GEOCHEMISTRY OF SILICIFIED WOOD AND ASSOCIATED SEDIMENTS, PETRIFIED-FOREST-NATIONAL-PARK, ARIZONA

The sediment mineral and trace-element contents of silicified wood and associated sediments from the Petrified Forest National Park, Arizona, indicate that silica mineralization occurs within the compositional range of most stream and groundwaters. The sandstones surrounding the silicified wood contain up to 15% authigenic montmorillonite which formed from volcanic ash, and shows evidence of coprecipitation with silica in exterior parts of the silicified wood. The distribution of variable-valence elements indicates that the wood was silicified in an anoxic environment such as the bottom muds of a swamp or stagnant pond. The total lanthanide concentrations of authigenic clay minerals suggest an intermediate to slightly acidic pH. There is no evidence of alkaline conditions or exceptionally high silica concentrations (> 140 mg/l) in solution. © 1979.