Long Pleistocene pollen sequences from the Velay Plateau (Massif Central, France)

Abstract

In June 1988, a 50-m-deep boring was made in the lacustrine infilling of the explosion crater of Ribains (Haute-Loire). On the basis of pollen analyses the following chronology is proposed for this sequence: 0–5.10 m, Holocene and Lateglacial (hiatus); 5.70–17.48 m, last pleniglacial; 17.48–27.70 m, early glacial; 27.70–31.55 m: last interglacial, referred to as the Ribains Interglacial; 31.55–53.50 m, penultimate glaciation. The zone between 32.0 and 22.5 m, corresponding to a thick diatomite layer, provided a detailed record of the last interglacial and the early glacial vegetation succession. This enabled precise correlations with the neighbouring site of Lac du Bouchet and other long European sequences, confirming the proposed chronology. In particular, the temperate phase correlated with the St-Germain I of Grande Pile is well characterized, as at Lac du Bouchet, by the presence of an abrupt cooling corresponding to the Montaigu Event. In contrast, the last pleniglacial deposits contain great amounts of reworked pollen from earlier temperate phases, this making a comparison with Lac du Bouchet impossible. The thick sequence representing the penultimate glaciation is also affected by sediment loss during coring. However, several cold episodes are recorded that are characterized either by a total absence of vegetation or by a treeless steppe vegetation or a Pinus woodland, like the successions observed in the last pleniglacial at Lac du Bouchet.