FIG. 14.

Smooth HFO filament formation schematic in remobilized iron deposits. (a) Mineral grains are transported and lithified. (b) Microbial filaments colonize the substrate to form spatially restricted microbial mats. (c) With no quartz boxwork to mediate water flow and mineral precipitation, smooth HFO filaments are continually coated with HFO precipitate during wet periods associated with precipitation events. (d) HFO filaments are coated to increase in diameter forming generally colloform mineral-coating structures. (e) The HFO continues to precipitate, filling in void space around the HFO filaments. Under rapid HFO precipitation conditions and without a filamentous template, HFO precipitates a laminated texture. (Color graphics available at www.liebertonline.com/ast)