Transcript Vendian, Cambrian and Early Ordovian

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.
• 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 (610550 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.
Assembly
of Rodinia
1200 – 750 Ma
Li et al., 2008
Li et al., 2008
Disassembly
of Rodinia by a
Superplume
750 Ma
Li et al., 2008
Laurentia Becomes Modern-day Africa
Surrounded by Rifted Passive Margins
Mid-Cambrian Plate Reconstruction
Laurentia becomes Isolated and Flooded
Laurentia
Siberia
Gondwanaland
Taconic Arc
Baltica
glaciation
Passive Margin Sedimentation
Western US
Glacial Deposits
(Snowball Earth)
Rift Basalts
(750 Ma)
Thinning of Cambrian Sediments
across the Laurentian Craton
Belt Supergroup
sediments preserved in
rift grabens (aulocogens)
Distribution of Cambrian Sediments
over Laurentia
MCR
Warping of the Craton
• Broad horizontal
tectonic stresses
related to plate
motion
• Sediment loading
• Isostatic adjustments
due to different
densities within the
crust
Was Craton Warping Syn- or PostDepositional?
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
MN/WI Strat Column
95-99% Quartz
Well Rounded
Well Sorted
Jordan SS
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
How Shallow is Shallow Marine?
Oolitic Carbonates
Agitated Water
Flat-pebble
Conglomerates
Storm Rip-ups
of the Seafloor
Stromatolitic Limestone
Fossilized Algal Mats
Tidal
Mud Cracks
Periodic
Drying
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
Actualism
Deposition accomplished mostly
by Hurricanes
“Fossil Hash” Mass-kills from
Hurricanes
Next Lecture
The Paleozoic Era
Part 2: Late Ordovician Period
Limestone, Limestone, and more Limestone
and The Emergence of the Appalachians