IMPACT OF EARLY DIAGENESIS ON SEDIMENTARY PALUDAL ORGANIC-MATTER - EXAMPLE OF TRITRIVAKELY LAKE (MADAGASCAR)

The petrographical and geochemical study of superficial sediments of T ritrivakely bog has enabled the determination of some parameters which account for variations in depositional conditions, especially water d epth, and their effects on the preservation mode of sedimentary deposi ted plant debris. Extensive amorphisation of plant tissues seems to be related to peaty phases, or even to almost total drying of the swamp, while these tissues are well preserved during swampy phases. Moreover , transmission electron microscopy, combined with lignin staining meth ods, revealed the distribution of lignin in plant tissues and enabled its evolution during early diagenesis to be followed. It appears that the morphologically bioresistant element is not the ligneous part of t issue, bur lipidic or polysaccharidic laminae which might be component s of plant cell walls. The information contained in the lignin will th erefore have to be looked for on the molecular level.