Figure 5
(a) Normalized XANES spectra and corresponding first-derivative spectra for manganese in samples from cores SC4 (at 1.5, 17.0, and 31.5 cm) and SC9 (at 0.0 and 10.2 cm) compared with reference spectra for synthetic manganese(IV) oxide (MnO2, pyrolusite), birnessite (layered Mn(III, IV) oxide) precipitated on quartz (birnessite/SiO2), a natural Mn-phosphate (Li(Fe, Mn)PO4, ferrisicklerite), and Mn(II) sulfide (MnS). (b) Normalized EXAFS and corresponding radial structure functions (uncorrected for phase shift of backscattering atoms) for iron in sediment samples from core SC4 (at 1.4 and 34.5 cm) compared to reference spectra of crystalline pyrite (FeS2(s)) and of iron substituted in reference illite IMt-1 (Clay Minerals Source Repository). Dashed red line is the non-linear least-squares best fit; green line is the fit component corresponding to pyrite; blue line is the fit for an iron-oxygen component that probably represents iron substitution in phyllosilicate or oxide minerals.