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 Panthalassa Pangaea was shaped like a ‘C’ Inside ocean: Tethys Sea Outside ocean: Panthalassa Tethys sea 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

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