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Chapter 14
Mesozoic Earth History
245-65 Million years ago
Triassic
Jurassic
Cretaceous
Geologic Time Scale
www.geo.ucalgary.ca/~macrae/timescale/time_scale.gif
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!
Climate information in the geologic
record
• Evaporites: precipitation < evaporation =
dry
• Coal = lots of vegetation + lots of moisture
• Sand dunes = dry
The hydrologic cycle and climate
Water moves heat from the
equator to the poles
• When water changes phase, it either
releases or takes up energy
• Evaporation: gaseous water carries energy
– Humid regions don’t get as hot
• Precipitation: releases energy as heat
– Humid regions don’t get as cold
• Ocean currents are the Earth’s heating and
AC ducts, moderating our climate
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
End Permian land and oceans
• Pangaea was shaped
like a ‘C’
• Inside ocean: Tethys
Sea
• Outside ocean:
Panthalassa
Panthalassa
Panthalassa
Tethys sea
www.ig.utexas.edu/research/projects/plates/images/pangea.jpg
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
Triple Junctions
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.
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
Gulf of Mexico Salt
http://oceanexplorer.noaa.gov/technology/tools/mapping/media/gis_gulf.html
Breakup of Pangaea 3:
Continued Widening of North Atlantic
• In Late Cretaceous, Atlantic widened rapidly
• Canada and Europe separated
Final Breakup
• In Late Cretaceous, Australia and Antarctica
separated
• In Cenozoic, Antarctica and South America separated
Global Plate Tectonics
Jurassic to Present Day
By
L.A. Lawver, M.F. Coffin, I.W.D. Dalziel
L.M. Gahagan, D.A. Campbell, and R.M. Schmitz
2001, University of Texas Institute for Geophysics
February 9, 2001
Paleogeography of the World
• During the Triassic Period
Paleogeography of the World
• During the Jurassic Period
Paleogeography of the World
• During the Late Cretaceous Period
Where did most North American
mountain-building occur during
Paleozoic?
Where did most North American
mountain-building occur during
Paleozoic?
East Coast - Appalachians
Cordillera
• Western margin of North America
• Spanish for “mountain range”
• Rocky Mountains, Sierra Nevadas
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
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
Cretaceous Flood
• Worldwide transgression
• 1/3 of land area of Earth submerged
• 100 Ma
• Cretaceous Interior Seaway in North America
Cretaceous Interior Seaway
• Paleogeography
of North America
during the
Cretaceous
Period
Western Interior Seaway
www.isgs.uiuc.edu/dinos/westernseaway.gif
Western Interior Seaway
www.colorado-mall.com/HTML/EDUCATIONAL/SCIENCES/GEOLOGY/COLO_GEOLOGY/COLO_CREATION/ANCIENT_SEAS/ancient_seas.html
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
Oceanic Circulation Evolved
• From a simple pattern in a single ocean
(Panthalassa) with a single continent (Pangaea)
Oceanic Circulation Evolved
• to a more complex pattern in the newly formed
oceans of the Cretaceous Period
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