Visions on the hidden face of the earth: perspective of the explorer - objective of the coach

1857: Eduard Suess inaugurates his course in geology in Vienna. In 1878, he undertakes his magnus opus, ‘Das Antlitz der Erde’, ‘The Face of the Earth’. In his earlier, most influential booklet ‘Die Entstehung der Alpen’, he had transported the reader mentally to the top of an Alpine peak. In ‘The Face of the Earth’, Suess invites the reader to imagine himself to be a visitor from space, pushing aside the clouds to contemplate the global scene of continental structures. The ocean realm, however, would still remain veiled by a thick cover of clouds, for decades. In his ‘Bathyfolages’ (1954), Théodore Monod would playfully evoke the cloud screen, in debating the fragmentary sampling through sounding and dredging. 1937: Auguste Piccard designs FNRS 2. After WW II, he resumes work with Cosyns. High time for me to get born. Man’s voyage to the ‘Hidden Face of the Earth’ begins. I would miss the FNRS 2 taxi, but get in time to join Jacques Piccard in diving with ‘Forel’, and to dive with ‘Nautile’ in Fracture Zone Kane, 4650m deep, through the Earth’s crust - into the Earth’s mantle. Jules Verne’s ‘Voyage au Centre de la Terre’ and ‘Vingt mille lieux sous les mers’ in one promotional ticket. 1957: Sputnik! Gagarin follows, remembering Suess. The International Geophysical Year heralds Global Earth Science. Tack: Space and the Antarctic. June ‘59: at the end of my school year I am awarded exciting books: ‘Verovering van de diepzee’, ‘Jagers voor de wetenschap’. Cinema Capitole features a free access documentary, sponsored by BP: rugged Sno-cats cross the Antarctic, shooting seismics with big dynamite blasts. Thrilled, I write to BP, and get in return a letter of two pages narrating exploration seismics. An exploration geophysicist is born, keen to hunt for science, from abyss to pole. Public outreach works. My first paper - ocean drilling - gets published in Iris, our school journal (1962, IF: 0, citations: 0). 1967: Plate Tectonics move out of abyss. All geology books have to be re-written. 1977: Zeebrugge harbour development leads our first steps in marine seismics. 1987: Belgium returns to the Antarctic. Tack: due South. RCMG is born. 1997: Margin Research gets momentum under MAST - discovery of the ‘Belgica’ carbonate mounds in Europe’s Western Frontier. ‘Geosphere-Biosphere Coupling Processes’ (IOC) move to the foreground. ‘Biosphere’… a word coined by Suess. 2007: while the IGY 1957-1958 had unveiled the Antarctic realm, the International Polar Year (IPY) 2007-2008 largely polarizes interest on the Arctic. The melting of the ice cover unveils the last ‘Hidden Face of the Earth’. Science and Industry move in fast. Visionary vessel projects, like ’Aurora Borealis’, break through scepsis. For young - 11 - scientists in Ocean and Polar Science, both an area and an era of exciting training through research opportunities are luring. Tack: due North

Modern carbonate mound systems

Carbonate mounds are prominent features throughout the geological record. In many hydrocarbon provinces, they form prime reservoir structures. But recent investigations have increasingly reported occurrences of large mound clusters at the surface of the seabed, or buried at shallow depth on modern ocean margins, and in particular in basins rich in hydrocarbons. Such exciting new observations along the West-European margin are promising for elucidating the setting and environment of modern carbonate mounds, but at the same time they confront us with puzzling or sometimes contradictory observations in the quest for their genesis.Spectacular cold-water coral communities have colonized such mounds, but convincing arguments for recognizing them as prime builders are still lacking. The geological record provides ample evidence of microbial mediation in mound build-up and stabilisation, but as long as mound drilling is lacking, we have no opportunity to verify the role of such processes and identify the key actors in the earliest stage of onset and development of modern mounds. Some evidence from the past record and from present very-high resolution observations in the shallow seabed suggest an initial control by fluid venting, and fluid migration pathways have been imaged or are tentatively reconstructed by modelling in the concerned basins, but the ultimate link in the shallow subsurface seems still to elude a large part of our efforts. Surface sampling and analyses of both corals and surface sediments have largely failed in giving any conclusive evidence of present-day or recent venting in the considered basins. But on the other hand, applying rigourously the interpretational keys derived from e.g. Porcupine Seabight settings off NW Ireland on brand new prospective settings e.g. on the Moroccan margin have resulted in the discovery of totally new mound settings, in the middle of a field of giant, active mud volcanoes. Keys are apparently working, but we still do not understand how or why. We are no doubt facing complex systems at the interface between the Biosphere and the Geosphere, owing their genesis and spectacular growth to a complex woven of internal and external controls, feedback and process relay processes

Seismic sequence stratigraphy of the Palaeogene offshore of Belgium, southern North Sea

A fine-scale seismic stratigraphic model has been developed for the Palaeogene of the southern North Sea on the basis of interpretation of a dense high-resolution reflection seismic grid, covering the Belgian sector of the continental shelf and the adjacent parts of the Dutch, French and UK sectors. Classical seismic stratigraphic criteria have allowed up to 13 major units to be defined; the geometry and seismic facies characteristics of each have been analysed in detail. The seismic stratigraphy has been compared with the results of four offshore boreholes. 'Events and trends' identified on seismic sections and in outcrops in northern Belgium have been correlated, and offshore seismic facies have been tentatively matched with onshore lithofacies. The geological history of the study area is discussed in terms of eustatic sea level changes and regional tectonic events, and the main characteristics of the offshore Palaeogene deposits are evaluated in a sequence stratigraphic context

Estimating crustal thickness in Belgium using Moho-reflected waves

We present the results of the determination of the Moho depth underneath Belgium using reflected P and S-waves (PmP- and SmS-waves). Previous studies suggest differences of the Moho depth in the different parts of the region. In the lower Rhine Embayment in the northeast, the Moho depth is considered to be shallow (25 km). In the Brabant Massif in the west the crustal thickness is supposed to be larger (up to 38 km). The southeast of Belgium is characterised by the Variscan allochtone, where the Moho depth is around 30 km. In this study, PmP/SmS-waves of ~150 well-located local earthquakes and explosions in the North Sea registered by 37 stations of the permanent seismic network and by mobile stations installed by the Royal Observatory of Belgium were used. More than 750 PmP/SmS-waves were modelled to determine the Moho depth with the following procedure. PmP-arrivals are picked and the locations of the PmP-bounce points are determined and mapped. Over this map a 20 x 20 km grid is placed and for each grid cell an iteration is performed to determine the Moho depth. The thickness of the crust varies between 25 and 36 km and is slightly shallower in the northeast of Belgium (28–30–32 km) than to the southwest (33-34 km). Underneath the Brabant massif however Moho depths of 31 km are found, which is in contradiction with previous results

A high-resolution magnetic record of drift sediments in the neighbourhood of mound provinces in the Porcupine Seabight

The Porcupine Seabight forms a deep embayment in the Atlantic margin, off the south-western coast of Ireland. Very-high resolution seismic profiling, acquired since 1997, revealed the presence of large (carbonate) mounds.In general, the mounds are surrounded by bottom-current related deposits. The changes of seismic characteristics within the uppermost unit are interpreted as phases in a slope parallel drift under changing oceanographic conditions.The magnetic susceptibility records of two giant piston cores (MD01-2450 and MD01-2452), taken respectively in the drift sediments at the SE-flank of a Belgica mound (eastern flank of the basin) and above a Magellan mound (northern flank of the basin), were analysed in order to provide a relative time frame and to investigate possible changes in paleoceanography and paleoclimatology.Core MD01-2450 enabled us to propose a relative dating of over 74 ka, which has been confirmed by comparing the intensity of the NRM (Natural Remanent Magnetization) to ARM (Anhysteretic Remanent Magnetization) ratio with known intensity data. Another very remarkable observation in this core is the presence of iron sulfides between 630 and 1080 cm depth. This local iron sulfide enrichment could be the result of an anaerobic process with sulfate reduction during a period of non-steady-state diagenesis.Core MD01-2452, located in the sediments on top of the buried Magellan mounds, shows more pronounced paleoclimatological changes than the core located at the SE-flank of the Belgica mound. Moreover, typical HL can be recognized very clearly from magnetic susceptibility and P-wave velocity data during the latest glacial. The influence of European HE in the northern part of the basin could be less than on the eastern flank. However, we should be bear in mind that currents seem to be much weaker in the Magellan province than in the Belgica province. These weaker currents can be responsible for better preserved and thus more pronounced paleoclimatological and paleoceanographic changes in the uppermost quaternary sediment layers

Spatial characteristics of a dense province of buried coral banks in the Porcupine Seabight, west of Ireland

Several provinces of carbonate mounds or deep-water coral banks have been discovered in the Porcupine Seabight along the continental margin W of Ireland. The mounds differ considerably in size, spatial density and morphology between the provinces, due to a difference in environmental conditions during their initiation and development.The Magellan mounds, located in the N of the Porcupine Seabight, have been studied by means of industrial 3D seismic data and high-resolution 2D seismic records. All mounds in this province are rooted on one reflection, invoking a single mound start-up event, and are embedded in semi-parallel stratified (drift-) sediments. Most of them are buried already under ca. 20 ms TWT of these sediments, only a limited number of mounds reach the present-day seafloor.The mounds, together with several morphological key reflections, were mapped from the seismic records, and were entered in a GIS. The variability of mound height, width and cross-sectional area was investigated over the area, together with the variability in spatial density of the mound structures. The spatial distribution of mound positions was tested by means of Ripley’s K- function.The spatial density of the Magellan mounds is very high, ca. 1 mound per km2. This value is constant over the area, and it has been estimated that the province contains more than 1000 mounds. The spatial variability in mound sizes and shapes indicates the importance of the interplay between current regime and sedimentation rate/pattern during mound development. In areas with stronger currents and/or less sedimentation stress, the mounds could develop into broader and multiple structures. In locations where the sedimentation stress was higher, they stayed narrow and developed a simple, conical shape. Overall, the mounds have a N/S elongated shape, attributed to N/S directed currents.On small inter-mound distances (<250 m), the mounds appear to be regularly spaced, due to competition for nutrients or space, or due to the fact that mounds, located that closely to each other, may have merged. From inter-mound distances of ca. 700 m onwards, the K-function indicates that there is significant clustering. The interaction between the (N/S-directed) currents and the mounds may have induced turbulence and enhanced currents in the water column, beneficial for mounds relatively close-by