RESULTS

The results of hydrocarbon analyses are shown in Table T1 and Figure F1 with composite core depth. Concentrations of total n-alkanes are comparatively high in depths from 200 to 400 mbsf (Subunit IIA), which is characterized by abundant sand and silt turbidites with carbonate-poor mudstones (Shipboard Scientific Party, 2001). Total n-alkane concentration (C₁₅-C₃₇) ranges from 1.63 to 6.23 µg/g. Variation of total n-alkane concentration corresponds well with the change of carbon preference index (CPI) and terrigenous to aquatic n-alkane ratio (H/L_AL) (Fig. F1). Total hopane concentrations are in the range from 50 to 120 ng/g (Table T1; Fig. F1).

Concentration of total fatty acids (C₁₂-C₃₄), terrigenous to aquatic fatty acids ratio (H/L_FA), and concentration of regular hopanoic acids (C₃₀-C₃₂) are shown in Table T2 and Figure F2. Concentrations of fatty acids range from 0.62 to 4.85 µg/g. Relative abundance of terrigenous fatty acids tends to be significantly high in Subunit IIA, showing high terrigenous organic matter contribution as indicated by terrigenous to aquatic n-alkane ratio (H/L_AL) (Fig. F1). Concentrations of hopanoic acids are also high in Subunit IIA, suggesting a terrestrial origin.

Concentrations of diploptene (Hop-22(29)-ene) and diploptene-related hopenes such as hop-21-ene, hop-17(21)-ene, and neohop-13(18)-ene are shown in Table T3 and Figure F3. Diploptene is present in various types of bacteria and occurs in diverse environments (Rohmer et al., 1984; Ourrisson et al., 1987). Concentrations of diploptene and hop-21-ene decrease quickly with depth. Diploptene and hop-21-ene were not detected in the samples below 200 mbsf. Concentration of hop-17(21)-ene tends to increase from 21.1 to 276.4 ng/g with increasing depth, whereas concentrations of neohop-13(18)-ene are in the range from 7.3 to 20.4 ng/g. Diagenetic transformation of diploptene to form hop-21-ene, hop-17(21)-ene, and neohop-13(18)-ene has been proposed by Brassell et al. (1980).