Mesozoic Earth History

245-65 Million years agoTriassicJurassic

Cretaceous

Chapter 14

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

Tethys sea

• Pangaea was shaped like a ‘C’

• Inside ocean: Tethys Sea

• Outside ocean: Panthalassa

Panthalassa

Panthalassa

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

• During the Triassic Period

Paleogeography of the World

• During the Jurassic Period

Paleogeography of the World

• During the Late Cretaceous Period

Paleogeography of the World

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

• A global rise in sea level during the Cretaceous – resulted in worldwide transgressions

– marine deposition was continuous over much of the North American Cordillera

Global Sea-Level Rise

Cretaceous Flood

• Worldwide transgression

• 1/3 of land area of Earth submerged

• 100 Ma

• Cretaceous Interior Seaway in North America

• Paleogeography of North America during the Cretaceous Period

Cretaceous Interior Seaway

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

• 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

The Effects on Global Climates and Ocean Circulation Patterns

• 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

Oceanic Circulation Evolved

• 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

Areas Dominated by Seas Are Warmer