Carrera  Jordi Massana  Maarten W. Saaltink  Sebastia Olivella  Carlos Ayora  Antonio Lloret 《Journal of Hydrology》2011,396(3-4):215-220

  相似文献   

Complex size-dependent habitat associations in potamodromous fish species     

José Maria Santos  Luís Reino  João Oliveira  Paulo Pinheiro  Pedro Raposo Almeida  Rui Cortes  Maria Teresa Ferreira 《Aquatic Sciences - Research Across Boundaries》2011,73(2):233-245

Knowledge of the distribution of species life stages at multiple spatial scales is fundamental to both a proper assessment of species management and conservation programmes and the ability to predict the consequences of human disturbances for river systems. The habitat requirements of three native cyprinid species—the Iberian barbel Barbus bocagei Steindachner, the Iberian straight-mouth nase Pseudochondrostoma polylepis (Steindachner), and the Northern straight-mouth nase Pseudochondrostoma duriense (Coelho)—were examined at 174 undisturbed or minimally disturbed sites in 8 river catchments across western Iberia, by modelling occurrence and counts of species life stages at two spatial scales—large (regional) and instream (local)—using hurdle models. All the life stages of the barbel showed a negative association with upstream high-gradient river reaches, whereas juvenile P. duriense favoured such areas. Stream width and openness were negatively related with the occurrence of juvenile and small adult barbel, but not with large adults. Juvenile nase, on the other hand, were found to be mainly confined to fast-flowing habitats with high instream cover and coarser substrata. Advanced life stages of the barbel were mainly associated with the “pure” regional and shared components, whereas the purely local attributes accounted for much of the model variation among nases, in particular juveniles, and juvenile barbel. The results of this study are useful for setting or refining management goals, and highlight the need to separately consider life stages when performing conservation-related studies of species distribution.  相似文献   

Geostatistics for radiological evaluation: study of structuring of extreme values   总被引：2，自引：2，他引：0  

Y. Desnoyers  J.-P. Chil��s  D. Dubot  N. Jeann��e  J.-M. Idasiak 《Stochastic Environmental Research and Risk Assessment (SERRA)》2011,25(8):1031-1037

Geostatistics applied to radiological evaluation of nuclear premises provides sound methods to estimate radiological activities, together with their uncertainty. Quantification and risk analysis of contaminated areas are initially performed by applying geostatistical methods relying on the multi-Gaussian assumption. However, the application of the classical bi-Gaussian model for disjunctive kriging proves sub-optimal due to the spatial structuring of high and low values. The beta model which pertains to the class of Hermitian isofactorial models is potentially better suited to radiological evaluation as it allows a continuous evolution from a mosaic to a pure diffusive model. In the test case, disjunctive kriging estimates are obtained by applying in turn the beta model and the pure diffusive model. The comparison of estimation outcomes shows rather limited differences, primarily located in and around the homogeneous contaminated areas.  相似文献   

Active surface faulting or landsliding in the Lower Tagus Valley (Portugal)? A solved controversy concerning the Vila Chã de Ourique site     

João Manuel Cabral  Fernando Marques  Paula Figueiredo  Luís Matias 《Journal of Seismology》2011,15(2):215-234

The Lower Tagus Valley has experienced significant (M 6–7) historical seismicity, evidencing the presence of seismogenic faults. These are still deficiently known due to the low strain rates and the recent alluvial sedimentation of the Tagus River that buries most of the structures, though Paleoseismic evidence was allegedly found by a research team in the Tagus valley, at a site 60 km N of Lisbon, near Vila Chã de Ourique (VCO). According to this team, trenching at the VCO site exposed an active thrust fault, evidencing the surface rupture of a large earthquake that occurred in 1531. Our studies performed at this site, comprising field observations with a reappraisal of the trench outcrops previously excavated, borehole drilling, soil mechanics laboratory testing, and seismic reflection acquisition, pointed to the alternative interpretation that the outcropping structures are gravitational and not of tectonic origin. The interpretation of new outcrops crosscutting the structures exposed at the trenches, as well as newly acquired high-resolution seismic reflection data, definitely exclude the active thrust fault explanation and support a gravitational slip model for all the observed structures. Gravitational slip in the river bank slope was promoted by low shear strength clays and high pore water pressure coupled with slope toe river erosion. Gravitational slides must have occurred prior to development of the present sedimentation level of the Tagus alluvial plain, which was attained in the last few thousand years as indicated by borehole data and estimations of sedimentation rates.  相似文献   

Helium irradiation study on zircon     

Lutz Nasdala  Dieter Grambole  Jens Götze  Ulf Kempe  Tamás Váczi 《Contributions to Mineralogy and Petrology》2011,161(5):777-789

Synthetic ZrSiO₄ and (mildly to strongly radiation-damaged) natural zircon samples were irradiated with 8.8 MeV ⁴He²⁺ ions (fluences in the range 1 × 10¹³–5 × 10¹⁶ ions/cm²). For comparison, an additional irradiation experiment was done with 30 MeV ¹⁶O⁶⁺ ions (fluence 1 × 10¹⁵ ions/cm²). The light-ion irradiation resulted in the generation of new (synthetic ZrSiO₄) or additional (mildly to strongly metamict natural samples) damage. The maximum extent of the damage is observed in a shallow depth range approximately 32–33 μm (8.8 MeV He) and ~12 μm (30 MeV O) below the sample surface, i.e. near the end of the ion trajectories. These depth values, and the observed damage distribution, correspond well to defect distribution patterns as predicted by Monte Carlo simulations. The irradiation damage is recognised from the notable broadening of Raman-active vibrational modes, lowered interference colours (i.e. decreased birefringence), and changes in the optical activity (i.e. luminescence emission). At very low damage levels, a broad-band yellow emission centre is generated whereas at elevated damage levels, this centre is suppressed and samples experience a general decrease in their emission intensity. Most remarkably, there is no indication of notable structural recovery in pre-damaged natural zircon as induced by the light-ion irradiation, which questions the relevance of alpha-assisted annealing of radiation damage in natural zircon.  相似文献   

Zooplankton succession during extraordinary drought–flood cycles: A case study in a South American floodplain lake     

Griselda Chaparro  María Cristina Marinone  Ruben J. Lombardo  María Romina Schiaffino  Alice de Souza Guimarães  Inés O’Farrell 《Limnologica》2011,41(4):371-381

We examined the zooplankton abundance and composition of Laguna Grande, a floodplain wetland of the Lower Paraná Basin (Argentina), during an extraordinary drought–flood cycle that affected both the environment and the biological conditions of the lake. Low waters were characterised by remarkably high conductivities and pH values, and high phytoplankton and bacterioplankton abundances with cyanobacterial blooms, while high waters showed opposite features. In relation to zooplankton, the mean abundances of all the taxonomic groups (rotifers, cladocerans, copepods, ciliates, and heterotrophic nanoflagellates) were slightly higher at low waters. Major changes were observed in the specific composition of metazooplankton: the euryhaline species assemblage that dominated in the dry warm period was replaced by several oligohaline littoral and planktonic species characteristic of the Paraná River Basin, when the water level rose. Mean species richness values at high waters doubled those of low waters and were directly correlated to water depth. Most of the rotifers of the genus Brachionus and the cladoceran Moina micrura switched from parthenogenetic to sexual reproduction during low waters, as a response to a harsh environment and crowding. We suggest that the main changes in the environmental conditions in this eutrophic floodplain lake are driven by the hydrology, which regulates the zooplankton succession. The herein described shifts in the zooplankton structure and dynamics of Laguna Grande over an extraordinary drought–flood cycle contribute to the understanding of the processes that might occur under the scenarios predicted by climate change models.  相似文献   

The Ellipsactinia Limestones of the Marsica area (Central Apennines): A reference zonation model for Upper Jurassic Intra-Tethys reef complexes     

G. Rusciadelli  C. Ricci  B. Lathuilière 《Sedimentary Geology》2011,233(1-4):69-87

This study presents a new and innovative distribution model of the main reef builders that thrived on bioconstructed margins of Upper Jurassic Intra-Tethys platforms. The proposed model is based on the zonation of an Upper Jurassic reef complex presently exposed in the central Apennines. Excellent exposures allow the reconstruction of the reef profile across the platform margin. Biota are mainly represented by corals and calcified demosponges, distributed with different amounts and aggregating structures along the reef complex. Microencrusters represent a secondary but important component that actively contributes to the reef construction process. Reef builders are distributed in variable quantities and with variable aggregating structures along the reef complex, revealing a strong reef zonation. Like the biota, the sedimentary features (grain size, sorting and reworking degree, bioerosion, cement crusts and cavities) show a distinctive distribution along the reef complex. Three main zones have been recognized along the studied reef complex: an internal, more protected and deeper zone, corresponding to a relatively deep back-reef/lagoon, is dominated by corals and chaetetids; a central zone (reef flat), where well-preserved coral bioconstructions give rise to a true, but discontinuous framework, and a more external zone, corresponding to the reef crest, characterized by the shallowest depths recorded across the reef complex and dominated by stromatopores. The latter forms mound-shaped structures, playing a role essential for the zoned character of the reef complex. These structures actively contribute to the construction of a moderately high topographic relief in the reef crest.  相似文献