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Orogenic enhancement of weathering and continental ice-sheet initiation

By
Thomas L. Moore
Thomas L. Moore
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Thomas R. Worsley
Thomas R. Worsley
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Published:
January 01, 1994

Although geochemical weathering of highlands associated with orogeny can sufficiently remove enough atmospheric CO2 to cool global climate and possibly initiate glacial epochs, the height of an orogenic belt is not the only major control of geochemical weathering rates. The latitudinal position of an orogenic belt also strongly influences the rate of geochemical weathering. If we assume as a first approximation that precipitation increases with temperature, the silicate weathering rate of an orogenic belt would always be greatest at the warm low latitudes and decrease toward higher latitudes. The actual weathering rate and its weathering gradient with latitude would depend on the specific equatorial and polar temperatures involved. Those temperatures are in turn governed by the geochemical weathering of the global landmass. Equatorial and polar temperatures are coldest when the continents are completely emergent and at the equator. They are warmest for maximally drowned continents situated on the pole. The cooling effect of geochemical weathering of a low-latitude orogenic belt is most intense for a warm world in which a majority of the global landmass is at high latitudes.

The relative silicate weathering enhancement rates for several orogenies that occurred during the Phanerozoic were estimated using initial geochemically modeled climatic conditions, the average latitude of the global landmass, and the average latitude of an orogeny (with orogenic characteristics “standardized” to the modern Himalayas). The only obvious case where an orogeny could have initiated a glacial epoch is during the Carboniferous, when the Alleghany orogen formed at low latitudes. Other cases are equivocal. The Taconic orogeny during the late Ordovician and early Silurian, the Acadian orogeny during the Early Devonian, and the early Himalayan orogeny during the Cenozoic could have contributed to the formation of continental ice sheets, but geochemical conditions for ice formation were already borderline favorable for continental ice, so it is not known whether the orogenies were actual triggers. Orogenies are certainly among the major contributors to global cooling but usually are not the sole cause of glacial epochs.

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GSA Special Papers

Pangea: Paleoclimate, Tectonics, and Sedimentation During Accretion, Zenith, and Breakup of a Supercontinent

George O. Klein
George O. Klein
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Geological Society of America
Volume
288
ISBN print:
9780813722887
Publication date:
January 01, 1994

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