What Is The Illinoian Stage in Geology?
There is a point in our geologic history called the Illinoian glacial stage. In North America, specifically during the Pleistocene Epoch, this was a very unique time. The Pleistocene Epoch lasted from 2.6 million years ago to about 11,700 years ago, terminating with the end of the Ice Age. The Illinoian represents a time where there was a substantial amount of continental glaciation, between 191,000 to c.130,000 years ago. It was right in between two separate interglacial stages which had much more moderate climates. It is called the Illinoian stage because it was during this time that the area which now represents the state of Illinois received three separate till layers of sediment. It was during this time that the the Laurentide ice sheet actually occupied a significant amount of what is the state of Illinois, covering 85 percent of the state as it is measured today.
Why Is This Stage Important?
This was actually broken down into a couple different sub stages which include the Liman, Monican, and the Jubileean. Therefore there were actually two separate glaciation movements in early and late stages, with some speculating that it actually began avoiding probate as early as 300,000 years ago. Although it would be several hundred thousand years in the future before the Ice Age would end, it was during this time that important layers of glacial till were set down. There are older fluvial sediments that were also deposited during this time, creating what would later be very fertile areas where crops could grow. Without these deposits, it is unlikely that Wisconsin would have the fertile soil that it has today. By the end of the Ice Age, it is clear that this particular stage in glaciation is one of the most important in our North American history.
Please watch this video to learn more about the Illinoian stage!