Mössbauer characterisation of sediments from ODP Sites 128-798 and 128-799

57Fe Mössbauer spectra for 26 sediment and 6 carbonate concretion samples from Sites 798 and 799 were recorded at 293 K. Most spectra were deconvolved to two quadrupole doublets without magnetic hyperfine structure. Typical Mössbauer parameters were: isomer shift (I.S.) = 0.34 mm/s and quadrupole splitting (Q.S.) = 0.64 mm/s for the paramagnetic Fe3+ component (partly, pyrite); I.S. = 1.13 mm/s and Q.S. = 2.64 mm/s for the high-spin Fe2+ component derived from iron-bearing aluminosilicates. A few spectra included other high-spin Fe2+ components ascribed to iron-bearing carbonate minerals (e.g., ferroan magnesite), according to the Mössbauer parameters for Fe2+ in the carbonate concretions. We present the distribution of iron among different chemical forms as a function of depth. These data might indicate changes of depositional and diagenetic conditions.

Mössbauer study at DSDP Hole 95-612

57Fe Mössbauer spectra of 15 oceanic sediment samples collected from Site 612 (Deep Sea Drilling Project Leg 95) were recorded. These spectra showed that most of the iron in the sediments was present as high-spin, paramagnetic Fe2+ and Fe3+. The ferrous iron was mainly distributed in terrigenous clays and biogenic carbonates. The variation of the Mössbauer parameters for Fe2+ with sub-bottom depth suggests that the main Fe2+-bearing component changed with geologic time. The amount of iron in each iron-bearing phase as estimated from the corresponding peak areas in the spectra also changed with depth. These variations in the Mössbauer parameters and peak areas are correlated with lithologic changes in the sediment column.