Continental-scale correlations of
a Middle Pennsylvanian fourth-order sequence have provided evidence for the
relative importance of allocyclic
controls on the formation of Pennsylvanian cyclothems. These correlations (and
related studies) indicate that eustasy was the primary control on accommodation
space in most basins. Tectonic subsidence was a secondary control and provided
additional accommodation space in a few basins. Temporal and spatial variations
in climate, however, were the primary controls on physical and chemical sedimentology.
Interpretations of
changes in weathering and fluvial and eolian sediment supply suggest the climate
was wetter during lowstands relative to highstands and that the
physical and chemical oceanography of epeiric seas responded to changing patterns
in atmospheric pressure regimes as sea level rose and fell. In addition, the
climate was wetter in the eastern part of the tropical regions of what is now
North America relative to the west. Temporal and
spatial changes in paleoclimate, therefore, appear to be the primary control
on the lithostratigraphy of Pennsylvanian cyclothems.