Figure 4
From: Anthropogenic Anoxic History of the Tuvalu Atoll Recorded as Annual Black Bands in Coral
(a,b) Photographs of the thin slab section of fg01–1 under an optical microscope. Black and brown microgranules (a) and black fibers (b) were observed only within the CBBs. (c) Locations of the X-ray absorption fine structure (XANES) measurement (three crosses: black, reddish-brown and white area). (d) XANES spectra of the black (blue line), reddish-brown (red line) and white (green line) areas. (e,f) Each spectrum was fitted based on linear fitting of the spectra of the white area, pyrite (iron sulfide, (e) and ferrihydrite (iron hydroxide, f). The color gradation of the CBBs indicates that these areas formed due to the redox state of iron.
