Abstract:

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 SH1B (261.86 m) and the top 23.85-meter core of hole SH5C (175.17 m) in Shenhu gas hydrate drilling area of South China Sea, and then the analytical results were used to delimit the stratigraphic stages of SH1B and SH5C combined with oxygen isotopic stratigraphy of planktonic foraminifera, AMS¹⁴C chronology and biological stratigraphy. The CaCO₃ curve of hole SH1B reveals apparent glacial-interglacial cycles since MIS12 and shows representative ‘Atlantic-type’ cycles which are characterized by low contents in glaciations and high contents in interglaciations, and it possesses stratigraphic significance. Compared to hole SH1B,the CaCO₃ content of hole SH5C 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 SH5C, meanwhile, the δ¹³C values of planktonic foraminifera Gruber in hole SH5C from MIS3 to MIS5 are remarkably depleted with-0.11‰ on average. Distinguished from previous researches, the sedimentation rates of both SH1B 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 CM event 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.

Key words: carbonate minimum, sedimentary hiatus, gas hydrate dissociation, Shenhu gas hydrate drilling area, South China Sea