The reason behind the repeated expansion and contraction of shallow seas over the midcontinent United States during Late Carboniferous time.
Answer to Problem 1RQ
The continual expansion and contraction of glaciers in Gondwanaland caused the expansion and contraction of shallow seas over the midcontinent United States.
Explanation of Solution
The alternative transgression and regression of shallow seas are described as cyclothems. Most cyclothems are of late Carboniferous (Pennsylvanian) age. The cyclothems are the result of repeated expansion and contraction of glaciers in Gondwanaland.
Coal deposits formed within the cyclothems. A transgression produces the lower part of a cyclothem, where marine sediments are superimposed on nonmarine sediments. Nonmarine material is underclay on which coal-swap plants grew and then died to produce the peat that ultimately would become coal.