Lee, J.R. and Phillips, E. 2013. Glacitectonics – a key approach to examining ice dynamics, substrate
rheology and ice-bed coupling. Proceedings of the Geologists’ Association, 124, 731-737. ACCEPTED
TEXT.
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Glacitectonics – a key approach to examining ice dynamics,
substrate rheology and ice-bed coupling
Jonathan R. Lee
1*
and Emrys Phillips
2
1
British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK.
2
British Geological Survey, Murchison House, West Mains Road, Edinburgh, EH9 3LA, UK.
*Corresponding author: J R Lee (Email: jrlee@bgs.ac.uk
Abstract
The role of ice masses within the Earth’s climate system and in landscape change is increasingly
being recognised within regions that are either currently glaciated or were glaciated during the
geological past. There are many different remote and field-based approaches to studying the
products of glaciation. One approach – that of glacitectonics, focuses on the styles of deformation
and tectonic imprint (folds, fractures, fabrics, foliations and lineations) produced as ice overrides or
pushes into pre-existing rocks or sediment. This approach, when used in combination with other
types of evidence, can be used to infer ice-dynamics, substrate rheology and ice-bed coupling. Of
equal significance is the influence of glacitectonic structure upon the applied properties of glaciated
terranes such as ground stability, hydrogeology and fluid migration (e.g. water, gas hydrates and
hydrocarbons). This paper provides an introduction to this Special Issue on Glacitectonics, outlining
the significance and historical development of this field of glacial geology, before introducing and
summarising the contributions that make up the volume.
Introduction and importance of glacitectonics
Deformation of rocks and superficial deposits by tectonic processes occur at a range of scales. The
largest and most obvious tectonic processes relate to the development of continental-scale
subduction and collision zones at convergent plate boundaries (Dewey and Bird, 1970). However,
similar tectonic processes, albeit operating at far smaller spatial scales and reduced pressure-
temperature conditions, can occur at the Earth’s surface as a glacier or ice sheet pushes into or
overrides a pre-existing sequence of sediments and/or bedrock. This phenomenon is referred to as
glacitectonics (Banham, 1977; Croot, 1987; van der Meer, 1987; Aber et al., 1989; Aber and Ber,
2007; Phillips and Lee, 2011) and is a process widely recognised by geologists since the mid- to late-
nineteenth century (Johnstrup, 1874; Reid, 1882). Evidence for glacitectonism can include a wide
range of secondary structural features including folds, fractures, fabrics, foliations and lineations
that are superimposed upon the primary structure of a rock or sediment (van der Meer, 1993; van
der Meer et al., 2003; Evans et al., 2006; Menzies et al., 2010; Phillips et al., 2008).
Glacitectonic processes are increasingly recognised as playing a critical role in the development of
complex glacigenic sedimentary sequences and landforms in both modern and ancient glacial
environments (Croot, 1988; Hart, 1990; Krüger, 1993; Hambrey and Huddart, 1995; Boulton et al.,
1996; Rocha-Campos et al., 2000; Williams et al., 2001; Larson et al., 2003; Evans and Hiemstra,
2005; Le Guerroué et al., 2005; Le Heron et al., 2005; Evans et al., 2006; Lee and Phillips, 2008; ;
Lee, J.R. and Phillips, E. 2013. Glacitectonics – a key approach to examining ice dynamics, substrate
rheology and ice-bed coupling. Proceedings of the Geologists’ Association, 124, 731-737. ACCEPTED
TEXT.
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Phillips et al., 2008; Benediktsson et al., 2010). The study of glacitectonic processes provide valuable
insights into the internal (e.g. substrate rheology, temperature and drainage) and external (e.g.
climate, mass balance) controls on glacier-induced sediment deformation, and in-turn, their
influence on ice mass dynamics (van der Wateren, 1995a; Bennett, 2001; Phillips et al., 2002;
Boulton et al., 2004; Thomas et al., 2004; Evans and Hiemstra, 2005; Thomas and Chiverrell, 2007;
Benediktsson et al., 2010; Waller et al., 2011; Phillips et al., 2012; Szuman et al., this volume).
Recognising and understanding glacitectonic structures and processes is also highly relevant to
applied geosciences. Sediment mixing and the presence of glacitectonic structures such as folds and
faults can have major implications for ground stability and foundation strength by altering material
properties and introducing substrate failure planes (Sauer, 1978; Kurfurst and Dallimore, 1991). For
example, there are many documented examples of glacitectonic structures exerting a dominant
control on the development and style of landslides (Campbell and Evans, 1990; Stauffer et al., 1990;
Lee et al., 2011). Indeed, many large-scale infrastructure developments in areas of formerly
glaciated terrain now carry out detailed ground investigations to determine whether or not
glacitectonic structures are present in the shallow sub-surface. Glacitectonic structures can also act
as fluid migration pathways or reservoir traps for water (Jørgensen and Holm, 1995; Scheytt et al.,
2001; Burschil et al., 2012), hydrocarbons (Levell et al., 1988; Huuse et al., 2012) and gas hydrates
(Hovland, 1990) and are therefore of importance with respect to hydrogeology, civil engineering,
hydrocarbon exploration and Carbon Capture and Storage (CCS).
This Special Issue of Proceedings of the Geologists Association has been compiled following a highly
successful workshop held in Sheringham (UK) during September 2011 on the topic of Glacitectonics
which examined their glaciological and applied significance. The workshop was organised by the
Quaternary Research Association in collaboration with the Glacial Landsystems Working Group
(GLWG) and the International Permafrost Association and attracted geologists from Denmark,
Iceland, Poland and the UK. The purpose of this Special Issue is to celebrate this workshop by
presenting a selection of topical research papers under the general banner of Glacitectonics. In this
introduction paper, we provide a historical and methodological context to this highly dynamic field
of glacial research as well as summarising the contributions to the Special Issue.
Evolution of Glacitectonic Theory
The study of glacitectonics is a relatively new phenomenon but has its origins and evolution can
ultimately be traced with major historic developments in Geology and Earth Sciences. During much
of the eighteenth century, the majority of naturalists and scientists related the geological history of
the Earth to the product of a biblical ‘Great Flood’ described within the Book of Genesis. This
includes the products of what we now know to be glacial origin such as moraines, erratics and glacial
scour features. However, the eighteenth century marks an important tipping point in scientific
philosophy with the emergence of sciences, including Geology and Earth Science, during the so-
called ‘Age of Enlightenment’. One significant concept to evolve during this era was the realisation
that many products of the ‘Great Flood’ (also known as the ‘Diluvial Theory’) could be explained by
worldly processes that can be interpreted from the rocks and landscape. One of the principal
pioneers of this movement was James Hutton who published his geological Theory of the Earth in
1775. Hutton together with several other important naturalists of the late eighteenth and early
nineteenth centuries, including Horace-Bénédict de Saussure, Jens Esmarck, Karl Freidrich Schimper
Lee, J.R. and Phillips, E. 2013. Glacitectonics – a key approach to examining ice dynamics, substrate
rheology and ice-bed coupling. Proceedings of the Geologists’ Association, 124, 731-737. ACCEPTED
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and Jean de Charpentier, speculated that glaciers had once covered far more of continental Europe
than their current extent. Louis Agassiz took this theory a step further by suggested that glaciers and
ice sheets had, within the recent geological past, been far more extensive throughout the northern
hemisphere. This Swiss-born geologist also had a significant role to play in introducing the concept of
glaciation in Britain. Alongside William Buckland, he toured the Scottish Highlands in 1840,
examining landforms and ‘recent deposits’, concluding that highland areas of Britain and Ireland had
acted as dispersal centres for ice masses with trains of sediment emanating away from them into
sediment accumulation areas.
Despite the contributions of geologists such as Louis Agassiz and William Buckland the specific
processes of erosion and deposition by ice within the landscape remained contentious. Many
geologists modified their ‘diluvial’ views to include the activity of floating ice (i.e. icebergs) and
phases of landscape submergence. Arguably the most significant figure in changing this perception
was James Geikie who developed the ‘land-ice’ theory based upon detailed observations made
throughout Scotland. His theories and models were published within a number a landmark papers
and monographs including three separate editions of book The Great Ice Age and its Relation to the
Antiquity of Man published in 1874, 1877 and 1894. Geikie’s work was clearly influenced by the
earlier studies of Ramsay (1862) who demonstrated that many of the ‘rock basins’ of Scotland (e.g.
U-shaped valleys and fjords) were the product of glacial scouring and erosion. In-turn, the
authoritative work of James Geikie influenced many other geologists working not just in the UK, but
elsewhere in North America and Europe who examined the landscape and especially ‘disturbed’
sequences with a fresh perspective. During the late nineteenth and early twentieth century’s,
disturbed glacial sequences were widely recognised with major studies undertaken in southern
Sweden (Torrel, 1872), parts of North America (Gilbert, 1899; Hopkins, 1923) and the classic site of
Møens Klint in Denmark (Johnstrup, 1874). In the UK, Clement Reid who undertook the first
geological survey of the Cromer District of north Norfolk described in detail the glacial geology of
many of the coastal sections and recognised that much of the sequence has been disturbed by ice.
He called the deformed sequence the ‘Contorted Drift’, a phrase that is still used informally to this
day, and likened their structure to the action of pushing a book over a table cloth. His findings were
published as an Old Series geological map and an accompanying memoir entitled The Geology of the
Country around Cromer (Reid, 1882).
The principal pioneer of glacitectonism, however, was George Slater who was the first geologist to
employ the phrase glacial tectonics within a landmark paper published in Proceedings of the
Geologists Association in 1926 (Slater, 1926). Slater worked extensively in modern glacial
environments including Spitsbergen (Slater, 1925) and Switzerland (Slater and Walker, 1929), but he
is perhaps most widely recognised for his studies of relict glacial sequences in Canada (Slater,
1927a), the United States (Slater, 1929) and Denmark (Slater, 1928a, b) (Figure 1). He also published
widely on glacially-deformed sediments in Britain. These studies include a detailed structural
interpretation of the Bride Moraine on the Isle of Man (Slater, 1931) and the Anglian ice margin in
the southern part of the Gipping Valley near Ipswich in southern East Anglia (Slater and Layard,
1907; Slater, 1927b). Slater also worked on the famous ‘Contorted Drift’ sequence of northeast
Norfolk which had previously been examined by Charles Lyell and Clement Reid. However, other
Lee, J.R. and Phillips, E. 2013. Glacitectonics – a key approach to examining ice dynamics, substrate
rheology and ice-bed coupling. Proceedings of the Geologists’ Association, 124, 731-737. ACCEPTED
TEXT.
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than a report on a field meeting in Cromer and Norwich (Boswell, 1923) this work and the stunning
cross-sections that he drew were never formally published.
Whilst Slater’s work was considered by many in the UK to be of only “...ephemeral interest...”
(Howarth in Slater, 1926), research elsewhere in Europe continued to gather pace. A particularly
significant piece of work was published by Gripp (1929) in which he drew the comparison between
relict glacitectonic structures in the geological record, and modern processes occurring within the
foreland of Holmströms Glacier on Spitsbergen. Systematic surveying of glacitectonic terrains also
began in several European countries including Denmark (Jessen, 1931, 1935, 1936; Gry, 1940;
Jessen, 1945), Poland (Lewiński and Różycki, 1929; Czajka, 1931; Dylik, 1961) and the Netherlands
(Crommelin and Maarleveld, 1949; Maarleveld, 1953) and has continued to the present day
(Overgaard and Jakobsen, 2001; Jakobsen, 2003; Rattas and Kalm, 2004). Similar surveys have also
been undertaken in North America and resulted in the publication of a national-scale glacitectonic
map (Aber et al., 1995) and several regional-scale data sets from Saskatchewan / Alberta (Byers,
1959; Christiansen and Division, 1961; Kupsch, 1962; Whitaker and Christiansen, 1972) and Yukon
(Mackay, 1959; Mackay and Mathews, 1964) territories of western Canada, and North Dakota in the
United States (Bluemle and Clayton, 1984).
Much of our modern understanding of glacitectonism stems from the work of Peter Banham (UK)
and Asger Berthelsen (Denmark) during the 1970s. Both geologists highlighted the structural
similarity between glacier-induced shearing and bedrock deformation structures associated with
continental shear zones (Berthelsen, 1973; Banham, 1975, 1977; Berthelsen, 1978). This period also
coincides with a marked divergence in the study of glacitectonics with research focussing on the two
principal end members: (i) subglacial and (ii) proglacial glacitectonism (Hart et al., 1990).
Banham (1977) introduced the now widely-used phrase glacitectonite, drawing analogies between
the products of subglacial glacitectonism and mylonitic metamorphic rocks, suggesting that
deformation within subglacially-sheared materials was partitioned between zones where elements
of the primary lithology and structure were preserved (exodiamict glacitectonite), and zones where
any primary lithology or structure could not be discerned (endodiamict glacitectonite) (Figure 2). The
importance of Banham’s (1977) observations can perhaps only be fully-rationalised within the
context of ‘subglacial deformable beds’ which has subsequently revolutionised glaciology and glacial
geology (Boulton and Jones, 1979; Clark and Walder, 1994; Hart, 1995; Boulton, 1996; Murray, 1997;
Evans et al., 2006). This ‘paradigm shift’ in glaciology (Boulton, 1986) was based upon theoretical
and field based models that demonstrated that a component of forward glacier motion was
accommodated by deformation within the substrate or subglacial bed (Boulton, 1986; Boulton and
Hindmarsh, 1987). Subglacial deformable beds have since been widely recognised or inferred
beneath both modern (Alley et al., 1986; Dowdeswell et al., 2004) and ancient ice masses (Hicock et
al., 1989; Clark and Walder, 1994; Hart, 2007; Maclachlan and Eyles, 2011). They possess a
distinctive glacitectonic structure characterised by a vertical variation in cumulative strain reflected
in systematic changes in the style and relative intensity of deformation (Banham, 1977; Hart and
Boulton, 1991; Benn and Evans, 1996; Evans et al., 2006). This profile, from the base upwards,
comprises: (a) undeformed substrate; (b) ‘type B’ glacitectonite with non-penetrative deformation
(slightly deformed primary structure); (c) ‘type A’ glacitectonite with penetrative deformation
(widespread shear structures); and (d) diamicton often referred to as either ‘deformation till’
Lee, J.R. and Phillips, E. 2013. Glacitectonics – a key approach to examining ice dynamics, substrate
rheology and ice-bed coupling. Proceedings of the Geologists’ Association, 124, 731-737. ACCEPTED
TEXT.
5
(Dreimanis, 1988) or ‘subglacial traction till’(Evans et al., 2006). Preservation of this idealised profile
is dependent upon active accretion of diamicton (d) and the immobilisation of lower strain areas as
the base of the deforming layer (a-b boundary) moves upwards (Figure 3). Subsequent studies have
shown that the base of the deforming layer and positions of different strain zones within the
deforming bed can vary in time and space due to variations in pore-water availability and cumulative
strain. This can cause the subglacial bed to lock (stick) and unlock (slip) repeatedly, and has been
recognised within the geological record as a mosaic-type partitioning of structural styles (Piotrowski
and Tulaczyk, 1999; Piotrowski et al., 2004; Piotrowski et al., 2006; Lee and Phillips, 2008; Phillips et
al., 2008; Menzies and Ellwanger, 2011).
Proglacial glacitectonism refers to the large-scale displacement and deformation of either lithified or
un-lithified proglacial or sub-marginal materials by stresses applied by active ice (Benn and Evans,
2010). Landform features attributed to this style of glacitectonism have been long-recognised,
including hill-hole pairs, composite ridges and thrust-block moraines, cupola hills and mega blocks
and rafts (Milthers, 1948; Smed, 1962; Banham, 1975; Ruszczynska-Szenajch, 1987; Aber et al., 1989;
Burke et al., 2009) and have been mapped extensively, for example, in Europe (Smed, 1962) and
parts of North America (Aber et al., 1995). Various models have been presented to explain the
mechanics of proglacial tectonics (Aber, 1982). However, it was Croot (1987) who drew analogues
with foreland fold-thrust belts within continental collision zones in his development of a thin-skinned
glacitectonic model. In this model, Croot argued that deformation was constrained above a basal
décollement surface with lateral stresses producing a series of proglacial imbricate thrust slices and
nappes. Whilst a fundamental step forward there were aspects of the model that could not easily be
explained, not least the tendency of proglacial landforms to be too large to be produced by the
shear stresses commonly observed at ice margins. This led to the conclusion that the force applied
by an ice-mass wasn’t lateral but rotational, leading to the production of a series of wedges
displaced upwards and down-ice by the load of the glacier (Bucher, 1956; Dahlen et al., 1984). This
process is now commonly referred to as the gravity spreading model (Rotnicki, 1976; van der
Wateren, 1985; Pedersen, 1987; Aber et al., 1989). The styles of deformation produced by proglacial
and subglacial glacitectonism are markedly different, and where superimposed, can be used to
reconstruct structural frameworks (kinetostratigraphy) relating to different ice-marginal positions
(van der Wateren, 1987, 1995a, b; Phillips et al., 2002; Thomas et al., 2004; van der Wateren, 2005;
Thomas and Chiverrell, 2007; Phillips et al., 2008; Rijsdijk et al., 2010). However, differentiating
specific glacitectonic settings that fall between these end members has proven problematic because
at a local-scale, the processes of deformation that exist between various tectonic styles are strikingly
similar (Phillips et al., 2007; Benn and Evans, 2010). One such historical debate surrounds whether
different types of subglacial diamicton (e.g. melt-out till, lodgement till, subglacial traction till) can
be recognised (van der Meer, 1993; McCarroll and Rijsdijk, 2003), or whether all subglacial tills are
essentially subglacial traction or deforming bed tills because they are the product of subglacial
shearing (van der Meer et al., 2003; Menzies et al., 2006). There has also been considerable research
attempting to distinguish between massive diamictons produced by subaqueous and subglacial
processes. This relates both to specific examples, for instance the Late Devensian glaciation of the
Irish Sea Basin, and to the development of analytical criteria to distinguish between subglacial and
waterlain sedimentation (Dreimanis, 1982; McCarroll and Harris, 1992; Hart and Roberts, 1994; Carr,
2001; Lee, 2001; McCarroll, 2001).
