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Earth History GEOL 2110

Earth History GEOL 2110. The Paleozoic Era The Vendian , Cambrian, and Early Ordovician Periods. Major Concepts. The long-lived supercontinent of Rodinia created a long period between 1,000 – 600 Ma with little deposition in the interior of most continents.

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Earth History GEOL 2110

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  1. Earth History GEOL 2110 The Paleozoic Era The Vendian, Cambrian, and Early Ordovician Periods

  2. Major Concepts • The long-lived supercontinent of Rodinia created a long period between 1,000 – 600 Ma with little deposition in the interior of most continents. • The break-up of Rodinia, which started around 750 Ma resulted in great amounts of sediment deposited on the passive margins of the disassembled continents. • In North America (Laurentia) great thicknesses of Vendian (610-550 Ma) to Cambrian (550-490 Ma) sediments accumulated along it continental edges. • Between middle Cambrian time and early Ordovician time, the dispersal of the Rodinian plates resulted in a global rise in sea level, which flooded the continents with shallow seas. • In North America, this is called the Sauk transgression and produced sedimentation of ultrapure quartz sands and later carbonates.

  3. Assembly of Rodinia 1200 – 750 Ma Li et al., 2008

  4. Li et al., 2008

  5. Disassembly ofRodinia by a Superplume 750 Ma Li et al., 2008

  6. Laurentia Becomes Modern-day AfricaSurrounded by Rifted Passive Margins

  7. Mid-Cambrian Plate ReconstructionLaurentia becomes Isolated and Flooded Laurentia Siberia Iapetus Ocean Gondwanaland Taconic Arc Baltica glaciation

  8. Passive Margin SedimentationWestern US Rift Basalts (750 Ma) Glacial Deposits (Snowball Earth)

  9. Thinning of Cambrian Sediments across the Laurentian Craton Belt Supergroup sediments preserved in rift grabens (aulocogens)

  10. Distribution of Cambrian Sediments over Laurentia • Warping of the Craton • Broad horizontal tectonic stresses related to plate motion • Sediment loading • Isostatic adjustments due to different densities within the crust MCR

  11. Was Craton Warping Syn- or Post-Depositional? Syn-depositional Warping Post-depositional Warping

  12. How do we tell Structure of the Crust?

  13. Sedimentary Facies and Paleogeography of Late Cambrian Sedimentary Deposits

  14. Ultrapure Quartz Cambrian Sandstone MN/WI Strat Column 95-99% Quartz Well Rounded Well Sorted Jordan SS

  15. Depositional EnvironmentShallow Marine or Eolian? Low –angle cross stratification -Marine Both Eolian – early transport Marine – final deposition Abraided quartz grains - Eolian Mod–angle cross stratification -Eolian

  16. How Shallow is Shallow Marine? Stromatolitic Limestone Fossilized Algal Mats Tidal Oolitic Carbonates Agitated Water Flat-pebble Conglomerates Storm Rip-ups of the Seafloor Mud Cracks Periodic Drying

  17. Modern Day Analog to the Sauk Sea • Gulf of Mexico • <200 Meters Deep • Carbonate deposition in detrital sediment starved areas • Differences • ¼ the area of Sauk Sea • Coral reefs not present until Silurian • No land vegetation in Cambrian - fine sediment winnowed from land by wind

  18. ActualismDeposition accomplished mostly by Hurricanes “Fossil Hash” - Mass-kills from Hurricanes

  19. Next Lecture The Paleozoic Era Part 2: Late Ordovician Period Limestone, Limestone, and more Limestone and The Emergence of the Appalachians

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