The Oldest Dryas, a climatic period, which occurs during the coldest stadial after the Weichselian glaciation in north Europe, corresponds to pollen zone Ia.

In the Alps, the Oldest Dryas corresponds to the Gschnitz stadial of the Würm glaciation.

The three “Dryas” periods (younger, older, oldest) are named for a marker species, Dryas octopetala, detected in core samples of glacial ice and peat bogs.