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Global perspective of Famennian-Tournaisian oceanography : geochemical analysis of brachiopods
No secular shift in seawater isotopic compositions is noted during the Famennian-Tournaisian. Instead, the observed variations in both oxygen and carbon isotopic compositions are ascribed to changing habitat conditions and settings. Modelled water temperatures shows that seas were generally warmer during the Famennian than during the Tournaisian. Tropical seas during the Famennian probably had temperatures ranging from 32-38°C for shallow waters, with temperatures of 17-18°C for deeper habitats, and show a steep latitudinal temperature gradient within the equatorial-subtropical belt. Temperatures and latitudinal variations were more moderate and gradual during the Tournaisian and water temperature ranged from 17-30°C for the equatorial-temperate belts. This general shift in global water temperatures towards more equitable conditions may be related to the postulated late Devonian-early Carboniferous glacial event in southern Gondwanaland. Tropical, shallow epeiric and shelf seas of central Europe were greatly influenced by fluvial run-off and thus were stratified during the Famennian. In the shallow seas, salinities were probably as low as 20 ppt, whereas the deeper parts experienced generally normal salinities (35 ppt). In contrast, normal (30-35 ppt) salinities characterized the shallow and deep waters of the tropical-subtropical Tournaisian seas.
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A propos de : Uwe Brand
Department of Geological Sciences, Brock University, St. Catharines, Ontario L2S 3A1 and McMaster University, Hamilton, Ontario L8S 4M1 Canada.