PROVENANCE EVOLUTION OF THE PALEO-HANJIAN RIVER IN THE NORTH SOUTH CHINA SEA
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摘要: 珠江和韩江是南海北部陆源物质的两个重要供给来源,南海北部陆丰-韩江地区自古近纪以来即接受两者的沉积。通过稀土元素配分特征及判别分析发现,在始新世,研究区沉积物稀土元素配分形式多样,不同地区差异明显,显示出在始新世沉积时,研究区尚不具备大的物源供给,基本以近源为主。在渐新世,韩江源区和珠江源区基本形成,但是古韩江对陆丰-韩江地区相对影响较大,主要影响研究区东部及中部的广大地区,而珠江则主要影响研究区西北及西部地区。到早中新世,韩江物源影响范围进一步扩大,一直影响到研究区西南部地区,并有部分物质到达研究区西部。但是,从中中新世开始,韩江物源逐步退缩,使西南地区受珠江和韩江来源沉积物的共同影响,而探井Lf14则主要受珠江的影响。到晚中新世,韩江和珠江来源沉积物均发生减弱,本地区主要接受浅海泥灰质沉积。研究区除了接受韩江和珠江带来的陆源碎屑沉积外,从渐新世开始,一直持续到早中新世均受到东沙隆起区的基性火山活动的影响,对研究区南部Lf7和Lf14探井影响较大。由于受火山活动的影响,使该地区沉积物的稀土元素Eu出现较多的正异常。Abstract: The Pearl and Hanjiang rivers are the two important terrigenous sediment sources for the Hanjiang-Lufeng area in the northern part of the South China Sea (SCS) since Paleogene. In Eocene, the partition coefficients of the rare-earth elements of the sediments varied from region to region,indicating that there is no large river dominating the region for sediments supply.The nearby uplifting areas were the major source areas. In the Oligocene, Hanjiang River and Pearl River just appeared,and the Hanjiang River was relatively larger than the Pearl River then and could provide most of the sediments to the east and middle part,whereas the Pearl River could only affect the northwest and west part of the research area.Up to early Miocene, the sediment from the Hanjiang River source area reached the southwest part, and even the west part of the research area, reflecting the expansion of the Hanjiang River source area.The Hanjiang River started retreating in the middle Miocene.As the result, the sediments from both rivers deposited together in the southwest part of the research area and the Lf14 region started receiving sediments from the Pearl River at this time. Because of the sea level rise,sediments from the two rivers were decreased in the research area, and brought about the deposition of the mixed mud and carbonate deposits in an epicontinental sea environment in late Miocene. Besides the terrigenous sediments from the two rivers, there were some basic volcanic materials coming from the Dongsa Uplift during the period from Oligocene to early Miocene that led to the positive anomaly of element Eu in the Lf7 and Lf14 regions in the south.
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Keywords:
- South China Sea /
- Hanjiang River /
- provenance /
- Rare earth element /
- sediment
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