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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