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Journal Articles

Diagenesis and distribution of sterenes in Late Miocene to Pliocene marine siliceous rocks from Horonobe (Hokkaido, Japan)

Amo, Miki*; Suzuki, Noriyuki*; Shinoda, Toshio*; Ratnayake, N. P.*; Takahashi, Kazuharu

Organic Geochemistry, 38(7), p.1132 - 1145, 2007/07

 Times Cited Count:13 Percentile:60.83(Geochemistry & Geophysics)

Late Miocene to Pliocene marine siliceous rocks in Horonobe, Hokkaido, Japan are rich in sterenes and steradienes. Diagenetic degradation and transformation of sterenes and steradienes in immature Horonobe marine siliceous rocks of Wakkanai and Koetoi Formations were studied using the borehole core samples from HDB-3 and HDB-4 drilled by Japan Atomic Energy Agency. The paleo-temperatures of marine siliceous rocks were estimated to be in the range from 30 to 60 $$^{circ}$$C considering the silica mineral transformation from Opal-A to Opal-CT during diagenesis and the present day geothermal gradient in Horonobe region. Concentrations of steradienes and sterenes decrease quickly in the temperature range from 45 to 60 $$^{circ}$$C. The significant increase of sterane concentration in the same temperature range shows that a part of steranes is derived from sterenes and steradienes. The sterane/sterene ratios of C$$_{27}$$, C$$_{28}$$, and C$$_{29}$$ compounds change similarly with increasing maturity. The sterane/sterene ratio of Horonobe marine siliceous rocks can be a useful indicator of paleo-temperature. Either sterenes or steranes, the relative abundance of C$$_{27}$$, C$$_{28}$$, and C$$_{29}$$ compounds is kept nearly similar all through the Horonobe boreholes, showing that their relative abundance is still applicable to the characterization of organic matter in immature sediments.

Oral presentation

Pristene, phytene, and sterenes in immature Horonobe diatomaceous sediments as potential indicators of paleo-temperature and depositional environment

Amo, Miki*; Suzuki, Noriyuki*; Shinoda, Toshio*; Ratnayake, N. P.*; Takahashi, Kazuharu

no journal, , 

Diagenetic degradation and transformation of steroid and acyclic isoprenoid hydrocarbons in immature Horonobe diatomaceous mudstones of Wakkanai and Koetoi Formations were studied using the borehole core samples from HDB-3 and HDB-4. Late Miocene to Pliocene marine diatomaceous mudstones in Horonobe, Hokkaido, Japan are rich in steroid hydrocarbon such as sterenes, steradienes and sterane and isoprenoid hydrocarbons such as pristenes, phytenes, pristane and phytane. The present study attempts to constrain the diagenetic pathway of these compounds in a thick sedimentary sequence of immature mudstones. Detailed geochemical analyses for Horonobe diatomaceous mudstones revealed the timing of transformation and the compositional change of isoprenoid hydrocarbons during diagenesis. Potential maturity parameters based on ratios of sterenes to steranes, pristene to pristane, and phytene to phytane are proposed in the present study. Possible potentials of these compounds as indicators of depositional environment for immature sediments are also investigated in the present study.

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