珠江口盆地白云凹陷晚渐新统-早中新统沉积特征及演化规律

摘要

Based on the studies of cores, well logs, seismic and paleontology data of Baiyun depression in Pearl River mouth basin, combined with previous research results, the paper synthetically analyzed the characteristics of sedimentary facies and evolution of sedimentary filling from Late Oligocene to Early Miocene in the depression. The results show that shallow delta deposition developed in Lower Zhuhai Formation, seismic reflection character-istics show that the delta has three phases, microfacies of underwater branching channel, inter-tributary bar,river mouth bar, distal bar were drilled, characterized by sand-rich sediments, washing-filling structure, graded bedding, thick horizontal burrows and other structures were developed. The upper of Zhuhai Formation was of neritic facies, characterized mainly by marine interbedded sandstone and mudstone.At that time the shelf slope–break zone was located on the southern slope of Baiyun depression. The eustatic cycles of sea level were frequent and the shelf slope–break zone moved to the northern slope of Baiyun depression during deposition of Zhujiang Formation. As the expansion of the ancient Pearl River, the input of sediment increased and a deep-water fan sedimentary system developed in Lower Zhujiang Formation.Sediments consisted mainly of fine sandstone to coarse sandstone, with a small quantity of siltstone and deep–sea mudstone. Four major gravity flows developed, including particle flow, liquid flow, turbidity flow and debris flow. Channel deposits of inner fan, deposits of abandoned channel of middle fan, overflow deposits between the channels and deep–sea sediments outside fan were drilled. The Upper Zhujiang Formation was of bathyal facies with abyssal mudstone as major sediments.%以珠江口盆地白云凹陷钻井、测井、地震和古生物资料为基础，结合前人研究成果，系统的分析了白云凹陷晚渐新统到早中新统沉积相发育特征及凹陷沉积充填演化过程。研究结果表明，珠海组下部发育大型陆架边缘三角洲沉积，地震反射特征表明该三角洲发育三期；钻遇水下分支河道、支流间湾、河口坝及远砂坝微相，沉积物以富砂为特征，发育冲刷–充填构造、递变层理及较粗的水平潜穴等多种构造；珠海组上部为浅海相，沉积物以海相砂泥岩互层为主，此时期陆架坡折带位于白云凹陷南坡；珠江组沉积时期，海平面升降旋回频繁，陆架坡折带迁至凹陷北坡。随着古珠江流域扩大，沉积物输入量增加，在珠江组下部发育了深水扇，沉积物以细–粗砂岩为主，夹少量粉砂岩及深海泥岩，发育颗粒流、液化流、浊流及碎屑流等四种主要的重力流，钻遇内扇水道，中扇废弃水道及水道间漫溢沉积，外扇深海泥沉积；珠江组上部为半深海相，沉积物以深海泥岩为主。