The De Geer moraines owe their name (Hoppe, 1959) to Baron Gerald Jacob De Geer (1858-1943), a pioneering geologist who was the first to observe these sedimentary structures in Sweden (De Geer, 1889). His work in geomorphology and geochronology had a major impact on the creation of the modern discipline of glacial geology. He is particularly recognized for identifying the importance of varves as a variable in establishing the relative chronology of past climates and environmental changes.
De Geer moraines appear as a series of thin, elongated, parallel ridges that may be symmetrical or asymmetrical in profile (Beaudry and Prichonnet, 1991). Ridges are regularly spaced: the distance between two ridges varies from 25 m to 400 m depending on the region (Norman, 1938; Shaw, 1944; Elson, 1968; Hardy, 1976; Bouchard, 1980; El Amrani, 2017; Lamarche and Dubé-Loubert. 2017; Lamarche et al., 2018). It is possible to observe moraines of this type with an arched morphology towards the downstream glacier (Norman, 1938). A few metres in height, they can be several kilometres in length in the most spectacular cases, although their width is limited to a few dozen metres. The regularity of these moraines makes them an easily identifiable landform which, seen from the air, takes on the appearance of a washboard, which is why they are called washboard moraines (Mawdsley, 1936).
The lithofacies of De Geer moraines is either glacial (till, diamicton) or fluvioglacial (stratified sandy deposits) in nature, or a combination of both (Virkkala, 1963; Beaudry and Prichonnet, 1991; Benn and Evans, 2010). Their nature is typically related to that of their immediate environment. These moraines are generally observed in association with glaciolacustrine or glaciomarine sediments (deep water, littoral, subaqueous outwash sediments). These moraines are generally covered, in whole or in part, by deep-water sediments. Hardy (1976) notes that De Geer moraines preferentially develop by stretching across drumlins, drumlinoids or other streamlined forms.
De Geer moraines are generally considered ridges that reflect a saccadic, annual retreat of a stable ice margin in contact with a water body. The formation of each ridge is thought to be the result of sediment accumulation in association with minor stagnation or recession in winter (Andrews and Smithson, 1966; Barnett and Holdsworth, 1984; Larsen et al., 1991; Blake, 2000; Benn and Evans, 2010). However, other mechanisms could be at the origin of these structures, such as filling of basal crevasses (Hoppe, 1957; Strömberg, 1965; Mickelson and Berkson, 1974; Ziliacus, 1989; Beaudry and Prichonnet, 1991; 1995), calving of icebergs (Holdsworth, 1973; Bennett and Glasser, 2009) or related to areas of high seismicity (Lundqvist, 2000).
The annual character of these structures has been questioned and defended several times in the literature. At first, De Geer (1889) believed that the origin of these moraines was annual. This interpretation was challenged in the second half of the 20th century by invoking alternative modes of formation as illustrated above. Lindén and Möller (2005) argued that although the mode of formation is indeed associated with periods of stagnation in the retreat of an ice margin, these need not be annual. Most publications support the concept of annual cycles for the formation of De Geer moraines (De Geer, 1940; Ignatius, 1958; Prichonnet et al., 1984; Boulton, 1986; Larsen et al., 1991; Bouvier et al., 2015). For these moraines to be preserved, temperature oscillations associated with annual cycles must produce periods of winter stagnation followed by marked summer retreat, otherwise the moraine that formed in the previous winter could vanish. The geomorphic resultant therefore does not unambiguously represent annually formed features, although locally it is possible that ridge series can be used to measure rates of retreat.
In Quebec, De Geer moraines have developed in various glaciolacustrine and glaciomarine basins. The most prominent examples are located in the La Grande River area (Eade et al., 1960; Vincent, 1985a; 1985b; 1985c) and between Kuujjuarapik and Puvirnituq (Allard and Seguin, 1985; Lajeunesse, 2008), although it is possible to observe them in the rest of the Ojibway Lake (Mawdsley, 1936; Norman, 1938, Wilson, 1941; Shaw, 1944, Ignatius, 1956; Hardy, 1976; Prichonnet et al., 1984; Beaudry and Prichonnet, 1991; El Amrani, 2017) and Tyrrell Sea (east of James Bay and Hudson Bay) basin. These moraines have been a primary tool for identifying the maximum extent of glaciolacustrine or glaciomarine water bodies (Norman, 1939; Shaw, 1944; Bouchard, 1980).
Moraines of this type have been observed in all northern countries that were glaciated during the Quaternary (Finland, Sweden, Norway, USA, Scotland and Canada).
Washboard moraines, annual moraines, submarine moraines, DeGeer moraines, push-moraines, minor moraines, cross-valley moraines, transverse eskers, till ridges.
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