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Titel |
Application of medical X-ray computed tomography in the study of cold-water carbonate mounds |
VerfasserIn |
L. De Mol, H. Pirlet, D. Van Rooij, D. Blamart, V. Cnudde, P. Duyck, H. Houbrechts, P. Jacobs, J.-P. Henriet, The Marion Dufresne 169 shipboard party |
Konferenz |
EGU General Assembly 2009
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 11 (2009) |
Datensatznummer |
250026648
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Zusammenfassung |
During the R/V Marion Dufresne 169 ‘MiCROSYSTEMS’ cruise (July 2008) to
the El Arraiche mud volcano field in the Gulf of Cadiz cold-water coral mounds
were targeted. Four on-mound gravity cores, with a total length of 17.5 m, were
obtained for sedimentological and palaeoceanographic analyses in order to unveil the
history of the uppermost meters of these cold-water coral build-ups. In parallel, four
on-mound cores were taken on approximately the same location for microbiological and
biogeochemical analyses. By comparing and correlating both results, more information can
be revealed about the processes acting in the dead coral rubble fields which cover these
mounds.
Computed X-ray tomography (CT) was used for the identification and quantification of
the corals inside the gravity cores. Furthermore, this technique is also useful for the
investigation of sedimentological features, i.e. bioturbation, porosity, laminations... In this
study, cores were scanned using a medical CT scanner on a relative high resolution which
allows the three-dimensional visualization of the corals and sedimentological features. Slices
were taken every 3 mm with an overlap of 1 mm.
Based on these data it was possible to delineate different “CT” facies within the cores. On
one hand there are intervals with a high amount of corals and on the other hand zones with a
very low amount of corals or even no corals at all. In the first case two different facies can be
distinguished: one facies with clearly recognizable, well preserved corals, and the second
facies with crushed coral fragments. In both facies the corals are embedded in a homogenous
matrix. Different facies could also be defined in the intervals containing little or no
corals. For example, a homogenous facies with bioturbations and/or cracks. Also
an important observation is the presence of pyrite which appears in all cores at a
certain depth. Sometimes the pyrite could be observed in bioturbations or inside the
corals.
Besides that also the percentage of corals in these gravity cores were quantified using the
“Morpho+” software, which was developed at the UGCT (Centre for X-ray Tomography,
Ghent University, Belgium). Based on these results, a clear difference can be noticed between
the four mounds. On Conger cliff, corals were only observed in the upper 34 cm while in the
other locations corals can be found throughout the entire core with significant variations in
the amount of corals.
Finally, it was possible to identify different species of cold-water corals, namely Lophelia
pertusa, Madrepora oculata, Desmophyllum cristagalli and Dendrophyllia. In conjunction
with dating and palaeoenvironmental analyses of the corals and the sediment matrix, this can
yield valuable information about the build-up of these cold-water coral mounds in the El
Arraiche mud volcano field and the palaeoenvironmental characteristics at the time the corals
were living. |
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