(Table 1) Organic geochemistry of ODP Site 128-799A

Pyrolysis techniques were used to characterize the organic matter contained within the penetrated section and to assess the presence of heavy hydrocarbon shows. The Rock-Eval data indicate a change in organic hydrogen enrichment within the middle Miocene sequence. It appears that the level of organic enrichment may be controlled by sedimentation rate, while the organic hydrogen enrichment, as shown in the hydrogen index, may reflect differences in preservation potential. Higher sedimentation rates would result in higher organic carbon contents. Higher hydrogen index values would reflect higher degrees of organic preservation resulting from more restricted circulation.The entire penetrated section is thermally immature and has not entered into the main phase of thermal hydrocarbon generation. Neither the Rock-Eval nor the pyrolysis-gas chromatographic data indicate the presence of thermally mature, migrated, heavy hydrocarbons. This absence of mature, heavy hydrocarbons includes Cores 128-799B-65R and 128-799B-66R, which exhibited cut fluorescence onboard the ship. Therefore, the fluorescence is considered to have resulted from indigenous, thermally immature bitumens.