Glacial stratigraphy of Koillismaa and North Kainuu, Finland

Abstract

Till stratigraphy and areal associations of landscape elements were studied in order to decipher the varying environmental characteristics within the ice sheet during each of the glacial phases recognized in the area. Drumlins and related glaciodynamic bedforms were found to date back to the ces­sation phases of ice flow during deglaciation. The formation of large­ scale crescentic troughs was found to have commenced prior to that of the drumlins. Boundaries of major ice‑flow units are often well‑marked by interlobate and terminal complexes of various kinds and of various magnitude. More detailed ice‑flow patterns within the lobes were recon­structed on the basis of striae, directional landforms and till studies. The oldest tills found in the area predate the Peräpohjola Interstadial. Their respective landscape elements could not be traced.

During the oldest deglacial flow phase the whole area was covered from the west by a single ice lobe, in the marginal zones of which a grey sandy till was deposited. Another facies, a dark grey, plastic till was deposited in the central parts of the ice lobe. The ice discharge pattern then changed and the flow split more or less simultaneously into three different lobes, which gave rise to three different tills respectively. This lobate arrange­ ment with three major flow units probably existed at the same time as the Second Salpausselkä phase.