 A  B 
C |
Figure 16. A, Conceptual model of Middle Pennsylvanian surface winds over Pangea during glacial intervals. Continental ice in the southern hemisphere limited the southern excursion of the intertropical convergence zone (ITCZ) during the southern hemisphere summer. Confinement of the ITCZ to equatorial regions created a low-pressure rainy belt (doldrums) that spanned approximately 10° of latitude. Schematic interpretation of continental ice is adapted from Caputo and Crowell (1985), Veevers and Powell (1987), Scotese (1998), and Frakes and others (1992). Paleogeography is modified from Scotese (1998). From Cecil and others (2003b). B, Conceptual model of Middle Pennsylvanian surface winds over Pangea during interglacial intervals. Interpreted northern excursion of the ITCZ during the northern hemisphere (Boreal) summer. Paleogeography is modified from Scotese (1998). C, Conceptual model of Middle Pennsylvanian surface winds over Pangea during interglacial intervals. Interpreted southern excursion of the ITCZ during the southern hemisphere (Austral) summer. The cross-equatorial movement of the ITCZ during interglacials resulted in significant increases in both dryness and seasonality of rainfall in low latitudes. Paleogeography is modified from Scotese (1998). |