--> ABSTRACT: Sedimentary Filling of the Pearl River Mouth Basin and Its Response to the Evolution of the Pearl River, by Shao, Lei; Pang, Xiong; Zhang, Gongcheng; #90142 (2012)

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Sedimentary Filling of the Pearl River Mouth Basin and Its Response to the Evolution of the Pearl River

Shao, Lei *1; Pang, Xiong 2; Zhang, Gongcheng 3
(1) School of Ocean & Earth Science, Tongji University, Shanghai, China.
(2) Shenzhen, CNOOC Ltd, Guangzhou, China.
(3) Research center, CNOOC Ltd, Beijing, China.

The Geochemical data of sediments from the South China Sea (SCS) provide constraints on both the composition of potential source rocks and the effects of sedimentary environments. In combination with knowledge of the regional geology, this data set allows us to decipher the tectonic implications since 32 Ma on the basis of trends and major discontinuities observed in the stratigraphic succession of geochemical sediments compositions.

According to geochemical data, the sedimentation in SCS can be subdivided into seven stages since 32 Ma: they are 32-29.5 Ma; 29.5-28.5 Ma; 26.5-23.3 Ma; 23.3-16 Ma; 16-8Ma; 8-3 Ma and 3-0 Ma, respectively. There are relatively large discontinuities between individual stratigraphic trends among these stages, and in most cases the differences of the variables among these time stages are larger than the variation within each partition, except for the samples from 26.5-23.3 Ma. The sedimentary rate and grain size has also changed on these relatively large discontinuities. There are strong deformed and slumped sediments, including some redeposits, existed from 488 mcd to 455 mcd of ODP site 1148 (26.5 to 23.3 Ma), which lead to the chemical variables strongly changed in this section.

The sediment geochemical composition between Oligocene and Miocene was different in the northern South China Sea, indicating a significant provenance change. This abrupt change coincided with a series of events including a seafloor spreading axis jump in the South China Sea and uplift of the Western Yunnan Plateau and Eastern Tibet Plateau, leading to obvious changes in drainage areas of the Pearl River and the sediment geochemical composition. The variations in Ca/Si,CIA and Al2O3 reflect that the erosion areas of the Pearl River transformed from close-to- source neighboring areas in the Oligocene to the Western Yunnan Plateau and Eastern Tibet Plateau since the early Miocene, and the provenance rock types changed from silicate to carbonate, as well as the main sediment composition changed from sand-dominated to mud-dominated material. Through this tectonic event, the sedimentary environment in the Baiyun Sag area transformed from continental shelf in the late Oligocene to continental slope since the early Miocene, and the sea level rose since the early Miocene in the area. Therefore, this abrupt change event has a profound influence on the evolution of petroleum offshore in the northern South China Sea.

 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California