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A Middle–Upper Miocene fluvial-lacustrine rift-sequence in the Song Ba Rift, Vietnam: an analogue to oil-prone, small-scale continental rift-basins

Nielsen, Lars Henrik; Petersen, Henrik Ingermann; Thai, N.D.; Duc, N.A.; Fyhn, Mikael B.W.; Boldreel, L.O.; Tuan, H.A.; Lindström, Sofie LU and Hien, L.V. (2007) In Petroleum Geoscience 13(2). p.145-168
Abstract
The small Neogene Krong Pa graben is situated within the continental Song Ba Rift, which is bounded by strike-slip faults that were reactivated as extensional faults in Middle Miocene time. The 500 m thick graben-fill shows an overall depositional development reflecting the structural evolution, which is very similar to much larger and longer-lived graben. The basal graben-fill consists of thin fluvial sandstones interbedded with well-oxygenated lacustrine siltstones in the basin centre, while very coarse-grained fluvial sandstones and conglomerates dominate at the basin margins. With increased subsidence rate and possibly a higher influx of water from the axial river systems the general water level in the graben rose and deep lakes... (More)
The small Neogene Krong Pa graben is situated within the continental Song Ba Rift, which is bounded by strike-slip faults that were reactivated as extensional faults in Middle Miocene time. The 500 m thick graben-fill shows an overall depositional development reflecting the structural evolution, which is very similar to much larger and longer-lived graben. The basal graben-fill consists of thin fluvial sandstones interbedded with well-oxygenated lacustrine siltstones in the basin centre, while very coarse-grained fluvial sandstones and conglomerates dominate at the basin margins. With increased subsidence rate and possibly a higher influx of water from the axial river systems the general water level in the graben rose and deep lakes formed. High organic preservation in the lakes prompted the formation of two excellent oil-prone lacustrine source-rock units. In the late phase of the graben development sedimentation rate outpaced the formation of accommodation space and fluvial activity increased again. During periods when the general sedimentation rate was in balance with the creation of accommodation space the environment changed frequently between lake deposition and intermittent vigorous fluvial activity. It is likely that the resulting interbedding of fluvial sandstones and lacustrine sediments reflects variations in precipitation. In periods of little precipitation the lakes diminished and lake bottoms became exposed. After heavy precipitation, transverse river systems transported sands from the rift shoulders across the exposed lake bottom and fluvial sands were deposited on lake bottom sediments. Subsequently, lake level rose due to increased water supply from the axial river and the sands were drowned and topped by transgressive lacustrine mudstones. These sandstones may function as carrier beds, whereas the braided fluvial sandstones and conglomerates along the graben margins may form reservoirs. The Krong Pa graben thus contains oil-prone lacustrine source rocks, effective conduits for generated hydrocarbons and reservoir sandstones side-sealed by the graben faults toward the footwall granites. In addition to the structural and climatic signals recorded by the graben-fill, sediment partitioning among the partly isolated basins along the rift axis seems to have been important. (Less)
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author
publishing date
type
Contribution to journal
publication status
published
subject
keywords
continental rift, fluvial-lacustrine, Miocene, Vietnam, oil-prone
in
Petroleum Geoscience
volume
13
issue
2
pages
145 - 168
publisher
Geological Society of London
external identifiers
  • scopus:34249786905
ISSN
1354-0793
DOI
10.1144/1354-079307-748
language
English
LU publication?
no
id
dc02369a-ae96-499b-873e-49a115323f2e (old id 1278512)
date added to LUP
2009-04-06 11:37:35
date last changed
2017-01-29 04:01:32
@article{dc02369a-ae96-499b-873e-49a115323f2e,
  abstract     = {The small Neogene Krong Pa graben is situated within the continental Song Ba Rift, which is bounded by strike-slip faults that were reactivated as extensional faults in Middle Miocene time. The 500 m thick graben-fill shows an overall depositional development reflecting the structural evolution, which is very similar to much larger and longer-lived graben. The basal graben-fill consists of thin fluvial sandstones interbedded with well-oxygenated lacustrine siltstones in the basin centre, while very coarse-grained fluvial sandstones and conglomerates dominate at the basin margins. With increased subsidence rate and possibly a higher influx of water from the axial river systems the general water level in the graben rose and deep lakes formed. High organic preservation in the lakes prompted the formation of two excellent oil-prone lacustrine source-rock units. In the late phase of the graben development sedimentation rate outpaced the formation of accommodation space and fluvial activity increased again. During periods when the general sedimentation rate was in balance with the creation of accommodation space the environment changed frequently between lake deposition and intermittent vigorous fluvial activity. It is likely that the resulting interbedding of fluvial sandstones and lacustrine sediments reflects variations in precipitation. In periods of little precipitation the lakes diminished and lake bottoms became exposed. After heavy precipitation, transverse river systems transported sands from the rift shoulders across the exposed lake bottom and fluvial sands were deposited on lake bottom sediments. Subsequently, lake level rose due to increased water supply from the axial river and the sands were drowned and topped by transgressive lacustrine mudstones. These sandstones may function as carrier beds, whereas the braided fluvial sandstones and conglomerates along the graben margins may form reservoirs. The Krong Pa graben thus contains oil-prone lacustrine source rocks, effective conduits for generated hydrocarbons and reservoir sandstones side-sealed by the graben faults toward the footwall granites. In addition to the structural and climatic signals recorded by the graben-fill, sediment partitioning among the partly isolated basins along the rift axis seems to have been important.},
  author       = {Nielsen, Lars Henrik and Petersen, Henrik Ingermann and Thai, N.D. and Duc, N.A. and Fyhn, Mikael B.W. and Boldreel, L.O. and Tuan, H.A. and Lindström, Sofie and Hien, L.V.},
  issn         = {1354-0793},
  keyword      = {continental rift,fluvial-lacustrine,Miocene,Vietnam,oil-prone},
  language     = {eng},
  number       = {2},
  pages        = {145--168},
  publisher    = {Geological Society of London},
  series       = {Petroleum Geoscience},
  title        = {A Middle–Upper Miocene fluvial-lacustrine rift-sequence in the Song Ba Rift, Vietnam: an analogue to oil-prone, small-scale continental rift-basins},
  url          = {http://dx.doi.org/10.1144/1354-079307-748},
  volume       = {13},
  year         = {2007},
}