The Mississippian Period was much like the earlier part of the Paleozoic Era in North America – much of the continent was covered by warm shallow seas in which abundant life contributed to the thick sheets of limestone that were laid down. Eastern North America was still a highland, the result of the ongoing collisions with Europe and the microcontinents that were rifting away from Gondwana, and the ocean between North America and Gondwana was getting narrower and narrower.
In western North America, the Antler uplift that we discussed at the end of May was still there, and it was shedding sediment into the western seaway. The combined weight of those sediments and the piles of thrusted rocks pushed over the western edge of North America by the Antler Orogeny pushed the earth’s crust downward, creating what’s called a foreland basin. The Antler foreland basin extended through what is now eastern Nevada, western Utah, and into parts of Idaho and California. It was a relatively deep trough, and the mud that found its way into it contained a lot of organic material, washing in from both the west and the east. The resulting rock is called the Chainman Shale – a rock we mentioned in the Devonian, in May, as the source rock for the oil fields of Nevada. The Chainman is an excellent source rock, as much as 8% total organic carbon in some places.
There was some tectonic activity in what is now Alaska’s North Slope and across the Arctic islands of northern Canada – it’s called the Innuitan or Ellsmerian Orogeny and it was mostly taking place toward the end of the Devonian and into the Mississippian Period.
In Europe, Gondwana was pretty much encroaching on the southern margin of Baltica, but it was a complex interaction with lots of smaller blocks colliding. The seaway between Gondwana and Europe, called the Tethys Sea, is actually still there. We call it the Mediterranean Sea today.
—Richard I. Gibson
Links to Paleogeographic maps:
Western North America