The Villafranchian Stage-Age and Its Radiometric Dating
Published:January 01, 1970
The Villafranchian, though identified by nonmarine phenomena, was one of the most precisely typified of the commonly used European stages of Cenozoic age. Monsieur le Marquis de Pareto (1865) gave exact geographic location and characteristic rocks for his stratotype of the Villafranchian Stage and listed the four species of proboscideans that had been obtained from the general district of the stratotype.
Villafranchian has been applied throughout Eurasia and Africa on the basis of a characteristic array of species of land mammals. These species were obtained first from sites in Italy and France that were believed to be the same age as Pareto’s Villafranchian. Neither the validity nor the utility of the Villafranchian, as recognized through most of the Eastern Hemisphere, is vitiated because some of its characterizing mammalian assemblages are younger than the type or because its lower boundary may not coincide with the currently accepted lower boundary of the Pleistocene.
Large mammals now known from the stratotype, together with small mammals, mollusks, and plants recently collected, provide a more secure paleontological basis for correlation with type-Villafranchian and will give better knowledge of type-Villafranchian ecology.
Although no materials suitable for radiometric dating have been found in the stratotype area, volcanic rocks associated with the correlative Etouaires fauna near Issoire in the Auvergne area of France have yielded a K/Ar date of 3.4 m.y. The nearby and younger Villafranchian fauna of Roca Neyra is 2.5 m.y. The oldest geological indications of glaciation that have been dated in the Auvergne are at Coupet (solifluction), 1.9 m.y. and Vazeills (crioturbated earth), 1.8 m.y. Lower in the section at Coupet is a mammalian fauna referable to the Villafranchian.
The oldest glacial deposit dated from the Northern Hemisphere (Sierra Nevada) is 2.7 m.y., whereas the oldest evidence of Pleistocene cold climate in the Southern Hemisphere (New Zealand) is slightly older than 2.5 m.y. On the basis of the date of inception of widespread glaciation, therefore, we place the beginning of the Pleistocene and Quaternary at about 2.6 to 3 m.y. B.P. This research project was supported by Grant No. GB-3508 from the National Science Foundation.