Earth History
GEOL 2110
The Pleistocene Epoch
The Ice Age
Major Concepts
• The gradual cooling evident in the mid to late Cenozoic
reached a critical threshold which triggered extensive
glaciation around 1.8 Ma.
• Causes for this general cool down are not generally
agreed upon but seem to be related to the dispersal and
enlargement of the continents (relative to ocean areas)
and thermal isolation of the polar regions.
• Multiple cycles of advance and retreat (with periods of
about 100,000 yrs most recently) appear to be related to
earth’s orbital motions (orbital eccentricity & axial
wobble.
• These glacial cycles have had a profound global effect on
climate, sea level changes, land elevation, distribution of
lakes and rivers, and the ecology of the land.
The Great Cenozoic Cool Down
Thermal Threshold
Recognition of Continental Glaciation
Drift, Erratics, and Moraines
• Hutton (1795) suggests Alpine
glaciers more extensive than today
• Esmark (1824) first to propose
continental glaciation of N Europe
• Venetz-Sitten & de Charpentier
(1830) confirm Alpine glaciers
extended to the Swiss Plain
Louis Agazzi – Father of Continental
Glaciation Theory (1840)
The Swiss-born naturalist came to the U.S. in the mid1800’s and founded the Museum of Comparative Zoology
at Harvard. Ichthyologist, paleontologist, geologist,
Agassiz mounted the first significant scientific expedition
on Lake Superior in the summer of 1848, delivering 12
papers describing his findings at the first annual meeting
of the American Association for the Advancement of
Science that fall.
Louis Agassiz (1807-1873)
The Last Peak of Glaciation
20,000ybp
Continental
Shelves
Exposed
Tropical
Belt
Shrinks,
but same
climate
Siberian Desert
The Last Peak of
Glaciation
20,000ybp
Continental
Shelves
Exposed
Missouri and Ohio –
Pro-glacial Drainage
Pathways of Glacial
Meltwaters
Semi-arid
desert - Loess
Effects of Glaciation
Isostatic Rebound
Effects of Glaciation
Sea Level Change
Minimum – 140m
Maximum + 65m
Effects of Glaciation
Sea Level Change
River Terraces Develop as Base Levels Drop in Steps
Effects of Glaciation
Large Meltwater Lakes
Ice
Dam
Lava
Dam
Potholes
Channeled Scablands of the Columbia Plateau
Carved 18,000ybp by catastrophic outletting of
Glacial Lake Missoula. Water velocities likely
topped 50 mph
Effects of Glaciation
Large Meltwater Lakes
Effects of Glaciation
Wind-blown Silt - Loess
Loess Hills of Western Iowa
Palouse Loess
of Southeastern
Washington
Dating Glacial Episodes
Techniques:
C14 isotopic dating (<80,000y)
Fission Track in obsidian
K-Ar isotopic dating (>100,000y)
Th-Pr dating of clays (<300,000)
The Current Glacial Stratigraphy
Correlating Glacial Episodes
Correlating Glacial Episodes
Ice Cores from Greenland and Antarctica
Correlating Glacial Episodes
Ice Cores from Greenland and Antarctica
Correlating Glacial Episodes
Lake Sediment Cores
Greenland ice core
warm
Piston Coring
cold
North Atlantic sediment core
Ice rafted
debris
% cold water
foram species
Last 650,000 yrs of Glacial Cycles
Antarctic Record
380!
Current CO2 level
Why the Cycles?
Possible Factors
• Changes in Solar Radiation Can’t Test
• Orbital Effects
• Changes in Atmospheric Transparency
• Changes in Reflectivity – Albedo
• Paleogeographic Controls of Climate
• Changes to Ocean Currents
Volcanism not apparently more prevalent in Pleistocene
Why the Cycles?
Orbital Effects
Milankovitch Cycles
Why the Cycles?
Orbital Effects
What Brought us to the Thermal Threshold?
Thermal Threshold
What Brought us to the Threshold?
Changes in Reflectivity - Albedo
•Land more reflective
than Oceans
•Land area has been
growing
•Land getting higher –
more cloud cover
•Ice caps increase albedo
- feedback
What Brought us to the Threshold?
Changes in Paleogeography
The Thermohaline Conveyer Belt
Brings warm waters to the Arctic
The Younger Dryas
Small Scale (1,000 y) Cycles
Fresh Meltwaters Shut Down the Conveyor
Catastrophic
Glacial Calving
Next Lecture
The Pleistocene Epoch
The Ice Age in Minnesota
Read MN at a Glance –
Quaternary Geology