Iodine concentration and radioisotopic composition ( 129 I/I) were measured in the pore waters from the gas hydrate occurrence in the forearc basin offshore Shimokita Peninsula, north-eastern Japan, to determine the source formation of I and accompanying hydrocarbons. Iodine concentrations correlate well with the alkalinity and SO4 patterns, reflecting degradation stages of I-rich buried organic matter, rapidly increasing in the sulfate reduction interval, and becoming constant below 250 meters below the seafloor with an upwelling flux of 1.5 ¥ 10 -11 mmol cm -2 year -400 ¥ 10 -15 in deep pore waters suggest ages for iodine and hydrocarbon sources as old as 40 Ma. These ages correlate well with the coaly source formations of the Eocene age thought to be responsible for the conventional natural gas deposits underlying the gas hydrate stability zone. Similar profiles are observed in 129 I/I ratios of pore waters in the gas hydrate stability zone from the forearc basin in the eastern Nankai Trough, offshore central Japan, where pore waters are enriched in I and reach ages as old as~50 Ma through the sediment column. At the outer ridge site along the trough, on the other hand, relatively younger I are more frequently delivered probably through thrusts/faults associated with subduction. The nature of source formations of I and hydrocarbons in the offshore Shimokita Peninsula has a more terrestrial contribution compared with those in the Nankai Trough, but these formations are also considerably older than the host sediments, suggesting long-term transport of I and hydrocarbons for the accumulation of gas hydrates in both locations.

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In the early 1970 s, oil and gas exploration was started in the west of Shetlands, United Kingdom, which is a part of the Atlantic Margin. One of the main exploration targets in the west of Shetlands is the Paleocene deepwater sandstones, some discoveries of which proceeded to development or production stages. The Laggan field discovered in 1986 is under development together with a neighboring discovery, Tormore field. The Foinaven field has been producing oil since 1997. These Paleocene fields are characterised by seismic attributes including amplitude and AVO anomalies, and understanding of these attributes enables reduced geological risks and estimation of reserves, not only in exploration but also in development and production stages. On the other hand, there are many failures of exploration wells in areas with seismic anomalies. Loizou 2005 examined all the exploration wells in the west of Shetlands drilled until 2005, and concluded that only 9 out of 39 wells, which have targeted Paleocene seismic anomalies, resulted in geological success. To improve the success-to-failure ratio in exploration associated with seismic anomalies, it is important to construct a plausible geological model including trapping mechanism, seal, reser voir, source rock and hydrocarbon migration that is consistent with hydrocarbon accumulations implied by seismic anomalies. The Tornado discovery was a prospect, which targeted the Paleocene deepmarine sandstone associated with a seismic amplitude anomaly. The rst exploration well con rmed a gas column with oil leg. Prior to the drilling, seismic data analysis was carried out together with a CSEM data acquisition. Those geophysical information was integrated with a geological model built on the information from nearby wells and other geological studies to reduce geological risks Pickering et al., 2011. This paper presents successful examples of integrated methods of exploration activities which do not rely only on seismic anomalies.