Silica phase-transformations during diagenesis within petrified woods found in fluvial deposits from Thailand–Myanmar

Transitions in petrified wood samples from several Thailand–Myanmar sites included opal-A to opal-CT, opal-A to metastable β-crystobalite and reordered opal-CT→quartz. The moganite in the samples indicates a potential volcanic silica source for the wood petrifactions. Silica phase transitions evident under SEM include opal-A→opal-CT, opal-A→cuboid quartz (pseudocubic) and opal-CT→quartz. Certain stages of silica transformation and transition processes seem to overlap. Such overlapping results when lepisphere blades transform to the high crystallinity of prismatic quartz through a solid-state mechanism. The results provide some insights into the petrified wood genesis in the region. Thermal inputs into the silicification process may have pre-dated final burial of woods in flood deposits.