| Popis: |
The early diagenesis of the superficial sediment of the Lac du Bouchet has been studied by analysis of interstitial water and solid phase. 14C dating of the sediment gives 2500±350 years at a depth of 80 cm below the sediment-water Interface (SWI). Solid phase is made of 19 to 49% clays (Mainly kaolinite), detrital minerals (quartz, feldspars, ferromagnesian), Diatoms frustules and organic matter (ligno-cellulosic debris, pollens, amorphous grey matter). The main part of organic matter (OM) mineralisation takes place in the first 10 to 20 centimetres under the SWI, but continues at a deeper level 3 to 4 times more slowly. Methanogenesis reaction is the dominant degradation process (90 to 93% in the upper section of the mud, up to 97% below), followed by sulphate reduction (4% in spring and 7% in autumn, only in the top section) and iron reduction (3 to 2%). A formula is proposed for OM undergoing oxidation: (CH2O)106(NH3)13.6(H3PO4)0.84. |
