Observations on dark grey basal till in Finland

Abstract

Dark grey basal till of boulder clay type is widespread throughout Finland. It occurs directly on the ice-polished bedrock surface on the lee-side of hills and is overlain by common till or sorted sediments. Presumably in secondary position, it occurs in a few places in Central Finland in the proximal part of ice-marginal formations. The basal till is richer in clay and humus and is also more compact than common till. In Central and Eastern Finland brown layers are encountered in the lower and upper parts of the basal till. The colour seems to be derived from oxidation. The pebble orientation in the basal till is parallel to the direction of the glacial striae on the underlying bedrock surface. The humus incorporated gives 14C ages exceeding 37,000 and 45,000 years. The basal till seems to date from the initial phase of the youngest Weichselian glaciation in Finland.