ORIGIN OF THE HIATUS OF LAST GLACIAL PERIOD IN COLD SEEP AREA of NORTHEASTERN SOUTH CHINA SEA

With the purpose to search for sedimentary evidence of gas hydrate dissociation, a thorough research on AMS¹⁴C chronology, high-resolution (2 cm sampling interval) carbon and oxygen stable isotope of benthic foraminifera and authigenic carbonate and sediment, as well as sedimentological studies has been accomplished for the core DH-CL10 and DH-CL5 located at the Dongsha cold seep area of the South China Sea. The analytical results show that a sedimentary hiatus occurs at the core depth of ~574 cm, the bottom of the Holocene. The AMS¹⁴C ages of the sediments above and below are 9 850 (9 680 to 9 950) cal.aBP and 27 610 (27 500 to 27 700) cal.aBP, respectively. The δ¹³C values of benthic foraminifera Uvigerina bifurcata vary from -0.37‰ to -1.91‰ with -1.11‰ on average, while the δ¹³C values of bulk samples range from -22.7‰ to -23.0‰, both within the normal range of variation. Although we do not find any geochemical evidence for dissociation and release of gas hydrate in the core DH-CL10, the authigenic carbonate and sediment from the neighbor site DH-CL5 reveal remarkable δ¹³C negative excursions, -55.24‰ and -25.9‰ to -27.9‰ in bulk respectively, suggesting the distinct influence of gas hydrate. The sedimentary hiatus occurred in the sea-level lowstand period of the Last Glacial Maximum, which was consistent with the time when gas hydrate tended to dissociate. Therefore, it can be concluded that the sedimentary hiatus was predominantly related to the sediment slump induced by the dissociation and release of the underlying gas hydrate.