University:
Massachusetts Institute of Technology
Course:
12.520 | Geodynamics
Academic year:

2023
Views:

225

Pages:

21
Author:

conedcuirassing

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. Niger Delta Niger Cross River delta Niger delta progradation since 38 Ma from Burke (1972) Modified from Short & Stauble (1970) 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) Niger pers. coms. (To Tim)from Exxon Mobil Kevin’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 unconformity East Antarctic Ice-sheet Formed ? Senegal Delta Nouakchott (N.headland) Cape Vert, Dakar (S. headland). Senegal R. diverted by active Dakar dome. Niger inland delta on E. of image. Senegal Congo Fan Congo/Zaire Orange River Delta Orange Nile Delta Nile There was no Nile Delta at 35 Ma but Fayum shore was Well-developed By 28 Ma delta was growing A mature Nile delta 150 km SE of present Site by 20 Ma NILE delta growth Since ca.23 Ma The Nile delta Has prograded Onto the Mediterranean Ocean floor Zambezi Delta Zambezi Zambezi delta Was much Smaller 25 Ma At 25 Ma most Of the sediment Entering the Deep channel Between Madagascar and Mozambique Came from the Rift to the north. Now deposition from The Zambezi dominates 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 of the continent’s area of 31 M km2 ). There are many mineral deposits in those outcrops.