Mesozoic Earth History Million years ago Triassic Jurassic Cretaceous

Transcription

1 Mesozoic Earth History Million years ago Triassic Jurassic Cretaceous

2 Geologic Time Scale

3 Main Happenings in Mesozoic Breakup of Pangaea Lots of mountain-building in western North America Appearance + extinction of dinosaurs More detail in the geologic record More climate information!

4 Climate information in the geologic record Evaporites: precipitation < evaporation = dry Coal = lots of vegetation + lots of moisture Sand dunes = dry

5 Tectonic drivers of climate Tectonics influences the hydrologic cycle Mountains can block rainfall Massive continents tend to have hotter, drier cores Coastal regions are more moderate Circumpolar currents prevent heat from reaching poles N/S currents move heat effectively

6 End Permian land and oceans Pangaea was shaped like a C Inside ocean: Tethys Sea Outside ocean: Panthalassa Panthalassa Panthalassa Tethys sea

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8 Breakup of Pangea 1: Triple Junctions Seafloor spreading creates a triple junction: a point where 3 tectonic plates diverge North America split off from S America and Africa

9 Triple Junctions

10 Seafloor spreading raises sea level Seafloor spreading causes bulges in ocean basins Big enough bulges and/or lots of them lowers the ocean volume This can cause flooding of the continents.

11 Breakup of Pangaea 2: Opening of Gulf of Mexico In Middle Jurassic, North America and South America separated Gulf of Mexico began to open Restricted basin at first lots of evaporites deposited

12 Gulf of Mexico Salt

13 Paleogeography of the World During the Triassic Period

14 Paleogeography of the World During the Jurassic Period

15 Breakup of Pangaea 3: Continued Widening of North Atlantic In Late Cretaceous, Atlantic widened rapidly Canada and Europe separated

16 Final Breakup In Late Cretaceous, Australia and Antarctica separated In Cenozoic, Antarctica and South America separated

17 Paleogeography of the World During the Late Cretaceous Period

18 At the end of the Triassic, Pangea began to rift apart. The supercontinent of Pangea, mostly assembled by the Triassic, allowed land animals to migrate from the South Pole to the North Pole. Life began to rediversify after the great Permo-Triassic extinction and warm-water faunas spread across Tethys.

19 Pangea was assembled piece-wise. The continental collisions that lead to the formation of the supercontinent began in the Devonian and continued through the Late Triassic.

20 In a similar fashion, the supercontinent of Pangea did not rift apart all at once, but rather was subdivided into smaller continental blocks in three main episodes. The first episode of rifting began in the middle Jurassic, about 180 million years ago. After an episode of igneous activity along the east coast of North America and the northwest coast of Africa, the Central Atlantic Ocean opened as North America moved to the northwest. This movement also gave rise to the Gulf of Mexico as North America moved away from South America. At the same time, on the other side of Africa, extensive volcanic eruptions along the adjacent margins of east Africa, Antarctica, and Madagascar heralded the formation of the western Indian Ocean.

21 During the Mesozoic North America and Eurasia were one landmass, sometimes called Laurasia. As the Central Atlantic Ocean opened, Laurasia rotated clockwise, sending North America northward, and Eurasia southward. Coals, which were abundant in eastern Asia during the early Jurassic, were replaced by deserts and salt deposits during the Late Jurassic as Asia moved from the wet temperate belt to the dry subtropics. This clockwise, see-saw motion of Laurasia also lead to the closure of the wide V-shaped ocean, Tethys, that separated Laurasia from the fragmenting southern supercontinent, Gondwana.

22 By the Early Jurassic, south-central Asia had assembled. A wide Tethys ocean separated the northern continents from Gondwana. Although Pangea was intact, the first rumblings of continental break up could be heard.

23 The supercontinent of Pangea began to break apart in the Middle Jurassic. In the Late Jurassic the Central Atlantic Ocean was a narrow ocean separating Africa from eastern North America. Eastern Gondwana had begun to separate form Western Gondwana.

24 During the Cretaceous the South Atlantic Ocean opened. India separated from Madagascar and raced northward on a collision course with Eurasia. Notice that North America was connected to Europe, and that Australia was still joined to Antarctica.

25 The second phase in the breakup of Pangea began in the early Cretaceous, about 140 million years ago. Gondwana continued to fragment as South America separated from Africa opening the South Atlantic, and India together with Madagascar rifted away from Antarctica and the western margin of Australia opening the Eastern Indian Ocean. The South Atlantic did not open all at once, but rather progressively "unzipped" from south to north. That is why the South Atlantic is wider to the south.

26 Other important plate tectonic events occurred during the Cretaceous Period. These include: - the initiation of rifting between North America and Europe, - the counter-clockwise rotation of Iberia from France, - The separation of India from Madagascar, the derivation of Cuba and Hispaniola from the Pacific, - the uplift of the Rocky mountains, - and the arrival of exotic terranes (Wrangellia, Stikinia) along the western margin of North America.

27 Globally, the climate during the Cretaceous Period, like the Jurassic and Triassic, was much warmer than today. Dinosaurs and palm trees were present north of the Arctic Circle and in Antarctica and southern Australia. Though there may have been some at the poles during the Early Cretaceous, there were no large ice caps at anytime during the Mesozoic Era. These mild climatic conditions were in part due to the fact shallow seaways covered the continents during the Cretaceous. Warm water from the equatorial regions was also transported northward, warming the polar regions. These seaways also tended to make local climates milder, much like the modern Mediterranean Sea, which has an ameliorating effect on the climate of Europe.

28 Shallow seaways covered the continents because sea level was meters higher than today. Higher sea level was due, in part, to the creation of new rifts in the ocean basins that displaced water onto the continents. The Cretaceous was also a time of rapid sea-floor spreading. Because of their broad profile, rapidly spreading mid-ocean ridges displace more water than do slow spreading mid-ocean ridges. Consequently, during times of rapid sea-floor spreading, sea level will tend to rise.

29 50-55 million years ago India began to collide with Asia forming the Tibetan plateau and Himalayas. Australia, which was attached to Antarctica, began to move rapidly northward.

30 20 million years ago, Antarctica was coverd by ice and the northern continents were cooling rapidly. The world has taken on a "modern" look, but notice that Florida and parts of Asia were flooded by the sea.

31 When the Earth is in its "Ice House" climate mode, there is ice at the poles. The polar ice sheet expands and contacts because of variations in the Earth's orbit (Milankovitch cycles). The last expansion of the polar ice sheets took place about 18,000 years ago.

32 Where did most North American mountain-building occur during Paleozoic?

33 Where did most North American mountain-building occur during Paleozoic? East Coast - Appalachians

34 Cordillera Orogenies General term refering to complex period of mountain-building Jurassic-Cenozoic Farallon plate goes below N American plate Nevadan orogeny Late Jurassic/Early Cretaceous Orogeny near the current W coast Slope of subducting Farallon plate decreased -> Sevier orogeny Late Cretaceous Further east (Utah) Laramide orogeny Late Cretaceous/Cenozoic Even FURTHER east! Rockies

35 Global Sea-Level Rise A global rise in sea level during the Cretaceous resulted in worldwide transgressions marine deposition was continuous over much of the North American Cordillera

36 Cretaceous Flood Worldwide transgression 1/3 of land area of Earth submerged 100 Ma Cretaceous Interior Seaway in North America

37 Cretaceous Interior Seaway Paleogeography of North America during the Cretaceous Period

38 Western Interior Seaway

39 The Effects on Global Climates and Ocean Circulation Patterns At the end of the Permian Period Pangaea extended from pole to pole Covered about one-fourth of Earth's surface Surrounded by a global ocean that encompassed about 300 degrees of longitude Such a configuration exerted tremendous influence on the world's climate resulted in generally arid conditions over large parts of Pangaea's interior

40 Oceanic Circulation Evolved From a simple pattern in a single ocean (Panthalassa) with a single continent (Pangaea)

41 Oceanic Circulation Evolved to a more complex pattern in the newly formed oceans of the Cretaceous Period

42 Areas Dominated by Seas Are Warmer Oceans absorb about 90% of the solar radiation they receive continents absorb only about 50% even less if they are snow covered The rest of the solar radiation is reflected back into space Therefore, areas dominated by seas are warmer than those dominated by continents

43 Mesozoic Tectonics (Key Events) Period North America Orogenies Cretaceous Jurassic Triassic Devonian Other Major Events Separation of India from Gondwanna Nevadan Orogeny (J-K) Sevier Orogeny (J-K) Opening of Atlantic Ocean Sonoma Orogeny (Triassic) Opening of Gulf of Mexico Antler Orogeny (Devonian)

44 Mesozoic Tectonics The separation of Gondwana and Laurentia began in the Triassic. Initial flooding of the Atlantic Ocean began in the Jurassic. This was the start of a new drift direction for North America; WNW

45 Mesozoic Tectonics Into the Triassic, many more terranes (mostly island arcs) began to be scooped up by North America as it drifted WNW

46 Mesozoic Tectonics Into the Triassic, many more terranes (mostly island arcs) began to be scooped up by North America as it drifted WNW Brooke Range Terrane (Alaska) Stikine Terrane (British Columbia) Sonoma Terrane (Nevada)

47 Mesozoic Tectonics Into the Triassic, many more terranes (mostly island arcs) began to be scooped up by North America as it drifted WNW Brooke Range Terrane (Alaska) Stikine Terrane (British Columbia) Sonoma Terrane (Nevada)

48 Mesozoic Tectonics The Sonoman Orogeny in the Triassic marks the start of the formation of the Cordilleran Mountains and the current active margin Mid-Triassic Paleogeography (source

49 Mesozoic Tectonics In the Jurassic, we start to see terranes with mixed lithologies docking with North America (e.g., Klamath Terrane) Major (felsic) intrusions begin

50 Mesozoic Tectonics The culmination of several hits and docking events as well as major phases of felsic intrusions is collectively called the Nevadan Orogeny Mid-Jurassic Paleogeography (source

51 Mesozoic Tectonics In the Cretaceous, more hits and more intrusions. More uplift Wrangellia Terrane docks

52 Mesozoic Tectonics The culmination of several hits and docking events from the Jurassic to the Cretaceous produced major phases of thrust faulting and is collectively called the Sevier Orogeny Early Cretaceous Paleogeography (source

53 Mesozoic Paleogeography Most continents were isolated Seas opened: South Atlantic; Gulf of Mexico; Caribbean Sea Mid-Cretaceous sea level high Tethys Seaway

54 Mesozoic Climate Wind belt Evaporite deposition

55 Mesozoic Climate High latitudes were warm 50 F / 10 C Dinosaurs near south pole

56 Mesozoic Climate Period of high sea level Associated with rapid sea floor spreading Long period without reversal

57 Mesozoic Climate Oceans stagnated Epicontinental black muds when seas spilled over Normally thin oxygen poor zone expanded This will change in the early Cenozoic (Late Eocene)

58 Cenozoic Climate Oxygen isotopes Late Eocene cooling Deep sea foraminifera

59 Cenozoic Climate Paleocene-Middle Eocene: No circumpolar current Late Eocene-today: Circumpolar current Permitted development of glaciers on Antarctica

60 Cenozoic Climate

61 Cenozoic Tectonic Events Final breakup of Gondwana (Australia separated from Antarctica in the Latest Paleocene earliest Eocene epochs) India began to collide with Asia forming the Himalayan Mountain Range (Oligocene to Recent) Africa started to shift northward, gradually sliding under Europe and uplifting the Alps (Oligocene to Recent) Continued westward movement of North America and South America formed an on again off again land bridge between the two continents. This gave rise to some interesting animal exchanges. North American orogenies become dominated by strike-slip faulting and uplift. Mountain building in the northern part of the Cordilleran mountains (mostly Canada) slows down stop during the Oligocene. Activity shifts to the southern part of the mountain chain (Colorado, Nevada etc.). Major late Tertiary flood basalt eruptions occur in Oregon and Washington state. Hot spot volcanism occurs in the area of Yellowstone (Pliocene to present). Composite volcanic eruptions (some incredibly explosive) periodically occurred and still do (e.g., Mt St Helen s).

62 Himalayan Mountains Indian craton collided with Eurasia