Silurian Period Notes

Silurian Period (444-419 Ma)

Silurian - Devonian Major Events

  • Land Plants and Arthropods Diversity: Significant increase in the variety of land plants and arthropods.
  • First Insects: Appearance of the first insect species.
  • First Land Vertebrates (Amphibians): Emergence of the earliest amphibians.
  • Late Ordovician Mass Extinction (RIP): Recovery from the mass extinction event.
  • Marine Recovery and Renewed Adaptive Radiation: Marine ecosystems rebounded with new species evolving.
  • Eurypterids Common: Eurypterids (sea scorpions) were prevalent.
  • Radiation of Jawed Fish: Jawed fish diversified.
  • First Seeds; First Large Trees and Forests: Development of seeds and the rise of large trees and forests.
  • Ammonoids Become Important Predators: Ammonoids evolved into significant predators.
  • Pentamerid Brachiopods Common: Prevalence of Pentamerid brachiopods.
  • Spirifer Brachiopods Common: Abundance of Spirifer brachiopods.
  • Mass Extinction in Tabulate-Stromatoporoid Reef: A mass extinction event affected tabulate-stromatoporoid reefs.
Biotic Events
  • Summarizes the key developments in life forms during the Silurian and Devonian periods.
Geologic Events
  • Caledonian Orogeny in Britain: Mountain-building event.
  • Extensive Reefs and Evaporites: Formation of large reefs and evaporite deposits.
  • Local Gondwana Glaciation (South America): Glaciation occurred in Gondwana.
  • Antler Orogeny: Another mountain-building event.
  • Acadian Orogeny Catskill Delta: Orogenic event leading to the formation of the Catskill Delta.
  • Tippecanoe Sequence: A geological sequence.
  • Kaskaskia Sequence: Another geological sequence.

Silurian Time Scale

  • Epochs/Ages/Stages: Early, Middle, Late Silurian.
  • GSSP Markers:
    • FAD of Monograptus uniformis: First Appearance Datum of Monograptus uniformis.
    • FAD of Neocolonograptus parultimus: First Appearance Datum of Neocolonograptus parultimus.
    • Near base of Saetograptus leintwardinensis: Close to the base of Saetograptus leintwardinensis.
    • FAD of Saetograptus varians: First Appearance Datum of Saetograptus varians.
    • FAD of Cyrtograptus lundgreni: First Appearance Datum of Cyrtograptus lundgreni.
    • Above LAD of Eocoelia intermedia (brachiopod): Above Last Appearance Datum of Eocoelia intermedia.
    • FAD of Monograptus austerus sequens: First Appearance Datum of Monograptus austerus sequens.
    • FAD of Akidograptus ascensus: First Appearance Datum of Akidograptus ascensus.
  • Sea Level: Fluctuations in sea level indicated as cooler or warmer.
  • Coastal Onlap: Indication of sea level rise and fall.
    *Adjusted Tropical SST

Silurian Paleogeography

  • Late Ordovician: Taconic Orogeny:
    • Closed the Iapetus Ocean between Baltica and Laurentia.
  • Queenston Delta:
    • A 300-mile-wide clastic wedge formed from the erosion of the Taconic Orogeny in the Late Ordovician.
    • Sedimentary signature of the Taconian Orogeny.
    • The clastic wedge is thickest and coarsest close to the mountain belt (in the east).
  • More Orogeny during Silurian: Caledonian, reaching a maximum in late Silurian/Early Devonian.
  • Continued closure of Iapetus ocean
  • Caledonian = collision of Baltica and North America
  • Acadian = collision of Avalonia with North America in Devonian
  • Gondwana still over south pole
  • Merger of Laurentia, Baltica, and Avalonia in orogeny = formation of continent Laurussia/Euramerica in Devonian
  • Early Silurian (430 Ma):
    • Position of Baltica, Laurentia, Avalonia, Siberia, and Gondwana.
  • Late Silurian (~420 Ma):
    • Location of Caledonides, Appalachians, Avalonia, Baltica, and Rheic Ocean.

Silurian Sea Level

  • Tippecanoe (until late Silurian to Early Devonian): High sea level.
    *Sea level curve

Silurian Climate

  • Some South American/Gondwanan glaciers in early Silurian, but less than during Ordovician icehouse.
    *Melting glaciers = high sea level
    *High sea level + Laurussia across the equator = lots of warm shallow oceans

Silurian Geography and Geology

  • Landscape Features: Mountains, barrier reefs, evaporites, epeiric sea, deep ocean, cordilleran mobile belt.
  • Regional Details:
    • Michigan Basin: Illustrates the conditions for evaporite formation.
    • Appalachian Basin: Shows the transition from Taconic Highlands to sedimentary environments.

Silurian Evaporites Formation

  • Evaporite Formation:
    • Evaporation leads to dense brines and precipitated salt in barred basins.
    • Precipitation of fine evaporite crystals in hypersaline conditions.
    • Fluid flow through barriers.

Terrestrial Life

  • First Vascular Land Plants (Cooksonia): Emergence of early land plants.
  • First Body Fossils of Fully Terrestrial Animals:
    • Myriapods, arachnids, hexapods.
Evolution of Plants

*Evolution of plants with timelines in millions of years ago (MYA)

Silurian Arthropods

  • Parascorpio venator: Silurian arthropod with adaptations for air breathing
  • Silurian terrestrial millipede Cowiedesmus

Silurian Reefs

  • First coral reefs in Silurian