This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
<p>New high-resolution seismic data (Sparker) and very-high-resolut... more <p>New high-resolution seismic data (Sparker) and very-high-resolution parametric echosounder (PES) data acquired in an area of the southern North Sea (the Flemish Bight) reveal its Quaternary seismic stratigraphy in unprecedented detail. The identified seismo-stratigraphic units and geomorphological features have been examined with the view to better understand the Quaternary evolution of the southern North Sea.</p><p>Seven acoustic units were recognised, including Lower Pleistocene deltaic sediments, Eemian to lower Weichselian shallow marine to coastal (lagoonal) clay-silt-sands, and Holocene coastal peat layers overlain by intertidal and marine sediments. Four erosional events were identified, two of which can be traced as regionally occurring surfaces, and two occurring as localised incisions. Mapping of geomorphological features revealed potential Elsterian moraines in the UK sector, an Elsterian ice-pushed ridge in the Dutch sector and possible permafrost-related structures (probably dating to MIS3).  Seven newly dated peat samples, acquired near a tidal sand ridge known as the Brown Bank from depths between 31 m and 34 m below sea level and dating to between 9.5 and 10.9 cal ka BP, indicate that this area was terrestrial during the early Holocene.</p><p>The results form the basis to further improve the regional Quaternary stratigraphic framework of the area, to better understand the region’s (de)glacial history, to enhance sea-level reconstructions and to examine the area’s geographical importance for human occupation during Prehistory.</p>
A field of sediment undulations has been mapped by means of high resolution multibeam bathymetry ... more A field of sediment undulations has been mapped by means of high resolution multibeam bathymetry and seismic reflection profiles in the Llobregat River prodelta, off the city of Barcelona, Catalonia, Spain. Similar features had previously been recognized in other prodelta environments and interpreted either as downslope sediment deformation or sedimentary structures induced by bottom currents or hyperpycnal flows. Since the study area is undergoing significant offshore development, proper interpretation of such sediment undulations is needed for a correct risk assessment. The occurrence of the sediment undulations is restricted to the prodelta front on slope gradients between 3 and 0.2º. The undulations have developed at the edge and atop an area of gas bearing sediments within the Late-Holocene high-stand mud wedge. An evaluation is made of the characteristics of the sediment undulations in order to determine the most likely process for the origin of these structures. Amongst these characteristics are the continuity of the reflections and lack of diffractions in between different undulations, their size distribution (large to small) both from shallow to deep and with depth in section, the asymmetry (decreasing from proximal to distal), the crest to trough vertical distance on the landward side of the undulations (up to 0.5 m), and the lack of features that could indicate a progressive movement such as growth structures and drag folds. These characteristics indicate that the sediment undulations on the Llobregat River prodelta do not result from sediment deformation, but rather from the interaction of bottom currents generated by hyperpycnal flows from the Llobregat River with regional sea water circulation. Their identification as sediment waves implies that such features do not pose a major hazard for further offshore development.
A previously unknown pattern of multiple bottom-simulating reflections (BSRs) occurs on high-reso... more A previously unknown pattern of multiple bottom-simulating reflections (BSRs) occurs on high-resolution reflection seismic data in the Danube deep-sea fan, associated with acoustic features indicating free gas. Our study provides evidence that this pattern is developed in relation with the architecture of distinct channel-levee systems of the Danube fan. Channel-levee systems hosting multiple BSRs act as relatively sealed gas-bearing systems whose top is situated above the base of the gas hydrate stability zone (BGHSZ). Inside these systems, free gas accumulates below the BGHSZ under a combined lithological, structural and stratigraphical control. The uppermost BSR marks the current equilibrium BGHSZ, for a gas composition of more than 99% methane. Model-derived depths of the BGHSZ for different gas compositions and pressure-temperature conditions show that multiple BSRs would correspond to the BGHSZ either for (1) layers of gas hydrates with high contents of heavy hydrocarbons or hydrogen sulphide, or (2) stable climatic episodes with temperatures between glacial values and the present-day conditions. As the gas hydrate compositions required by hypothesis (1) are in sharp contradiction with the general background of the gas composition in the study area, we suggest that multiple BSRs are most probably relics of former positions of the BGHSZ, corresponding to successive steps of climate warming. In this case, they can provide sea-bottom paleotemperature values for these episodes, and hence they are potential new proxies for deciphering past climate conditions.
The research vessel Simon Stevin, operating mainly in the Belgian part o f the North Sea, has bee... more The research vessel Simon Stevin, operating mainly in the Belgian part o f the North Sea, has been servicing marine scientists fo r almost two years. With a high resolution multibeam, a current profiler, a dynamic positioning system, two laboratories, a large aft A-frame and a data-acquisition system the ship is well designed to support marine science. Moreover the low underwater noise generated by the vessel allows acquisition o f high quality acoustic data.
Standard 3D seismic acquisition methods developed in the petroleum exploration industry can be do... more Standard 3D seismic acquisition methods developed in the petroleum exploration industry can be downscaled to any application in the world of university research or civil engineering. Depending on the areal extent, positioning accuracy and scale of the Wbgical target structures, we argue that the most cost efficient solution entails the substitution of a , h e 3D approach with a pseudo-3D one, with an appropriately dense network of 2D profiles, in combination with computer aided 3D modelling. This method has been used to map e.g. clay tectonic faults in the Ypresian Clay on a hectometric scale. However, we also demonstrate that water-born high resolution 3D seismic acquisition is possible with the novel SEISCAT method, developed at RCMG for mapping a small singular clay diapir under the river Scheldt near Antwerp on a metric scale.
Multidisciplinary characterisation of sedimentary processes in a recent maar lake (Lake Pavin, Fr... more Multidisciplinary characterisation of sedimentary processes in a recent maar lake (Lake Pavin, French Massif Central) and implication for natural hazards
Between the 14th and the 16th century our coast repeatedly suffered from severe storms as a resul... more Between the 14th and the 16th century our coast repeatedly suffered from severe storms as a result of which large stretches of land were lost to the sea. The flooding of the oldest Ostend in 1394 is one of the most famous examples. After the 1394 disaster the city was rebuilt further inland. During the siege of Ostend (1601–1604) the church ruins were still visible before the coast. Nowadays the remnants of the old medieval city lie largely buried below the (intertidal) beach and the seafloor. The main question is to what extent these relics, including harbour walls and housing structures, have been preserved today.
The processing of a small-scale, very high resolution (VHR) shallow marine 3D data volume is desc... more The processing of a small-scale, very high resolution (VHR) shallow marine 3D data volume is described. The data were acquired over a small clay diapir, on the river Schelde, in 1990. Using an array of 12 dual-channel microstreamers towed from a catamaran, a network of 1 m × 1 m bins could be produced over an area of 50 m × 180 m (< 100 m penetration). Positioning was performed with an autotracking laser ranging system, assuring an absolute accuracy of a few decimetres. Preliminary processing steps included tidal correction and multiple removal. An important step concerned the application of 3D prestack Kirchhoff depth migration. Indeed this processing allows easy handling of the exact positions of both source and receivers as the latter were not set out on a conventional regular grid due to navigation difficulties. Because of the restricted data volume and the more-or-less stratified medium, a 1D velocity model could be used. This allowed a considerable simplification of the migration algorithm, based on summation. Traveltimes were calculated only once, using a 2D time grid with 0.1 m intervals. This migration method proved very efficient, greatly improving the seismic image, and involved only limited CPU time on a small computer (Sparc 10 workstation). It clearly demonstrates that advanced seismic processing can form a valuable and economically feasible tool for VHR shallow subsurface 3D seismics, as long as the velocity field is not too complex. This method should therefore no longer be restricted to large computers and hydrocarbon exploration, but should also become a routine for VHR 3D shallow seismic work.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
&amp;amp;lt;p&amp;amp;gt;New high-resolution seismic data (Sparker) and very-high-resolut... more &amp;amp;lt;p&amp;amp;gt;New high-resolution seismic data (Sparker) and very-high-resolution parametric echosounder (PES) data acquired in an area of the southern North Sea (the Flemish Bight) reveal its Quaternary seismic stratigraphy in unprecedented detail. The identified seismo-stratigraphic units and geomorphological features have been examined with the view to better understand the Quaternary evolution of the southern North Sea.&amp;amp;lt;/p&amp;amp;gt;&amp;amp;lt;p&amp;amp;gt;Seven acoustic units were recognised, including Lower Pleistocene deltaic sediments, Eemian to lower Weichselian shallow marine to coastal (lagoonal) clay-silt-sands, and Holocene coastal peat layers overlain by intertidal and marine sediments. Four erosional events were identified, two of which can be traced as regionally occurring surfaces, and two occurring as localised incisions. Mapping of geomorphological features revealed potential Elsterian moraines in the UK sector, an Elsterian ice-pushed ridge in the Dutch sector and possible permafrost-related structures (probably dating to MIS3).&amp;amp;amp;#160; Seven newly dated peat samples, acquired near a tidal sand ridge known as the Brown Bank from depths between 31 m and 34 m below sea level and dating to between 9.5 and 10.9 cal ka BP, indicate that this area was terrestrial during the early Holocene.&amp;amp;lt;/p&amp;amp;gt;&amp;amp;lt;p&amp;amp;gt;The results form the basis to further improve the regional Quaternary stratigraphic framework of the area, to better understand the region&amp;amp;amp;#8217;s (de)glacial history, to enhance sea-level reconstructions and to examine the area&amp;amp;amp;#8217;s geographical importance for human occupation during Prehistory.&amp;amp;lt;/p&amp;amp;gt;
A field of sediment undulations has been mapped by means of high resolution multibeam bathymetry ... more A field of sediment undulations has been mapped by means of high resolution multibeam bathymetry and seismic reflection profiles in the Llobregat River prodelta, off the city of Barcelona, Catalonia, Spain. Similar features had previously been recognized in other prodelta environments and interpreted either as downslope sediment deformation or sedimentary structures induced by bottom currents or hyperpycnal flows. Since the study area is undergoing significant offshore development, proper interpretation of such sediment undulations is needed for a correct risk assessment. The occurrence of the sediment undulations is restricted to the prodelta front on slope gradients between 3 and 0.2º. The undulations have developed at the edge and atop an area of gas bearing sediments within the Late-Holocene high-stand mud wedge. An evaluation is made of the characteristics of the sediment undulations in order to determine the most likely process for the origin of these structures. Amongst these characteristics are the continuity of the reflections and lack of diffractions in between different undulations, their size distribution (large to small) both from shallow to deep and with depth in section, the asymmetry (decreasing from proximal to distal), the crest to trough vertical distance on the landward side of the undulations (up to 0.5 m), and the lack of features that could indicate a progressive movement such as growth structures and drag folds. These characteristics indicate that the sediment undulations on the Llobregat River prodelta do not result from sediment deformation, but rather from the interaction of bottom currents generated by hyperpycnal flows from the Llobregat River with regional sea water circulation. Their identification as sediment waves implies that such features do not pose a major hazard for further offshore development.
A previously unknown pattern of multiple bottom-simulating reflections (BSRs) occurs on high-reso... more A previously unknown pattern of multiple bottom-simulating reflections (BSRs) occurs on high-resolution reflection seismic data in the Danube deep-sea fan, associated with acoustic features indicating free gas. Our study provides evidence that this pattern is developed in relation with the architecture of distinct channel-levee systems of the Danube fan. Channel-levee systems hosting multiple BSRs act as relatively sealed gas-bearing systems whose top is situated above the base of the gas hydrate stability zone (BGHSZ). Inside these systems, free gas accumulates below the BGHSZ under a combined lithological, structural and stratigraphical control. The uppermost BSR marks the current equilibrium BGHSZ, for a gas composition of more than 99% methane. Model-derived depths of the BGHSZ for different gas compositions and pressure-temperature conditions show that multiple BSRs would correspond to the BGHSZ either for (1) layers of gas hydrates with high contents of heavy hydrocarbons or hydrogen sulphide, or (2) stable climatic episodes with temperatures between glacial values and the present-day conditions. As the gas hydrate compositions required by hypothesis (1) are in sharp contradiction with the general background of the gas composition in the study area, we suggest that multiple BSRs are most probably relics of former positions of the BGHSZ, corresponding to successive steps of climate warming. In this case, they can provide sea-bottom paleotemperature values for these episodes, and hence they are potential new proxies for deciphering past climate conditions.
The research vessel Simon Stevin, operating mainly in the Belgian part o f the North Sea, has bee... more The research vessel Simon Stevin, operating mainly in the Belgian part o f the North Sea, has been servicing marine scientists fo r almost two years. With a high resolution multibeam, a current profiler, a dynamic positioning system, two laboratories, a large aft A-frame and a data-acquisition system the ship is well designed to support marine science. Moreover the low underwater noise generated by the vessel allows acquisition o f high quality acoustic data.
Standard 3D seismic acquisition methods developed in the petroleum exploration industry can be do... more Standard 3D seismic acquisition methods developed in the petroleum exploration industry can be downscaled to any application in the world of university research or civil engineering. Depending on the areal extent, positioning accuracy and scale of the Wbgical target structures, we argue that the most cost efficient solution entails the substitution of a , h e 3D approach with a pseudo-3D one, with an appropriately dense network of 2D profiles, in combination with computer aided 3D modelling. This method has been used to map e.g. clay tectonic faults in the Ypresian Clay on a hectometric scale. However, we also demonstrate that water-born high resolution 3D seismic acquisition is possible with the novel SEISCAT method, developed at RCMG for mapping a small singular clay diapir under the river Scheldt near Antwerp on a metric scale.
Multidisciplinary characterisation of sedimentary processes in a recent maar lake (Lake Pavin, Fr... more Multidisciplinary characterisation of sedimentary processes in a recent maar lake (Lake Pavin, French Massif Central) and implication for natural hazards
Between the 14th and the 16th century our coast repeatedly suffered from severe storms as a resul... more Between the 14th and the 16th century our coast repeatedly suffered from severe storms as a result of which large stretches of land were lost to the sea. The flooding of the oldest Ostend in 1394 is one of the most famous examples. After the 1394 disaster the city was rebuilt further inland. During the siege of Ostend (1601–1604) the church ruins were still visible before the coast. Nowadays the remnants of the old medieval city lie largely buried below the (intertidal) beach and the seafloor. The main question is to what extent these relics, including harbour walls and housing structures, have been preserved today.
The processing of a small-scale, very high resolution (VHR) shallow marine 3D data volume is desc... more The processing of a small-scale, very high resolution (VHR) shallow marine 3D data volume is described. The data were acquired over a small clay diapir, on the river Schelde, in 1990. Using an array of 12 dual-channel microstreamers towed from a catamaran, a network of 1 m × 1 m bins could be produced over an area of 50 m × 180 m (< 100 m penetration). Positioning was performed with an autotracking laser ranging system, assuring an absolute accuracy of a few decimetres. Preliminary processing steps included tidal correction and multiple removal. An important step concerned the application of 3D prestack Kirchhoff depth migration. Indeed this processing allows easy handling of the exact positions of both source and receivers as the latter were not set out on a conventional regular grid due to navigation difficulties. Because of the restricted data volume and the more-or-less stratified medium, a 1D velocity model could be used. This allowed a considerable simplification of the migration algorithm, based on summation. Traveltimes were calculated only once, using a 2D time grid with 0.1 m intervals. This migration method proved very efficient, greatly improving the seismic image, and involved only limited CPU time on a small computer (Sparc 10 workstation). It clearly demonstrates that advanced seismic processing can form a valuable and economically feasible tool for VHR shallow subsurface 3D seismics, as long as the velocity field is not too complex. This method should therefore no longer be restricted to large computers and hydrocarbon exploration, but should also become a routine for VHR 3D shallow seismic work.
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