¡¡¡¡WU Bi-hao1, ZHANG Guang-xue2, ZHU You-hai1, LU Zhen-quan1,
CHEN Bang-yan2
1Institute of Mineral Resources, Chinese Academy of Geological Sciences,
Beijing 100037, China 2Guangzhou Marine Geological Survey, Guangzhou
510075, China
¡¡¡¡In the South China Sea (SCS) and the East China Sea (ECS),
there exist favorable dynamic conditions and abundant hydrocarbon
sources for forming hydrate, According to the long-term observations
of anomalously increased sea-surface temperature scanned by satellite-based
thermal infrared, and the investigations of the gas geochemistry
of bottom water, the authigenic minerals and the fluid composition,
it was concluded that there exist strong degassing and hydrocarbon
fluid activities in the submarine. The main composition of submarine
gas in the southern and northern continental slopes of the SCS
is CH4, mainly biogenic for the southern slope and thermogenic
for the northern slope. The gas of hydrothermal sedimentary region
of the Okinawa Trough, that is a part of the ECS, consists of
86% of CO2 and 14% of CH4, H2, and H2S; CO2 is possibly from magma
fluid and the other components are from decomposition of the land
organic substance. The seismic geophysical studies are still on
the beginning and concentrated in northeastern, northern slopes
of the SCS and the southern Okinawa Trough. BSR marks show up
in many places, but only for some areas of the northeast active
continental margin and of the north passive continental margin
in the SCS, the existence of BSR is rather credible. On the basis
of studies of the hydrocarbon gases and the radioactive thermoluminescence
in the sediments, the SCS and the ECS are divided into 6 geochemical
anomalous regions. By synthetically comparing the geophysical,
geochemical and geothermal data, we have preliminarily confirmed
that: the Bijia¡¯nan (¢ñ), the Taixi¡¯nan-Dongsha (¢ò) anomalous regions
are the most optimistically potential regions for gas hydrate
formation; the Qiongdongnan (¢ó), the Zhongjiannan (¢ô) regions
and the south part of the Okinawa Trough (¢ö) are favorable of
exploring hydrate, oil and gas; the ¢ó and ¢ö regions are more favorable
for hydrate; the ¢ô region is more favorable for traditional oil
and gas. Generally speaking, the investigation work of Nansha
area (¢õ) is far from adequate, but for the Nansha Trough Basin
therein, the geophysical and geochemical anomalies are quite good
for gas hydrate, which are worthy of further study. For the ODP
184-1144 site in the Taixi¡¯nan-Dongsha region the depth of the
gas anomaly and the pore-water chlorinity anomaly are consistent
with the BSR, which predicts the existence of gas hydrate.
|
