gas hydrate - CCOP

Summary of a Study on Miocene to Holocene Sediments from
the Continental Slope of the South China Sea and the Potential
Distribution of Gas Hydrate
Su Xin 1 , Chen Fang 2 , Yu Xinghe 1 , Lu Hongfeng 2 ,
Huang Yongyang 2 , Zhang Hongtao 3
1) School of Marine Geosciences, China University of Geosciences, Beijing 100083;
2) Guangzhou Marine Geological Survey Bureau, Guangzhou 510760;
3)China Geological Survey, Beijing 100011
SUMMARY
A study on Miocene through Holocene sediments throughout the continental slope of the
South China Sea was carried out for evaluating possible sediment regions and layers which
are suitable for hosting gas hydrates. Several main results of this study are presented:
The components for the major lithological units are clay minerals, quartz, feldspar, siliceous
and calcareous microfossils (foraminifers, nannofossils, diatoms and radiolarians ect.).
Authigenic minerals, such as calcite or pyrite, are present in varied amounts throughout these
cores. The minor lithology intervals are about 4~100 cm in thickness, containing abundant
silty sand, sand and biogenic particles.
The sediments from most cores are dominated by clayey silt, interbedded with turbidite layers
of sandy silt, silty sand and sand layers. Turbidite thicknesses vary from 4 to 100 cm.
Abundant turbidites were observed in Cores HD77, HD133 and GC10. These turbidite
sediments were deposited during the last glaciation and at the low sea level, according to data
of ASM 14 C measurements.
Sedimentary evidence in correlation with methane cold seeps was obtained. Authigenic
carbonate concretions and chimneys were observed. Results of X-ray analyses suggested that
these carbonate concretions and chimneys are primarily composed of aragonite, high-Mg
calcite, with lesser dolomite, and siderite. The δ 13 C values of these carbonate samples range
from -56.878‰ to -32.829‰ PDB, suggesting a microbial methane-associated carbon
reservoir.
Sediment areas at the continental slope or the thick sediments near the depositional center,
where the depositional rate is very high; such as turbidites and the front of various kinds of
delta and fans (alluvial fans, low stand fans and fan deltas) are considered to be the favorable
facies for the accumulation of gas hydrate.
Among the Miocene through Holocene sedimentary sequences, the highest sedimentation
rates occurred primarily during the Holocene, and secondly during the Pleistocene. This result
suggests that Pleistocene and Holocene sediments might be the best host for gas hydrates
rather than sediments formed during other periods in the South China Sea. Four areas
(Dongsha area, Xisha Trench, Zhongjiannan area and Nansha area) with high sedimentation
rates were recognized.
New Energy Resources in the CCOP Region - Gas Hydrates and Coalbed Methane 23