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Abstract: Raft Tectonics and Sedimentary Supply in the Bas-Congo Tertiary Basin, Offshore Angola (Seismic And Analogical Modelling Approach)

S. Raillard, G. Guerin, T. Mauduit, P. Allix, P. Doucet, H. Lecanu

Raft tectonics over a salt decollement characterizes deformation of the Albian to Recent section in the offshore Angola. During the evolution of the passive margin, two major phases of rafting can be demonstrated:

The phase 1 occurred during Albian to lower Senonian time, developing small-scale tilted rafts.

The phase 2 occurred during Oligocene to Recent time, developing large scale rafts separated by wide, mainly asymmetric, depocentres.

This present study is focused on the phase 2 deformation.

From East to West (e.g. from upslope to downslope), three main sedimentary and tectonic domains can be defined:

- the updip domain shows tertiary progradations overlying with no deformation the previous phase 1 rafts;

- the deltaic domain corresponds to the major tertiary depocentres. In this domain, the extension is very important. The previous phase 1 rafts are ruptured by creation of wide tertiary troughs showing growth sequences along listric faults.

The limit of updip and deltaic domains is characterized by a complex faulted area with listric faults rooted on the salt decollement on overpressured shales.

- the downdip domain shows shortening structures with reverse faults and squeezed diapirs.

Based on seismic data, depth cross-sections and applied analogical modelling (Sand-Silicone, performed by the CNRS, Geosciences, Rennes), the following points are demonstrated:

- influence of delta progradation shifts on the migration of the deformation.

- influence of the volume of sediment supply on the amount of extension.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France