Transcript Great Rift Valley and Kenyan Cenozoic Stratigraphy

Great Rift Valley
and Kenyan
Cenozoic
Stratigraphy
http://earth.imagico.de/comment.php?site=eafrica
Rift Valleys
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Form in regions of extensional stress
As the lithosphere and crust pull apart, the area
between sinks down.
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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
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The largest rift valley in world
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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
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East Africa Rift Valley began 14
Mya
http://neuropolitics.org/defaultjun06.asp
East Africa Rift Valley
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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
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Place of human origins
Kenyan Stratigraphy - Marine
Age
Formation
M Pleistocene Mombasa
Island
Kilindi Sands
Components
Pliocene
Marafa Beds
L Miocene
Baratum Beds
White sand, red sand,
clay, pebbles
marls, sand, clay,
conglomerates,
limestone
limestone
Fundi Isa Beds
Crags, calcareous sand
Kenyan Stratigraphy - Continental
Age
Formation
M Pleistocene Kanjera
Rawi
Kanam
Kiaherra Series
L Miocene
Hiwegei
Components
Ashes, clay, limestone
Clay, gravel, volcanic SS
Clay, gravel, ash
tuffs, limestone, grit,
pisolithic earth
Red clay, boulders,
limestone
Kathawant Point
Dull, flaggy mudstones
Kathawanage
mudstone, sandstone
Mpesida Beds
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Miocene age
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Volcanoclastic horizons interbedded with
trachytic flows
Examination of three sites helped reveal
Miocene conditions, time when humans were
evolving
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Chimps and humans split 6-5 Mya, Miocene starts
~ 5 Mya
Mpesida Beds
From Kingston et al.
2002
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Site 1:
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Pyroclastic rock is massive, unsorted, entirely
ash
contains silicified wood
Fossil trees are up to 50 m tall
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Indicative of a wet forest
Mpesida Beds
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Site 2:
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Pyroclastic layer that is grey to buff colored, coarse
sandstone
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Vertebrate fossils confined to this layer
Shows new families establishing themselves in SubSaharan Africa
Savannah and forest environments
Site 3:
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Lacustrine facies of clays, silts, fine sandstone
interbedded with diatomite
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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
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
Homo rudolfensis3