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. 
56Fe values range between 0.02
± 0.09 and –0.77 ± 0.05 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 (56Fe = 0.74 ± 0.08 and 0.63 ± 0.04), which suggests isotopic partitioning between different mineral components in the sediment.
1Clayton, R.E., Nederbragt, A.J., Malinovsky, D., Andersson, P., and Thurow, J., 2006. Data report: iron isotope geochemistry of mid-Cretaceous organic-rich sediments at Demerara Rise (ODP Leg 207). In Mosher, D.C., Erbacher, J., and Malone, M.J. (Eds.), Proc. ODP, Sci. Results, 207: College Station, TX (Ocean Drilling Program), 1–14. doi:10.2973/odp.proc.sr.207.109.2006
2Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, UK. Correspondence author: a.nederbragt@ucl.ac.uk
4Division of Applied Geology, Luleå University of Science and Technology, S-97187 Luleå, Sweden.
5Laboratory for Isotope Geology, Swedish Museum of Natural History, Box 50007, 10405 Stockholm, Sweden.
Initial receipt: 16 September 2005
Acceptance: 13 July 2006
Web publication:
17 January 2007
Ms 207SR-109
