Shipboard determinations of total organic carbon by difference between total carbon and carbonate carbon contents were compared to direct measurements of organic carbon in carbonate-free sediments and found to be in generally good agreement. The direct measurement procedure tends to give slightly higher organic carbon concentrations and slightly lower organic C/N ratios. Organic C/N ratios and organic delta13C values indicate that the organic matter contained in Pleistocene to Pliocene turbidites encountered at Sites 897, 898, 899, and 900 is predominantly marine in origin. Depressed C/N ratios and results of Rock-Eval pyrolysis indicate that the marine organic matter in these sequences has been extensively degraded, presumably by microbial reworking. Organic matter at Site 897 has been less degraded than at the other three sites.
Date of initial receipt: 1 December 1994
Date of acceptance: 19 May 1995
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