Study on the system of deposition of organic matter in fore-arc basin and accretionary prism during Paleogene and Neogene

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'2004-2006'In order to make clear the system of deposition of organic matter in fore-arc basin and accretionary prism, we investigated mud-rocks, oils, bacteria and micro-fossiles from Kakegawa area of Sizuoka prefecture, MITI "Sagara" (cuttings) and Shimant zone of Muroto Peninsula. Results are followings : 1. The oils from the northwest Megami anticline contained highly matured aromatic hydrocarbon and lowly matured steranes and hopanes. The oils from the southeast of the anticline steranes and hopanes were highly matured. These results suggest that the oil could be contaminated by another oil with different maturity. 2. Siliceous mudstones for the lower Miocene Matsuba Formation of Mikura Group showed a good potential source rock (TOC=0.9%, S2=c.a.2.8mgHC/gRock, HI=c.a.350mgHC/gC) in the Kakegawa area, but did not show a good potential in MITI "Sagara" from off shore area. 3. Heating rate during Paleogene and Neogene was high in the Kakegawa area and low in the off shore MITI "Sagar … More a" area. Only Paleogene Mikura Group reached to the deep zone which generated condensates. 4. Based on the computer simulation of basin modeling (Basin-Mod), the fore-arc basin in the Sagara oil field generated oils in 29Ma (the Mikura Group) and 15Ma (the Kurami Group), and then generated condensates in 2 Ma (the Mikura Group). 5. The condensate from the Mikura Group could migrated from source bed to the Megami trap with contamicating oils from the Kurami Group during migration. 6. Fossils of calcareous nannoplankton were Sphenolithus heteromorphus, Hericosphaera ampliaperta and the other 11 species suggested that the age of the middle-lower Saigo Group was CN3 zone (18.2-15.6 Ma). 7. Bacteria HD-1 was not found in the Sagara oils suggesting that HD-1 could not generate the main part of the Sagara oils. Toluene-bacteria was found. 8. In the accretionary prism from the Muroto Peninsula showed that organic rich sediments were deposited in Cretaceous ocean in this area, but the sediments contain a lot of terrestrial organic matter. Less