The First Salpausselkä at Lohja, southern Finland

Abstract

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 1. 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.

Submarine groundwater discharge site in the First Salpausselkä ice-marginal formation, south Finland

“…The First Salpausselkä was deposited as a narrow ridge of contiguous glaciofluvial fans and local feeding eskers that were formed along the ice-margin grounding line (Virkkala, 1963;Glückert, 1986;Fyfe, 1990;Kujansuu et al, 1993), in an icecontact lake that was more than 100 m deep in Hanko (Fyfe, 1990). After the ice margin retreat, the till and glaciofluvial gravel and sand deposits were successively covered by glaciolacustrine rhythmically alternating (varved) silt and clay, and postglacial lacustrine poorly-bedded clay (Virtasalo et al, 2007(Virtasalo et al, , 2014.…”

“…The top of the ice-marginal formation was exposed to waves and eventually to wind as it gradually rose from the sea. The original ridge morphology became truncated and flattened from the top, the glaciolacustrine and postglacial lake silts and clays were removed, and the underlying glaciofluvial deposits were reworked by wind waves and currents (Virkkala, 1963;Glückert, 1986;Fyfe, 1990;Kujansuu et al, 1993). Fine sand was redeposited as beach ridges on the south side of the peninsula and partially reworked into aeolian dunes (Fyfe, 1990).…”

“…The stratigraphical position immediately above till, as well as the proximity and increasing unit thickness toward the First Salpausselkä ice-marginal formation indicate glaciofluvial origin for the sandy deposit. SU3 is interpreted to comprise distal foreset and possibly bottomset beds of an ice-contact subaqueous fan that is part of the First Salpausselkä (Virkkala, 1963;Glückert, 1986;Fyfe, 1990;Kujansuu et al, 1993). The poorly stratified fine sand beds were deposited by turbidity currents and occasional debris flows from the upper fan slope (Winsemann et al, 2009;Lang and Winsemann, 2013;Lang et al, 2017;Winsemann et al, 2018).…”

“…-The sheet-like geometry and high-amplitude sub-horizontal downlapping internal reflectors indicate a coarse shoreface lag deposit, likely composed of gravel (Tamura et al, 2008). Such a deposit was formed by wave, current and winter-ice reworking of the primary ice-contact fan deposits (RU1) during emergence from the sea (Virkkala, 1963;Glückert, 1986;Fyfe, 1990;Kujansuu et al, 1993;Nemec et al, 1999).…”

“…CC BY 4.0 License. independent processes, namely the retreat of the Fennoscandian continental ice-sheet and the dynamics of the ice margin, the relative water level fall due to postglacial land uplift, the mid-Holocene marine incursion and the associated short-lived transgression and the establishment of brackish-water conditions, and, finally, coastal and aeolian processes (Virkkala, 1963;Glückert, 1986;Fyfe, 1990;Kujansuu et al, 1993;Virtasalo et al, 2007Virtasalo et al, , 2014Virtasalo et al, , 2016. As a result of the complex depositional history, allostratigraphy has recently gained popularity as a stratigraphical classification approach both in the Baltic Sea (e.g.…”