南海北部深水区古近系沉积物源演变及古地理意义^*

Paleogene sediment source evolution and palaeogeographic significance in deep-water area of the northern South China Sea

摘要

南海北部深水区古近纪经历了由陆到海的环境转换过程,沉积物源也随时间发生明显改变。由于水深的限制,目前对深水区的沉积物来源及古地理背景存在争议。通过碎屑锆石U-Pb年龄谱系源汇对比方法,对南海北部珠二坳陷古近系沉积物来源进行系统研究。结果发现,在早中始新世,珠二坳陷沉积物以近源输入为特征,沉积物主要来自坳陷周缘的局部隆起区; 晚始新世,源自坳陷西侧的昆莺琼古河为盆地提供大量沉积物,坳陷北侧的珠江沉积物对珠二坳陷影响较小; 渐新世,珠江沉积物从北向南越过番禺低隆起进入珠二坳陷,与昆莺琼古河沉积物在白云凹陷北部和中西部混合沉积,形成大型河流三角洲体系。南海北部深水区古近系物源演变过程明显受中生代末区域构造古地理控制,查明该时期物源演变对恢复区域古地理格局具有重要意义。

Abstract

The deep-water area of the northern South China Sea experienced a transition from lacustrine to marine environments in the Paleogene,and has rich oil and gas resources and broad exploration prospects. Due to the limitation of water depth,the provenance of sediments and the palaeogeographic evolution of the basin are not clear. In this paper,the Paleogene of the Zhu-2 depression in the Pearl River Mouth Basin is systematically studied by means of detrital zircon U-Pb ages and source-sink correlation. The results show that in the Early and Middle Eocene,the sediments of the Zhu-2 depression were mainly from local uplift area around the depression. In the Late Eocene,the Kunyingqiong River originated from the western side of the depression provided a large amount of sediments for the basin,whereas the Paleo-Pearl River sediments had little influence on the deposition in the depression. In the Oligocene,the Paleo-Pearl River crossed the Panyu low uplift and entered the Baiyun sag,carrying sediments mixed with the Kunyingqiong River sediments in the form of delta deposition in the north and mid-west of the sag,forming a dual provenance river-delta system. The Paleogene provenance evolution of the deep-water area of the northern South China Sea was obviously controlled by regional tectonic palaeogeography of the Mesozoic. Identifying the provenance evolution during this period is of great significance for restoring the regional palaeogeography pattern.

关键词

南海 / 珠二坳陷 / 古近纪 / 物源 / 古地理

Key words

South China Sea / Zhu-2 Depression / Paleogene / provenance / palaeogeography

基金资助

*国家自然科学基金项目(编号: 42076066, 92055203)和中海油综合科研项目“南海东部大中型天然气田勘探潜力与突破方向”联合资助