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Palaeoenvironmental reconstruction of Neoproterozoic successions has been the subject of long-standing debate, particularly concerning the interpretation of diamictites. The Wilsonbreen Formation of north-east Svalbard is a 130 to 180 m thick diamictite-dominated glacigenic succession deposited during a late Cryogenian (Marinoan) glaciation. Previous research has highlighted a complex sedimentary architecture with evidence of subaqueous, subglacial and non-glacial conditions. This study combines well-established sedimentological techniques with the first sedimentological application of the anisotropy of magnetic susceptibility technique in Neoproterozoic glacial sediments, to investigate the origin and palaeoenvironmental significance of glacigenic sediments within the Wilsonbreen Formation. A range of lithofacies occurs within the succession, dominated by massive diamictites, sandstones and conglomerates. Some of these facies display evidence of primary deformation and can be grouped into a Deformed Facies Association; these are interpreted to have been formed through glacitectonic deformation in a subglacial environment. Fabric investigation reveals that this deformation was associated with glacier flow towards the north. In addition, an Undeformed Facies Association records deposition in ice-proximal and ice-distal subaqueous environments. Taken together with intervening non-glacial facies, the glacigenic sediments record a series of advance-retreat cycles, with ice flow involving sliding and sediment shearing below wet-based ice.
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Glacitectonism, subglacial and glacilacustrine processes during
a Neoproterozoic panglaciation, north-east Svalbard
EDWARD J. FLEMING*
,1
,DOUGLASI.BENN†‡, CARL T. E. STEVENSON*,
MICHAEL S. PETRONIS§, MICHAEL J. HAMBREYand IAN J. FAIRCHILD*
*School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham,
B15 2TT, UK (E-mail: edward.fleming@casp.cam.ac.uk)
Department of Geology, The University Centre in Svalbard (UNIS), P.O. Box 156, Longyearbyen, Norway
Department of Geography and Sustainable Development, University of St Andrews, St Andrews, KY16
9AL, UK
§Natural Resource Management, New Mexico Highlands University, Las Vegas, NM, 87701, USA
Centre for Glaciology, Department of Geography and Earth Sciences, Aberystwyth University,
Aberystwyth, Ceredigion, SY23 3DB, UK
Associate Editor – Dan Le Heron
ABSTRACT
Palaeoenvironmental reconstruction of Neoproterozoic successions has been
the subject of long-standing debate, particularly concerning the interpretation
of diamictites. The Wilsonbreen Formation of north-east Svalbard is a 130 to
180 m thick diamictite-dominated glacigenic succession deposited during a
late Cryogenian (Marinoan) glaciation. Previous research has highlighted a
complex sedimentary architecture with evidence of subaqueous, subglacial
and non-glacial conditions. This study combines well-established sedimento-
logical techniques with the first sedimentological application of the aniso-
tropy of magnetic susceptibility technique in Neoproterozoic glacial
sediments, to investigate the origin and palaeoenvironmental significance of
glacigenic sediments within the Wilsonbreen Formation. A range of lithofa-
cies occurs within the succession, dominated by massive diamictites, sand-
stones and conglomerates. Some of these facies display evidence of primary
deformation and can be grouped into a Deformed Facies Association; these are
interpreted to have been formed through glacitectonic deformation in a sub-
glacial environment. Fabric investigation reveals that this deformation was
associated with glacier flow towards the north. In addition, an Undeformed
Facies Association records deposition in ice-proximal and ice-distal subaque-
ous environments. Taken together with intervening non-glacial facies, the gla-
cigenic sediments record a series of advanceretreat cycles, with ice flow
involving sliding and sediment shearing below wet-based ice.
Keywords Anisotropy of magnetic susceptibility, Cryogenian, glacitecton-
ism, Snowball Earth, subglacial.
INTRODUCTION
The aim of this paper is to evaluate the evolu-
tion of one of the best-preserved Cryogenian gla-
cigenic successions in the Northern Hemisphere,
and in particular the newly recognized role
played by glacitectonism. This then allows the
authors to throw light on inferred ‘Snowball
1
Present address: CASP, University of Cambridge, 181a Huntingdon Road, Cambridge CB3 0DH, UK
411©2015 The Authors. Sedimentology ©2015 International Association of Sedimentologists
Sedimentology (2016) 63, 411–442 doi: 10.1111/sed.12251
Earth’ conditions, with which these strata have
long been associated. In a companion paper,
Fairchild et al. (2015) investigate the carbonates
that are intimately associated with these glaci-
genic deposits. Together, this research provides
new insights concerning the role of the Snow-
ball Earth theory in explaining geological evolu-
tion at the end of the Cryogenian Period.
The Wilsonbreen Formation of north-east
Svalbard is composed of up to 180 m of excep-
tionally well-preserved glacigenic sediments,
deposited during the second of two Neoprotero-
zoic panglaciations, where ice sheets existed on
all continents at all latitudes (Hoffman, 2009).
This period of glaciation is now equated with
the Marinoan glaciation of South Australia, and
the panglaciation of the same name (Halverson
et al., 2004). Previous interpretations of these
Marinoan deposits have suggested an interplay
of glacial processes representing both subaque-
ous and subglacial environments (Fairchild &
Hambrey, 1984, 1995). In the present study, the
origin and significance of these deposits is
investigated in detail. Processes of sediment
transport, deposition and deformation were
determined using a combination of facies analy-
sis, structural geology, clast shape and macrofab-
ric analysis, and the anisotropy of magnetic
susceptibility (AMS) technique.
Massive diamictites, such as those that domi-
nate the Wilsonbreen Formation, are inherently
difficult to interpret (Eyles & Januszczak, 2004).
This is, in part, because similar properties can
develop in various depositional environments,
including glacial (glacimarine, glacilacustrine,
subglacial and proglacial) and non-glacial (Dow-
deswell et al., 1985) settings. Research on the Wil-
sonbreen Formation to date has provided a broad
depositional interpretation (e.g. Hambrey et al.,
1981; Fairchild & Hambrey, 1984); however,
uncertainty exists over the precise glacideposi-
tional regimes that occurred and their association
with Neoproterozoic climatic conditions.
Since the previous research on the Wilsonbreen
was undertaken, there have been significant
advances in the understanding of the processes
leading to the deposition of till (Benn & Evans,
2010, and references therein). There is now a
greater knowledge of sediment assemblages asso-
ciated with different depositional environments
(e.g. Evans, 2005), which enables reliable
palaeoenvironmental interpretations to be made
with reference to the modern sedimentary record.
Glacigenic deformation structures (for exam-
ple, glacitectonites) are now also better under-
stood than in the early 1980s (Benn & Evans,
1996; van der Wateren, 2002; Aber & Ber, 2007).
Glacitectonic structures are common in both
modern and Quaternary sediments and have
also been observed in many pre-Quaternary sed-
iments (e.g. Le Heron et al., 2005; Benn & Prave,
2006; Busfield & Le Heron, 2014). Analysis of
these structures can provide important informa-
tion about genetic environments and deforma-
tional histories.
New techniques have also been developed for
understanding glacial sediments. Of these, AMS
analysis has been applied to tills by several
authors (e.g. Fuller, 1962; Stupavsky & Grave-
nor, 1975; Eyles et al., 1987) and it has been
shown that, in conjunction with other petro-
fabric techniques, AMS can provide invaluable
information on the formation and subsequent
deformation of glacial sediments, particularly
where visible structures are lacking. In recent
years, the technique has been applied to a vari-
ety of topics in glacial geology, such as in the
determination of palaeoflow from subglacial sed-
iments (Shumway & Iverson, 2009; Thomason &
Iverson, 2009; Gentoso et al., 2012), investiga-
tions of glacitectonism (Fleming et al., 2013b)
and deformation within debris-rich basal ice
(Fleming et al., 2013a).
Utilizing current understanding of deposi-
tional environments, combined with the novel
application of the AMS technique, it is possible
to extract detailed information from the glacial
facies of the Wilsonbreen Formation. The objec-
tives of this study are to: (i) describe the glacial
lithofacies observed within the succession in
terms of their facies associations; (ii) determine
the origin of the soft-sediment deformation fea-
tures (glacitectonic or slumping); and finally (iii)
use a combination of clast fabric analysis and the
application of AMS to identify strain signatures
and preferred orientations within the sediment
to determine ice flow and sediment transport
directions. The present paper focuses on well-
exposed sections at Reinsryggen, Andromedafjel-
let, Dracoisen and Ditlovtoppen (Fig. 1). An
overview of the Wilsonbreen Formation and an
assessment of its significance for the Snowball
Earth theory are provided by Benn et al. (2015).
GEOLOGICAL BACKGROUND
The Polarisbreen Group (Fig. 2) is a Neoprotero-
zoic mixed siliciclastic–carbonate unit and
forms part of the Hecla Hoek tectono-sedimen-
©2015 The Authors. Sedimentology ©2015 International Association of Sedimentologists, Sedimentology,63, 411–442
412 E. J. Fleming et al.
tary sequence of north-east Svalbard (Fig. 1), a
7 km thick succession of Neoproterozoic to
Ordovician sedimentary strata and metamorphic
rocks exposed along a Caledonian fold belt. The
Svalbard archipelago (Fig. 1) consists of three
tectonic terranes juxtaposed during the Caledo-
nian Orogeny (Harland, 1971; Harland et al.,
1992; Lyberis & Manby, 1993). The relatively
undeformed Hecla Hoek succession is exposed
on the northern part of the Eastern Terrane. The
section has been correlated with the southern
north-east Greenland Caledonides, suggesting an
origin on the Laurentian margin (Fairchild &
Hambrey, 1995). Sedimentation of the Hecla
Hoek succession was probably related to the
breakup of Rodinia (Halverson et al., 2004).
After the initial deposition of the siliciclastic
Veteranen Group, a broad carbonate platform
developed in a slowly subsiding basin opening
towards the south (Halverson et al., 2004). Fol-
lowing this, renewed subsidence has been sug-
gested to have followed, based on basin-
deepening in Northeast Greenland and the depo-
sition of the mostly siliciclastic Polarisbreen
Group of which the Wilsonbreen Formation
forms part.
The Polarisbreen Group (Fig. 2) is divided
into three formations (Elbobreen, Wilsonbreen
and Dracoisen), conformably overlying the
Akademikerbreen Group and underlying the
Cambrian Tokammane Formation (Harland
et al., 1993). Two major glacigenic units have
been described; an older, Petrovbreen Member
(E2) of the Elbobreen Formation and the younger
Wilsonbreen Formation (Fairchild & Hambrey,
1984). These units are closely correlated with
diamictite pairs in Northeast Greenland (Kul-
ling, 1934; Knoll et al., 1986; Fairchild & Ham-
brey, 1995) and are very similar to other
diamictite pairs in the North Atlantic region,
although geochronological evidence is com-
monly lacking which precludes accurate correla-
tion (Hambrey, 1983). The Wilsonbreen
Formation is the younger and thicker glacial
interval within the Polarisbreen Group, consist-
ing of 130 to 180 m of a grey to maroon, massive
Non-carbonate shallow lake
Elbobreen Formation
Dracoisen Formation
Wilsonbreen Formation
km
m
Poorly exposed
Fully
exposed
Marine carbonate
Glacitectonite
Fluvial (Carbonate) Lacustrine and Fluvial Subglacial: till
Proximal Glaciolacustrine Distal Glaciolacustrine Periglaciated horizon
Fig. 1. Stratigraphic summary of facies within the Wilsonbreen Formation of north-east Svalbard with a location
map of the study area showing the main exposures of the Wilsonbreen Formation. Red box denotes the area of
focus in this study. DRA, Dracoisen; DIT, Ditlovtoppen; AND, Andromedafjellet; REIN, Reinsryggen; KLO, Klofjel-
let; McD, MacDonaldryggen; BAC, Backlundtoppen; PIN, Pinnsvinfjellet; ORM, Ormen; SLA, Slangen.
©2015 The Authors. Sedimentology ©2015 International Association of Sedimentologists, Sedimentology,63, 411–442
Glacitectonism in a Neoproterozoic panglaciation 413
to weakly bedded diamictite-dominated unit
overlying the Slangen Member in the south and
the Br
avika Member in the north (which thins
and becomes absent in the south) and underly-
ing the Dracoisen Formation (Halverson et al.,
2004).
The Wilsonbreen Formation was key in the
development of the early ideas about wide-
spread glaciation in the Neoproterozoic (Kulling,
1934; Harland, 1964; Harland & Rudwick, 1964;
Hambrey, 1992) and throughout the latter part of
the 20th Century, the glacigenic rocks of the
Polarisbreen Group were subject to various sedi-
mentological studies (e.g. Chumakov, 1968;
Hambrey et al., 1981; Hambrey, 1982; Fairchild,
1983; Fairchild & Hambrey, 1984; Fairchild
et al., 1989; Harland et al., 1993). After the
strong advocation of Snowball Earth theory
(Hoffman et al., 1998), geochemical and strati-
graphic analyses of Halverson et al. (2004) were
used to argue that the glacigenic sediments of
the Polarisbreen Group were deposited within a
single global glaciation. However, Halverson
et al. (2007) and Hoffman et al. (2012) subse-
quently revisited the succession and reinter-
preted it as representing two Snowball Earth
panglaciations.
The Wilsonbreen Formation is subdivided
into the Ormen (W1), Middle Carbonate (W2)
and Gropbreen (W3) members (Hambrey, 1982).
The W1 Member consists mostly of poorly strati-
fied diamictite, but also includes lenses and
interbeds of sandstone, conglomerate and brec-
cia. The Middle Carbonate Member is marked
by the presence of precipitated carbonates,
interbedded with clastic fluvial and lacustrine
facies and diamictite. The W3 Member is litho-
logically similar to W1 and consists of massive
to weakly stratified diamictite with interbedded
sandstones. The overall depositional setting was
a large, closed lacustrine basin that underwent
repeated cycles of desiccation and flooding
(Benn et al., 2015). Detailed descriptions and
interpretations of the carbonate and associated
facies in the W2 Member (Fig. 1) are provided
by Fairchild et al. (2015).
METHODS
Sections through the Wilsonbreen Formation
were examined and logged at Dracoisen, Ditlov-
toppen, Andromedafjellet and Reinsryggen in
north-east Svalbard (Figs 1 and 2) during the
summer 2010 and 2011 field seasons. Sections
were analysed following the lithofacies
approach, originally developed for fluvial sedi-
ments by Miall (1977), adapted for glacial sedi-
ments by Eyles et al. (1983) and subsequently
modified for the present study where necessary.
Diamictites were classified using the scheme
developed by Moncrieff (1989) and modified by
Hambrey (1994), based on the relative propor-
tions of gravel, sand and mud (silt and clay). In
this scheme, diamictites are defined as rocks
that contain 1 to 50% gravel with a matrix com-
prising greater than 10% of sand, mud or both
sand and mud.
In many places, diamictites of the Wilson-
breen Formation are friable, allowing included
clasts to be removed intact from the surrounding
matrix; this permitted measurements of both
clast morphology and orientation, using meth-
ods developed for unlithified sediments. Clast
morphology (shape, roundness and surface tex-
ture) was measured for samples of 50 clasts
taken from diamictites of the W1, W2 and W3
Fig. 2. Summary of the Cryogenian stratigraphy of
north-east Svalbard with the stratigraphic interval of
focus in this paper shown in red (Wilson & Harland,
1964; Hambrey, 1982; Fairchild & Hambrey, 1984;
Fairchild et al., 1989). Complete logs of the Wilson-
breen Formation in all sections are shown in the sup-
plementary information.
©2015 The Authors. Sedimentology ©2015 International Association of Sedimentologists, Sedimentology,63, 411–442
414 E. J. Fleming et al.
to weakly bedded diamictite-dominated unit
overlying the Slangen Member in the south and
the Br
avika Member in the north (which thins
and becomes absent in the south) and underly-
ing the Dracoisen Formation (Halverson et al.,
2004).
The Wilsonbreen Formation was key in the
development of the early ideas about wide-
spread glaciation in the Neoproterozoic (Kulling,
1934; Harland, 1964; Harland & Rudwick, 1964;
Hambrey, 1992) and throughout the latter part of
the 20th Century, the glacigenic rocks of the
Polarisbreen Group were subject to various sedi-
mentological studies (e.g. Chumakov, 1968;
Hambrey et al., 1981; Hambrey, 1982; Fairchild,
1983; Fairchild & Hambrey, 1984; Fairchild
et al., 1989; Harland et al., 1993). After the
strong advocation of Snowball Earth theory
(Hoffman et al., 1998), geochemical and strati-
graphic analyses of Halverson et al. (2004) were
used to argue that the glacigenic sediments of
the Polarisbreen Group were deposited within a
single global glaciation. However, Halverson
et al. (2007) and Hoffman et al. (2012) subse-
quently revisited the succession and reinter-
preted it as representing two Snowball Earth
panglaciations.
The Wilsonbreen Formation is subdivided
into the Ormen (W1), Middle Carbonate (W2)
and Gropbreen (W3) members (Hambrey, 1982).
The W1 Member consists mostly of poorly strati-
fied diamictite, but also includes lenses and
interbeds of sandstone, conglomerate and brec-
cia. The Middle Carbonate Member is marked
by the presence of precipitated carbonates,
interbedded with clastic fluvial and lacustrine
facies and diamictite. The W3 Member is litho-
logically similar to W1 and consists of massive
to weakly stratified diamictite with interbedded
sandstones. The overall depositional setting was
a large, closed lacustrine basin that underwent
repeated cycles of desiccation and flooding
(Benn et al., 2015). Detailed descriptions and
interpretations of the carbonate and associated
facies in the W2 Member (Fig. 1) are provided
by Fairchild et al. (2015).
METHODS
Sections through the Wilsonbreen Formation
were examined and logged at Dracoisen, Ditlov-
toppen, Andromedafjellet and Reinsryggen in
north-east Svalbard (Figs 1 and 2) during the
summer 2010 and 2011 field seasons. Sections
were analysed following the lithofacies
approach, originally developed for fluvial sedi-
ments by Miall (1977), adapted for glacial sedi-
ments by Eyles et al. (1983) and subsequently
modified for the present study where necessary.
Diamictites were classified using the scheme
developed by Moncrieff (1989) and modified by
Hambrey (1994), based on the relative propor-
tions of gravel, sand and mud (silt and clay). In
this scheme, diamictites are defined as rocks
that contain 1 to 50% gravel with a matrix com-
prising greater than 10% of sand, mud or both
sand and mud.
In many places, diamictites of the Wilson-
breen Formation are friable, allowing included
clasts to be removed intact from the surrounding
matrix; this permitted measurements of both
clast morphology and orientation, using meth-
ods developed for unlithified sediments. Clast
morphology (shape, roundness and surface tex-
ture) was measured for samples of 50 clasts
taken from diamictites of the W1, W2 and W3
Fig. 2. Summary of the Cryogenian stratigraphy of
north-east Svalbard with the stratigraphic interval of
focus in this paper shown in red (Wilson & Harland,
1964; Hambrey, 1982; Fairchild & Hambrey, 1984;
Fairchild et al., 1989). Complete logs of the Wilson-
breen Formation in all sections are shown in the sup-
plementary information.
©2015 The Authors. Sedimentology ©2015 International Association of Sedimentologists, Sedimentology,63, 411–442
414 E. J. Fleming et al.
AB C D
2015)
Fig. 3. Detailed sedimentary logs with lithofacies interpretation of the W1W2W3 Member transition for: (A) Reinsryggen; (B) Andromedafjellet; (C) Dit-
lovtoppen; and (D) Dracoisen. Height refers to stratigraphic distance from the base of the formation.
©2015 The Authors. Sedimentology ©2015 International Association of Sedimentologists, Sedimentology,63, 411–442
416 E. J. Fleming et al.
the AMS data are not directly comparable to
clast fabric data, because they are a function of
both mineral magnetic properties and grain ori-
entation. The AMS fabrics of the Wilsonbreen
Formation typically reflect the preferential align-
ment of paramagnetic phyllosilicate clay miner-
als, with a minor contribution of multidomain
titanomagnetite and fine-grained maghaemite in
some cases (Fleming, 2014). A minor anomalous
single domain ferromagnetic source was identi-
fied in some samples and these were omitted
from subsequent analysis.
FACIES DESCRIPTIONS
Diamictite makes up over 80% of the Wilson-
breen Formation (Fig. 3). For the purposes of
description, the diamictites and associated sedi-
ments are subdivided into Undeformed and
Deformed Facies Associations.
Undeformed Facies Association
The Undeformed Facies Association occurs at
all the studied outcrops, but is generally thicker
in sections to the north. It can be subdivided
into (A-1) diamictite facies and (A-2) sandstone
and conglomerate facies (summarized in
Table 1).
Diamictite facies (A-1)
The Undeformed diamictite (Dm and Ds) is typi-
cally greenish-grey or maroon, clast-poor, with a
poorly sorted sandy matrix (Fig. 4A, B and D).
Clasts make up between 3% and 10% of the
facies, although clast-rich and sand-poor vari-
eties occur and all proportions up to gravel may
be present. The majority of clasts are intrabasi-
nal (60 to 80%) and can be matched with under-
lying strata, particularly the Elbobreen and
Backlundtoppen Formations (dolostone, lime-
stone, chert, breccia and siltstone; Fairchild &
Hambrey, 1984). The remainder are extrabasinal
and some have an unknown source area. Of
these, coarse-grained pink granite is most com-
mon, but other granite as well as basalt, banded
gneiss, quartzite and amphibolite also occur.
Clast size spans a wide range and boulders
>80 cm are observed locally.
The sand fraction is composed predominantly
of subangular quartz with minor dolostone, mica
and other lithic fragments. Opaque minerals are
common and are mostly composed of pyrite,
hematite or magnetite; they often form separate,
subangular to rounded grains which suggest a
Table 1. Summary of the lithofacies that make up the Undeformed Facies Association of W3.
Facies association Description
Lithofacies
codes* Interpretation
Diamictite and
conglomerates (A-1)
Massive and stratified diamictites,
consisting of poorly sorted, subangu-
lar to subrounded, intrabasinal and
extrabasinal clasts in a fine-grained
sandy matrix, sometimes with a
well-pronounced hematite staining.
Intercalated with lenses of conglo-
merate, sometimes displaying channel
geometries
Dm
Ds
Gm
Gs
Sm
Ss
Subaqueous deposition from
either: (i) rainout from a high con-
centration of debris-rich icebergs;
or (ii) from sediment-laden efflux
jets close to the grounding line
of a glacier or ice sheet. Conglo-
merate facies represent erosional
lags or mass flow deposits. In
places (e.g. at Dracoisen), the sed-
iment architecture suggests depo-
sition as a grounding-line fan
Lenticular and
tabular sandstones (A-2)
Pale yellow to greenish-grey, mode-
rate to well-sorted sandstones, con-
sisting of quartz with minor feldspar
and lithic fragments. Bed thickness
is normally 01to40 m thick and
can display either channel-like and
lenticular or tabular geometries. Rare
cross-bedding and ripple lamination
Sm
Ss
Dm
Ds
Gm
Gs
Proximal subaqueous deposition
through the release of debris from
subglacial conduits at the ground-
ing-line fan, which can progress
into subaqueous channels in a
more distal location. Tabular
sandstones are interpreted as
deposition as a subaqueous out-
wash fan
*Bold denotes Domiant lithofacies. Italics denotes Associated lithofacies.
©2015 The Authors. Sedimentology ©2015 International Association of Sedimentologists, Sedimentology,63, 411–442
Glacitectonism in a Neoproterozoic panglaciation 417
AB C D
2015)
Fig. 3. Detailed sedimentary logs with lithofacies interpretation of the W1W2W3 Member transition for: (A) Reinsryggen; (B) Andromedafjellet; (C) Dit-
lovtoppen; and (D) Dracoisen. Height refers to stratigraphic distance from the base of the formation.
©2015 The Authors. Sedimentology ©2015 International Association of Sedimentologists, Sedimentology,63, 411–442
416 E. J. Fleming et al.
detrital origin. This is presumably derived from
the weathering and erosion of the igneous and
metamorphic lithologies; however, secondary
growth of hematite and pyrite is seen in places.
The silt fraction grades into a dolomicrite matrix
with varying proportions of quartz and clay min-
A
III
VI
C
DI
III
VII VIII
IV V
BIII
©2015 The Authors. Sedimentology ©2015 International Association of Sedimentologists, Sedimentology,63, 411–442
Glacitectonism in a Neoproterozoic panglaciation 419
erals. This is commonly obscured by a well-
developed hematite staining, particularly pro-
nounced in maroon diamictites.
Bedding is poorly developed and can usually
only be seen where diamictites are interbedded
with associated facies (for example, conglome-
rates and sandstones). Where it is seen, bed
thickness ranges from 2 to 5 m. ‘Wispy’ stratifi-
cation is seen in some cases (for example,
Fig. 4A), which is normally defined by changes
in the sand content of the diamictite matrix and
is sometimes associated with colour change or
mottling.
Clast-shape data are shown on ternary shape
diagrams and roundness histograms in Fig. 5A
and B. Relatively low C
40
indices are seen indi-
cating large proportions of ‘blocky’ as opposed
to platy or elongate clasts. In all sites, most of
the clasts are subangular to subrounded, and
very angular and well-rounded clasts are rare or
absent. Covariance plots of RWR-C
40
and RA-C
40
for the diamictites are shown in Fig. 5C,
together with data from modern control sites
(Fig. 5D; Hambrey & Glasser, 2012). Clast shape
is very similar to samples from modern sub-
glacial till, and differs from both passively and
fluvially transported clasts from modern envi-
ronments. A variety of surface textures occur on
the clasts. Striations are common on the fine-
grained lithologies, affecting up to 28% of the
clasts, and are orientated randomly or form sub-
parallel sets. Facets are common (affecting up to
50% of clasts). The textural data thus support
the conclusion that the clasts underwent sub-
glacial transport prior to deposition.
Sandstone and conglomerate facies (A-2)
Pale yellow to greenish-grey, moderately to well-
sorted sandstones (Sm and Ss) are commonly
interbedded with the diamictite, and form later-
ally continuous sheets or discontinuous lenses
(for example, Fig. 4C). Bed thickness varies
widely, from <10 cm to 1/2 m. In total, the sand-
stone facies make up 4 to 8% of the Wilson-
breen Formation (Fig. 3).
Grain size is mostly fine to medium sand but
is highly variable. Quartz is the predominant
grain lithology in the majority of cases (>95%),
defining a quartz arenite, with minor feldspar,
dolomite and other lithic fragments. Outsized
clasts are common and are composed of the
same lithologies as those contained in the sur-
rounding diamictites. Opaque minerals are
observed in thin section and are composed pre-
dominantly of subrounded grains of hematite
and magnetite with local development of authi-
genic pyrite. Both silica and carbonate cements
are observed, and quartz overgrowths are com-
mon at grain boundaries. A silty sand matrix
with varying proportions of dolomicrite, clay
minerals and quartz, sometimes obscured by
hematite cement, is also seen in places. The
proportion of this matrix relative to encompass-
ing grains varies considerably from being
almost absent up to near greywacke propor-
tions.
Bedding geometry typically is either channel-
like and lenticular (for example, Fig. 4C) or lat-
erally extensive and planar. The contacts with
overlying and underlying diamictites are
mostly sharp. The channel-like sandstone beds
display an erosive base that cuts into underly-
ing diamictites. Occasionally, rippled tops are
seen. Stratification is typically wavy and dis-
continuous where observed, but is chaotic in
places. In addition, both trough and planar
cross-stratification is developed locally, particu-
larly in the sandstone beds displaying channel
geometries.
Conglomerate interbeds (Gm and Gs) are also
commonly associated with the diamictites (for
example, Fig. 4E); these form either isolated
lenses or continuous sheets up to 50 cm thick.
The interbeds can be laterally extensive and
remain fairly uniform in thicknesses, or they
can be discontinuous and lenticular in form.
Some show subtle reverse grading, whilst
others have a sharp undulating base with evi-
dence of erosion and channel forms. Normal
grading into overlying massive diamictites is
seen locally. The clast fraction (50 to 90%) is
composed of similar lithologies to the diamic-
tites. Grains are angular to rounded (predomi-
nantly subrounded), and sorting is poor to
medium. The matrix is typically a medium to
poorly sorted, fine to coarse sand, and is com-
posed predominantly of angular quartz grains,
sometimes surrounded by a muddy dolomi-
crite.
At both Dracoisen and Ditlovtoppen, there are
high concentrations of sandstone and conglo-
merate beds in parts of the W3 Member (Fig. 3C
and D). These are interbedded with diamictite
beds and form tapering wedge-shaped structures
apparently thinning to the north and dipping
10°more steeply than the regional bedding
(Fig. 6). The sandstone and conglomerate beds
in these areas are commonly affected by convo-
lute bedding and slump structures, indicating
local syn-depositional deformation.
©2015 The Authors. Sedimentology ©2015 International Association of Sedimentologists, Sedimentology,63, 411–442
420 E. J. Fleming et al.
AB
CD
E
Fig. 4. Field photographs of the typical sediments associated with subaqueous facies associations of the W3
Member. (A) Clast-poor muddy diamictite horizon from Reinsryggen, displaying wispy undulating sand-rich lami-
nation. (B) Massive maroon, clast-poor intermediate diamictite from Dracoisen showing a patch of clast-rich
diamicton. (C) Channelized sandstone grey sandstone body cut into massive diamictite from Reinsryggen. (D) Mas-
sive friable, maroon, clast-rich sandy diamictite from Dracoisen. (E) Lenticular conglomerate (mass flow deposit)
within massive diamictites forming part of the grounding-line fan at Dracoisen.
Fig. 5. Clast morphological data. (A) Visual representation of triangular diagrams showing blocky, platy and elon-
gate end members (after Benn & Ballantyne, 1993). (B) Data for clast shape (triangular diagrams) and roundness
(histograms) from massive diamictites from the Wilsonbreen Formation. (C) Covariance plots for all data from the
Wilsonbreen Formation and (D) Modern control sites for comparison (after Hambrey & Glasser, 2012) showing
variation in RA versus C
40
-index from polythermal glaciers in Svalbard (Midre Lov
enbreen, Austre Lov
enbreen
and Austre Brøggerbreen).
©2015 The Authors. Sedimentology ©2015 International Association of Sedimentologists, Sedimentology,63, 411–442
418 E. J. Fleming et al.
The deformed zone can be traced 200 m later-
ally along strike. Deformed rhythmites are also
seen at Andromedafjellet in a 1 m thick zone
located beneath massive maroon diamictites of
the W3 Member. The rhythmites are composed
of 2 to 10 mm silt/sandcarbonate couplets with
a slightly greater sand fraction than those at Dit-
lovtoppen.
It is important to assess whether the deforma-
tion structures are primary, related to deposition
mechanisms (for example, glaciotectonism or
slumping), and not the result of subsequent tec-
tonic overprinting. A tectonic origin for the
deformation structures can be ruled out for sev-
eral reasons. The deformation is localized and
does not cross-cut formation boundaries. It
occurs within distinct horizons where, based on
sedimentary structures, a relationship with
depositional processes can be demonstrated.
Furthermore, the deformation is not dependent
on lithology but varies stratigraphically through
the section. For example, both deformed and
undeformed rhythmite varieties occur at differ-
ent stratigraphic levels. Finally, although the
rocks have been folded into a syncline during
the Caledonian Orogeny, pervasive tectonic
AB
CD
EF
©2015 The Authors. Sedimentology ©2015 International Association of Sedimentologists, Sedimentology,63, 411–442
422 E. J. Fleming et al.
Origin of sandstone and conglomerate lenses
within diamictites
Lenses of sand and gravel within massive
diamicton are a common feature of subglacial
traction tills (e.g. Hart & Roberts, 1994; Evans &
Campbell, 1995). A variety of mechanisms has
been proposed for their formation (see review in
Waller et al., 2011), including entrainment of
the sand through thrusting or folding from an
underlying layer (e.g. Hart & Boulton, 1991) and
the melt-out of sand from the overlying basal ice
(e.g. Hoffmann & Piotrowski, 2001). Alterna-
tively, sands and gravels may be produced sub-
glacially by the deposition of sorted sediments
flowing within subglacial channels at the ice
bed interface (Alley, 1991; Clark & Walder,
1994). Although being originally fluvial in ori-
gin, these deposits can be cannibalized and
deformed by the array of processes associated
with the formation of a subglacial traction till
(Hart, 1998; Evans et al., 2006; Benn & Evans,
2010), and they are subsequently incorporated
as deformed lenses in otherwise massive diamic-
ton.
Within the sandstone lenses of the Deformed
Facies Association, a mechanism through thrust-
ing of pre-existing sands is unlikely owing to
the lack of similar sands lower down in the
sequence. Furthermore, the identification of
channel-like geometries on some of the lenses
with deformed cross-bedding is consistent with
a glacifluvial origin. For example, the large
channelized sandstone body occurring immedi-
ately below the boulder pavement at Rein-
sryggen (Fig. 10A) has a geometry typical of a
subglacial channel. Therefore, the sandstone and
conglomerate lenses of the Deformed Facies
Association are interpreted as subglacial chan-
nels, some of which have been deformed and
incorporated into a subglacial traction till, while
others remain undeformed such that their depo-
sitional geometries are preserved.
Development of the boulder pavements
Striated Boulder pavements are considered diag-
nostic of subglacial environments (e.g. Boyce &
Eyles, 2000). A boulder pavement in a till suc-
cession consists of a thin, laterally extensive
layer of clasts, commonly with planar and some-
times striated upper surfaces. A number of dif-
ferent mechanisms have been proposed for their
formation. The most straightforward suggestion
is that they represent the former position of the
icebed interface, where the combined effects of
subglacial meltwater and glacier sliding progres-
sively remove fine-grained sediment from the
underlying till, leading to a concentration of lar-
ger clasts (Boyce & Eyles, 2000). However, Clark
(1991) and Boulton (1996) suggested that pave-
ments could also form within the deforming bed
itself, as a result of clasts sinking through soft
sediment or excavation at the base of the
deforming layer.
The boulder pavements at Ditlovtoppen and
Reinsryggen represent very prominent surfaces
that can be traced for several hundred metres
along strike; they possibly mark periods of dis-
tinctive subglacial conditions, when erosional
and deformational processes dominated over
depositional ones within the deforming bed
mosaic. Although the Ditlovtoppen and Rein-
sryggen pavements occur at a similar stratigraphic
level, it is not known whether they are precisely
synchronous, or represent diachronous shifting of
subglacial environments in different areas.
At both Ditlovtoppen and Reinsryggen, sand-
filled channels occur in association with the
boulder pavements, incised down into the under-
lying diamictite and with planar tops level with
the boulder pavement surfaces. These channel
structures are significant because they indicate
the presence of meltwater at the icebed inter-
face.
At Ditlovtoppen, striations on the upper sur-
face of clasts in the pavement are orientated to
130°; this is almost parallel to the V
1
eigenvector
from a clast fabric (136°) and the K
1
vector of an
AMS fabric (139°) from the underlying diamictite.
This indicates that the boulder pavement and the
underlying diamictite were formed while ice was
flowing in a consistent direction.
Boulder pavements are a distinctive feature in
subglacial sediments. Importantly for Neopro-
terozoic palaeoclimatic interpretations, the
occurrence of boulder pavements and associated
subglacial channel deposits clearly indicate a
warm-based thermal regime for at least part of
the depositional phase, with abundant water at
the icebed interface.
DISCUSSION
The present study has obtained the first results
from the application of anisotropy of magnetic
susceptibility (AMS) to Neoproterozoic diamic-
tites for sedimentological analysis. The use of
AMS in combination with facies analysis,
microstructural analysis and more traditional
clast fabric analysis has enabled the depositional
©2015 The Authors. Sedimentology ©2015 International Association of Sedimentologists, Sedimentology,63, 411–442
438 E. J. Fleming et al.
deformation is absent at the study sites and
there is no associated cleavage formation. The
folding pattern is not consistent with the Cale-
donian trend. Instead, the folds are either chao-
tic or show dominant vergence to the north.
Deformation occurred in both ductile and brit-
tle manners, the style of which appears, at least
in part, to be controlled by sediment composi-
tion and texture. The carbonate fraction displays
brittle deformation, whilst the silt–sand matrix
is deformed in a ductile manner (for example,
Fig. 8A and B). This appearance can be
explained by early cementation of the carbonate
horizon, prior to deformation and water satura-
tion of the silt–sand matrix; this is also consis-
tent with the occurrence of carbonate intraclasts
in undeformed sediments. The brittle faults typi-
cally form conjugate pairs or appear chaotic,
and they show no uniform pattern in shear in
any particular direction. However, high-angle
Table 2. Summary of the lithofacies that make up the Deformed Facies Association.
Facies
association Description
Lithofacies
codes* Interpretation
Deformed
rhythmites (B-1)
Intercalated siltsandcarbonate
rhythmites exhibiting both ductile
(recumbent folds) and brittle (nor-
mal and reverse offset faulting
and brecciation) deformation.
Exhibits an increase in intensity
of deformation towards the top.
Often overlain by massive diamic-
tite with intraclasts and lenses of
the underlying rhythmite
Fl(d)
Dm
Dm(d)
Fl
Quiescent subaqueous sedimenta-
tion during an ice retreat phase.
Overridden by grounded ice dur-
ing an ice advance phase and
glaciotectonized by an ice
advance to the north. The
increase in apparent deformation
reflects strain profile through the
sediment. Rhythmite lenses are
interpreted as rafts, dislocated
from underlying sediments and
emplaced within a subglacial till
Diamictites (B-2) Massive diamictite, occasionally
exhibiting deformed stratification
(Fig. 8B) showing strong, consis-
tent clast fabric and AMS fabrics.
Predominantly subrounded to
subangular clasts (low Ra-RWR;
Fig. 11). Often associated with
lenticular sandstone and conglom-
erate (below)
Dm
Dm(d)
Sm(d)
Ss(d)
Fl(d)
Fm(d)
Subglacial debris originating
through subglacial erosion and
transportation. When associated
with other subglacial facies, mas-
sive diamictites are interpreted as
subglacial tills deposited by
grounded ice. If associated with
glacio-aqueous facies it may also
form in subaqueous environment
Lenticular sandstones
and conglomerates (B-3)
Lens shaped sandstone and con-
glomerate bodies (<1 to 5 m thick)
occurring with massive diamic-
tite. Sometimes show internal
stratification with cross-stratifica-
tion and rare climbing ripples.
Commonly show visible disrup-
tion around margins such as fold-
ing and faulting. Surrounding
diamictite often envelops the lens
Gm(d), Gs(d)
Sm(d), Ss(d)
Fl(d)
Fm(d)
Dm
Dm(d)
Subglacial channel deposits dur-
ing ice-grounding. Deposits may
have initially eroded into under
lying sediments. Subsequently
deformed and sheared during as
part of the subglacial till mosaic
Boulder
pavements (B-4)
Prominent surfaces within other
wise massive diamictites contain-
ing a high proportion of large
(>10 cm diameter) clasts with
consistent striations (north-west/
south-east). Clasts commonly dis-
play stoss and lee forms, often
with a faceted upper surface.
Strong, consistent AMS and clast
fabrics
Gm
Dm
Dm(d)
Formed through subglacial depo-
sition and erosion by either: (i) a
period of erosion at the icebed
interface and faceting and realign-
ment of clasts because of the over-
riding ice; or (ii) decoupling
within the bed at a d
ecollement
surface, within sediment
*Bold denotes Domiant lithofacies. Italics denotes Associated lithofacies.
©2015 The Authors. Sedimentology ©2015 International Association of Sedimentologists, Sedimentology,63, 411–442
424 E. J. Fleming et al.
A
C
D
B
Fig. 8. Microstructural analysis of deformed rhythmites. (A) Recumbent fold structure in faulted rhythmites, Dit-
lovtoppen. (B) Recumbent fold within deformed rhythmite at Ditlovtoppen showing brittle deformation and brec-
ciation of carbonate horizons and ductile flow of sandsilt horizons, with sand-filled veins interpreted as
hydrofractures cutting brecciated carbonate horizons. (C) Conjugate faulting in deformed rhythmites from
Andromedafjellet. (D) Intense deformation from rhythmites at the boundary with overlying diamictite from
Andromedafjellet displaying augen-like silty sand lens cut by low-angle shear zones.
©2015 The Authors. Sedimentology ©2015 International Association of Sedimentologists, Sedimentology,63, 411–442
Glacitectonism in a Neoproterozoic panglaciation 425
normal faults and low-angle reverse faults are
identified in places. These display possible Rie-
del shear geometries (Riedel, 1929) that may
highlight simple shearing. In addition, the pres-
ence of sand veins in between the faulted car-
bonate laminae suggests that the sand fraction
C
A
B
Fig. 9. Interpretative sketches of macroscopic deformational structures at the W2/W3 Member transition. (A)
Deformed rhythmite showing conjugate, brittle faulting becoming progressively brecciated and disrupted towards
the top, overlain by a deformed dolostone raft with internal faulting and brecciation that passes into a subglacial
diamictite. (B) South-verging thrust-fault with pop-up structures within a mottled silt/sandcarbonate rhythmite.
(C) Extensive brittle and ductile deformation of rhythmites dominated by north-dipping, low-angle normal faults.
©2015 The Authors. Sedimentology ©2015 International Association of Sedimentologists, Sedimentology,63, 411–442
426 E. J. Fleming et al.
A B
C
D
Fig. 10. Interpretative sketch and photographs of the Deformed Facies Association at Andromedafjellet. (A) Field photograph and subsequent interpretative
sketch displaying a boulder pavement overlying a subglacial diamictite (B-2) with lenticular sands and channel structures (B-3). Also shown are the AMS
and fabric data obtained from the exposure (See Fig. 13 for Key), corrected for the tectonic dip. (B) Faceted granite clast at the top of a clast-poor boulder
pavement (B-4), overlain by massive maroon diamictite. (C) Conjugate faulting and folding of wispy lamination surrounding a sandstone lens (B-3). (D)
Sandstone lens with displaying disrupted, overturned cross-stratification (B-3).
©2015 The Authors. Sedimentology ©2015 International Association of Sedimentologists, Sedimentology,63, 411–442
Glacitectonism in a Neoproterozoic panglaciation 427
ABC
Fig. 11. Clast A axis orientation plotted on to equal-area stereonets from (A) Dracoisen, (B) Ditlovtoppen and (C)
Andromedafjellet (See Table 3 for data). All plots are corrected for tectonic dip. Facies codes in brackets where
A-1 =Undeformed Facies Association, B-2 =Deformed Facies Association and U =Unknown.
©2015 The Authors. Sedimentology ©2015 International Association of Sedimentologists, Sedimentology,63, 411–442
428 E. J. Fleming et al.
was subject to liquefaction and remobilization
during folding.
There is typically an increase in the intensity
of deformation up-section, and the deformed
rhythmites pass upward into massive diamic-
tites (B-2). At the base of the deformed rhyth-
mites, deformation is typically small-scale and
is characterized by the occurrence of conjugate
faults, showing both low-angle and high-angle
reverse offset. Some display possible Riedel
shear geometries (for example, Fig. 8C). The off-
set along faults is typically low (up to several
centimetres). In addition, small-scale thrust-
faults and augen-like structures are seen. The
offset along conjugate brittle faults and thrusts
increases upward in the section towards the
boundary with the diamictite. Larger scale
recumbent folds are seen on the 02to10m
scale (Fig. 7F, I and K). Smaller scale parasitic
folding is sometimes seen on fold limbs. Fold
vergence is typically to the north, although pre-
cise measurement is often not possible because
of a lack of three-dimensional exposure. Larger
scale thrusts are also observed showing dis-
placement of 50 cm or more (Fig. 7G and J),
with dips towards the south.
The boundary with the overlying diamictites
is typically transitional. At the top of the
deformed rhythmites, north-verging, low-angle
reverse faults are observed (Fig. 7G and J), some
showing displacement over 1 m. At Ditlovtop-
pen (Fig. 9A), dolostone rafts occur at the
boundary between the diamictites and the rhyth-
mites, showing internal folding and faulting and
brecciation. In places, overlying diamictites
envelop 05to20 m lenses of deformed rhyth-
mite (Fig. 7E).
Evidence of intense folding and faulting in the
deformed rhythmite facies is also seen micro-
scopically (Fig. 8), with both brittle and ductile
deformation. As is the case at the macroscopic
scale, deformation style is determined in part by
composition. Rhythmite couplets composed of
carbonate display brittle deformation, often
breaking into fragments separated by faults
(Fig. 8A and B). In contrast, the silt–sand com-
ponent of the rhythmite behaved in a ductile
manner as it is commonly folded and fills in the
space between the carbonate layers. This effect
is clearly seen in Fig. 8B where the rhythmite
displays a close monocline structure. At a large
scale, the bed appears to be folded; however,
microscopic analysis reveals that the folding is
partially facilitated through faulting. Brittle
deformation has occurred within the carbonate
lamellae which produces tabular fragments,
whereas the silt–sand fraction has undergone
predominantly ductile deformation.
Faulting within the deformed rhythmites
appears chaotic in places (for example, Fig. 8A)
and the analysis of fault kinematics is challeng-
ing. However, high-angle reverse faults and low-
angle normal faults (Fig. 8D) dipping to the
south are common; these are interpreted as P
and R
2
Riedel shear geometries, associated with
shear to the north. Low-angle thrusts are also
present, typically dipping to the south (Fig. 8A).
In places at the boundaries between faulted car-
bonate laminae, a network of sand-filled veins
can be observed microscopically (for example,
Fig. 8B). Sand within these veins has the same
composition as the silt–sand component of the
rhythmite couplet, but typically contains less of
the silt fraction. An increase in the amount of
folding and faulting is seen up to the boundary
with the overlying diamictite. Figure 8D shows
a highly deformed rhythmite taken from close to
this boundary at Andromedafjellet. Sand within
the rhythmites displays an augen-like geometry
with asymmetrical tails suggesting shear to the
north. On either side of this augen structure, a
low-angle shear zone dipping to the north sepa-
rates the augen from the surrounding sandy lam-
ination.
Diamictite facies (B-2)
Massive diamictite (Dm) is widespread in the
Deformed Facies Association, occurring immedi-
ately above and below the W2 Member at Rein-
sryggen, Andromedafjellet and Ditlovtoppen
(Fig. 3). Similar facies are also seen higher in
the succession at these sites. The Diamictite is
similar both compositionally and texturally to
that seen in the Undeformed Facies Association.
It consists of a poorly sorted mixture of clasts
(both intrabasinal and extrabasinal) in a matrix
dominated by fine–medium quartz sand, with
minor amounts of lithic particles. It has subtle
textures and fabric characteristics not seen in
the Undeformed Facies Association, but the key
difference is the presence of deformed lenses
and rafts of underlying units, and the close rela-
tionship with other deformed facies. For exam-
ple, at Reinsryggen (Fig. 10) diamictites beneath
a boulder pavement contain deformed lenses of
sandstone and conglomerate bodies (for exam-
ple, Fig. 10C and D). The surrounding diamictite
displays a weak fabric that appears to envelop
the lens structure. Wispy lamination is some-
times observed immediately surrounding the
©2015 The Authors. Sedimentology ©2015 International Association of Sedimentologists, Sedimentology,63, 411–442
Glacitectonism in a Neoproterozoic panglaciation 429
Table 3. Data table of clast fabrics analysed using the eigenvalue method (Mark, 1973) where the data is resolved into three mutually orthogonal eigenvec-
tors (V
1
,V
2
and V
3
).
Fabric Latitude/longitude Lithology No Location Unit FA
Bed-
ding
Eigenvectors Eigenvalues
S
1
S
2
S
3
S
1
S
2
S
3
IE
F9 79.20549/18.4023 Diamictite 50 Dracoisen W1 A-1 343 51 184 4 86 61 276 29 0527 04161 00582 011044 021044
F10 79.2055/18.4025 Diamictite 50 Dracoisen W1 U 343 51 168 22 60 38 281 44 06537 02849 00614 009393 056417
F13 79.21481/18.3997 Diamictite 50 Dracoisen W2 A-1 342 50 343 1 75 55 363 46 04676 03144 0218 046621 032763
F14 79.20561/18.4047 Diamictite 50 Dracoisen W2 A-1 326 40 174 16 82 8 328 72 05393 03656 0095 017615 032208
F15 79.20479/18.4111 Diamictite 50 Dracoisen W1 A-1 338 40 151 19 37 48 155 35 05885 03496 00619 010518 040595
F17 79.20561/18.4047 Diamictite 50 Dracoisen W2 A-1 320 65 144 40 17 35 264 30 04956 03337 01707 034443 032667
F1 79.083677/18.41481 Diamictite 50 Ditlovtoppen W3 A-1 003 30 320 0 230 13 51 77 05221 03589 01189 022773 031258
F4 79.0794574/18.39083 Diamictite 50 Ditlovtoppen W1 A-1 26 32 44 10 139 26 296 62 04684 04188 01128 024082 010589
F5 79.08309/18.4135 Diamictite 50 Ditlovtoppen W3 B-2 003 30 162 23 65 17 302 61 06081 02988 00931 01531 050863
F6 79.08236/18.4111 Diamictite 50 Ditlovtoppen W3 B-2 003 30 184 14 81 42 289 45 06053 03256 00691 011416 046208
F7 79.08019/18.403 Diamictite 50 Ditlovtoppen W3 B-2 004 42 136 30 39 13 289 57 06976 02658 00366 005247 061898
F3 79.0832/18.4129 Diamictite 50 Ditlovtoppen W3 B-2 020 32 200 6 292 10 81 79 06584 0252 00897 013624 061725
F2 79.0832/18.4129 Diamictite 50 Ditlovtoppen W3 B-2 003 30 178 5 84 32 276 57 07026 02179 00795 011315 068987
F22 78.9386/18.440 Diamictite 50 Andromedafjellet W1 A-1 247 48 150 17 258 46 45 39 05717 02388 01895 033147 05823
F21 78.9383/18.433 Diamictite 50 Andromedafjellet W3 B-2 253 40 192 10 285 13 67 74 04809 03801 0139 028904 020961
The shape and strength of the fabric is represented by the Eigenvalues S
1
,S
2
and S
3
. FA = facies association where A = Undeformed Facies Association,
B = Deformed Facies Association and U = Unknown. Bold denotes Domiant lithofacies.
©2015 The Authors. Sedimentology ©2015 International Association of Sedimentologists, Sedimentology,63, 411–442
430 E. J. Fleming et al.
lenses, showing evidence of small-scale folding
and faulting (Fig. 10C). The sandstone lenses
themselves are massive or stratified. Where pre-
sent, the stratification is commonly undulating
and folded, and faulting is common, especially
at the margins of the lenses.
Clast-matrix ratios and composition are vari-
able, but both ratios and the proportion of extra-
basinal clasts are typically higher than in the
undeformed diamictite lithofacies. At Ditlovtop-
pen, for example, a granite-rich horizon occurs
in diamictites at the base of the W3 Member
with a clast-matrix ratio above 40%. The clasts
consist predominantly of granule to pebble-
sized, subangular to subrounded red granite.
Immediately overlying deformed rhythmites of
the W2 Member at the same section, diamictites
contain subangular fragments of rhythmite and
carbonate. Diamictites of the Deformed Facies
Association commonly display a fissile weather-
ing pattern and are almost exclusively maroon,
although mottling occurs locally (for example,
Fig. 7C and D); in other cases, the diamictites
are massive.
Clast-shape data for the diamicties of the
Deformed Facies Association are shown in
Fig. 5. The data resemble those for the diamic-
tites of the Undeformed Facies Association. The
majority of the clasts are subangular to sub-
rounded and very angular and well-rounded
clasts are rare or absent. Comparison with con-
trol data indicates that the debris has undergone
subglacial transport, a conclusion consistent
with the abundance of striated and faceted
clasts, particularly on the carbonate lithologies.
Sandstone and conglomerate facies (B-3)
Occurring within the diamictites are lenses of
maroon and pale yellow-grey sandstone (Sm and
Ss) and conglomerate bodies (Gs and Gm;
Fig. 3). Lenses typically have a planar upper
surface and concave-up lower surface, and are
generally less than 2 m in lateral extent, but are
locally up to 25 m wide (Fig. 10). The sandstone
is predominantly medium-grained, but is locally
much finer. In addition, conglomerates occur
locally, either as isolated lenses or as dispersed
clasts within sandstone lenses. Sandstones are
typically poorly sorted and are dominated by
subangular to subrounded grains of quartz, lithic
fragments and opaque minerals in a fine-grained
matrix of varying proportions (5 to 20%).
A
III
B
III III
Fig. 12. Fabric shape diagram showing a continuum between isotropic, girdle and cluster fabrics, in which the
eigenvalues (V
1
,V
2
and V
3
) are depicted as the axes of ellipsoids, the lengths of which are proportional to S
1
,S
2
and S
3
. (A) Clast fabric data from undeformed diamictites (I) and deformed diamictites (II). (B) AMS fabric data,
calculated using the eigenvalues of the K
1
axes from (I) undeformed diamictites, (II) deformed diamictites and (III)
glacitectonite. See Tables 3, 4 and 5 for the data.
©2015 The Authors. Sedimentology ©2015 International Association of Sedimentologists, Sedimentology,63, 411–442
Glacitectonism in a Neoproterozoic panglaciation 431
Table 4. Mean site anisotropy of magnetic susceptibility (AMS) data.
Site
Latitude/
longitude Lithology FA Location Unit Bedding Dip No
Km
(SI) K
1
K
1
95%
Error K
2
K
2
95%
Error K
3
K
3
95%
Error LFP
j
T
DC2 79.2055/18.4020 Diamictite A Dracoisen W1 343 51 18 336 350 31 32 11 122 48 32 20 243 25 21 12 1003 1005 1008 0273
DC5 79.2057/18.4056 Carbonate A Dracoisen W2 341 51 6 123 194 6 51 9 106 16 51 17 308 73 21 13 1001 1002 1003 0090
DC57 79.2153/18.3980 Diamictite A Dracoisen W3 334 43 10 272 132 28 27 7 27 26 27 15 261 50 16 7 1004 1006 1010 0251
DC6 79.2056/18.4073 Rhythmites A Dracoisen W2 341 51 11 188 131 38 62 17 20 25 62 23 266 43 27 15 1002 1024 1026 0844
DC61 79.2153/18.3979 Diamictite A Dracoisen W2 341 51 17 198 151 22 16 7 50 25 22 16 277 55 23 5 1004 1008 1013 0299
DC62 79.2153/18.3979 Diamictite A Dracoisen W3 341 51 10 216 355 4 24 13 86 17 26 15 254 73 22 9 1004 1009 1014 0448
DC63 79.2153/18.3982 Diamictite A Dracoisen W3 341 51 18 260 9 25 25 6 133 40 24 7 254 32 7 6 1002 1011 1015 0657
DC65 79.2151/18.4003 Diamictite A Dracoisen W3 330 46 18 50 23 47 41 15 114 2 45 35 206 43 40 17 1003 1002 1005 0096
DC7 79.2058/18.4082 Carbonate A Dracoisen W3 341 51 11 239 123 2 64 9 33 3 64 14 239 87 20 8 1002 1009 1012 0663
DF25 79.0816/18.4104 Diamictite A Ditlovtoppen W3 004 42 15 357 133 50 62 10 3 29 62 15 258 26 17 11 1001 1021 1025 0900
DF26 79.0815/18.4103 Diamictite A Ditlovtoppen W3 001 30 9 368 176 17 30 9 75 34 30 10 288 51 10 9 1004 1015 1021 0557
DF29 79.0809/18.4079 Rhythmites B1 Ditlovtoppen W2 003 30 15 197 146 20 39 3 46 26 39 5 269 56 11 3 1002 1029 1035 0881
DF30 79.0809/18.4079 Rhythmites B1 Ditlovtoppen W2 003 30 13 147 174 10 8 2 78 28 9 3 282 60 5 2 1004 1036 1045 0799
DF31 79.0807/18.4077 Diamictite B Ditlovtoppen W3 002 39 16 395 139 38 37 8 31 21 38 15 279 45 17 7 1004 1012 1016 0536
DF32 79.0807/18.4077 Diamictite B Ditlovtoppen W3 002 39 11 446 98 44 57 16 189 1 57 16 280 46 17 16 1003 1009 1013 0477
DFB2A 79.0819/18.4093 Diamictite B Ditlovtoppen W1 004 42 7 186 159 34 15 2 29 43 15 12 269 28 12 2 1004 1008 1012 0396
DFB4D 79.0833/18.4129 Rhythmites B1 Ditlovtoppen W3 004 42 12 435 351 14 16 7 92 40 25 7 256 47 25 10 1007 1005 1011 0152
DFB4F 79.0833/18.4129 Rhythmites B Ditlovtoppen W3 004 42 8 579 186 11 44 7 86 39 44 9 289 49 12 7 1004 1023 1029 0676
EFA121 78.9528/18.4257 Sandstone B1 Andromedafjellet
East
W2 253 40 12 171 263 42 16 4 160 14 16 7 55 45 7 5 1005 1003 1008 0273
EFA128 78.9528/18.4257 Diamictite B Andromedafjellet
East
W3 251 40 7 409 154 24 16 3 259 30 15 2 32 50 4 2 1005 1020 1027 0578
EFA146 78.9528/18.4257 Diamictite B Andromedafjellet
East
W3 251 40 11 561 190 22 12 6 296 34 13 6 74 48 9 5 1008 1010 1018 0108
EFA10 78.9383/18.4281 Sandstone A Reinsryggen W3 256 40 9 496 322 18 14 4 222 27 16 6 82 57 10 5 1006 1011 1018 0261
EFA103 78.9383/18.4325 Diamictite A Reinsryggen W3 256 40 12 533 298 12 12 5 31 13 16 12 165 74 16 4 1013 1017 1031 0116
EFA92 78.9383/18.4325 Diamictite B Reinsryggen W3 253 40 11 227 190 17 7 5 287 20 7 5 64 63 6 4 1007 1008 1015 0087
No =number of samples; Km =mean susceptibility; K
1
,K
2
,K
3
=orientations (trend and plunge) of the principal susceptibility axes with 95% confidence
ellipses; L=lineation (L=K
1
/K
2
); F=foliation (F=K
2
/K
3
); P
j
=corrected degree of anisotropy; T=shape parameter; Fabric =whether the fabric can be
classified as ‘normal’ (K
3
perpendicular, K
1
/K
2
parallel to the bedding plane), ‘inverse’ (K
1
perpendicular and K
2
/K
3
parallel to the bedding plane) or
anomalous (K
1
/K
2
deviation by >25°from bedding). FA =facies association where A =Undeformed Facies Association, B =Deformed Facies Association
and B1 =glaciotectonite.
©2015 The Authors. Sedimentology ©2015 International Association of Sedimentologists, Sedimentology,63, 411–442
432 E. J. Fleming et al.
ABC
Fig. 13. Anisotropy of magnetic susceptibility (AMS) orientation data showing the maximum (K
1
), intermediate
(K
2
) and minimum (K
3
) axes of the susceptibility ellipsoid from all subsamples, plotted onto equal area, lower hemi-
sphere stereonets from (A) Dracoisen, (B) Ditlovtoppen and (C) Andromedafjellet. See Tables 4 and 5 for the data.
©2015 The Authors. Sedimentology ©2015 International Association of Sedimentologists, Sedimentology,63, 411–442
Glacitectonism in a Neoproterozoic panglaciation 433
Contacts with surrounding diamictites are typ-
ically sharp, although a 5 cm thick reduced zone
is seen occasionally within the maroon diamic-
tite that envelops the lenses. The sandstone and
conglomerate is either massive or displays sub-
tle stratification (Fig. 10C), and is commonly
folded and faulted. Some lenses appear less
deformed and display subtle cross-lamination
with rare climbing ripples (Fig. 10D). At Rein-
sryggen, small (2 to 4 m wide) deformed sand-
stone lenses are overlain by a large 10 m wide
sandstone body (Fig. 10); this has a distinctive
erosive base and a truncated top at the boundary
with a nascent boulder pavement (Fig. 10A).
Boulder pavements (B-4)
Boulder pavements occur at two localities
within the Wilsonbreen Formation. At Ditlov-
toppen (Fig. 3C), a distinct boulder pavement,
previously described by Chumakov (1968) and
Fairchild & Hambrey (1984), is seen 2 m above
the contact with deformed rhythmites of the W2
Member. It is composed of a boulder conglome-
rate with clast a-axes predominantly 10 to
20 cm, but up to 50 cm. Clast lithologies are
mostly dolostone, but other intrabasinal and
extrabasinal lithologies are present. The clasts
sit in maroon sandy matrix that is composed of
fine-grained, subangular quartz and lithics in a
silty sand matrix. Clasts at the top surface of the
pavement show a flat, planed-off top, on which
unidirectional striations trend at 130°. Overlying
the boulder pavement is a massive, maroon
diamictite of the Deformed Facies Association
(B-2). Twenty-five metres along strike, the boul-
der pavement changes to a granite-rich horizon
with clast concentrations of over 30%.
A second boulder pavement occurs at Rein-
sryggen (Fig. 10), occurring 30 m above the con-
tact with the W2 Member. In contrast to the
boulder pavement at Ditlovtoppen, the clasts are
matrix-supported and concentrations are dis-
Table 5. Anisotropy of magnetic susceptibility (AMS) orientation data analysed using the eigenvalue method
(Mark, 1973) where the K
1
data are resolved into three mutually orthogonal eigenvectors (V
1
,V
2
and V
3
). The
shape and strength of the fabric is represented by the eigenvalues S
1
,S
2
and S
3
.
Site No Location FA S
1
S
2
S
3
IE
DC2 18 Dracoisen A 07722 01725 00553 0071614 0776612
DC5 6 Dracoisen A 07069 02647 00284 0040175 0625548
DC57 10 Dracoisen A 08899 0095 00151 0016968 0893246
DC6 11 Dracoisen A 0761 0219 00201 0026413 0712221
DC61 17 Dracoisen A 08574 01084 00343 0040005 0873571
DC62 10 Dracoisen A 08176 01325 00499 0061032 083794
DC63 18 Dracoisen A 08137 01754 00109 0013396 0784441
DC65 18 Dracoisen A 07226 02155 00619 0085663 0701771
DC7 11 Dracoisen A 0523 04114 00656 012543 0213384
DF25 15 Ditlovtoppen A 06198 03147 00655 0105679 0492256
DF26 9 Ditlovtoppen A 07047 02764 00188 0026678 0607776
DF29 15 Ditlovtoppen B1 06218 03702 0008 0012866 0404632
DF30 13 Ditlovtoppen B1 09705 00284 00011 0001133 0970737
DF31 16 Ditlovtoppen B 05898 03232 0087 0147508 0452018
DF32 11 Ditlovtoppen B 06054 03706 0024 0039643 0387843
DFB2A 7 Ditlovtoppen B 09422 00562 00015 0001592 0940352
DFB4D 12 Ditlovtoppen B1 09226 00686 00089 0009647 0925645
DFB4F 8 Ditlovtoppen B 06529 03289 00181 0027722 0496248
EFA121 12 Andromedafjellet East B1 09548 004 00052 0005446 0958106
EFA128 7 Andromedafjellet East B 09101 00877 00022 0002417 0903637
EFA146 11 Andromedafjellet East B 09522 00379 00099 0010397 0960197
EFA10 9 Reinsryggen A 09407 00533 0006 0006378 094334
EFA103 12 Reinsryggen A 08997 00943 00059 0006558 0895187
EFA92 11 Reinsryggen B 09802 00145 00053 0005407 0985207
FA =facies association where A =Undeformed Facies Association, B =Deformed Facies Association and
B1 =glaciotectonite.
©2015 The Authors. Sedimentology ©2015 International Association of Sedimentologists, Sedimentology,63, 411–442
434 E. J. Fleming et al.
tinctly lower (10%). The clasts are enclosed
within a maroon sandy diamictite with a silty
sand matrix. Forty metres along strike to the
north, the boulder pavement lies at the top of a
30 m wide channelized maroon sandstone body
composed of poorly sorted, fine-grained suban-
gular quartz grains. Clasts have a faceted top
surface (Fig. 10B), but striations were not
observed at this locality.
Clast and anisotropy of magnetic
susceptibility (AMS) fabrics
Clast fabric data (Table 3) are shown on lower
hemisphere, equal-area stereographic projections
(Fig. 11) and fabric shape triangles (Fig. 12).
Nine of the samples are from diamictite of the
Undeformed Facies Association at Dracoisen
(A-1), Ditlovtoppen and Andromedafjellet, and
six from diamictite of the Deformed Facies (B-2)
at Ditlovtoppen (5) and Andromedafjellet (1).
Four of the Ditlovtoppen Deformed facies sam-
ples are from the near the base of W3, and the
fifth from near its top. Fabrics from the two
diamictite facies have contrasting characteristics,
plotting in almost distinct fields on shape trian-
gles (Fig. 12A). Fabrics from the Undeformed
diamictites (A-1) (Fig. 12A-i) are mostly girdles
with insignificant to weak preferred orientations,
whereas those from the Deformed diamictites
(B-2) (Fig. 12A-ii) are moderate to strong clus-
ters. The latter are similar to fabrics from mod-
ern subglacial traction tills (e.g. Benn, 1994,
1995), consistent with orientation of clasts by
simple shear (Benn, 1995). Preferred orientations
(V
1
) of the deformed facies samples lie in the
range 136°to 184°(Table 3). Although the fab-
rics from the undeformed facies (A-1) are much
weaker, their preferred orientations span a simi-
lar range (144°to 192°) with two outliers. It
should be noted that vector azimuths are relative
to modern True North, and do not take into
account any net rotation of the Svalbard land-
mass since the Neoproterozoic.
Samples for AMS analysis were taken from
sandstone and diamictite of the Undeformed
Facies Association (A-1), and diamictites and
deformed rhythmites of the Deformed Facies
B-1
B-2
B-3
B-4
SUMMARY OF THE DEFORMATIONAL FACIES ASSOCIATIONS
Rafts of
deformed
rhythmite with
massive
diamictite
Undeformed rhythmite
Deformed
cross-
lamination
Enveloping
diamictite
fabric around
lens
Weak boulder
pavement e.g.
Reingryggen
Striated boulder
pavement e.g.
Ditlovtoppen
Massive diamictite
Subglacial channel with cross-
stratification
MIDDLE CARBONATE MEMBER (W2)
W3
Increasing intensity of
deformation
5 metres
Fig. 14. Summary diagram showing the Deformational Facies Association referred to in Table 2: (B-1) glacitec-
tonized rhythmites, (B-2) subglacial diamictite with rhythmite rafts, (B-3) subglacial diamictite with deformed
lenses of sandstone and conglomerate (subglacial channel deposits) and (B-4) a striated boulder pavement.
©2015 The Authors. Sedimentology ©2015 International Association of Sedimentologists, Sedimentology,63, 411–442
Glacitectonism in a Neoproterozoic panglaciation 435
Association (B-2). Sandy diamictite was prefe-
rentially targeted because sampling of the
muddy diamictites of the Undeformed Facies
Association was problematic due to their fri-
able nature. In most samples, the AMS is con-
trolled by preferential alignment of
paramagnetic phyllosilicate clay minerals
(Fleming et al., 2013a,b).
The AMS results are shown in Table 4 and
are plotted on to stereonets in Fig. 13. The
distribution of the K
1
vector (Table 5) is anal-
ysed through shape triangles in Fig. 12. The
magnetic anisotropy is typically low, mean
values of the corrected degree of anisotropy P
j
were close to one and showed no variation
with depositional facies. These results follow
the experimental results of Hooyer et al.
(2008), where no correlation between shear
strain and the degree of anisotropy was
observed. In these experiments, however, dis-
tinct correlation was found in the alignment
of K
1
orientations with increasing shear
strains, measured through the S
1
eigenvalues.
Similarly in this study, distinct variation can
be seen in the alignment of the K
1
axes with
depositional facies, visualized through the
shape triangles (Fig. 12B). In these plots, there
is an almost complete distinction between the
fabric shape of samples from the Undeformed
Facies Association (A-1) (Fig. 12B-i) and
Deformed Facies Associations (B-2) (Fig. 12B-
ii and B-iii). The samples from the Unde-
formed Facies Association (A-1) are moder-
atelytostronglyelongate(E=038 to 089),
with the azimuth of the K
1
axes spanning a
very broad range. In contrast, five of the six
samples from diamictites of the Deformed
Facies Association (B-2), and three of the four
samples from the deformed rhythmites (B-1)
are very strongly elongate (E=090 to 098).
The K
1
axis azimuths of the deformed facies
diamictite samples lie in the range 154°to
190°, similar to the V
1
orientations of the
clast fabrics. Two of the K
1
axis azimuths for
the deformed rhythmites are similar, and a
third lies at 180°to the main trend.
Variation in azimuth of the mean K
1
axes is
seen within the stratigraphic section at some
sites (Fig. 13). For example, at Ditlovtop-
pen there is a possible switch in fabric orien-
tation up-section. The AMS fabrics at the base
of the W3 Member typically lie in a north
south orientation, whilst higher in the
sequence a shift is seen to predominantly
north-west/south-east orientated K
1
azimuths.
In spite of this local variation, the dominant
fabric trend lies in a north–south orientation at
all sections.
LITHOFACIES INTERPRETATION
Undeformed Facies Association
Diamictite
The presence of subtle stratification, the close
association with facies typical of subaqueous
deposition and a lack of associated subglacial
facies (for example, boulder pavements and
glacitectonic deformation) suggest that deposi-
tion of the diamictites of the Undeformed Facies
Association occurred mainly in a subaqueous
glacial environment. The occurrence of faceted
and striated clasts indicates that, prior to depo-
sition, the debris underwent subglacial transport
below warm-based ice (e.g. Boulton, 1978).
In subaqueous environments, thick structure-
less diamictites can form by release of sediment
from a high concentration of debris-rich icebergs
(e.g. Dowdeswell et al., 1994; Syvitski et al.,
1996), close to a grounding line. The subtle
stratification can be interpreted as the product
of minor subaqueous current reworking and sub-
sequent removal of fines during rainout deposi-
tion of diamictite from floating ice.
The girdle clast fabrics from the diamictites
are consistent with a dropstone origin (Dowdes-
well et al., 1985). Weak preferred orientations
can develop in response to bottom currents or
reorientation by mass flow. The preferred orien-
tations (V
1
) of these samples suggest persistent
bottom currents or mass flow along a north–
south axis.
Sandstone and conglomerate facies
Channelized sandstones (Fig. 4C) are a com-
mon feature of glacially influenced subaqueous
environments (e.g. Le Heron et al., 2014) and
are particularly associated with the influx of
sorted sands from subglacial channels emerg-
ing at the grounding line (Powell, 1990). The
conglomerate facies is interpreted as either
mass flow deposits or erosional lags. Lags can
form in subaqueous environments during peri-
ods of non-deposition or at times of increased
bottom water flow. In these situations, finer
material is removed by bottom water currents
(e.g. Powell, 1984). Conglomerates displaying
reverse grading and sharp contacts with overly-
ing diamictites are interpreted as lags. In con-
©2015 The Authors. Sedimentology ©2015 International Association of Sedimentologists, Sedimentology,63, 411–442
436 E. J. Fleming et al.
trast, those that have lenticular or channel-like
geometries and display normal grading are
interpreted as mass flows. These are common
in both glacimarine and glacilacustrine envi-
ronments where deposition occurs on a slope
steep enough to facilitate failure (Laberg &
Vorren, 1995; Eyles & Eyles, 2000; Hambrey &
McKelvey, 2000). Such slopes can be created
readily in glacial environments, particularly in
the proximal zone close to the grounding line
(Powell, 1990). Here, the emergence of sedi-
ment-laden water from subglacial tunnels
results in high rates of deposition. As such,
local topographic highs and associated slopes
develop at the grounding line. In these set-
tings, sediment remobilization events, such as
debris flows, occur in tectonically quiescent
basins where the bathymetry is otherwise flat.
The distinctive architecture of tapering beds
of diamictite, sandstone and conglomerate
sloping at 10°to the upper and lower bound-
ing surfaces is characteristic of proximal
grounding-line fans (Fig. 6). The associated
sandstone and conglomerate debris-flow depo-
sits are interpreted as episodic sediment pulses
delivered from the subglacial drainage system.
Convolute bedding and slump structures
record local failure of these sediments. The
interbedded massive diamictites are interpreted
as rainout deposition from suspended sedi-
ment, combined with background sedimenta-
tion from icebergs.
The AMS fabrics from the sandstone and
conglomerate facies (Fig. 13) are consistent
with particle orientation by shearing in cohe-
sionless flows, with relatively low cumulative
strains (Hooyer et al., 2008). Taken together
with the geometry of the grounding-line fan
deposits, K
1
azimuths suggest sediment trans-
port in a broad arc towards the north or north-
west.
Non-glacial lacustrine, evaporite, fluvial and
periglacial sediments occur at several levels
within the Wilsonbreen Formation, and the
basin appears to have been isolated from the
sea throughout (Benn et al., 2015; Fairchild
et al., 2015). The present authors therefore
interpret the Undeformed Facies Association as
glacilacustrine, deposited in a large proglacial
lake. At times, deposition occurred in an ice-
proximal setting close to the glacier grounding
line, but at other times deposition was domi-
nated by rainout in a more distal environment.
The occurrence of carbonate lacustrine facies
with dropstones in the W2 Member (Fairchild
et al., 2015) indicates that periodic input of
glacial sediment to the lake was much
reduced. The massive diamictites formed by a
combination of rainout from a high concentra-
tion of debris-rich icebergs and the settling of
material from meltwater plumes. High rates of
sedimentation resulted in the development of
local palaeoslopes and the formation of
grounding-line fans (Fig. 6). Sediment remobi-
lization events resulted in the emplacement of
debris-flow deposits. In addition, subaqueous
currents, possibly created by emerging sub-
glacial channels, formed lag deposits.
Deformed Facies Association
Origin of the deformed rhythmites and
overlying diamictite
On the basis of their structural style and close
association with sheared diamictites, the
deformed rhythmites are interpreted as glacitec-
tonite (cf. Benn & Evans, 1996, 2010). Prior to
deformation, these rhythmites were originally
both structurally and compositionally similar to
the rhythmites of the undeformed W2 Member
(Fairchild et al., 2015). The original deposition
of the unit occurred in a lacustrine environ-
ment with the lamination reflecting daily, mete-
orological or annual variations in sediment
discharge into a lake. The deformation of the
rhythmite records glacier advance over the site.
Evidence for partial liquefaction and local
upward injection of sediments suggests
hydrofracturing, which is a common feature of
subglacially deformed sediments (Phillips et al.,
2013).
The diamictites that overlie these deformed
rhythmites are interpreted as subglacial traction
tills (Benn & Evans, 2010). The tills formed par-
tially by the deformation of the immediately
underlying sediments (recorded by the presence
of rafts of lacustrine carbonates, glacitectonite
and other deposits) and partially by the trans-
port of intra-basinal and extra-basinal debris
from up-glacier. The clast fabrics from the
diamictite and the AMS fabrics from the diamic-
tite and the glacitectonites are consistent with
particle orientation by shearing, with high
cumulative strains (Benn, 1994, 1995; Iverson
et al., 2008). The transitional contacts between
the rhythmites and the overlying diamictites
and consistent fabric orientations suggest that
the deposition of both deposits occurred during
the same glacial advance, with ice movement
from the south or south-south-east.
©2015 The Authors. Sedimentology ©2015 International Association of Sedimentologists, Sedimentology,63, 411–442
Glacitectonism in a Neoproterozoic panglaciation 437
Origin of sandstone and conglomerate lenses
within diamictites
Lenses of sand and gravel within massive
diamicton are a common feature of subglacial
traction tills (e.g. Hart & Roberts, 1994; Evans &
Campbell, 1995). A variety of mechanisms has
been proposed for their formation (see review in
Waller et al., 2011), including entrainment of
the sand through thrusting or folding from an
underlying layer (e.g. Hart & Boulton, 1991) and
the melt-out of sand from the overlying basal ice
(e.g. Hoffmann & Piotrowski, 2001). Alterna-
tively, sands and gravels may be produced sub-
glacially by the deposition of sorted sediments
flowing within subglacial channels at the ice
bed interface (Alley, 1991; Clark & Walder,
1994). Although being originally fluvial in ori-
gin, these deposits can be cannibalized and
deformed by the array of processes associated
with the formation of a subglacial traction till
(Hart, 1998; Evans et al., 2006; Benn & Evans,
2010), and they are subsequently incorporated
as deformed lenses in otherwise massive diamic-
ton.
Within the sandstone lenses of the Deformed
Facies Association, a mechanism through thrust-
ing of pre-existing sands is unlikely owing to
the lack of similar sands lower down in the
sequence. Furthermore, the identification of
channel-like geometries on some of the lenses
with deformed cross-bedding is consistent with
a glacifluvial origin. For example, the large
channelized sandstone body occurring immedi-
ately below the boulder pavement at Rein-
sryggen (Fig. 10A) has a geometry typical of a
subglacial channel. Therefore, the sandstone and
conglomerate lenses of the Deformed Facies
Association are interpreted as subglacial chan-
nels, some of which have been deformed and
incorporated into a subglacial traction till, while
others remain undeformed such that their depo-
sitional geometries are preserved.
Development of the boulder pavements
Striated Boulder pavements are considered diag-
nostic of subglacial environments (e.g. Boyce &
Eyles, 2000). A boulder pavement in a till suc-
cession consists of a thin, laterally extensive
layer of clasts, commonly with planar and some-
times striated upper surfaces. A number of dif-
ferent mechanisms have been proposed for their
formation. The most straightforward suggestion
is that they represent the former position of the
icebed interface, where the combined effects of
subglacial meltwater and glacier sliding progres-
sively remove fine-grained sediment from the
underlying till, leading to a concentration of lar-
ger clasts (Boyce & Eyles, 2000). However, Clark
(1991) and Boulton (1996) suggested that pave-
ments could also form within the deforming bed
itself, as a result of clasts sinking through soft
sediment or excavation at the base of the
deforming layer.
The boulder pavements at Ditlovtoppen and
Reinsryggen represent very prominent surfaces
that can be traced for several hundred metres
along strike; they possibly mark periods of dis-
tinctive subglacial conditions, when erosional
and deformational processes dominated over
depositional ones within the deforming bed
mosaic. Although the Ditlovtoppen and Rein-
sryggen pavements occur at a similar stratigraphic
level, it is not known whether they are precisely
synchronous, or represent diachronous shifting of
subglacial environments in different areas.
At both Ditlovtoppen and Reinsryggen, sand-
filled channels occur in association with the
boulder pavements, incised down into the under-
lying diamictite and with planar tops level with
the boulder pavement surfaces. These channel
structures are significant because they indicate
the presence of meltwater at the icebed inter-
face.
At Ditlovtoppen, striations on the upper sur-
face of clasts in the pavement are orientated to
130°; this is almost parallel to the V
1
eigenvector
from a clast fabric (136°) and the K
1
vector of an
AMS fabric (139°) from the underlying diamictite.
This indicates that the boulder pavement and the
underlying diamictite were formed while ice was
flowing in a consistent direction.
Boulder pavements are a distinctive feature in
subglacial sediments. Importantly for Neopro-
terozoic palaeoclimatic interpretations, the
occurrence of boulder pavements and associated
subglacial channel deposits clearly indicate a
warm-based thermal regime for at least part of
the depositional phase, with abundant water at
the icebed interface.
DISCUSSION
The present study has obtained the first results
from the application of anisotropy of magnetic
susceptibility (AMS) to Neoproterozoic diamic-
tites for sedimentological analysis. The use of
AMS in combination with facies analysis,
microstructural analysis and more traditional
clast fabric analysis has enabled the depositional
©2015 The Authors. Sedimentology ©2015 International Association of Sedimentologists, Sedimentology,63, 411–442
438 E. J. Fleming et al.
regimes of the Wilsonbreen Formation to be elu-
cidated. In particular, AMS has allowed the
kinematics of deformation to be constrained in a
much more objective manner than was previ-
ously possible. It has also allowed the interroga-
tion of parts of the section where structures are
missing. Finally, it has allowed the analysis of
fabric at a smaller and more precise scale than
could be obtained through clast macrofabric
analysis alone. These results suggest that, in
addition to modern and Quaternary glacial sedi-
ments, AMS can be used as an effective petro-
fabric indicator in pre-Quaternary glacial
sediments. This technique could be particularly
useful where clast fabrics cannot be measured
(for example, where they are too indurated to
allow extraction of clasts).
The fabric data presented provides insight
into palaeoflow during deposition. Fabric max-
ima in both the clast fabrics and AMS ellipsoids
trend northsouth in both the glacilacustrine
and subglacial facies. In the glacilacustrine
deposits, this probably reflects the direction of
bottom currents and mass flows, whereas in the
tills and glacitectonite, the (stronger) fabric max-
ima reflects the direction of shear beneath the
glacier.
Iverson et al. (2008) showed that during sub-
glacial shear of till, AMS fabrics develop with
an up-glacier dip of K
1
. The same up-glacier dip
has been noted in the V
1
direction of clast fab-
rics from deformation tills (e.g. Benn, 1995). A
slight predominance of dips towards the south
is seen in the K
1
AMS and V
1
clast fabrics of the
Deformational Facies Association, which could
be considered consistent with shear towards the
north. Both structural analysis of the glacitec-
tonites and larger scale sediment architecture
support the interpretation of ice flow and sedi-
ment transport to the north. Subglacial tills,
indicative of grounded ice, are absent from the
northernmost section (Dracoisen). At this latter
site, a grounding-line fan occurs at the same
stratigraphic level, with beds tapering and dip-
ping towards the north (Fig. 6). Thus, it is con-
cluded that the glacigenic facies in the
Wilsonbreen Formation were formed in associa-
tion with a lobe of ice flowing into a large lake
from the south. This conclusion is consistent
with previous reconstructions of the palaeoenvi-
ronment (Fairchild & Hambrey, 1984; Halverson
et al., 2004), and from the contiguous sediments
of Northeast Greenland (Moncrieff & Hambrey,
1988; Herrington & Fairchild, 1989).
The extent of the outcrop of the Wilsonbreen
Formation (and its correlatives in Northeast
Greenland), and the wide range of both intra-
basinal and extrabasinal clasts in the diamic-
tites, suggests that deposition occurred in
association with a large, possibly continental-
scale ice sheet. The total thickness of the
diamictite beds in the Wilsonbreen Formation
(>100 m at most sites) implies a high sediment
flux. Sediment was delivered into the lake by
both glacial meltwater and calved icebergs,
forming grounding-line fans and thick rainout
diamictites. The Deformed Facies Association
provides abundant evidence of warm-based
subglacial conditions, in the form of striated
and polished clasts with compact ‘blocky’
shapes, sheared subglacial traction tills and
glacitectonites, striated boulder pavements and
subglacial channel deposits. Therefore, it is
clear that in the area of outcrop (and, by
implication, upstream) the ice was warm-based
during the deposition of the preserved sedi-
ments. Warm ice occurs beneath many thick
glaciers and ice streams even in modern polar
environments, where the bulk of the ice is
below the pressure melting point. The lack of
facies with supraglacial attributes, and only a
small proportion of fluvial sediment, is consis-
tent with low topography and the presence of
an ice stream, feeding into the lacustrine
basin.
This study has focused on one particular
part of the succession and has shown evidence
of a major ice advance. However, this was not
the only advance recorded in the Wilsonbreen
Formation, because both glacilacustrine and
subglacial sediments are interbedded with non-
glacigenic facies in other parts of the succes-
sion (see Fig. 1; Fairchild et al., 2015; Benn
et al., 2015). The interplay of glaciolacustrine,
subglacial and non-glacial conditions indicates
that the Marinoan glaciation in north-east Sval-
bard was characterized by repeated advance
and retreat cycles. Model results and geochemi-
cal analyses presented by Benn et al. (2015)
indicate that these cycles are likely to have
occurred in response to orbital forcing in the
late stages of the panglaciation. The evidence
presented in the current paper for warm-based
ice, subglacial fluvial systems and thick glacila-
custrine deposits shows that, for at least part
of the Marinoan glaciation, glacier systems
were dynamic and subject to repeated major
changes.
©2015 The Authors. Sedimentology ©2015 International Association of Sedimentologists, Sedimentology,63, 411–442
Glacitectonism in a Neoproterozoic panglaciation 439
CONCLUSIONS
Detailed investigations of the Wilsonbreen For-
mation have been undertaken utilizing facies
analysis, structural geology and fabric analyses.
The following conclusions can be drawn:
1Deposition of the Wilsonbreen Formation
occurred in subaqueous, subglacial and terres-
trial settings, with advances of glacier ice along
the axis of the basin. Glacigenic sediments were
deposited in a predominantly subaqueous envi-
ronment in the north and alternating subglacial
and subaqueous environments in the south.
2A range of soft-sediment deformational struc-
tures occur within the Wilsonbreen Formation.
Through detailed sedimentological and struc-
tural analysis, these are shown to be primary in
origin, relating to deformation and deposition in
a subglacial environment.
3This study has built on the previous work of
the examination of anisotropy of magnetic sus-
ceptibility (AMS) of glacial sediments and
shows that AMS in combination with clast fab-
ric and facies analysis has the potential to pro-
vide significant insights into the deposition of
well-preserved Neoproterozoic glacial sedi-
ments.
4Both Clast and AMS fabrics are found to
exhibit consistent differences in shape and
strength depending on the depositional mecha-
nism. Subglacial tills and glacitectonites have
very strong, elongate cluster fabrics parallel to
the direction of shear. In contrast, clast fabrics
from glacilacustrine diamictites are typically gir-
dles, with weak preferred orientations possibly
reflecting bottom currents or sediment flow. Ani-
sotropy of magnetic susceptibility (AMS) fabrics
from subaqueous mass flow deposits have mod-
erate to strong preferred orientations through a
broader range of orientations.
5In combination with analysis of the sediment
architecture, the AMS and clast fabric data sup-
port the overall sedimentary architecture and
indicate ice flow to the north and continued
northward sediment transport into a proglacial
lake.
ACKNOWLEDGEMENTS
This work forms part of the NERC-funded
GAINS (Glacial Activity in Neoproterozoic Sval-
bard) grant (NE/H004963/1) with a tied PhD stu-
dentship held by EJF. We thank the logistical
staff at UNIS for their help in the planning of
the fieldwork. Finally, we would like to thank
the reviewers, Flavia Girard and anonymous,
and the Associate Editor (Dan Le Heron), for
their comments and suggestions, which have
considerably improved the manuscript.
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©2015 The Authors. Sedimentology ©2015 International Association of Sedimentologists, Sedimentology,63, 411–442
442 E. J. Fleming et al.
... These data are integral to differentiating mass flow and subglacial depositional histories, in distinguishing proglacial and subglacial deformation regimes, and in recognizing diagnostic glacial indicators in typically massive diamicts. With very few exceptions (Menzies 2000;Denis et al. 2009;Menzies and Whiteman 2009;Busfield and Le Heron 2013;Ravier et al. 2015;Fleming et al. 2016;Delpomdor et al. 2017), thin-section analysis (or micromorphology) has enjoyed little serious application in ancient diamictite-rich successions. The reason for this is unclear, particularly because the study of Phanerozoic and Precambrian diamictites has much to gain from an adoption or adaptation of techniques and methodologies commonly applied to their younger counterparts. ...
... In tandem with careful outcrop study, and when dovetailed with appropriate analytical methodologies, micromorphology has the potential to greatly enhance understanding of Cryogenian deposits laid down under a glacial influence. The approach is well established in Quaternary investigations and is underutilized in deep-time studies, in spite of some excellent recent attempts by other workers (e.g., Ravier et al. 2015;Fleming et al. 2016;Delpomdor et al. 2017). An important issue in these ancient successions, as evidenced in the present paper by the Ghaub Formation of Hartbeespoort, is tectonic overprint. ...
... To overcome these challenges, semiquantitative fabric analysis techniques could potentially be used to constrain fabric orientations more objectively. In this respect, in their study in the Wilsonbreen Formation of Svalbard, Fleming et al. (2016) showcased the use of anisotropy of magnetic susceptibility (AMS)-a technique that complements analysis of sedimentary fabrics by generating a 3D set of magnetic data. ...
Article
Micromorphology is a well-established technique adopted by Quaternary scientists which has received wide application in the study of glacial sediments and in soil science. One area where the approach is far less developed is in the analysis of ancient successions and, in particular, rocks of Cryogenian age that are purported to have been deposited during snowball Earth conditions. Here, we integrate micromorphology with outcrop data in the analysis of three contrasting diamictite-bearing successions of Cryogenian age. The successions include two units in Namibia (the Chuos Formation and the Ghaub Formation: diamictites of Sturtian and Marinoan age, respectively), and a formation in Scotland (the Macduff Slates Formation). In the Chuos Formation, which has been metamorphosed to lower greenschist facies, a well expressed primary stratification is clearly developed in clastic diamictites, in spite of a fracture cleavage that crosscuts the lamination. In the Ghaub Formation, which is dominated by carbonate diamictites, local incorporation into fault zones has resulted in a greater postdepositional overprint during tectonic uplift. At the macro-scale, dropstone textures are well expressed, in addition to highly attenuated, fabric-forming clasts. At the micro-scale, sedimentary boudins, load structures, and galaxy structures are observed which imply shearing and deformation of soft sediment. Strain dissolution has an effect on clast morphology, and in some cases carbonate obstacle clasts show sutured contacts with one another. In our third example, at Macduff, micromorphological analysis reveals granule-size ice-rafted debris (IRD) in fine-grained laminites, but the origin of soft-sediment deformation structures in overlying diamictite is inconclusive. We conclude that the technique has the potential to unravel the origins of soft-sediment deformation structures (e.g., whether deformation structures record glaciotectonic origins or nonglacial origins), but its application must take into account the variability in stratified and unstratified sediments, alongside the later overprint of tectonic deformation. Bizarrely, in the Ghaub Formation, both tectonic fabrics (dissolution cleavage) and sedimentary fabrics (e.g., galaxy structures) survive side-by-side in the same thin sections. Thus, a full awareness of the effects of tectonic overprint is essential in examining Snowball Earth under the microscope.
... Le Heron et al., 2014;Link and Gostin, 1981;Preiss et al., 2011;Gostin, 1988, 1991). Due to the deposition of both thick, massive diamictites, and well-sorted and/or current reworked stratified diamictites, this succession was likely deposited in a subglacial to grounded ice-margin environment (G1) (Anderson, 1989;Boggs, 2014;Le Heron, 2013, 2016;Eyles et al., 2007;Fleming et al., 2016;Le Heron et al., 2013Powell and Domack, 2002;Young and Gostin, 1988). ...
... Le Heron et al., 2014;Link and Gostin, 1981;Preiss et al., 2011;Gostin, 1988, 1991). Differentiating the depositional setting of these thick, massive diamictite units can be ambiguous (Anderson, 1989;Eyles et al., 2007), therefore, a more generalised subglacial to grounded ice-margin setting (G1) has been interpreted (Anderson, 1989;Powell and Domack, 2002;Boggs, 2014;Fleming et al., 2016). ...
Article
The Tonian–Cryogenian transition (ca. 720 Ma) represents a period of significant environmental change in Earth history, involving variations in oceanic and atmospheric oxygenation, significant changes in the biosphere, tectonic reorganisation, and the onset of the global ‘Sturtian’ glaciation. South Australia has some of the thickest, continuous and best exposed sections of this unique interval globally. Here we present detailed palaeoenvironmental interpretations for a complete, ca. 3 km thick, pre- to post-glacial succession near Copley in the northern Flinders Ranges, South Australia. Elemental concentration data, complemented by screening for diagenesis, demonstrates the preservation of marine or primary REE signatures for studied carbonate samples and supports the proposed sedimentological and palaeoenvironmental interpretations. Multiple Tonian regressive-transgressive cycles are defined, which are recorded by deltaic rippled and cross-stratified sandstones (Copley Quartzite), through inner platform intraclastic magnesite and stromatolitic carbonates (Skillogalee Dolomite), to subtidal laminated siltstone and platform carbonates (Myrtle Springs Formation). The REE patterns from carbonate samples in the Skillogalee Dolomite and Myrtle Springs Formation indicate low Y/Ho, slight light rare earth element (LREE) depletion, weak negative Ce/Ce* and high Eu/Eu*. This suggests a nearshore, dysoxic setting fed by anoxic deep waters and more oxic shallow waters. In combination, the sedimentological and geochemical data build a picture of a partially restricted, shallow marine to lagoonal setting for the northern Flinders Ranges directly before the climate pivot to the Sturtian glaciation. These pre-glacial formations are unconformably overlain by Cryogenian subglacial to grounded ice-margin pebbly diamictites with immature, massive sand interbeds (Bolla Bollana Tillite). We suggest these facies reflect glacial grounding-line advance and retreat in a glaciomarine setting. These grade into turbiditic laminated sandstone and mudstone with dropstones (Wilyerpa Formation), which were likely deposited at the onset of deglaciation in a subaqueous proglacial environment. The post-glacial succession (Tapley Hill Formation) consists of subtidal laminated shales and carbonates, which are represented by increased Y/Ho, moderate LREE depletion, slight negative Ce/Ce* and low Eu/Eu*. This significant geochemical shift to a more open, oxic to suboxic subtidal setting coincides with widespread transgression and relative sea level rise after one of the most severe glaciations ever recorded.
... It displays interstratified limestone and glacigenic sediments near its top and is succeeded by a thin limestone interpreted as an offshore deposit, typical for a Sturtian cap (Fairchild et al., 2016a). The upper glacigenic unit, the Wilsonbreen Formation (Figure 2), is non-marine (Benn et al., 2015;Fleming et al., 2016;Fairchild et al., 2016b), and is overlain by a cap dolostone which is the subject of this paper (Figure 3). This is correlated with the Marinoan cap carbonate, the lower boundary of which was used to define the base of the Ediacaran System in South Australia (Knoll et al, 2006). ...
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Two cap carbonates overlying Cryogenian panglacial deposits are found in North‐East Svalbard of which the younger (635 Ma) forms the base of the Ediacaran Period. It is represented by a transgressive succession in which laminated dolostone, typically around 20 m thick (Member D1), is succeeded transitionally by a similar thickness of impure carbonates (Member D2). In Spitsbergen, there is evidence of microbially influenced sediment stabilisation and carbonate precipitation in the lower part of D1, whilst the upper part of D1 and D2 show centimetre‐decimetre‐scale graded units with undulatory lamination interpreted as evidence of storm activity. Carbonate originated as possible freshwater whitings, as well as microbial precipitates. Exhumed and eroded hardgrounds display replacive 10‐30 μm dolomite crystals with cathodoluminescence characteristics consistent with early diagenetic manganese and iron reduction. Regionally, carbon isotope values consistently decrease by around 2‰ from around ‐3‰ over 30 m of section which is both a temporal and a bathymetric signal, but not a global one. An exponential decline in carbonate production predicted by box models is fitted by a semi‐quantitative sedimentation model. A mass‐anomalous 17O depletion in carbonate‐associated sulphate in dolomite, inherited from precursor calcite, decreases from ‐0.6 to ‐0.3‰ in the basal 15 m of section and then approaches background values. The post‐glacial anomalous 17O depletion in carbonate‐associated sulphate and barite elsewhere has been interpreted in terms of ultra‐high pCO2 at the onset of deglaciation. Such anomalies, with larger amplitude, have been reported in Svalbard from underlying lacustrine and tufaceous limestones representing a hyperarid glacial environment. The anomalous sulphate could be produced contemporarily, or the internally drained landscape may have continued to release 17O‐anomalous sulphate as it was transgressed during cap carbonate deposition. The late Cryogenian to earliest Ediacaran record in Svalbard provides the most complete record of the basal 17O‐depletion event in the world.
... Thus, the preservation of striated clasts throughout this facies together with the abundance of sub-angular components provides credence to both minimal transport and deposition proximal to a glacial source. However, there is no evidence of sedimentary features unique to the icemarginal or ice-contact environment, such as glacio-tectonites, basal striated and boulder pavement, clastic dykes, till pellets, sheared and deformational patterns compatible with glacier overriding and large scale lithofacies heterogeneities (e.g., Arnaud and Etienne, 2011;Evans et al., 2006;Eyles and Eyles, 2010;Fleming et al., 2016;Hu and Zhu, 2020). Therefore, it is presumed that either secondary reworking complicates the original depositional feature or the deposition took at some distance from a glacial terminus. ...
Article
One of the central tenets of the snowball Earth hypothesis is the global recognition of the glacial diamictite-cap carbonate couplets in the Cryogenian sedimentary record. However, the scarcity of such peculiar stratigraphic elements in the Neoproterozoic successions of the Himalaya brings into question the severity and global extent of the snowball Earth event and likewise hampered glacio-stratigraphic correlation within the Himalaya and elsewhere. This study provides the first convincing evidence of the glacial diamictite-cap carbonate couplet from the Tanakki Member of the basal Kakul Formation, previously unknown from the Western Himalaya in North Pakistan. Detailed sedimentological analysis of the diamictite from the Tanakki Member reveals deposition in glacially-influenced proximal to distal subaqueous debris apron. The presence of glaciogenic clasts (striated, facetted and bullet-shaped) together with evidence of the ice-rafted dropstones in pervasive facies association provides credence to the glaciogenic affinity. The thin cap carbonate (herein referred to as Tanakki-cap dolomite; TCD) overlying the glacial diamictite record deposition in a deeper shelf (offshore) setting. The lithological, depositional and persistent negative C-isotope characteristics (ca. −3.2 to −5.8‰) combined with regional stratigraphic and available geochronological data allow us to interpret TCD as a ‘Marinoan’ cap carbonate and the underlying diamictite as an expansion of the terminal-Cryogenian (Marinoan) glaciation in the Western Himalaya. Moreover, the analyses of the tectonic and depositional history of the Tanakki Member coupled with the Neoproterozoic paleogeographic evolution of the northern margin of the Indian Plate argue against a previous interpretation of the culminating foreland basin orogeny and instead support deposition in an extensional fault-controlled rift basin. Finally, this study permits us to revise the Neoproterozoic stratigraphic framework of the Western Himalaya by describing the Cryogenian-Ediacaran boundary interval in the region that ultimately helps to overcome the previous glacio-stratigraphic discrepancies in the Neoproterozoic record of the Himalaya.
... Thus, the preservation of striated clasts throughout this facies together with the abundance of sub-angular components provides credence to both minimal transport and deposition proximal to a glacial source. However, there is no evidence of sedimentary features unique to the icemarginal or ice-contact environment, such as glacio-tectonites, basal striated and boulder pavement, clastic dykes, till pellets, sheared and deformational patterns compatible with glacier overriding and large scale lithofacies heterogeneities (e.g., Arnaud and Etienne, 2011;Evans et al., 2006;Eyles and Eyles, 2010;Fleming et al., 2016;Hu and Zhu, 2020). Therefore, it is presumed that either secondary reworking complicates the original depositional feature or the deposition took at some distance from a glacial terminus. ...
Article
One of the central tenets of the snowball Earth hypothesis is the global recognition of the glacial diamictite-cap carbonate couplets in the Cryogenian sedimentary record. However, the scarcity of such peculiar stratigraphic elements in the Neoproterozoic successions of the Himalaya brings into question the severity and global extent of the snowball Earth event and likewise hampered glacio-stratigraphic correlation within the Himalaya and elsewhere. This study provides the first convincing evidence of the glacial diamictite-cap carbonate couplet from the Tanakki Member of the basal Kakul Formation, previously unknown from the Western Himalaya in North Pakistan. Detailed sedimentological analysis of the diamictite from the Tanakki Member reveals deposition in glacially-influenced proximal to distal subaqueous debris apron. The presence of glaciogenic clasts (striated, facetted and bullet-shaped) together with evidence of the ice-rafted dropstones in pervasive facies association provides credence to the glaciogenic affinity. The thin cap carbonate (herein referred to as Tanakki-cap dolomite; TCD) overlying the glacial diamictite record deposition in a deeper shelf (offshore) setting. The lithological, depositional and persistent negative C-isotope characteristics (ca. −3.2 to −5.8‰) combined with regional stratigraphic and available geochronological data allow us to interpret TCD as a ‘Marinoan’ cap carbonate and the underlying diamictite as an expansion of the terminal-Cryogenian (Marinoan) glaciation in the Western Himalaya. Moreover, the analyses of the tectonic and depositional history of the Tanakki Member coupled with the Neoproterozoic paleogeographic evolution of the northern margin of the Indian Plate argue against a previous interpretation of the culminating foreland basin orogeny and instead support deposition in an extensional fault-controlled rift basin. Finally, this study permits us to revise the Neoproterozoic stratigraphic framework of the Western Himalaya by describing the Cryogenian-Ediacaran boundary interval in the region that ultimately helps to overcome the previous glacio-stratigraphic discrepancies in the Neoproterozoic record of the Himalaya.
... Analysis of glacial macrofabrics has become more sophisticated through time but the net consequences of these advances has been less confident interpretation as the number of recognised influences on fabric patterns has increased (cf., Mark, 1974;Rose, 1974;Benn, 1994;Hicock et al., 1996;Bennett et al., 1999;Fleming et al., 2016). Moreover, the fabric pattern obtained from chalky till S6 (Fig. 7) is exceptionally unusual, occupying uncomfortable ground between the bimodal cluster and polymodal/girdle-like categories sensu Hicock et al. (1996). ...
Article
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Despite limited exposures, detailed field mapping and sedimentological analyses – particle size, clast petrography and fine-sand mineralogy (plus limited coarse silt and clay mineralogy) – have elucidated the ages, provenance and depositional environments of the complex and controversial Quaternary deposits covering the Ayot Paleogene Outlier. Most of the sediments were largely derived directly and/or indirectly from local facies of the Woolwich and Reading Formation. The oldest deposits are (Pre-)Pastonian proto-Thames gravels overlain by thin sands, which collectively represent crucial evidence for the earliest (Stoke Row) terrace of the proto-Thames. These materials were later thrust southwards by the Anglian ice close to its margin, which deposited a thin yet heterogeneous till at Ayot. This unit is correlated with the Ware Till, suggesting that the Anglian ice was thicker during the earlier of its two major southwestward incursions into the Vale of St Albans. An aeolian mantle was deposited on the Outlier during the Late Devensian; most of the blown material was incorporated into the upper regions of the till but some accumulated in depressions to form brickearths that resemble some Chiltern Brickearths. A colluvial apron developed during the Holocene, together with three swallow-holes. Some of these depositional events were separated by periods of poorly-preserved pedogenesis.
... Thus, a study bridging the SEM and thin section scales for the ancient record is long overdue. With few exceptions (e.g., Fleming et al., 2016;Busfield and Le Heron, 2018) the micromorphological approach is rare in deeptime glacial successions, let alone when simultaneously coupled with interrogation of SEM data. A major question is whether evidence for glacial process is visible at the microscale in materials that are apparently homogeneous (sandstone) at the hand specimen scale. ...
Article
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The expansion of ice sheets over soft, sandy substrates was widespread in the Early Palaeozoic, during the Late Ordovician glaciation of North Africa and Arabia. Similarly, large parts of southern Africa were glaciated by soft bedded ice sheets in the Late Palaeozoic Ice Age. An unanswered question is the extent to which subglacial deformation involved the passive recycling of unconsolidated materials, or the active production of new sediment through erosion and shearing. Here, we compile thin section data dovetailed with scanning electron microscope imagery from sandy subglacial substrates from South Africa, Algeria and Libya. Six samples were collected from soft-sediment striated pavements, i.e., surfaces that were sheared and deformed subglacially in an unconsolidated state. The samples show a considerable variation in deformation style but a unifying trait is the occurrence of striated and facetted quartz sand grains. These textural features testify to grain-grain attrition, and the potential production of sediment in the subglacial environment.
... There have been numerous publications documenting the Cryogenian glacial record but far fewer that have provided deformation analyses (Benn and Prave, 2006;Busfield and Le Heron, 2013) and particularly with reference to subglacial bedrock (Domack and Hoffman, 2011;Arnaud, 2008Arnaud, , 2012Fleming et al., 2016). To the best of our knowledge, the complete deformation succession of Stages Z1-Z5 in this study has never been reported for Cryogenian strata before but whether our proposed Crushed Ductile Deformation Model is merely a local phenomenon or one that could have broader applications remains to be tested. ...
Article
The Cryogenian Period (~720–635 Ma) witnessed the most extensive and prolonged glaciation events in Earth history. Vast ice sheets of at least two global glaciations, the Sturtian (~720–660 Ma) and Marinoan (< 654–635 Ma), advanced to sea level at low latitudes, a scenario that is at the heart of the general Snowball Earth hypothesis. This hypothesis is supported by results of recent work in geochronology and geochemistry, but certain parts of the glacial sedimentary records remained debated regarding ice sheet dynamics. Here we report findings from four sections of the Sturtian-age Tiesi'ao/Dongshanfeng Formation and related strata on the Yangtze Block in South China. Our work has documented the presence of four lithofacies: massive diamictite, crudely stratified diamictite, stratified to massive pebbly sandstone and dropstone-bearing laminated siltstone and our interpretation is that these rocks were deposited in proximal glacio-marine environments during five successive episodes of glacial advance and retreat. We have also identified an interval of deformation structures near the base of the Tiesi'ao/Dongshanfeng Formation that is characterized by upward increasing strain intensity, indicating that these structures were caused by overriding ice sheets. All the observations collectively suggest that the Sturtian ice sheets in South China were warm-based, rapidly moving, and sensitive to changes in climate. Further, our data suggest that the ice grounding line reached the slope area, implying a major drop in global sea level, enormous ice sheet thickness, or both during the Sturtian Glaciation.
... The contact between both units is sharp and is cut by discrete shear planes developed within the tills (Fig. 3a, b) with lengths of up to 50 cm (cf. Busfield and Le Heron, 2013;Fleming et al., 2016). Additionally, sharp, straight shear planes occur in the tills at the macroscale (Fig. 3c). ...
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Tills from an exposure in Wildschönau Valley, northern Austria were examined using microsedimentological techniques. The tills exhibit a range of microstructures indicative of soft sediment deformation within temperate subglacial bed conditions. The tills can be subdivided at the macroscale into a lower grey and upper red till both of which exhibit some sedimentological variations; however, at the micro-level the tills appear essentially identical. The microstructures in the tills are illustrative of structures developed during deformation both during and following their emplacement. Of note are the microshears within these tills that are demonstrative of changes in applied stress. Both low (<25°) and high angle (>25°) microshears were mapped and their fabric data analyzed. The microshears show a change in stress levels ascending through successive till units. The changes in stress are demonstrative of spatially and temporally changing rheological conditions undergone by the subglacial tills during deformation, ongoing deposition/ emplacement and stress localization. These findings indicate that microstructures reveal local deformation conditions in tills and a more detailed micro-history of paleo-stress.
... By studying present-day glacial environments and sedimentological processes, considerable knowledge can be gleaned as to how sediments of past glacial events have been derived, transported, and finally deposited both on land and in water (Chapters (8,9,10). Pleistocene glacial sediments cover today at least 30% of the Earth's continental landmasses, and an even greater area must be included when Pre-Pleistocene sediments ranging over vast areas of India, Australia, Africa and South America are considered (Hambrey and Harland, 1981;Arnaud et al., 2011;Young, 2013;Fleming et al., 2016;Spence et al., 2016) (Chapters 7, 11). These sediments affect almost every aspect of human life from establishing foundations and footings for buildings, windmills, roads and runways; the nutrient content of soils; the nature of groundwater supplies; to the potential soil routes for contaminant waste disposal and the location of landfill sites (Chapters 12, 13). ...
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Introdction to new Past Glacial Environemtns textbook
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A theory of erosion, transport and deposition of unlithified sediments by glaciers is presented. It predicts the large-scale areal distribution of zones and rates of erosion and deposition in time and space through a complete glacial cycle, together with the resultant intensity of large-scale lineations (drumlins) which will be incised in the landscape. The theory also predicts the dispersal patterns of subglacial lithologies, together with the form of dispersal trains derived from distinctive sources and the vertical and horizontal distribution of lithologies within a till. It predicts major erosional discontinuities within tills and the formation of boulder pavements. It suggests that the dominant proportion of the lowland tills produced by Pleistocene mid-latitude ice sheets was generated by subglacial deformation and explains why they are predominantly fine-grained. The theory is based on an analysis of glacier-dynamic processes and therefore can be used to infer the dynamic behaviour of former ice sheets from the distribution of tills and their lithologic composition.
Article
The widespread, uniform till sheets of the southern margin of the Laurentide ice sheet were deposited by fast-moving, wet-bedded ice over relatively short periods of time. Characteristics of these till sheets are entirely consistent with deposition from deforming subglacial sediment layers; it is difficult (although not impossible) to explain their origin through debris transport in basal ice. Careful estimation of debris budgets and studies of sorted sediments contained in the till sheets may clarify their origin further.
Article
The intracratonic Canning Basin is Western Australia's largest sedimentary basin (>400 000 km(2)) and has experienced repeated episodes of Phanerozoic extension and subsidence, resulting in deposition of a number of first-order 'megasequences'. A major phase of basin extension and sedimentation (Grant Group) occurred in the Late Carboniferous/Early Permian when Australia lay at high palaeolatitudes. Facies analysis of 5000 m of drill core from 25 continuously cored wells in Grant Group strata on the fault-bounded Barbwire Terrace in the northern Canning Basin identified three facies associations (FAs). These record the predominance of fault-generated, subaqueous mass flow and sediment reworking. The lowest association (FA I; up to 355 m thick) rests unconformably on tilted older strata and consists of coarse-grained, subaqueously deposited, sediment gravity flow facies. These include fault-generated breccias, massive and graded sandstones and conglomerates deposited by turbidity currents and diamictites generated by mixing of different textural populations during downslope remobilization. FA I is overlain abruptly by relatively fine-grained deposits of FA II (up to 140 m thick), which consist of laminated to thin-bedded mudstone and sandstone turbidites, recording an abrupt increase in relative water depths. In turn, these facies coarsen upwards and are transitional into shallow-water, swaley cross-stratified and rippled sandstones of FA III (up to 125 m thick). The overall stratigraphic succession probably records an initial phase of faulting and accommodation of coarse sediment (FA I), a subsequent phase of rapid subsidence, increasing water depths and 'sediment underfilling' (FA II) and, finally, a regressive phase of shoreface progradation. The occurrence of rare striated clasts in FA I suggests reworking of glacial sediment, but no direct glacial influence on sedimentation can be identified.
Article
The Vendian Period is represented in Svalbard by a remarkable range of sedimentary, with some volcanic, rocks that were formed in at least three contrasting environments. The bulk of the record is Early Vendian (i.e. Varanger); however, some evidence obtains for a Late Vendian (Ediacara) record. The best-preserved succession belongs to the Hecla Hoek Geosyncline of northeast Svalbard. It contains a variety of carbonates and clastic rocks, including tillites, deposited in a stable, dominantly marine environment (with periodic emergence). A Varanger (Vendian) age has been established on the basis of an exceptionally well-preserved microflora. Two main glacial stages are recorded. In western Svalbard, from Engelskbukta to outer Hornsund, a very different terrane (the Holtedahl Geosyncline) contains tillites sensu lato, carbonates, volcanics, subaqueous debris-flows and finer-grained facies, possibly related to crustal rifting. The third terrane of supposed Vendian rocks, in middle Hornsund, also includes two glacially influenced units and a post-glacial succession, the overall sequence having affinities with and differences from each of the above-mentioned terranes. Detailed comparison with other North Atlantic successions shows that the northeast Svalbard succession closely matches the Tillite Group of East Greenland. Indeed these two areas must have been juxtaposed in Vendian time. Therefore, to bring the different environment of western Svalbard and middle Hornsund into their present intervening position, major post-Vendian strike-slip movements are necessary. -from Authors
Chapter
Two sections through 1 km of Upper Riphean carbonates have been studied in the fjord zone of central East Greenland at Ella O and just west of Kap Weber, which lies 65 km north. A close stratigraphic resemblance exists that highlights some confusions in previous literature about correlations in the fjord zone. The lower 700 m lies within Bed group 18 of the standard lithostratigraphy and can be divided into 16 correlatable members. Deposition on a stable carbonate shelf is inferred. Bed group 19 (c200 m) can be divided into seven members that are correlatable between the two sections. The basal member contains peritidal carbonates and is abruptly overlain by dolomitic shales interpreted as slope-apron environment deposits. The original sediments were rich in kaolinite and iron oxides, derived from a humid land area. Overall, there is a shallowing upwards trend and this is demonstrated both by an upward development of carbonaceous laminae within background sediments, interpreted as microbial mats, and also by an upward increase in the development of submarine lithification of carbonate-rich turbidites. The sudden development of slope deposits is attributed to a phase of basin extension. -from Authors