Gas chromatograms of the saturated hydrocarbon fraction show remarkable unimodal distribution of n-alkanes with strong odd–carbon number preference peaking at n-C31. The C29 n-alkane becomes as abundant as n-C31 below the P/E boundary in Cores 208-1263A-35X, 37X, and 38X. In Cores 208-1263A-33H and 34X, near the P/E boundary, abundances of C29, C31, and C33 dominate over other odd carbon numbers as well as even carbon numbers (Fig. F1). The carbon preference index (CPI) for this carbon range varies from 4.9 to 12.5 (Table T1). Three samples far below the P/E boundary in the Paleocene section have higher CPI values (8.3, 9.5, and 12.5), whereas samples near the boundary show CPIs of 4.9–7.6. The magnitude of this odd–carbon number preference in n-alkane homologs of C29–C33 is common in epicuticular leaf waxes of terrestrial higher plants (Eglinton and Hamilton, 1967).
UCMs observed in samples from Core 208-1263A-34X could not be found in deeper horizons to show the extent of obstruction for compound-specific isotope analyses. This indicates that UCMs are not a consequence of thermal maturation. Core 208-1263A-34X was the first core drilled with the extended core barrel system following refusal by the advanced piston corer system. As such, petroleum contamination from the drill bit might be the source of UCMs. UCMs were effectively removed by urea adduction.
CPI values for the samples from Core 208-1263A-34X, which are as high as those from Core 208-1263A-33H, indicate the consistent origin of n-alkanes from terrestrial higher plant waxes, and no substantial contribution of n-alkanes from the petroleum contamination is associated with UCMs.