The Quaternary Period

1. The Quaternary Period • 1.64 Ma • Only 38 seconds long!

2. Cenozoic Time Scale

3. Pleistocene—Holocene Tectonism and Volcanism • Best known for glaciation • but also a time of volcanism and tectonic activity • Continuing orogeny • Himalayas • Andes Mountains • Deformation at convergent plate boundaries • Aleutian Islands • Japan • Philippines

4. Uplift and Deformation • Interactions between • North American and Pacific plates • along the San Andreas transform plate boundary • produced folding, faulting, and a number of basins and uplifts • Marine terraces • covered with Pleistocene sediments • attest to periodic uplift in southern California

5. Marine Terraces • marine terraces on San Clemente Island, California • each terrace represents a period when that area was at sea level • highest terrace is now about 400 m above sea level

6. N Ca marine terraces

7. Cascade Range • Ongoing subduction of remnants of the Farallon plate • beneath Central America and the Pacific Northwest • account for volcanism in these two areas • The Cascade Range • of California, Oregon, Washington, and British Columbia • has a history dating back to the Oligocene • but the large volcanoes now present formed during the last 1.6 million years

8. Lassen Peak—Lava Dome • Lassen Peak, a large lava dome, • formed on the flank of an older, eroded composite volcano in California about 27,000 years ago • It erupted most recently from 1914 to 1917

9. Pleistocene Stratigraphy • Began 1.6 Ma • Ended 10,000 years ago • Pleistocene-Holocene (Recent) boundary • Based on • climate change to warmer conditions concurrent with melting of most recent ice sheets • oxygen isotope ratios determined from shells of marine organisms • changes in vegetation

10. Glaciers in North America

11. Glaciers in Europe

12. Four Glacial Stages • Detailed mapping reveals several glacial advances and retreats • North America had at least four major episodes of Pleistocene glaciation • Each advance was followed by warmer climates • The four glacial stages • Wisconsin • Illinoian • Kansan • Nebraskan • named for the states of the southernmost advance

13. Four Glacial Stages

14. How Many Stages? • Recent detailed studies of glacial deposits indicate • there were an as yet undetermined number of pre-Illinoian glacial events • history of glacial advances and retreats in North America is more complex than previously thought

15. Correlation • six or seven major glacial advances and retreats are recognized in Europe • at least 20 major warm–cold cycles can be detected in deep-sea cores • Why isn't there better correlation among the different areas if glaciation was such a widespread event? • chaotic sediments difficult to correlate • minor fluctuations

16. Evidence for Climatic Fluctuations • Changes in surface ocean temperature • recorded in the O18/O16 ratio in the shells of planktonic foraminifera • provide data about climatic events

17. Oxygen Isotope Ratio

18. Onset of the Ice Age Today 10,000 QUATERNARY ~2 Ma - Northern Hemisphere CENOZOIC ERA ~30 Ma - West Antarctic ~45 Ma - East Antarctic 60 Ma Cenozoic Glaciations

19. Why the Icehouse? • Long-term climate drivers: • Plate tectonics • Opening/closing of seaways • Ocean currents are our heat and AC • Uplift and erosion of mountains • Weathering reduces atmospheric CO2 • Life: catastrophic evolution of new capabilities • O2 • Astronomical drivers • Other bodies (moon, sun) pull on the Earth, changing its distance to the sun

20. Why the Pleistocene Icehouse ? • Long-term tectonic driver: • Redirection of ocean currents: • Isolation of Antarctica • Collision of N and S America • New mountains = more weathering • Mineral weathering reduces atmospheric CO2 • less CO2 = less greenhouse effect

21. Antarctica became isolated:– ocean circulation changes, cools

22. Why the Icehouse? • Shut off E/W global ocean flow Isthmus of Panama: North & South American plates collided ~ 3.5 Ma

23. Glaciers need precipitation Caribbean warms Gulf Stream moves warm water north Increases ocean evaporation and precipitation on land

24. Pleistocene Underway • By Middle Miocene time • an Antarctic ice sheet had formed • accelerating the formation of very cold oceanic waters • About 1.6 million years ago • continental glaciers began forming in the Northern Hemisphere • The Pleistocene Ice Age was underway

25. But we didn’t just get ONE ice age… You Are Here!

26. We got dozens of them.

27. The Milankovitch Theory • Put forth by the Serbian astronomer • Milutin Milankovitch while interned by Austro-Hungarians during WWI • Minor irregularities in Earth's rotation and orbit • are sufficient to alter the amount of solar radiation that Earth receives at 65° N • and hence can change climate • (criticism at the time: why 65° N?!?)

28. Three Variables Ellipticity • about 100,000 years

29. Axis Tilt • The angle between • Earth's axis • and a line perpendicular to the plane of its orbit around the Sun • This angle shifts about 1.5° • from its current value of 23.5° • during a 41,000-year cycle

30. Precession • Earth moves around the Sun • spinning on its axis • which is tilted at 23.5° to the plane of its orbit • Earth’s axis of rotation • slowly moves • and traces out the path of a cone in space Plane of Earth’s Orbit

31. Effects of Precession • At present, Earth is closer to the Sun in January • In about 11,000 years, closer to the Sun in July

32. Makes a tippy system

33. Convolve 100,000 + 41,000 + 26,000 years…

34. Pleistocene Glacial cycles

35. Warming Trend • 10,000-6,000 years ago, a warming trend • pollen • tree rings • ice advance/retreat • Then the climate became cooler and moister • favoring the growth of valley glaciers on the Northern Hemisphere continents • Three episodes of glacial expansion took place during this neoglaciation

36. Little Ice Age • The most recent glacial expansion • between 1500 and the mid- to late 1800s • was a time of generally cooler temperatures • It had a profound effect on • the social and economic fabric of human society • accounting for several famines • migrations of many Europeans to the New World • Local phenomenon Pieter Bruegel the Elder (1525–1569)

37. Glaciers—What Are They and How Do They Form? • Geologists define a glacier • as a mass of ice on land that moves by plastic flow • internal deformation in response to pressure • and by basal slip • sliding over its underlying surface

38. How do glaciers form? • Any area receiving more snow in cold seasons • than melts in warm seasons • has a net accumulation over the years • As accumulation takes place • snow at depth is converted to ice • when it reaches a critical thickness of about 40 m • it begins to flow in response to pressure Marguerite Bay, 2002

39. Glaciers Move • Once a glacier forms • it moves from a zone of accumulation • toward its zone of wastage • As long as a balance exists between the zones, • the glacier has a balanced budget Amundsen Sea, 1999

40. Glaciation and Its Effects • Climate itself • Sea level change • Sediments • Landforms and topography • Isostatic rebound

41. Isostatic Rebound in Eastern Canada • Uplift in meters • during the last 6000 years

42. U-Shaped Glacial Trough • This U-shaped glacial trough in Montana • was eroded by a valley glacier

43. Proglacial Lakes • Form where meltwater accumulates along a glacier's margin • Deposits in proglacial lakes • vary considerably from gravel to mud • of special interest are the finely laminated mud deposits • consisting of alternating dark and light layers • Each dark–light couplet is a varve • representing an annual deposit

44. Characteristics of Varves • Light-colored layer of silt and clay • formed during the summer • The dark layer made up of smaller particles and organic matter • formed during the winter when the lake froze over Varves with a dropstone

45. Moraines • Most important glacial deposits • chaotic mixtures of poorly sorted sediment deposited directly by glacial ice • An end moraine is deposited • when a glacier’s terminus remains stationary for some time Mt. Cook, 1999

46. Recessional Moraine • If the glacier’s terminus • should recede and then stabilize once again • another end moraine forms • known as a recessional moraine

47. Glacial Features • Features seen in areas once covered by glaciers • glacial polish • the sheen • striations • scratches? Devil’s Postpile National Monument, California

48. Glacial Sediment • Glaciers typically deposit poorly sorted nonstratified sediment

49. Cape Cod Lobe • Position of the Cape Cod Lobe of glacial ice • 23,000 to 16,000 years ago • when it deposited the terminal moraine • that would become Cape Cod and nearby islands

50. Recessional Moraine • Deposition of a recessional moraine • following a retreat of the ice front