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1.
The Outardes Bay delta constitutes one of the best sites to study the formation of failure deposits in a modern lowstand environment.
These deposits are located in a pseudo-shelf-edge position along the northern part of the Laurentian Channel in the St. Lawrence
Estuary. The site has been investigated over the past 20 years with a Raytheon model RTT1000 boomer (3.5 kHz, 400 J) on the
shelf, and most recently with a Simrad model EM 1000 multibeam sonar (95 kHz) on the slope to provide high-resolution seismic
and bathymetric data. The seismic data show wavy, chaotic and contorted reflectors which are typical in marine environments
characterised by instability features. The multibeam sonar data have revealed many slope instability features such as creep
folds, channel incisions, debris flows, and rotational slide scars. Thus, these interpreted features are in direct relationship
with the seismic interpretation of the data collected upslope. These geomorphological and geophysical signatures express both
past and present sedimentological processes. Some of the mass movement signatures observed in the surveyed area are believed
to be related with the great MS~7 Charlevoix earthquake in 1663. 相似文献
2.
The Outardes Bay delta constitutes one of the best sites to study the formation of failure deposits in a modern lowstand environment. These deposits are located in a pseudo-shelf-edge position along the northern part of the Laurentian Channel in the St. Lawrence Estuary. The site has been investigated over the past 20 years with a Raytheon model RTT1000 boomer (3.5 kHz, 400 J) on the shelf, and most recently with a Simrad model EM 1000 multibeam sonar (95 kHz) on the slope to provide high-resolution seismic and bathymetric data. The seismic data show wavy, chaotic and contorted reflectors which are typical in marine environments characterised by instability features. The multibeam sonar data have revealed many slope instability features such as creep folds, channel incisions, debris flows, and rotational slide scars. Thus, these interpreted features are in direct relationship with the seismic interpretation of the data collected upslope. These geomorphological and geophysical signatures express both past and present sedimentological processes. Some of the mass movement signatures observed in the surveyed area are believed to be related with the great MS~7 Charlevoix earthquake in 1663. 相似文献
3.
Evidence for current-controlled morphology along the western slope of Hatton Bank (Rockall Plateau, NE Atlantic Ocean) 总被引：1，自引：0，他引：1
Miriam Sayago-Gil David Long Kenneth Hitchen Víctor Díaz-del-Río Luis Miguel Fernández-Salas Pablo Durán-Muñoz 《Geo-Marine Letters》2010,30(2):99-111
A multibeam bathymetric and high- (airgun and sparker) to very high-resolution (Topas) seismic study of the western slope
of Hatton Bank (NE Atlantic), located between 600 m and 2,000 m water depth, has revealed a highly variable range of current-controlled
morphological features. Two major seabed areas can be distinguished: (1) a non-depositional area corresponding to the top
of the bank and (2) a depositional area in which the Hatton Drift has developed. Both areas are characterised by distinct
morphologies associated either with rock outcrops and rocky ridges or with smooth surfaces, slides and bedforms controlled
mainly by bottom currents interacting with the topography of the bank. The water depth separating the morphological areas
probably coincides with the boundary of the Labrador Sea Water and the Lower Deep Water. Morphological features identified
in the study area include contourite channels (moats, furrows and scours), fields of sediment waves, edges of contourite deposits,
ponded deposits, scarps, gullies, ridges, depressions, slides and slide scars. These morphological features do not necessarily
reflect present-day conditions but may have been associated with past current events, consistent with earlier interpretations. 相似文献
4.
The seafloor morphology and the subsurface of the continental slope of the Olbia intraslope basin located along the eastern, passive Sardinian margin (Tyrrhenian Sea) has been mapped through the interpretation of high-resolution multibeam bathymetric data, coupled with air-gun and sparker seismic profiles. Two areas, corresponding to different physiographic domains, have been recognized along the Olbia continental slope. The upper slope domain, extending from 500 to 850 m water depth, exhibits a series of conical depressions, interpreted as pockmarks that are particularly frequent in seafloor sectors coincident with buried slope channels. In one case, they are aligned along a linear gully most likely reflecting the course of one of the abandoned channels. The location of the pockmarks thus highlights the importance of the distribution of lithologies within different sedimentary bodies in the subsurface in controlling fluid migration plumbing systems. A linear train of pockmarks is, however, present also away from the buried channels being related to a basement step, linked to a blind fault. Two bathymetric highs, interpreted as possible carbonate mounds, are found in connection with some of the pockmark fields. Although the genetic linkage of the carbonate mounds with seafloor fluid venting cannot be definitively substantiated by the lack of in situ measurements, the possibility of a close relationship is here proposed. The lower slope domain, from 850 m down to the base of the slope at 1,200 m water depth is characterized by a sudden gradient increase (from 2° to 6°) that is driven by the presence of the basin master fault that separates the continental slope from the basin plain. Here, a series of km-wide headwall scars due to mass wasting processes are evident. The landslides are characterized by rotated, relatively undeformed seismic strata, which sometimes evolve upslope into shallow-seated (less than 10 m), smaller scale failures and into headless chutes. Slope gradient may act as a major controlling factor on the seafloor instability along the Olbia continental slope; however, the association of landslides with pockmarks has been recognized in several continental slopes worldwide, thus the role of over-pressured fluids in triggering sediment failure in the Olbia slope can not be discarded. In the absence of direct ground truthing, the geological processes linked to subsurface structures and their seafloor expressions have been inferred through the comparison with similar settings where the interpretation of seafloor features from multibeam data has been substantiated with seafloor sampling and geochemical data. 相似文献
5.
The Red Sea is an unusual example of a rift basin that transitioned from its evaporitic stage to fully open-ocean conditions at the end of the Miocene (∼5.3 Ma), much more recently than older Mesozoic margins around the Atlantic and Gulf of Mexico. The patterns of halokinetic deformation occurring in the Red Sea are potentially of interest for understanding more generally how evaporite deposits deform during this early stage. Relevant to this issue, a line of reconnaissance sidescan sonar data (GLORIA) collected along the Red Sea in 1979 is re-evaluated here. We first interpret the data with the aid of newly compiled bathymetry from multibeam sonars in the central and southern Red Sea. Features in the acoustic backscatter data are associated with ridges, valleys and rounded flow fronts produced by halokinetic deformation. Some areas of higher acoustic backscattering from the evaporites are suggested to relate to roughness produced by deformation of the evaporite surface. Within the volcanic (oceanic) axial valleys, areas of differing high and low backscattering suggest varied sediment cover and/or carbonate encrustations. With the benefit of the above experience, we then interpreted data from the northern Red Sea, where there are fewer multibeam data available. Rounded fronts of halokinetic deformation are present in the Zabargad Fracture Zone, a broad, shallow valley crossing the Red Sea obliquely. The presence of halokinetic deformation here is evidence that subsidence has occurred along the fracture zone. Elsewhere in the northern Red Sea, the GLORIA data reveal folds in the evaporite surface, suggesting local areas of convergence, like those implied by multibeam data from inter-trough zones further south. Some linear features are observed, many of which are likely to be ridges overlying salt walls. Interestingly, several such features are oriented along an accommodation zone that is oriented parallel to the plate spreading direction. Several rounded, corrugated features are interpreted as possible evaporite flow fronts. Overall, the impression from the data is of a strongly mobile seabed in the Red Sea because of halokinetic deformation, involving both vertical and horizontal movements. However, salt walls appear more common than in the central and southern axial Red Sea, where horizontal movements instead tend to dominate. 相似文献
6.
M. C. Fernández-Puga J. T. Vázquez L. Somoza V. Díaz del Rio T. Medialdea M. P. Mata R. León 《Geo-Marine Letters》2007,27(2-4):213-221
Recently developed high-resolution profiling (multibeam, sonar) and surface sampling were used to map seafloor morphology of the Gulf of Cádiz middle continental slope. Multichannel seismic profiling has made it possible to elucidate the geologic origin of these features as well as the main triggering mechanisms of gas-related morphologies, principally mud volcanoes, carbonate mud mounds, pockmarks and slides. Throughout the entire Gulf of Cádiz, from the continental slope to the shelf and even on land, a close correlation between morphology and gas mobility and associated diapirism can be observed. The middle slope area is strongly deformed by several diapiric ridges, named Guadalquivir, Cádiz and Doñana. Most of the diapirs identified in this study are related to the Allochthonous Unit of the Gulf of Cádiz, a chaotic body emplaced during the Tortonian, containing salt and shale nappes affected by later gravitational extension collapse and reactivated compression thrusts. It can be proposed that diapirism and related tectonics provided gas migration pathways. 相似文献
7.
Sumanta Dandapath Andrew Menezes Bishwajit Chakraborty John Kurian Koppella N. Prudhvi Raju 《Marine Geodesy》2018,41(2):177-200
An assessment of the multibeam sonar data of the central Western Continental Margins of India has been carried out to evaluate the seafloor geomorphology and processes by examining the geomorphological attributes e.g., slope, sediments, structures, etc. associated with geomorphic features. The variation in relief and the features located in the region have been mapped and interpreted collectively by utilizing several geospatial mapping tools. The backscatter strength across the area, apparently congruent with the local relief, has helped to examine the sediment movement on the seafloor. The prominent features found in the region include faults, pockmarks, mounds, submarine terraces, and submerged fossil reefs. Several areas with varying topography engender comparable fractal dimension at short scale breaks, and the probability density functions (PDFs) utilizing backscatter data depicting overlapping classes. The present study highlights how fractals and scale break parameters can be utilized to determine the seafloor processes and associated sedimentological dynamics in a complex geographical environment with strong bottom currents, seasonal upwelling, and faulted structure. The role and impact of the various geomorphic processes on the reworking of sediment movement and the overall progression of the seafloor morphology has been revealed for the first time in this part of the ocean bottom. 相似文献
8.
《Marine Geology》2005,216(3):101-106
A multibeam bathymetric crossing of Bounty Channel, east of South Island New Zealand fortuitously imaged a large recent slump that partially dammed the channel. Together with a later, adjacent multibeam crossing, these bathymetric data show the average gradient for this section of the channel to be 15 m per km, steeper than the general average for the whole channel (∼3 m per km). In the immediate vicinity of the slump, there is a negative gradient followed downstream by a maximum gradient of 1450 m/km for a 70 m section of the channel. Typical riverine erosional features are seen in this section of the channel including an over-deepened basin at the bottom of the greatest slope as well as additional major slump features. 相似文献
9.
基于多波束声呐的人工鱼礁区地形特征分析 总被引：4，自引：3，他引：1
建设人工鱼礁(Artificial Reef,AR)是恢复和养护近海渔业资源的重要措施。尽管中国沿海各地人工鱼礁规模宏大,但对于鱼礁投放后的监测明显不足。传统调查方法存在效率低、成本高等缺点,多波束测深系统(Multibeam Echo Sounder,MBES)为探测鱼礁区地形地貌提供了一种有效的技术手段。本文利用高分辨率的多波束测深系统,获取礁区详细的测深数据,快速确定鱼礁位置、形态等信息;应用地形分析工具提取地形变量(坡度、曲率、粗糙度、地形耐用指数及地形起伏度),分析投石后海底地形特征。研究表明,礁石投放后海底地形发生显著变化(水深5~10 m),礁石发生沉降现象(下沉深度约0.45 m),礁石周围出现冲淤地形(礁石堆高1.65 m,影响范围5 m左右)。分析人工鱼礁引起的微地形地貌的变化,可以为鱼礁的监测与效果评估工作提供一种新的技术方法,具有较强的现实意义。 相似文献
10.
Lies Loncke Virginie Gaullier Laurence Droz Emmanuelle Ducassou Sébastien Migeon Jean Mascle 《Marine and Petroleum Geology》2009,26(5):633-646
The Nile deep-sea fan (NDSF), turbiditic system reaching a size of about 90,000 km2, has been investigated since 1998 by several geophysical methods (multibeam bathymetry, backscatter imagery, seismic data, 3–5 kHz echo-sounding). The analysis of this important data set evidenced that the NDSF is the locus of numerous multi-scale slope instabilities. Three main types of instabilities have been defined, mainly on the basis of their size or origin. (1) First type of instabilities related to the generalized gravity spreading of the Plio-Quaternary deep-sea fan on Messinian salt layers. This global spreading is accommodated by numerous localized slides. (2) Second type of instabilities correspond to giant mass movements probably triggered either by earthquakes, fluids, or climate and eustatic oscillations. Finally, (3) third type of instabilities correspond either to localized levee liquefactions or to thin-skinned slides on the steep slopes of the Eratosthenes seamount. The deposits generated by these slope movements greatly participate in the building of the NDSF. The characterization of these different instabilities, in a petroleum province as the NDSF, has important implications in terms of risk assessments when considering drilling operations. 相似文献
11.
12.
The Queen Charlotte Fault Zone (QCFZ) off western Canada is the northern equivalent to the San Andreas Fault Zone, the Pacific–North American plate boundary. Geomorphologic expression and surface processes associated with the QCFZ system have been revealed in unprecedented detail by recent seabed mapping surveys. Convergence of the Pacific and North American plates along northern British Columbia is well known, but how the QCFZ accommodates this convergence is still a subject of controversy. The multibeam sonar bathymetry data reveal, for the first time, evidence of a fault valley with small depressions on the upper slope, offshore central Haida Gwaii (Queen Charlotte Islands). The depressions form where strike-slip right-step offsets have realigned the fault due to oblique convergence. Core stratigraphy and radiocarbon dating of sediments within the fault valley and small depressions suggest that these features are recent in origin. In addition, the development of the fault valley and dislocation of submarine canyons control sediment migration from the continental shelf through to the lower slope. This interpretation of the geomorphic expression of major plate tectonic processes along the QCFZ can now be tested with new surveys subsequent to the October 2012 magnitude 7.7 earthquake. 相似文献
13.
Dimitrios Eleftherakis Laurent Berger Naig Le Bouffant Anne Pacault Jean-Marie Augustin Xavier Lurton 《Marine Geophysical Researches》2018,39(1-2):55-73
The calibration of multibeam echosounders for backscatter measurements can be conducted efficiently and accurately using data from surveys over a reference natural area, implying appropriate measurements of the local absolute values of backscatter. Such a shallow area (20-m mean depth) has been defined and qualified in the Bay of Brest (France), and chosen as a reference area for multibeam systems operating at 200 and 300 kHz. The absolute reflectivity over the area was measured using a calibrated single-beam fishery echosounder (Simrad EK60) tilted at incidence angles varying between 0° and 60° with a step of 3°. This reference backscatter level is then compared to the average backscatter values obtained by a multibeam echosounder (here a Kongsberg EM 2040-D) at a close frequency and measured as a function of angle; the difference gives the angular bias applicable to the multibeam system for recorded level calibration. The method is validated by checking the single- and multibeam data obtained on other areas with sediment types different from the reference area. 相似文献
14.
Recent habitat suitability models used to predict the occurrence of vulnerable marine species, particularly framework building cold-water corals, have identified terrain attributes such as slope and bathymetric position index as important predictive parameters. Due to their scale-dependent nature, a realistic representation of terrain attributes is crucial for the development of reliable habitat suitability models. In this paper, three known coral areas and a noncoral control area off the west coast of Ireland were chosen to assess quantitative and distributional differences between terrain attributes derived from bathymetry grids of varying resolution and information content. Correlation analysis identified consistent changes of terrain attributes as grain size was altered. Response characteristics and dimensions depended on terrain attribute types and the dominant morphological length-scales within the study areas. The subsequent effect on habitat suitability maps was demonstrated by preliminary models generated at different grain sizes. This study demonstrates that high resolution habitat suitability models based on terrain parameters derived from multibeam generated bathymetry are required to detect many of the topographical features found in Irish waters that are associated with coral. This has implications for marine spatial planning in the deep sea. Supplemental materials are available for this article. Go to the publisher's online edition of Marine Geodesy to view the free supplemental file. 相似文献
15.
David C. Mosher 《Marine Geophysical Researches》2011,32(1-2):25-35
Most modern submarine geohazard investigations rely heavily on multibeam sonar data, yet there are limitations to these data that must be respected. Disregard of fundamental aspects of spatial sampling, averaging and interpolation, and statistical parameters that accompany all forms of measurement, can lead to over-interpretation of data. Beam spreading and sounding density govern spatial resolution and therefore limit seafloor features that are resolved and interpreted as indicative of geohazards. These resolution limitations are shown with a synthetic model of the seafloor convolved with a spherically spreading wavefront approximated with a spherical smoothing algorithm. This simulation shows the inability to resolve metrics of objects, as well as determine critical parameters such as slope angles with increasing water depth. As well, real case examples are presented showing these effects on identification of targets, slope angles and pockmarks. Misinterpretation of seafloor features is common in multibeam data, particularly without the benefit of coincident subbottom data. Thus it is critical to image the third dimension below the seafloor. Finally, seafloor mapping for geohazards is just one step in a geohazard assessment: it is critical to know frequency of recurrence of geohazard events and their modern geologic context in order to appropriately assess risk. 相似文献
16.
多波束水体数据对台西南盆地天然气水合物的揭示 总被引：1，自引：1，他引：0
在台西南盆地陆坡上进行了多波束测量，获取了海底地形数据和水体数据。对多波束数据进行处理，展示了多波束水体数据形成的声学水柱影像。研究表明：在台西南盆地天然气水合物富集区，多波束水柱影像异常，呈现羽状流特点，揭示了台西南盆地的天然气资源，多波束声呐系统为探测海底天然气水合物提供了精确高效的方法。 相似文献
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18.
《Marine Policy》2014
During 2010 a set of 22 voluntary closed areas, distributed around Shetland, were proposed by local industry in order to help protect and conserve threatened habitats from potential physical disturbance from scallop dredging. Initially, closed areas were implemented on a precautionary basis over predicted beds of maerl and horse mussel (Modiolus modiolus) derived from historical data. Horse mussel and maerl beds are classed as priority habitats which have been identified as being threatened and requiring conservation under the UK Biodiversity Action Plan (UK BAP). Legalisation of the voluntarily adopted closed areas occurred in 2011. Detailed surveys were conducted to map each closed area with specific reference to the defining features located within. Closed areas were surveyed using a hull mounted multibeam system and ground-truthed with an underwater camera system. Information was imported to a Geographic Information System (GIS) in order to create georeferenced habitat maps of the two species of interest. The appropriateness of each closed area was assessed and a proposed methodology and procedure outlined for any future closed areas. The primary aim was to provide information on which to test the validity of initial closed area boundaries and subsequently allow managers to refine and add to them in the future. The survey illustrated the need to have good quality acoustic and visual survey work undertaken whenever areas have been closed based on historical data and/or predicted habitats. Predicted beds were not found to be representative of the survey findings. The survey highlighted the lack of good quality, robust, accurate, and up to date species information for the waters around Shetland, especially with regard to priority marine features. Although some were neither fully protecting the UK BAP habitats they were designed to protect nor were protecting any UK BAP habitats, a degree of protection had been conferred to some priority features in the first iteration of implementation of closed areas. Survey data were subsequently used to legally alter the closed area boundaries to more appropriately reflect the distribution of priority features. Recommendations were made on appropriate procedures for defining a species bed and on the wider implications of the study’s findings for other fisheries areas developing spatial management plans. 相似文献
19.