Quaternary Sedimentary Processes on the Northwestern African Continental Margin--An Integrated Study Using Side-Scan Sonar, High-Resolution Profiling, and Core Data

MASSON, D. G., Q. J. HUGGETT, and P. P. E. WEAVER, Institute of Oceanographic Sciences, Wormley, Surrey, United Kingdom, R. B. KIDD, University College of Wales, Cardiff, Wales, United Kingdom, and J. V. GARDNER, U.S. Geological Survey, Menlo Park, CA

Side-scan sonar data, cores, and high-resolution profiles have been used to produce an integrated model of sedimentation for the continental margin west of the Canary Islands. Long-range side-scan sonar (GLORIA) data and a grid of 3.5-kHz profiles, covering some 200,000 km2 allow a regional appraisal of sedimentation. More detailed studies of selected areas have been undertaken using a new 30 kHz deep-towed side-scan sonar (TOBI) developed by the U.K. Institute of Oceanographic Sciences. Sediment cores have been used both to calibrate acoustic facies identified on sonographs and for detailed stratigraphic studies.

The most recent significant sedimentation event in the area is the Saharan Sediment Slide, which carried material from the upper continental slope off West Africa to the edge of the Madeira Abyssal Plain, a distance of some 1000 km. Our data shows the downslope evolution of the debris flow. Near the Canaries, it is a 20-m-thick deposit "rafting" coherent blocks of more than 1 km diameter; side-scan records show a strong flow-parallel fabric on a scale of tens of meters. On the lower slope, the debris flow thins to a few meters, the flow fabric disappears, and the rafted blocks decrease to meters in diameter.

Side-scan data from the lower slope show that the Saharan Slide buries an older landscape of turbidity current channels, typically 1 km wide and 50 m deep. Evidence from the Madeiran Abyssal Plain indicates a history of large but infrequent turbidity currents, the emplacement of which is related to the effects of sea level changes on the northwest African margin. One turbidite has a similar age to the Saharan Slide, but a generic link between the two has not yet been established.

AAPG Search and Discovery Article #91007© 1991 AAPG International Conference, London, England, September 29-October 2, 1991 (2009)