Atlas Inversion Tectonics, Uplift and Erosion in Atlantic Morocco: Implications for Hydrocarbon Exploration

Gabor C. Tari¹, David Einarsson², and Mahmoud Zizi^3
1Exploration and Production, OMV, Vienna, Austria
²Geophysical Services Incorporated, Houston, TX
³Ziz Geoconsulting, Rabat, Morocco

Neogene to Recent inversion, uplift and erosion of the Atlas system, the result of African-Eurasian plate convergence, is well documented onshore Morocco. However, recently acquired non-proprietary 2D reflection seismic data by GSI in the offshore Essaouira-Safi segment of the Atlantic passive margin of Morocco show the presence of inverted structures of mid-Tertiary age in the deepwater area as well.

These unusual structures are best imaged outboard of the widespread salt basin of Late Triassic/Early Jurassic age, some 200 km to the west from the coastline in water depth of 2,000-4,000 m. The anticlines have a general NW-SE/WNW-ESE trend and their growth, uneffected by erosion frequently observed onshore, can be dated by deepwater DSDP and exploration wells.

The areal extent of the inverted structures coincides with that of the deepwater Tafelney Plateau and show not only anticlines as the result of the overall N-S compressional stress field, but also a broad, neotectonic updoming of the Tafelney Plateau as the offshore continuation of the uplifting Atlas trend. This interpretation is supported by several observations: a) unusual concave-upward bathymetric profile, b) lack of a pronounced shelf-break; c) truncation of Tertiary and Cretaceous rocks at the seafloor; d) isopaching and flattening on several Tertiary seismic horizons and e) analog, well-exposed and eroded E-W trending anticlines in the onshore Essaouira Basin.

The late post-rift inversion, neotectonic arching, uplift and erosion of the Tafelney Plateau, as the offshore continuation of the Atlas, is the result of its syn-rift structural inheritence, as it acted as an accommodation zone during the opening of the Central Atlantic between Morocco and Nova Scotia. The inverted structures represent an untested deepwater play type in the Atlantic region.

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