A cryptotephra from the Upper Pleistocene volcanism of the Bas-Vivarais in the sedimentary infilling of the Chauvet-Pont d'Arc cave (Ardeche, France)

A cryptotephra belonging to the Upper Pleistocene volcanism of the Bas-Vivarais was identified for the first time in the sedimentary infilling of the entrance area of the Chauvet-Pont d'Arc cave. This slightly reworked tephra fall is characterized by its heavy minerals assemblage, among which magnesian olivine, enstatite, and chromian diopside issued from peridotites and olivine and diopside of basaltic origin. This composition likely refers to a phreatomagmatic eruption of a maar crater. The C-14 datings of the cryptotephra beds are contemporaneous with the Aurignacian settlement and paintings, that is, an age slightly older or close to 36 ka. Among the maar craters from the Bas-Vivarais, the Ray-Pic maar have the closest Ar-40/ Ar-39 age (36.2 +/- 11.3/32.2 +/- 11.1 ka). By contrast, the Vestide du Pal, the biggest maar crater of this country, seems to have a younger age, but the Ar-40/ Ar-39 dating was measured on a basalt which could have occurred later and been the source of the tephra fall, since its tephras contain the same minerals of unknown origin as those found in Chauvet cave. This discovery strengthens the previous hypothesis according to which the humans living in the Chauvet-Pont d'Arc area during the Upper Paleolithic have witnessed eruptions from the Bas-Vivarais volcanic field and other phenomena.