The Quaternary Period 1 64 Ma Only 38

The Quaternary Period • 1. 64 Ma • Only 38 seconds long!

Cenozoic Time Scale

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

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

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

N Ca marine terraces

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

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

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

Glaciers in North America

Glaciers in Europe

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

Four Glacial Stages

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

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

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

Oxygen Isotope Ratio

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

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 CO 2 – Life: catastrophic evolution of new capabilities – O 2 – Astronomical drivers • Other bodies (moon, sun) pull on the Earth, changing its distance to the sun

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 CO 2 • less CO 2 = less greenhouse effect

Antarctica became isolated: – ocean circulation changes, cools

Why the Icehouse? • Shut off E/W global ocean flow Isthmus of Panama: North & South American plates collided ~ 3. 5 Ma

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

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

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

We got dozens of them.

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? !? )

Three Variables Ellipticity • about 100, 000 years

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

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

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

Makes a tippy system

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

Pleistocene Glacial cycles

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

Little Ice Age • The most recent glacial expansion – between 1500 and the mid- to late 1800 s – 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)

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

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

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

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

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

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

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

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

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

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

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

Glacial Sediment • Glaciers typically deposit poorly sorted nonstratified sediment

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

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

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

Changes in Sea Level • 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

Land Bridge • 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

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

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

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

Change is ongoing Anderson et al. , 2002

Difficult to Predict