古气候事件对刚果扇浊积水道发育的控制作用

刚果扇是渐新世以来快速堆积的巨型深水扇体，浊积水道广泛发育，油气成藏条件优越。精细标定水道集中发育的年龄、期次及其与同期地质事件之间的关联，对认识水道发育的主控因素和分布规律具有重要意义。基于测井、地震和古生物资料的综合分析，将盆地北部渐新统—中新统划分为2个二级层序、8个三级层序；通过微体古生物带和海平面变化旋回精细确定了各层序界面的年龄；进而在层序格架内明确了刚果扇北部浊积水道的发育期次和演化规律，认为刚果扇在盆地北部可划分为3个演化期次，即渐新世晚期快速填充期、中新世早—中期稳定沉积期和中新世晚期大规模水道发育期。实验研究发现，盆地中新统孢粉化石由早到晚出现水藓孢属-栎粉属、光面球藻属-盘星藻属-单束松粉属、拟桫椤孢属-凸瘤水龙骨单缝孢属、粗肋孢属-水龙骨单缝孢属-拟桦粉属4种组合类型，表明盆地中新世气候变化频繁，且大规模水道发育期与降温事件及海平面快速下降期高度吻合。此外，3次大规模水道发育期与西非海岸3次构造抬升事件关系密切。由此认为，刚果扇浊积水道的发育直接受控于降温事件，而构造隆升是源头性的触发因素。

CLIMATE EVENTS AND THEIR BEARING ON TURBIDITE CHANNELS OF THE CONGO FAN

The Congo Fan is a huge deep water fan with high sedimentation rate since Oligocene, decorated by widely developed turbidite channels, which provided excellent geologic conditions for hydrocarbon to accumulate. To recognize the key controlling factors and distribution patterns of these channels, it is significant to establish the stratigraphic frameworks by dating sediments, dividing evolutionary phases and defining isochronous geological events. Based on a comprehensive analysis of logging, seismic and palaeontological data, two 2nd order and eight 3rd order sequences have been identified. The age of each sequence boundary is dated by biostratigraphic evidence and global sea-level cyclicities. Under the sequence stratigraphic framework, three evolutionary periods of turbidite channels have been recognized: the rapid filling period of Late Oligocene, the stable depositional period of Early-Middle Miocene, and the massive channels developing period of Late Miocene. The three periods are closely related to the three uplifting events widely observed in the West African coastal basins. In addition, palynological assemblages suggest that climate changed very frequently in Miocene. And the massive channels developing period is in response to the cooling events when the sea-level dropped rapidly. Therefore, the development of turbidite channels is mainly controlled by both the tectonic and cooling events in West Africa. They are supplementary to each other and have joint effect on the development of channels.