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1.64 Ma Only 38 seconds long! The Quaternary Period.

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Presentation on theme: "1.64 Ma Only 38 seconds long! The Quaternary Period."— Presentation transcript:

1 1.64 Ma Only 38 seconds long! The Quaternary Period

2 Cenozoic Time Scale

3 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 Pleistocene—Holocene Tectonism and Volcanism

4 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 Uplift and Deformation

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 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 Cascade Range

8 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 Lassen Peak—Lava Dome

9 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 Pleistocene Stratigraphy

10 Glaciers in North America

11 Glaciers in Europe

12 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 Four Glacial Stages

13

14 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 How Many Stages?

15 –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? Correlation chaotic sediments difficult to correlate minor fluctuations

16 Changes in surface ocean temperature –recorded in the O 18 /O 16 ratio in the shells of planktonic foraminifera –provide data about climatic events Evidence for Climatic Fluctuations

17 Oxygen Isotope Ratio

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

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

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

24 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 Pleistocene Underway

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

26 We got dozens of them.

27 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?!?) The Milankovitch Theory

28 Three Variables about 100,000 years Ellipticity

29 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 Axis Tilt

30 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 Precession Plane of Earth’s Orbit

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

32 Makes a tippy system

33 Convolve 100, , ,000 years…

34 Pleistocene Glacial cycles

35 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 Warming Trend

36 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 Little Ice Age Pieter Bruegel the Elder (1525–1569)

37 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 Glaciers—What Are They and How Do They Form?

38 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 How do glaciers form? Marguerite Bay, 2002

39 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 Glaciers Move Amundsen Sea, 1999

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

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

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

43 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 Proglacial Lakes

44 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 Characteristics of Varves Varves with a dropstone

45 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 Moraines Mt. Cook, 1999

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

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

48 Glaciers typically deposit poorly sorted nonstratified sediment Glacial 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

51 Cape Cod By about 6000 years ago –the sea covered the lowlands –between the moraines –and beaches and other shoreline features formed

52 Today, between 28 and 35 million km 3 of water –frozen in glaciers During the maximum extent of Pleistocene glaciers –more than 70 million km 3 of ice These huge masses of ice contained enough frozen water –to lower sea level by 130 m Changes in Sea Level

53 Large areas of today's continental shelves were exposed The Bering Strait exposed –Alaska connected with Siberia via a broad land bridge –Native Americans and various mammals, such as the bison, migrated Land Bridge

54 Sea level would rise about 70 m –many of the world's large population centers would be flooded What would happen if all glaciers melted?

55 Where is all that ice? 66 m is in Antarctic a

56 Isn't it stable? We can watch it breaking up

57 Anderson et al., 2002 Change is ongoing

58 Difficult to Predict


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