View
235
Download
0
Category
Preview:
DESCRIPTION
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.
Citation preview
Earth History GEOL 2110
The Paleozoic EraPart 1: 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.
• 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.
Assemblyof Rodinia
1200 – 750 Ma
Li et al., 2008
Li et al., 2008
Li et al., 2008
Disassemblyof Rodinia by a
Superplume750 Ma
Laurentia Becomes Modern-day AfricaSurrounded by Rifted Passive Margins
Mid-Cambrian Plate ReconstructionLaurentia becomes Isolated and Flooded
Laurentia
Baltica
Siberia
Gondwanaland
glaciation
Iapetus Ocean
Taconic Arc
Passive Margin SedimentationWestern US
Rift Basalts(750 Ma)Glacial Deposits
(Snowball Earth)
Thinning of Cambrian Sediments across the Laurentian Craton
Belt Supergroup sediments preserved in rift grabens (aulocogens)
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
Was Craton Warping Syn- or Post-Depositional?
Syn-depositional Warping
Post-depositional Warping
How do we tell Structure of the Crust?
Sedimentary Facies and Paleogeography of Late Cambrian Sedimentary Deposits
Ultrapure Quartz Cambrian Sandstone
95-99% Quartz
Well Rounded
Well Sorted
Jordan SS
MN/WI Strat Column
Depositional Environment
Shallow Marine or Eolian?
Low –angle cross stratification -Marine
Mod–angle cross stratification -Eolian
Abraided quartz grains - Eolian
BothEolian – early transport
Marine – final deposition
How Shallow is Shallow Marine?
Oolitic CarbonatesAgitated Water
Stromatolitic LimestoneFossilized Algal Mats
Tidal
Mud CracksPeriodic Drying
Flat-pebble ConglomeratesStorm Rip-ups
of the Seafloor
Modern Day Analog to the Sauk SeaGulf 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
Actualism Deposition accomplished mostly
by Hurricanes
“Fossil Hash” -Mass-kills from Hurricanes
Next Lecture
The Paleozoic EraPart 2: Late Ordovician Period
Limestone, Limestone, and more Limestone and The Emergence of the Appalachians
Recommended