珠江口盆地白云凹陷13.8 Ma前后深水扇差异沉积过程及主控因素

Differential deposition and controlling factors of deep-water fan around 13.8 Ma in the Baiyun Sag,Pearl River Mouth Basin

珠江口盆地白云深水区是南海北部油气勘探重要的前景地区,但是目前对白云深水扇的体系域构成及沉积演化过程的理解仍有待加强。基于三维地震剖面、钻测井数据和平面属性综合分析,探讨了珠江口盆地白云凹陷13.8 Ma前后FSST和LST的划分识别依据,描述并对比了两体系域内深水扇的沉积展布特征和时空演化过程。分析后认为FSST为垂向上砂质单点源供给的小型舌状扇体,而LST扇体脱离三角洲主物源,为砂泥混合、多线源供给的大型不规则多期叠合扇体。多因素耦合条件下前者可向后者逐渐转化,推测陆架坡折处充足的沉积物供给和相对海平面变化等综合因素提供了背景基础,同时,强烈的自西南向东北的沿岸流是转化的有利因素。

The deep-water zone in the Baiyun Sag,Pearl River Mouth Basin,is an important prospect area for oil and gas exploration in the northern South China Sea,but the understanding of the system tracts’composition and the depositional evolution process of the deep-water fans is still to be strengthened.Based on the comprehensive analysis of 3-D seismic profile,well logging and drilling data and plane properties,we discussed the evidences to identify FSST and LST,described and compared the sedimentary facies distribution characteristics and spatio-temporal evolution processes of the deep-water fans in the two system tracts.The result suggests that the fan in FSST is a small tongue-shaped fan,supplied by single sandy source vertically,whereas the fan in LST is a large irregular superposed fan with multi-line sources of mixed sand and mud,getting rid of major provenance supply from the delta.During the transformation from the former to the latter with multi-factors coupling,we speculate that such synthetic factors as sufficient sediment supply at the continental shelf break and relative sea level changes,function to provide a fundamental background;simultaneously,the strong coastal currents from southwest to northeast can be a favorable factor for the transformation.