GSC 111 Lecture Notes - Lecture 14: Rugosa, Taconic Orogeny, Tabulata
13 Jan 2017
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Ordovician Radiations and Mass Extinctions (495-440 Mya)
1. 4 major continents
a. Gondwana, Laurentia, Baltica, and Siberia
b. Avalonia breaks off from Gondwana
i. A rift opened up
c. Continents will start to collide more
2. Started major transgression
a. Seas were flooding up into Precambrian rock all the way up to Wisconsin
3. Ordovician had first major mountain building event in Eastern North America, The
Taconic Orogeny
a. Collision between Laurentia and some small island arcs
i. When island arcs get pasted onto the eastern coast of North America, it
causes significant changes in the margins
ii. When they collide, area between island arc and collision subsides and
becomes the foreland basin, and this buoys the continent up to more
mountain
b. flysch is the first thing that goes into the foreland basin
c. sea starts to transgress into Precambrian rocks
i. in upper ordovician, we see transition in sediment from limestone to flysch
1. this means we have uplifted the mountains and started to fill in the
foreland basin
d. ended at the end of the Ordovician
i. we had a mountain range in Eastern coast of North America
ii. large clastic wedge was spreading into the interior of the continent
iii. epicontinetal seas
iv. patches that stood up out of these seas
v. western margin continues to be a passive continental shelf
4. Ordovician Life
a. Adaptive radiations followed by first major mass extinction
b. Burrowing
i. Was intensive by the Upper Ordovician
ii. Lots of worms, bivalve mollusks, and trilobites were burrowing
c. Important organisms in benthic sea floor
i. Benthic inhabit more than the cambrian
ii. Almost everything is in the marine realm at this time (not a lot of
terrestrial organisms)
iii. Echinoderms
iv. Brachiopods
1. The dominant Ordovician fossil
2. Symmetrical across valves
3. Have a locophord
4. Have pediment that comes out of one of the valves
5. Not very common today, but it was the opposite in the Ordovician
a. Not a lot of bivalves back then
v. Mollusks
vi. Trilobites- have highest diversity at the end of Ordovician
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