1. The Pleistocene Epoch The Ice Age
Earth History GEOL 2110
The Pleistocene Epoch The Ice Age

2. 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.

3. The Great Cenozoic Cool Down
Thermal Threshold

4. 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
Jura Mtns
Swiss Plains
Swiss Alps

5. Louis Agazzi – Father of Continental Glaciation Theory (1840)
The Swiss-born naturalist came to the U.S. in the mid-1800’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 ( )

6. The Last Peak of Glaciation 20,000ybp
Siberian Desert
Continental Shelves Exposed
Tropical Belt
Shrinks, but same climate

7. The Last Peak of Glaciation 20,000ybp
Continental Shelves Exposed
Missouri and Ohio – Pro-glacial Drainage Pathways of Glacial Meltwaters
Semi-arid desert - Loess

8. Effects of Glaciation Isostatic Rebound

9. Effects of Glaciation Sea Level Change
Minimum – 140m
Maximum + 65m

10. Effects of Glaciation Sea Level Change
River Terraces Develop as Base Levels Drop in Steps

11. 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

12. Effects of Glaciation Large Meltwater Lakes

13. Effects of Glaciation Wind-blown Silt - Loess
Loess Hills of Western Iowa
Palouse Loess of Southeastern Washington

14. 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)

15. The Current Glacial Stratigraphy

16. Correlating Glacial Episodes

17. Correlating Glacial Episodes Ice Cores from Greenland and Antarctica

18. Correlating Glacial Episodes Ice Cores from Greenland and Antarctica

19. Correlating Glacial Episodes Lake Sediment Cores
North Atlantic sediment core
Greenland ice core
% cold water
foram species
Ice rafted
debris
warm
cold
Piston Coring

20. Last 650,000 yrs of Glacial Cycles
Antarctic Record
380!
Current CO2 level

21. Why the Cycles? Possible Factors Changes in Solar Radiation
Orbital Effects
Changes in Atmospheric Transparency
Changes in Reflectivity – Albedo
Paleogeographic Controls of Climate
Changes to Ocean Currents
Can’t Test
Volcanism not apparently more prevalent in Pleistocene

22. Why the Cycles? Orbital Effects
Milankovitch Cycles

23. Why the Cycles? Orbital Effects

24. What Brought us to the Thermal Threshold?

25. 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

26. What Brought us to the Threshold? Changes in Paleogeography

27. The Thermohaline Conveyer Belt
Brings warm waters to the Arctic

28. The Younger Dryas Small Scale (1,000 y) Cycles

29. Fresh Meltwaters Shut Down the Conveyor
Catastrophic
Glacial Calving

30. Next Lecture The Pleistocene Epoch The Ice Age in Minnesota Read MN at a Glance – Quaternary Geology