Le gisement pliocène supérieur de Saint-Vallier (Drôme, France): synthèse biostratigraphique et paléoécologique

Abstract

New fieldwork undertaken at Saint-Vallier from 1993–1999 has revealed that the site has two fossiliferous horizons of hardened loess, of which the upper (LD 3) is richer and may be considered the reference locality for the Middle Villafranchian. The lower horizon, LD 2, yields many fewer taxa but is distinguished by the presence of an Allohippus stenonis quite different from that in LD 3. The faunal list includes six genera of molluscs, eight species of birds and 42 mammalian species, including three insectivores, six rodents, two lagomorphs, one primate, 15 carnivores, two proboscideans, four perissodactyls, and night artiodactyls. We have recovered fourteen taxa new to the locality: four molluscs, a bird, three insectivores, two rodents, two perissodactyls, and two artiodactyls. Pollen is relatively rare, but it is interesting to note the presence of cedar and plane trees. The mammalian community reflects a mosaic environment of steppe punctuated by open woodland, near a body of water and under a relatively moist but not especially cold climate. The age of the upper horizon is estimated at about 2 Ma; the mammalian fauna is characterized by eight species representing each an evolutionary stage in a defined lineage, two typical associations of taxa, and the first appearances (FADs) of seven taxa. Many European localities yield a comparable fauna with some or all of these features, and their ages correspond to the same biozone MNQ 17.