南海神狐海域MIS12期以来的碳酸盐旋回与水合物分解

Carbonate Cycles and Gas Hydrate Dissociation in Shenhu Area of the South China Sea since MIS12 Stage

对南海神狐海域水合物钻探区SH1B和SH5C等2个钻孔顶部0-39.41 m和0-23.85 m的连续沉积物开展高分辨率碳酸盐旋回研究,结合浮游有孔虫氧同位素地层学、AMS^14C年代学和生物地层学进行地层划分。结果表明：SH1B孔MIS12期以来Ca CO3曲线总体上具有明显的冰期和间冰期旋回,表现为较典型的冰期低、间冰期高的＂大西洋型＂旋回特征,具有良好的地层意义;SH5C孔除MIS1—MIS2期外,MIS3—MIS8期的Ca CO3含量较SH1B孔的要低,冰期和间冰期旋回性较差,MIS3—MIS 4和MIS7期出现明显的低钙事件;同时,SH5C孔MIS3—MIS5期浮游有孔虫G.ruber的δ13C值明显负偏,平均值为-0.11‰;两孔MIS1期的沉积速率是MIS2期的近2倍,与前人的研究结果相反,为MIS2期部分地层缺失所致。SH1B孔受水合物分解影响不大,而SH5C孔受水合物分解影响明显。SH5C孔MIS2期的地层缺失事件和MIS3—MIS4、MIS7期的低钙事件以及MIS3—MIS5期δ^13C值负偏事件主要发生在末次冰期,推测与下伏水合物分解产生的海底滑塌、海水酸化等环境效应有关。

A research on the high-resolution carbonate cycles of sediments has been accomplished,which were continuously derived from the top 39. 41-meter core of hole SH1 B （261 . 86 m）and the top 23. 85-meter core of hole SH5 C （1 75. 1 7 m）in Shenhu gas hydrate drilling area of South China Sea,and then the analytical results were used to delimit the stratigraphic stages of SH1 B and SH5 C combined with oxygen isotopic stratigraphy of planktonic foraminifera,AMS ^14C chronology and biological stratigraphy.The CaCO3 curve of hole SH1 B reveals apparent glacial-interglacial cycles since MIS1 2 and shows representative ‘Atlantic-type’cycles which are char-acterized by low contents in glaciations and high contents in interglaciations,and it possesses stratigraphic sig-nificance.Compared to hole SH1 B,the CaCO3 content of hole SH5 C is lower during MIS3 to MIS8 except MIS1 and MIS2,and the characteristics of glacial-interglacial cycles were not evident with less oscillations.The carbonate minimum （CM）in stages of MIS3 to MIS4 and MIS7 has been recognized in hole SH5 C,meanwhile,the δ^1 3 C values of planktonic foraminifera G. ruber in hole SH5 C from MIS3 to MIS5 are remarkably depleted with-0. 1 1‰ on average.Distinguished from previous researches,the sedimentation rates of both SH1 B and SH5C in MIS1 are almost twice as those in MIS2,thus it is inferred that the sedimentary hiatus probably occurred in portion of the MIS2 formation.Therefore,it can be concluded that the sedimentary hiatus during MIS2,the CMevent and the δ13C negative excursion in hole SH5C are intensely related to the environmental effects,for instance,submarine slump and environmental acidification resulting from gas hydrate dissociation.