Historical Geology 102
Cenozoic Era II


Cenozoic Era

Quaternary Period
Ice Ages - extensive continental glaciation in northern and southern hemispheres
Estimated 40 million km3 snow and ice
Period of cooling began ~35 m.y. ago - Oligocene
Glaciers begin development in Antarctica

Pleistocene - 1.6 m.y. to 10,000 yr

Main period of glaciation
Traditionally the Pleistocene was defined to start at the time of glaciation
Modern definition is based on fossil evidence
On land - first appearance of modern horse and elephant
Marine - disappearance of discoaster (plankton)
Widespread glaciation begins 1 m.y. ago
Pleistocene Paleogeography

End of the Pleistocene

End of glaciation - 10,000 years ago
Disappearance of continental glaciers from mid-latitudes
These glaciers are still present at high latitudes

Glaciers

Glacier - large mass of flowing ice
Form from the build up of snow
Glaciers will only form if snow fall in winter is greater than snow melt in summer
Pressure from overlying layers will compress earlier snow layers into ice
Under pressure, ice will flow like a viscous fluid
Flow is down hill, or away from the zone of accumulation
Glacial ice always flows away from the zone of accumulation
Glaciers will advance if accumulation is greater than melting
Glaciers will retreat if melting is greater than accumulation

Glacial Types

Alpine glaciers
- occur in mountainous terrains
- confined to valleys
Continental glaciers
- large ice sheets that cover all but the highest peaks of a continent
- Greenland and Antarctica
- only present day continental glaciers
Ice Shelf
- floating ice sheet

Pleistocene Glaciation

Glacial cycles - advance and retreat of the glaciers
Evidence for these is found in glacial landforms and deposits in N. America and Europe, ice cores, and marine sediments
Europe - 3 to 6 cycles
N. America - 4 cycles
Marine sediments and ice cores - 30 cycles

North American Glacial Cycles

Nebraska Cycle
- 2.1 to 1.7 m.y.
- advanced to Nebraska and northern Missouri
Kansas Cycle
- 1.3 to 0.9 m.y.
- advanced to KS, NE, MO, IL, IN, OH
Illinoian Cycle
- 0.7 to 0.3 m.y.
- advanced to IL, IN, OH
Wisconsin Cycle
- 75,000 to 10,000 yr
- advanced to WI, SD

Causes of Pleistocene Glaciation

Milankovitch Cycle
Milutin Milankovitch, Yugoslav mathematician
Proposed a theory which explained the glacial period based on variations in Earth's orbital position and orientation

Milankovitch Cycle Variables

1) Axial tilt
- currently 23.5 degrees
- can vary between 22 and 24 degrees
- period of 41,000 years
2) Precession
- currently axis points at Polaris
- axis "wobbles" like a spinning top
- period of 26,000 years
3) Orbital Eccentricity
- orbits of the planets are ellipses
- variations can increase the eccentricity

Combination of these variation results in periods when the intensity of solar radiation flucuates in the middle to high latitudes. These flucuations can then result in periods of global cooling or warming.
Comparison of the Milankovitch cycle with glaciation over the past 100,000 years results in a very close match

Albedo

Amount of solar radiation reflected from the Earth's surface
~33% of solar radiation is currently reflected
Calculations show that a 1% increase in albedo could lead to an 8° C drop in temperature
Increased albedo can be caused by - increased snow/ice cover, volcanic ash

Continental Location

Based on the location of the continents and relative to polar regions
Antarctica is presently located at the South Pole
Most of the continental land masses are located in the Northern Hemisphere
Cooler T promotes retention of snow on land
Increased snow = increased albedo = decreased temperature
Glaciers advance
Eventually water supply is cut off as Arctic Ocean freezes over
Glaciers retreat
Repeat cycle as water becomes available once Arctic Ocean melts

Himalaya Theory

Formation of the Himalayas results in the development of the Monsoons
Heavy seasonal precipitation
Washes CO2 out of the atmosphere
Decreases the Greenhouse Effect and results in cooler global temperatures.

Ice Age

Have the Ice Ages ended or is this simply an interglacial period?
How will increased levels of CO2 affect this cycle?

Global Tectonic Events

Two major tectonic events
Formation of the Alps in Europe
Formation of the Himalayas in Asia

Plate tectonic motions during the past 200 million years.
This link requires that Java be enabled on your computer. Once the applet is loaded click and hold your mouse pointer on the image. Move the mouse to the left to go forward in time, to the right to back in time. WARNING - This may take a long time to load but is worth the wait.

Pay close attention to the development of the Alpine and Himalayan orogenies.

Alpine Orogeny

Zone of deformation along southern margin of Europe from Spain to Turkey
Began in the Mesozoic
Major period of deformation from Eocene to late Miocene
Continental collision as Africa/Arabia moved northward into Europe

Himalayan Orogeny

India splits away from Africa - early Cretaceous - and drifts northward
Oceanic crust between India and Asia is subducted beneath Asia
- results in a volcanic arc
India collides with Asia
Collision begins 40-50 m.y. ago
~2000 km of India thrust beneath Asia
Asia overrides India forming Himalaya Mountains
Collision continues today
India is still moving northward at a rate of 5 cm/y