1. Part 1: The Vendian, Cambrian, and Early Ordovician Periods
Earth History GEOL 2110
The Paleozoic Era
Part 1: 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 ( Ma) to Cambrian ( 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. of Rodinia by a Superplume
Disassembly
of Rodinia by a Superplume
750 Ma
Li et al., 2008

6. Laurentia Becomes Modern-day Africa Surrounded by Rifted Passive Margins

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

8. Passive Margin Sedimentation Western 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 Environment Shallow 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. Actualism Deposition 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