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04/04/12
Permian/Triassic


 

The Permian Period of the Paleozoic Era, like the earlier periods alas left no rocks behind in Minnesota.  But in the western US there are evaporites left when the seas dried up.  The interior of the continent was hot and dry, with periodic rains that left mud in low places.  There were quite a few reptiles, including finbacks, and considerably fewer amphibians.

As we measure geologic time, the Paleozoic Era was followed by the Mesozoic, the first period of which was the Triassic, occurring 225 to 190 million years ago.  Again, Triassic deposits are not found in Minnesota.  In the western US there are some, which are red from hematite in an oxidizing atmosphere.  The continent slow moved north, so the equator was around by Texas and Florida.  Life forms included some dinosaurs, flying reptiles, and small mammals. 


Posted by oh5/ojhoff at 7:40 AM CDT
Updated: 04/04/12 8:35 AM CDT
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