Geological constraint on the distribution of gas hydrate in the Dongsha continental slope of South China Sea
Geological constraint on the distribution of gas hydrate in the Dongsha continental slope of South China Sea
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作者：
W. Shi
分析了南海东沙陆坡天然气水合物生成的地质构造特征，认为构造和沉积作用在天然气水合物生成中起着重要作用，并利用高分辨率遥感技术，对南海东沙陆坡拟海底反射层（BSR）的产状范围进行了填图。BSR清晰地出现在下斜坡的地震剖面上，BSR主要分布在东沙群岛西南部的陆壳-洋壳过渡带，该区域的背景特征为被动沉积，在东沙群岛的沉积背景中，BSR主要分布在东沙群岛西南部的陆壳-洋壳过渡带，在东沙群岛西南部的陆壳-洋壳过渡带BSR分布在碎屑流和浊流沉积的范围内，这意味着碎屑和浊流的高度足以使大量甲烷垂直运移并形成天然气水合物。BSR的发生是异常超压流体（包括气和水）的结果，由于ODP钻井和活塞岩心揭示的晚新生代沉积速率快，高热流值表明该地区的活动构造和地壳深部流体有利于天然气水合物的生成，另外，斜坡上部沉积层薄，构造剥蚀严重，BSR和天然气水合物发育较少。
The geological and tectonic characteristics for generating gas hydrate in the Dongsha continental slope of the South China Sea were analyzed.It is suggested that tectonics and sedimentation play the important roles in the generation of methane hydrate.The range of occurrence of bottom simulating reflector(BSR) in the Dongsha continental slope of the South China Sea was mapped by means of some high-resolution seismic data.The BSR clearly appeared on the seismic profiles of the lower slope,whereas it was few discovered in the upper slope.The BSR was mainly distributed in the transition zone between the continental crust and oceanic crust southwestward the Dongsha Islands.The background of the region was characterized by the passive continental margin.The BSR were distributed in the range of debris flow and turbidity sedimentation.This means that debris and turbidity are sufficiently high to allow the vertical transport of large volumes of methane and to form the gas hydrate.The occurrence of BSR was resulted from anomaly overpressure fluid including gas and water,because of the rapid sedimentary rate revealed by ODP drilling and piston cores during the Late Cenozoic.The high heat flow values indicate that the active tectonics and deep crust fluid in the region benefit to the generation of gas hydrate.Otherwise,few BSR and gas hydrate occurred in the upper slope,because of the thin sedimentary layers and serious tectonic erosion.