First report of a newly discovered Ediacaran biota from the Irkineeva Uplift, East Siberia

Abstract

New Ediacara-type macrofossils are described from the Irkineeva Uplift of East Siberia, Russia. Preliminary field studies within the Taseeva Group reveal probable examples of the Ediacaran taxa Arkarua adami and Beltanelliformis minutae; the organo-sedimentary structure `Arumberia'; and `elephant skin' micro bial mat fabrics. These impressions are consistent with a latest Ediacaran age for the units of the upper Taseeva Group, suggesting that they are tens of millions of years younger than has previously been reported. Large discoidal specimens from the upper part of the Sukhoy Pit Group, likely to be Middle Riphean (Mesoproterozoic) in age, are tentatively assigned to the taxon Nimbia occlusa, and are suggested to be microbial in origin. These discs, and a contemporaneous acritarch assemblage of long-ranging sphaeromorphic taxa, cannot be precisely geochronologically constrained at present, but are highly likely to be pre-Ediacaran in age. The Irkineeva finds supplement a diverse suite of Russian Ediacaran (Vendian) fossil localities, and may be of considerable importance in correlating disparate Meso- and Neoproterozoic stratigraphic units across the Siberian Platform. This report emphasises the largely unexplored potential of the Irkineeva Uplift for palaeontological study, and provides tantalising evidence for the preservation of Late Ediacaran macro-organisms in this region

Full text

1. Introduction
The Ediacaran biota is currently known from more
than 35 localities worldwide (Fedonkin et al. 2007),
with more fossil assemblages being discovered and
documented each year. The unusual morphological
attributes of many Ediacaran macrofossils, and the
difficulties encountered in attempting to identify their
phylogenetic position, mean that new sites and speci-
mens are of huge importance to our understanding of
these soft-bodied organisms. Given our ever improv-
ing knowledge of the stratigraphy of global Ediacaran
successions (e. g. Narbonne et al. 2012), such new
finds can also assist in constraining the age of Neo-
proterozoic strata, particularly in areas that have not
yet been radiometrically dated.
Russia has proven a particularly rich source of
Ediacaran material, with multiple localities preserving
taxa in a variety of depositional environments and
lithologies (cf. Fedonkin et al. 2007, fig. 65). Russian
Newsletters on Stratigraphy, Vol. 46/2 (2013), 95–110 Article
Stuttgart, August 2013
First report of a newly discovered Ediacaran biota
from the Irkineeva Uplift, East Siberia
Alexander G. Liu
1
, Martin D. Brasier
2
, Olga K. Bogolepova
3, 5
,
Elena G. Raevskaya
4
, and Alexander P. Gubanov
3
With 4 figures
Abstract. New Ediacara-type macrofossils are described from the Irkineeva Uplift of East Siberia, Russia.
Preliminary field studies within the Taseeva Group reveal probable examples of the Ediacaran taxa Arkarua
adami and Beltanelliformis minutae; the organo-sedimentary structure ʻArumberiaʼ; and ʻelephant skinʼ micro -
bial mat fabrics. These impressions are consistent with a latest Ediacaran age for the units of the upper Taseeva
Group, suggesting that they are tens of millions of years younger than has previously been reported. Large dis-
coidal specimens from the upper part of the Sukhoy Pit Group, likely to be Middle Riphean (Mesoproterozoic)
in age, are tentatively assigned to the taxon Nimbia occlusa, and are suggested to be microbial in origin. These
discs, and a contemporaneous acritarch assemblage of long-ranging sphaeromorphic taxa, cannot be precisely
geochronologically constrained at present, but are highly likely to be pre-Ediacaran in age. The Irkineeva finds
supplement a diverse suite of Russian Ediacaran (Vendian) fossil localities, and may be of considerable impor-
tance in correlating disparate Meso- and Neoproterozoic stratigraphic units across the Siberian Platform. This
report emphasises the largely unexplored potential of the Irkineeva Uplift for palaeontological study, and pro-
vides tantalising evidence for the preservation of Late Ediacaran macro-organisms in this region.
Key words. Palaeontology, Ediacaran, Vendian, Irkineeva, Neoproterozoic, Mesoproterozoic
© 2013 Gebrüder Borntraeger, Stuttgart, Germany
DOI: 10.1127/0078-0421/2013/0031
www.borntraeger-cramer.de
0078-0421/2013/0031 $ 4.00
Authorsʼ addresses:
1
Corresponding author: Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ,
U.K. E-Mail: agscl2@cam.ac.uk
2
Department of Earth Sciences, University of Oxford, South Parks Road, Oxford, OX1 3AN, U.K. E-Mail: martinb@
earth.ox.ac.uk
3
CASP, West Building, 181a Huntingdon Road, Cambridge, CB3 0DH, U.K.
4
Geologorazvedka, 11 block 2 Knipovich Street, St. Petersburg, 192019, Russia
5
Museum of Evolution (Evolutionsmuseet), Uppsala Universitet, Norbyvägen 16, SE-75236 Uppsala, Sweden
eschweizerbart_xxx

Alexander G. Liu
96
Fig. 1. Map of the Siberian Platform, showing the new Siberian Ediacaran fossil localities in their geographical and geological context. (a) Modern Russia, showing the bound-
ary of the Siberian Platform (black outline) and the courses of major rivers (blue). Star indicates the position of the localities in (b). (b) Geological map of the Irkineeva Up-
lift region (redrawn based upon Kavitsky 2005). Stars indicate the fossil localities; 1) K025 Artyugino 1 road section, ʻArumberiaʼ locality. 2) K030 Moshakov Fm. Arkarua
locality, 3) K036, site of possible Bergaueria, 4) K041, Kartochka Fm. disc locality. (c) Stratigraphic columns showing the position of the Irkineeva Uplift successions, rela-
tive to the International Stratigraphic Chart, and the Russian Stratigraphic Chart. The levels of fossils found in this study are shown on the far right. Correlation between the
International and Siberian Chart (red lines) is based on Rozanov and Varlamov (2008) and Mel’nikov et al. (2005). Bold red dashed line shows the Neoproterozoic–Cam brian
boundary, bold red solid line shows correlation based on this study. Question mark indicates uncertainty in correlation. For interpretation of the references to colour in this art-
work, the reader is referred to the web version of the article.
eschweizerbart_xxx

Ediacaran palaeontological localities broadly outcrop
within two main Terranes; the Siberian Platform
(which includes sites around the Olenek Uplift, Lake
Baikal, Patom Uplift and Yudoma River; e. g. Sokolov
1975, Chumakov and Semikhatov 1981, Fedonkin et
al. 2007, Leonov and Rud’ko 2012, Zhuravlev et al.
2012), and the East European Platform (including the
White Sea, Podolia, and areas in the South and Central
Ural Mountains; Becker 1977, Grazhdankin 2004,
Fedonkin et al. 2007, Grazhdankin et al. 2009, 2011).
Palaeontological research in these regions has docu-
mented diverse assemblages of Ediacaran taxa (e. g.
Fedonkin 1981), with important discoveries including
carbonate-hosted and carbonaceous preservation of
Ediacaran organisms (within the Khatyspyt Forma-
tion; Grazhdankin et al. 2008), and detailed facies
analyses of the Ediacaran biota (Grazhdankin 2004).
Some of the earliest potential evidence for metazoan
locomotion and grazing in the fossil record comes
from Russian Ediacaran sections (Seilacher et al.
2005, Ivantsov 2011), as well as suggestions of meta-
zoan body fossils, such as the candidate stem-group
mollusc Kimberella (Fedonkin and Waggoner 1997,
though see Ivantsov 2010).
Although Russian stratigraphic sections of Edi-
acaran age are relatively common, reliable correlation
of Neoproterozoic sections across such a vast country
is challenging. This problem stems from a paucity of
palaeontological and reliable geochronological data
in many areas, as well as considerable variability in
facies, even within individual terranes (Mel’nikov et
al. 2005, Kochnev et al. 2007). Attempts have been
made to correlate sedimentary successions across the
Siberian Platform, and then to the rest of the world
(e. g. Pelechaty 1998), but the sheer size of the region,
the facies variation, diverse and disparate stratigraph-
ic records, and challenges in correlating the interior of
the region with the periphery (Mel’nikov et al. 2005)
have made this task difficult. Additional complications
are introduced when attempting to correlate sections
described under Russian stratigraphic terminology
(e. g. Vendian, Riphean; see Semikhatov et al. 2009,
and Sokolov 2011, for further information), with those
described under terms agreed by the Neoproterozoic
Subcommission of the International Commission on
Stratigraphy (Cryogenian, Ediacaran; cf. Gradstein et
al. 2012). Current difficulties in accurately correlating
the Russian and International Stratigraphic Charts ar-
guably make use of a single nomenclatural system
problematic. Therefore, in this publication we use the
terms Vendian and Riphean when describing and dis-
cussing Russian published material, but use Interna-
tional nomenclature wherever possible. Hopefully,
future stratigraphic work will be aided by the drilling
of new boreholes (e. g. Kochnev et al. 2007, Kon-
torovich et al. 2011), together with correlative studies
utilising data from industrial sources (e. g. Frolov et
al. 2011), and the expansion of chemostratigraphic
techniques across Russia (e. g. Podkovyrov et al.
2011). It should also be noted that geochronological
data for late Ediacaran fossil-bearing sections are
gradually becoming more comprehensive, particularly
from the East European Platform (e. g. Martin et al.
2000, Grazhdankin 2004, Llanos et al. 2005, Popov et
al. 2005, Ronkin et al. 2006, Grazhdankin et al. 2011),
which will significantly aid future attempts at region-
al correlation.
We here describe the discovery of apparent Edia -
caran macrofossils from the Irkineeva Uplift of the
East Angara terrane, an area that borders the south-
western Siberian Platform (Gallet et al. 2012). The
only previously reported occurrence of Ediacaran
macrofossils from this region is a single putative
Cyclomedusa specimen from the Redkolesnaya For-
mation (Chechel’ 1976). Fossils in this study were dis-
covered in the summer of 2009 by geologists under-
taking field reconnaissance work for CASP, U.K.
Stratigraphic units in this area have previously been
interpreted to be of Middle Riphean (Mesoprotero-
zoic) to Early Cambrian age (Kavitsky 2005), but pre-
cise geochronological constraints have been lacking.
Revised biostratigraphic understanding resulting from
the palaeontological finds presented herein may sug-
gest a Late Ediacaran age for the upper Taseeva Group,
whilst also extending the fossil record of Mesopro-
terozoic discoidal macrofossils into the Irkineeva re-
gion. Although these new assemblages do not current-
ly show significant taxonomic diversity, and their in-
terpretation is based only upon a handful of specimens,
aspects of their preservation suggest the region has
much promise for further detailed palaeontological in-
vestigation.
2. The geological setting
of the Irkineeva Uplift
The new fossil localities lie along the Irkineeva and
Nizhnyaya Terya Rivers (tributaries of the Angara
River), on the southwestern margin of the Siberian
Platform, to the southeast of the Yenisei Ridge (Fig. 1).
Fossils are found within several geological formations,
First report of a newly discovered Ediacaran biota from the Irkineeva Uplift, East Siberia
97
eschweizerbart_xxx

namely the Moshakov Formation (previously consid-
ered to be mid-Vendian, ~ 617
앐 17 Ma, in age; K-Ar
date from the Agaleev-1 well, in Gutina 2007), the
Aleshino and Chistyakov Formations (mapped as ear-
ly Vendian, on the basis of poorly constrained Rb-Sr
dates ranging between 619–740 Ma; Kavitsky 2005,
Gutina 2007), and the Kartochka and Alad’in Forma-
tions (which have been suggested to be late-Middle
Riphean in age; i. e. Mesoproterozoic, ~ 1.1–1.0 Ga,
based on K-Ar dating of glauconites in the Potoskuy
and Pogoryuy Formations; Shenfil’ 1991, Maslov et al.
2009; Fig. 1). No diamictite horizons indicative of gla-
cial events have yet been found within the Irkineeva
succession, precluding regional or global correlations
based on these prominent Neoproterozoic event beds.
It is worth noting that the precise names of these for-
mations vary across the literature as a result of differ-
ences in transliteration (e. g. Mel’nikov et al. 2005,
Kochnev et al. 2007, Sovetov et al. 2007). In this pub-
lication we use consistently transliterated versions of
the geological units.
The entire succession in the Irkineeva region is
~ 1–1.5 km thick, but this thickness includes several
mapped unconformities of uncertain temporal extent
(Kavitsky 2005). At the base of the succession, the
limestones of the Kartochka Formation are considered
to lie conformably upon the Pogoryuy Formation, and
beneath the Alad’in, with these three units together
comprising the shallow-water Upper Subgroup of the
Sukhoy Pit Group (Fig. 1c; Postel’nikov 1980). These
three formations have more recently been elevated
in rank to the Bol’shoi Pit Group (Khomentovsky
2007), though we follow Gallet et al. (2012) in utilis-
ing the prior terminology. A significant unconformity
separates this Group from the younger Potoskuy For-
mation, which is itself capped unconformably by the
Vendian Taseeva Group (comprising the Aleshino,
Chistyakov and Moshakov Formations; Fig. 1c). This
second, angular, unconformity is observed across
much of the Siberian Platform (Sovetov et al. 2007),
and has been ascribed to southern East Siberia being
located within the continental interior during the
early Neoproterozoic (Gladkochub et al. 2010). The
sedimentology of the Taseeva Group records a shallow
marine, largely terrigenous succession, passing through
numerous anhydrites and dolomites within the Chist -
yakov Formation, to coarse-grained fluvial arkosic
sandstones at the top of the Moshakov Formation (cf.
Mel’nikov et al. 2005, Gallet et al. 2012).
The Taseeva Group is conformably overlain by the
Redkolesnaya Fm., which contains ladder-like inter-
ference ripples within shallow marine red sandstones
and siltstones, indicating at least some tidal influence
in that depositional environment. The top of the
Redkolesnaya Fm. (previously part of the Ostrov For-
mation; Kochnev 2002), has yielded one specimen
assigned to Cyclomedusa davidi (Chechel’ 1976),
though no subsequent palaeontological finds have
been reported. The specimen described by Chechelʼ is
incomplete, but does show a broadly concentric dis-
coidal structure that is similar to those found in other
Late Ediacaran sections worldwide (e. g. Fedonkin et
al. 2007). However, correlation by some authors of the
Redkolesnaya Fm. with the Ust Tagul Fm. (Kochnev
and Karlova 2010), which may contain trace fossils
similar to Treptichnus pedum, would suggest the Edi-
acaran-Cambrian boundary lies either within or just
beneath the Redkolesnaya. The carbonates of the Os-
trov Formation, as most recently defined, have been
found to contain small shelly fossils, including Tik-
sitheca, along the southern Yenisei Ridge, indicating a
lower Cambrian age for that Formation (Koch nev and
Karlova 2010). Above the Ostrov are seen several
predominantly shallow marine carbonate formations,
which contain abundant trilobites and brachiopods
(Rozanov et al. 1992), and finally the Ver kho lensk
Formation at the top of the sequence contains numer-
ous bioturbated horizons. The palaeontological assem-
blages of all of these post-Ostrov units are consistent
with a Cambrian or younger age (Fig. 1c).
The Sukhoy Pit Group is found in outcrop along the
Irkineeva River (Fig. 1b), whereas the younger Tasee-
va Group of Vendian to Cambrian units outcrops in
the Nizhnyaya Terya sections. In this paper, the fossil
assemblages from these two geographic locations are
described separately.
3.1 Fossils from the Nizhnyaya Terya
sections
Strata on the banks of the Nizhnyaya Terya River con-
stitute a conformable succession of late Neoprotero-
zoic to Cambrian units. Although the clastic units
within this succession have been extensively traced
around the Siberian Platform (Sovetov et al. 2007),
their perceived age in the Russian literature varies
considerably. For example, the Taseeva Group, which
contains the fossils we describe herein, has been
regarded as either Early (Mel’nikov et al. 2005) or
Late (Sovetov et al. 2007) Vendian in age, on the basis
of correlation and seismostratigraphy. The Ediacaran
macrofossil impressions we describe all come from
Alexander G. Liu
98
eschweizerbart_xxx

units beneath the Ostrov Formation, thus implying a
pre-Cambrian age for certain pre-Ostrov members of
the succession.
3.1.1 Arumberia-like markings
A specimen from the upper Moshakov Formation,
taken from a road-cut section (Artyugino 1; Fig. 1b.1),
possesses markings directly comparable with the late
Neoproterozoic impression Arumberia banksi Glaess-
ner and Walter 1975 (Fig. 2a). This specimen (K025/1)
occurs upon a fine to medium-grained, micaceous,
well-sorted red sandstone, within a unit of cross-bed-
ded fine to coarse-grained sandstones and conglomer-
ates. Preservation of these features on the lower sur-
face (base) of a bedding plane show parallels with the
taphonomy of biological impressions in the Ediacaran
units of central and southern Australia (e. g. Glaessner
and Walter 1975, Gehling 1999). The surface of the
specimen shows significant topographic undulation
due to the presence of large, isolated ripples. ʻArum-
beriaʼ is characterised by multiple divergent linear
features, spaced 1–5 mm apart, and is here found
alongside 1–3 mm diameter circular bumps (the latter
most common on the ridges of the specimen, i. e. in
the troughs of ripples, and seemingly randomly posi-
tioned; Fig. 2a–b). Both the linear and discoidal im-
pressions are preserved only on the uppermost 0.5 mm
of the surface – observations of a layer directly be-
neath reveal that they are not transmitted through to
the next sediment layer. The linear ʻArumberiaʼ-like
features show a striking regularity within the hollows
on the specimen surface, but their appearance changes
on the ridges, and individual grooves can be seen to
branch and radiate in places (Fig. 2a).
ʻArumberiaʼ is a cosmopolitan Neoproterozoic
impression, described from Australia (Glaessner and
Walter 1975), the White Sea (Marusin et al. 2011),
Newfoundland (Bland 1984), India (Kumar and
Pandey 2009), the Urals (Fedonkin et al. 2007, p. 172),
China (Liu 1981), and the Long Mynd of the U.K.
(Callow et al. 2011b, Liu 2011). More recently, exam-
ples have also been described from ~ 1 Ga lacustrine
settings in Scotland (Callow et al. 2011a, fig. 10). All
of these occurrences occur in shallow marine to ter-
restrial deposits, and they are often associated with ʻpit
and moundʼ structures (e. g. Salter 1856, Bland 1984),
and microbial fabrics (McIlroy et al. 2005, Callow et
al. 2011a, Callow et al. 2011b, Liu 2011), as is also the
case here (Fig. 2). The biogenicity of ʻArumberiaʼ has
been a subject of much debate (e. g. Brasier 1979,
Bland 1984, McIlroy and Walter 1997, Kumar and
Pandey 2009). However, recent reviews seem to agree
that ʻArumberiaʼ is best explained as an organo-sedi-
mentary structure produced by the interaction of a
shallow water current with microbial mats (e. g. Mc -
Ilroy et al. 2005).
On the same bedding plane, millimetre-scale dis-
coidal impressions are observed (Fig. 2a–b). These are
circular to elliptical in shape, and corresponding pits
were found on the counterpart specimen (which re-
mains in the field). Some pits show a pronounced pim-
ple in their centres, while others show a depression,
giving the overall morphology a ʻdonutʼ shape. These
morphological and taphonomic characteristics make
abiogenic interpretations such as raindrop impres-
sions, gas escape structures, or bubble imprints, high-
ly unlikely. The impressions are directly comparable
with specimens from the Long Mynd of Shropshire,
U.K., described as Medusinites aff. asteroides Sprigg
1949, and Intrites punctatus Fedonkin 1980 respec-
tively (cf. McIlroy et al. 2005), and are similarly pre-
served in positive hyporelief. The majority of the sim-
ple discoidal forms are more similar to the type speci-
mens of Beltanelliformis minutae McIlroy et al. 2005.
Their occurrence in association with ʻArumberiaʼ
(Bland 1984), and their resemblance to similar speci-
mens seen on sandstones in other Neoproterozoic lo-
calities (e. g. Kumar and Pandey 2009), support this
classification (though such simple discoidal structures
are not confined to the Ediacaran Period; e. g. Grazh-
dankin et al. 2012). Furthermore, the co-occurrence of
these discrete impressions is also seen in similar shal-
low-marine to fluvial settings of Ediacaran age in the
Long Mynd, U.K. (e. g. Liu 2011). None of the simple
discoidal specimens from the Moshakov Formation
exhibit concentric or radial structures within their in-
teriors (other than the dimples or depressions), and
they possess surface topographies of
ⱕ 1 mm. Discs
occur in both the ridges and troughs of the sample
surface, and do not appear to have a consistent spatial
relationship with the ʻArumberiaʼ features (Fig.
2a).
3.1.2 Microbial mats
Also occurring at this locality within the Moshakov
Fm., but on different bedding planes to the ʻArumbe-
riaʼ, are several wrinkle structures and sedimentary
features considered to represent the preserved surfaces
of microbial mats (e. g. Fig. 2c). The figured example
shows a 2–3 mm diameter polygonal mesh of sharp-
crested thin ridges, reminiscent of ʻelephant skinʼ tex-
tures (sensu Porada and Bouougri 2007, fig. 2b–c).
Such impressions are common in Neoproterozoic sili-
First report of a newly discovered Ediacaran biota from the Irkineeva Uplift, East Siberia
99
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Alexander G. Liu
100
Fig. 2. Impressions from the Artyugino 1 road-cut section, Moshakov Formation, East Siberia. (a) Specimen K025/1, show-
ing regularly spaced grooves, referred to ʻArumberiaʼ, and small positive relief bumps, on the base of a red sandstone.
(b) Close up image of the bumps, often similar to Beltanelliformis minutae, present on the surface of K025/1. White arrows
show specimens with a positive bump in the centre of the disc, similar to Medusinites aff. asteroides (cf. McIlroy et al.,
2005). Orange arrow indicates a specimen with a central depression, similar to that seen in Intrites punctatus. (c) Elephant
skin microbial mat fabric, observed in the field on the top surface of a bedding plane (this specimen remains in the field).
Scale bars in (a) and (b) = 10 mm, (c) = 50 mm.
eschweizerbart_xxx

ciclastic successions (e. g. Gehling 1999, Steiner and
Reitner 2001), and are part of a suite of surface fea-
tures termed Microbially Induced Sedimentary Struc-
tures (MISS, sensu Noffke et al. 2001). MISS also po-
tentially include biofilms, and wrinkle structures (ex-
hibiting reticulate and linear fabrics amongst others;
Hagadorn and Bottjer 1997, Gehling 1999, Porada and
Bouougri 2007), and are mostly found in shallow wa-
ter depositional environments. The Moshakov Forma-
tion examples are found through a ~ 20 m zone within
the succession, and include not only ʻelephant skinʼ
fabrics, but also more linear ʻKinneyiaʼ-like structures
(cf. Porada et al. 2008). Microbial mat fabrics are also
present within the Aleshino Formation on the tops of
fine-grained dark siltstones (e. g. specimen K036/1).
However, the broad stratigraphic ranges of such struc-
tures mean that, like ʻArumberiaʼ, their usefulness in
determining the precise age of the unit is limited.
3.1.3 Complex discoidal fossils
Potentially the most significant find comes from a
locality within the base of the Moshakov Formation,
on the Nizhnyaya Terya River (Fig. 1b.2). Specimen
K030/4 contains two discoidal impressions, each ex-
hibiting a four- or five-rayed star within their internal
structure (Figs. 3a–c). Both circular impressions are
preserved in negative hypo-relief, on a micaceous grey
siltstone slab, and are 13 mm in diameter (Fig. 3a). The
depressed centres of the discs are smooth, apart from
the four- or five-rayed collection of ridges centred on
the middle of each impression (Fig. 3b–c), and the
discs possess a pronounced lowered rim, 1 mm in
thickness, around their edges. They reach up to 3 mm
in depth, with the internal rays all ~ 1 mm in width, and
up to 4 mm in length. The two specimens both lie in
the centre of a symmetrical ripple. Although the exact
arrangement of internal ridges varies between speci-
mens, the gross morphological similarities between
the discs suggest that the impressions were made by
the same type of object, with variation being poten-
tially taphonomic in nature. Unfortunately, without
additional specimens, it is not possible to investigate
this hypothesis further at the present time.
Concretions or septarian nodules are found in this
region, and occur in underlying strata as 15–20 mm
diameter pyrite concretions. However, these features
were rather evident in the field, and did not possess
pronounced rims as in these specimens. In septarian
nodules, calcite septa are typically positive in relief,
and therefore would produce negative relief ridges on
any external mould – the opposite relationship to that
seen here (Fig. 3a–c). It is possible that similar struc-
tures could be formed by compaction of a domal struc-
ture, with the rays within the dome being cracks or
fractures. The rims of the two specimens, however, are
more difficult to explain abiogenically.
If biological, the five-rayed specimen is comparable
with the Australian Ediacaran organism Arkarua ada-
mi Gehling 1987, which was originally described as
a potential early echinoderm (Gehling 1987), largely
on the basis of its pentameral symmetry. Arkarua was
previously known only from three localities within the
Ediacara Member of the Rawnsley Quartzite, Flinders
Ranges, South Australia, where it ranges from 3.5 to
10.2 mm in diameter (Gehling 1987).
Bergaueria?
One specimen from the Aleshino Formation (K036/2;
Fig. 1b.3) possesses a disc, 19 mm in diameter, which
shows considerably more topographic relief (6 mm)
than any other specimen yet found by us from the
Taseeva Group (Fig. 3d–e). It is preserved in positive
relief on the lower surface of a siltstone bed, and is
similar in several respects to the predominantly
Palaeozoic trace fossil Bergaueria Prantl 1946. The
overall morphology of the impression is cylindrical
rather than conical, with a rounded base and a diame-
ter:height ratio of ~ 3, again consistent with Bergaue-
ria (Pemberton et al. 1988). There is also an obvious
concentricity (Fig. 3d), and one side of the impression
tapers more gently than the others. There is no pre-
served ornamentation or lining to the walls of the
impression, but there is a slight invagination in its
centre, leading us to tentatively suggest that in terms
of biological interpretations, this specimen most simi-
lar to Bergaueria perata Prantl 1946 (Pemberton et al.
1988). Although the specimen was found in float, its
lithological characteristics can be matched directly
with in situ beds of the Aleshino Fm. seen nearby.
Somewhat controversially, Bergaueria has previ-
ously been described from the Stirling Ranges of Aus-
tralia (Cruse and Harris 1994), but a date of
⬎ 1.8 Ga
(Rasmussen et al. 2004), and the fact that those speci-
mens are quite unlike typical Phanerozoic Bergaueria
specimens (sensu Pemberton et al. 1988), would sug-
gest that the Stirling examples are not true examples
of Ber
gaueria. Several further Neoproterozoic Ber -
gaueria occurrences, in Namibia (Crimes and Germs
1982), the Mackenzie Mountains of Canada (Hofmann
and Aitken 1979), and the White Sea of Russia (Fe-
donkin 1981), can be either assigned to other taxa, or
explained as sedimentological structures (Hofmann
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Alexander G. Liu
102
eschweizerbart_xxx

1985; AGL pers. obs.). Bergaueria specimens de-
scribed from the Zigan Formation of the Southern
Urals represent more promising occurrences, but these
are likely to be of very latest Ediacaran age (Grazh-
dankin et al. 2011). While there is currently no con-
vincing Ediacaran body-fossil evidence for actinian
anemones of the kind usually inferred to have created
Bergaueria s. s. impressions in the Phanerozoic (cf.
Alpert 1973), trace fossils from Mistaken Point in
Newfoundland raise the possibility that actinian-like
organisms inhabited Ediacaran palaeoenvironments
c. 565 Ma (Liu et al. 2010). The discovery of this new
specimen associated with nearby Arkarua specimens,
and beneath a demonstrably Cambrian biota seen in
younger units, could suggest a late Ediacaran age for
this specimen, and would generate considerable inter-
est. However, caution should always be exercised with
individual occurrences of this kind. The recognition of
nodules in younger units of the Taseeva Group serves
as a warning against interpreting simple discoidal im-
pressions as biological structures, and at this point in
time we are not prepared to formally assign this spec-
imen to Bergaueria until further, more convincing
specimens can been obtained.
3.1.4 Microfossils
Samples collected from the Aleshino and Chistyakov
Formations were examined for microfossil taxa, and
a range of simple sphaeromorphic acritarchs were
recovered. These include specimens comparable to
Leiosphaeridia crassa, L. jacutica, L. minutissima,
L. tenuissima, and L. spp. (cf. Jankauskas et al. 1989),
along with Synsphaeridium sp. cell clusters. All of
these taxa are long-ranging, being found in rocks of
Mesoproterozoic to Cambrian age worldwide, and
therefore they are of limited use for biostratigraphic
correlation.
3.2 Fossils from the Irkineeva River
The successions examined in the vicinity of the Irki-
neeva River contain rocks purported to be considerably
older than those so far discussed. They belong to the
undifferentiated Kartochka and Alad’in Formations
of the Sukhoy Pit Group (a.k.a. Bolshoi Pit Group;
Khomentovsky 2007), which have previously been as-
signed to the Kerpylian strata of the Middle Riphean
(Kavitsky 2005, Gallet et al. 2012; Fig. 1c). The
Sukhoy Pit Group comprises silty shales, sandstones,
and carbonates, considered to represent shallow ma-
rine regressive cycles (Nozhkin et al. 2011). Our field
studies show that the Kartochka Formation is repre-
sented mainly by grey-green to pink, thinly laminated
siliciclastic siltstones alternating with lenses and thin
beds of limestones and dolostones. Hummocky cross-
stratification suggests deposition above storm wave
base (Gallet et al. 2012). Beds of intraformational car-
bonate breccia occur in the upper part of the succes-
sion. No macrofossils have previously been described
from this unit, but rare occurrences of the stromatolite
Malginella have been reported (Rund qvist and Mitro-
fanov 1992). The Sukhoy Pit Group also outcrops
along the Yenisei Ridge, and may show similarities
with the potentially correlative Kerpyl Regional Stage
of the Turukhansk Uplift some 400–500 km to the
North (Chumakov and Semikhatov 1981), and the
Uchur-Maya Region far to the East (Gallet et al. 2012).
3.2.1 Discoidal fossils
The most notable fossils discovered by us in these beds
comprise relatively large, simple discs with smooth in-
terior surfaces, free from concentric, radial or invagi-
nated markings, and bounded by a raised (by no more
than 1 mm topographic relief) rim (Fig. 4). Such spec-
imens, found on the top surface of a single bedding
plane, seem to have undergone remarkably little tec-
tonic deformation, with several discoidal impressions
approaching an almost perfectly circular outline
(Figs. 4b, 4d). Interestingly, two specimens from the
same bedding plane are observed to have strikingly
ovate morphologies (Fig. 4b; these specimens remain
in the field; see Fig. 1b.4 for locality information). Of
the specimens collected, two complete circular speci-
mens are 70 and 81 mm in diameter respectively
(Fig. 4b–c), with an additional fragmentary specimen
being 85 by 66 mm in maximum and minimum dia -
First report of a newly discovered Ediacaran biota from the Irkineeva Uplift, East Siberia
103
Fig. 3. Specimens from the Taseeva Group, Nizhnyaya Terya River, East Siberia. (a) Specimen K030/4, showing two small
discs with internal, four- or five-fold structure, similar to Arkarua adami. From the Moshakov Fm. (b–c) Close-up images
of the two Arkarua specimens figured in (a). Insets show digitised overlays of the fossils, emphasising the internal symme-
try within each specimen. (d–e) Specimen K036/2, showing a high-relief discoidal impression similar to Bergaueria cf. per-
ata within a mudstone, in plan and lateral view respectively. The beige colouration is a modern lichen overgrowth. From the
Aleshino Formation. All scale bars = 10 mm.
eschweizerbart_xxx

meter. The variation observed in discoidal morpholo-
gy, amongst specimens in close proximity, suggests
that the original impressions had highly variable ellip-
ticities.
The Sukhoy Pit discs bear some similarities, particu-
larly their flat and featureless interiors, to several spec-
imens described from the Neoproterozoic Miette Group
(Windermere Supergroup) of the Rocky Mountains;
namely Nimbia occlusa (Hofmann et al. 1991, fig. 6F),
Beltanella sp. cf. B. grandis (Hofmann et al. 1991,
fig. 6G), and “Dubiofossil A” (Hofmann et al. 1991,
fig. 6I). These macroscopic ʻTwitya discs’ (named after
the formation from which they are described) are small-
er than those described here, but are likely to be at least
pre-Marinoan (i. e. pre-Ediacaran) in age (Hofmann et
al. 1990). Somewhat older discoidal specimens of sim-
ilar morphology exist in Kazakhstan (Meert et al. 2011).
The Kazakh fossils are again considerably smaller than
Alexander G. Liu
104
Fig. 4. Simple discoidal fossils from the upper part of the Sukhoy Pit Group, Irkineeva River, East Siberia. (a) Field local-
ity, with the bed containing the discoidal fossils arrowed. (b) Specimen K041/5, Nimbia occlusa. (c) Two elliptical (uncol-
lected) specimens. (d) Unlabelled specimen, showing a simple spherical discoidal impression, assigned to Nimbia occlusa.
Scale bars: (b) and (d) = 10 mm, (c) = 50 mm.
eschweizerbart_xxx

those seen in East Siberia (only reaching about 20 mm
diameter; Meert et al. 2011), but they occur in sections
considered to be pre-Sturtian in age, i. e., ⬎ 750 Ma
(Levashova et al. 2011, Meert et al. 201
1). Additional
examples of simple discoids documented from such
Proterozoic successions are discussed in Grazhdankin
et al. 2012. A precedent therefore exists for simple
macroscopic discoidal forms in rocks of pre-Ediacaran
age, though existing dates for units from the Sukhoy
Pit Group are not sufficiently accurate to geochrono-
logically constrain them (701–1390 Ma; K-Ar dating
of Gutina 2007).
These large discoidal fossils are here assigned
to Nimbia occlusa (Fedonkin 1980), a species also
known from the White Sea of Russia, the Dniester
River Basin of Ukraine, and the Mackenzie Mountains
of north-western Canada (Fedonkin et al. 2007 and
references therein). For the most part, the term Nimbia
has been applied to forms that are broadly circular in
outline with a flat, featureless interior and a slight
raised rim or depression (e. g. Hagadorn and Waggoner
2000), with few taxonomic connotations. The mor-
phology of Nimbia is very unlike that of known Edi-
acaran frond holdfasts, and we do not consider Nimbia
to represent such a feature. Simple and annulated
Neoproterozoic discoidal fossils have previously been
suggested to represent preserved microbial colonies
(Grazhdankin and Gerdes 2007). We feel that the spec-
imens described herein are also likely to represent mi-
crobial colonies, due to their extremely simple internal
structure, low surface relief, and considerable varia-
tion in gross morphology within single populations
(Fig. 4c). There is currently no additional positive
evidence for the preservation of microbial fabrics or
filaments on this particular bedding plane, though
Kinneyia-like mat fabrics were observed by us from
the Kartochka Fm. elsewhere.
3.2.2 Microfossils
A well-preserved acritarch assemblage of simple
leiosphaerid taxa was recovered from two samples
from the Kartochka and Alad’in Formations, compris-
ing specimens similar to Leiosphaeridia crassa, L. ja-
cutica, L. minutissima, L. tenuissima, L. spp., and Syn-
sphaeridium sp. These are long-ranging acritarchs,
exhibiting ranges spanning Middle Riphean to Late
Vendian ages (Golubkova and Raevskaya 2005). Giv-
en the uncertain extent of taphonomic variation with-
in Proterozoic acritarch assemblages, we cannot con-
strain the age of these successions further until more
characteristic acritarchs can be confidently identified.
4. General discussion
Correlation of many Siberian sections to the Neo -
proterozoic stratigraphy outlined by the International
Stratigraphic Subcommission (Gradstein et al. 2012),
remains largely unresolved in the geological literature.
Although many localities on the periphery of the Siber-
ian Platform exhibit a similar gross stratigraphy (i. e.
mixed Riphean sedimentary units overlain uncon-
formably by Vendian-Cambrian clastic successions),
the relative ages assigned to many of these localities
can differ widely (e. g. Kochnev 2002, Mel’nikov et al.
2005, Sovetov et al. 2007). The fossils described from
the Irkineeva Uplift may enable us to better constrain
the ages of the various units found in the region.
The youngest fossil-bearing unit observed in this
study, the Ostrov Formation, is considered to be of
Nemakit Daldynian age (Early Cambrian of the Inter-
national Stratigraphic Chart), on the basis of the small
shelly fossil Tiksitheca sp. (characteristic of the Purel-
la antiqua Zone), and other shell fragments found
within its type section in the southern Yenisei Range
(Kochnev and Karlova 2010). However, the precise
age of the Redkolesnaya Formation, to which the Cy-
clomedusa found by Chechel’ (1976) has since been
assigned (Kochnev 2002), remains to be determined.
Cyclomedusa specimens from the Perevalok Forma-
tion of the Central Urals have been used as evidence
to suggest a Redkino or younger age (Marusin et al.
2011), and we concur that, based on macro-fossil
evidence and stratigraphic position, the Redkolesnaya
Fm. is likely to have been deposited in the latest Edi-
acaran to earliest Cambrian Periods.
Previous attempts to correlate the Taseeva Group
with other Siberian units have provided multiple inter-
pretations. Mel’nikov et al. (2005) consider the Tasee-
va Group to be lower Vendian/upper Baikalian in age
(Upper Cryogenian to Lower Ediacaran), and correlate
it with the Vanavara and Oskoba Formations of the
Siberian interior. However, a study correlating the
Taseeva Group of the southern Yenisei Ridge with
successions around the south and west of the Siberian
craton suggests a younger, early to mid-Ediacaran age
(Sovetov et al. 2007). The absence of diamictite hori-
zons beneath the Chistyakov Fm. in the Yenisei area
precludes a simple lithostratigraphic solution to this
problem. Furthermore, even though the Yenisei units lie
only a relatively short geographic distance (~ 300 km)
from the Irkineeva Uplift, they may not stratigraphical-
ly correlate at a formational level. Some authors do not
recognise the Moshakov Formation, instead replacing it
First report of a newly discovered Ediacaran biota from the Irkineeva Uplift, East Siberia
105
eschweizerbart_xxx

with the Grebenʻ and Veselaya Formations, which lie
conformably between the Chist ya kov and Redkoles -
naya Formations (Sovetov et al. 2007; though these
alternative terms are not widely utilised).
The Moshakov Formation macrofossil assemblage
we describe exhibits some similarities with the late
Ediacaran sections of the Flinders Ranges in Australia,
at least in terms of the depauperate biota currently
recognised (Arkarua adami, ʻArumberiaʼ, and Belta -
nel li formis minutae). In Australia, Arkarua is found
amongst diverse and morphologically disparate
palaeocommunities containing iconic Ediacara-type
organisms such as Tribrachidium, Dickinsonia, Par-
vancorina and Cyclomedusa (Gehling 1987). The pre-
liminary documentation of the latter taxon from the
Irkineeva Uplift (Chechel’ 1976), supports the possi-
bility that there may be significant potential for further
palaeontological discoveries in this region. On the ba-
sis of crude biostratigraphic correlation with Australian
sections (themselves correlated to East European sec-
tions on the White Sea coast), the fossil assemblage
we report suggests that sections of the upper Taseeva
Group are latest Ediacaran in age (~ 555–549 Ma;
Martin et al. 2000), and therefore considerably younger
(by anything between 60 and 190 million years) than
the dates previously reported for the Group would im-
ply (740–617 Ma; Gutina 2007). Such an interpreta-
tion would suggest at least a broad temporal correlation
with other Russian sites containing Ediacaran macro-
organisms, such as the Ustʼyudoma Formation of the
Yudoma-Maya region, and the Khatyspyt Formation
of the Olenek Uplift (Grazhdankin et al. 2008), both
of which have previously been correlated with the Red-
kino horizons of the East European Platform (e. g. the
White Sea; Mel’nikov et al. 2005).
Fossils described from the Oselok Uplift of the
Sayan region, and compared to Dickinsonia, Pteri-
dinium, Tirasiana and Nemiana (Sovetov and Komlev
2005, fig. 10), have previously provided evidence for
an Ediacaran age for both that unit and other correla-
tives (including both the Chistyakov and Aleshino
Formations of the Yenisei ridge; Sovetov et al. 2007).
However, those specimens are not accepted by the
present authors as examples of the taxa they are
claimed to represent; the figured material in Sovetov
and Komlev (2005) seems more akin to simple discs
or sedimentological structures.
On the basis of the few collected specimens we have
from the Irkineeva River, we propose a Late Ediacaran
age for the Taseeva Group, though we acknowledge
that further palaeontological and stratigraphic research
is required to convincingly confirm this, and we en-
courage such future endeavours.
The older Sukhoy Pit Group has previously been
assigned to the mid-Riphean (Mel’nikov et al. 2005). It
is considered to be intruded by ca. 850 Ma granites on
the north-eastern Yenisei Ridge (Sovetov et al. 2007),
but dating of the Garevka granite leaves open the
possibility that the Kartochka and Alad’in Formations
may be younger than ~ 752 Ma (U-Pb TIMS date in
Verni kovsky et al. 2003). A borehole drilled and
analysed along the Angara River within the southern
Yenisei Range, 50–100 km west of the Irkineeva sites,
finds the same Sukhoy Pit Group units (Kochnev et al.
2007), and may prove useful for future sedimentologi-
cal facies analyses and geochronological correlation.
Interestingly, correlative units of the Kamo Series,
Baykit Anticlise (Nagovitsin et al. 2010), and the
Debengde Fm. of the Olenek Uplift (Stanevich et al.
2009), both contain rich microfossil assemblages
bearing the Riphean taxon Tappania. The Kartochka
and Alad’in units sampled herein, in contrast, contain
no definitively Riphean palynological taxa, instead
bearing a long-ranging assemblage of sphaeromorphic
taxa, and making age-determination inconclusive. The
Nimbia occlusa specimens we describe from the upper
part of Sukhoy Pit Group may compare favourably with
some Ediacaran discoidal impressions, but are most
similar in their morphologies to macroscopic discoidal
fossils (mostly considered to record microbial colonies)
described from multiple pre-Ediacaran localities (sum-
marised in Grazhdankin et al. 2012). If the Nimbia
specimens we report are microbial colonies, this would
provide further support for a very broad stratigraphic
range for such specimens, perhaps back to the Palaeo-
proterozoic (Rasmussen et al. 2004). However, consid-
ering previous stratigraphic studies in this region, we
feel that until further evidence becomes available, it is
not possible to classify the Sukhoy Pit Group as any-
thing other than Meso- to Neoproterozoic.
5. Conclusions
The discovery of probable Ediacaran fossils in rocks
from the Irkineeva Uplift adds to the growing list of
Ediacaran fossil localities worldwide. The presence of
impressions typical of latest Ediacaran assemblages,
namely Arkarua adami, Beltanelliformis, and the late
Neoproterozoic organo-sedimentary structure ʻArum-
beriaʼ, suggest that the shallow marine Moshakov For-
mation of the Taseeva Group is late Ediacaran in age,
Alexander G. Liu
106
eschweizerbart_xxx

and thus tens of millions of years younger than previ-
ously thought. The unit may contain the first known
occurrence of the problematic five-rayed fossil Arkarua
outside of Australia. Microfossil specimens from the
Aleshino and Chistyakov Formations are broadly con-
sistent with a late Ediacaran age, but the putative
Bergaueria? specimen we describe ideally requires
validation via additional discoveries. The palynological
assemblages and simple large discoidal fossils from
the Kartochka Formation (the upper part of Sukhoy Pit
Group), which has previously been described as Middle
Riphean, are not currently sufficient to suggest anything
other than a Meso- to Neoproterozoic age. If a mid-
Riphean age were to be confirmed for the Sukhoy Pit
Group, the discoidal specimens we describe add to a
growing list of pre-Ediacaran simple discoidal impres-
sions (cf. Grazhdankin et al. 2012 and references there-
in). Further field exploration of the Irkineeva Uplift
would be highly beneficial, both to constrain the
geochronology of these units, and to investigate the
taxonomic diversity of the Ediacaran biota in this
region.
These finds demonstrate the palaeontological poten-
tial of the remote Irkineeva Uplift region. It is hoped
that as palaeontological records from the Siberian Plat-
form increase in number, accurate correlation of Pro-
terozoic units can be achieved across Russia (i. e. with
the Vendian sections of the White Sea and Urals, which
are themselves undergoing significant study and revi-
sion at present; e. g. Grazhdankin et al. 2011, Marusin
et al. 2011), and beyond. Such a synthesis would bene-
fit not only our understanding of the evolution of life
during the Ediacaran Period, but also research into min-
eral and hydrocarbon deposits across Eastern Siberia.
Acknowledgements. Field materials presented in this
paper were collected during the CASP expedition to East
Siberia. This work was supported by CASP sponsors. AGL
is grateful to Girton College, Cambridge, and the Cambridge
Philosophical Society, for the financial support of a Henslow
Research Fellowship. The suggestions and comments of
Sören Jensen and two anonymous reviewers have greatly
improved this manuscript. Specimens referred to in the text
are part of the sample collections from East Siberia, stored
at CASP, University of Cambridge, UK.
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