Large Submarine Slides from a Steep and Narrow Continental Margin (Camamu Basin, NE Brazil)

Peter R. Cobbold¹, Gil Marais-Gilchrist², Dario Chiossi², Fabiana Fonseca Chaves², Fernando Gomes de Souza², and Ragnhild Lilletveit^2
1Geosciences, University of Rennes, Rennes, France
²Global exploration, Statoil do Brasil, Rio de Janeiro, Brazil

We describe a set of unusually large submarine slides from the Camamu Basin, on the continental margin of NE Brazil. Today the margin there is about 50 km wide and the sea floor has a slope of up to 4°. As such, it is prone to gravitational sliding, especially where there are surfaces of ready detachment.

The sedimentary fill of the Camamu Basin is up to 7 km thick. Unconformable upon Precambrian basement are Jurassic sandstones of regional extent. Neocomian strata, up to 3 km thick, accumulated in a continental rift. Shale in the lower part is equivalent to the main source rock of the neighboring Reconcavo Basin. Aptian strata are also continental, but consist mainly of coarse clastic sediment and evaporite. Late Cretaceous strata are thin or absent and the Tertiary succession is only about 1 km thick, above a prominent Eocene unconformity.

The Neocomian and Aptian sequences contain abundant thin-skinned structures, which are extensional near the edge of the continental platform, and compressional toward the toe of slope. The structures have detached on Aptian evaporite, and at the base of Neocomian shale. The structural patterns are characteristic of gravitational sliding. The largest slide is about 5 km thick, and occupies the entire continental slope, for about 100 km along strike. It has a strong degree of mirror symmetry about a vertical plane perpendicular to the margin. The main phase of sliding occurred sometime between the late Aptian and the middle Eocene. The trigger may have been a regional phase of uplift and exhumation, for which there is good evidence on the continental shelf and within the Reconcavo basin. Sliding continued in the Neogene, albeit at a slower rate, and active sliding today is responsible for characteristic scars on the sea floor.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas