Caractérisation géochimique des sédiments de surface du golfe de Tunis

Abstract

The general current of the Gulf of Tunis are dependent of the general Mediterranean current. This last divides to the level of the Gulf of Tunis in two branches; a first connects by pass west coasts of the gulf while the second branch crosses the centre of the gulf with a NNW - SSE direction. The passage of this second branch of the general current creates a central zone characterised by a sediment relatively sandier than what surrounds it and controls the distribution of the different metallic elements that have for main origin the Oued Mejerda. The metallic elements here analyzed are the Fe, Zn, Ni, Co, Cu and Pb. Their concentrations vary respectively between 0,5. and 1,6%; 279 and 447 ppm; 39 and 67 ppm; 20 and 34 ppm; 9 and 20 and between 56 and 142 ppm. Also
sediments of surface of the Gulf of Tunis can be considered as little contaminate by the Fe, Mn, Co and Ni and very contaminated by the Pb. This last presents therefore a supplementary source that is the Lake to Tunis. For surface sediment identification, we were equally interested to the distribution of carbonate and COT percentages: Carbonates have shown high percentages in the Small Gulf of Tunis in accord of vegetation who is very dense in this one (she may play as a traps of carbonate); the COT has on the other hand shown very important percentage at the vicinity of Mejerda mouth following a weak decomposition of the organic matter in this zone. The horizontal distribution of these different metallic elements shows three zones to raised high concentration: near mouthpieces of the Oued Mejerda, near theZembra island and to the north of the Small Gulf of Tunis. This distribution shows that the main origin of the totality of these metals is weIl the Oued Mejerda and it reflects the influences of the general current of the gulf that allows the presence of the corridor with a low metallic concentration the long of it path.