Figure 2
Shell cross section showing the light/dark (winter/summer) banding and corresponding Mn X-ray fluorescence map of a Diplodon shell from River Manso Inferior (a) and from Lake Steffen (b). The black frames in the photographs show the region of mapping; this region is shown enlarged at the bottom at the same scale as the fluorescence map: higher concentrations of Mn are found in the darker bands of the external nacre in both shells and in the portion of internal nacre mapped in (a). Beam size on the sample was 70 µm × 50 µm; a.u.: arbitrary units. In (b), double arrow = one year; w = winter; s = summer; single arrows = intra-annual variations. |