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1. Introduction
In the eld of science, if formerly accepted interpre-
tations are too easily endorsed and not thoroughly
reviewed, especially if these have been built on old-
er and not updated information or knowledge, this
may have hampered which research questions have
been investigated and consequently what has been
documented. Lithied mixtures of non-weathered
sediments of various grain sizes, displaying clasts
and rock fragments of different shapes and sizes
embedded in a matrix of clay, which originated
from, for example, mass ow or glaciation, are la-
belled with the non-genetic term diamictite. Pebbly
sandstone, matrix-supported conglomerates, brec-
cias and weathered bedrock displaying core stones
or less weathered rock fragments in a matrix, are
(commonly) not labelled diamictites. The origin of
diamictites and other geological features that are
produced from erosion and deposition, which have
Geologos 29, 3 (2023): 139–166
https://doi.org/10.14746/logos.2023.29.2.15
Patterns, processes and models – an analytical review
of current ambiguous interpretations of the evidence
for pre-Pleistocene glaciations
Mats O. Molén
Umeå FoU AB, Vallmov 61, 903 52 Umeå, Sweden
Abstract
Models (paradigms) and former interpretations have often been presupposed when conducting eld research. In the
19th century diamictites were for the rst time interpreted to have originated from ancient glaciations. These interpre-
tations have to a large part prevailed in the geological community, although there has been much progress in the areas
of sedimentology, glaciology and physical geography. The present work is an effort to nd criteria which most clearly
discriminate between geological features produced by different processes, mainly glaciation and mass ow, the latter
predominantly sediment gravity ows. Geological features which have been interpreted to have formed by glaciation
throughout pre-Pleistocene Earth history are compared to similar-appearing geological features formed by mass ow
and tectonics, so as to uncover variations in the appearance between features resulting from these different processes.
The starting point for this comparison is documentation of the appearance of Quaternary products of erosion and
deposition, in order to discern the origin of older formations. It is shown that the appearance and origin of pavements,
dropstones, valleys, small-scale landforms, surface microtextures and most other geological features may in some cases
be equivocal, but in others the details are indicative of the process which generated the feature. Detailed geological eld
data which have been compiled by geologists from outcrops of pre-Pleistocene strata, more often than is considered in
most papers, commonly point to a mass ow origin, mainly a sediment gravity ow origin, rather than a glaciogenic or-
igin. A process of multiple working hypotheses or interpretations is therefore advocated, based mainly on a comparison
of the appearance of features formed by different geological processes documented from different research disciplines.
Instead of starting with current interpretations or models, this multiple working hypothesis or methodology helps to
avoid conrmation bias and jumping to conclusions.
Keywords: Diamictite, pavement, dropstone, sediment gravity ow vs glaciogenic characteristics, tectonics
© 2023 Molén M.O. This is an open access article licensed under the Creative Commons Attribution-NonCommercial-NoDerivs License (http://
creativecommons.org/licenses/by-nc-nd/4.0/).
Patterns, processes and models – an analytical review of current ambiguous interpretations of the evidence for...
140 Mats O. Molén
been interpreted to be from pre-Pleistocene glacia-
tions, is the scope of the current article.
For the present review, which is concerned only
with geological features interpreted to be evidence
of cold climates (not climates per se) throughout
pre-Pleistocene Earth history, the starting point is
the year 1855 when Ramsay interpreted some Per-
mian boulder deposits in England to be of glacial
origin (Hoffman, 2011). Ever since that publication
there has been controversy over the interpretation
of diamictites. The Gondwana Late Palaeozoic
Ice Age, probably best represented by the Dwyka
Group in South Africa, was rst interpreted to be
from an ancient glaciation in 1870, and this inter-
pretation was generally accepted in 1898 (Sandberg,
1928; Hancox & Götz, 2014; Molén & Smit, 2022).
In 1891, Reusch described a striated pavement be-
low a diamictite, which was interpreted to be from
a Neoproterozoic glaciation, in the Varanger Fjord
area (northern Norway), which has since then been
a very popular excursion locality (Bjørlykke, 1967;
Molén, 2017). In 1908, Coleman interpreted diam-
ictites in the Palaeoproterozoic Gowganda For-
mation as evidence of glaciation (Coleman, 1908;
Molén 2021). These inuential early papers were
published before detailed documentations from
studies of sediment gravity ows (SGFs) became
well known amongst geologists, and these early
interpretations have prevailed and often direct-
ed later interpretations and research questions of
diamictites worldwide. Papers describing deposits
interpreted to have been produced by former gla-
ciations have been published for thousands of sites,
from all geological periods (e.g., ve episods in the
Cretaceous), in the Precambrian interpreted to have
covered probably the complete Earth one or many
times (Snowball Earth or Slushball Earth), includ-
ing major glaciations during the Hirnantian (Late
Ordovician) and the Late Palaeozoic (Hambrey &
Harland, 1981a; Deynoux, 1985a; Deynoux et al.,
1994; Molén, 2023a).
The birth of sediment gravity ow (SGF) re-
search can be said to have been in the year 1827,
with the introduction of the term ysch (Studer,
1827). The rst mention of a submarine fan dates
from 1955 (Menard, 1955), and the rst mention of
a turbidite-fan link in ancient fans was from 1962
(Bouma, 1962; Shanmugam, 2016). Former inter-
pretations of diamictites as glaciogenic, without
taking into account the more recent understanding
of the importance of SGFs in the geological record
(Shanmugam, 2016, 2020, 2021), have often resulted
in underestimation of SGFs in favour of glaciation,
even if SGF deposits have often been document-
ed in papers concerning diamictites. As the un-
derstanding of the geological work resulting from
gravity ows is a recently growing research area
(e.g., Ogata et al., 2019), more diamictites and co-oc-
curring geological features have been interpreted
as non-glacial. As a consequence of the general lack
of sufcient knowledge of this research area, Shan-
mugam (2016) was invited to write a review con-
cerning deposition by gravity ows in fan environ-
ments. This paper was a reaction generated because
another major paper concerning global geological
studies had missed 60 years of research on the im-
portance of deposition in submarine fans. Lately,
hyperpycnal ows, i.e., highly dynamic dense and
often long-lived (up to months) subaqueous under-
ows orginating from land-derived gravity ows
(including from sediments transported by rivers),
have been recognised to be far-transporting agents
of sediments and organic matter. These ows may
transform, after deposition, into a full spectrum of
SGF deposits, including cohesive debris ows and
rhythmites, which adds one more dimension to this
research area (Zavala & Arcuri, 2016; Shanmugam,
2021; Zavala, 2019, 2020).
The transformation in the geological communi-
ty to a reinterpretation of the origin of diamictites,
started in the early 1970s, but could be said to have
begun with an earlier paper by Crowell (1957).
Out of this came recognition that many “ice-age
remains” had been deposited by different kinds of
SGFs, for example by turbidity currents, but more
commonly by cohesive debris ows. For example,
in the Cenozoic of Alaska, twelve major glacia-
tions were reinterpreted as having formed largely
by SGFs (Plafker et al., 1977; Eyles & Eyles, 1989).
Schermerhorn documented similar reinterpreta-
tions shown in his classic work on Late Precambri-
an diamictites (Schermerhorn, 1974, 1977). Many
researchers in addition to Schermerhorn have com-
pared tills, glaciomarine sediments and different
kinds of SGFs, but the work may have been ham-
pered by the assumption that outcrops with equivo-
cal origin are ice-age deposits (Hambrey & Harland,
1981b; Boulton & Deynoux, 1981; Anderson, 1983;
Wright et al., 1983; Eyles, 1993). The documentation
in Schermerhorn´s classic paper (1974), of criteria
showing differences between the appearance of fea-
tures from SGFs and glaciation, has to a large part
gone unnoticed, even though this article may have
been referred to in passing by many geologists (e.g.,
mentioned by Le Heron et al., 2017).
By using multiple working hypotheses, the cur-
rent analytical review documents detailed descrip-
tions of geological features from pre-Pleistocene de-
posits and compares these to Quaternary geological
features. However, this analytical review does not
Patterns, processes and models – an analytical review of current ambiguous interpretations of the evidence for... 141
start with models or former interpretations. Litera-
ture from relevant areas of physical geography and
glacial geology, including mass wasting processes
and tectonics, has been reviewed. Field work com-
bined with literature studies have been applied to
reports of pre-Pleistocene sections where the geo-
logical features had been interpreted to be glacio-
genic. It is evident that Quaternary erosional and
depositional landforms are often dissimilar to those
which are interpreted from the pre-Pleistocene
when studied in detail, even if there are similari-
ties in the more general appearances. Quaternary
landforms are commonly described in great detail
and have on occasions even been observed during
formation. The same holds true for sediment grav-
ity ows (SGFs) and other mass movements (e.g.,
Shanmugam, 2016, 2021; Ogata et al., 2019; Peakall
et al., 2020; Rodrigues et al., 2020; Dufresne et al.,
2021; Kennedy & Eyles, 2021).
Interpretations of the origin of diamictites and
co-occurring geological features may vary widely
even though an origin by mass ow or glaciation
constitutes the most common interpretations (e.g.,
Dufresne et al., 2021; Isbell et al., 2021). However,
as knowledge about geological processes has ex-
panded, it has become more apparent which inter-
pretation - glaciogenic or mass ow - the origin of
an ancient formation is better justied. Research on
diamictites and their surrounding geological fea-
tures needs to be reconciled with recent scientic
progress in many different research disciplines of,
e.g., sedimentology, physical geography and geo-
chemistry. In particular, research progress on Qua-
ternary glaciations and sediment gravity ows has
revealed both similarities and differences, the most
important of which are easily documented in the
eld.
Thousands of papers have been published on
diamictites and pre-Pleistocene climates, and a
subsample of the most detailed of these are sum-
marised or cited below. Older papers may contain
details about geological features which are relevant
to the interpretation of an outcrop, but such details
may not always be documented in more recent pa-
pers which have accepted former interpretations.
The classic 150-page paper by Schermerhorn (1974)
provided inspiration for the present work when it
was suggested that everything maybe did not ap-
pear to be what it was supposed to be. Results of
the process-related studies by Shanmugam (2012,
2021) are also informative as are other papers like
Peakall et al. (2020), who documented the origin
of soft sediment striated and grooved surfaces/
pavements and the transport of large clasts by
SGFs. Furthermore, papers describing how mass
movements have changed from e.g., slides, to de-
bris ows and nally to turbidity currents (Ogata
et al., 2019; Rodrigues et al., 2020; Kennedy & Eyles,
2021), have helped in the interpretation of ancient
deposits. The work by the present author (Molén,
2017, 2021; Molén & Smit, 2022) has benetted from
the combination of studies from different research
areas used in a paper by Kennedy and Eyles (2021).
A summary of process-related research is similar
to the Lyellian statement that, “The present is the
key to the past”, i.e., to study recent geological fea-
tures with known origins, assumes that the natu-
ral laws have not changed over time (even though
not all processes can be mathematically described),
and applies documented observations to ancient
deposits. However, classic uniformitarianism is sci-
entically dead (Romano, 2015), i.e., processes may
not have operated with the same “momentum” all
throughout Earth history, and different kinds of
sediments have different preservational potential.
Whether or not an area should be interpreted to
have formed by glaciation, is a matter for the eld
geologist to determine. Accepted interpretations of
an ancient outcrop or area, while describing the ap-
pearance of the geological features from that area as
evidence of similar interpretations of other ancient
deposits, may lead to mistakes. Old interpretations
and paradigms may not always be correct, and re-
cent progress in sedimentology and glaciogenic
processes needs to be acknowledged.
The geological features discussed below are
those which most commonly are interpreted to be
from glaciation. The different features are rst de-
scribed in a more general context, and then details
are provided which makes it possible to interpret
the origin of these features more conclusively from
either glaciation or some other processes, the latter
mainly SGFs.
2. Geographical extent, thickness of
deposits and tectonics
It has recently been acknowledged that the main
depositional areas of sediments today are subma-
rine fans and mass transport in areas of subsiding
basins (Shanmugam, 2016). Even on land the most
important process of moving material is mass wast-
ing (Shanmugam, 2020), while other processes may
be dominant in conned areas (i.e., areally and/or
environmentally restricted) and/or during short-
er time intervals. Quaternary tills are commonly
thin (2–15 m, more often on the lower end), except
in conned areas with general thicker tills (e.g.,
142 Mats O. Molén
10–52 m in a 300-km-long band at the southern bor-
der of the North American inland ice sheet; Molén,
2023a), and therefore their preservation potential
for deep time would be low. These observations in-
dicate that, whatever the climate was during Earth
history, there would be few preserved features orig-
inating from earlier glaciations on former higher,
stable bedrock. That especially concerns subglacial
sediments, as most material would have been trans-
ported into marine settings and subsiding basins. In
the Neoproterozoic, diamictites are commonly pre-
served in thick sequences in tectonically unstable
subsiding basins at the edges of cratons, and would
therefore not easily qualify as subglacial sediments
in situ (Eyles, 1993). Furthermore, geological fea-
tures from the Late Paleozoic Ice Age and the Hir-
nantian (Ordovician) glaciation, in most places, are
preserved in areas of subsiding basins and/or areas
affected by transgressions (Ghienne, 2003; Buatois et
al., 2010; López-Gamundí, 2010; Schatz et al., 2011;
Molén & Smit, 2022; Molén, 2023a). The progress in
knowledge of SGFs has changed interpretations of
most ancient diamictites which had formerly been
interpreted to be commonly primarily subglacial,
to instead be (to a large part) reworked SGFs, es-
pecially cohesive debris ows. This reinterpretation
is absolutely not controversial. A provisional older
estimate is that 95 per cent of pre-Pleistocene “gla-
ciogenic” diamictites have now been reinterpreted
to be SGF deposits (Eyles 1993), even though a gla-
cial marine interpretation displaying SGFs is not
excluded.
3. Diamict structure
At rst glance, diamictites formed by cohesive SGFs
and till deposited by glaciers, may be difcult to
distinguish (e.g., Lowe, 1982; Visser, 1983; Wright
et al., 1983), and there have been many mistakes
of interpretation (e.g., Dufresne et al., 2021; Molén,
2023a). Cohesive debris ow deposits may contain
all particle sizes, including a large fraction of clay,
similar to tills (e.g., Molén & Smit, 2022), and there-
fore these may be difcult to distinguish by particle
size analyses, contrary to other sediments which are
more easily separated, e.g., outwash, sheet ow and
loess (Blott & Pye, 2012). In many cases, however, it
is possible to document other patterns/properties
of diamictites that are more characteristic of either
SGFs or tills.
Diamictites which commonly have been inter-
preted to be tillites, even to this day, often display
grading, bedding and amalgamation, similar to
SGF deposits (Visser, 1983; Domack & Hoffman,
2011; Kennedy & Eyles, 2021; López-Gamundí et al.,
2021; Shanmugam, 2021; Molén & Smit, 2022). They
are often covered by laminated deposits and/or
sediments with marine fossils (Sterren et al., 2021).
Occasionally, there is even a gradational transition
from the diamictite into the overlying (sorted) bed
(Cuneo et al., 1993; Isbell, 2010), but there may be
long time periods in between the deposition of
diamictites and the subsequent (sorted) beds.
Glaciers process all kinds of sediments and bed-
rock, slowly turning these into rock our, and do
not sort out the ner material (albeit, of course,
with the exception of sediments from small alpine
glaciers which are processed during a very short
time, and produce deposits which would be more
vulnerable to erosion and would be difcult to
document in the rock record). In pre-Pleistocene
diamictites which are interpreted to be glaciogen-
ic and displaying outcrops over large areas, there
is often no rock our, contrary to Quaternary tills
(Frakes 1979; Le Heron et al., 2005, 2006; Yassin &
Abdullatif, 2017; Molén 2017; Chen et al., 2021). Soft
sediment clasts may be common (Deynoux, 1985b;
Molén, 2017; Kennedy & Eyles, 2019, 2021), and
sometimes clasts in diamictites have been pressed
into underlying surfaces (Isbell et al., 2021), or the
overlying sediment has been pressed down into the
diamictite, or the diamictite has been pressed up-
wards into the overlying sediments (Cuneo et al.,
1993; Isbell, 2010), i.e., features which frequently ac-
company SGF deposits (Shanmugam, 2012; Molén,
2017, 2023a; Vesely et al., 2018; Kennedy & Eyles,
2019, 2021; Rodrigues et al., 2020; Kraft & Vesely,
2023).
4. Fabrics
Fabrics in subglacial tills are less varied and azi-
muth constrained than those in SGF deposits. While
glaciogenic fabrics may often be unimodal or bi-
modal, with a common updip of 10 to 20° in the di-
rection of the ice movement (e.g., Evans et al., 2016),
this can also be displayed by gravity ow deposits
(including in ow tills). In gravity ow deposits the
fabric also may be planar or steeper than in tills, but
the main difference is that it commonly differs in
vertical section (Lindsay, 1968).
5. Erratics
There has never been a systematic study of differ-
ences in size of clasts in tills and SGF deposits, even
though clast size is often mentioned. In tills there
Patterns, processes and models – an analytical review of current ambiguous interpretations of the evidence for... 143
are almost always numerous large clasts, many me-
tre-sized (Fig. 1A). In mass movements clasts also
may be large, and kilometre-sized blocks are not
uncommon in slides (Nwoko et al., 2020a, 2020b;
Puga Bernabéu et al., 2020; Kennedy & Eyles, 2021;
Kumar et al., 2021). If clasts in SGFs are large, it is
commonly easy to see evidence of soft sediment
structures originating from the movement.
Calculations show how much cohesive strength
is needed to transport large clasts in a mud-rich u-
id, which could be a cohesive debris ow (Peakall
et al., 2020). The increase in buoyancy needed for
clast size is exponential, and clasts larger than 1
m in diameter would need so much yield/matrix
strength that it would be suspected that such trans-
port would be rare (Peakall et al., 2020). Thus, if
>1m clasts are transported, one would suspect to
see clear evidence of the ow mechanism, i.e., any
kind of disturbances in the sediments. This size
pattern is exactly displayed in diamictites which
have been interpreted to be glaciogenic: the largest
clasts are seldom more than 1 m in diameter, even
though clasts in SGF and other deposits from the
same area may include much larger sizes than those
parts which are considered to be subglacial (Molén,
2023a). In conclusion, the presence of large clasts is
almost always much rarer in pre-Pleistocene diam-
ictites than more recent glaciogenic sediments, and
they are smaller than in tills.
In many diamictites there appears to be a mix
of different clast types and no/few intermediate
clasts, e.g., rounded, long-transported clasts and
highly irregular and sharp short-transported clasts
together (Molén, 2021; Molén & Smit, 2022). This is
easily explained by mixing of material from differ-
ent sources, like in SGFs which have mixed material
transported for distances of 2,000 km and depositing
material over areas of 132,000 km2 (Molén, 2023a),
but is not implausible for tills, even though glaciers
commonly quickly abrade sharp edges (Eyles & Ey-
les, 2000; Ortiz-Karpf et al., 2017; Ogata et al., 2019;
Nugraha et al., 2020; Rodrigues et al., 2020).
In some diamictites there is a correlation be-
tween bed thickness and the diameter of the errat-
ics (Schermerhorn, 1974; Martin et al., 1985; Eyles &
Januszczak, 2007). In quite a few diamictites, clasts
or bedrock are fractured into a jigsaw puzzle texture
(Fig. 1B); this is common in mass wasting deposits
but has never been recorded from Quaternary tills
(Ui, 1989; Thompson, 2009; Ali et al., 2018; Dufresne
et al., 2018, 2021; Molén, 2021). There are, of course,
fractured rocks in tills, but these do not display a
jigsaw puzzle texture.
Boulder pavements (i.e., at-topped accumula-
tions of large clasts or boulders) are produced by
glaciers in a process almost like a slow gravity ow
(Clark, 1991; Hicock, 1991), and therefore there may
be similarities to boulder accumulations formed by
SGFs, e.g., planed-off boulders displaying striations
as if processed by glaciers (e.g., Scott, 1988). If the
boulders are more sorted, like a train (Bussert, 2014;
Kennedy & Eyles, 2019), this may be more consist-
ent with SGFs.
6. Polished, facetted and striated clasts
Clasts can be striated in many different environ-
ments. The variety of striations, and the number
of striated clasts, may be similar in SGF deposits
and tills (Atkins, 2003, 2004; Molén, 2023a). Often
there is no detailed systematic documentation of
any pattern in the appearance of striations, neither
by researchers working with mass wasted deposits
or those working with diamictites which have been
interpreted to be tillites. However, Kennedy & Ey-
les (2021) documented that there were more striat-
ed clasts in SGFs in places where more clasts were
present.
Detailed documentation of different combina-
tions of processes which produce clast form is also
Fig. 1. A – Example of the common size of a Pleistocene
erratic. Västerbotten County, Sweden; B – Jigsaw
puzzle texture, where ne-grained sediment has been
pushed in between the fractured clasts. Gowganda
Formation, Canada (Molén, 2021). Marker is 20 cm.
144 Mats O. Molén
often inconclusive, and it may be possible that the
only exclusive glaciogenic form is clasts that dis-
play double stoss-lee forms (Sharp, 1982; Krüger,
1984; Rowe & Backeberg, 2011).
7. Striated, grooved and polished
surfaces/pavements
Surfaces may become striated and grooved by dif-
ferent kinds of movements, such as glaciation, mass
wastage and tectonism, and it is not always easy to
determine the origin of a striated surface.
Clasts which are transported within glacier
ice are always moving slightly, vertically up and
down, and laterally from side to side, more or less
depending on the temperature of the ice, which is
also evidenced by the appearance of Pleistocene
and more recent glaciogenic striations and grooves
(Chamberlin, 1888; Sugden & John, 1982; Iverson,
1991) (examples in Fig. 2). It is less well known that
clasts within SGFs may be stuck in the same po-
sition for very long distances, almost like a small
plough moving over the subsurface (Peakall et
al., 2020), e.g., Figure 2A. In SGFs striations and
grooves may also change direction and display an
appearance similar to glaciogenic pavements (Enos,
1969; Kneller et al., 1991; Pickering et al., 1992; But-
ler & Tavarnelli, 2006; Draganits et al., 2008; Peakall
et al., 2020).
Outcrops of pre-Pleistocene striated areas com-
monly display regularly parallel, straight striations
and grooves, both in soft sediments and in sedi-
mentary and igneous/metamorphic bedrock (Fig.
3). They are commonly dispersed and cover more
restricted areas. Surfaces are often not covered by
diamictite, which may indicate bypass zones as
in SGFs. The striated surfaces are often vertically
stacked, and may display many unique features
that are not produced beneath glaciers (examples in
Table 1).
One main difference between pre-Pleistocene
pavements and Quaternary glacial pavements is the
Fig. 2. A – Clast in situ in a SGF-deposit showing long parallel striations, similar to those in many pre-Pleistocene pave-
ments and different from Quaternary striations and grooves. Compare with Figure 3. (Picture from: Enos, 1969.
Used with permission from Journal of Sedimentary Research); B–D – Examples of Pleistocene striations on gneissic
metamorphic bedrock, in the city of Umeå, Västerbotten County, Sweden. Note that the striations are semi-parallel,
waxing and waning, commonly short and turning (especially on steep surfaces); D – This is an appearance of stri-
ations that has been well documented from Quaternary glaciers. Even if there are variations in the appearance of
the striations, they are different from all documented pre-Pleistocene striations that the present author is aware of.
Patterns, processes and models – an analytical review of current ambiguous interpretations of the evidence for... 145
presence of soft sediment surfaces. Soft sediment
striated and grooved surfaces are commonly very
regular, recorded from SGFs soon after formation in
soft sediments (Peakall et al., 2020), and they are not
present with similar appearance in any Pleistocene
or younger subglacial environment, except possibly
very locally. Soft sediment striated or grooved sur-
faces may often be interpreted to be glaciogenic if
Fig. 3. Straight and parallel striations and grooves on pre-Pleistocene pavements, Dwyka Group, South Africa, com-
monly interpreted to be evidence from the Late Paleozoic Ice Age. A – Pavement on Precambrian Ghaap Formation
Dolomite, close to Douglas, where striations are long and unbroken (photograph and pers. comm., Johan N.J. Viss-
er); B – Pavement in Neoarchean Ventersdorp andesitic/basaltic lava, at Douglas, with similar appearance as the
striations and grooves in the pavement in the Precambrian Ghaap Formation Dolomite (scale is 30 cm, pavement
has been recently weathered); C – Striations leap over a small scarp (apparently formed by sheet jointing; Molén &
Smit, 2022) between the Ventersdorp andesitic/basaltic lava and Dwyka Group diamictite, at the famous Nooitge-
dacht pavement. There are striations in different directions, but commonly in regular groups and not displaying the
common curvilinearity of Quaternary striations (Molén & Smit, 2022). (Photograph J. Johan Smit).
Fig. 4. Examples of multiple stacked surfaces displaying striations and grooves produced from turbidities, negative
view. These are reminiscent both in detail and in overview of striations or grooves in stacked soft sediment pave-
ments that often are interpreted to be linked to pre-Pleistocene glaciations, but then the positive, rather than the neg-
ative, side is visible. Pictures are at c. 100 m distance from each other. Arrow is 25 cm. This outcrop was described in
detail by Bischoff (2002) and in general by Hoffman (2016). Lower Saxony, Germany, Lower Carboniferus (Visean).
146 Mats O. Molén
they are recorded in positive relief, but similar ap-
pearing surfaces are commonly from SGFs if they
are negative (Fig. 4) (compare Molén, 2023a, Sup-
plementary Material Table S2; Peakall et al, 2020;
Baas et al., 2021).
Below SGF diamictites there are often traction
carpets, i.e., thin beds of granular sediment be-
tween the diamictite and the underlying sediment
or bedrock (Georgiopoulou et al., 2010; Talling et
al., 2012; Dakin et al., 2013; Cardona et al., 2020;
Peakall et al., 2020; Molén & Smit, 2022). Similar
sediments may also be present beneath supposed
tillites but are seldom documented in publications
(Molén & Smit, 2022; Molén, 2023a). Soft sediment
may also be moulded into strings displaying stria-
tions or grooves, by SGFs on top of hard surfaces,
and the latter may become striated by the same pro-
cess (Molén & Smit, 2022).
There are pre-Pleistocene soft sediment grooves
and striations which have been interpreted to
have been formed by iceberg keels (Vesely & As-
sine, 2014), but these surfaces display no denite
evidence of waves, currents or tides, even if there
may be occasional changes of direction even up to
180° for some features (Isbell et al., 2023). However,
changes in directions up to 180° are also displayed
by SGFs (Kneller et al., 1991). Surfaces interpreted
to have been formed by pre-Pleistocene icebergs
are rare, areally restricted, and often only isolated
examples from single “icebergs”, contrary to areas
of Quaternary ice-keel marks (Woodworth-Lynas
& Guigné, 1990; Bennett & Bullard, 1991; Wood-
worth-Lynas, 1992; Woodworth-Lynas & Dowde-
swell, 1994; Dowdeswell & Hogan, 2016).
8. Are outsized clasts dropstones?
Outsized clasts are dened as clasts evidently larger
than the particle size in the surrounding sediments.
Outsized clasts which are present in ne-grained
sediments in pre-Pleistocene formations, in either
stratied or unstratied sections, often are labelled
dropstones and interpreted to stem from input from
icebergs or lake or sea ice (Bronikowska et al., 2021;
Molén 2021). This is evident from a large number of
papers on the subject, in which outsized clasts are
described as dropstones and advanced as evidence
for a glaciogenic interpretation of a formation (Le
Heron et al., 2022b; Molén, 2023a), or not glaciogen-
ic if there are, e.g., no outsized clasts (Clapham &
Corsetti, 2005). Systematic descriptions of outsized
Table 1. Appearances of pre-Pleistocene “glaciogenic” striated surfaces/pavements, which are commonly generated by
SGFs and tectonics, and are commonly not (or never) displayed by Quaternary glaciogenic pavements. Left-hand
column: Examples of features of pavements which have been interpreted to be glaciogenic, but display unique
appearances that have seldom or never been observed to have been produced by glaciers. Right-hand column: Pres-
ence of features produced by SGFs or tectonic movements, in comparison to formation by glaciers, approximate:
1 = may possibly and occasionally, more or less by chance, be produced by glaciers, but may be rare or commonly
present on surfaces produced by SGFs or tectonics. 2 = never or almost never produced by glaciers but may be
present or are common on surfaces produced by SGFs or tectonics (for eld data and references, references is made
to Molén & Smit, 2022; Molén, 2023a).
Straight, regular, striations and grooves 2
Perfectly parallel striations and grooves 2
Soft sediment surfaces 2
Pavements commonly without diamictite 1
Striations continue from top of “tillite” into striations on pavement below 2
Superposed/stacked striated soft sediment surfaces 2
Striated or “uted” sediment internally in diamictite 2
Sediment between pavement and diamictite, i.e., traction carpet 2
A soft sediment striated surface is cut into ripple laminated siltstone 2
Fossil plants jammed in between “tillite” and the striated pavement 2
A soft sediment pavement is draped with mudrock displaying crustacean track ways 1
Slickensides turn into striations, tectonic and “glacial” striations on same surface 2
Sand ows cover striations 2
Striations pass from lava to soft sediment stacked striations 2
Striations in same direction as foliation in underlying bedrock 1
Overhanging walls in striations 2
Molded sediment turns into striations 2
Bifurcating striations 2
Push up rinds at striations 1
Patterns, processes and models – an analytical review of current ambiguous interpretations of the evidence for... 147
clasts, formerly interpreted to be dropstones, are
the studies by Kennedy & Eyles (2021) and Molén
(2021). Researchers may document different dis-
turbances in sediments close to outsized clasts, and
label these disturbances after similar structures
described in the much-quoted paper by Thomas &
Connell (1985) describing Pleistocene dropstones,
e.g., rucking structures (Fig. 5). Yet, such compar-
isons are seldom mentioned or fully documented.
However, clasts up to sizes of metres in diam-
eter can be lifted and transported by agents other
than ice, i.e., vegetation and macro algae, and clasts
transported with such agents may display the same
appearance and thus be impossible to discriminate
from clasts transported by glaciers, icebergs and sea
ice. Even at this moment an estimated hundreds of
thousands of clasts, most small but up to metres in
diameter, are lifted and transported with kelp (Wa-
ters & Craw, 2017). Marine macro algae which can
transport clasts of up to a few centimetres in diame-
ter, have been present from the Neoproterozoic and
possibly even earlier (Bengtson et al., 2017; Gibson
et al., 2018; Del Cortona et al., 2020). Therefore, the
appearance of sedimentary structures next to out-
sized clasts (as documented by Thomas & Connell,
1985) are always problematic for discrimination be-
tween transport by vegetation or ice.
Outsized clast are almost always transported
with SGFs, larger clasts in denser, more cohesive
and stronger ows. If clasts are transported with-
in more cohesive and denser parts of gravity ows,
the resulting deposit will be a (non-glacial) diamic-
tite. Otherwise, it may be a laminated deposit where
clasts may penetrate and disturb laminae in a simi-
lar way as dropstones. Therefore, the appearance of
outsized clasts has to be documented in more detail
in order to determine their origin.
Outsized clasts in rhythmites or other ne-
grained sediments which have been transported
by SGFs are commonly smaller than glaciogenic
dropstones, they are commonly smaller than clasts
in nearby diamictites which are interpreted to be
tillites, and they are also smaller than clasts in more
clearly evident SGF deposits, i.e., deposits which
are not massive but display much evidence of
movement and therefore do not display freezing of
the movement as is common in cohesive debris ow
deposits. Many inferred dropstones are so small
(<1 cm) that they would hardly make an impact on
the bottom sediment (Bronikowska et al., 2021; Le
Heron et al., 2022b; Molén, 2021), while such small
clasts would commonly impact sediments trans-
ported with SGFs only because of owage or later
compaction (Molén, 2023a).
Non-glaciogenic outsized clasts may display a
fabric similar to SGFs, they may be sorted where
there is a correlation between clast size and sedi-
ment thickness, they are often draped with sedi-
ment, but they more seldom clearly penetrate lami-
nae (Molén, 2021, 2023a). The beds or laminae where
the clasts are present often display a thickening next
to the clast, and occasionally there may be a pushed-
up sediment bulge in front of the clast. The latter
may often be labelled a rucking structure if the de-
Fig. 5. Left: Schematic denition of sedimentary structures next to dropstones. 1–4 are bottom contact, 5–7 are top
contact. 1 = bending. 2 = penetration. 3 = rucking. 4 = rupture. 5 = bending. 6 = on-lap. 7 = rupture (after Thomas &
Connell, 1985). Right: Photograph of an outsized clast commonly interpreted as a dropstone, Gowganda Formation
at Cobalt, Ontario, Canada (Molén, 2021). The appearances of the sedimentary structures next to this clast conform
to the denitions of a “leftover”, i.e., a clast that has been transported with a SGF, as dened in the right-hand col-
umn of Table 2 (marker is 10 cm).
148 Mats O. Molén
posit is interpreted to be glaciogenic (Valdez Buso
et al., 2021), i.e., a structure that develops when a
dropstone penetrates laminae and pushes sediment
to the sides of a clast. On closer inspection it may
be possible to document if it is a push or current
structure from lateral movement, or if it is a struc-
ture formed by vertical penetration from above.
This may be deduced from the lateral length of the
disturbance, the thickness of the disturbance, if lam-
inae are moved to different heights or splits/joins
at the outsized clast, or if the disturbance is only on
one side. If clasts are dropped in owing water, or if
there are SGFs at the bottom, or if clasts are stuck to
a piece of ice and only sink slowly to the bottom, the
appearance of the structures surrounding the clasts
will display similarities to those in SGF deposits.
Table 2 lists differences between the structures
labelled by Thomas & Connell (1985) from drop-
stones (Fig. 5) compared to pre-Pleistocene “drop-
stones,” and also special features only present in
connection to diamictites (not counting those that
have already been interpreted by researchers to be
from SGFs, as they all fall in the same category). It
is, of course, not possible to decide whether each
single outsized clast is a dropstone or not, but the
evidence from appearances of many outsized clasts
present together in a bed or area will indicate the
best interpretation of that area.
The most denite pattern of sedimentary fea-
tures indicating a non-glacial origin includes com-
parative clast size, correlation between sediment
thickness and clast size, if there is little or no pen-
etration (i.e., the clasts are within a single lamina
or group of laminae) and the length of deformation
surrounding the clasts, i.e., a pattern which is much
fullled in e.g., Late Paleozoic Ice Age outcrops in
Australia that are commonly considered to be gla-
ciogenic (see gures in Eyles et al., 1997 and Field-
ing et al., 2023). There should also be a correlation
between clast size and impact force, but such a cor-
relation has not been studied systematically in the
eld (Bronikowska et al., 2021).
A more neutral label for dropstones, except for
outsized clasts, would be lonestones, which is a
non-genetic label (Neuendorf et al., 2005).
9. Erosional structures, lineations,
valleys, fjords and sculpted bedrock
Lineations formed by Pleistocene glaciers may cov-
er large areas, from glaciers moving over heights
and down in valleys (Eyles et al., 2018; Bukhari
et al., 2021), while those present in the pre-Pleis-
tocene are commonly few or only single and may
Table 2. Sedimentary structures next to outsized clasts. The upper seven structures were mentioned and dened by
Thomas & Connell (1985) from dropstones (see Figure 5), and the data below the line are from the documentation in
the main text. The differences between documented (Quaternary) dropstones, compared to outsized clasts that are
commonly interpreted to be dropstones in pre-Pleistocene deposits, are described in the right-hand column.
Documented structures of glacial dropstones Common appearance of pre-Pleistocene “glaciogenic drop-
stones”
Bending below Similar, but may be less; more often like draping all around
the clasts
Penetration, laminae are disrupted, commonly 1/3 to
2/3 of clast size Possible, but commonly less penetration and more often only
at sharp edges of clasts
Rucking below Present, but more often only one sided
Rupture below May be present if at front of a SGF in soft sediment
Bending above Similar, but may be less; more often like draping all around
the clasts
On-lap above, laminae are disrupted Similar, but more often sediments thin out and are draped
around the clast; there may be a bulge upwards too
Rupture above, laminae are disrupted May be present, but would be more common if a clast has
been dropped
Dropstones come in all sizes Commonly small, only a few cm
Approximately similar clast size of dropstone as in till Smaller size than in “tillite” or accepted SGF deposits
No correlation between sediment thickness and clast
size May be correlation between sediment thickness and clast size
Deformation of sediment locally and probably quite
similar on both sides of clast Deformation of sediment more extensive, including push
and current structures, and different on opposite sides
Penetration common Clast often within single beds
Fabric may be inclined or subvertical Fabric similar to SGF deposits
Patterns, processes and models – an analytical review of current ambiguous interpretations of the evidence for... 149
be more bevelled or downcutting. Lineations in
the Ordovician of Sahara, interpreted from satel-
lite imagery to be glaciogenic (Le Heron, 2018; Le
Heron et al., 2022a), follow the structure of under-
lying and planed-off dipping sandstone beds (Fig.
6). On closer inspection, the lineations are irregular,
meaning that they may not be lineations but sur-
faces exposed to non-glaciogenic erosion (detailed
Google Earth study of the area which is interpret-
ed to display lineations by Le Heron, 2018). Glacial
lineations would be independent of the linearity
of underlying sediments, and some lineations are
probably produced from tectonics (Le Heron, 2016,
2018). Sculptured areas, including pavements, have
also been shown to have originated in dipping stra-
ta probably by tectonics and recent erosion, above
a palaeolandscape with an equivocal origin (Van-
dyk et al., 2021; Le Heron et al., 2022a). Lineations
in southern Africa interpreted to be from glaciation
are shorter and wider than their Pleistocene “coun-
terpart” (Andrews et al., 2019).
SGFs and water currents have been shown to
sculpture large areas, including positive landforms
with an appearance of nunataks or drumlins, espe-
cially if there are catastrophic ooding events, but
these commonly leave more bevelled landforms
and downcutting lineations than glaciation (Burr et
al., 2002; Plescia, 2003; Rodriguez et al., 2005; Ma-
jor et al., 2005; Moscardelli et al., 2006; Leask et al.,
2007; Gupta et al., 2007, 2017; Robinson et al., 2017;
Ortiz-Karpf et al., 2017; Nwoko et al., 2020a, 2020b).
Glaciogenic (alpine) valleys are supposed to be
commonly U-formed in shape, while uvial or oth-
er valleys are supposed to be more often V-shaped.
However, research on almost 900,000 transverse
logs and shapes of different valleys have shown
that this is a truth with modication, i.e., different
shapes are possible in many environments (ex-
amples in van der Vegt et al., 2012; Coles, 2014;
Gales et al., 2014; Ortiz-Karpf et al., 2017; Pehlivan,
2019; Puga Bernabéu et al., 2020). Also, thousands
of different canyons and other valleys are formed
by processes that are non-glacial, including tecto-
nism and SGFs, in all kinds of bedrock, including
hanging valleys (Shepard & Dill, 1966; Clapham &
Corsetti, 2005; Mitchell, 2006; Lamb, 2008; Amblas
et al., 2011; Normandeau et al., 2015), so there may
be many different interpretations of pre-Pleistocene
valleys that have been interpreted to be glaciogenic
(Giddings et al., 2010; Macdonald et al., 2011; Coles,
2014; Ortiz-Karpf et al., 2017; Bechstädt et al., 2018;
Pauls et al., 2019; Isbell et al., 2021; Vandyk et al.,
2021). If valleys display an irregular (not polished/
abraded/sculptured) basal boundary geometry,
they may be more compatible with SGFs and slides
than glaciation, even though this is not always the
interpretation made (Dakin et al., 2013; Sobiesiak et
al., 2018; Soutter et al., 2018; Dufresne et al., 2021;
Molén 2021).
Recent research at Namibian basins displays ar-
eas below diamictites where the basal unconformity
may be undulating, highly irregular and heteroge-
neous, with areas of heavy sediment injections into
fractured bedrock that are interpreted to be sub-
glacial (Le Heron et al., 2021b) and not only clastic
dykes; the latter may be common subglacially (e.g.,
Sokołowski & Wysota, 2020). Sediment injections
are regular features of SGFs, and together with the
general appearance of the area, this may indicate an
origin by SGFs and not glaciation (Dufresne et al.,
2021; Molén, 2021, 2023a; Molén & Smit, 2022).
Fig. 6. In the area which is interpreted to display glacial
lineations in Chad, the underlying bedrock consists
of superimposed dipping sandstone beds. Erosion-
al processes on roughly level areas may produce an
appearance of lineations from these dipping beds, in-
dependent of the erosional process. The photograph
shows one example of dipping sandstone beds from
the area in question, but here displaying curved and
not straight erosional surfaces. An intermittent creek is
visible in the centre of the photograph. Other detailed
photographs from the same area were published by
Le Heron (2018, gs 3, 4) showing juxtaposition to the
underlying dipping sandstones, including positive
features labelled nunataks or drumlins by Le Heron
(2018), with an appearance similar to those made by
ooding, rather than deep erosion made by glaciers
(photograph from Google Earth/Google Maps).
150 Mats O. Molén
The most interesting valleys from a glaciogenic
point of view are fjords. These display a very char-
acteristic appearance, i.e., narrow, overdeepened
and with a prominent transverse “sill” or ridge at
the outlet into the sea (or lake) (Fig. 7). If a valley
has no transverse ridge at the outlet, it is probably
not a fjord, even if that may be the interpretation
which is published (e.g., Dietrich et al., 2021). Over-
deepening of ancient valleys may be more difcult
to document, because surrounding mountains may
have eroded away, but if there is evidence of deep-
er areas where the surroundings are higher, it may
provided evidence of a fjord. No valley has ever
been documented in a pre-Pleistocene formation
that displays the typical appearance of a fjord. But,
fjords are very common in Pleistocene and more re-
cent glaciated areas, and it could be suspected that
they should be similarly prominent in more ancient
areas, as these landforms do not readily vanish.
Plucking, which is a typical glacial phenomenon,
also may be induced by water currents and gravity
ows (Dakin et al., 2013; Lamb et al., 2014; Hodgson
et al., 2018), but these often display steep stoss sides
and gentle lee sides in bedrock (Molén, 2023a), con-
trary to glaciogenic landforms (e.g., Krabbendam &
Glasser, 2011). Tectonic forms may be moulded into
sculpted glacial-apparent bedrock by uvial action,
including shapes reminiscent of roches moutonnées
(Vandyk et al., 2021).
10. Channels, tunnel valleys and eskers
Channels are excavated by many non-glacial pro-
cesses, including SGFs (Talling et al., 2007; Keller et
al., 2011; Macdonald et al., 2011; Dakin et al., 2013;
Kneller et al., 2016; Shanmugam, 2016; Baas et al.,
2021). If channels are later lled with more resist-
ant sedimentary material, and the material around
erodes away, the resulting land form will appear
to be a longitudinal ridge, i.e., a topographic rever-
sal. In northern Africa and the Arabian Peninsula,
Fig. 7. One of the smallest (former) fjords, which is now the c. 2-km-long lake Ågvatnet next to the small village of Å in
Lofoten, Norway. All characteristic appearances of fjords are present even in these smallest fjords. They are narrow,
overdeepened and display a prominent transverse ridge at the outlet. At this former fjord the ridge has been the
foundation for the road and house in the lower picture (the fjord is barely visible behind the house and ridge).
Patterns, processes and models – an analytical review of current ambiguous interpretations of the evidence for... 151
there are thousands of channels which have been
lled with sediment, and many of these now dis-
play an appearance that is in part similar to eskers
(Zaki et al., 2018, 2020, 2021). Le Heron et al. (2018)
recognised that there are no “suitable modern ana-
logues” to channels which have been interpreted to
be Ordovician tunnel valleys, which make the inter-
pretations equivocal (Molén, 2023a).
Pleistocene and recent esker sediments are com-
monly sorted, with large rounded clasts in the bot-
tom middle, and then ner on top and at the mar-
gins, even though many eskers are made up mostly
from sand. There is often tectonic deformation
displayed by eskers. Large clasts, which have col-
lapsed from the overlying glacier, are often present
on their tops (Frakes, 1979). There is some evidence
of tectonics in longitudinal landforms which have
been interpreted as eskers (Allen, 1975; Biju-Duval
et al., 1981), but not so much that it has to be more
than local deformation which could have occurred
simply by gravitational collapse. No large clasts
have been documented on top of esker-like forma-
tions from pre-Pleistocene deposits.
11. Laminated sediments
Recent experiments have shown that clay laminae
can form as quickly as sand or silt laminae, not
only in turbidites but also during slower deposition
(Schieber et al., 2007, 2013; Sutherland et al., 2015;
Yawar & Schieber, 2017). This process results from
clay particles occulating and therefore quickly
sinking. Earlier settling experiments with umes
had disintegrated these occules, and therefore clay
particles did sink much more slowly. A recently de-
scribed process which more clearly unfolded how
laminae are quickly produced and able to cover
large areas, is a combination of high uid shear and
sediment concentration (Al-Mufti & Arnott, 2023).
In conclusion, there are many indications that pre-
sumed varves in pre-Pleistocene outcrops have been
deposited much more quickly than on a yearly basis,
which may be discovered by detailed studies (Mat-
ys Grygar, 2019; Smith, 2019, 2023 reinterpreting 60
recently published papers on this subject; Kochhann
et al., 2020; Isbell et al., 2021; Molén, 2021).
12. Periglacial structures, soft sediment
deformation and tectonism
Geological features which may appear to be formed
by permafrost, such as patterned ground and ice
wedges, also may form by desiccation, small-scale
tectonics, and almost any volume change in sedi-
ments (Bryan, 1983; Eyles & Clark, 1985; Eyles,
1990; Tipper et al., 2003; Robinson et al., 2017), and
they may therefore be easily misidentied (Molén,
2023c).
Large-scale soft sediment deformation may be
difcult to evaluate if it is glaciogenic or SGF. So far,
no clear characteristics have been identied for one
or the other potential origin (Sobiesiak et al., 2018;
Rodrigues et al., 2020; Molén, 2023a).
13. Glaciomarine and glaciolacustrine
environments
Yearly varves only form in fresh water, but apart
from that there is no great difference between sedi-
mentation in glaciomarine and glaciolacustrine en-
vironments. In Quaternary glaciomarine and glaci-
olacustrine environments there is an abundance of
linear, transverse and irregular geological features
(Dowdeswell et al., 2016a, 2016b). In pre-Pleisto-
cene deposits interpreted as glaciomarine or gla-
ciolacustrine these features are generally absent,
even though subaqueous depositional areas should
be excellent for the preservation of such geological
landforms. Single examples of geological landforms
with such an appearance in ancient deposits may be
intepreted to be glaciogenic, but there are no large
areas demonstrating these features, even if the ar-
eas under study ought to display such landforms
in large numbers (Molén, 2021). Almost the sole
piece of evidence given for a glaciomarine or gla-
ciolacustrine origin for a pre-Pleistocene outcrop is
the interpretation of outsized clasts as dropstones
(this includes the majority of papers mentioning
outsized clasts; e.g., Freitas et al., 2011; Figueiredo
& Babinski, 2014, Milana & Di Pasquo, 2019; Molén,
2023a).
14. Fossil vegetation
Plant fossils, commonly as coal but also separate
fossils, are often deposited next to or occasionally
even within diamictites which are interpreted to
have formed from large-scale Late Paleozoic gla-
ciations. There is evidence for more plant refugia
than earlier recognised during the last continental
Pleistocene glaciation (Birks & Willis, 2008; Bin-
ney et al., 2009; Westergaard et al., 2019). Howev-
er, there is no evidence from large forests next to
the continental glaciers during the Pleistocene, and
152 Mats O. Molén
both recent forests growing at former glaciated
areas and Pleistocene refugee plants have typical
cold weather species (e.g., Picea, Larix, Betula). The
fossil plants stratigraphically and palaeogeograph-
ically next to Late Palaeozoic diamictites are con-
sidered to be near continental glaciers, or close to
palaeopoles in the same sedimentary successions
as geological features that have been interpreted
to be glaciogenic. Therefore these plants are often
considered to have been adapted to cold climate.
However, these plants commonly display large,
complete, non-toothed leaves which are typical of
warm-weather plants, possibly subtropical or trop-
ical, and not small, toothed leaves indicative of po-
lar/subpolar climates (Götz et al., 2018; DeVore &
Pigg, 2020; Gastaldo et al., 2020a, 2020b; Mays et al.,
2020; Tripathy et al., 2021). Plants are better climate
indicators than sediments, which would undermine
interpretations of former cold climates in the Late
Palaeozoic.
15. SEM studies
After reorganisation of patterns of data from older
studies, and conducting process-oriented studies of
Fig. 8. SEM images of quartz sand grains from diamictites which have been interpreted to be glaciogenic; compare these
to grains in Figure 9. Except for a few grains displaying fractures, these are more or less spherical and display a com-
bination of regular abrasion all over the grain surfaces combined with weathered surfaces, i.e., surface microtextures
which are typical of multicyclical grains. The grain surfaces display no evidence of glaciation, i.e., irregular abrasion
and especially irregularly abraded fractures. A few grains display fractures that are either sharp or otherwise regu-
larly abraded all over the fracture faces, i.e., these grains are still not similar to glaciogenic grains but only display
fractures that are produced in any high-energy environment and no irregular abrasion. A – Ordovician Pakhuis
Formation, South Africa; B – Carboniferous Dwyka Group, South Africa; C-D – Hirnantian Kosov Formation, Czech
Republic. C is the most common appearance; D is rare; E-H – Neoproterozoic diamictites, Varanger, Norway. E, G
and H display the most common appearances; F is rare. Notice the non-abraded sharp fractures in F, indicating only
fracturing, yet no abrasion following fracturing.
Patterns, processes and models – an analytical review of current ambiguous interpretations of the evidence for... 153
how surface microtextures on quartz sand grains
originate in different environments (Molén, 2014,
2017), this area of research has become a well-func-
tioning working tool for the study of all kinds of
sediments, including diamictites (e.g., Mahaney,
2002; Molén, 2014, 2017, 2023a; Molén & Smit 2022).
Minerals are fractured in many environments,
and therefore solitary fresh and sharp fractures by
themselves do not indicate glaciation (Molén, 2014).
Glaciers simultaneously both irregularly fracture
and irregularly abrade rock material (i.e., not even-
ly/regularly spread on rocks or grain surfaces but
more or less in separate patches), so in glaciogen-
ic sediments evidence from both these processes
is present. There is often overprinting of fractured
and abraded surface microstructures on glaciogenic
grains, i.e., recurrent fracturing and irregular abra-
sion on the same grain surface. Therefore there are
unique combinations of surface microtextures that
have been generated by glaciers, i.e., fresh fractures
that have probably at the same time become irreg-
ularly abraded during short, intense contacts with
hard clasts or bedrock (Molén, 2014). In less ener-
getic environments, e.g., transport by wind or wa-
ter, regular small scale abrasion/comminution will
spread over the complete grain surface, and such
abrasion will round off the grain surfaces regularly
because of the continual and slight abrasion/com-
minution, and also, at the same time, will induce
physical and/or chemical weathering. Subglacially,
grains are not abraded constantly, but when abra-
sion takes place it is commonly strong and in more
conned areas. This has been documented in Pleis-
tocene and more recent deposits and is clearly test-
ed (Mahaney, 2002, Molén, 2014; Kalińska-Nartiša
et al., 2017, Passchier et al., 2021; Kut et al., 2021;
Kalińska et al., 2021).
SEM studies conducted on samples from
pre-Pleistocene diamictites indicate a non-glacial
origin of Neoproterozoic outcrops in northern Nor-
way (Molén, 2017), Upper Ordovician outcrops in
South Africa (Rowe & Backeberg, 2011) and in the
Czech Republic (Štorch, 1990), and in Upper Pal-
aeozoic deposits from the Dwyka Group in South
Africa (Molén & Smit, 2022). From the evidence
displayed by macroscopic geological features, there
is no denitive evidence of glaciation displayed by
these outcrops (Rowe & Backeberg, 2011; Molén,
2017; Molén & Smit, 2022) (however, the outcrops in
the Czech Republic have previously only been mac-
roscopically studied and considered to be of glaci-
omarine origin; Štorch, 1990). Typical examples of
quartz sand grains from these areas are here shown
in Figure 8 and are compared to examples of Pleis-
Fig. 9. Typical surface microtextures on quartz sand grains from Pleistocene glacial environments; compare these to
grain surfaces in Figure 8. All these grains display a combination of multiple fractures, irregular (strong) abrasion
both on many fractures and on non-fractured parts of the grains. The upper three pictures are from an area of
granitic and gneissic bedrock, Västerbotten County, Sweden. The lower three pictures are from an area displaying
mainly Phanerozoic sedimentary bedrock in southern Ontario, Canada. The small areas of weathered parts of the
grains from southern Ontario are original quartz sand grain surface microtextures from the non-glacial Phanerozoic
sedimentary bedrock, and are similar to the grain surfaces in Figure 8. More examples of glaciogenic grain surface
microtextures were published in Mahaney (2002), Molén (2014, 2017, 2023a) and Molén & Smit (2022).
154 Mats O. Molén
tocene glaciogenic quartz grains from Scandinavia
and Canada in Figure 9 (Molén, 2014). The evidence
is clear cut, where the glaciogenic grains display a
combination of multiple fractures, irregular abra-
sion is present both on parts of the fractures and on
non-fractured parts of the grains. The grains from
(nonglacial) diamictites display a combination of
more or less spherical grains, and they are regularly
abraded all over the grain surfaces combined with
weathered surfaces. They display a few fractures
that are either sharp or otherwise regularly abraded
all over the fracture faces. In view of the fact that we
assume that natural laws have not changed, and the
process of inducing surface microtextures of (recur-
rent) fracturing and (irregular) abrasion is strictly
mechanical (purely chemical processes change the
surfaces in different ways and articial coatings can
be easily traced; Somelar et al., 2018; Molén & Smit,
2022), these features positively indicate that the de-
posits are non-glacial.
16. Discussion
Studies of diamictites have often been based on
models and have adhered to older interpretations
as a starting point (e.g., Le Heron et al., 2022b). This
is reasonable, but progress in sedimentology and
other research disciplines which may be relevant
for studies of ancient glaciations and diamictites,
during the c. 50 last years, have shown that many
former interpretations need to be abandoned (e.g.,
see: Rodrigues et al., 2020; Kennedy & Eyles, 2021;
Molén, 2023a). Proxies for ancient climates based
on geochemistry, including carbon and oxygen iso-
topes, chemical weathering index (CIA), ikaites/
glendonites and cap carbonates, are not set in stone
either, but may be more clearly connected to envi-
ronment than to climate (Vickers et al., 2023; Molén,
2024).
If a certain area formerly has been interpreted
to have been glaciated, then the appearance of geo-
logical features of that area may have been used as
evidence of glaciation also in other areas, instead of
searching for eld evidence for possible alternative
interpretations. The geological features most easily
evaluated which are interpreted to be glaciogenic,
are as follows:
1. Striated surfaces, where papers may describe
these as glaciogenic even though the appearanc-
es are different from both Quaternary subglacial
and iceberg-produced striations and pavements.
These pre-Pleistocene surfaces are often planar,
displaying straight and invariably striations and
grooves (e.g., Fig. 3), displaying appearances not
observed to have been produced by glaciers in
the Quaternary, but commonly by SGFs (Table
1). These pavements are often soft sediment sur-
faces (Le Heron et al., 2020).
2. Outsized clasts interpreted to be dropstones,
where the patterns of deposition and sedimen-
tary structures are seldom recognised or even
reported in detail or in great numbers, e.g., the
often small size of these clasts (one or a few cen-
timetres), or if large size the appearance and
position may indicate SGFs, for example, in the
Cryogenian deposits of Namibia (Domack &
Hoffman, 2011; Hoffman et al., 2021; Le Heron
et al., 2021a).
3. Small size and number of erratics in diamic-
tites, compared to erratics present in parts of
the outcrops interpreted by most researchers
to be from SGFs, and compared to Quaternary
glaciations.
4. Surface microtextures where researchers have
to abandon or not refer to documented differenc-
es (e.g., Mahaney, 2002, Molén, 2014) to interpret
the data in a glaciogenic framework. Soreghan et
al. (2022, p. 3) wrote that, „More recent work has
argued that only large-scale fractures that cov-
er at least one-quarter of the grain surface can
be considered glaciogenic, as smaller scale frac-
tures can be produced in a wide variety of en-
vironments (Molen, 2014).” Those authors had
to abandon the documentation in the quoted
paper, of the unimportance of simple fracturing,
and the mandatory presence of combined abra-
sion and fracturing, as is described in the con-
clusion as, “A glacigenic grain typically exhibits
largescale fractures (F1) and irregular abrasion
(A1)” (Molén, 2014, 2023b). Similarly, Le Her-
on et al. (2020) studied grain surfaces on small
grains displaying minute surface microtextures
which did not show irregularly abraded glacio-
genic fractures.
Therefore, if the interpretation of an outcrop
is wrong, then other areas studied with the same
mindset may also have been misinterpreted. In-
stead, it is always more appropriate to start from
recent observations and experiments and compare
the outcrops with recent and Pleistocene geologi-
cal features so as to arrive at a correct interpreta-
tion. Otherwise it may be as Moncrieff & Hambrey
(1990) suggested, that an ancient outcrop (in this
case Neoproterozoic) “... does not have a suitable
modern analogue” (p. 389) and “... can aid interpre-
tation of modern sediments ...” (p. 408), instead of
the opposite.
Patterns, processes and models – an analytical review of current ambiguous interpretations of the evidence for... 155
17. Conclusions
It has been shown that many similarly appearing
geological features may form in different environ-
ments. There are considerable differences in the ap-
pearance of the details of these features, which after
documentation may indicate a different origin than
if a study starts with a formerly accepted interpreta-
tion. Often details which are necessary to document
if the study is going to discriminate if an outcrop has
been generated by SGFs or glaciation are not con-
sidered, let alone documented, in cases where there
is a consensus interpretation of a deposit, or where
the researchers have already developed an interpre-
tative framework. This is a hindrance to progress
in the area of diamictites, mainly in the documen-
tations of glaciogenic and SGF features. Therefore,
it may be necessary to restudy many outcrops and
start with multiple working hypotheses rather than
with a paradigm, model or formerly long-held in-
terpretation, e.g., not, “Our interpretation builds on
a rich tradition that envisage a glacial origin ...” and
“Even diamictites known to have been deposited
during a major ice age may paradoxically contain
little to no evidence for direct glacial processes” (Le
Heron et al., 2022b, pp. 1, 8).
As has been shown earlier, evidence from pat-
terns displayed by appearance, size and sorting
of erratics, striated surfaces/pavements, outsized
clasts/dropstones and surface microtextures, is
easily documented and evaluated if an area/out-
crop/formation is glaciogenic or not (see Table 3).
For more extensive documentation of the geological
features mentioned here, and also of other geologi-
cal features which discriminate between glaciation
and other processes, reference is made to the dis-
cussion, tables and Appendix in Molén (2023a).
Table 3. Diamict Origin Table of geological features formed in environments of glaciation, mass wasting and tectonics.
Columns display how common a feature may be, and whether it is glaciogenic or non-glaciogenic. Tabulated fea-
tures in the upper part of the table differ substantially between glaciogenic and non-glaciogenic deposits, and the
more provisionally documented features are in the lower part. Even though the absolute differences are not known
between different processes, relative values have been provided. In the column for glaciogenic processes, structures
that form by non-glaciogenic processes in a glacial environment are not included, e.g., not debris ows in a glacial
environment. However, if clasts in debris ow deposits are glacially striated, this may be evidence of glaciation. By
contrast, debris ow deposits with no other evidence of a glacial environment than clasts displaying striations that
may form in debris ows, is not helpful in interpreting a former glaciation.
Feature Origin
Glacial Non–glacial
Areally continuous 2 1
Areally dispersed 1 2
Large areal extent 2 1
Warm climate sediments 0–1 2
Warm climate fossils 0–1 2
Fine grained and matrix supported 2 1–2
Clast diameter/bed thickness correlation 0–1 2
Sorting and/or grading 0–1 2
Streaks of different deposits/diamictites 1 2
Entrenched contorted slabs of unconsolidated soft sediments 1 2
Fabrics
strong 2 1
weak 1 2
bimodal 2 1
planar 1 2
variable in sections 1 2
Erratics 2 2
low-inclination transport, slopes close to 0.001° 2 1–(2)
> 1–3 m diameter 2 1–(2)
smaller in “tillites” than in accepted concomitant SGF deposits 0 2
jigsaw fractures – 1
Striated clasts 1–2 1–2
subparallel striations 2 1
parallel striations 1 2
156 Mats O. Molén
Feature Origin
Glacial Non–glacial
curved and/or random striations 1 2
crossing striations 2 1
soft, angular, not striated co-occurring with hard, rounded, striated 1 2
Faceted and/or polished clasts 1–2 1–(2)
Pavement/striations/grooves 2 1
subparallel striations 2 1
parallel striations 1 2
crossing striations 2 1
polished striations 2 1
soft-sediment pavements 0–1 2
sediment pressed down – 2
pressed-up ridges – 2
stacked pavements 0–1 1–2
irregular horizontally and vertically 2 1–2
regular striations 0–1 1–2
continue over extensive areas 2 1
interlaminated sediments/traction carpet – 1
ripples, laminae – 1
brecciation 1 1
overhanging walls 0–1 1
rock polish chemical (?) 1
Iceberg keel scour marks and mimics 2 0–1
abundant where present 2 –
changing directions 2 0–1
superposed/stacked in same direction – 1
parallel striations/grooves 1 2
undulous in cross-section 2 0–1
evidence of tides, wind and waves 2 0–1
grounding pits 2 (?)
glacier grounding-zone wedges 2 0–1
Boulder pavements 2 1–2
Roches moutonnés/plucking 2 (0–1)
uneven surfaces 0–1 1
Fjords, overdeepened, regular, ridged outlet 2 (0–1)
Eskers (or otherwise not eskers) 2 (0–1)
sorted deposits 2 1
large clasts on top 2 (?)
Glaciouvial restricted by ice, kames 2 –
Dropstones/lonestones 2 2
random fabric 2 1
weak fabric 1 2
varied size of clasts 2 1
small grain size 1 2
obvious small size compared to other sediments which are interpreted to be glaciogenic – 2
correlation: clast size and sediment thickness – 2
larger clasts in thicker sediments 1 2
sorted 0–1 1–2
differently compressed laminae 1 2
no/little penetration 1 2
1/3 of clasts penetrate 2 1
sediment thickness changes around clast 1 2
lee side structures/movement/wake eddies 1 2
Patterns, processes and models – an analytical review of current ambiguous interpretations of the evidence for... 157
Acknowledgements
Thanks are due to a large number of geologists who
have provided critical and enhancing comments
from their specialities to the research presented
here; the present work has benetted greatly from
their assistance. The manuscript was considerably
improved by comments from two anonymous re-
viewers. The sample from the Kosov Fomation in
the Czech Republic was provided by Peter Štorch.
There is no conict of interest.
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Manuscript submitted: 28 October 2023
Revision accepted: 1 December 2023