深水浊积岩有机质富集规律研究进展

Progress in Accumulation of Organic Matter in Deepwater Turbidite

浊流是深水环境中重要的侧向搬运过程之一,大量陆源有机质贡献及快速的搬运沉积等特点,使其相对于正常的深水沉积具有较强的有机质富集能力。不同的浊积系统、浊积系统的不同时期、同一浊积系统的不同沉积单元及浊积岩层之间,有机质富集程度差别很大。低水位型、高水位-持续型和海侵型深水浊积系统的划分,有利于预测高频率、大规模浊积事件发育的地质条件和地质时期以及有机质富集的有利区域和时期。同一浊积系统内,朵叶体和峡谷-天然堤的下游区域可能为更有利的有机质富集区域。浊积岩中细粒层的有机质丰度差异主要取决于粉砂质组分的含量;而砂岩层中的有机质丰度变化较大,主要取决于较大的植物碎屑的贡献。浊积厚度、浊积频率等原因造成的有机质保存的差异则进一步造成了浊积岩中有机质含量的不均衡。这种不同尺度上的有机质富集的差异性分析,对探讨深水浊积岩的生烃潜能及能否作为有效烃源岩具有一定的启示意义。

Turbidite process is one of the most important ways for sediments to be transferred from shallow to deep water. Due to significant terrestrial organic carbon input and high accumulation rate, turbidites have a higher source rock potential than normal deepwater background sediments, but the source rock potential varies in different turbidite systems, different periods, different architectural elements of turbidite systems and turbidites with different grain sizes. The turbidite systems can he classified into highstand and sustained, lowstand-dominant, transgression-dominant in terms of turbidite frequency which can be used to indicate the ideal geological settings and geological periods that the high frequency and large scale turbidites may occur. This classification could also suggest the favorable area and peroid of organic matter accumulation due to the correlation between high frequency and high organic content of turbidites. Comparing to other architectural elements, the lobes and downstream of channel-leeves may be the promising areas for hydrocarbon generation. Moreover, the TOC content of fine-grained rocks in turbidites mainly depends on the contribution of silt-sized material, while the organic matter content of sandstones is affected greatly by the content and hydrodynamical behavior of large plant remains. In addition, the thickness and frequency of turbidites could influence the preservation of organic matter which may make TOC of turbidites much more inhomogeneous. In conclusion, the survey and analysis of organic matter content variation of deepwater turbidite systems in different scales would have implication for assessing source rock potential of deepwater turbidite systems.