Comparison of Near-surface Depositional Settings in Two Large 3D Surveys, Deepwater Tarfaya-Agadir Basin, Offshore Morocco
Investigation of two large 3D seismic surveys to assess potential drilling hazards provided an opportunity to conduct a comparison of the seafloors and near-surface depositional settings (Quaternary through Lower Tertiary section). Both 3D surveys are in the deepwater Tarfaya-Agadir Basin in offshore Morocco, which is a rank frontier exploration area with very sparse well control (mostly updip). In the northern part of the basin, the Rimella survey area is characterized by generally smooth, gently dipping (<2o) seafloor immediately downdip of the shelf edge. This slope is interrupted basinward by the seafloor expression of shallow salt and is dissected by several prominent channel systems in the mid-slope area. The near-surface interval of the Rimella area contains prominent unconformities within a thick Tertiary sequence, where reflection character reveals depositional fairways between salt domes. In the southern part of the basin, the Cap Draa survey area is characterized by a seafloor with a steeper upper slope (3-4o) that changes to a gentler slope (<2o) further basinward. The mid-slope also is influenced by prominent salt domes. Unlike Rimella, the seafloor on the upper slope of the Cap Draa area shows evidence of several episodes of near-surface failure, which produce a prominent array of mass transport complexes (MTCs). A thinner Tertiary sequence in the near-surface interval of the Cap Draa area is also dominated by depositional fairways between salt domes, but also consists of several distinctive intervals of MTCs. The different between the near-surface intervals in these survey areas appears to be a function of sediment supply. The Rimella area’s proximity to the Tertiary sediment source accounts for its thicker section, abundant channels, and prominent unconformities. In contrast, the more distal-sourced Cap Draa area has a thinner Tertiary section, dominance by MTCs, and more conformable sedimentation.
Deep- and Ultra-Deepwater Provinces (SEPM/AAPG)
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