TY - JOUR
T1 - Factors controlling accumulation of organic carbon in a rift-lake, Oligocene Vietnam
AU - Rizzi, M.
AU - Hovikoski, J.
AU - Schovsbo, N.H.
AU - Therkelsen, J.
AU - Olivarius, M.
AU - Nytoft, H.P.
AU - Nga, L.H.
AU - Thuy, N.T.T.
AU - Toan, D.M.
AU - Bojesen-Koefoed, J.
AU - Petersen, H.I.
AU - Nielsen, L.H.
AU - Abatzis, I.
AU - Korte, C.
AU - Fyhn, M.B.W.
N1 - Funding Information:
Drilling of the ENRECA-3 core well was funded by DANIDA and PetroVietnam. MR was funded by Geocenter Denmark; PetroVietnam, GEUS and IGN sponsored the co-authors. MBWF acknowledges the Carlsberg Foundation for cosponsoring fieldwork on the Bach Long Vi Island. We are indebted to PetroVietnam and Vietnam Petroleum Institute for permission to publish the material. The Niton XL3t GOLDD+ XRF Analyser was put at disposal by the Geological Survey of Denmark and Greenland (GEUS). GEUS is also thanked for making laboratory facilities for SR, biomarker and maceral analyses available. The Department of Geosciences and Natural Resource Management, University of Copenhagen is acknowledged for additional total OC and XRD analyses and for making work facilities available to MR and CK.
Publisher Copyright:
© 2020, The Author(s).
PY - 2020/9/11
Y1 - 2020/9/11
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=85090891530&partnerID=8YFLogxK
U2 - 10.1038/s41598-020-71829-7
DO - 10.1038/s41598-020-71829-7
M3 - Article
C2 - 32917944
AN - SCOPUS:85090891530
SN - 2045-2322
VL - 10
JO - Scientific Reports
JF - Scientific Reports
M1 - 14976
ER -