DEEP SEISMIC REFLEXION STUDY OF THE ANGOLA MARGIN

In March – April 2000, deep seismic reflection data have been acquired on the west african margin, offshore Angola with the framework of Ifremer - Total Fina Elf Production. The data have been acquired with a new digital 4.5 km long streamer and using a "single bubble" air gun array (Avedik et al., 1993). This cruise was undertaken together with a seismic refraction cruise using OBSs (Ocean Bottom Seismometer). We obtain both an image and a velocity model of the ground structures under the aptian salt layer. Despite the complexity of the margin (5 s TWT of sediment, salt tectonics), we have first results with the combinaison of seismic reflexion and refraction. In the deepest part of the margin, moho’s reflections are observed on all profiles, only beneath the continental shelf and the oceanic domain. Beneath the compressive salt domain, we don’t see any deep continuous reflectors. No tilting blocks has been found on the margin though the maximum thinning seems to be localized beneath the continental slope. MCS data show a subsalt basin 5.5 km thick on the eastern part of the margin. Its base and geographical limits can not be easily defined due to the salt screen. However, the maximum depth of the basin coincides with both maximum depth of the tertiary trough and high velocity zone (7.2 to 7.4 km/s). On this oceanic crust, two areas are delimited : the deepest part characterized by a rough topography, the other one is much smoother. This limit is different from the ocean continent boundary commonly used.

Avedik, F., V. Renard, J-P. Allenou, B. Morvan, "Single bubble" air gun for deep exploration, Geophysics, 58, 366-382, 1993.