After the end of the glacial period at about the end of Devonian time, most of the Mississippian was ice-free around the world until near the end of the period. There is evidence for episodic glaciation in Australia and South America at this time.
It’s possible that the Mississippian glaciers were predecessors to the well-defined Permian glaciation, although that ice age was still at least 25 million years in the future as the Mississippian ended. The onset of glacial episodes would have contributed to sea-level changes that in turn would be contributing factors in the increase in clastic sediments in Late Mississippian time. The shallow seas so common earlier in the period would have become reduced in size as sea levels fell.
One possible contributing factor in the beginning of the glacial period is the tectonic closing of the Tethys Sea and the ocean between Gondwana and North America. Disrupting what was a major equatorial ocean circulation pattern could have impacted global distribution of heat in the oceans and therefore in the atmosphere, and could have helped continental ice sheets to form and grow.
—Richard I. Gibson