东太平洋水合物海岭BSR以上沉积物粒度变化与气体水合物分布

文中对国际大洋钻探204航次在太平洋水合物海岭8 个站位BSR深度以上气体水合物稳定带的沉积物进行了粒度分析和对比研究。结果表明,该稳定带内沉积物总体粒径变化特征为:粉砂质量分数在60%~75%之间,为气体水合物稳定带内沉积组分的主体组分。粘土质量分数一般小于35%,砂质量分数小于5%。该结果获得的粒径变化范围,与204 航次中沉积学研究所确定的粘土质粉砂、粉砂质粘土夹含砂质粉砂、含砂质粘土岩性特征一致。各站位沉积粒径变化和代表气体水合物存在的岩心红外照相IR异常低温记录之间的初步对比说明,气体水合物主要富集在沉积组分较粗,相当于粉砂或者砂级质量分数较高的粒度层。统计学的相关性研究结果定量地揭示了各个站位沉积物粒径变粗与气体水合物的存在有不同的相关关系。归纳起来发现,不同构造部位沉积物中气体水合物赋存层段的粒径范围不同。坡后盆地由于当地总体沉积物颗粒细,气体水合物赋存在极细粉砂粒级(8~26μm)的沉积物中。水合物海岭南峰顶部附近站位气体水合物主要赋存在粗粉砂和细砂(50~148μm)之间。

Variation in grain size of sediments above BSR and correlation with the occurrence of gas hydrates on Hydrates Ridge, East Pacific

Grain size of sediments from eight drill holes of Ocean Drilling Program Leg 204 are analyzed to understand the relationship between the variation in grain-size of sediments and the occurrence of gas hydrates on the Hydrate Ridge, the East Pacific.The results suggest that the silt fraction is the dominant component of sediments above BSR, making up about 60%～75% of the sedimentary grains. The second component is clay, with less than 35%; whereas the sand fraction is less than 5%. A number of sandy layers from each drill hole were recognized. These layers can be correlated with layers where gas hydrate samples were recovered or recognized during Leg 204. Results of a statistical analysis of grain-size variation and low temperature values of infrared images (IR images) suggest that grains of coarse silt to fine sand (50～148 μm) can be correlated with sediment layers where gas hydrates were recovered or recognized. It further suggests that the occurrence of gas hydrates on the top of the southern summit is mainly correlated with grains sized between 50 to 148 μm, whereas gas hydrates occur in very fine silt grain (8～26 μm) sediments in the slope basin of the Hydrate Ridge.