Great Rift Great Rift Valley and Valley and

Kenyan Kenyan Cenozoic Cenozoic

StratigraphyStratigraphyhttp://earth.imagico.de/comment.php?site=eafrica

Rift ValleysRift Valleys

Form in regions of extensional stressForm in regions of extensional stress As the lithosphere and crust pull apart, the As the lithosphere and crust pull apart, the

area between sinks down.area between sinks down. This is called the This is called the grabengraben The graben is flanked by steep boundariesThe graben is flanked by steep boundaries

They start when plumes form beneath They start when plumes form beneath continents continents

The lighter crust cracks, and subduction The lighter crust cracks, and subduction zones continue to pull the crust apartzones continue to pull the crust apart

Rift Valley Rift Valley FormationFormation

Great Rift ValleyGreat Rift Valley

The largest rift valley in The largest rift valley in worldworld 6400 km long and 48-64 km 6400 km long and 48-64 km

widewide Stretches from southern Turkey Stretches from southern Turkey

to Mozambiqueto Mozambique Visible from the MoonVisible from the Moon

Began 30 Mya in Gulf of AdenBegan 30 Mya in Gulf of Aden East Africa Rift Valley began 14 East Africa Rift Valley began 14

MyaMya http://neuropolitics.org/defaultjun06.asp

East Africa Rift ValleyEast Africa Rift Valley Valley is filled with interbeded Valley is filled with interbeded

volcanic rock and sedimentsvolcanic rock and sediments Ethiopia’s Afar Triangle is Ethiopia’s Afar Triangle is

triple junction of the African, triple junction of the African, Arabian, and Somalian platesArabian, and Somalian plates

Early hominid fossils have Early hominid fossils have been found herebeen found here Place of human originsPlace of human origins

http://www.answers.com/topic/great-rift-valley

Kenyan Stratigraphy - Kenyan Stratigraphy - MarineMarine

AgeAge Formation Formation ComponentsComponents

M M PleistocenePleistocene

Mombasa Mombasa IslandIsland Crags, calcareous Crags, calcareous

sandsand

Kilindi SandsKilindi Sands

PliocenePliocene Marafa BedsMarafa Beds White sand, red White sand, red sand, clay, pebblessand, clay, pebbles

L MioceneL Miocene Baratum Baratum BedsBeds

marls, sand, clay, marls, sand, clay, conglomerates, conglomerates, limestonelimestone

Fundi Isa Fundi Isa BedsBeds

limestonelimestone

Kenyan Stratigraphy - Kenyan Stratigraphy - ContinentalContinental

AgeAge Formation Formation ComponentsComponents

M M PleistocenePleistocene

KanjeraKanjera Ashes, clay, Ashes, clay, limestonelimestone

RawiRawi Clay, gravel, volcanic Clay, gravel, volcanic SSSS

KanamKanam Clay, gravel, ashClay, gravel, ash

L MioceneL Miocene Kiaherra Kiaherra SeriesSeries

tuffs, limestone, grit, tuffs, limestone, grit, pisolithic earthpisolithic earth

HiwegeiHiwegei Red clay, boulders, Red clay, boulders, limestonelimestone

Kathawant PointKathawant Point Dull, flaggy Dull, flaggy mudstonesmudstones

KathawanageKathawanage mudstone, mudstone, sandstonesandstone

Mpesida BedsMpesida Beds

Miocene ageMiocene age Volcanoclastic horizons interbedded with Volcanoclastic horizons interbedded with

trachytic flowstrachytic flows Examination of three sites helped reveal Examination of three sites helped reveal

Miocene conditions, time when humans Miocene conditions, time when humans were evolvingwere evolving

Chimps and humans split 6-5 Mya, Miocene Chimps and humans split 6-5 Mya, Miocene starts ~ 5 Myastarts ~ 5 Mya

Mpesida BedsMpesida Beds

Site 1:Site 1: Pyroclastic rock is massive, unsorted, Pyroclastic rock is massive, unsorted,

entirely ashentirely ash contains silicified woodcontains silicified wood Fossil trees are up to 50 m tallFossil trees are up to 50 m tall

Indicative of a wet forestIndicative of a wet forest

From Kingston et al. 2002

Mpesida BedsMpesida Beds Site 2:Site 2:

Pyroclastic layer that is grey to buff colored, Pyroclastic layer that is grey to buff colored, coarse sandstonecoarse sandstone

Vertebrate fossils confined to this layerVertebrate fossils confined to this layer Shows new families establishing themselves in Shows new families establishing themselves in

Sub-Saharan AfricaSub-Saharan Africa Savannah and forest environmentsSavannah and forest environments

Site 3: Site 3: Lacustrine facies of clays, silts, fine sandstone Lacustrine facies of clays, silts, fine sandstone

interbedded with diatomiteinterbedded with diatomite A hiatus from volcanic activityA hiatus from volcanic activity

Fossil Mammals of Great Rift Fossil Mammals of Great Rift ValleyValley

1) http://www.answers.com/topic/deinotherium

3) http://paleo.amnh.org/bjburger/fossilmammal/u3.html

2) http://www.ucmp.berkeley.edu/mammal/eutheria/creodonta.html

Creodont2

Chalicotherium3Deinotherium1

Fossil Mammals of Great Rift Fossil Mammals of Great Rift ValleyValley

3) http://www.nature-wildlife.com/girskel08.html

2) http://www.crockerfarm.org/ac/rm02/pratt99/pratt99mammals.htm

1) http://www.nature-wildlife.com/girskel11.html

Hippopotamus1

Leporid3

Equus2

Fossil Mammals of Great Rift Fossil Mammals of Great Rift ValleyValley

2) http://www.achievement.org/autodoc/photocredit/achievers/joh1-0213) http://en.wikipedia.org/wiki/Homo_rudolfensis

1) http://www.oursci.org/magazine/200108/010814.htm

Orrorin turgenensis1

Australopithecus afarensis2

Homo rudolfensis3