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Rizzi M, Hovikoski J, Schovsbo NH, Therkelsen J, Olivarius M, Nytoft HP, Nga LH, Thuy NTT, Toan DM, Bojesen-Koefoed J, Petersen HI, Nielsen LH, Abatzis I, Korte C, Fyhn MBW. Factors controlling accumulation of organic carbon in a rift-lake, Oligocene Vietnam. Sci Rep 2020; 10:14976. [PMID: 32917944 PMCID: PMC7486892 DOI: 10.1038/s41598-020-71829-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2019] [Accepted: 07/30/2020] [Indexed: 11/30/2022] Open
Abstract
Understanding of the processes of petroleum source rock (SR) accumulation in lacustrine rift basins and the behavior of lake systems as long-term carbon sinks is fragmentary. Investigation of an 800 m thick (500 m core and ~ 300 m outcrop), deep-lacustrine, Oligocene section in Vietnam, provides a rare insight into the controls and deposition of organic carbon (OC) and SR formation in continental rift basins. A multidisciplinary dataset, combining elemental data, inorganic and organic geochemistry with sedimentology, shows that the richest alginite-prone, sapropelic SR developed during periods of relative tectonic quiescence characterized by moderate primary productivity in a mainly dysoxic lacustrine basin. Increased rift activity and further development of graben morphology intensified water column stratification and anoxia, which hindered nutrient recycling. Sapropelic organic matter (OM) continued to accumulate, but with increasing amorphous OM content and decreasing total OC values. Periods of increased seasonality were characterized by thermocline weakening, enhanced mixing of water columns, increased primary productivity and diatom blooming. The results suggest that a change from dysoxia towards anoxia or extreme primary productivity does not necessarily enhance OC burial and SR quality. External nutrient input from a phosphate-rich hinterland is sufficient for sapropel formation, whereas the main limiting factor is methanogenesis.
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Affiliation(s)
- M Rizzi
- Department of Geosciences and Natural Resource Management, University of Copenhagen, Øster Voldgade 10, 1350, Copenhagen, Denmark.
| | - J Hovikoski
- Geological Survey of Denmark and Greenland, Øster Voldgade 10, 1350, Copenhagen, Denmark
| | - N H Schovsbo
- Geological Survey of Denmark and Greenland, Øster Voldgade 10, 1350, Copenhagen, Denmark
| | - J Therkelsen
- Geological Survey of Denmark and Greenland, Øster Voldgade 10, 1350, Copenhagen, Denmark
| | - M Olivarius
- Geological Survey of Denmark and Greenland, Øster Voldgade 10, 1350, Copenhagen, Denmark
| | - H P Nytoft
- Geological Survey of Denmark and Greenland, Øster Voldgade 10, 1350, Copenhagen, Denmark
| | - L H Nga
- Exploration & Production Centre, Vietnam Petroleum Institute, 167 Trung Kinh, Yen Hoa, Cau Giay, Hanoi, Vietnam
| | - N T T Thuy
- Exploration & Production Centre, Vietnam Petroleum Institute, 167 Trung Kinh, Yen Hoa, Cau Giay, Hanoi, Vietnam
| | - D M Toan
- Exploration & Production Centre, Vietnam Petroleum Institute, 167 Trung Kinh, Yen Hoa, Cau Giay, Hanoi, Vietnam
| | - J Bojesen-Koefoed
- Geological Survey of Denmark and Greenland, Øster Voldgade 10, 1350, Copenhagen, Denmark
| | - H I Petersen
- Total Upstream Danmark A/S, Amerika Plads 29, 2100, Copenhagen, Denmark
| | - L H Nielsen
- Geological Survey of Denmark and Greenland, Øster Voldgade 10, 1350, Copenhagen, Denmark
| | - I Abatzis
- Geological Survey of Denmark and Greenland, Øster Voldgade 10, 1350, Copenhagen, Denmark
| | - C Korte
- Department of Geosciences and Natural Resource Management, University of Copenhagen, Øster Voldgade 10, 1350, Copenhagen, Denmark
| | - M B W Fyhn
- Geological Survey of Denmark and Greenland, Øster Voldgade 10, 1350, Copenhagen, Denmark
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