珠江口盆地白云凹陷中央底辟带的发现及识别

Discovery and Recognition of the Central Diapiric Zone in Baiyun Depression, Pearl River Mouth Basin

白云凹陷属珠江口盆地的一个次级构造单元.通过对二维地震剖面上模糊带的分析,凹陷中心发育北西西向展布、面积约1000km2的底辟带,底辟幅度最大可达8km.高精度磁力资料显示底辟带为一个低磁异常区.底辟构造包括龟背上拱、弱刺穿、气烟囱、底辟断层(或裂缝)、海底麻坑等类型,主要发源于断陷期深湖相的文昌组(始新统)—恩平组(上始新统-下渐新统),其次为坳陷期浅海-深海相沉积的珠江组(下中新统)—韩江组(中中新统)的两套巨厚富泥沉积层.白云凹陷具有快速沉降、细粒充填为主、以及新生代的右旋张扭性应力场,共同造就了凹陷中央底辟带的发育.底辟构造的存在反映了白云凹陷中心曾经蕴育着高温、超压系统,与之密切伴生的大量亮点指示着沿底辟构造的天然气垂向输导,构成了古近系油气运移到新近系—第四系的成藏动力系统.

The Baiyun depression is a sub-unit of the Pearl River Mouth basin. In the center of this depression, fuzzy zones on 2D seismic profiles and low magnetic anomalies have been analyzed. A diapiric zone has been revealed, with a WNW directional distribution, about 1 000 km^2 planar area and about 8 km most pierced thickness. The diapiric structures display various types such as a turtleback-like arch, weak piercing, gas-chimney, fault （or crack） and seabed pit, originated in two huge mud-rich strata the Wenchang Formation （Eocene） and the Enping Formation （Upper Eocene-Lower Oligocene）. There are deep-lake facies in the rift period of the depression; the secondary is the Zhujiang Formation （Lower Miocene） and Hanjiang Formation （Middle Miocene）, which have shallow or deep-marine facies in down-warping period. In the depression, factors are favorable for diapirism such as rapid subsidence, fine-grain sediment mainly filling, and dextral tenso-shear stress-field since the Cenozoic. The structures indicate a high temperature-overpressure system ever developed. Closely associated and abundant bright-spots show natural gas has migrated vertically, and a dynamic system has existed for petroleum transported from the Paleogene to the Neogene and Quaternary.