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Gassy Sediment in the Amazon Submarine Delta
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 3rd International Congress of the Brazilian Geophysical Society, Nov 1993, cp-324-00238
Abstract
Organic matter from plankton bloom, fishes and sewage outflow are common source for generating gaseous sediments. Presence of organic matter combined with high rate of sedimentation are common characteristics of estuaries though creating an appropriate setting for gas generation. The Amazon system at maximum discharge can reach of 354,793 m3/sec (Figueiredo et al. 1993) and sediment transport estimation 1.2 x 10 tons/yr (Mead et al. 1985). Because of the enormous discharge and associated sediment, a submarine delta is being constructed in the Amazon shelf (Figueiredo et al., 1972, Milliman et aI., 1975). Besides sediment Amazon river brings 3.1 x 10 12gC y*ą of organic carbon (Showers and Angle, 1986) and also great nutrients which are mainly used by planktonic community in the continental shelf. Rates of primary production in the shelf using C14 tracer technique measured by De Master et al. (1991) indicate mean values of 5.8 gCm-2d-1 in the high productivity zone. Organic matter incorporated in bottom sediment are reduced by bacteria generating methane gas that may- be trapped or liberated to the water column. Seismic surveys and core collection in the region during Amasseds cruises have indicated presence of gas in several areas as indicated in figure I. This paper presents results of seismic survey during Amasseds cruise III, leg. 2 and coring collection during others Amasseds cruises in the north Brazilian continental shelf. Amasseds is a cooperative, multi-disciplinary research between Brazilian and American universities.