Life Long Learning: Fall 2012
Vagabonds Tramp Eastern AfricaSession Three
“Vagabonds Tramp through Eastern Africa: where the unique geology of the East African Rifts produced the advent of the human species and the Nile flood plain
shaped the beginning of human history”
Let’s recall from last week that the great nations of human history were located in the Northern Temperate Zone, that they had extensive farmland, plus iron and coal
Then let’s apply what we’re learned to the country of Zimbabwe
First, remember the amazing geological discoveries of the last half of the 20th century
Five Amazing Geological Discoveries of the Second Half of the 20th Century
2. Continental Drift3. Absolute Age Dating4. Paleo-magnetics5. Plate Tectonics
Last week we mentioned the discovery of Oceanic Crust which is one of five amazing geological discoveries in the last half of the
20th century
1. Oceanic Crust
Continental Crust
Co
ntin
ental C
rust
Continental Crust
Oceanic Crust
Mid Ocean “ridge”
African Plate: African Continental crust
plus surrounding oceanic crust
Last week we also showed the location of the world’s great nations
Tropics
Northern Temperate Zone
Southern Temperate Zone
What we’ll try to get you to believe in the next 5 weeks
First Empires (farming major river flood plains)
Green hills lands with Fe and Coal (invade farming lands)
Conclusions on what is required for a land to become a world power1. Continental drift and plate tectonic put Eurasia in the ideal
location for early farming empires2. Plate tectonics (mountain building) exposed Fe and Coal in
hill lands initiating conflict with farming empires (except in China)3. No world powers or sustainable religions have or will be
developed in the tropics or the southern in the southern temperate zone
Where did the world-wide religions originate?
Tropics
Northern Temperate Zone
Southern Temperate Zone
What we’ll try to get you to believe in the next 3 weeks
First Empires (farming major river flood plains)
Green hills lands with Fe and Coal (invade farming lands)
Where did the world-wide religions originate?
Judaism
HinduismConfucianismBuddhism
ChristianityMohammedism
Conclusions: Geological events that shape human history are;Continental driftPlate tectonicsAbsolute age datingPaleo-magneticsNatural resources of farm land, iron, coal, and oil
Then let’s see if this can be applied to the country of Zimbabwe
But first let’s see where the greatest concentrations of iron and coal are located
Tropics
Northern Temperate Zone
Southern Temperate Zone
What we’ll try to get you to believe in the next 3 weeks
First Empires (farming major river flood plains)
Green hills lands with Fe and Coal (invade farming lands)
Where are the greatest concentrations of Iron & Coal?
Judaism
HinduismConfucianismBuddhism
ChristianityMohammedism
Conclusions: Geological events that shape human history are;Continental driftPlate tectonicsAbsolute age datingPaleo-magneticsNatural resources of farm land, iron, coal, and oil
Now let’s see if this can be applied to the country of Zimbabwe
Course definition of eastern Africa
Focus on Zimbabwe
Tropics
What rocks are at the surface in Zimbabwe?
Geologic Map of Africa Shows the age of rocks at the surface
Zimbabwe
500 million year old rocks at the surface
Tropics
Geologic Map of Southern Africa Focus on Zimbabwe
Zimbabwe
500 million year old rocks at the surface
Remember that rivers historically are important for farming. Are there rivers in Zimbabwe that support large scale farming?
Tropics
Zimbabwe
Tropics
Zimbabwe
Tropics
Zambezi River
Limpopo River
Tropics
Zimbabwe
River drainage divide
Conclusion: No major river flood plains
But let’s look at the topographic map
Limpopo River
Zambezi River
Zimbabwe
Tropics
What are the rocks like at the surface in Zimbabwe?
Very complex geology
What are the archeological historic ages &the geological ages of geology?
Geological Map of ZimbabweGeologic Maps show age and rock type at the surface if all soil
& vegetation were removed
Note that the Limpopo drainage has the most very old rocks
Major river drainage divide line
Geologic Ages of Historic TimeGeologic Ages of Historic Time
Iron, Coal, Petroleum, & Uranium Age 1950 to PresentIron, Coal, Petroleum, & Uranium Age 1950 to PresentIron, Coal, & Oil AgeIron, Coal, & Oil Age 1900 to 1950 AD 1900 to 1950 AD
Iron & Coal: Industrial Age 1700 to 1830 ADIron & Coal: Industrial Age 1700 to 1830 ADIron & Coal: RenaissanceIron & Coal: Renaissance
1450 to 1700 AD1450 to 1700 ADIron & Coal: Middle AgesIron & Coal: Middle Ages
470 to 1450 AD 470 to 1450 ADIron Age 2 Rome to 470 ADIron Age 2 Rome to 470 AD
750 BCE750 BCEIron Age 1 GreeceIron Age 1 Greece 1400 to 750 BCE 1400 to 750 BCEBronze AgeBronze Age 3300 to 1400 BCE 3300 to 1400 BCE
Copper AgeCopper Age 3300 to 3000 BCE 3300 to 3000 BCEStone Age (end of Ice Age) 70,000 to 3300 BCEStone Age (end of Ice Age) 70,000 to 3300 BCE
Copper, tin, arsenic, & zinc
Flint & Obsidian
Iron Age
Iron-Coal Age
Iron, Coal, Oil AgeNow the geologic ages of the 4.8 billion year
old Earth
Large scale Farming
Geologic Time: 4.8 Billion Years
Pre-Cambrian
570 million to 4.9 billion years
ago
Age of most rocks at the surface in ZimbabweVery old, may have metal ores
What are the natural resources of Zimbabwe, is there farm-land, iron, and coal in Zimbabwe?
The natural resources of southern Africa
Focus on Zimbabwe
Coal
Iron
The natural resources of Zimbabwe
Farmland
Grazing land
Tropics
Conclusions: Even thought Zimbabwe is in the Tropics, it is high enough to be largely
above jungle and it has significant farm land plus iron and coal that could support the
development of a important nation.
What does Google-earth show us about the farm and grazing land of Zimbabwe?
Google-Earth: Southern Africa
Zimbabwe
Limpopo River
Zambezi River
Carving Landscapes (topography)Destruction of the Continental Crust
Focus on possible farming areas in Zimbabwe
Focus on possible farming areas in Zimbabwe
Focus on this province
Focus on possible farming areas in Zimbabwe
Note: no farming in river flood plain but all the surrounding hills are cultivated
Back to the regional view and another possible area of farming
Focus on this province
The regional view and another possible area of farming
Again the river flood plain is not cultivated but the surrounding hills are completely farmed
Conclusion: Zimbabwe, Southern Rhodesia, though in the Tropics has great potential for becoming a prosperous nation
based on its natural resources
What geological processes created this topography of Zimbabwe?
Carving Landscapes (topography)Destruction of the Continental Crust
Geologic ProcessesWeathering & Erosion
Destruction of rocks which creates soil, rock debris, & topography 28
WEATHERING;What are the products of weathering
Rock Debris:Size classification;
Boulders, cobbles, gravel, pebbles, sands, and mud
Rock “Solutions”Composition; Debris:
Quartz Sand (silica) Muds (clays: hydrous Al Silicates) Solutions (mostly Ca, C, O) 29
WEATHERING: How is it done?
Water!!!
Sun Light
Heating and Cooling
Natural Acids
TIME TIME TIME30
WEATHERING: How is it done?
Water!!!
Abrasion by: Falling RainFlowing Streams and Rivers
31
WEATHERING: How is it done?
Water!!!
Sun Light (radiation)
32
WEATHERING: How is it done?
Water!!!
Sun Light
Heating and Cooling daily expansion and contraction
33
WEATHERING: How is it done?
Water
Sun Light
Heating and Cooling
Natural AcidsAcid Rain (natural)
Humic Acid (plant decay)34
WEATHERING: How is it done?
Water!!!
Sun Light
Heating and Cooling
Acids
GEOLOGIC TIME
Erosion: Erosion: Creating Topography & SoilsCreating Topography & Soils
Disposing of the weathered debris atDisposing of the weathered debris at the margins of continentsthe margins of continents
Exposing different rocks & resourcesExposing different rocks & resources
35
An example from Central Texas
Sun City &Lake Georgetown
Erosion in Williamson County TodayErosion in Williamson County Today
More rock erodedMore rock eroded than remains!than remains!
36
Land surface today
Summary: The fate of all rocks at the earth’s surface
The Fate of All Rocks at the Earth’sThe Fate of All Rocks at the Earth’s Surface: Surface:
Destruction by Weathering & ErosionDestruction by Weathering & Erosion
Weathering of: Weathering of: Igneous Rocks=Clays & SandIgneous Rocks=Clays & Sand
Metamorphic Rocks=Clays & SandMetamorphic Rocks=Clays & Sand
Sedimentary Rocks=Clays, Sand, &Sedimentary Rocks=Clays, Sand, &Calcium SolutionsCalcium Solutions
37
The Fate of All Rocks at the Earth’sThe Fate of All Rocks at the Earth’s Surface: Surface:
Destruction by Weathering & ErosionDestruction by Weathering & Erosion
Erosion: Erosion: Moving weathered debris to theMoving weathered debris to the oceans at continental margins:oceans at continental margins: Clays, Sand and Calcium SolutionsClays, Sand and Calcium Solutions38
Erosional debris broughtto the Indian Ocean by theLimpopo and Zambezi rivers
Thick erosional debris deposited in the ocean at the continental margin is called a geosyncline
How thick is the sedimentary debris in a geosyncline?
Geosyncline Debris Thicknesses
Sea Level
Continental Crust
Oceanic Crust; 5 miles thick
Ocean 3 miles deep
Debris thickness = 3 miles (15,000 feet) if we just fill the ocean
How thick is the river debris?
Let’s look at the Niger River Debris
Niger River Delta: Geological Cross Section
The top of the oceanic crust has been depressed from 3 miles deep to 8 miles deep! This huge debris mass is called a geosyncline
Ocean3 miles deep
Niger Geosynclinal debris12, 000 meters = 40,000 feet= 8 miles thick
Let’s look at the Gulf of Mexico geosyncline as a well known example of a geosyncline
Example of a Geosyncline:Gulf of Mexico
1. Integration of the debris of several rivers
Modern Sediment
Accumulations
Swamp Muds
Shallow water Sands
Deep water Muds
2. Accumulation of thick layers of debris
New Orleans
Subsurface Cross Sections Gulf of Mexico Geosyncline
Austin
Sun City
Gulf of Mexico Geosyncline
MatureSourceRocks
SandstoneReservoirRocks
3. Accumulation of thick layers of debris
65,
00
0 fe
et t
hic
k Shale SourceRocks
Gulf ofMexico
New Orleans
Subsurface Cross Sections Gulf of Mexico Geosyncline
Sun City
Gulf of Mexico Geosyncline
SourceRocks
MatureSourceRocks
4. Expulsion & Up-dip Migration of gas first, then oil, & finally gas
Gas
Gas
OilFinally, Trapping of Migrating Oil & Gas
New Orleans
Subsurface Cross Sections Gulf of Mexico Geosyncline
Sun City
Gulf of Mexico Geosyncline
Muds in bays &
swamps
Sands at b
each & shelf
Sands & Muds m
ixed
Deep water Muds
5. Trapping of Migrating Oil & Gas
The Initial, Soft SedimentsNow a cross section of these sediments converted into Rocks
Subsurface Cross Sections Gulf of Mexico Geosyncline
Gulf of Mexico Geosyncline
Shales
Sandstone re
servoirs
Sandstone & Shales
4. Trapping of Migrating Oil & GasNow a map of these sediments converted into Rocks
Star=Trap
Source shales
Lignite and Coal
Reservoir Rocks
Mixed Source &
Reservoir Rocks
Source Rocks
Limestones
5. Trapping of Migrating Oil & Gas
Conclusion: Geosynclines are primary sites for the accumulation of oil & gas
What is the “fate” of all geosynclines?
IllinoisIllinois OhioOhio PennsylvaniaPennsylvania VirginiaVirginia
Mountain Building: Crushing& melting of the geosyncline
Appalachian Example
Flat LimestonesFlat Limestones Gently dippingGently dippingSands & ShalesSands & Shales
FoldedFoldedSands &Sands &ShalesShales
Crushed &Crushed &MeltedMeltedGeosynclinalGeosynclinalRocks form aRocks form aMountains rangeMountains rangeFuture MountainsFuture Mountains
welded ontowelded onto continentcontinent
Now let’s apply what we’ve learned to Africa
Weathering is destroying the continent and erosion is moving the debris to the oceans atthe continental margins
The major and minor rivers of Africa that move debris to the continental margins
Today’s African geosynclines
Tropical Climate Zone
Remember: No world nation or sustained religion has ever developed in the TropicsWhat is the fate of all geosynclines?
The Big Rivers create thick deposits ofsand and mud called a geosynclines in the oceans at their deltas
Building a newMountain Range by melting & crushing of the sediments in the geosyncline
The Fate of Every Geosyncline: Mountain Building
Crushing and Melting a Geosyncline
Building a newMountain Range by melting & crushing
Collision of an Oceanic Plate with a Continental Plate
Mountain BuildingOriginal Geosyncline
ContinentalCrust
OceanicCrust
Ocean
ThickSediments
Thick debris accumulation at the margin of the continent
Note the dislocation of the contact between the Oceanic & and Continental Crust
When the Geosyncline exceeds a critical thickness, here’s what happens!
Melting of a geosyncline
Hot molten magma from the mantel rocks
Mountain BuildingEarly Stage: Geosyncline being crushing &
partially melting formingBasalt, Granite, & Rhyolite
BasaltGranite
OceanicCrust
ContinentalCrust
Heat from colliding crustal plates melts the base of the Oceanic crust and the “face” of the Continental crust
And then!!!!
Mountain BuildingBasaltic Island Arc and Granite Strato
VolcanoesBasalticIslandArc
RhyoliteStrato Volcano
A chain of volcanoes erupts: transferring material up through the sediments of the Geosyncline
And finallyGeosynclinal deposits being melting and welded back into the continent
Mountain BuildingGeosyncline Melted and Crushed
Welded ontocontinent
New mountain Range
The Geosyncline is welded onto the continent forming a new mountain range, and thus RENEWING the eroded continental land mass
What would happen if the continents were not renewed periodically?
The continents would be eroded down to slightly below sea level!
What would happen if the continents were not renewed periodically?
A Worldwide Ocean! No land: no plants, no animals, no us
In addition to renewing the continents, mountain building brings metallic ores, coal, and oil deposits to or near the surface
Mountain BuildingGeosyncline Melted and Crushed
Welded ontocontinent
New mountain Range
MetalsDistilled here
Metallic OresDeposited Here
Coal formed here
Modern Geosynclines of the Eurasia
NileNile
IndusIndus
From: Hammond Atlas, 1972From: Hammond Atlas, 1972
GangesGanges
YellowYellowYangtze Yangtze
Tigris Tigris Euphrates Euphrates
Nile Nile
Modern Geosynclines of the Eurasia
Potential Oil Sources and Future Mountains
Now back to Africa and the country of Tanzania
Regional View of Southern Africa
Zimbabwe
Tanzania
Ruvuma River
Tanzania
Ruvuma River