Allochthonous Salt Sheets Associated with Cretaceous Rifting in the North African Margin, Examples from North Tunisia and Petroleum Implication

Amara Masrouhi and Olivier Bellier

The eastern part of the Atlas system, in the North African margin, exposes a Triassic salt (200-250 Ma). Salt structures in this area, which range in size from few meters to few hundred km2, are the subject of debate. Two models have been proposed, i.e.: (i) a diapir or dome model, describing a scenario where the salt actively pierced the overburden and tectonically reduced the thickness of the overburden sequences in the limbs of the structure; and (ii) an allochthonous salt model which is based on a scenario where salt flows at the sediment-water interface or below a thin layer of marine sediments forming a sheet of allochthonous salt concordant with the underlying sediments. In Mesozoic times, North Africa (south margin of Tethys Ocean) was an extensional margin showing salt movement. The context of the extensional tectonic regime related with the Cretaceous margin structural setting offers at least two factors allowing salt to extrude onto sea floor and flowing downslope toward deeper marine conditions: (i) tectonic extension, which weakened the overburden units by forming the main normal faults and creating the space for the rise of the salt. This tectonic regime was also responsible for a sub-marine slope, on which salt can fled and spreadow; (ii) differential sedimentation; this structural setting led to differential sedimentation that drove the salt. This scenario is similar to the sheets of allochthonous salt described in other salt provinces, such as the Gulf of Mexico, the Atlantic margin of Morocco, the Brazilian Atlantic margin, the Angolan margin. These salt categories, which characterize some passive continental margins, can be a new way for the Petroleum exploration in North Africa.

AAPG Search and Discovery Article #90161©2013 AAPG European Regional Conference, Barcelona, Spain, 8-10 April 2013