Earth History GEOL 2110

The Paleozoic EraLate Ordovician Period

Limestone, Limestone, and more Limestone and The Emergence of the Appalachians

Major Concepts• The great Sauk sea retreated to the edge of the NA craton about

480 Ma, when it transgressed the craton again (the Tippecanoe Transgression) over the next 50 million years, a whole new diversity of marine live came with it.

• While Cambrian sands were initially spread over the craton as the Tippecanoe beach trangressed over the land, creating another ultrapure quartz sandstone formation – the St. Peter, this was quickly followed extensive deposition of fossil-rich limestone.

• In the late Ordovician, the eastern margin of Laurentia transformed from a passive continental slope margin to a tectonically active volcanic arc – the Taconic.

• Immature sediments shed westward from this arc accumulated between the continent and the volcanic arc and eventually became deformed and metamorphosed when the arc eventually collided and was thrust onto the continental edge –Penokean-like.

The Tippecanoe TransgressionMid- to Late Ordovician

The Ordovician “Explosion”Changes in Ordovician from Cambrian Fauna

• more complex food chain

• extend higher above the seabed

• hard part made of calcite rather than phosphate

Ecological Diversification of Ordovician FaunaIncreasingly Complex Food Web

Multi-tiered Feeding Levels

Arrival of Classic “Paleozoic” FaunaArticulated

BrachiopodsBryzoans Crinoids

“Sea Lillies”

Sea Shells Twigs Cheerios

…and the world’s best Index fossils!

Conodonts Graptolites Ostracodes

New Kids on the BlockJa

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Fish

Carniverous Nautiloid

Nautiloid fragment found last year on field trip

Why This Explosive Radiation?An Early Ordovician regression followed by the most extensive transgression up to that point in Earth historyEnormous areas of shallow marine environments - niches

Atmospheric oxygen reaches modern-day levels

The Tippecanoe Trangression

St Peter SS – Platteville LS, St. Paul

Capping the Craton in Limestone

Except Here

The Taconic Orogeny

The Taconic Orogeny

The Taconic Orogeny

Modern-Day Analog

Prior-Day Analog1.85 Ga Penokean Orogeny

Next Lecture

The Paleozoic EraCambrian and Ordovician History

of Minnesota and WisconsinHave a Great Spring Break!!!