Carbon and nitrogen composition and isotope ratios of bulk and decarbonated sediments from ODP Leg 207 sites

Organic carbon, total nitrogen, carbonate carbon, and carbonate oxygen isotopic compositions were measured for 95 samples selected from the black shale sequences drilled during Ocean Drilling Program Leg 207 on the Demerara Rise. Most samples have organic d13C values smaller than -27 per mil, with the exception of several samples that have values between -24.9 per mil and -23.9 per mil that may correspond to oceanic anoxic events. Bulk d15N values range between -4.2 per mi and +4.4 per mil and become smaller as organic carbon concentrations increase. Comparison of the d15N values of nondecarbonated samples to their decarbonated analogs reveals no systematic effect of the acid treatment used in the decarbonation.