FIG. 8.

SEM images showing modes of early diagenetic mineralization of cyanobacterial mats of Niuafo‘ou Island. (A) Silicified section of a cyanobacterial filament embedded in silica matrix. (B) A tangential section through a silicified cyanobacterial filament with a well-preserved silicified cell wall (arrows); the cell wall still contains a lot of organic matter [see energy-dispersive spectroscopy (EDS) spectrum in D]. (C) A tangential section through several filaments mineralized with aragonite; note the destruction of the cell walls with only traces of organics (see EDS in E). (D and E) EDS spectra from cell walls mineralized with silica (D) and aragonite (E). All samples etched with formic and hydrofluoric acids.