南海北部莺-琼盆地轴向水道沉积特征及成因演化

Sedimentary characteristics and genetic evolution of axial channels in Ying-Qiong basin,northern South China Sea

近年来,南海北部莺-琼盆地深水区发现的众多轴向水道沉积体系已成为该地区油气勘探的重点领域。从岩心及古生物定量分析出发,综合考虑宏观物源体系、古地貌及海平面变化等因素,分析了莺-琼盆地轴向水道沉积充填特征和成因演化,结果表明:轴向水道发育于上中新统黄流组—上新统莺歌海组,以琼东南盆地中央峡谷、莺歌海盆地乐东10-1水道为代表。其中:晚中新世琼东南盆地中央峡谷水道沉积物源主要来自西侧的昆嵩隆起秋盆河流域,受海平面波动上升影响而呈退积型,上新世琼东南盆地中央峡谷水道表现为以海南岛为主物源的多分支水道汇聚型,受海平面波动下降影响而呈进积的水道-海底扇复合体;莺歌海盆地乐东10-1水道主要在晚中新世发育,水道沿中央底辟带与莺东斜坡带之间的负地形展布,与盆地长轴方向一致,纵向上多期叠置。上中新统水道砂体和上新统水道-海底扇复合体与深海泥岩耦合而形成的岩性圈闭群是莺-琼盆地下一步油气勘探的重要领域。

The axial channel systems discovered in the deep water area of Ying-Qiong basin have become impor- tant targets of petroleum exploration recently. From the quantitative paleontology analysis, along with analysis of macroscopic provenance, ancient land{orms and sea level changes, it is found that the axial channel systems were developed in Huangliu Formation of Miocene and Yinggehai Formation of Pliocene, represented by the central canyon in Qiongdongnan basin and the LD 10-1 channel in Yinggehai basin. The sedimentary charac- teristics and evolution of the central canyon are that the sediments from the Qiupen river of Kunsong upli[t de- posited retrogradational type sequence under the influence of sea level fluctuating rises during late Miocene and sediments from the rivers of Hainan Island formed progradational deposit as a channel-fan complex under the influence of sea level fluctuating drops during Pliocene. The LD 10-1 channel was mainly developed during late Miocene, striking along the central diapir belt and eastern Yinggehai slope area which coincides with the axial direction of the basin and vertically superimposed with several phases. In conclusion, it is considered that the lithologic trap groups coupled by channel sandstone of late Miocene and channel-fan complex of Pliocene and a- byssal mudstone are significant prospects of Ying-Qiong basin in the future.