Large submarine slides on a steep and narrow continental margin (Camamu Basin, NE Brazil)
Résumé
We describe a set of thin-skinned structures from the offshore Camamu Basin. The margin is about 40 km wide and the sea floor has a slope of up to 10%. The sedimentary cover is up to 7 km thick. Neocomian strata accumulated during continental rifting. Aptian strata consist mainly of coarse clastic sediment and evaporite. Late Cretaceous strata are thin or absent and the Tertiary succession is about 1 km thick, above a prominent Eocene unconformity. The Neocomian and Aptian sequences contain abundant thin-skinned structures, which are extensional near the continental shelf and compressional toward the toe of the slope. The structures have detached on Aptian evaporite and on the base of Neocomian shale. One giant slide is about 5 km thick and 60 km wide. It displays mirror symmetry about a vertical plane perpendicular to the margin, as occurs in physical models. The main phase of sliding occurred between the Campanian and the middle Eocene. The trigger may have been a regional phase of uplift and exhumation, for which there is independent evidence on the shelf and inland.