Observations of the surface of the Petuniabukta tidal flat showed the occurrence of dead forms indicating a relative lowering of the sea level. Under the silt deposits of the tidal flat a gravel-clay series was found to occur. Connecting this series with the glacial till covering the lowest marine terrace and with the erosion pavement in the lowest part of the outwaśh plain gave rise to the hypothesis that there might be a record of glacier oscillation. By dating a sample taken from the gravel series substrate, the age of the oscillation was estimated at less than 6370+/- 120 years BP.