末次冰期以来珠江口盆地深水区天然气水合物稳定带演化

珠江口盆地深水区具备优良的天然气水合物成藏条件,是南海重要的天然气水合物资源勘探区。利用CSMHYD软件模拟预测了天然气水合物相平衡条件下,现今珠江口盆地的天然气水合物稳定带厚度分布和末次冰期以来水合物稳定带厚度的演化特征,同时讨论了晚更新世冰期以来海平面、底水温度对该区天然气水合物稳定带变化的影响,以及水合物分解对环境的影响。结果表明：（1）水深超过600 m的海域具备形成天然气水合物的温压条件;水合物稳定带平均厚度245 m,其中南部稳定带的最大厚度超过330 m,是有利的水合物勘探区;（2）中层水团温度上升很可能是新仙女木末期珠江口盆地深水区天然气水合物分解的主要诱发因素;（3）B/A暖期到YD冷期结束时水合物稳定带面积减少约0.65×10⁴ km²,分解释放的甲烷量约0.38×10¹³ m³,折算成总碳量约为1.9 Gt。

Evolution of Gas Hydrate Stability Zone in Deep Water Area of Pearl River Mouth Basin since the Last Glacial Period

The deep water area of the Pearl River Mouth Basin possesses excellent gas hydrate forming conditions and is a favorable exploration prospect area for gas hydrate resources. In this paper, the Sloan’s CSMHYD program was used to calculate the current thickness of the gas hydrate stability zone (GHSZ), and simulate the evolution process of GHSZ thickness since the last glacial period in the Pearl River Mouth Basin. The effects of the changes in the bottom water temperature and the sea level on GHSZ, as well as the effects of methane release from hydrate decomposition on the environment were discussed. The results indicated that: (1) the modeled minimum water depth at which methane gas hydrates crystallize at present in the Pearl River Mouth Basin was about 600 m. The average thickness of the GHSZ was 245 m, and the maximum thickness of the GHSZ was more than 330 m, which was a favorable target hydrate exploration area. (2) The temperature rise of the Intermediate Water might be the main triggering factor for gas hydrate decomposition in the deep water area of the Pearl River Mouth Basin at the Late Younger Dryas. (3) The area of GHSZ decreased by about 0.65×10⁴ km² from Bølling-Allerød to Younger Dryas period, the amount of methane released by decomposition was about 0.38×10¹³ m³, which was equivalent to the total carbon content of 1.9 Gt.