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Cenozoic Earth History

Cenozoic Plate TectonicsProgressive breakup of PangeaChanging isolation and connection of land massesSymmetrical opening of the Atlantic; mid-Atlantic ridgeAsymmetric spreading in the East Pacific Rise; Subduction of the eastern Pacific basinNorthward Movement of the Indian Plate; collision with AsiaMovement of the African Plate to cause volcanism and seismic activity of the Mediterranean and Middle East

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Cenozoic Plate Tectonics continuedRifting in East Africa; Red Sea and Gulf of AdenWestward movement of North American and South American Plates causing subduction on the Western marginsTransformation of subduction zone to San Andreas Fault System in North America

Cenozoic Orogenic Belts2 major zones: Alpine-Himalayan & circum-PacificAlpine Europe

Movement of Africa and India closed the Tethys except for the MediterraneanThrust and fold mountain building in Pyrenees and Alps made nappes; Also Atlas Mtns of AfricaOceanic crust forced beneath Turkey, Greece and Italy cause volcanos such as Vesuvius, still active; large scale eathquakes

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Cenozoic Orogenic BeltsHimalayan

Transition from volcanoes in Tibet to collision and thrust and fold mountiansOld rock of the Indian Plate is underthrustbeneath AsiaOld sedimentary rocks of Asia thrust over Indian PlateP.327 fig. 16.7

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Cenozoic Orogenic BeltsCircum-Pacific Belt

Mainly formed by subduction and related orogeny; volcanic mountains and thrusting.Japan may be complicated by back-arc spreadingCentral and South America marked by huge volcanic continental arcs e.g., the Andes North American Cordillera extends from East flank of the Rockies to the Pacific Ocean

Cenozoic Orogenic BeltsNorth American Cordillera

Sedimentary rock collected since PrecambrianPaleozoic Antler OrogenyCordilleran Orogeny consists of Nevadan (Jur.), Sevier (Cret.) and Laramide (Cret.-Eo.)Laramide Orogeny

Change in the angle of subduction to nearly horizontalSubduction of a mantle plume?Buckling of overlying crust made vertical faults with huge blocks uplifted into mountains (Rockies of Colorado)Fold and Thrust mountains to the north and south

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Cordilleran Igneous ActivityPlutonic – Paleogene intrusions bear ore deposits of southwestern USAVolcanic

Miocene lava flows of the Columbia PlateauMantle plume?

Snake river flows/ash beds proceed West to EastMantle plume now under Yellowstone National Park?

Oligocene activity in Colorado and ArizonaPliocene, Pleistocene and Holocene fields in California and ArizonaCascade Range of Pacific Northwest – e.g. Lassen Peak

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Basin and Range ProvinceNevada, extending to adjacent states and MexicoStretching and Thinning of the crust to form elongate N-S ranges and intervening basins bounded by normal faultsBack-arc spreading? Spreading of the east-pacific rise under the continent? Spreading above a mantle plume? Deformation related to San Andreas Fault system?

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Colorado Plateau and Rio Grande RiftColorado Plateau

Neogene uplift gradual enough to allow for deep river canyons such as the Grand CanyonMesozoic red beds uplifted and eroded for spectacular scenery and fossils

Rio Grande RiftMay be a North American Rift Zone in early stages

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California – San Andreas Fault Westward moving N. American plate collides with Pacific-Farallon spreading ridgeTriple junctions form transform fault that gradually spreads north and south to form San Andreas FaultStopped volcanism from subduction; made for large earthquakes

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San Andreas Fault

Photograph of San Andreas fault rift valley in the Mecca Hills, southern California. Strike-slip motion along the fault grinds and crushes the rocks. They more easily erode forming the linear rift valley.

This photograph shows right lateral displacement along a stream as it crosses the trace of the San Andreas fault (running horizontally) on the Carrizo plain in California.

The Pleistocene and HoloceneGlaciers and Ice Ages

Glacier: body of ice on land that moves as a result of plastic flow and basal slip. Continental glacier: large (50,000 km2) glaciers that are unconfined by topography and flows outward from a central point of accumulationValley glacier: long narrow tongues of ice confined to mountain valleys where they flow downhill

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Bucher Glacier

The Pleistocene and HoloceneGlaciers

Form when an area receives more snow in the cold season than melts in the warm season over many years so that snow accumulatesSnow turns to firn, then glacial ice, begins to move outward or downhillZone of Accumulation builds up and moves toward Zone of Wastage; balance or advance or retreat

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Snowline: elevation above which snow doesn’t melt seasonally

Plastic flow in glacier ice

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1. Latitude2. Rainfall3. Elevation

Mt. Rainier, Washington Coast

Stanton Mt., Montana (inland)

Three factors determine glacial accumulation:

GlaciersCarve out distinctive landscape features such as U-shaped valleys, cirques, horns, hanging valleys, striations and polishLeave behind distinctive deposits such as moraines, drumlins, outwash plain deposits, erratic boulders, tillLeave lakes such as tarns, pater-nosters, kettle lakes

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Glacial Erosion• Abrasion - as sediment-laden ice moves over rocks, it abrades (polishes) them and may leave grooves or glacial striations on the rock surface. Abrasion can grind rock in to a very fine powder known as rock flour.

Glacial Erosion

Glacial Polish on Granitic RockSierra Nevada Mtns., California

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Yosemite

Glacial Landforms: Glaciated ValleysPrior to glaciation, mountain valleys are

typically V-shaped from stream erosion.During glaciation they are deepened and widen - creating a U-shaped valley.

When glaciers recede, the smaller tributaries form valleys (hanging valleys) that may be left standing above the the main glacial valley.Bridle veil falls in Yosemite falls from a

hanging valley.

Glacier Natl ParkMontana

•Cirques represent the zone of accumulation - the focal point of glacier growth.• After the glacier has melted away, the cirque basin commonly contains a small lake called a tarn or cirque lake.

Glacial Landforms: CirquesAt the head (top) of a glacial valley, there is a bowl-shaped depression with

walls on three sides and is open on the down-valley side known as a cirque.

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Horns are sharp, pyramid-shaped peaks formed by a group of cirques around a single high mountain. As the cirquesenlarge, an isolated horn is produced. The photo to the left is the Matterhorn in Switzerland.

QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture.

QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture.

Glacier Natl. Park

Aretes are sharp-edged ridges that are formed by headward erosion with cirques on opposite sides of the divide.

Cirque and Horn

Glacier Natl. Park, Montana

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Cirques, Horns, Aretes

Mt. Rainier Natl. Park

Glacial TillGlacial till consists of rounded to angular fragments that are not sorted by size and not laid down in horizontal beds.

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Stratified DriftStratified drift is sorted by size because the sediment is deposited by a stream (glacial meltwater).

Glacial Erratics

Near Echo LakeTuolome Meadows

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Glacial MorainesMoraines are any number of landforms composed of till. There are many different types:

End Moraine - a ridge of till that forms at the terminus (end) of a glacier.

The IR satellite image shows a glacier in Patagonia. The semicircular ridge at the far left of the image is an end moraine.

Lateral moraines are formed from material that accumulates on the sides of alpine glaciers.

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End moraines make up a large portion of Long Island and Cape Code. These moraines are the result of the retreat of the glaciers during the last glacial cycle ~20,000 years ago.

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Typical Morainal TopographyLeft by Ice SheetsSouth Dakota

DrumlinsDrumlins are streamlined deposits of till that are dropped off the bottom of glaciers and are elongate in the direction of ice flow. They are asymmetric in cross-section (parallel to flow) with the steep side up-flow.

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Kettle Lakes, Cape Cod

The Pleistocene and HoloceneIce Ages

Prolonged periods when glaciers covered as much 30% of the land surfaces of the earth.Glacial conditions started 40mya when Tethysclosed; Miocene antarctic ice sheetGlobal warming in the PlioceneContinental Glaciation started in North America about 1.8 mya

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The Pleistocene and HoloceneIce Ages

Climates varied in areas not covered with ice, e.g. Sahara was lush forested areaPollen analysis can be used to track ice development and analyse local climatic conditionsAt least 4 episodes of glaciation in N. America6 or 7 in EuropeLittle ice age in 1500-1800

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Glaciers of the Ice Age

Geologic data indicate that glacial/interglacial cycles have occurred about every 100,000 years. The time that we commonly call the Ice Ages includes about 20 cycles of cooling and warming. We are currently in an interglacial period.

The figure shows the extent of glaciation during glacial periods -as much as 30% of the land surface was covered in ice.

The Pleistocene and HoloceneIce ages caused changes in sea level, widespread regression

Land bridge in Siberia/AlaskaBritish Isles and Europe connectedErosion of rivers into continental slope

Eastern US with flooded river valleysWestern US with submarine canyons

If all ice melted now, rise would be 70m

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The Pleistocene and HoloceneGlaciers and Isostasy

Isostasy is the equilibrium of crust floating on the mantleAdded weight of ice caused continents to sink further into mantleNow continents are rebounding from ice melting

Coastal cities of ScandinaviaCanada and New York - earthquakes

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The Pleistocene and HoloceneWhat caused Pleistocene Glaciation?

Few Glacial periods separated by long intervals of mild climate in Geologic HistoryPlate tectonics – continents move over poles; continents collide forming high mountainsDecrease in CO2?Intermediate climate changes- glacial/interglacial cycles of few thousand years –hard to explainMilankovitch theory – widely accepted

What caused Pleistocene Glaciation?Milankovitch theory

Minor irregularities in Earth’s rotation and orbit alter the amount of sunlight Earth receives at given latitudeVariations in 3 parameters of Earth’s orbit

Orbital eccentricity- maximum every 100,000 yrs.Angle of Earth’s axis- varies 23.5 degrees over 41,000 yr cyclePrecession of the equinoxes and solstices- shift around orbit in a 23,000 year cycle

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Milankovitch cyclesSee p. 366 fig 17.18

Glaciers and the Study of ClimateShort term climatic change can be monitored by glacial advance and retreat – little ice age.Glaciers still cover 10% of Earth’s land surfacesGlobal warming

Glaciers in N. Hemisphere are retreatingPossible greenhouse gas increase is causing?Is it man caused or natural?Are we in an interglacial and can expect another ice age?