|
The brazilian continental margin is approximately 7000 km long extending from the latitudes 31° S and 5°N. Its territorial sea, today under discussion at the United Nation, may be as large as 350 NM, resulting in an area of 4.5 million km2, about the half of Brazil's inland territory. Despite this enormous area, very few have been done concerning research on seafloor stability. Today, the main projects are conducted by oil companies for their own specific exploration projects. Academic research on this topic is particularly limited by the elevated costs related to ship's rental. However, there are some important works on seafloor stability developed over the last 20 years along the brazilian coast. These are most qualitative, are concentrated in the southeastern region and do not account for geotechnical evaluations.
At the Campos basin (CB), the most oil productive area in Brazil, several different instability features have being identified. They range from small scale creeps to large slumps, responsible for shaping the seafloor morphology. High-resolution seismic records show some periodicity with recent instability events overlaying older ones. At the southern portion of the CB multibeam bathymetry and high-resolution seismic survey identified a region with several small slumps, which were firstly mapped as a series of canyons. Up north, at the Espirito Santo basin, canyons and gullies have been identified as the result of instability processes associated to a shelf-margin delta during the Pleistocene. Studies conducted at the forests of the Amazon river delta observed presence of several geological factors that contribute to seafloor instability, like biogenic gas and high sedimentation rates. Preliminary studies at four offshore basins concluded that shelf-originating canyons are derived from catastrophic failure on the slope though gravity flows, creep, undercutting and turbidity currents. More recently, during the first cruise of the RETRO project, several kilometers of high-resolution seismic data have been acquired at the northern cost of Brazil. The data showed several mass movements features (recent and ancient), canyons and faults at the continental slope probably associated with neotectonic activity related to transform faults that reach the area.
However, the limited area of investigation in most seafloor instability research projects in Brazil, usually limited to the exploration blocks, restricts the overall understanding of the geological processes involved on these instability events not allowing the determination of the causes for the observed submarine mass movements. A large project for the research of seafloor stability is now being prepared to be submitted to brazilian's science funding agencies.
|
