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Earth History GEOL 2110

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.

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Earth History GEOL 2110

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  1. Earth History GEOL 2110 The Pleistocene EpochThe 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 (1807-1873)

  6. The Last Peak of Glaciation20,000ybp Siberian Desert Continental Shelves Exposed Tropical Belt Shrinks, but same climate

  7. The Last Peak of Glaciation20,000ybp Continental Shelves Exposed Missouri and Ohio – Pro-glacial Drainage Pathways of Glacial Meltwaters Semi-arid desert - Loess

  8. Effects of GlaciationIsostatic Rebound

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

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

  11. Effects of GlaciationLarge 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 GlaciationLarge Meltwater Lakes

  13. Effects of GlaciationWind-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 EpisodesIce Cores from Greenland and Antarctica

  18. Correlating Glacial EpisodesIce Cores from Greenland and Antarctica

  19. Correlating Glacial EpisodesLake 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? 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 DryasSmall Scale (1,000 y) Cycles

  29. Fresh Meltwaters Shut Down the Conveyor Catastrophic Glacial Calving

  30. Next LectureThe Pleistocene EpochThe Ice Age in MinnesotaRead MN at a Glance – Quaternary Geology

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