相对海平面变化与南海珠江深水扇系统的响应

根据微体古生物分析建立起来的珠江口盆地第三系相对海平面曲线,具有与全球海平面变化相一致的三级旋回和不一致的二级旋回。三级海平面升降导致了各沉积层序体系域在宽广陆架和陆坡之间的迁移,研究证实,位于南中国海北缘、珠江口外的陆坡深水区广泛发育第三系多层序叠置的南海珠江深水扇系统。区域性构造作用使得珠江口盆地二级海平面变化与全球海平面变化具有不一致性,并形成与全球海退趋势相反的海侵型海平面曲线。受相对海平面变化的控制,现今处于陆坡深水区的白云凹陷自32Ma南海扩张以来经历了三台阶式的海侵事件,形成了台阶式退积层序组合,具有下粗上细的沉积序列;造就了23.8Ma以前的浅水三角洲-滨岸砂泥岩沉积组合;23.8~10.5Ma的深水扇砂泥岩为主的沉积组合;以及10.5Ma以来主要为远端的细粒沉积为主。

Response between relative sea-level change and the Pearl River deep-water fan system in the South China Sea

A Tertiary relative sea-level change curve built from micropaleontological analysis demonstrates that the Pearl River Mouth Basin (PRMB) in the northern margin of the South China Sea developed the third order cycle which is the same as that of global eustasy, however, the second order cycle is different. The third order eustasy led to a system tract shift of each sequence between the broad shelf and slope. Sequence stratigraphy shows that the Tertiary multi-sequences overlapped the Pearl River deep-water fan system which developed broadly in the slope deep-water area outside of the Pearl River Mouth. Regional tectonism resulted in the differences between PRMB second order sea-level change and the change of global eustasy. The transgressive sea-level curve was developed here, which is opposite to the global regressive eustatic cycle. Baiyun Sag, now sitting on the slope deep-water area went through three step transgressive events controlled by the relative sea-level change, since the expansion of the South China Sea at 32 Ma B.P.. Stepping retrogradation sequence sets were developed and display upward-fining depositional sequence. Consequently, it shows the characteristics of shallow delta-littoral sand-shale depositional assemblage before 23.8 Ma B.P., of a deep-water fan sand-shale depositional assemblage during 23.8～10.5 Ma B.P., and of distal fining deposition since 10.5 Ma B.P..