Contourites drifts and cold-water coral mounds in the Atlantic Moroccan coral province : origin, evolution and driving factors

Research highlights: - Topographic obstacles have a profound effect on sedimentation patterns. When bottom currents encounter topographic obstacles, they focus and intensify, leading to sediment drifts at the base. Along the tectonic ridges of the Atlantic Moroccan margin, 11° is the threshold for sediment drift formation, while along the mud volcanoes, sediment drifts are present at the southern and/or northern side and are related to the size of the mud volcano. - Internal tides play an important role in the build-up of sediment drifts. Although the sediment drifts along the Atlantic Moroccan margin were mainly driven by glacial water masses, internal tidal currents play an important role in their development. They are driving long-term bottom currents and consequently influence sediment drift deposition along the tectonic ridges and mud volcanoes. Sediment drifts created or influenced by internal tidal currents could be named tidal sediment drifts and a limited extent is proposed. - Coral mound build-up is related to climatic changes and interferes with its immediate surroundings. The Atlantic Moroccan coral province is the largest discovered coral mound province in the world so far and possesses stratigraphic evidence, 10 different initiation horizons in the subsurface, of climate-dependant growth cycles of cold-water corals. Small-scale sediment drifts are created around some of the coral mounds, evidencing deviated and intensified bottom currents. This creates elevated fluxes of food particles and sediment towards the corals, allowing proliferation. - Diagnostic criteria for contourites could be developed based on CT analyses of sediment cores. A workflow for analysing CT-scans, based on the grey values within the radiographs, of sediment cores has been developed which can aid in the discovery of diagnostic criteria to distinguish contourites from turbidites and pelagites. Higher Hounsfield unit values have been linked to more energetic sedimentation environments, related to the strength of the bottom currents at the time of deposition.

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