珠江口盆地珠一坳陷西部中新世早-中期沉积特征及控制因素*

大型海相三角洲分布范围广,沉积动力复杂,其精细层序—沉积构型和演化规律是沉积学领域长期研究的热点。综合岩矿、测井和三维地震资料,充分结合高精度层序地层学和三维地震沉积学分析方法,对古珠江三角洲西侧的恩平地区中新世早-中期沉积特征进行了精细研究,识别出了辫状河道、曲流河道等河控三角洲的主要微相单元,同时也揭示出海岸砂脊等浪控三角洲中发育的典型微相类型。在高精度层序格架约束下,揭示出单一典型层序内古珠江三角洲的演化特征: 低位体系域以河控三角洲为主,发育大型交切状辫状水道;海侵和高位体系域河道规模明显减小,以小规模曲流河道为主,且易于见到海岸砂脊等波浪作用的典型特征。此外,针对恩平地区中新世早-中期沉积相带的系统编图和演化分析,在大约6 ^Ma时间内识别出6次河道大规模改道现象,推测恩平地区沉积演化明显受到自旋回沉积过程的影响。

Sedimentary characteristics and controlling factors of the western ZhuⅠdepression during the early-middle Miocene,Pearl River Mouth Basin

Large marine deltas are widely distributed and their sedimentary dynamics are complex. Their fine stratigraphic-sedimentary architecture and evolution are the focus of research in the field of sedimentology for a long term. By integrating core,logging and 3D seismic data,this paper combines the analysis methods of high-resolution seismic sequence stratigraphy and seismic sedimentology to make a comprehensive investigation of the sedimentary characteristics of the early-middle Miocene in the Enping area on the west side of the paleo Pearl River Delta. The main microfacies units of river-controlled deltas such as braided channels and meandering channels are identified,and the typical microfacies developed in wave-controlled deltas such as coastal sand ridge are also revealed. Under the constraint of high-frequency sequence framework,the evolution characteristics of the paleo Pearl River Delta in an individual typical sequence system are revealed: the lowstand systems tracts are dominated by river-controlled delta,with the occurrence of large intersecting braided channels;while within the transgressive and highstand systems tracts,channels are significantly smaller in scales,dominated by small-scale meandering channels,and have typical characteristics of wave movement such as coastal sand ridges. In addition,according to the systematic mapping and evolution analysis of the early Miocene sedimentary facies belt in the Enping area,six large river diversion phenomena were identified within ca. 6 Ma. It is speculated that the sedimentary evolution in the Enping area is obviously affected by the autogenic process.