The Middle Paleozoic
• The Silurian and Devonian
• High global sea levels (end Tippecanoe, Kaskaskia)
• tropical “greenhouse” environments
• reefs & mountain building
• plants and animals on land
Recovery and Expansion of Life
• many groups go extinct at the end of the Ordovician
• survivors radiate into many new groups
• marine vertebrates & terrestrial flora/fauna
Wave-resistant Reefs
• diversification of reef building organisms
• massive colonial skeletons -> tabulate-rugose-strome reefs
• large - Silurian (North America); Very large - Devonian (Australia &
Canada)
• environments -> forereef, reef crest, lagoon
Expansion and diversification of vertebrates - fish
• first appear - Early Paleozoic = marine
• most evident in Silurian and Early Devonian - fresh water
• jawless fish - jawed fish
ostraderms acanthodians
Diversification of important groups = “Age of Fish”
• marine fish
• placoderms
• sharks
• ray-finned fish
• lobe-finned fish - lung fish• swimming predators
• decline of the trilobites
Land Plants
• Problems => dry land; 1) tissues dry out ; 2)Fluid Transport, reproduction
• Solutions: Tough outer cells; Long inner cells;
Spores
• First appear - Silurian - simple vascular, spores
• Diversify - Devonian - trees - leaves - seeds
Land Plants = A very important event in Earth History
• most of the Early Paleozoic = an Ocean Realm
• Plants => weathering, soils, atmosphere (O2 & Ozone)
• make it possible for other organisms to colonize land
Geology and Geography of the Middle Paleozoic
• The Silurian
• quiet period tectonically
• high global sea level = large part of North America flooded
• tropical climates
Geology and Geography of the Middle Paleozoic
• Silurian = shallow tropical sea in North Americal
• limestone - clear, warm water
• barrier reefs in the Midwest
• reduced circulation and evaporites in basin areas
Geology and Geography of the Middle Paleozoic
• The Devonian
• high global sea level = North America flooded
• - end of Tippecanoe - beginning of Kaskaskia
• tropical environments
• major mountain building events = eastern and western North America
• glaciation, lower sea level, and colder/drier climates = Late Devonian
Geology and Geography of the Middle Paleozoic
• eastern mountain building - Acadian Orogeny
• Baltica and Western Europe (Avalonia) - collide with North America
• suturing and continental collision = major mountain building event
• accreted terranes in North America
• ancient mountains in western Europe
Geology and Geography of the Middle Paleozoic
– pronounced change in sediments in North America = Acadian Orogeny
– limestone to silicaclastics
– Catskill Delta & foreland basin in eastern North America
– 100’s of meters of sediment
– influences Midwest as well
Geology and Geography of the Middle Paleozoic
• western North America
• extensive barrier reef systems during Middle Devonian
• western mountain building = Antler Orogeny
• collision with Klamath island arc
• rapid change in sediment types
• reefs choked out
Middle Paleozoic Summary