Deposition during the past 30 My in Africa's great deltas and deep ...
Transcript of Deposition during the past 30 My in Africa's great deltas and deep ...
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Deposition during the past 30 My in Africa’s great deltas and deep sea fans
Six Examples
Only thin sedimentary sections (< 1 km) have accumulated in interior basins since 30 Ma.Lakes Malawi and Tanganyika probably hold several km
Thanks to Tim Chapman for delta and deep water work.Image courtesy of NASA and USGS.
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Niger Delta
Image courtesy of NASA and USGS.
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Niger
Image courtesy of NASA and USGS.
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Niger deltaprogradationsince 38 Ma from Burke(1972)
ModifiedfromShort& Stauble(1970)
CrossRiverdelta
Progradation of the Niger delta since 34 Ma as a result of increased erosion of the African continent since that time. From Short and Stauble (1972)
Image courtesy of The Geological Society of South Africa.
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Niger pers. coms. (To Tim)from Exxon MobilKevin’s speculations are in blue
• 23.8 Ma major unconformity
• 28.3 Ma major unconformity when shelf started developing (major sedimentation starts)
• Consequence of plate arrest ?
• 31 Ma minor unconformity (minor eustatic change, major stratigraphic change) Consequence of plate arrest ?
• 34 Ma major unconformityEast Antarctic Ice-sheetFormed ?
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Senegal Delta
Image courtesy of NASA and USGS.
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Nouakchott (N.headland) Cape Vert, Dakar (S. headland). Senegal R. diverted by active Dakar dome. Niger inland delta on E. of image.
Senegal
Image courtesy of NASA and USGS.
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Congo Fan
Image courtesy of NASA and USGS.
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Congo/Zaire
Image courtesy of NASA and USGS.
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Orange RiverDelta
Image courtesy of NASA and USGS.
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Orange
Image courtesy of NASA and USGS.
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Nile Delta
Image courtesy of NASA and USGS.
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Nile
Image courtesy of NASA and USGS.
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There was no NileDelta at 35 Ma butFayum shore was Well-developed
By 28 Ma delta wasgrowing
A mature Nile delta150 km SE of presentSite by 20 Ma
Image courtesy of The Geological Society of South Africa.
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NILE delta growth
Image courtesy of The Geological Society of South Africa.
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Since ca.23 MaThe Nile deltaHas progradedOnto the MediterraneanOcean floor
Image courtesy of The Geological Society of South Africa.
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Zambezi Delta
Image courtesy of NASA and USGS.
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Zambezi
Image courtesy of NASA and USGS.
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Zambezi deltaWas much Smaller 25 Ma
Image courtesy of The Geological Society of South Africa.
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At 25 Ma mostOf the sedimentEntering the Deep channelBetweenMadagascar andMozambiqueCame from theRift to the north.Now deposition fromThe Zambezi dominates
Image courtesy of The Geological Society of South Africa.
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CONCLUSION:AFRICAN PLATE WAS PINNED AT 30 Ma
CONSEQUENCES:Shallow mantle convection was set up as a result of which:(1) Basins, Swells and Rifts are forming.(2)Intraplate volcanic activity on swells.(3) Erosion of high ground. (4) Deposition, mainly offshore.Secondary consequences include establishment of a benign environment for human evolution, deep water oil formation, huge Precambrian outcrop (half ofthe continent’s area of 31 M km2 ). There are many mineral deposits in those outcrops.