Study on sedimentary characteristics and its effects on the formation and decomposition of gas hydrate on continental slope of the northern South China Sea

南海是中国最大的边缘海，覆盖着巨厚的富含有机质的沉积地层，沉积速率高，具备良好的生油生烃能力，具有巨大的资源潜力，是我国的海洋油气资源宝库。天然气水合物作为分布广储量大且对环境友好的资源，具有极高的科学意义和社会意义，南海北部陆坡是我国天然气水合物赋存的最有利海域。近年来南海北部多处天然气水合物钻探采样为我国天然气水合物资源的研究提供了强有力的支撑。本文通过对南海北部陆坡台西南盆地邻近海域地质调查所获沉积物柱状样进行粒度、有机碳、孔隙水、元素矿物等地球化学分析，以研究南海北部陆坡沉积物的分布特征及变化规律，并对比天然气水合物赋存区的沉积环境特征，探讨研究区域沉积物特征对天然气水合物形成、分解的...The South China Sea is the largest marginal sea of China, covered with thick sedimentary strata rich in organic matter, with high deposition rate, it is a good source of hydrocarbon generation ability, which has a great resource potential, it is a precious ocean oil and gas resource of China. As a widely distributed,large reserved and friendly to the environment resources, gas hydrate has importa...学位：理学硕士院系专业：海洋与环境学院_海洋地质学号：2242010115131

A model to calculate the depth of the SMI in sediments of the northern South China Sea

硫酸盐作为电子受体,在有机质早期成岩作用中扮演着十分重要的角色,且较浅的硫酸盐甲烷作用带往往预示着下部有较大的甲烷逸散,或下部暗含天然气水合物藏(或天然气藏)。南海北部作为天然气水合物赋存区,了解赋存区沉积物中硫酸盐浓度变化对我们研究沉积物早期成岩作用和水合物的赋存是有重要帮助的。本文在分析了南海北部陆坡多个站位的沉积物柱状剖面中硫酸盐浓度变化特征之后,提出了南海北部硫酸盐变化模型及SMI界面深度计算方法。根据南海北部硫酸盐变化特征由浅至深可依次划分为有机质氧化驱动硫酸盐还原带、中层过渡带及下部甲烷厌氧氧化还原硫酸盐带。其中部分站位下部甲烷厌氧氧化硫酸盐还原带可分为上、下两层,两者硫酸盐还原速率以及硫酸盐梯度具有明显差异。有机质氧化带与甲烷厌氧氧化还原硫酸盐带在区内各处广泛发育,中层过渡带的存在与否取决于下部甲烷通量,在通量较大的地区中层过渡带消失。表层硫酸盐浓度增大是由有机硫氧化产生硫酸盐引起的。还应该注意的是,在计算SMI界面深度时,应剔除上部有机质氧化消耗硫酸盐的相关数据后进行计算,若下部甲烷厌氧氧化层根据硫酸盐还原速率可以划分成不同的两层,则应该使用下层数据进行拟合,计算SMI界面深度。As an acceptor of electrons,sulfate plays a significant role in eodiagenesis.A shallow methanesulfate interface(SMI)suggests that there may be a mass of gas hydrate beneath it.The South China Sea is a typical gas hydrate occurrence zone.Knowing about the sulfate reduction model in this area will help us understand the eodiagenesis system and the resource potential of gas hydrate.On the basis of analysis of sediments from multiple places on the north continental slope of the South China Sea,we propose a model that uses sulfate concentrations at different levels to calculate the depth of SMI.Sulfate reduction from shallow to deep can be divided into three zones:the organic matter oxidation zone,the transition zone and the anaerobic methane oxidation zone.The anaerobic methane oxidation zone can be divided into two layers based on their vastly different sulfate reduction rates and sulfate gradients.The organic oxidation zone and the anaerobic methane oxidation zone occur throughout the region.Whether or not the central transitional zone exists depends on the methane flux under the methane oxidation zone.An increase in surface sulfate concentration may be caused by organic sulfur oxidation.Before calculating the SMI depth,we should eliminate the relevant data caused by the consumption of organic matter.If the anaerobic methane oxidation layer can be divided into two layers based on the rate of sulfate reduction,we should use the lower layer to determine the depth of the SMI.国家自然科学基金项目(40976035;41276046); 国家重点基础研究发展计划“973”项目子课题(2009CB21951