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Great Rift Valley and Kenyan Cenozoic Stratigraphy

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									           Great Rift Valley
             and Kenyan
               Cenozoic
             Stratigraphy
http://earth.imagico.de/comment.php?site=eafrica
                     Rift Valleys
   Form in regions of extensional stress
   As the lithosphere and crust pull apart, the area
    between sinks down.
       This is called the graben
       The graben is flanked by steep boundaries
   They start when plumes form beneath
    continents
   The lighter crust cracks, and subduction zones
    continue to pull the crust apart
Rift Valley
Formation
                      Great Rift Valley
   The largest rift valley in world
       6400 km long and 48-64 km
        wide
       Stretches from southern Turkey
        to Mozambique
       Visible from the Moon
   Began 30 Mya in Gulf of Aden
       East Africa Rift Valley began 14
        Mya                            http://neuropolitics.org/defaultjun06.asp
             East Africa Rift Valley
   Valley is filled with interbeded
    volcanic rock and sediments
   Ethiopia’s Afar Triangle is triple
    junction of the African, Arabian,
    and Somalian plates
   Early hominid fossils have been
    found here                 http://www.answers.com/topic/great-rift-valley

        Place of human origins
      Kenyan Stratigraphy - Marine
Age           Formation         Components
M Pleistocene Mombasa
              Island            Crags, calcareous sand
              Kilindi Sands
Pliocene       Marafa Beds      White sand, red sand,
                                clay, pebbles
L Miocene      Baratum Beds     marls, sand, clay,
                                conglomerates,
                                limestone
               Fundi Isa Beds   limestone
   Kenyan Stratigraphy - Continental
Age           Formation          Components
M Pleistocene Kanjera            Ashes, clay, limestone

              Rawi               Clay, gravel, volcanic SS
              Kanam              Clay, gravel, ash

L Miocene     Kiaherra Series    tuffs, limestone, grit,
                                 pisolithic earth
               Hiwegei           Red clay, boulders,
                                 limestone
               Kathawant Point   Dull, flaggy mudstones
               Kathawanage       mudstone, sandstone
                    Mpesida Beds

   Miocene age
       Volcanoclastic horizons interbedded with
        trachytic flows
       Examination of three sites helped reveal
        Miocene conditions, time when humans were
        evolving
           Chimps and humans split 6-5 Mya, Miocene starts
            ~ 5 Mya
                      Mpesida Beds

                                              From Kingston et al.
                                              2002




   Site 1:
       Pyroclastic rock is massive, unsorted, entirely
        ash
       contains silicified wood
       Fossil trees are up to 50 m tall
            Indicative of a wet forest
                        Mpesida Beds
   Site 2:
       Pyroclastic layer that is grey to buff colored, coarse
        sandstone
            Vertebrate fossils confined to this layer
       Shows new families establishing themselves in Sub-
        Saharan Africa
       Savannah and forest environments
   Site 3:
       Lacustrine facies of clays, silts, fine sandstone
        interbedded with diatomite
            A hiatus from volcanic activity
 Fossil Mammals of Great Rift Valley




                                         Creodont2


Deinotherium1                    Chalicotherium3


                                           1) http://www.answers.com/topic/deinotherium
                2) http://www.ucmp.berkeley.edu/mammal/eutheria/creodonta.html
                               3) http://paleo.amnh.org/bjburger/fossilmammal/u3.html
     Fossil Mammals of Great Rift Valley

                                                                   Equus2




 Hippopotamus1
                                              Leporid3


1) http://www.nature-wildlife.com/girskel11.html
2) http://www.crockerfarm.org/ac/rm02/pratt99/pratt99mammals.htm
3) http://www.nature-wildlife.com/girskel08.html
       Fossil Mammals of Great Rift Valley
                                   Australopithecus afarensis2




  Orrorin turgenensis1
                                                                       Homo rudolfensis3


1) http://www.oursci.org/magazine/200108/010814.htm
2) http://www.achievement.org/autodoc/photocredit/achievers/joh1-021
3) http://en.wikipedia.org/wiki/Homo_rudolfensis

								
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