North American depositional environments

There are big differences in North American depositional environments between the Mississippian and Pennsylvanian periods. While non-US geologists consolidate these periods into the “Carboniferous,” US geologists felt a division was needed because of very different rock types and deposition within the Mississippian and Pennsylvanian. Can you hypothesize the different types of organisms that proliferated during these periods, and whether they contributed to the types of rocks that dominate each period?