Earth History
GEOL 2110
The Paleozoic Era
Silurian and Devonian Periods – Part II
Stratigraphy and Tectonics
Major Concepts
• The proliferation of coral reefs caused restricted basins
wherein great thickness of limestone and evaporites
were deposited.
• Along the eastern margin of North America the collision
with the European craton and Avalonian microcontinents and volcanic arcs created a new orogenic belt
in the Devonian
• This orogenic event caused intense warping of the craton
that accentuated the arches and basins that had begun
to form in the Ordovician.
• It also generated a new clastic wedge of redbed mollasse
sediments in eastern NA and northern Europe
• Devonian tectonism also affected arctic regions and the
western margin of North America
Silurian – Devonian Major Events
Proliferation of Organic Reefs in the Silurian and Devonian
Carbonate Reefs and Evaporites
Carbonate Reefs
Inorganic Precipitation of Calcite
Ca++ + 2HCO-3
CaCO3 + H2O + CO2
Increased temperature reduces the
solubility of Ca in seawater and drives the
reaction to the right
Dolomitization
Sabhkas
River Water | Sea Water
Ca
73%
3%
Mg
11%
11%
Na
9%
84%
K
7%
3%
Relative solubility
Na>> K > Mg >> Ca
Calcite  Dolomite
2CaCO3 + Mg+2  CaMg(CO3)2 + Ca+2
Evaporites
Salts in Normal Seawater
NaCl – 2.72% Halite(Salt)
MgCl2 – 0.38%
MgSO4 – 0.16%
CaSO4 – 0.12% Anhydrite
K2SO4 – 0.08%
CaCO2 – 0.01% Calcite
Density of Brines
Evaporite Basins
of the Silurian
Salt Mine under Detroit
Early Devonian Regression
Break between Tippecanoe and Kaskasia Sequences
Early Devonian Regression
Much of the Silurian Removed on Arches
Silurian Missing from MN
Kaskasia Sequence of the Devonian
Mountain-building and Craton-warping affects Sedimentation
Craton Warping Creates Multiple
Unconformities
Mississippian LS
Devonian Missing
thin Silurian LS
Unconformities
draping the Ozark
Dome, Missouri
Ordovician LS
Acadian Orogeny
A New Clastic Wedge Forms
Organic
Black Shale
(Flysch)
Coarse
Immature
Sandstone and
Conglomerate
(Molasse)
Redeformation of
Late Ordovician
Taconian Deformation
The Devonian
Marcellus
Shale
Acadian Orogeny Overprints Precusor Orogens
Late Ordovician
K-Ar ages
Middle Silurian
Late Devonian
Remember the Grenville
Collision of
Laurentia with
Amazonia (SA)
at 1 Ga
Caledonian Orogeny
Europe Docks to the North in Early Devonian
Caledonian Orogeny
A Continent-Continent Collision
Devonian Old Red Sandstone
Clastic Wedge on European Side of the Caledonian Orogen
Minor Devonian Orogenies
Ellesmerian (Arctic) Antler (Western NA)
More to Come
Making Pangea
Feedback of the Organic and Physical
World
Next Lecture
The Paleozoic Era
The Carboniferous and Permian Periods
The Making of Pangea
QUIZ on Chapter 13