DOI 10.1016/j.dsr2.2017.03.010 The detailed structure and composition of turbiditic channel-mouth lobes is still largely unknown because they commonly lie at abyssal water depths, are very thin and are therefore beyond the resolution of hull-mound acoustic tools. The morphology, structure and composition of the Congo turbiditic channel-mouth lobe complex (90×40 km; 2525 km2) were investigated with hull-mounted swath bathymetry, air gun seismics, 3.5 kHz sub-bottom profiler, sediment piston cores and also with high-resolution multibeam bathymetry and video acquired with a Remote Operating Vehicle (ROV). The lobe complex lies 760 km off the Congo River mouth in the Angola abyssal plain between 4740 and 5030 m deep. It is active and is fed by turbidity currents that deposit several centimetres of sediment per century. The lobe complex is subdivided into five lobes that have prograded. The lobes are dominantly muddy. Sand represents ca. 13% of the deposits and is restricted to the feeding channel and distributaries. The overall lobe body is composed of thin muddy to silty turbidites. The whole lobe complex is characterized by in situ mass wasting (slumps, debrites). The 1-m-resolution bathymetry shows pervasive slidings and block avalanches on the edges of the feeding channel and the channel mouth indicating that sliding occurs early and continuously in the lobe build-up. Mass wasting is interpreted as a consequence of very-high accumulation rates, over-steepening and erosion along the channels and is therefore an intrinsic process of lobe building. The bifurcation of feeding channels is probably triggered when the gradient in the distributaries at the top of a lobe becomes flat and when turbidity currents find their way on the higher gradient on the lobe side. It may also be triggered by mass wasting on the lobe side. When a new lobe develops, the abandoned lobes continue to collect significant turbiditic deposits from the feeding channel spillover, so that the whole lobe complex remains active. A conceptual lithostratigraphic model is proposed for five morpho-sedimentary environments: lobe rims, lobe body, distributaries, levees, feeding channel. This study shows that high-resolution bathymetry ROV observations are necessary to fully understand the build-up processes of modern channel-mouth lobes.
Congo deep-sea fan, Lobe, Lobe complex, Channel, Channel-Lobe Transition Zone, Angola basin, Slump, Slide, Debrite, Turbidite, ROV, Bathymetry, Seismic, Sediment core
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Author's final draft | 83 | 25 Mo | ||
Fig. S1. SM1 EM12 bathymetric map of the study area (same as Fig. 2) with location of seismic and chirp lines shown on SM3 and SM4. | - | 652 Ko | ||
Fig. S2. SM2 EM12 acoustic backscatter map of the study area (same as Fig. 3) with location of seismic and chirp lines shown on SM3 and SM4. | - | 1 Mo | ||
Fig. S3. SM3 Location of seismic lines on the Congo lobe complex. Yellow: levees; pink: lobe. The dashed line indicates the boundaries of the Congo lobe complex as indicated on Fig. 2, Fig. 3 ; Fig | - | 1 Mo | ||
Fig. S4. SM4 Location of 3.5 kHz lines on the Congo lobe complex. Yellow: levees; pink: lobe. The dashed line indicates the boundaries of the Congo lobe complex as indicated on Fig. 2, Fig. 3 ; Fig | - | 1 Mo | ||
Fig. S5. SM5 Interpretative map of the Congo lobe complex (same as Fig. 5) with location of seismic and chirp lines shown on SM3 and SM4. Feeding channel (black), lobes rim and body (pink),... | - | 1 Mo | ||
Fig. S6. SM6 Seabed photos at site A (cf. Fig. 2). Location of images is shown in Fig. 7. A1 and A3: Stratified muddy turbidites on the northern steep flank of the feeding channel. A2: ... | - | 1 Mo | ||
Fig. S7. SM7 Seabed photos at sites B and E. (cf. Fig. 2). B1: Block with sharp angles; the ROV arm was able to break the block, showing that the sediment is soft. B2: Block showing oblique... | - | 750 Ko | ||
Fig. S8. SM8 Seabed photos at sites F (cf. Fig. 9), along the western levees of the feeding channel. Location of images is shown in Fig. 9. F1 and F3: Buried block with still outcropping sharp... | - | 643 Ko | ||
Fig. S9. SM9 Photos summarizing the lithofacies recovered in the sediment cores at the Congo lobe complex. A: pelagic lithofacies composed of siliceous or carbonate pelagic ooze. B: turbidite ... | - | 1 Mo | ||
Fig. S10. SM10 Photos summarizing the lithofacies recovered in the sediment cores at the Congo lobe complex. F and G: folded or faulted muddy turbidite. H: muddy conglomerate or debrite, J: matrix.. | - | 1 Mo | ||
Publisher's official version | 25 | 3 Mo |
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