Field investigations of Middle Miocene fluviatile sediments in an open sand pit at Voervadsbro, Denmark suggest that the transformation processes of wood (lignification and petrifaction) depend on the permeability of the sediment. The petrifying agent in the wood is silica, which must have originated from weathering (and/or soil formation) of silicate minerals as the sediments have seen no history of volcanism. Petrographic investigations (by transmitted light microscopy and SEM) and X-ray diffraction have revealed the resultant of the petrifying agent to be quartz with a remarkably high crystallinity considering its age. The radial structures of the cell walls and the rim around the cell lumina-filling indicate that the first precipitation has been on the cell walls. The zonation of the quartz shows that its precipitation proceeded with interruptions, due to local differences in silica supply, seasonal changes and/or ground-water fluctuations.
- Programme Area 3: Energy Resources