Sequence stratigraphy and depositional architecture of the Pearl River Delta system,northern South China Sea: An interactive response to sea level,tectonics and paleoceanography |
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| Institution: | 1. State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China;2. CNOOC Limited – Shenzhen Branch, Shenzhen 518000, China;3. Ocean College, Zhejiang University, Zhoushan 316021, China;4. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249, China;1. Research Institute of Unconventional Petroleum and Renewable Energy, China University of Petroleum, Room 222, Qingdao 266580, China;2. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249, China;3. CNOOC Research Institute, Beijing 100027, China;1. Key Laboratory of Tectonics and Petroleum Resources, China University of Geosciences, Ministry of Education, Wuhan 430074, China;2. Faculty of Earth Resources, China University of Geosciences, Wuhan 430074, China;3. Shenzhen Branch of China National Offshore Oil Corporation Ltd., Shenzhen 510240, China;1. Ocean College, Zhejiang University, Zhoushan 316000, China;2. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249, China;3. China National Offshore Oil Corporation Limited, Shenzhen, Guangzhou 510240, China;4. Key Laboratory of Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China;5. University of Chinese Academy of Sciences, Beijing 100049, China;1. School of Ocean Sciences, China University of Geosciences, Beijing, 100083, China;2. Shenzhen Branch of CNOOC Ltd., Guangzhou, 510240, China;3. School of Energy Resources, China University of Geosciences, Beijing, 100083, China;1. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249, China;2. College of Geosciences, China University of Petroleum, Beijing 102249, China;3. China National Offshore Oil Corporation Limited-Shenzhen, Guangzhou 510000, China |
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| Abstract: | Using a combined dataset including 3D seismic volumes, 2D profiles and 127 industrial wells, this study systematically investigated sequence stratigraphy and depositional architecture of the Pearl River Delta system (PRDS) during the Middle Miocene. In total, six stratigraphic sequences (SQ1 to SQ6) were recognized for the Hanjiang Formation, each of which could be further subdivided into a transgressive systems tract (TST) and a regressive systems tract (RST) according to a T-R sequence stratigraphic model. Seismic geomorphologic approaches were then conducted to interpret and map the key depositional elements, including fluvial channel systems, river mouth bars, longshore bars, shelf sand ridges and shelf sand sheets. After a detailed construction of the paleogeography for each of the twelves systems tracts, it was found that the types, geometries and depositional regimes of PRDS significantly altered at ca. 13.8 Ma. Before ca. 13.8 Ma, the PRDS were dominated by well-developed fluvial systems and an overall lobate shape, indicating a fluvial-dominated process. However, after 13.8 Ma, the whole PRDS began to form enormous shoreline-parallel depositional elements such as longshore bars, shelf sand ridges and shelf sand sheets, indicating dominant shore-parallel regimes. Besides, the whole deltaic system displayed obvious southwest deflection in map view after 13.8 Ma.Detailed analysis showed that this sudden change in the evolution of the PRDS could be ascribed to an interactive response to several factors. At ca. 13.8 Ma, the sea level began to rapidly rise and caused the fluvial energy to decrease, which was likely to lead to the diversion of the fluvial systems. Besides, the gradual uplift of the Dongsha Rise resulted in the raised shelf topography in the east region, thus confining the fluvial channels to flow southwestward. What's more, a few key paleoceanographic events, including the reglaciation of the Antarctic ice-sheet and the shoaling of the Pacific-Indian Ocean Seaway, might have contributed to the intensification of the southwesterly flowing paleocurrent along the northern South China Sea, thus triggering the delta asymmetry and deflecton of the PRDS after 13.8 Ma. |
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| Keywords: | Pearl River Mouth Basin South China Sea Tectonic Paleoceanography Ocean current Delta asymmetry |
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