Stratigraphy of the Koivusaarenneva exposure and its correlation across central Ostrobothnia, Finland

Abstract

A multiple till succession at Koivusaarenneva in Central Ostrobothnia, adjacent to the Gulf of Bothnia, was studied using conventional sedimentological techniques. In addition, a sand-rich unit between two till beds was dated by the Optical Stimulated Luminescence (OSL) method and organic-bearing silt was subjected to pollen analysis. The methods were applied to determine the Pleistocene sedimentation history of the area. The results obtained indicate that the lowest till above the crystalline bedrock at Koivusaarenneva was deposited from the NNW during the Saalian glaciation, whereas the organic-bearing sediments and deformed sand and silt above, were laid down during the Eemian and the Early Weichselian stages. Two till beds above the Early Weichselian sediments indicate that at least two separate Scandinavian Ice Sheet advances took place in the area, most likely in the early Middle Weichselian and the Late Weichselian