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41.
Luc G. Bulot Jean-Louis Latil Alex Hairabian Arnaud Fournillon 《Proceedings of the Geologists' Association. Geologists' Association》2014
Nolaniceras nolani ( Seunes, 1887) has been widely quoted in the Upper Aptian literature over the years. Re-examination of the holotype of the species shows that it has always been misidentified and that this taxon is represented by a single specimen, the holotype, of uncertain age. As a consequence, its use as an index species for the Upper Aptian should be reconsidered and abandoned. 相似文献
42.
Abstract– Northwest Africa 4859 (NWA 4859) is a meteorite of LL chondrite parentage that shows unusual igneous features and contains widely distributed pentlandite. The most obvious unusual feature is a high proportion of large (≤3 cm diameter) igneous‐textured enclaves (LITEs), interpreted as shock melts that were intruded into an LL chondrite host. One such LITE appears to have been produced by whole rock melting of LL chondrite, initial rapid partial crystallization, and subsequent slow cooling of the residual melt in the host to produce a differentiated object. Other unusual features include mm‐sized “overgrowth objects,” fine‐grained plagioclase‐rich bands, and coarse troilite (≤7 mm across) grains. All these features are interpreted as having crystallized from melts produced by a single transient shock event, followed by slow cooling. A subsequent shock event of moderate (S3) intensity produced veining and transformed some of the pyroxene into the clinoenstatite polytype. Pentlandite (together with associated troilite) in NWA 4859 probably formed by the breakdown of a monosulfide precursor phase at low temperature (≤230 °C) following the second shock event. NWA 4859 is interpreted to be an unusual impact‐melt breccia that contains shock melt which crystallized in different forms at depth within the parent body. 相似文献
43.
Joaquín Chaves Christopher Neill Sonja Germer Sérgio Gouveia Neto Alex Krusche Helmut Elsenbeer 《水文研究》2008,22(12):1766-1775
Forest clearing and conversion to cattle pasture in the lowland Amazon region has been linked to soil compaction and increased soil water storage, which combine to diminish soil infiltration, enhance quick lateral flows and increase the stream flow response to precipitation. Quantifying the importance of quick surficial flow in response to this land use change requires identification of water sources within catchments that contribute to stream flow. Using an end member mixing analysis approach, potential contributing sources of stream flow were evaluated during an entire rainy season in a forest and a pasture watershed drained by ephemeral‐to‐intermittent streams in the south‐western Amazon. Water yield was 17% of precipitation in the pasture and 0·8% of precipitation in the forest. During the early rainy season, throughfall, groundwater, and soil water contributed 79%, 18%, and 3%, respectively, to total forest stream flow. Over the entire rainy season, throughfall, groundwater, and shallow soil water provided 57%, 24%, and 19%, respectively, of stream flow. In the pasture watershed, overland flow dominated stream flow both in the early (67%) and late (57%) rainy season, with a mean contribution of 60% overland flow, 35% groundwater, and 5% soil water. The uncertainty associated with those estimates was studied using a Monte Carlo approach. In addition to large changes in total surface flow, marked differences were found in the proportions of total stream flow in the second half of the rainy season between the forest and pasture watershed. These results suggest that (1) there is great potential for alteration of the hydrological budgets of larger watersheds as the proportion of deforested land in the Amazon increases, and (2) as more rainfall is diverted into fast flowpaths to streams in established pastures, the potential to deliver water with higher solute concentrations generated by erosion or by bypassing sites of solute removal increases. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
44.
45.
Basement lithostratigraphy of the Adula nappe: implications for Palaeozoic evolution and Alpine kinematics 总被引:1,自引:0,他引:1
Mattia Cavargna-Sani Jean-Luc Epard François Bussy Alex Ulianov 《International Journal of Earth Sciences》2014,103(1):61-82
The Adula nappe belongs to the Lower Penninic domain of the Central Swiss Alps. It consists mostly of pre-Triassic basement lithologies occurring as strongly folded and sheared gneisses of various types with mafic boudins. We propose a new lithostratigraphy for the northern Adula nappe basement that is supported by detailed field investigations, U–Pb zircon geochronology, and whole-rock geochemistry. The following units have been identified: Cambrian clastic metasediments with abundant carbonate lenses and minor bimodal magmatism (Salahorn Formation); Ordovician metapelites associated with amphibolite boudins with abundant eclogite relicts representing oceanic metabasalts (Trescolmen Formation); Ordovician peraluminous metagranites of calc-alkaline affinity ascribed to subduction-related magmatism (Garenstock Augengneiss); Ordovician metamorphic volcanic–sedimentary deposits (Heinisch Stafel Formation); Early Permian post-collisional granites recording only Alpine orogenic events (Zervreila orthogneiss). All basement lithologies except the Permian granites record a Variscan + Alpine polyorogenic metamorphic history. They document a complex Paleozoic geotectonic evolution consistent with the broader picture given by the pre-Mesozoic basement framework in the Alps. The internal consistency of the Adula basement lithologies and the stratigraphic coherence of the overlying Triassic sediments suggest that most tectonic contacts within the Adula nappe are pre-Alpine in age. Consequently, mélange models for the Tertiary emplacement of the Adula nappe are not consistent and must be rejected. The present-day structural complexity of the Adula nappe is the result of the intense Alpine ductile deformation of a pre-structured entity. 相似文献
46.
The mercury (Hg) deposition history in the Darién Gulf is reconstructed from three sediment cores spanning up to 1,000 years. Knowledge on the contribution to global Hg budget from the Caribbean is limited. Patterns of water circulation, sediment deposition rates, cataclysmic atmospheric inputs, and post-depositional migration have been considered in Hg trapping in the seabed. The sediment delivery rates to the coastal zone over the Late Holocene have increased from 0.2 to 1 cm year?1 owing to anthropogenic influence. This alteration took the form of geological effects, like coastal morphology change, that played a major role in Hg downcore signal preservation. Natural background Hg levels in Southern Caribbean sediments (77.0 μg kg?1) are up to three times higher than preindustrial signals at other latitudes, because of volcanic contributions from the Pacific ring of fire. Enrichment factors rose from 0.9 to 1.5 (70.1–113.5 μg kg?1) within profiles related to Hg usage since Spanish colonial times between the calendar years 1550 and 1811. 相似文献
47.
Alex K. Manda Angela S. Giuliano Thomas R. Allen 《Environmental Earth Sciences》2014,71(10):4409-4419
Saline water intrusion is degrading water quality in the channelized coastal wetlands of the southern Albemarle estuarine system (AES). The source, transport and fate of the saline water in the southern AES was determined by monitoring specific conductivity and water levels in small artificial channels, the Alligator River, the Alligator–Pungo Canal and the groundwater system for ~12 months. Results indicate that water levels are affected by wind tides which trigger the movement of saline water into the interior of the wetlands via the small canals. The wind tides are mostly driven by episodic southerly winds pushing saline water into the canal network and the groundwater regime proximal to the Alligator River. The saline waters persist in the canals as long as the wind tide events last. Specific conductivities from canals and groundwater are shown to be unexpectedly higher closer to the source of the Alligator River than toward the Albemarle Sound, suggesting that the large Alligator–Pungo Canal facilitates the northward migration of saline water from the Pamlico Sound to the Alligator River. Overwash and reversals in the flow directions between groundwater and surface water bodies suggest that saline water that is present during wind tide events may migrate into the groundwater system from surface water bodies. The results of this study reveal that whereas the large Alligator–Pungo Canal channels saline water to the AES, small artificial channels may also play significant roles in degrading water quality in the interior of channelized coastal wetlands. 相似文献
48.
Richard C. Franklin Jemma C. King Peter J. Aitken Peter A. Leggat 《Natural Hazards》2014,73(3):1977-1998
This article explored the perceptions of residents of a regional city in North Queensland of how to remain safe during flood events. It also explored reasons for and how to prevent risk-taking behaviour in floodwater using the protection motivation theory (PMT). PMT is a psychological theory which has recently been applied to assess behaviour during floods and was used as a framework to analyse the themes of responses to the online survey. The online survey was conducted prior to the wet season of 2011/2012 with 130 Townsville residents participating. The results indicate that about half of respondents (55 %) had some experience with floods of which driving through floodwater (38 %) was the most common type of flood experience listed and was more common amongst male respondents. Respondents’ advice to keep friends and family safe during floods was consistent with “coping appraisal”, which would improve their ability to cope with the flood. Prior experiences with floodwater influenced the reasons given for why people drive through floodwater and were taken to be indicative of an actor/observer bias. Respondents who had experience driving through floodwater (the actors) indicate how the context of the situation can influence decision-making, whereas those respondents who had no personal experience of driving through floodwater (the observers) were more likely to cite low perceived vulnerability of harm as a motivator. Prevention strategies focused on structural mechanisms to block access, information provision and punishment of offenders. It is suggested that in communities which regularly experience flooding, timely and context-specific reminders of the dangers inherent in floodwater along with the type, effectiveness and cost of protective action could minimise the public’s contact with floodwater and prove useful regardless of past experiences. 相似文献
49.
Hydraulic roughness over simple subaqueous dunes 总被引:1,自引:1,他引:1
Jesper Bartholdy Burg W. Flemming Verner B. Ernstsen Christian Winter Alex Bartholom ä 《Geo-Marine Letters》2010,30(1):63-76
Detailed studies of flow over subaqueous dunes in laboratory flumes were used to suggest a virtual near-bed layer of twice
the dune height in which the mean velocity is accelerated towards the crest by contraction. The mean flow velocity in this
layer above the crest, transformed into friction velocity by means of the surface skin roughness, is shown to give values
consistent with measured values. The resulting dimensionless shear stress due to skin friction is depth-independent, in contrast
to that derived by means of often cited traditional methods. As a result of the relationship between dune height and the thickness
of the near-bed layer, an expression for the expansion loss behind dunes was formulated and used to relate form resistance
directly to dune height. 相似文献
50.
Alex E. Il'In 《Astrophysics and Space Science》1995,224(1-2):233-233
The absorption features of ice at 3µm and of silicate at 10 and 20µm as well as the linear polarization across it have been calculated. The interpretations of data for protostellar objects BN and AFGL 2591 are made.The model of partially aligned spinning spheroidal grains with the Purcell's suprathermal alignment mechanism and the power law size distribution are considered. Core-mantle, porous and composite particles are investigated in the Rayleigh approximation. In the case of composite and porous grains the effective refractive indices are computed with the approximate Bruggeman rule.The influence of grain chemical composition, elongation and structure has been investigated. The distinctions in polarization between composite and core-mantle models are found. The mixing of grain materials smooths the individual spectral features of chemical components. The adding of graphite causes the shift of the 10µm peak position to shorter wavelengths. When the fraction of graphite increases, the peak at 20µm decreases and shifts to shorter wavelengths. The increase of elongation reduces the negative polarization at the 3µm feature, shifts the 10µm and 20µm peak positions to longer wavelengths, and raises the strength of the 20µm band. The porosity leads to similar effects.It was found that the studied grain models are in good agreement with observational data for BN and AFGL 2591 objects. The absence of polarization excess near 3µm for AFGL 2591 is attributable to a decrease in elongation of large grains as a result of coagulation. The attention is attracted to the problem of real distribution of the interstellar dust grains over the elongation parameter. The determination this distribution function and the study of its evolution in the processes of accretion and coagulation are necessary. 相似文献