Gas hydrates in Nankai Trough
Gang-Yu Chan
Abstract:
BSRs are distributed widely in the Nankai accretionary prism and associated forearc basins and 90%of them have migration and recycling origins. The widest distribution of the BSRs can be seen at the prism. A correlation between the BSR distributions and prism size shows that the BSRs tend to be more well-developed in a prism of large size. This suggests that a large prism may prouduce much amount of gas-bearing fluids that migrate to the BGHS and form the BSRs (tectonic control). In the forearc basins, the BSRs are identified at topographic highs, anticlines and basin margins (structural control). The upward migration of gas-bearing fluids is carried out through permeable sand layers and as a result, the distribution of BSRs is confined to alternating beds of sand and mud facies (sedimentary control). However, if there is enough time for upward migration and accumulation of gas to the BGHS, the BSRs can be generated widely in low-permeable mud facies(time control). The phenomena of double BSRs could have followed a recent migration of the base of the methane hydrate stability zone from the lower BSR to upper one. As possible causes for the migration this paper discusses sea bottom warming and tectonic uplift. Those results imply that structural, sedimentary tectonic and time controls are primary factors to decide the distribution of BSRs in the Nankai Trough area.
References
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Jean-Paul Foucher et al., (2002) Observation and tentative interpretation of a double BSR on the Nankai slope. Marine Geology 187, 161-175
(Abstract)(Full text)