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Tidal deposits dating from the penultimate interglacial (Oxygen Isotope Stage 7) are preserved on a bank of the River Seine at Tancarville. The foraminiferal assemblages indicate a gradual cooling towards Arctic conditions, which corresponds to the onset of the penultimate cold period. This cooling started before or during the drop in sea level in Europe, in contrast to the situation at the end of the last interglacial (Eemian) when Europe remained warm even during the period of falling sea level. 相似文献
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KIEFFER BRUNO; ARNDT NICHOLAS; LAPIERRE HENRIETTE; BASTIEN FLORENCE; BOSCH DELPHINE; PECHER ARNAUD; YIRGU GEZAHEGN; AYALEW DEREJE; WEIS DOMINIQUE; JERRAM DOUGAL A.; KELLER FRANCINE; MEUGNIOT CLAUDINE 《Journal of Petrology》2004,45(4):793-834
The Ethiopian plateau is made up of several distinct volcaniccentres of different ages and magmatic affinities. In the NE,a thick sequence of 30 Ma flood basalts is overlain by the 30Ma Simien shield volcano. The flood basalts and most of thisshield volcano, except for a thin veneer of alkali basalt, aretholeiitic. In the centre of the province, a far thinner sequenceof flood basalt is overlain by the 22 Ma Choke and Guguftu shieldvolcanoes. Like the underlying flood basalts, these shieldsare composed of alkaline lavas. A third type of magma, whichalso erupted at 30 Ma, is more magnesian, alkaline and stronglyenriched in incompatible trace elements. Eruption of this magmawas confined to the NE of the province, a region where the lavaflows are steeply tilted as a result of deformation contemporaneouswith their emplacement. Younger shields (e.g. Mt Guna, 10·7Ma) are composed of Si-undersaturated lavas. The three maintypes of magma have very different major and trace element characteristicsranging from compositions low in incompatible elements in thetholeiites [e.g. 10 ppm La at 7 wt % MgO (=La7), La/Yb = 4·2],moderate in the alkali basalts (La7 = 24, La/Yb = 9·2),and very high in the magnesian alkaline magmas (La7 = 43, La/Yb= 17). Although their Nd and Sr isotope compositions are similar,Pb isotopic compositions vary considerably; 206Pb/204Pb variesin the range of 相似文献
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