Palaeoenvironmental changes inferred from malacofaunas in the Lateglacial and early Holocene fluvial sequence at Conty, northern France

Environmental changes are reconstructed from a Lateglacial and early Holoce ne sequence at Conty, northern France. The molluscan succession is put into a chronostratigraphic framework supported by numerous radiocarbon dates. M alacofaunas from the Bolling chronozone are reported for the first time in northern France and show progressive expansion of marshy communities within organic deposits. This biozone ended in a calcareous silt with the appeara nce of several species of arctic-alpine affinities. These sedimentological and malacological data point to colder climatic conditions after 12 220 +/- 90 BP, but before 11 640 +/- 80 BP, allowing allocation to the Older Dryas event. The first part of the Allerod appears to have been drier and relati vely stable. After 11 400 BP. a decline in species richness and diversity i n the malacofaunas suggests increasing dryness. During the Younger Dryas, t wo molluscan biozones are identified in a homogeneous calcareous silt, refl ecting an early wet phase followed by a drier episode. At the onset of the Holocene malacofaunas show a higher diversity, suggesting climatic improvem ent.