从生物脂类化合物到沉积有机质的变化及其对正演烃源岩有机质形成的启示

现代海洋生物有机组分的动态变化过程是利用正演法评价海相优质烃源岩的重要中间环节,可以为估算沉积过程中有机质的损耗提供参考.从化学组成来看,生物体的脂类与原油成分最为接近,而且与其他生化组分相比,脂类的化学性质相对稳定,可以长期保存在地层中,因此脂类是最重要的生油母质.温度、盐度、CO2等环境条件以及生物的种类和生长阶段对生物脂类组成有重要影响,不同环境条件和不同种类的生物对烃源岩有机质的贡献也不同.海水中的有机质在沉积过程中受原始生产力和氧化还原条件的影响.在特定生境中,在一定的生产力范围内,沉积有机质的通量与生产力有正相关关系.超过此范围,沉积有机质通量与生产力关系不大.氧化条件下有机质降解速度快,而还原条件则有利于沉积有机质的保存.生物膜的形成不仅使有机质更容易沉积,而且降低了有机质被降解的机会.地质历史时期生物膜的识别对研究烃源岩有机质的保存具有重要意义.

Chemical Variation from Biolipids to Sedimentary Organic Matter in Modern Oceans and Its Implication to the Geobiological Evaluation of Hydrocarbon Source Rocks

Understanding the dynamics of organic matter in marine water columns greatly favors the geobiologcal evaluation of hydrocarbon source rocks. Biolipids could make great contribution to petroleum due to their comparable chemical components and the slightly refractory characteristics of biolipids during the microbial/thermal degradation. A variety of environmental factors such as temperature, CO2 and salinity could affect the biochemical contents in microorganisms. As a result, microorganisms living in a changing environmental condition might have a different contribution to petroleum formation. Organic carbon flux shows a positive correlation with biological productivity only within a certain range of biomass volumes in a specific biohabitat. Furthermore, organic matter is degraded much more quickly in a water column with oxic conditions. Therefore the anoxic condition, along with the enhanced biological productivity, would be one of the significant factors in contributing the formation of high-quality hydrocarbon source rocks. The formation of biofilms favors the preservation of sedimentary organics by enhancing the deposition rate and decreasing the degradation rate of organics. Identification of biofilms in sedimentary rocks will thus greatly help to understand the depositional processes of organic matter finally preserved in hydrocarbon source rocks.