Stratigraphical evidence of Baltic water level changes between 8 and 6 ka BP in a small lake basin on the coast of the Gulf of Finland, SE Finland

A sediment core from Lake Saarasjärvi at 19.5 m a.s.l. in Virolahti near the coast of the Gulf of Finland, SE Finland, was studied for lithology and diatom stratigraphy. The core records changes in the Baltic relative sea level over the last 8000 years. The basin was first isolated from the Baltic slightly before 8000 yrs BP as a result of the rapid regression towards the end of the Ancylus Lake stage. It was reconnected to the Baltic ca 7600 yrs BP when the transgressive Litorina Sea invaded the basin, and a brackish lagoon was created. The final isolation of the basin from the Baltic occurred ca 6000 yrs ago. The results indicate that the Virolahti area experienced a slow, gradual rise in the relative sea level since about 7600 years ago until between 6500 and 6000 years ago, after which the transgressive trend rapidly turned into a regression still going on. The lake and lagoonal stages in the basin history are clearly reflected in the lithostratigraphy, but the lithological changes are markedly delayed in comparison with the changes in the ecological conditions as indicated by the diatoms