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doi:10.2204/iodp.proc.311.207.2009 MethodsElemental analysisA total of 311 squeeze cake samples from Sites U1325–U1329 were used for geochemical analyses. A part of each squeeze cake was dried for 24 h using a freeze dryer at the Korea Institute of Geoscience and Mineral Resources. After drying the bulk sediment samples were ground and homogenized in an agate mortar. TC and TN contents were measured by combustion method using a LECO CHN-900 apparatus with detection limits of 0.001% for TC and 0.01% for TN. TS contents were determined using a LECO SC-132 apparatus with a detection limit of 0.001%. Rock-Eval pyrolysisUsing Rock-Eval pyrolysis, free and adsorbed hydrocarbons released during programmed heating of a sample are recorded as the first peak in a pyrogram (S1) under low temperature. The second peak (S2) in the pyrogram represents hydrocarbons released by kerogen cracking when the sample is heated to 550°C. The temperature at the maximum of the S2 peak is defined as Tmax. CO2, shown as the third peak (S3) in the program, is also generated by kerogen degradation. When these components are normalized to the TOC content, the S2 peak becomes the hydrogen index (HI = S2 x 100/TOC) and S3 becomes the oxygen index (OI = S3 x 100/TOC) (Tissot and Welte, 1984; Peters, 1986). Rock-Eval pyrolysis and TOC were determined by Rock-Eval 6. Isotope analysisPowdered bulk samples were pretreated with 3N HCl to remove carbonate (CaCO3) and inorganic nitrogen for the analysis of organic carbon (δ13Corg) and nitrogen (δ15Norg) isotope ratios. δ13Corg and δ15Norg were measured by a VG Optima stable isotope ratio mass spectrometer at the National Instrumentation Center for Environmental Management. The analytical reproducibility was ±0.1‰ for δ13Corg and ±0.2‰ for for δ15Norg. All carbon and nitrogen isotopes are reported in the usual δ notation relative to Vienna Peedee belemnite (VPDB) for carbon and atmospheric N2 for nitrogen:
where R represents the 13C/12C ratio and 15N/14N ratio of the sample and standard for each isotope. |
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