南海神狐海域水合物钻探区钙质超微化石生物地层与沉积速率

2007年我国首次在南海北部陆坡神狐海域实施了天然气水合物钻探, 并钻取水合物实物样品.为了解钻区地层、水合物产出带(the zone of gas hydrate occurrence)或水合物储层的地层时代以及沉积速率特征, 对其中4口钻孔(SH1B、SH2B、SH5C和SH7B)岩心沉积物进行钙质超微化石年代地层学和沉积速率变化的研究.本次工作识别出17个新近纪钙质超微化石事件, 确定了神狐钻探所钻达最老地层为新近系上中新统; 水合物产出带的地层为上中新统-上新统.这4个钻井地层沉积速率的变化特征因站位和时期而异.中新世以来各地质时期沉积速率差异较大, 全新世最高(20~34.16 cm/ka之间), 其次为更新世和晚中新世(3.14~5.74 cm/ka), 上新世最低(1.88~3.27 cm/ka).此外, 水合物产出带地层的沉积速率在各钻孔也有差异, SH2B孔为4.18 cm/ka, SH7B孔为1.88 m/ka.表明南海水合物产出层位沉积速率差异较大, 沉积速率与水合物成藏的关系可能比前期的认识更为复杂. 

Late Miocene-Pleistocene Calcareous Nannofossil Biostratigraphy of Shenhu Gas Hydrate Drilling Area in the South China Sea and Variations in Sedimentation Rates

The first Chinese gas hydrate drilling program was carried out on the Shenhu area in 2007 and obtained gas hydrate samples. In order to understand the strata, age of the zone of gas hydrate occurrence and features of sedimentation rates, Late Miocene to Pleistocene calcareous nanofossil biostratigraphy in 4 holes (SH1B, SH2B, SH5C and SH7B) from the Shenhu gas hydrate drilling area of the northern South China Sea have been studied. A total of 17 Late Miocene to Pleistocene nanofossil events are recognized. The oldest sediments recovered are in an age of late Miocene, younger than 7.362 Ma, and the age assigned for gas hydrate occurrence zone is late Miocene in Hole SH2B and late Miocene to early Pliocene in Hole SH7B. Sedimentation rates varied with holes and times, increasing from Pliocene, and reaching the highest values in Holocene, for example, 1.88-3.27 cm/ka during Pliocene and 20-34.16 cm/ka in Holocene, respectively. Sedimentation rates of 1.88 cm/ka to 4.18 cm/ka were estimated for sediment sequences in gas hydrate occurrence zone. The results suggest that the relationship between sedimentation rates and occurrence of gas hydrates should be more complicated than our earlier knowledge.