FIG. 11.

μ-Raman spectral mapping of the red boxed areas in Fig. 10c. (a–c) Optical micrograph (a) and Raman maps (b, c) of the disseminated distribution of carbon in the late diagenetic, cross-cutting hydrothermal chert vein in Zone 1 (Fig. 10c). (d–i) Distribution of carbon around the edges of angular volcanic grains (d) in Zone 2 (Fig. 10c). Particles in Zone 2 are fine sand–sized. Note that the carbon (f) colocates with edges of the volcanic particles (now largely replaced by silica) where the presence of (g) muscovite (the metamorphic equivalent of smectite) and (h) anatase pseudomorph the volcanic particles, indicating aqueous alteration. The SEM micrograph in (i) shows a small colony of coccoidal microorganisms colonizing a muscovite-altered volcanic grain. (j–n) Light micrograph and Raman maps of carbon distribution in Zone 3 (Fig. 10c). This area is characterized by finer-grained and poorly sorted sediment, consisting mostly of silt to clay-sized particles, as well as a few sand-sized grains. Carbon (l) is finely disseminated throughout this layer although concentrated on the surface of the ghost volcanic particle in the middle of the image. The disseminated distribution of (m) muscovite and (n) anatase here documents the original volcanic nature of the fine-grained dust. Here also the sediment has been thoroughly silicified. (Color graphics available at www.liebertonline.com/ast)