沉积体系域类型、特征及石油地质意义

Types and characteristics of depositional systems tract and its petroleum geological significance

不同学者对体系域的分类及体系域界面的划分有不同的理解,甚至在体系域的发育和分布上,不同盆地都会得出不同的研究结论。滨线迁移类型决定了特定沉积趋势下地层单元的外形和堆积模式,即体系域类型。文中把体系域划分为常规体系域和非常规体系域两大类,常规体系域指经典层序地层学中定义的常见体系域,即低位体系域、海侵体系域(或湖侵体系域)和高位体系域,这些体系域与基准面(相对海平面或相对湖平面)变化引起的滨线迁移密切相关。非常规体系域泛指常规体系域以外的与特定沉积环境相关的所有体系域类型,包括冲积扇—河流沉积体系中的高可容空间体系域和低可容空间体系域、缓坡背景下滨浅海的强制海退体系域、大陆架背景下浅海—深海体系的下降期体系域、滨浅海(湖)环境的海退体系域(或湖退体系域)。体系域和基准面关系的可预测性使得层序地层学成为一种寻找盆地内自然资源的极为有效的工具,通过它可以追踪盆地演化不同体系域阶段沉积相的横向变化,帮助认识有经济价值的沉积矿床以及油气储集层、烃源岩和盖层在时间和空间范围内的发育区。这也导致了油气勘探从构造圈闭向复合圈闭和岩性圈闭的转变。

Different scholars have different understanding about the classification of systems tract and division of systems tract surface. Even with regard to the development and distribution of systems tract, they have different conclusions from different basins. The shapes and accumulative models of strata unit,i.e. the types of systems tracts in a given depositional trend depend on types of shoreline shift. Systems tracts are divided into conventional and unconventional ones in this paper. The conventional systems tract is the common systems tract defined in classical sequence stratigraphy, which includes highstand systems tract（HST）, lowstand systems tract（LST）and transgressive systems tract（TST）（lacustrine transgressive systems tract）.They are closely related to shoreline shift which is caused by base-level（relative sea level or relative lake level）changes. The unconventional systems tract includes all other systems tracts in given depositional environments except the conventional systems tract, which are low-and high-accommodation systems tracts（LAST、HAST）in alluvial fan-fluvial depositional system, coastal to shallow marine forced regression systems tract（FRST）in gentle slope depositional environment, shallow to deep marine falling stage systems tract（FSST）in continental shelf depositional environment, and coastal to shallow marine（lacustrine）regressive systems tract（RST）. The predictability of the connection between systems tracts and base-level changes makes sequence stratigraphy as an effective tool in finding natural resources. By means of sequence stratigraphy, we can trace the lateral changes of sedimentary facies at different systems tracts stages of basin evolution and understand the economically valuable sedimentary facies. They are sedimentary deposits and the development districts of reservoirs, source rocks and cap rocks in space and time. This also leads to a conversion from structural trap to combination and lithologic traps in oil and gas exploration.