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大陆边缘海底冷泉活动区往往赋存有大量的冷泉碳酸盐岩,冷泉碳酸盐岩的类型和地球化学特征记录了过去海底富甲烷冷泉流体活动的状况.相对于在海水-沉积物界面上生长的化学礁灰岩和碳酸盐结壳等冷泉碳酸盐岩类型,形成于海底以下流体通道周围的烟囱状冷泉碳酸盐岩能更忠实地反映过去海底冷泉流体的信息.本文对采集自南海东沙东北的高镁方解石质烟囱状冷泉碳酸盐岩进行了详细研究,在定量分析碳酸盐物相及其碳氧同位素组成的基础上,结合产出环境特征和年龄对其形成温度进行约束,利用高镁方解石-水体系氧同位素分馏方程计算沉淀流体的氧同位素组成,研究古富甲烷冷泉流体的来源与性质,并探讨其与海底天然气水合物藏之间潜在的成因联系.研究认为,南海东沙东北陆坡烟囱状冷泉碳酸盐岩的碳源自生物成因甲烷,它的形成与海底天然气水合物藏的破坏密切相关.古冷泉流体的δ18O值为(1.9‰±0.3‰)~(0.6‰±0.3‰)V-SMOW(Vienna standard mean ocean water)之间变化,平均1.4‰±0.3‰ V-SMOW.经估算,水合物分解释放出来的流体在冷泉流体中的贡献最高可达45.7%.分析认为,古海平面下降和陆缘海底峡谷的下切,以及海底滑坡等气候与环境变化因素是导致南海东北陆坡水合物藏曾经遭受破坏的主要原因.研究区广泛分布的烟囱状冷泉碳酸盐岩指示水合物分解释放的甲烷在渗漏出海底之前已经有相当一部分被硫酸盐-甲烷转换带附近的微生物捕获和消耗转化,最终以冷泉碳酸盐岩形式实现了永久封存.
A large number of cold spring carbonate rocks are often present in the seabed cold springs in the margins of the continental margin, and the types and geochemical characteristics of the cold spring carbonate rocks record the fluid activities of methane-enriched cold springs in the seafloor compared to those at the seawater-sediment interface Growth of chemical reef limestone and carbonate rock crusts and other types of cold spring carbonate rocks formed below the seafloor chimney-like cold spring carbonate rocks can more faithfully reflect the seabed cold spring fluid information.In this paper, the collection A detailed study has been conducted on high-Mg calcite chimney-like cold spring carbonate rocks in northeastern Dongsha, South China Sea. Based on the quantitative analysis of the carbonate phases and their carbon and oxygen isotopic compositions and their combination with the environmental characteristics of output and their age, , The oxygen isotopic composition of sedimentary fluid was calculated by using the oxygen isotope fractionation equation of high-Mg calcite-water system, and the origin and nature of the fluids and the potential causal relationship with the submarine gas hydrate reservoir were studied. It is believed that the carbon of chimney-like cold-spring carbonate rocks in the northeastern slope of Tungsha in the South China Sea originates from biogenic methane, which forms with the hydration of submarine natural gas The δ18O values of the ancient cold spring fluid are between (1.9 ‰ ± 0.3 ‰) ~ (0.6 ‰ ± 0.3 ‰) V-SMOW (Vienna standard mean ocean water) with an average of 1.4 ‰ ± 0.3 ‰ V- SMOW. It is estimated that the contribution of hydrate dissociation to fluid released by cold spring fluid can reach up to 45.7% .According to the analysis, climate change and environmental change such as the decline of paleo-sea level and submarine canyon, as well as the submarine landslide, The main cause of the damage to the northeastern slope hydrate reservoir was the widespread distribution of chimney-like cold spring carbonate rocks in the study area indicating that the methane released by hydrate dissociation had a significant portion of the methane released near the seafloor Microbial capture and depletion transformation, and eventually permanent storage in the form of cold spring carbonate rock.