Jurassic-Recent Structure, Stratigraphy, and Basin Modeling of the Rifted-Passive Margin of Southern Morocco

Abstract

The Tarfaya-Dakhla Basin (TDB) is located in the southern part of the Moroccan Atlantic rifted-passive margin. Oblique rifting with its conjugate margin in eastern Canada started at the Late Triassic-Early Jurassic by splitting of the northeast, structural grain inherited from the late Paleozoic, Appalachian-Atlas orogeny. A massive, 14-km-thick, reefal-carbonate platform was formed above the rifted margin during the Early Jurassic and was subsequently buried by the 6-km-thick, Early Cretaceous (Berriasian) Boujdour deltaic complex. Continued high rates of clastic sedimentation resulted in margin steepening and gravitational collapse during the Valanginian, to form a 480-km-long and 68-km-wide passive margin fold belt system. This deformed segment of the passive margin includes an up-dip, extensional listric fault zone that passes downslope into a down-dip, folded zone. This study of the Tarfaya-Dakhla basin includes stratigraphic mapping of 4885-line km of depth-converted industry seismic data that are tied to three DSDP wells in the deepwater part of the study area along with published exploratory wells on the slope and shelf. The results of the study are based on regional isopach and structural maps of Jurassic, Berriasian, Valanginian, Lower, and Upper Cretaceous that range from top oceanic and continental basement to the seafloor. Landward dips in the top basement surface are linked to localized loading by the Jurassic carbonate margin and its overlying Boujdour deltaic complex. Late Cretaceous erosion that removed 1-2 km of clastic, slope sediments is attributed to submarine erosional processes with a similar unconformity observed along other areas of the northwest Africa passive margin. Mapping of the passive margin fold belt revealed the updip extension zone to be 480 km long and 30 km wide and the downdip compressional zone to be 117 km long and 15 km wide. The basal detachment beneath the zones of updip extension and downdip compression is estimated from area depth strain analysis to be at a depth of ± 9900 m. Geochemical data from DSDP 397 and 369 wells, and two pseudo-wells were used to evaluate source rock potential and hydrocarbon prospectivity in the Jurassic to Recent section. Results showed that the Jurassic source rocks are overmature in the study area with hydrocarbon generation beginning in the Upper Jurassic-Lower Cretaceous. The Lower Cretaceous source rocks are immature except for localized areas, and the Upper Cretaceous is immature across the study area.