SUMMARY

Shipboard determinations of total organic carbon by difference between total carbon and carbonate carbon contents and direct measurements of organic carbon in Carbonate-free sediments are 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 ¹³C 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 in sediments from Sites 897 and 898 is at higher concentrations and has been less degraded than that from Sites 899 and 900. Variability in the amounts and types of organic matter at these four locations indicates that (1) their turbidity layers originated from different shallow-water locations that changed through time, even though their sediment lithologies are generally the same, and (2) differences in thicknesses of the turbidity layers at the four sites have contributed to the differing degrees of organic matter preservation.