科研之友
微信
新浪微博
Facebook
分享链接
摘要
Volcanic ash-falls from Mont-Dore or Vivarais volcanoes have been discovered in different karstic sites of the "Basse-Ardeche" region. After the ash-fall of the Sancy volcano dated ca. 0.3 Ma described in Orgnac 3 aven and the ash-fall from an Upper Pleistocene Ardeche maar, 72 +/- 12 ka ago, found in the Moula rock-shelter, two new tephra have been discovered in the Marzal II aven. The middle part of the filling includes a zircon-sphene association which is typical of a Mont-Dore differentiated volcanism and could be connected with pyroclastic outbursts ca. 0.45 Ma old. In the upper part of the filling, other minerals such as olivine, orthopyroxenes, diopside, brown clinopyroxene, correspond to a basaltic volcanism with mantellic enclaves. This association is typical of a phreatomagmatic ash-fall probably emitted by a maar in the Vivarais region. Biochronological and C-14 data situate this latter tephra in the most recent phase of the Vivarais volcanism, between 40 - 30 ka. The Deves de Reynaud aven includes a third tephra also emitted during a phreatomagmatic event, probably due to the eruption of a Vivarais maar. These results show the interest of karstic fillings as they preserve the vestige of dynamic events today unknown on land surface.
- 出版日期2008-6
