LECTURE NOTES: EARTH HISTORY: The Mesozoic Era

In this this exercise we compiled a fact sheet for all three period of the Mesozoic Era: Triassic, Jurassic & Cretaceous Period, using information provided by University of California Museum of Paleontology at Berkeley ( http://www.ucmp.berkeley.edu/mesozoic/)Web site,  and Stanley's Earth Systems History text.  The follow should serve as a guide for understand this important period. 


Triassic (252 -206 mybp)

TECTONICS: What important Tectonic events occurred during this period? For example, what continents were present and where their geographic location? (Record the URL of any pictures that would be useful to show the class)

  1. Using this Map: http://www.scotese.com/newpage8.htm, we see that Pangea has begun to rift starting in the Tethys Sea (sea floor spreading along a mid-ocean ridge) which spreads westward into Pangea forming Laurasia (northern continent) and Gondwana (the southern continent) by late in the Triassic period
  2. Evidence for these extensional pressure can be found along eastern portion of the US where rift basins formed (normal faults produced “hinge basins” trapping sediments during the late Triassic
  3. For most of the Triassic, Pangea is centered over the equator with a lower sea level

ANCIENT LIFE: What forms of life that inhabited the Earth during the Triassic? HINT: From the Introduction Page, click on the links that describe those plants and animals. Then visit the Localities Link to find places where Triassic Fossils and rock have been studied. (Record the URL of any pictures that would be useful to show the class)

  1.  Early dinosaur are found in Triassic-age rocks in Argentina
  2.  Survived the Late Permian extinctions to dominate in the Triassic Lycophytes (club mosses) while glossopteris (large leaf: seed plant) become extinct by the late Triassic.
  3. Conifer (evergreen trees), Ginko, ferns and horsetails are abundant. 
  4.  

CLIMATE & ENVIRONMENT

  1. Because of Pangea' s geographic location the climate recorded was very arid and dry. Larger continental landmass were subject to seasonal changes (at high latitudes) but, overall large landmasses become very hot dry.
  2. No polar ice caps

Jurassic (206- 142 mybp)

TECTONICS: What important Tectonic events occurred during this period? For example, what continents were present and where their geographic location? 

  1. Pangea gives way to Laurentia in the north and Gondwana in the south in the Jurassic Period. North America separates from North Africa and South America creating the early Atlantic Ocean and shifts northward
  2. Exotic terrains (island arcs) become accreted onto the western margin North America (Laurentia)
  3. Gondwana begins to separate by rifting separating India/Antarctica from Africa/South America

ANCIENT LIFE: What forms of life that inhabited the Earth during this period? HINT: From the Introduction Page, click on the links that describe those plants and animals. Then visit the Localities Link to find places where Jurassic Fossils and rock have been studied. (Record the URL of any pictures that would be useful to show the class)

  • Archyopteryx (a dinosaur-like bird) appears for the first time in the Solenhofen Limestone in Germany. This early bird had winged claws and no teeth.

  • Dinosaurs dominate the land! Famous locations for dinosaur fossils are the Morrison Formation in western US.

 

  • Plants: Ginkos, Cycads (palm trees) flourish and are the dominant land plant

CLIMATE & ENVIRONMENT: Write a description of what type of climate and/or environment is preserved in the rocks of this period?

  1. Sea Floor spreading adds new ocean crust and sea level rises. So, some continental regions become flooded but, overall still a very arid environment dominates.
  2. As Pangea split and move poleward, more dramatic changes in seasonal climate are preserved. There is evidence that ice and snow formed at the poles during this time.

Cretaceous (142 – 65 mybp)

TECTONICS:  What important Tectonic events occurred during this period?  http://www.scotese.com/cretaceo.htm

  1. By the Late-Cretaceous, Gondwana is rifted apart separating South America from Africa and completing the formation of the Atlantic Ocean.
  2. India and Madagascar split from Africa and Europe and Asia separate from North America.
  3. Sea level continues to rise (because of new ocean crust formation) forming many inland seas (North America, Africa and southern Europe.
  4. The Tethys Ocean begins to close as Eurasia moves toward the equator.
  5. Recall Paul's Case Study regarding the Break Up of Pangea

ANCIENT LIFE: What forms of life that inhabited the Earth during this period?  

  • Conifer Trees begin to dominate over Cycads
  • Angiosperms (FLOWERING Plants) first appear in the fossil record
  • A mass extinction (the famous one) at the end of the Cretaceous leads to the disappearance of most dinosaurs, ammonites and many foraminifera (marine organisms).  
  • This extinction is believed to have occurred as a result of 1) a meteorite impact on the Yucatan Peninsula a Chicxulub, Mexico Primary evidence has been the worldwide appearance of an iridium-rich layer of clay marking the boundary of the Cretaceous (K) and Tertiary periods.  Meteorites appear to be enriched in iridium.  With the discovery of a 180 mile wide crater at Chicxulub provided a support for this hypothesis.  Ejecta from the impact could have blocked out the sun’s energy resulting in massive cooling of the Earth’s surface.  

    • Recall the case studies by Willie describing this theory
  • Other geologists have argued that the source of the iridium is massive volcanic eruptions. The Deccan Traps in India provide evidence of such volcanic activity. If enough pyroclastic material were ejected into the atmosphere, significant cooling of the atmosphere could also result.
    • Recall the case studies by Jacob and Brian describing this evidence

 

CLIMATE & ENVIRONMENT:

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