Fe isotope measurements are presented for 10 samples from the Cenomanian-Turonian black shale unit in Hole 1260B at Demerara Rise. The samples bracket the latest Cenomanian ocean anoxic event and were selected to ascertain whether Fe isotopes can be used to gain a better understanding of oceanic redox conditions during the mid-Cretaceous. Three extraction procedures were used to provide Fe extracts that represent the Fe oxide (average FeCBD = 0.07 wt%, N = 8), Fe oxide-sulfide-carbonate (average FeAR = 0.34 wt%, N = 10), and total Fe fractions (average FeHF = 0.81 wt%, N = 10). Fe isotope measurements were conducted on all FeAR extracts as a priority as these were considered to best reflect changes in the redox environment. d56Fe values range between 0.02 per mil ± 0.09 per mil and -0.77 per mil ± 0.05 per mil and appear to correlate negatively with the C/N ratio and oxygen index of total organic carbon. Isotopic measurements of two Fe oxide (FeCBD) extracts show a much heavier isotopic composition (d56Fe = 0.74 per mil ± 0.08 per mil and 0.63 per mil ± 0.04 per mil), which suggests isotopic partitioning between different mineral components in the sediment.

Sediment depth is given in mcd. Note: the amount of sample digested with Na citrate-Na bicarbonate-dithionite method is negligible.

Supplement to: Clayton, Robin E; Nederbragt, Alexandra J; Malinovsky, Dmitry; Andersson, Per S; Thurow, Juergen W (2007): Data report: iron isotope geochemistry of mid-Cretaceous organic-rich sediments at Demerara Rise (ODP Leg 207). In: Mosher, DC; Erbacher, J; Malone, MJ (eds.) Proceedings of the Ocean Drilling Program, Scientific Results, College Station, TX (Ocean Drilling Program), 207, 1-14