Silurian

What is the time scale of the Silurian?

443 to 419 mya

Silurian and Devonian:

– High sea levels
– Shallow, epi-continental seas
– Diverse marine life
– Existing species radiated, new species evolved, especially reef ecosystems
– Large jawed fishes
– On land: plants emerge, thrive in Devonian, as do insects, other vertebrates

Renewal of Life

Renewal of Life
• Coral-strome reefs flourished
– Greatest size in Devonian
• Ecologic succession
– Tabluates and rugose corals colonized seafloor
– Other animals populated reef

Fishes evolved.

Fishes evolved.

–some pieces found in Ordovician
-First fully preserved specimens found in Silurian
-Many found in freshwater habitats

Major changes on Earth:

Major changes on Earth:
-albedo, impacts climate
-biogeochemical cycles

– enhanced weathering
-biogeochemical cycles

– enhanced carbon sequestration
-expands habitat for life

 – new animals evolve because new food sources
-new habitat; allows aquatic animals to move in land; plants provide protection from wind, sun,
dry conditions

Plants

• Invaded land by developing rigid
stem and root system

Vascular plants

Vascular plants
– Tubes deliver water and nutrients
– Rhynia

Early Terrestrial Animals

Early Terrestrial Animals
-Some fragmentary, simple terrestrial animal fossils from Late Silurian
-Once land plants expanded, more invertebrate animal fossils found in early Devonian sediments.

Eastern North American passive margin

-Erosion decreased elevation, seas flooded shelf, western carbonate deposition.
• Shallow seas in the west

– Middle Silurian

– Middle Silurian
• Muddy carbonate basins

Late Silurian

– Late Silurian
• Evaporite pans
-WARM climate

Ordovician Events: Laurentia

• Carbonate platform
– Seaward of siliciclastic

Laurentia: Taconic Orogeny
-Ordovician Mountain building: seen in modern New England

-By Silurian, eastern mountains were largely eroded, regions with clastic deposition were flooded by shallow seas, with carbonate accumulation

Silurian regional paleogeography:

Silurian regional paleogeography:
reef accumulation on top of clastics
Silurian
-Coral-strome reefs
-muddy carbonates accumulate in MI basin, N Central OH
-siliciclastic muds accumulate to east on tidal flats

– To east (PA), siliclastics transitioned to carbonates
– Evaporites dominated MI Basin; reflects progressive reefgrowth
– Reefs died – grew high, maybe SL
lowered

-Reefs grew only in Illinois and Indiana
– Thornton Reef exposed in Chicago
– Behind ridge were tabulate, rugose corals

Euramerica and Orogenies

Euramerica and Orogenies
• Most famous angular unconformity: in Scotland, between non-marine Devonian Old Red Sandstone (younger), atop the near
vertical Silurian marine beds (older)

-Old Red Sandstone deposited after Silurian mountain building episode

-Old Red Sandstone includes late Silurian, all Devonian, early Carboniferous sediments;

Plate tectonics:

Plate tectonics: Laurentia collided w/ Baltica during mid-Paleozoic, formed Euramerica

Acadian Orogeny

Acadian Orogeny
• Second phase of Appalachian mountain building
• Double collision of larger cratons
– Northern Laurentia = Baltica
• Mid Silurian
– Southern Laurentia = Avalonia
• elongate microcontinent that broke off of Gondwanaland in Ordovician
• Also acquired Carolina terrane