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101.
102.
Anis Gasmi Cécile Gomez Hédi Zouari Antoine Masse Danielle Ducrot 《Arabian Journal of Geosciences》2016,9(20):753
The purpose of this study was to examine the efficiency of Advanced Space Borne Thermal Emission and Reflection Radiometer (ASTER) data in the discrimination of geological formations and the generation of geological map in the northern margin of the Tunisian desert. The nine ASTER bands covering the visible (VIS), near-infrared (NIR) and short-wave infrared (SWIR) spectral regions (wavelength range of 400–2500 nm) have been treated and analyzed. As a first step of data processing, crosstalk correction, resampling, orthorectification, atmospheric correction, and radiometric normalization have been applied to the ASTER radiance data. Then, to decrease the redundancy information in highly correlated bands, the principal component analysis (PCA) has been applied on the nine ASTER bands. The results of PCA allow the validation and the rectification of the lithological boundaries already published on the geologic map, and gives a new information for identifying new lithological units corresponding to superficial formations previously undiscovered. The application of a supervised classification on the principal components image using a support vector machine (SVM) algorithm shows good correlation with the reference geologic map. The overall classification accuracy is 73 % and the kappa coefficient equals to 0.71. The processing of ASTER remote sensing data set by PCA and SVM can be employed as an effective tool for geological mapping in arid regions. 相似文献
103.
Jean Delteil Jean-François Stéphan Bernard Mercier de Lépinay Étienne Ruellan 《Comptes Rendus Geoscience》2003,335(9):743-750
In eastern North Island New Zealand, oblique subduction of the Pacific Plate beneath the Australian Plate is associated with strain partitioning. Dextral along-strike component of displacement occurred first at Early Miocene major faults within the eastern fore-arc domain. These faults were active from Early Miocene to Pliocene times. Since Pliocene times, most of the movement occurs at western faults such as the Wellington Fault. The latter joins the back-arc domain to the north. The jump of wrench faulting is related to the oblique opening of the back-arc domain. Both phenomena are impeded southwards by the Hikurangi oceanic plateau entering the subduction zone. To cite this article: J. Delteil et al., C. R. Geoscience 335 (2003). 相似文献
104.
Frederick J. Swanson Stanley V. Gregory Andres Iroumé Virginia Ruiz-Villanueva Ellen Wohl 《地球表面变化过程与地形》2021,46(1):55-66
Dynamics and functions of large wood have become integral considerations in the science and management of river systems. Study of large wood in rivers took place as monitoring of fish response to wooden structures placed in rivers in the central United States in the early 20th century, but did not begin in earnest until the 1970s. Research has increased in intensity and thematic scope ever since. A wide range of factors has prompted these research efforts, including basic understanding of stream systems, protection and restoration of aquatic ecosystems, and environmental hazards in mountain environments. Research and management have adopted perspectives from ecology, geomorphology, and engineering, using observational, experimental, and modelling approaches. Important advances have been made where practical information needs converge with institutional and science leadership capacities to undertake multi-pronged research programmes. Case studies include ecosystem research to inform regulations for forest management; storage and transport of large wood as a component in global carbon dynamics; and the role of wood transport in environmental hazards in mountain regions, including areas affected by severe landscape disturbances, such as volcanic eruptions. As the field of research has advanced, influences of large wood on river structures and processes have been merged with understanding of streamflow and sediment regimes, so river form and function are now viewed as involving the tripartite system of water, sediment, and wood. A growing community of researchers and river managers is extending understanding of large wood in rivers to climatic, forest, landform, and social contexts not previously investigated. © 2020 John Wiley & Sons, Ltd. 相似文献
105.
On November 4th 2007, along the Grijalva River in the state of Chiapas, Mexico, has occurred one of the largest landslides
ever known. This landslide, known as Juan del Grijalva, destroyed the town of the same name, killing 20 people, and moved 55 million cubic meters of rock and debris down slope
to completely block the Grijalva River. In order to understand the characteristics and factors that triggered the Juan del
Grijalva landslide, geologic studies were conducted at the site. The results indicate that the landslide was composed of a
lithologic sequence of thin-bedded shales and thin to medium-thick-bedded sandstones. This was faulted into several blocks
dipping in the same sense as the mass movement. The main triggering factor was the increment of the pore pressure into the
lithologic unit due to water saturation after 5 days of heavy rain before the incident. According to records from the last
century, the Juan del Grijalva mass movement represents one of the largest mass movements recorded all over the world. The
risk conditions of the area after the landslide lead to the rapid construction of an artificial channel to drain the accumulating
mass of water upstream and therefore prevent a future catastrophic inundation down stream. 相似文献
106.
107.
Philippe Meus Pierre Moureaux Sébastien Gailliez Jérémy Flament Francis Delloye Philippe Nix 《Environmental Earth Sciences》2014,71(2):533-541
The implementation of the Water Framework Directive, as well as the forthcoming entry into force of other European water policies focusing on water resources, require a thorough reorganization of groundwater resources monitoring in most European countries. In Wallonia, monitoring programs were initiated in 2005 to control the quantitative and chemical statuses of groundwater bodies, as well as the effectiveness of management plans aimed at achieving environmental objectives. In karst aquifers, springs are preferential monitoring targets even if, as a result of the high heterogeneity of this type of aquifer, the interpretation of time series and spatial data remains a challenge. Since 2006, a “springs” monitoring network has been progressively set up in the southern part of Belgium. Currently, in situ measurements of discharge, temperature, conductivity, turbidity and fluorescence of water are conducted at nine karstic outlets in the Devonian and the Carboniferous limestone aquifers of Wallonia. The main objective of this ongoing research is to evaluate the suitability and the robustness of such standard measurements to discriminate anthropogenic impacts from natural variations, at both short- and long-term scales. Discharge and temperature data revealed being useful in the assessment of regional hydro-climatic trends. Groundwater proved to be a better natural filter for the assessment of long-term climatic changes than mathematical filtering of noisy surface signals. Investigations of such data at a European scale could therefore give additional insight into the impacts of climate change on groundwater resources. Conductivity, turbidity and fluorescence data characterize the particulate, mineral and organic health of water and a better understanding of their natural dynamics could help in the early detection of anthropogenic deviations. However, the current reproducibility of these measurements is too low to ascertain observed trends and fluctuations, and further research is still needed. 相似文献
108.
Tomoko Komada David J. Burdige Cédric Magen Huan-Lei Li Jeffrey Chanton 《Aquatic Geochemistry》2016,22(5-6):593-618
Geochemical and isotopic data for the uppermost 1.2 m of the sediments of the central Santa Monica Basin plain were examined to better understand organic matter deposition and recycling at this site. Isotopic signatures (Δ14C and δ13C) of methane (CH4) and dissolved inorganic carbon (DIC) indicate the occurrence of anaerobic oxidation of CH4 that is fueled by CH4 supplied from a relict reservoir that is decoupled from local organic carbon (Corg) degradation and methanogenesis. This finding was corroborated by a flux budget of pore-water solutes across the basal horizon of the profile. Together these results provide a plausible explanation for the anomalously low ratio between alkalinity production and sulfate consumption reported for these sediments over two decades ago. Shifts in Δ14C and δ13C signatures of Corg have previously been reported across the 20-cm depth horizon for this site and attributed to a transition from oxic to anoxic bottom water that occurred ~350 years BP. However, we show that this horizon also coincides with a boundary between the base of a hemipelagic mud section and the top of a turbidite interval, complicating the interpretation of organic geochemical data across this boundary. Radiocarbon signatures of DIC diffusing upward into surface sediments indicate that remineralization at depth is supported by relatively 14C-enriched Corg within the sedimentary matrix. While the exact nature of this Corg is unclear, possible sources are hemipelagic mud sections that were buried rapidly under thick turbidites, and 14C-rich moieties dispersed within Corg-poor turbidite sections. 相似文献
109.
V. A. Pervov S. V. Somov A. V. Korshunov E. V. Dulapchii J. T. Félix 《Geology of Ore Deposits》2011,53(4):295-308
The Catoca kimberlite pipe is among the world’s largest primary diamond deposits. The Catoca volcanic edifice is only slightly
eroded. Kimberlitic rocks of various facies compose a crater of about 1 km in diameter and a diatreme. The structure of the
pipe and mining conditions of the deposit are complicated by intense intrapipe tectonic processes related to large-amplitude
subsidence. Based on geological data, we propose a structural model of the deposit and a paleovolcanological model of the
Catoca pipe formed during a full cycle beginning with a stage of active volcanism and completed by stages of gradually waning
volcanic activity and sedimentation. It is suggested that the banded tuffisitic kimberlite of the crater zone was deposited
at the stage of active volcanic eruption from specific pyroclastic suspension as a low-viscosity mixture of crystals and aqueous
sol rich in serpentine. 相似文献
110.
Ricardo León Luis Somoza Teresa Medialdea Francisco Javier González Carmen Julia Gimenez-Moreno Raúl Pérez-López 《Geo-Marine Letters》2014,34(2-3):131-151
Integrating novel and published swath bathymetry (3,980 km2), as well as chirp and high-resolution 2D seismic reflection profiles (2,190 km), this study presents the mapping of 436 pockmarks at water depths varying widely between 370 and 1,020 m on either side of the Strait of Gibraltar. On the Atlantic side in the south-eastern Gulf of Cádiz near the Camarinal Sill, 198 newly discovered pockmarks occur in three well localized and separated fields: on the upper slope (n=14), in the main channel of the Mediterranean outflow water (MOW, n=160), and on the huge contourite levee of the MOW main channel (n=24) near the well-known TASYO field. These pockmarks vary in diameter from 60 to 919 m, and are sub-circular to irregularly elongated or lobate in shape. Their slope angles on average range from 3° to 25°. On the Mediterranean side of the strait on the Ceuta Drift of the western Alborán Basin, where pockmarks were already known to occur, 238 pockmarks were identified and grouped into three interconnected fields, i.e. a northern (n=34), a central (n=61) and a southern field (n=143). In the latter two fields the pockmarks are mainly sub-circular, ranging from 130 to 400 m in diameter with slope angles averaging 1.5° to 15°. In the northern sector, by contrast, they are elongated up to 1,430 m, probably reflecting MOW activity. Based on seismo-stratigraphic interpretation, it is inferred that most pockmarks formed during and shortly after the last glacial sea-level lowstand, as they are related to the final erosional discontinuity sealed by Holocene transgressive deposits. Combining these findings with other existing knowledge, it is proposed that pockmark formation on either side of the Strait of Gibraltar resulted from gas and/or sediment pore-water venting from overpressured shallow gas reservoirs entrapped in coarse-grained contourites of levee deposits and Pleistocene palaeochannel infillings. Venting was either triggered or promoted by hydraulic pumping associated with topographically forced internal waves. This mechanism is analogous to the long-known effect of tidal pumping on the dynamics of unit pockmarks observed along the Norwegian continental margin. 相似文献