Experimental taphonomy: silicification of plants in Yellowstone hot-spring environments

During experiments conducted within the vent pool of Medusa Geyser, Norris Geyser Basin, Yellowstone National Park, USA, amorphous opaline silica (opal-A) was deposited on/within plant tissues within 30 days of immersion. Initially, deposition created inter/intra-cellular films which lined cell walls plus intercellular colloid suspensions (sols) of opal-A nano/microspheres. By 330 days, opal-A deposition created a robust external and internal matrix that stabilised tissues against collapse and replicated plant structure. Opal-A films increased to micron-order thicknesses and intracellular sols were created. Systematic variation of opal-A fabric between tissues comprising living/dead cells at the time of deposition indicate that cell function, architecture and shape influence fabric development. Heterogeneity of opal-A fabric within adjacent cells of similar structure/function indicates spatially/temporally fluctuating physicochemical conditions and the presence of intraorganic microenvironments. Early deposition of opal-A films suggests a period of low silica supersaturation and slow opal-A deposition. In contrast, intracellular sols suggest high levels of supersaturation. and rapid opal-A deposition. Shell-like microsphere growth suggests cyclic variation of silica supersaturation, and alternations between rapid and slower opal-A deposition. Microsphere growth to the upper limit of colloidal stability and colloidal crystal structures indicate prolonged sol stability, whilst floc-like microsphere networks indicate localised sol instability.