The Role of Mountains, Polar Ice, and Vegetation in Determining the Tropical Climate During the Middle Pennsylvanian: Climate Model Simulations
Bette L. Otto-Bliesner, 2003. "The Role of Mountains, Polar Ice, and Vegetation in Determining the Tropical Climate During the Middle Pennsylvanian: Climate Model Simulations", Climate Controls on Stratigraphy, C. Blaine Cecil, N. Terence Edgar
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During the Middle Pennsylvanian, peat-producing swamps of year-round wetness must have occupied a broad tropical zone based on our knowledge of paleolatitudes of coal deposits formed during this period in North America, Europe, and Ukraine and the absence of growth rings in preserved wood found coexisting in these deposits. Here, we describe a series of global climate model simulations that evaluate the roles of tropical mountains, polar ice, and vegetation in determining the climate over tropical Gondwana. Our results suggest that the tropical mountains played the dominant role in allowing climatic conditions for tropical coal formation. The Central Pangean Mountains acted to impede the July excursion of the Intertropical Convergence Zone (ITCZ) north of the Equator and allowed the tropical everwet band to extend from 10° N to 12° S. The presence of permanent polar ice as a mechanism for increased year-round equatorial rainfall is shown to be less important. Polar ice on the southern supercontinent of Gondwana would have restricted the southward shift of the January tropical precipitation maximum but would have had no effect on the movement back northward in July. Forest vegetation over southern Gondwana would have warmed the southern high latitudes, melting the summer snowcover needed to accumulate into a polar ice sheet. These results define the large-scale boundary conditions necessary for Middle Pennsylva-nian coal formation.
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The role of climate as a primary control on stratigraphy is the cornerstone of this volume. The emphasis on climate is in distinct contrast to most previous studies, in which stratigraphic variability has been related to changes in sea level and in tectonic activity. Furthermore, the findings, derived from several years of detailed study of modern and ancient key geologic sections around the world, indicate that traditional depositional models generally do not fully explain the origin of fossil fuels. Although the results of the studies presented in this volume are intended to contribute to the disciplines of sedimentary geology and stratigraphy, the contributors recognize that their results may also contribute to a better understanding of global climate change. The theoretical background of climate control on sediment supply and stratigraphy is presented in the volume. With this background in place, detailed documentation and analysis of climate control on the lithologic variation of a single Middle Pennsylvanian.