The silicification of trees in volcanic ash - An experimental study

The permineralization of trees by pervasive silicification, that is, when forests are buried by volcanic pyroclastics, is simulated with closed-system experiments at 100 °C. The silica source was a ground rhyolitic obsidian glass. The wood samples were coniferous, (Pseudotsuga menziesii, Douglas fir) from the family Pinaceae, and the medium transporting silica from the lithic matrix into the wood tissue was water. Reaction of wood with silica-enriched water shows that wood has a marked affinity to scavenge silica complexes from an aqueous solution and precipitate them on organic surfaces inside the wood cells in the form of opal. Diffusion and advection models are used to estimate how long it may take to permineralize wood logs as massive as those found in petrified forests worldwide. The time scales are on the order of thousands of years.