05/06/2026
https://www.facebook.com/share/p/1DVzLituYu/
Michiganโs underground layers record two very different ancient worlds.
One left behind thick limestone filled with fossils. It records long periods when warm shallow seas covered the basin and marine life thrived.
The other left behind massive salt deposits with very little record of life at all.
For tens of millions of years, shallow seas repeatedly flooded parts of the Michigan Basin and surrounding areas while this region sat much closer to the equator than it does today. Warm tropical waters supported reefs, corals, shellfish, and other marine life that built up thick layers of carbonate sediment that eventually became limestone.
But the basin did not always stay connected to the open ocean.
As sea levels shifted and circulation became restricted, evaporation sometimes concentrated the salt faster than seawater could replace it. Conditions became increasingly hostile to most marine life.
Those periods left behind enormous salt and gypsum deposits instead of fossil rich limestone.
That cycle repeated again and again across immense spans of geological time.
Today those ancient environments are still preserved underground beneath Michigan.
Image: Middle Devonian paleogeographic reconstruction of eastern North America by Dr. Ron Blakey, modified by dhaluza and Hike395 via Wikimedia Commons.