珠江口盆地韩江-陆丰凹陷珠江组下段碎屑锆石来源与储层物源示踪

Detrital zircon genesis and provenance tracing for reservoirs in the Lower Zhujiang Formation in Hanjiang-Lufeng Sag,Pearl River Mouth Basin

珠江组下段作为珠江口盆地东部优质的油气储层,其物源分布特征至今仍存在争议。为了研究韩江-陆丰凹陷珠江组下段物源分布特征及其岩性组成,利用LA-ICP-MS定年技术对珠江口盆地东部7个不同局部构造区的下中新统珠江组下段砂岩样品进行了碎屑锆石U-Pb定年分析。结果显示,样品中碎屑锆石以岩浆成因为主,主要存在98~114,137~163,211~247和387~428 Ma四个年龄区间,变质成因为次。通过与周缘潜在物源区岩层(体)年龄对比,并结合年龄频谱特征,认为研究区早中新世珠江早期至少存在4条供给碎屑物质的水系,其中,海丰28构造区和陆丰2构造区的沉积物源主要来自韩江物源;南侧东沙隆起为陆丰22构造区主物源区;汕尾物源除为惠州10构造区供源外,还与珠江物源在惠州08构造区交汇;陆丰13构造区以东沙隆起物源为主,可能有部分韩江物源的加入。韩江-陆丰地区具备发育浅层和中深层优质储层的地质条件,仍是今后珠江口盆地东部油气勘探的重要领域。

High-quality reservoirs in the Lower Zhujia Formation in eastern Pearl River Mouth Basin have trigged many disputes over their provenance distribution patterns and lithologies. As an attempt to dispel the doubts over the issue,we performed U-Pb dating on some detrital zircons in sandstone samples from the Lower Zhujiang Formation in the Lower Miocene of 7 different structural zones in eastern Pearl River Mouth Basin with LA-ICP-MS dating technology. The results show that the zircons were mostly magmatic origin,followed by metamorphic origin. The zircons of magmatic origin showed up during four age intervals： 98-114,137-163,211-247 and 387-428 Ma. By comparing the ages of the zircons with those of potential provenance rocks and combining the age spectrum,we suggest that there were at least 4 water systems serving as detrital material providers during the early Zhujiang time of the Early Miocene. Hanjiang provenance was the source of sediments in Haifeng 28 and Lufeng 2 structural zones,Dongsha uplift provenance provided sediments for Lufeng 22 structural zone,Shanwei provenance generated materials for Huizhou 10 structural zone and joined Zhujiang provenance at Huizhou 08 structural zone,and Dongsha uplift provenance,possibly together with Hanjiang provenance,provided materials for Lufeng 13 structural zone. Based on the above analyses,we propose that Hanjiang-Lufeng area,with favorable geological conditions for the formation of shallow and medium to deep reservoirs,be the key future explorationtarget in Pearl River Mouth Basin.