琼东南盆地断陷期层序地层模式

SEQUENCE STRATIGRAPHIC MODEL IN NEARSHORE FAULT BASIN-CASE STUDY ON THE RIFTING STAGE OF QIONGDONGNAN BASIN

琼东南盆地断陷期指示了从陆相向滨海环境演化的完整序列,因而断陷期层序的形成和演化既受幕式裂陷作用控制,又受区域海平面变化的影响。盆地断陷期代表一个巨层序(或构造层序),由3个层序组和6个层序组成,其中层序组分别对应于断陷期3次构造幕,层序则与全球三级海甲面旋回吻合。层序内部体系域特征与幕式构造作用的演化阶段有关,根据沉积环境差异可以划分为冲积平原型和滨海湖盆型两种层序模式。在裂陷作用阶段,幕式构造作用是断陷盆地内层序形成和演化的主导因素,区域海平面变化仅相对加强或减弱构造作用的影响;而在裂后热沉降作用阶段,随着构造沉降作用减弱,海平面变化影响更显著,其层序样式与陆表海环境的层序相似。

Qingdongnan basin developed a pararic plain environment during rifting period. Therefore, the formationand evolution of all the sequences was not only controlled by the episode riftings but also influenced by the regional sea-level changes. The megasequence formed in riftings period consists of six sequences which are grouped into three sequence sets indicating corresponding three tectonic episodes in rift period. Each sequence corresponds to the third order of global sea-level change. The internal architecture character of the system tracts in each sequence is relevant to the rifting episode location where the sequence developed. The sequence is dominated by lowstand system tract and transgressive system tract, and highstandsystem tract is usally absent or less developed during violent tectonic movement in early rifting episode. But transgressive system tract and highstand system tract are dominant, and lowstand system tract is usallyabsent during slow tectonic movement or reverse tectonics in late rifting stage.