ORGANIC TRACERS IN THE SEDIMENTS OF THE WEST GIRONDE MUD PATCH (BAY-OF-BISCAY)

Mud fields located In the inner part of shelves in front of large estu aries are preferential environments for the investigation of the mecha nisms and evolution in time of the supply of such sedimentary bodies. The study of different constituents of the particulate organic matter trapped in the sediments of the West Gironde mud patch contributes to the knowledge of the input origins. This study was carried out with di fferent techniques, including pyrolysis-gas chromatography-mass spectr ometry and high performance liquid chromatography, on samples from a c ore collected in the centre of the mud field. At the bottom of the cor e, the increase of sugars, amino-sugars and some aromatic hydrocarbons may indicate a more marine character of organic components. The same appears to be the case at the top of the core, where, despite a finer sedimentation, biochemical characteristics could show a more pronounce d marine influence than in the middle part. In the middle part of the core, on the other hand, the increase in phenols could result from an increase in lignin-derived. terrestrial inputs. The increase in pyroly sis-derived cyclopentenone may indicate the same terrestrial influence , because this component has its origin in aliphatic polycarboxylic ac ids resulting from sail leaching. The continental character of the sed imentation is also reflected in the increase of the silt-clay fraction s representative of suspended matter originating in the Gironde estuar y, associated with a slight carbonate decrease. The taxonomic signific ance of some phenols is noteworthy: this is especially the case of til e cinnamyls which, in the middle part of the core, emphasize the input of herbaceous debris and of the hydroxybenzyls which, at the bottom, provide evidence of the algal origin of part of the organic material. Thus, by means of pyrolysis results and HPLC phenol analysis, it is po ssible to establish the more or less continental signature of organic components trapped in the ''Ouest-Gironde'' mud patch. This study of o rganic matter, which confirms earlier sedimentological and micropaleon tological data, constitutes a new approach, adapted to the identificat ion of the origin of carbon sources.