NEOGENE CONTINENTAL-MARGIN SLOPE PROGRADATION DOMINATED BY MASS TRANSPORT COMPLEXES, OFFSHORE SURINAME

Mass transport complexes are an important component of the deep water slopes in large-scale degradation and aggradation. They can build up and modify substantial geomorphology on the continental slopes and the basin floor. Furthermore, they can even construct continental slope margins. Utilizing 3000km² of 3D seismic data from the Atlantic continental margin of Suriname, the paper aims to describe extraordinarily thick series of mass transport complexes, which build up the continental slope (more than 2500millisecond TWT in thickness) that were deposited during the Plio-Pleistocene, and discuss the forcing factors controlling the deposition of the mass transport complexes.

The Suriname shelf margin is composed of carbonate and siliciclastic sediments. During the late Eocene to the middle Miocene the siliciclastic deposition dominated the shelf margin and created a turbidite depositional succession on the continental slope. After the late Miocene, when Carbonate Platform developed on the shelf, the mass transport complexes developed on the slope during the Plio-Pleistocene.

The sediment caliber on the shelf in the Plio-Pleistocene succession is similar to that of the late Eocene to the middle Miocene siliciclastic succession, as both successions are mainly composed of medium to coarse grained sandstone and mudstone. The slope gradient and the progradation rate in the Pio-Pleistocene succession are 3 to 4 degrees and 13km/Ma, which are average among other progradational continental-margins, not dominated by the mass transport complex. However, the subsidence rate of 400m/Ma and sediment flux of 50m²/year was high. Thus we hypothesize that during the Plio-Pleistocene the high subsidence rate created and maintained steep slopes of around 4 degrees as compared to 2 degrees during the late Eocene to the middle Miocene, and the large amount of sediment supply caused rapid unstable sediment accumulation which promoted sediment failure and created the thick series of mass transport complexes.