Ch15 Cenozoic Events Notes.docx

The Earth Through Time Chapter 15—Cenozoic Events CHAPTER OUTLINE FOR TEACHING I. Overview of Cenozoic A. Subdivision of Cenozoic (m.y. = million years) 1. Three periods a. Paleogene: 65.5 to 23 m.y. b. Neogene: 23 m.y to 1.8 m.y. c. Quaternary: 1.8 m.y. to present 2. Epochs of the Paleogene a. Paleocene: 65.5 to 55.8 m.y. b. Eocene: 55.8 to 33.9 m.y. c. Oligocene: 33.9 to 23.0 m.y. 3. Epochs of the Neogene a. Miocene: 23 to 5.3 m.y. b. Pliocene: 5.3 to 1.8 m.y. 4. Epochs of the Quaternary a. Pleistocene: 1.8 to 0.01 m.y. b. Holocene: 0.01 m.y. to present B. Plate Tectonics 1. Vast seafloor expansion a. 50% of seafloor produced during last 65.5 m.y. b. most new seafloor in Atlantic and Indian Oceans 2. Significant westward movement of N. and S. America a. San Andreas fault system produced b. Andean trench deformed c. Cascade-Panamanian-Andean volcanic chain developed d. extensive west coast orogensis 3. Significant rifting a. North Atlantic: Greenland split from Scandinavia b. South Pacific: Australia split from Antarctica c. Indian Ocean: Arabia split from Africa (creating Gulf of Aden and Red Sea) 4. Significant collision events a. Africa-Eurasia: Alps built b. India-Eurasia: Himalayas built 5. Cenozoic characteristics a. continents stood high: transgressions limited b. sharply defined climatic zones c. cooling trend culminated in Pleistocene Ice Ages II. Pre-Pleistocene Cenozoic History A. Eastern United States 1. Structural changes a. broad gentle uplifts b. eastern tilting of Atlantic Coastal Plain and shelf c. subsiding platforms in Florida-Bahamas area d. Neogene uplift of Florida 2. Sedimentation and erosion a. Appalachian plains beveled by erosion b. valley and ridge topography sculpted c. coastal plain alluvial sedimentation d. reworking by marine transgressions e. coralline carbonates (2500 m) in Florida area B. Gulf Coast 1. Best stratigraphic record in N. America 2. 8 major cycles of transgression/regression 3. Paleocene transgression as far north as Illinois 4. Common cyclic sequence: deltaic above offshore deposits 5. Comprise seaward-thickening wedge of clastics 6. Carbonates absent in region C. Rocky Mountains and Cordillera 1. Structural changes a. Late Cretaceous-Paleogene accretion events account for major structural features of western Cordillera b. Miocene uplift and erosion exposed present topography (e.g., Rocky Mountains) c. Miocene uplift resulted in re-deposition of Paleogene sediments of intermountain basins d. Neogene normal faults elevated the Teton Range (6000 m displacement): Teton fault scarp is 2500 m high 2. Volcanic activity: widespread in the region 3. Sedimentation a. Paleocene (e.g., Fort Union Fm., 1800 m thick): clastics in intermountain basins (silt, sand, shale, coal, lignite) b. Eocene lake deposits in intermountain basins (e.g., Green River Fm. in basins between Wind River and Owl Creek Mountains: 600 m of freshwater limestone and shale; seasonal varves; 6.5 m.y record of insect, plant, and fish fossils; oil shales c. Eocene stream deposits (e.g., Wasatch Fm.): intermountain basin fills, red colors; fine upward from conglomerates to siltstones d. Eocene-Oligocene floodplain deposits (e.g., White River Fm.): clays, silts, and ash with extensive mammal accumulations in flood deposits e. Oligocene lacustrine deposits filled with volcanic ash (e.g., Florissant beds): spectacular preservation of insects, leaves, fish, birds, spores, pollen f. Miocene fluvial and lacustrine sedimentation (intermountain basins) and piedmont plains (east of Rocky Mountains: grasslands with camels, horses, rhinoceroses, deer, other grazing animals; Great Plains developed; spectacular erosional features g. Pliocene floodplain deposits: reflect cooler, drier conditions D. Basin and Range Province: Nevada-Utah to Mexico 1. Structural history a. Mesozoic over-thrusting b. Paleogene regional arch c. Miocene-Holocene arch subsidence and normal faulting: north- south trending fault-block mountains (horsts and grabens) developed by tensional forces 2. Causes of structural development: four hypotheses a. subduction hypothesis: Pacific spreading center active below region as it was subducted b. oblique shearing hypothesis: tension due to west coast shearing 3. Sedimentation a. Miocene evaporites in lakes b. Miocene-Holocene coarse clastic shed off of mountains c. Miocene-Holocene clastics fill grabens 4. Volcanism: different styles on different sides of province a. western side: extensive lava flows b. eastern side: explosive volcanism (ash and pumice deposits) E. Colorado Plateau 1. Region of non-folded, flat-lying Paleozoic and Mesozoic rocks a. crustal buttress with deformation all around it b. plateau raised repeatedly during Early to Middle Pliocene (5 to 10 m.y. ago) 2. Structure and volcanics: steep faults are avenues for lavas (e.g., in the San Francisco Mountains, AZ) 3. Uplift and erosion: Grand Canyon cut down 2600 m into crystalline Precambrian rocks F. Columbia Plateau and Cascades 1. Region built by two styles of volcanic activity a. relatively quiet fissure eruptions covering 1/2 million km2 with 2800 m of lava b. explosive, violent volcanic mountain chains issuing lava, pyroclastics, and ash clouds (nuée ardente) 2. Columbia Plateau: Neogene basaltic fissure eruptions; layered basalts 3. Cascade range a. volcanism due to melting of down-going Juan de Fuca plate b. volcanism began 4 m.y. ago (Pliocene) c. recent eruptions: Mt. St. Helens, WA (1980) d. other recent eruptions: Mt. Lassen (1914-15); Mt. Rainier (2000 years ago) e. caldera-producing eruption: Mt. Mazama exploded to form Crater Lake (OR) today G. Sierra Nevada and western California 1. Sierra Nevada Mountains a. not supported by thick crust, rather by buoyant liquid rock b. Jurassic: formed by plutonism in Nevadan orogeny c. Cretaceous and Cenozoic: eroded deeply d. Pliocene-Pleistocene: range uplifted 4000 m along huge normal faults on east side; range tilted west depressing the California trough on west side e. Pliocene-Pleistocene: rejuvenated streams and valley glaciers cut present topography (e.g., Yosemite Park) 2. California west of Sierra Nevada Mountains a. Paleocene-Miocene: affected by subduction tectonics, deformation, volcanism b. Miocene: conversion to strike-slip (transform) fault tectonics; cease subduction in area c. Miocene-Pliocene: regression due to uplift d. Miocene-present: creation of submarine basins due to fault movements; clastics, cherts, diatomites e. Holocene: final regression from most western California marine basin 3. Alaska and arctic islands of Canada a. Aleutian chain volcanics b. Aleutian back-arc basin: clastics, pyroclastics, lavas c. Alaska and Canada: clastics with coal 4. West Coast tectonics a. East-dipping subduction: Mesozoic and Paleogene orogenesis b. Orogenic effects: batholiths, compressional structures, volcanism, metamorphism, ore emplacement c. Farallon plate: extensively melted (including spreading ridge); northern segment = Juan de Fuca plate; southern segment = Cocos plate d. Pacific plate: moving northeast prior to west coast contact, therefore strike-slip fault motion was assumed (Miocene) e. Baja California split from Mexico: Pliocene (5 m.y. ago); moving north on Pacific plate H. South America: Andean orogenic belt 1. Cretaceous: deformation, metamorphism, granitic plutonism 2. Cenozoic (especially Miocene): folding and volcanism 3. Miocene-Pliocene: highlands eroded 4. Late Pliocene: renewed uplift; present-day relief 5. Cenozoic tectonics due to continual subduction of South Pacific plate under western S. America 6. Cenozoic clastics shed off Andes: Amazon and Orinoco basins or intermountain rifts I. Tethyan Realm (Europe) 1. Eocene deformation a. Africa moves north toward Eurasia deforming Europe and creating Pyrenees and Atlas Mountains b. Northern movement converts to scissor-like closure: beginning formation of Alps c. Flysch deposition in basins: dark marine shales, immature sands, cherts 2. Oligocene deformation a. enormous recumbent folds form and rise to form mountains from Tethys marine sediments b. compression forces folds to north on to Eurasia c. thrust faults cut folds on undersides d. molasse deposits: Piedmont clastic wedge shed on north side of rising Alps 3. Miocene deformation and sedimentation a. glacial-induced sea-level drop of 50 m b. tectonic restriction of inlet at straits of Gibraltar c. factors above isolated the proto-Mediterranean from global sea; evaporation 5.5 m.y. ago turned basin into an evaporitic basin and eventually a desert (like Death Valley, CA today) 4. Pliocene-Holocene deformation a. Jura folds form: older rocks transported over molasse; form northern front of Alps today b. Post-Pliocene uplifts continued to today 5. Similar age deformation: Apennines, Caucasus, Carpathians, and Himalayas J. Tethyan Realm (India) 1. Paleocene-Oligocene: folding, thrusting, granitic plutonism as ocean closed between India and Eurasia 2. Miocene: intensive orogenic episode; elongate tracts of seafloor folded and thrust south onto India; northern trough of India formed (5000 m continental clastics) 3. Pliocene-Holocene: great elevation of plateaus and folded ranges; retreat of marginal seas; continued collision of India-Eurasia; Himalaya Mountains thus built K. Northern Europe (France, Scotland, Ireland, Spitzbergen, Greenland, Baffin Island) 1. Early Cenozoic lavas: Giant’s Causeway of Ireland; same age as Greenland-Europe split 2. Paleocene-Eocene-Oligocene: repeated cyclic transgressions and regressions into Europe a. Oligocene: greatest transgression b. Flooding from North Sea toward SE c. Paris Basin: thick section above Cretaceous chalks 3. Miocene-Holocene: uplift prevented further transgressions L. Africa 1. Northern region near Tethys: little deformation, flat-lying rocks 2. Southern region: emergent in Cenozoic 3. Eastern region: Cenozoic uplift and rifting a. 3000 m of uplift in a broad arch b. fracturing and normal faulting on arch crest c. east African rift valleys formed d. volcanic development in rifts (e.g., Mt. Kenya and Mt. Kilimanjaro) e. elongate lakes formed in rifts M. Antarctica 1. Paleocene-Eocene: Antarctica was joined with Australia and was relatively warm 2. Miocene: Separation from Australia caused warm currents to flow northward and Antarctica became cold like today III. Quaternary (Pleistocene and Holocene) History: the last 1.8 m.y. A. Overview of Epochs 1. Time of ice ages a. 40 million km3 snow and ice covered 1/3 Earth’s surface b. glacial terrains created c. climatic zones shifted southward d. Arctic conditions in Europe, N. America e. intensive rain in lower latitudes f. human evolution and migrations 2. Climatic characteristics a. glacial and integlacial intervals b. ocean cooling events independent from glaciation B. Pleistocene-Holocene Chronology (m.y. = million yrs) 1. Original concept of Pleistocene base (Lyell, 1839) a. Marine strata young enough to contain 90-100% of presently living mollusks as fossils b. Lyell’s concept applied to marine strata in Italy, not worldwide c. Non-marine record not well defined as a result 2. Modern concept: Pleistocene base = 1.8 m.y. ago a. 1.8 m.y. widely accepted date of base b. 1.8 m.y. does not coincide with onset of glaciation; glaciation not a synchronous event; oldest extensive glaciation = 1.0 m.y. c. Marine sediments: base is extinction (last occurrence) of discoasters d. Continental deposits: base is first occurrence of modern horse fossils (Equus), elephants, etc. 3. Modern Concept: Holocene base a. base defined as level (age) of melting of ice sheets to approximately their present position and sea level rise to near present level b. base defined as above = 8000 yr ago c. some geologists define base as mid-point in glacial retreat and sea-level rise d. base defined as above = 11,000-12,000 yr ago 4. Independence from “ice age” concept a. pre-1975 concept: Pleistocene consisted of 4 glacial intervals and 3 interglacial intervals; Holocene was final interglacial interval b. post-1975 concept: glacial intervals are not synchronous and more than 4 occurred, therefore epochs independent of such constraints c. reasoning for above: discovery of 30 intervals of severe cold over last 3 m.y. 5. Variables affecting Earth’s climates over time a. atmospheric changes: greenhouse versus icehouse b. geographic and tectonic changes c. oceanographic changes d. astronomic changes: sunspot cycles, Milankovitch cycles, etc. C. Terrestrial Stratigraphy of Pleistocene 1. Sedimentary deposits by environment (facies) a. glacial (till): terminal moraine, ground moraine b. fluvial (stratified drift): braided and meandering streams c. lacustrine 2. Erosion surfaces a. bedrock scour by ice b. melt-water stream incision c. melt-water flood (scablands) 3. Correlation and relative-age determination requires mutually sustaining criteria a. degree of stream dissection of moraine b. depth of oxidation of sediment layer c. degree of chemical weathering of layer d. fossil pollen as climatic indicators e. varved clays in lake deposits f. C14 dating of wood, bone, shell, peat (note: 1/2 life = 5,570 yr) D. Marine Stratigraphy of Pleistocene: correlation methods in continuous core 1. Oxygen-isotope ratios in calcareous planktonic foraminifers: indicator of water volume stored as ice in glaciers a. O18 is heavier and is not evaporated as readily as O16, thus snow and ice are enriched in O16 b. O18/O16 ratios from cores plotted versus depth in core show variations in ice volume (thus, sea level) over time; also shows climate changes 2. Relative abundance of foraminifera sensitive to temperature changes a. Globorotalia menardii: tropical species associated with warm waters b. Globorotalia truncatulinoides: coils right in warm water; coils left in cold water c. Background sedimentation rates and ages in core determined by C14 dating of foraminiferal tests 3. Remnant magnetism a. depositional remnant magnetism may be correlated with known geomagnetic time scale b. age check by allied C14 dating c. magnetism may be disturbed by bioturbation E. Effects of Pleistocene Glaciation 1. Sea-level drop: 75 m below today’s level at maximum a. continental shelves as dry lands (forests, grassland, plains) inhabited by humans b. land bridges: British Isles-Europe, Siberia-Alaska c. interglacial intervals inundated shelves and bridges; forced animal migrations 2. Glacial physical effects a. ice-caused erosion b. weight of ice depressed crust 200-300 m below pre-glacial level; interglacial crustal rebound (as today); elevation of glacial coastlines c. obliteration of river systems by continental glaciers d. establishment of new glacial and interglacial river drainage basins (e.g., Missouri and Ohio Rivers) e. changes in stream gradient and sediment load in glacial versus interglacial times; sea level affected base levels worldwide f. continental lakes (e.g., Great Lakes of N. America) scoured in lowlands by continental ice sheets g. development of huge ice-dammed lakes of a temporary nature; huge lake bed deposits exist today (e.g., Lake Agassiz of ND, MN, and central Canada) h. pluvial lakes formed: thousands of large and small lakes formed in low latitudes by excess rainfall in glacial intervals (dry during interglacials); example: Lake Bonneville, site of salt flats and Great Salt Lake, UT today i. glacial impoundment lakes: impoundment floods created channeled scablands (e.g., draining of Lake Missoula (MT) resulted in flood of 2000 km3 water and severe erosion j. soil erosion: soil stripped off craton of Canada and transported south k. loess-blanket deposition: dense, cold air flowing off glaciers blew fine material from tills and drift to lower latitude areas (e.g., loess blankets of Missouri River valley U.S.; central Europe; northern China) F. Causes of Pleistocene Climates 1. Any theory must account for reasons why- a. climates grew cooler from Middle Cenozoic to Pleistocene (long-term trend) b. glacial-interglacial intervals alternate (short term trends) c. temperature and precipitation conditions mitigate to form proper combination d. many factors may be involved 2. Milankovitch theory of solar radiation a. Earth’s astronomical motion accounts for changes in amount of solar energy received, thus spawning glacial intervals b. Earth’s axial tilt: varies 22o to 24o over 41,000 year period (changes seasonal length-of-day and amount of solar energy at high latitude) c. Earth’s axial precession: axis of rotation moves in circle with period of 26,000 yr d. Earth’s orbital eccentricity: varies by 2% with a period of 100,000 yr (thus Earth is closer to the sun at times) e. Support for theory: radiometric and oxygen-isotope studies show strong correlation to Milankovitch calculations, especially to role of eccentricity at 100,000 yr intervals over last 600,000 yr f. Criticism of theory: why not operative over all of geological time? 3. Other factors affecting Milankovitch climatic change a. albedo (reflectivity of Earth): currently 33% solar energy reflected during this interglacial and sea level high stand; during extreme low sea levels more continent would be exposed and albedo higher (thus lower global temperatures); 8o C drop per - 1% change b. cloud-ash-dust absorption of solar energy c. greenhouse gas content (especially CO2); decrease CO2 = cooling, increase = warming temporarily but cloud cover and excess precipitation may trigger ice buildup d. oceanic effects: northward deflection of Gulf Stream-type currents (e.g., 3.5 m.y. ago when Isthmus of Panama formed) would send warmth and moisture to northern regions e. Continental positions: continents must be at or near poles or snow will fall in ocean and melt 4. Milankovitch predictions of future a. 20,000 cooling trend going into next glacial b. unknown factors: CO2 and other atmospheric changes by humans G. Cenozoic Climates: Global Warming, then Cooling 1. PETM – Paleocene-Eocene Thermal Maximum a. Global warming from carbon-dioxide buildup in atmosphere b. Gradual event spanning 10,000 years c. Melting of sea-floor methane hydrate released methane, which formed carbon dioxide in the atmosphere d. Global temperatures rose 8oC during the PETM e. Disastrous effects (i) acid rain and acidification of the oceans (ii) foraminiferal extinction in the oceans (iii) major shifts of plants and animals on land 2. Oligocene cooling 3. Miocene warming 4. Pleistocene and Holocene cooling and the ice ages Answers to Discussion Questions 1. (a) Mountains of the Basin and Range were formed during Miocene when the crust under that region was stretched and such tension caused up-thrown blocks (horsts) to become mountains and down-dropped blocks (grabens) to become valleys. (b) The Great Plains was formed during Miocene when uplift of the Rocky Mountains caused great volumes of clastic sediments to be eroded from the mountains and deposited eastward. (c) Columbia and Snake River Plateau were formed during Cenozoic by vast outpouring of basaltic lavas erupted along deep fissures in an area of 500,000 km2. (d) The Red Sea was formed during Cenozoic when a branch of the Indian Ocean rift split Arabia away from Africa and in the process opened this seaway. (e) The Teton Range was formed when normal faulting accompanying Neogene uplifts affected northwestern Wyoming. (f) The Cascade Range was formed over the last 4 million years as viscous lavas were intruded into the western margin of the American plate as a result of subduction of the Juan de Fuca plate of the eastern Pacific. 2. The Alps, Atlas, Apennines, Carpathians, Caucasus, Pyrennes, and Himalayas are all mountain ranges formed by the closure of the Tethys seaway. 3. Paleogene Period includes (in order from oldest) Paleocene, Eocene, and Oligocene. Whereas, Neogene includes Miocene, Pliocene, Pleistocene, and Holocene Epochs. 4. The Green River Formation is economically significant because it contains shales rich in waxy hydrocarbons, a deposit called oil shale that can be processed to yield petroleum. The Green River Formation is also the source of crude oil pumped from the adjacent Wasatch Formation. The Fort Union Formation is economically significant because it contains immense tonnages of low-sulfur coal in its lower levels. 5. Lake Nyasa and Lake Tanganyika are lakes formed by fault-bounded, down-dropped crustal blocks. This normal faulting is the result of Cenozoic rifting along a north-south trend in eastern Africa. 6. The Great Salt Lake is part of a much larger, Pleistocene lake called Lake Bonneville which once covered an area of 50,000 km2 and was as deep as 300 m. Lake Bonneville formed during pluvial or high-precipitation periods that were the result of glacial stages. Such lakes shrink during drier interglacial stages like the current stage. 7. Glacial versus interglacial (i.e., cold versus warm) sediment records may be determined by study of oxygen-isotopic ratios (O18 versus O16) in shells of planktonic marine invertebrates and (or) by studying changes in relative abundances of foraminifers known to be sensitive to temperature. 8. The Bering land bridge across the Bering Straight was an important connection between Asia and America. A 50-meter sea-level drop will cause the land bridge to develop. This event likely occurred occasionally during Cenozoic. 9. Land-level rise around Hudson Bay, the Great Lakes, and Baltic Sea during historic time is the result of removal of the last glacial ice sheet (which had down-warped the crust owing to its weight) and a resultant rebound of land elevation. 10. New and faster, Cenozoic westward movement on the American plate and northward movement of the Pacific plate caused a lateral fault (strike-slip) boundary to develop in the San Andreas fault of California. 11. Deposition of a seaward-thickening wedge of clastic sediments many 1000s m thick under relatively shallow-water conditions indicates profound and continual subsidence during Cenozoic. 12. The Green River oil shales contain prolific amounts of hydrocarbons and thus are a rich energy source. They are located at surface or shallow depth and thus easily obtained. Unfortunately, the mining of such deposits deeply scars and affects the land. Hydrocarbons are tightly bound in the rock and much energy is required to liberate them. Processing oil shales is not a clean or efficient operation. 13. Albedo (reflectivity) can be increased by exposing more land surface (as in regression or deforestation), adding cloud cover or dust/ash content to the atmosphere (as in volcanic eruptions, great dust storms, or great fires), or adding snow/ice cover. Such changes generally accompany global climatic change. At the beginning of Pleistocene, sea levels were significantly lowered and increased snow/ice cover was forming at high latitudes due to oceanic current diversion. 14. Thick Pleistocene loess deposits formed as cold moist winds flowed toward lower latitudes from continental ice sheets. The winds picked up fine material from glacial surfaces and out-washed drift and transported it to new sites away from glacial margins. The sediments were originally soils and pulverized rock entrained by mountain and continental glaciers at higher latitudes. The narrow size range of loess particles reflects the wind’s narrow size-range capacity for moving particles and keeping them suspended for significant times in air. 15. O18, being relatively heavy as compared to O16, is preferentially left behind in sea water upon evaporation. During cool periods the O18 precipitated in snow does not return to the sea, thus the sea is enriched in heavy O18. The foraminifers taking oxygen to build their carbonate (CaCO3) tests do not discriminate between isotopes; therefore their tests are enriched in O18 during cool intervals. 16. Methane hydrates are cold, sea-floor deposits of methane gas (CH4) that is dissolved in or trapped in water ice. As methane hydrates melt due to volcanic activity on the sea floor or global warming effects, the released methane gas breaks down and the carbon in the methane combines with oxygen in the atmosphere to make carbon-dioxide, a greenhouse gas. 17. d 18. a 19. d 20. c Chapter Activities Student activities for in-depth learning. 1. Using the resources on this page about the Channel Scablands (http://www.uwsp.edu/geo/ projects/geoweb/participants/dutch/vtrips/Scablands0.HTM), describe how these unusual Pleistocene features formed and their relationship to glacial ice melting. What is the relationship of the scablands deposits to the Columbia Plateau? 2. Use the web resources of the University of California, Berkeley, Museum of Paleontology web page on the Green River Formation (http://www.ucmp.berkeley.edu/tertiary/eoc/greenriver.html) to learn about how that formation was deposited and the types of fossils found there. Describe these fossils and the environment of the lake during Eocene. Chapter 15—Cenozoic Events CHAPTER OVERVIEW The era we call Cenozoic is divided into three periods: Paleogene; Neogene; and Quaternary. The Cenozoic, although covering only the last 65 million years of Earth’s history, encompasses major worldwide changes. One such change occurred when the North Atlantic rift extended to the north, separating Greenland from Scandinavia and thereby destroying the land connection between Europe and North America. During late Eocene, Australia separated from Antarctica and then began its journey to its present location. This is considered the only major continental breakup during Cenozoic; however, it appears to have affected climates around the world. The stratigraphy of the Cenozoic of North America is explored with some of the more noteworthy exposures: the Gulf Coast, Rocky Mountains, High Plains, Basin and Range, Colorado Plateau, Columbia Plateau and Cascades, Sierra Nevada, and California are discussed. Cenozoic sedimentation and deformation outside North America is also discussed in order to complete this phase of Cenozoic history. Pleistocene glaciation is a focal point in this chapter which highlights the glacial and interglacial stages in North America and Europe as well as discussing variations in climatic conditions. LEARNING OBJECTIVES By reading and completing information within this chapter, you should gain an understanding of the following concepts: Sketch and label the three periods - Paleogene, Neogene, and Quaternary - and the epochs within each. Discuss the tectonic-climate connection. Locate on a map the major mountain systems that were formed by the northward moving African block as it collided with the southern margin of Europe. Explain the origin of the following physiographic features of North America – Rocky Mountains/High Plains, Basin and Range, Colorado Plateau, Columbia Plateau and Cascades, Sierra Nevada, and California. Describe the origin of the San Andreas Fault. Explain the orogenic events along the Tethys seaway and the orogenic events that led to the formation of the Alps, Carpathian, Pyrenees, Apennines, and Himalayas. Discuss the origin of Lake Molawi and Lake Tanganyika in eastern Africa. List the four Glacial/Interglacial Stages for North America and Europe from oldest to youngest. Discuss the impacts of Pleistocene glaciation. Explain the Milakovich effect (theory) and its possible interpretation of the Pleistocene glaciation including the three variables in your explanation. CHAPTER OUTLINE The Tectonics-Climate Connection Stability and Erosion Along the North American Margin Gulf Coast: Transgressing and Regressing Sea The Mighty Cordillera Sediment and Mineral Wealth Remarkable Fossils Majestic Scenery Creating the Basin and Range Province Colorado Plateau Uplift Columbia Plateau and Cascades Volcanism Sierra Nevada and California The New West Coast Tectonics Meanwhile, Drama Overseas … Northern Europe Rifting Africa Semitropical Antarctica Big Freeze: the Pleistocene Ice Age Pleistocene and Holocene Chronology Stratigraphy of Terrestrial Pleistocene Deposits Pleistocene Deep-Sea Sediments Many Impacts of Pleistocene Glaciation Shifting Sea Level Depressed Crust Rebounds Redirecting Mighty Rivers Forming Lakes, Great and Small Washington’s Alien Land: the Channeled Scablands Windblown Sediment What Caused the Ice Age? Milankovitch Cycles Earth’s Albedo Other Factors Cenozoic Climates: Global Warming then Cooling Key Terms (pages given in parentheses) albedo (500): The fraction of solar energy reflected back into space is termed the Earth’s albedo. channeled scablands (497): With the recession of the glacier, the ice dam broke, and tremendous floods of water rushed out catastrophically across eastern Washington, causing severe erosion and depositing huge volumes of gravel, boulders, and cobbles. The dissected region is appropriately termed the channeled scablands. This event was associated with the formation of Pleistocene lakes in the northwestern corner of the United States. discoasters (493): Calcareous, often star-shaped fossils believed to have been produced by golden-brown algae related to coccoliths. kettle (496): A depression in glacial drift that is formed by the melting of a detached block of ice that was buried in the drift. little ice age (493): The four-century period (AD 1540 and 1890) when temperatures were often 1.5° C cooler than today in Europe and the United States. loess (497): Deposits of thick layers of windblown silt formed from fine-grained glacial sediments that have been spread across outwash plains and floodplains by wind transportation. Neogene (470): The middle period during Cenozoic that encompasses two ages, Miocene and Pliocene. Neogene is followed by the latter period of Cenozoic, called Quaternary, which is comprised of Pleistocene and Holocene. oil shale (476): A dark-colored shale rich in organic material that can be heated to liberate gaseous hydrocarbons. Paleogene (470): The initial period of Cenozoic that encompasses three ages, Paleocene, Eocene, and Oligocene. Pleistocene Ice Age (491): About one-third of the Earth’s land surface became buried beneath more than 40 million cubic kilometers of snow and ice. pluvial lakes (496): A lake formed in an earlier climate when rainfall was greater than at present. precession (499): The way the axis of rotation moves slowly in a circle that is completed every 26,000 years. stratified drift (494): Deposits of glacial clastics that have been sorted and stratified by the action of meltwater. Tethys sea (488): A great east-west trending sea which laid between Laurasia and Gondwonland during the Paleozoic and Mesozoic from which arose the Alpine-Himalayan mountain range. till (494): Unconsolidated, unsorted, unstratified glacial debris. varves (475): Seasonal layers of dark and light sediment formed in glacier-related lakes. 1 THE EARTH THROUGH TIME TENTH EDITION H A R O L D L. L E V I N CHAPTER 15 Cenozoic Events 2 THE CENOZOIC ERA ?65.5 million years ago to the present ?Name "Cenozoic" = "new life" or "recent life" 3 ?The Cenozoic Era followed a mass extinction of the dinosaurs and many other organisms ?Cenozoic rocks contain modern types of plants and animals, more advanced than those of Paleozoic and Mesozoic. ?Cenozoic is the era of: ?Adaptive radiation of the mammals ?Cooling of the Earth's climate resulting in the Ice Ages ?Evolution of humans THE CENOZOIC ERA 4 PERIODS OF CENOZOIC ?The Cenozoic Era consists of three periods: ?Youngest Quaternary Period ?Younger Neogene Period ?Older Paleogene Period ?Until 2003, the two periods of Cenozoic were Tertiary and Quaternary. You will see these terms on older maps and in older publications. ?In 2003, the an international commission revised the nomenclature, dropping the terms Tertiary and Quaternary. The two new periods of the Cenozoic are now internationally recognized as Paleogene and Neogene. 5 PALEOGENE PERIOD Paleogene is divided into three epochs: ? Oligocene (youngest) ? Eocene ? Paleocene (oldest) 6 NEOGENE PERIOD Neogene is divided into four epochs: ?Pliocene ? Miocene (oldest) 7 QUATERNARY PERIOD Quaternary is divided into two epochs: ? Holocene (the current epoch) ? Pleistocene 8 NAMING THE EPOCHS ?Some of the epochs were proposed by Lyell in 1832 on the basis of proportions of species of fossil marine invertebrates, found in rocks of that time, that are still living. ?For example, only 3% of Eocene organisms found as fossils are still living, whereas 17% of Miocene organisms found as fossils are still alive, and 50-67% of Pliocene fossils are still living. 9 NAMING THE EPOCHS The meanings of the root words for the epochs refer to the proportions of fossil species that are still alive. Pleist = most Pleion = more Meion = less Oligos = few Eos = dawn Paleo = ancient 10 PALEOGEOGRAPHY AND PLATE TECTONICS ?During Cenozoic, the Atlantic and Indian Oceans widened, and the continents moved to their current positions. ?Half of the present ocean crust has formed at the mid-ocean ridges since the beginning of Cenozoic. 11 Position of the continents during Eocene, about 50 m.y. ago. ?Antarctica and Australia are still connected. ?India has not yet collided with Asia. ?North and South America are not yet connected. ?South America is connected or nearly connected with Antarctica. Yellow = areas of major tectonic changes. PALEOGEOGRAPHY AND PLATE TECTONICS (J. C. Brider, G. E. Dreway, and M. G. Smith, 1974, Jour. Geol., 82:556–558.) 12 Position of the continents today . ?Antarctica has completely separated from neighboring continents, and is surrounded by ocean. ?Antarctica is centered on the South Pole. Yellow = areas of major tectonic changes. PALEOGEOGRAPHY AND PLATE TECTONICS (J. C. Brider, G. E. Dreway, and M. G. Smith, 1974, Jour. Geol., 82:556–558.) 13 EOCENE VS. TODAY Yellow = areas of major tectonic changes. PALEOGEOGRAPHY AND PLATE TECTONICS (J. C. Brider, G. E. Dreway, and M. G. Smith, 1974, Jour. Geol., 82:556–558.) 14 EXOTIC TERRANES As the North American plate moved westward (accompanying the widening of the Atlantic Ocean), subduction of ocean crust and accretion of exotic terranes occurred along its western edge. 15 ?The western edge of the North American plate came into contact with the northwestward-moving Pacific Plate, forming the San Andreas Fault system. SAN ANDREAS FAULT SYSTEM 16 CLOSURE OF THE TETHYS SEA ?Collision of Africa and India with Eurasia, forming the Alps and Himalayas. ?Tethys Sea deposits were deformed into mountain ranges. 17 TECTONIC AND PALEOGRAPHIC CHANGES AND THEIR EFFECTS ON CLIMATE ?Orogenic and volcanic activity were intense along the western edge of the North and South American plates. ?This caused the formation of the Isthmus of Panama, a land bridge linking North and South America. ?The land bridge provided a path for plant, animal, and human migration between the Americas. 18 TECTONIC AND PALEOGRAPHIC CHANGES AND THEIR EFFECTS ON CLIMATE ?The Panama land bridge blocked the westward flow of the North Atlantic Current. The current was deflected to the north (turning to the right, as a result of the Coriolis Effect), and formed the Gulf Stream. ?The Gulf Stream transported warm water northward and resulted in bringing warmer climates to northwestern Europe. ?Gulf Stream also supplied warm, moist air toward the North Pole, which would ultimately result in precipitation which helped build the glacial ice sheets. 19 IMPORTANT CONTINENTAL BREAKUPS: 1.North Atlantic rift separated Greenland from Scandinavia 2.Australia separated from Antarctica. Circumpolar currents isolated Antarctica from warmer waters. Led to cooling of Antarctica. 3.Cold, dense ocean waters around Antarctica drifted northward along ocean floor, contributing to global cooling and the Ice Age. 4.Rifting occurred between Africa and Arabia, forming the Red Sea and the Gulf of Aden. 20 TECTONIC AND PALEOGRAPHIC CHANGES AND THEIR EFFECTS ON CLIMATE ?Glaciation led to regressions. ?Continental interiors were not flooded by epicontinental seas during Cenozoic. ?Marine transgressions were limited. ?Overall cooling trend during Cenozoic. ?Tropical and subtropical plants were replaced by temperate plants, such as grasses. ?Tropical plants retreated toward the equator. 21 PALEOGENE PERIOD Paleogene was dominated by: ?The deposition of marine sediments in eastern and southeastern North America ?The presence of mountains and lakes in western North America. FIGURE 15-7 22 EASTERN AND SOUTHEASTERN NORTH AMERICA ?Ridges and valleys of the Appalachian Mountains were carved by erosion. As erosion proceeded, gentle isostatic uplift occurred. This stimulated more erosion, as streams cut downward. 23 EASTERN AND SOUTHEASTERN NORTH AMERICA Uplift in the eroding Appalachians was coupled with downward tilting and deposition of sediments on the Atlantic Coastal Plain and continental shelf. Sediments thicken seaward forming a clastic wedge. 24 EASTERN AND SOUTHEASTERN NORTH AMERICA ?Carbonate sediments accumulated in Florida where less terrigenous clastic sediment was available. ?Eight marine transgressions and regressions are recorded in Cenozoic sediments on the Atlantic and Gulf Coastal Plains. ?On the Gulf Coastal Plain, transgressions brought Gulf of Mexico waters inland as far as southern Illinois. 25 EASTERN AND SOUTHEASTERN NORTH AMERICA ?During regressions, deltaic sands were deposited over offshore shales in the Gulf of Mexico region. These sediments provided ideal conditions for formation and entrapment of oil and gas. Much of the oil was trapped around salt domes. ?A clastic wedge of sediments thickens seaward in the Gulf of Mexico region, where Paleogene sediments are >10,000 m (>5.5 mi) thick. ?Gulf of Mexico region has been subsiding rapidly. 26 ROCKY MOUNTAINS AND HIGH PLAINS ?Structural features of the Cordillera were created by Late Cretaceous and Paleogene deformation. ?Sediments eroded from the mountains were trapped in low areas between the mountains, or intermontane basins. ?Sediment from erosion of Rockies was spread over the plains to the east. Oligocene through Pliocene sands, shales, and lignites were deposited on western high plains. 27 ROCKY MOUNTAINS AND HIGH PLAINS ?Beds of volcanic ash are interlayered with these sediments, indicating volcanic activity, and providing radiometric dates for correlation. ?Paleocene Fort Union Formation contains gray sandstones and siltstones, carbonaceous shales, lignites, and low sulfur coals, deposited in swamps in the intermontane basins. ?These coals are used for electricity generation and produce very little pollution because of the low sulfur content. 28 ROCKY MOUNTAINS AND HIGH PLAINS ?Eocene Green River Formation is a lake deposit with fossil fish, insects, plants, varves, laminated oil shale, and limestone. The Green River fish, Diplomystis The Green River Formation, Utah 29 ROCKY MOUNTAINS AND HIGH PLAINS ?Late Eocene and Oligocene volcanic activity in Yellowstone National Park area. ?White River Formation contains well-preserved skeletons of Oligocene mammals. Also makes up the Badlands of South Dakota. ?Well preserved fossil insects and leaves are found at Florissant Fossil Beds National Monument in Colorado. They were buried when Oligocene volcanic ash settled into a lake. Large petrified stumps of sequoia trees are also present. Harold Levin 30 ROCKY MOUNTAINS AND HIGH PLAINS ?Fluvial and lacustrine sedimentation continued in intermontane basins and on plains to east into the Miocene epoch. ?Climates had cooled by Miocene time. ?As the climate cooled, the grasslands expanded and were populated by Miocene camels, horses, rhinos, deer, and other grazing mammals. 31 ROCKY MOUNTAINS AND HIGH PLAINS ?Volcanic activity occurred during Miocene in the central and southern Rockies. ?Gold deposits at Cripple Creek, Colorado formed in association with a Miocene volcano. ?Regional uplift of Rockies began in Miocene. ?Increased erosion rates. ?Sediment spread eastward, helping to build the Great Plains. 32 ROCKY MOUNTAINS AND HIGH PLAINS ?Fossils in Pliocene sediments indicate cooler and drier conditions. ?Normal faulting and volcanism accompanied Cenozoic uplifts and produced spectacular scenery. 33 BASIN AND RANGE PROVINCE ?The Basin and Range Province occupies a broad area in Nevada and western Utah, extending southward into Mexico. ?The province is dominated by up-faulted mountain ranges and down-faulted basins. 34 THE BASIN AND RANGE FORMED AS FOLLOWS: 1.The region was up-arched during Mesozoic. 2.Subsidence occurred along normal faults beginning during Miocene. 3.Up-faulted crustal blocks formed linear mountains that shed sediment into the adjacent down-dropped basins. 4.Faults opened conduits for igneous rock, producing lava flows and volcanism. 35 5.Erosion followed the volcanism. Sediments eroded from the mountains filled the down-faulted basins, clogged rivers, and caused closed-basin (no outlet) lakes to form. 6.Evaporite minerals (gypsum and salt) were deposited as the lakes evaporated. THE BASIN AND RANGE FORMED AS FOLLOWS: 36 COLORADO PLATEAU UPLIFT The best-known feature in the Colorado Plateau is the Grand Canyon. Eroded by the Colorado River to a depth of more than 1.6 miles. The river eroded through Phanerozoic strata and into the Precambrian basement rocks. Harold Levin 37 COLORADO PLATEAU UPLIFT ?The rocks are relatively flat-lying. They were not deformed during Mesozoic orogenies. ?The Colorado Plateau has been subject to uplift and erosion. Uplift occurred during Pliocene. ?Faults formed locally, providing conduits for volcanic rocks. ?Example: San Francisco Peaks near Flagstaff, Arizona. 38 COLUMBIA PLATEAU AND CASCADE RANGE VOLCANISM ?Columbia Plateau is named for the Columbia River, between Washington and Oregon. ?Columbia Plateau was built by volcanic activity. ?Basaltic lava poured out of deep fissures and buried more than 500,000 km2 of land in Washington, Oregon, and parts of Idaho during Miocene, about 15 m.y. ago. ?Lava flows are more than 1.5 miles thick. ?One of the largest volcanic regions on Earth. 39 COLUMBIA PLATEAU AND CASCADE RANGE VOLCANISM Above: Columbia Plateau basalts in a canyon of the Snake River. Right: Mt. St. Helens, Washington, prior to eruption and during eruption (1980). 40 COLUMBIA PLATEAU AND CASCADE RANGE VOLCANISM ?West of the Columbia Plateau, more viscous lava produced the volcanoes of the Cascade Range. ?Volcanism is caused by the North American plate overriding the Juan de Fuca plate in the eastern Pacific. FIGURE 15-23 The small Juan de Fuca plate plunges beneath Oregon and Washington. 41 VOLCANOES OF THE CASCADE RANGE ?Mt. St. Helens ?Mt. Rainier ?Mt. Adams ?Mt. Hood ?Mt. Jefferson ?Mt. Lassen ?Mt. Shasta ?Others 42 CRATER LAKE Crater Lake, Oregon formed from the eruption and collapse of Mt. Mazama in the Cascade Range about 6800 years ago. 43 The Sierra Nevada batholith formed as the Farallon plate was being subducted under the western edge of the North American continental plate during Mesozoic. SIERRA NEVADA BATHOLITH 44 SIERRA NEVADA MOUNTAINS Erosion during Paleogene removed the overlying rocks and caused the granite batholith to be exposed at the surface. 45 SIERRA NEVADA MOUNTAINS ?During Pliocene and Pleistocene, the Sierra Nevada batholith was raised up along normal faults to a height of 4000 m (more than 2 miles) above the California trough to the west. ?Streams and glaciers carved the landscape. ?Examples – Yosemite, Lake Tahoe 46 CALIFORNIA ?During Paleogene, the region west of the Sierra Nevada was affected by subduction. ?During Miocene, strike-slip movement replaced subduction. ?Faulting created islands and sedimentary basins. ?Marine clastic sediments, diatomites, and bedded cherts were deposited in the basins. ?Folding and uplift led to regression. 47 NEW WEST COAST TECTONICS ?During most of Cenozoic, subduction occurred along the west coast. ?The Farallon plate was almost completely subducted under North America. ?Only the small Juan de Fuca plate remains as a corner of the once much larger Farallon plate. ?Part of the East Pacific rise spreading center was subducted under North America. 48 NEW WEST COAST TECTONICS ?Once the Pacific plate came into contact with the North American plate, the direction of movement changed. ?Instead of being subducted, the Pacific plate slid laterally along the edge of the North American plate. ?This formed the San Andreas fault with its strike-slip motion, and ended subduction in this area. 49 AROUND THE WORLD ?Active volcanism in many areas –New Mexico, Arizona, Idaho –Mexico –Iceland –Pacific rim ?Crustal uplift in many areas –Tetons of Wyoming –Sierra Nevada –central and northern Rockies –Alps –Himalayas 50 EOCENE VS. TODAY Yellow = areas of major tectonic changes. (J. C. Brider, G. E. Dreway, and M. G. Smith, 1974, Jour. Geol., 82:556–558.) 51 Basaltic lava flows in northern Europe and neighboring areas that resulted from Greenland rifting from Europe ?Ireland - columnar basalts of Giant's Causeway ?Scotland ?Greenland ?Baffin Island ?Norway's Svalbard Islands CLOSING OF TETHYS SEA AND FORMATION OF MOUNTAIN RANGES 52 ?Transgressions and regressions in the Paris Basin area and formation of evaporitic "Plaster of Paris" gypsum deposits during Paleogene (Eocene to Oligocene) ?Formation of rift valleys in East Africa, along with associated lakes and volcanoes ?Separation of Australia from Antarctica ?Cooling and accumulation of snow and ice in Antarctica EUROPE, AFRICA, AUSTRALIA, AND ANTARCTICA 53 CENOZOIC PALEOCLIMATES 54 GLOBAL SURFACE COOLING ?There was a 10o C (18o F) temperature drop at end of Cretaceous Period. ?Several warming trends occurred during late Paleocene and Eocene, as indicated by: ?Fossils of palm trees and crocodiles in Minnesota, Germany, and near London. ?Fossils of trees from temperate zones in Alaska, Norway and Greenland. ?Coral reefs in latitudes 10-20o closer to the poles than at present. 55 ANTARCTICA DURING PALEOGENE ?The climate was semitropical and mild in Antarctica during Paleogene, as indicated by fossil spores and pollen, despite the fact that it sat on the South Pole. ?Before Antarctica separated from Australia, it was warmed by currents moving southward from more equatorial latitudes. 56 ?Australia began to separate from Antarctica during early Eocene, about 55 m.y. ago. ?After separation, circumpolar currents developed around Antarctica, cutting it off from equatorial currents. ?This resulted in temperature decrease and glacial conditions over Antarctica. Yellow = areas of major tectonic changes. ANTARCTICA DURING PALEOGENE (J. C. Brider, G. E. Dreway, and M. G. Smith, 1974, Jour. Geol., 82:556–558.) 57 GLOBAL SURFACE COOLING ?Temperatures dropped by about 8-13o C (roughly 22o F) near the Eocene-Oligocene boundary, as indicated by isotope data from brachiopods from New Zealand. ?Antarctic sea ice began to form by 38 m.y. ago. ?Greenhouse conditions were replaced by icehouse conditions. 58 WORLDWIDE COOLING RESULTED IN: 1.First Cenozoic widespread growth of glaciers in Antarctica about 38-22 m.y. ago. 2.Global sea level dropped by about 50 m during early Oligocene, as glaciers formed. 3.Cold, dense polar water flowed northward across ocean bottom. 4.Upwelling of cold bottom waters affected world climate. 59 5.Decrease in diversity and extinctions of many: ?marine molluscs ?planktonic and benthonic foraminifera ?ostracodes 6.Extinctions were earlier and more severe at higher latitudes. 7.Reefs shifted toward the equator. 8.Calcarous biogenic deep sea sediments (foraminiferal ooze) shifted toward the equator and were replaced by siliceous biogenic sediments (diatom and/or radiolarian ooze) at higher latitudes. WORLDWIDE COOLING RESULTED IN: 60 9.Changes in pollen indicate long term cooling and drying. ?Temperate and tropical forests shifted toward the equator. ?Grasslands expanded. ?Rainforests became confined to tropical, equatorial areas. 10.Glaciation occurred in other areas in Pliocene (and younger) deposits - Sierra Nevada, Iceland, South America, and Russia. WORLDWIDE COOLING RESULTED IN: 61 MEDITERRANEAN EVAPORITE DEPOSITS ?Sea level drop, associated with glaciation during Miocene, resulted in the isolation of the Mediterranean basin. ?Deep canyons were cut by rivers feeding the Mediterranean. ?The Mediterranean Sea dried up producing thick (1000-2000 m) evaporite deposits (gypsum, halite), 5-6 m.y. ago. 62 ANTARCTIC ICE ?Antarctica has been covered by glaciers for at least the past 15 m.y. ?The Antarctic ice sheet began to form during Eocene. ?Glacial conditions established by Miocene ?East Antarctic ice cap present since middle Miocene. ?During latest Miocene (about 5 m.y. ago), ice volume in Antarctica was greater than today. 63 ANTARCTIC BOTTOM WATERS ?The cold waters around Antarctica were dense, and sank to the ocean floor around Antarctica. (Cold water is denser than warmer water.) ?Cold, dense ocean-floor waters moved downward and outward, away from Antarctica. ?The northward movement of cold dense waters contributed to cool conditions during late Eocene and early Oligocene, and ultimately led to the Pleistocene Ice Age. 64 PLEISTOCENE ?Pleistocene began 1.8 m.y. ago. ?The most extensive glaciations began about 1 m.y. ago. ?The end of Pleistocene is when the ice sheets melted to approximately their current extent. ?The Pleistocene-Holocene boundary is placed between about 12,000 and 11,000 years ago, at the midpoint of the warming of the oceans. ?This coincides with a rise in sea level. 65 PLEISTOCENE ICE AGE ?Pleistocene is significant as the time in which humans evolved. ?More than 40 million km3 of snow and ice covered about 1/3 of Earth's land area. ?Continental glaciers covered much of North America and Europe. ?Alpine glaciers covered parts of the Cordilleran Mountain range in western North America, the Alps, and other mountain ranges of Europe. 66 AS A RESULT OF THE ICE AGE: 1.Climatic zones in the Northern Hemisphere were shifted southward. 2.Arctic conditions prevailed across Europe and the U.S. 3.Sea level dropped as much as 75 m (225 ft) and the shoreline shifted seaward, exposing the continental shelves as dry land. 4.Streams cut deep canyons into the continental shelves and on land. 67 5.Land bridges existed and led to migrations of mammals, including humans ?Across the Bering Sea between Siberia and Alaska ?Between Australia and Indonesia ?British Isles were attached to Europe 6.The land was sculpted by glaciers in Europe and North America. 7.U-shaped valleys formed in mountainous areas AS A RESULT OF THE ICE AGE: 68 8.Rainfall increased at lower latitudes. 9.Large lakes formed in the Basin and Range Province. ?Lake Bonneville in Utah covered more than 50,000 km2 and was about 1000 ft deep in places. ?The Great Salt Lake is a small remnant of Pleistocene Lake Bonneville. ?The Bonneville salt flats were formed as the lake evaporated. AS A RESULT OF THE ICE AGE: 69 10.Winds coming off glaciers blew sediment southward forming löess deposits (Missouri River area, central Europe, northern China) 11.Parts of northern and eastern Africa that are currently arid had abundant water and were fertile and populated by nomadic tribes. 12.Nomadic tribes hunted along the edges of the continental glaciers. Wild game was abundant, furs provided warm clothing, and there were less problems with spoiled meat in the cold temperatures. AS A RESULT OF THE ICE AGE: 70 13.Formation of the Great Lakes (depressions scoured by glaciers and flanked by moraines) 14.Formation of Cape Cod, MA - a moraine 15.Formation of Long Island, NY - a terminal moraine 16.Formation of Niagara Falls 17.Formation of large ice-dammed lakes, including Lake Missoula which drained catastrophically, forming the channeled scablands 18.Formation of hummocky topography and Pleistocene sand dunes AS A RESULT OF THE ICE AGE: 71 19.Weight of the ice depressed the continental crust to as much as 200-300 m downward. 20.Uplift (isostatic rebound) after ice melted. Coastal features are now elevated high above sea level. Map illustrating post-glacial uplift in North America. AS A RESULT OF THE ICE AGE: FIGURE 15-43 72 ADVANCE OF THE ICE SHEETS ?Late Pliocene and Pleistocene had strong, rapid, climatic fluctuations. ?Ice ages are characterized by glacial expansions separated by warmer interglacial intervals. ?Before the mid-1970's, Pleistocene was divided into four glacial stages with intervening warmer interglacial stages. ?More recent investigations have shown that there may have been as many as 30 glacial advances over the past 3 million years (roughly every 100,000 years.) 73 NAMES OF THE "TRADITIONAL" GLACIAL AND INTERGLACIAL STAGES IN NORTH AMERICA 74 STRATIGRAPHY OF PLEISTOCENE DEPOSITS Pleistocene deposits are difficult to date and correlate. Pleistocene sedimentary deposits, however, may show evidence of fluctuating climatic conditions, which can be used to mark times of glacial advance and retreat. 75 1.Evidence of Glacial Conditions ?Glacial till - unsorted mixture of clay to boulder-sized particles. Amount of weathering of glacial deposits or soils, and the amount of dissection by streams may help with relative dating. ?Bedrock with glacial striations ?Stratified drift - glacial deposits which have been washed and sorted by meltwater ?Varved clays - seasonal laminations deposited in glacial lakes. Counting varves may reveal the number of years during which they clay was deposited. STRATIGRAPHY OF PLEISTOCENE DEPOSITS 76 2.Plant Remains ?Pollen grains - types of plants indicate climate ?Fossil angiosperm leaf shapes indicate climate Smooth margin = WARM climate Jagged margin = COOL climate STRATIGRAPHY OF PLEISTOCENE DEPOSITS 77 3.Radiometric dating of wood, bone, or peat using carbon-14. ?For materials less than 100,000 years old due to the short half-life of carbon-14 (5730 yrs). ?Only useful for the most recent glacial stage. 4.Magnetic stratigraphy The record of magnetic reversals in cores of deep sea sediments can be correlated to magnetic reversals in volcanic rocks. ?Volcanic rocks can be dated radiometrically, and the dates applied to the sediments with the same magnetic characteristics. STRATIGRAPHY OF PLEISTOCENE DEPOSITS 78 5.Correlation of deep-sea sediments from cores, using fossil remains, particularly microfossils such as foraminifera. Fossils can be dated by relating them to paleomagnetic data and to radiometric dates. STRATIGRAPHY OF PLEISTOCENE DEPOSITS 79 6.Oxygen Isotope Ratios ?Ratio of O-18 to O-16 in foram shells from cores tells us the volume of water stored in glacial ice. ?Numbers 16 and 18 refer to atomic mass or total number of protons and neutrons in the O atom. ?Atomic number of O is 8 (O has 8 protons). ?Oxygen-16 has 8 neutrons, and ?Oxygen-18 has 10 neutrons. ?An atom of oxygen with 10 neutrons is heaver than an atom of oxygen with 8 neutrons. STRATIGRAPHY OF PLEISTOCENE DEPOSITS 80 6.(cont.) Oxygen Isotope Ratios ?Oxygen is present in water (H2O) and in some minerals, such as calcite or aragonite (CaCO3), that make up the shells of forams. ?Ratio of O-18 to O-16 in the water (and in shells) depends on temperature. ?Lighter oxygen isotopes (O-16) accumulate in glacial ice. Why? During evaporation, lighter isotopes are concentrated in the water vapor in the air. Water with lighter oxygen (O-16) is easier to evaporate than water with heavier oxygen (O-18). STRATIGRAPHY OF PLEISTOCENE DEPOSITS 81 6.(cont.) Oxygen Isotope Ratios ?Water vapor condenses and falls as rain or snow. Snow may accumulate to form glaciers. As a result, O-16 becomes trapped in glacial ice. ?O-18 remains in the oceans, because water with O-18 did not evaporate as readily. ?As temperatures drop, air becomes drier, and the percentage of O-18 in seawater (and in foram shells) increases. STRATIGRAPHY OF PLEISTOCENE DEPOSITS 82 6.(cont.) Oxygen Isotope Ratios ?Foraminifera and the oxygen-16/18 signal: ?Foram shells rich in O-18 = COLD & DRY, or glacial conditions. ?Foram shells rich in O-16 = WARM & WET, or interglacial conditions. STRATIGRAPHY OF PLEISTOCENE DEPOSITS 83 Graph representing variations in the oxygen isotope ratios in foram shells (and in the global volume of ice) over the past 500,000 years. 6.(cont.) Oxygen Isotope Ratios STRATIGRAPHY OF PLEISTOCENE DEPOSITS 84 7.The type of foraminifera fossil present may indicate something about the paleoclimate. Some species live in warmer water. If those species are absent, it may indicate that the water was colder due to a glaciation. STRATIGRAPHY OF PLEISTOCENE DEPOSITS 85 8.Coiling directions in foraminifera shells One particular species of foraminifera, Globorotalia truncatulinoides, is known to coil: ?to the right in warmer waters, and ?to the left in colder waters. By examining the percentage of right- and left-coiled specimens, a cyclic pattern representing glacial advances and retreats can be determined. STRATIGRAPHY OF PLEISTOCENE DEPOSITS 86 Graphs illustrating the percentages of right-coiling and left-coiling foraminifera, Globorotalia truncatulinoides. The vertical scale is depth in deep sea sediment cores, in centimeters. STRATIGRAPHY OF PLEISTOCENE DEPOSITS 87 WHY DID EARTH'S SURFACE COOL? There was both a long-term decline in temperatures, as well as an oscillation of glacial and interglacial stages. Any hypothesis for the cooling must consider both of these factors. 88 MILANKOVITCH CYCLES ?A widely accepted hypothesis for the temperature fluctuations is related to Earth's orbital oscillations. ?This hypothesis was developed by Yugoslavian mathemetician Milutin Milankovitch, and it is referred to as the Milankovitch cycles. 89 MILANKOVITCH CYCLES ?The cyclic climatic changes result from changes in the distance and angular relationships between the Earth and Sun due to periodic fluctuations in Earth's orbit. ?Precession - Earth's axis wobbles or moves in a circle like a spinning top over 26,000 years, affecting the amount of solar radiation received at the poles. 90 MILANKOVITCH CYCLES 2.Orbital eccentricity - Earth's orbit around the Sun changes from more circular to more elliptical by about 2% over about 100,000 years, moving the Earth closer to or farther from the Sun, and varying the amount of solar radiation received by the Earth. 91 MILANKOVITCH CYCLES 3.Angle of tilt of Earth's axis - currently about 23.5o, this tilt angle causes the seasons. Tilt angle varies from about 21.5o - 24.5o over about 41,000 years, changing length of days and amount of solar radiation received at the poles. 92 MILANKOVITCH CYCLES ?The combination of these variables periodically results in a change in the amount of solar radiation received by the Earth, which causes cycles of cooling and periodic glaciations. ?Milankovitch cycles correspond well to glaciation episodes, which have occurred every 100,000 years over the past 600,000 years, as indicated by oxygen isotope data. 93 1.Albedo or reflectivity of the Earth If Earth's albedo increased, due to snow cover, cloud cover, or dust in the atmosphere, the atmospheric temperatures would decrease due to reflection of solar radiation into space. As snow cover increased, albedo would increase, producing a positive feedback relationship, accelerating the rate of glacial growth. A 1% loss of incoming solar energy would result in a temperature drop of about 8o C, which might be sufficient to trigger glacial buildup. NON-MILANKOVITCH FACTORS IN GLOBAL CLIMATE CHANGE 94 2.A decrease in atmospheric CO2 would cause a decrease in the greenhouse effect, and lead to cooling. 3.Conversely, an increase in atmospheric CO2 would cause warming, which would result in more rapid evaporation, more cloud cover, and an increase in albedo, which could trigger glaciation. NON-MILANKOVITCH FACTORS IN GLOBAL CLIMATE CHANGE 95 4.Plate tectonics is important in that a continent must lie on or near a pole for snow to build up to form a glacier. 5.Plate tectonics is further involved because the formation of the Isthmus of Panama diverted the Gulf Stream northward about 3.5 million years ago. The warm, moist air associated with this ocean current led to an increase in snowfall in northern areas and the development of continental glaciers. NON-MILANKOVITCH FACTORS IN GLOBAL CLIMATE CHANGE 96 6.The impact of human activities, such as increased burning of fossil fuels and the associated buildup of greenhouse, is having and will continue to have an effect. NON-MILANKOVITCH FACTORS IN GLOBAL CLIMATE CHANGE 97 THE "LITTLE ICE AGE" ?Cold spells recurred periodically into Holocene. ?The "Little Ice Age" lasted from 1540 – 1890. Temperatures were several degrees cooler than today. ?Loss of harvests, famine, food riots, and warfare in Europe. ?Cold conditions correlate with periods of low sunspot activity. ?A time of extremely low sunspot activity from 1645 -1715 is known as the Maunder Minimum. 98 THE "LITTLE ICE AGE" – CONT’D ?Heightened volcanic activity occurred during the Little Ice Age. ?Volcanic ash and aerosols in the atmosphere caused temperatures to drop by blocking out incoming solar radiation. ?The eruption of Mount Tambora in Indonesia in 1815 was followed by the "Year Without A Summer." ?Frost and snow were reported during June and July of 1816 in New England and Northern Europe. 99 END OF THE "LITTLE ICE AGE" ?Human-induced warming may be the reason for the end of the "Little Ice Age." ?Greenhouse gases associated with the Industrial Revolution are the major factors influencing global warming and climate change today. 100 • FIGURE 15-7 Generalized paleogeographic map of North America during the Paleogene. Source: • FIGURE 15-23 The small Juan de Fuca plate plunges beneath Oregon and Washington. Source: • FIGURE 15-43 Postglacial uplift (rebound). Source: IMAGE CREDITS 101