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海洋中的天然气水合物主要发育在有机质供应充分、沉积速率快、热流值较高、水深大于 30 0m的大陆斜坡和活动边缘的增生楔发育区 ;沉积物类型主要以泥质砂岩、砂质泥岩和浊积岩为主。似海底反射层 (BSR)和极性反转是识别天然气水合物层的关键标志。冲绳海槽中段西陆坡下缘水深大于 10 0 0m ;沉积物类型主要为粉砂质泥和泥质粉砂 ,在部分层位见浊积层。与东海陆架相比 ,西陆坡下缘的有机质含量、沉积速率的热流值都较高 ,其范围分别为0 .75 %～ 1.2 5 %、10～ 40cm/ka和 70～ 437mw/m2 ;单道地震剖面具有明显的似海底反射层 (BSR)和极性反转特征 ,因此 ,推断冲绳海槽中段西陆坡下缘可能存在天然气水合物层。
The natural gas hydrate in the oceans mainly develops in continental accretion area and active edge of accretion zone with sufficient supply of organic matter, rapid deposition rate, high heat flow value and water depth greater than 300 m. Sediment types mainly include shaly sandstone, sandy mudstone And turbidite-based. Like seafloor reflector (BSR) and polarity reversal are key hallmarks for identifying gas hydrate layers. The water depth at the lower edge of the western slope of the middle Okinawa Trough is more than 100 m. Sediment types are mainly silty mud and muddy silt. Turbidity accumulations are found at some layers. Compared with the East China Sea Shelf, the heat flow values of the organic matter and deposition rate at the lower edge of the western slope are all higher, ranging from 0 .75% to 1.2 5%, 10 to 40 cm / ka and 70 to 437 mw / m2, respectively. The seismic profile has obvious BSR and polarity reversal characteristics. Therefore, it is concluded that there may be gas hydrate layer at the lower edge of the western slope of the middle Okinawa Trough.