The First Salpausselkä at Lohja, southern Finland

Four morphogenic types of the First Salpausselkä can be distinguished in the Lohja area: glaciofluvial marginal deltas, incompletely developed deltas, other ridges and hills, and formations with a rock core. The primary morphology has been considerably deformed by shore action during the stages of the Baltic Ice Lake, the Yoldia phase and the Ancylus Lake of the ancient Baltic. The Salpausselkä is composed of glaciogenic waterlain sediments, consisting of well-washed and sorted delta beds of sand and gravel, and of poorly sorted till layers. This Salpausselkä till was deposited partly as subaquatic flow till or subglacial meltout till from the debris-loaded ice margin in the proximal part of the formation. The distal and central parts of a typical marginal delta are characterized by undeformed regular flow (delta) structure. The proximal part often contains heterogeneous material, is complicated in structure and has been deformed mainly by glaciotectonic and load deformation structures, such as flow and load casts, faults and folds. The First Salpausselkä has a complex polygenetic genesis. It was formed in several phases at the ice margin, mainly under subaquatic glaciolacustrine conditions at the same time as the water level of the Baltic was gradually rising from a low level to the highest level of the Baltic Ice Lake, B I. The stratified core and distal strata were deposited first, and then the heterogeneous proximal sediments under conditions associated with a floating and oscillating ice margin before the final retreat of the ice. The trend of deglaciation within the Salpausselkä belt is closely connected with the genesis of these ice-marginal formations. The general position and formation of the Salpausselkä seem to have been controlled primarily by climatic and topographic factors