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Ammonite assemblages in the Lower to Upper Kimmeridgian boundary interval (Cymodoce to Mutabilis zones) of Tatarstan (central European Russia) and their correlation importance

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For the first time upper part of the Cymodoce Zone sensu lato (mostly Askepta Subzone) of the Lower Kimmeridgian and the Mutabilis Zone of the Upper Kimmeridgian are described in detail from the Russian Platform. The most fully developed ammonite succession, which includes Boreal, Subboreal and Submediterranean faunal elements, is recognized in southern Tatarstan (Tarkhanovskaya Pristan and Memei sections). The lowermost assemblage, consisting of late representatives of Rasenia and Zonovia was found in the Memei section only (cf. Hantzpergue et al. 1998). Well above, numerous Submediterranean Crussoliceras occurrences were discovered in the upper part of the Cymodoce Zone of the whole area, whereas younger assemblages yielded Boreal Amoebites and/or Subboreal Rasenioides followed by Aulacostephanoides with some addition of Aspidoceras and Orthaspidoceras above. The aulacostephanid genus Zenostephanus is recorded in the studied region for the first time. Significant lateral variability of the deposits of the Cymodoce and Mutabilis zones in thickness and completeness through a small distance in South Tatarstan along with other evidence suggests the strong influence of synsedimentary tectonics on sedimentation at the Early to Late Kimmeridgian transition of this region. Mass immigration of the Submediterranean ammonites Crussoliceras into the Subboreal Russian Sea resulted in their short-time dominance over a wide area. The Crussoliceras ammonites are recognized also in the condensed sections of the Moscow and Kaluga areas in the north, and their re-deposited records are known (along with uncommon Zenostephanus, Aulacostephanoides and Amoebites) from the basal phosphorite band of the Middle Volgian of the Unzha river (Kostroma area). This “Crussoliceras event”, which is well-recognized in Submediterranean areas, as well as the subsequent expansion of Zenostephanus, both correspond to a sea-level high-stand, which resulted in faunal mixing of ammonites indicative of different bioprovinces. They provide key correlative levels which can be recognized around the Lower/Upper Kimmeridgian boundary, especially in the ecotone area of the Russian Sea. These levels include also occurrences of Crussoliceras, Rasenoiodes and rare Amoebites of the kitchini group in the Askepta Subzone, of Aulacostephanoides spp. along with Amoebites peregrinator and Zenostephanus sachsi in the lower part of the Mutabilis Subzone as well as of Aspidoceratidae and Aulacostephanoides in higher parts of this subzone, followed by Orthaspidoceras. At least six successive ammonite assemblages can be recognized through the studied part of the Kimmeridgian, providing interregional correlation with Submediterranean and Boreal sections
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Ammonite assemblages in the Lower to Upper Kimmeridgian
boundary interval (Cymodoce to Mutabilis zones) of Tatarstan (central
European Russia) and their correlation importance
Mikhail A. Rogov, Andrzej Wierzbowski, and Elena Shchepetova
With 13 figures
Abstract: For the first time upper part of the Cymodoce Zone sensu lato (mostly Askepta Subzone) of
the Lower Kimmeridgian and the Mutabilis Zone of the Upper Kimmeridgian are described in detail
from the Russian Platform. The most fully developed ammonite succession, which includes Boreal,
Subboreal and Submediterranean faunal elements, is recognized in southern Tatarstan (Tarkhanovs-
kaya Pristan and Memei sections). The lowermost assemblage, consisting of late representatives of
Rasenia and Zonovia was found in the Memei section only (cf. Hantzpergue et al. 1998). Well above,
numerous Submediterranean Crussoliceras occurrences were discovered in the upper part of the
Cymodoce Zone of the whole area, whereas younger assemblages yielded Boreal Amoebites and/
or Subboreal Rasenioides followed by Aulacostephanoides with some addition of Aspidoceras and
Orthaspidoceras above. The aulacostephanid genus Zenostephanus is recorded in the studied region
for the first time. Significant lateral variability of the deposits of the Cymodoce and Mutabilis zones
in thickness and completeness through a small distance in South Tatarstan along with other evidence
suggests the strong influence of synsedimentary tectonics on sedimentation at the Early to Late Kim-
meridgian transition of this region. Mass immigration of the Submediterranean ammonites Crusso-
liceras into the Subboreal Russian Sea resulted in their short-time dominance over a wide area. The
Crussoliceras ammonites are recognized also in the condensed sections of the Moscow and Kaluga
areas in the north, and their re-deposited records are known (along with uncommon Zenostephanus,
Aulacostephanoides and Amoebites) from the basal phosphorite band of the Middle Volgian of the
Unzha river (Kostroma area). This “Crussoliceras event”, which is well-recognized in Submediter
-
ranean areas, as well as the subsequent expansion of Zenostephanus, both correspond to a sea-level
high-stand, which resulted in faunal mixing of ammonites indicative of different bioprovinces. They
provide key correlative levels which can be recognized around the Lower/Upper Kimmeridgian
boundary, especially in the ecotone area of the Russian Sea. These levels include also occurrences
of Crussoliceras, Rasenoiodes and rare Amoebites of the kitchini group in the Askepta Subzone, of
Aulacostephanoides spp. along with Amoebites peregrinator and Zenostephanus sachsi in the lower
part of the Mutabilis Subzone as well as of Aspidoceratidae and Aulacostephanoides in higher parts
of this subzone, followed by Orthaspidoceras. At least six successive ammonite assemblages can be
recognized through the studied part of the Kimmeridgian, providing interregional correlation with
Submediterranean and Boreal sections.
Key words: Kimmeridgian, Askepta Subzone, Mutabilis Zone, Russian Platform, biostratigraphy,
palaeobiogeography, Crussoliceras migration event, Zenostephanus.
1. Introduction
Changes in ammonite assemblages during the latest
Early Kimmeridgian and the beginning of the Late
Kimmeridgian in the northern shelf of the Tethys in
Western and Central Europe have been the subject of
several studies. They indicated an abrupt appearance
of Subboreal ammonites of the family Aulacostepha-
©2017 E. Schweizerbart’sche Verlagsbuchhandlung, Stuttgart, Germany www.schweizerbart.de
DO I : 10 .1127/ n jgpa /2017/ 0 675 007 7-7 74 9/2017/0675 $ 6. 2 5
N. Jb. Geol. Paläont. Abh. 285/2 (2017), 161–185 Article
Stuttgart, August 2017
E
eschweizerbart_xxx
162 M.A. Rogov et al.
nidae – mostly of the genus Rasenioides in the north,
and the time-corresponding appearance of new Tethyan
representatives of the family Ataxioceratidae – such
as Crussoliceras and Garnierisphinctes in the south,
during the latest Early Kimmeridgian. These changes
which have a fundamental significance for stratigraphy
and palaeogeography were also related to marked facies
transformations – mostly the appearance of the “facies
virgulien”, and similar siliciclastic and lumachelle de-
posits over wide areas of Europe (e.g., Birkelund et al.
1983; Hantzpergue 1989, 1995; Matyja & WierzBoWski
2000; enay et al. 2014, and earlier papers cited therein).
The succeeding changes in ammonite assemblages dur-
ing the early Late Kimmeridgian showed, on the other
hand, a marked northward distribution of Tethyan am-
monites – mostly Aspidoceratidae – which ranged so
far north as eastern England (see Geyssant 1994) and
the Middle Volga area (Pavlow 1886). These episodes
of maximum distribution of Submediterranean and/or
Subboreal ammonites at the Early/Late Kimmeridgian
transition are commonly interpreted as a consequence
of transgressive impulses related to sea-level rises (e.g.,
Marques & olóriz 1992; Hantzpergue 1995).
This study presents the results of field-investiga-
tions at Memei and Tarkhanovskaya Pristan on the right
bank of the Volga river of the Kuybyshev reservoir in
southern Tatarstan (central European Russia) conducted
by the authors in August, 2010 and 2011. The study
revealed the presence of an uppermost Lower Kim-
meridgian to lowermost Upper Kimmeridgian succes-
sion with abundant ammonites. The succession may
be correlated also with that described previously by
Hantzpergue et al. (1998) from Mimei (Memei herein,
as this is more correct transliteration of Russian «Ме-
мей», nearby village), which also yielded some late
Early Kimmeridgian ammonites, unfortunately non-
illustrated. Because the stratigraphical interval in ques-
tion has been so far generally poorly known in Euro-
pean Russia being mostly referred to the occurrence
of the Aspidoceras – fauna in the Ulyanovsk (formerly
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Fig. 1. Locality map. A – Distribution of localities with ammonites of the Lower/Upper Kimmeridgian transitional strata
in European Russia. Open stars: sections in which re-deposited ammonites of the Mutabilis Zone were found; filled stars:
sections yielding in situ ammonite records. Numbers refer to the following sections: 1 – Ignatievo, 55º36’56” N, 36º29’20”
E; 2 – Serensk, 54º18’36” N, 35º33’11” E; 3 – Voskresensk, mine no.9, 55º21’24” N, 38º51’21” E; 4 – Kimry, 56º53’20” N,
37º27’07” E; 5 – Koprino, 58º03’50” N, 38º20’16” E; 6 – Unzha river, few sections; 7 – southern Tatarstan, few sections (see
Fig. 1B for details); 8 – Stoilensk open mine, 51º15’45” N; 37º43’40” E. B Details of the localities in the Southern Tatarstan,
studied in detail. 1 – Memei 1; 2 – Memei 2; 3 – T5; 4 – locality with loose Crussoliceras (TP); 5 – T3, 4; 6 – T1; 7 – T2.
eschweizerbart_xxx
Ammonite assemblages in the Lower to Upper Kimmeridgian boundar y interval 163
Simbirsk) area by p
avloW
(1886), and poorly known
occurrences from abandoned sites in the Yaroslavl re-
gion (nikitin 1881, 1884), the new material offers the
possibility of wider recognition of the ammonite as-
semblages and their palaeogeographical interpretation
in relation to those of Western and Central European
areas (Fig. 1A). The preliminary results of the study
were presented by the authors during the 9
th
Jurassic
Congress in Jaipur, India in 2014 (rogov et al. 2014).
Besides the ammonites from Tatarstan discussed
here (collected by the authors), and including those
collected by vladiMir efiMov (Undory), some addi-
tional material was considered in this study – such as
that collected in the Moscow area (1990-1993, 2011)
and the Kaluga region (1999, 2007) by the first author
(M.R), and donated by denis gulyaev (Yaroslavl), as
well as a
ndrey
s
Hkolin
(Moscow). Figured specimens
are stored in State Vernadsky Geological Museum,
Moscow (SGM) and Museum of Geological Faculty,
University of Warsaw (MWG UW ZI/80). Specimens
described by S.N. nikitin (1881, 1884) are kept in the
Central Geological-Prospecting Museum, Saint-Peters-
burg (CNIGR).
Analyses determining the СаСО
3
and C
org
content
were performed by elena sHcHepetova (Geological
Institute of RAS); she also improved the descriptions
of the rocks occurring in the sections T1, T3 and T4 as
based on investigation of thin sections.
2. Stratigraphy
2.1. Description of the sections
The sections showing particular parts of the succession
studied were easily accessible in the steep slopes on the
right hand side of the Volga valley east of Tarkhanovs-
Fig. 2. Memei 2 locality – general view.
eschweizerbart_xxx
164 M.A. Rogov et al.
kaya Pristan during the summer season of 2011. They
were, however, only temporary in character, as shown
by observations in 2015, when almost all the sections
described herein appeared completely destroyed by
landslides. Five sections described as T1, T2, T3, T4
and T5 (see Figs. 1B, 2, 5) show the succeeding parts
of the succession studied.
Section T1 begins at the water-table and shows Up-
per Jurassic deposits about 3.20 m in thickness. These
deposits rest on Middle Jurassic non-calcareous silty
dark grayish-green clay (0.68% СаСО3), with thin
laminations of yellowish-grey silty to sandy laminae
(1-5 mm); the lamination is not observed in the upper-
most part of the deposits which is heavily bioturbated.
The following members have been distinguished above
(from the base):
Member 1 – 1.4-1.5 m thick – calcareous, light
greenish-grey clay and marl (26.90-45.29% СаСО
3
),
with glauconite, semi-rounded quartz grains and frag-
ments of ferruginous oolites. In the lower part of the
member the clays are characterized by their darker
colour and the presence of numerous Chondrites bur-
rows. The base of the bed is characterized by the pres-
ence of phosphorite conglomerate (0.05-0.07 m), which
consists of angular fragments of phosphorites, some
of them containing ammonite fragments (identified as
Cadoceras). Such pieces of phosphorite are also rela-
tively abundant some 10-15 cm above the phosphorite
layer; moreover there occur ferruginous concretions,
and fragments of various fossils (fragments of large
bivalves, belemnite rostra, fragments of large ammo-
nites including that of Crussoliceras); the following
ammonites have been identified in the overlying part
of the member 1: Crussoliceras atavum (s
cHneid
) (at
0.35 m above the base) (Fig. 6A), C. cf. atavum (0.85 m
above the base), C. lacertosum (fontannes)/cf. lacerto-
sum (fontannes) (0.15 and 0.55 m above the base, Fig.
10G), and several fragments of inner whorls possibly
representing the genus Crussoliceras;
Member 2 – about 1.8 m thick – is composed of
calcareous greenish-grey silty clay (22.59-26.67%
СаСО3), with numerous thin pyritized ichnofossil
tubes with glauconite grains. At the base of the mem-
ber a thin (up to 0.1 m) band of greenish-grey dark clay
(1.04-2.00% С
org
; 8.29-24.51% СаСО
3
) with numerous
yellowish bodies of gypsum and iron hydroxides could
be recognized. Pyritized ammonites occurring in the
lower part of this member are generally of small size,
but some larger specimens in the clays were encoun-
tered as well; the findings include: Crussoliceras cf.
atavum (scHneid) (0.3 m above the base), Crussoliceras
lacertosum (fontannes) (0.45 m above the base) (Fig.
6B), C. cf. lacertosum (base of member 2), and several
fragments of inner whorls possibly representing the ge-
nus Crussoliceras in the whole member; also present
were Amoebites kitchini (s
alfeld
) (0.25 m above the
base) and A. cf. kitchini (0.55 m above the base) (Fig.
13B, C).
Section T2 was situated about 500 m east of sec-
tion T1. The deposits are dark clays and marls about 2
meters in thickness. These are of the ʻFleckenmergelʼ-
type calcareous marls in their upper part and show the
presence of numerous burrows. Here, a several cen-
timeters thick level with common ammonites (partly
pyritized) and rare phosphorites occurs. The identified
ammonites are mostly small-sized representatives of
the genus Aulacostephanoides such as Aulacostepha-
noides eulepidus (scHneid) and A. cf. desmonotus (op-
pel
) (Fig. 12I, R); a single specimen of Eurasenia or
heavily ornamented Involuticeras (Fig. 12P) and two
specimens of Amoebites kitchini (s
alfeld
) (Fig. 13L)
were also found here.
Sections T3 and T4 (Fig. 3) located at about one
hundred meters west of section T1 included deposits
about 14-15 m in thickness – from the base: calcareous
greenish-grey platy clay (7.95-15.78% СаСО
3
), show-
ing an alteration of light highly bioturbated clay and
darker clay with abundant subhorizontal ichnofossil
tubes (member 3, nearly 5 m thick). Small (1-2 cm)
phosphorite concretions occur in some levels. These
deposits could represent at their base the uppermost
part of member 2 from locality T1, but because there
is no direct correlation possible between sections T1
and T3, they are distinguished as belonging to a sepa-
rate rock-unit – member 3. The deposits of member 3
resemble those of member 5, but are characterized by
a bigger size of silt particles and the constant presence
of glauconite. Calcareous bluish-grey clays and silty
marls (16.57-23.27 % СаСО3), highly bioturbated and
massive, with occasional pyrite and phosphorite con-
cretions, represent member 4, about 5-5.5 m thick. The
lower part of the member, which has been sampled in
the T3 section, is characterized by its higher СаСО
3
content (28.03-31.21 %); a similar lithological character
is also present in the upper part of the member. These
deposits are overlain by calcareous greenish-grey well-
bedded silty clay (9.19-13.05 % СаСО3), belonging to
member 5 (1.5-1.6 m thick). Small (2-3 cm) pyrite and
phosphorite concretions occur on some levels. At the
top of section T4, calcareous finely-laminated black
shales (member 6, up to 1.2 m thick) occur which are
dark-grey to brownish in colour (9.3%-12.4% Сorg;
eschweizerbart_xxx
Ammonite assemblages in the Lower to Upper Kimmeridgian boundar y interval 165
11.92%-14.87% СаСО
3
). Flattened pyrite concretions
up to 10-15 cm in diameter occur in the upper part of
the shale bed. Fossils are mainly represented by the
bivalve Aulacomyella and gastropods; ammonites (As-
pidoceras sp. indet., Aulacostephanoides sp. ind. (Fig.
12C-E) are very rare and were collected from loose
blocks only. The sections T4 and T5 were described in
detail by sHcHepetova & rogov (2013, fig. 1 – where
the succession of their locality 1 corresponds to the
deposits of sections T1, T3 and T4 as shown herein),
who also provided results of Rock-Eval analysis of or-
ganic matter derived from black shales at the top of
the succession.
The identified ammonites from sections T3 and
T4 include: an assemblage composed of Crussoliceras
spp. from the lower part of the light-gray marls (section
T3) of member 3 (partly found in the rubble; Fig. 9A,
C-F), followed by an assemblage of Rasenioides spp.
The partially preserved imprints of a finely ribbed car
-
dioceratid ammonite, strongly resembling Amoebites
(?) kapffi (o
ppel
) (Fig. 13A) and Amoebites sp. were
collected at the level with Rasenioides, 1.9 m above the
base of the section T3. Ammonites of the genus Aula-
costephanoides (Fig. 12F, G) and small-sized Amoe-
bites peregrinator rogov (Fig. 13D, E; see description
in r
ogov
2016) occur in the upper part of the light-grey
marls of member 3, and the lower part of member 4
(section T3). The characteristic species Zenostephanus
sachsi (MesezHnikov), the index-species of the hori-
zon, well-recognized through the different parts of the
Arctic (i.e. Franz-Josef Land, Spitsbergen, Khatanga
depression, Western Siberia and possibly British Co-
lumbia – see rogov 2014, 2016; rogov & poulton
2015) was found in the upper part of the marly unit of
member 4 and in the rubble (section T4; Fig. 13G-I, K).
A still younger assemblage of ammonites composed of
Aulacostephanoides and Aspidoceras sp. indet. (Fig.
12A, B) is known from marls in a higher part of section
T4 and it occurs up to the black shale unit at the top of
the succession studied (see rogov et al. 2014).
Section Memei-2 (Figs. 2, 5) is located slightly east-
wards from the Memei section (distinguished herein as
Memei-1) as described by Hantzpergue et al. (1998); it
was studied during the field season of the year 2010,
when it was easily accessible due to the very low water
level in the Kuybyshev reservoir. The succession given
below is exposed here (from the base).
Member 1 – calcareous light-grey to white if weath-
ered clay (1 m thick), strongly bioturbated (especially at
the top of the bed and in its middle part), with phospho-
rite concretions 0.7 m below the top; numerous Crus-
soliceras lacertosum (fontannes) (Figs. 9B, 10C, F)
were found between 0.25 and 0.55 m below the top;
in addition one indeterminable Amoebites sp. ind. has
been collected 0.3 m below the top of this member.
This member correspondings to the upper part of bed
Ta 1, bed Ta 2, and bed Ta 3 of Hantzpergue et al.(1998)
where only the presence of indeterminate “perisphinc-
tids” in bed Ta 2 has been mentioned. A few bands
of grey and light grey clays without macrofossils with
a total thickness 1.65 m could be recognized above
(member 2). These beds are overlain by member 3 -
dark-grey to brown black shales (0.4 m), with numerous
Aulacomyella bivalves on the bedding planes, while
ammonites (indeterminable juvenile cardioceratid and
Aspidoceras sp. indet.) are very uncommon.
Between the Tarkhanovskaya Pristan and Memei
sections the Crussoliceras-bearing beds are not
exposed but a few big-sized Crussoliceras atavum
(s
cHneid
) were found loose in rubble (locality TP; Figs.
7A, 8A).
Fig. 3. Tarkhanovskaya pristan T3-T4 localities – general
view.
eschweizerbart_xxx
166 M.A. Rogov et al.
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Fig. 4. Ammonite distribution and stratigraphical correlation of the sections
T1-T4 at the Tarkhanovskaya Pristan.
eschweizerbart_xxx
Ammonite assemblages in the Lower to Upper Kimmeridgian boundar y interval 167
An additional small section (T5) is located be-
tween this locality with Crussoliceras found loose and
the Memei sections discussed above. Here, above the
Middle Jurassic cliff of Bathonian silts (~ 4-5 m high),
calcareous greenish-grey clays (2 m thick) appear. The
clays yield septarian limestone concretions occurring
at 0.7 m above the base of the unit. Such concretions
are unknown from units exposed at localities T1-T4
of Tarkhanovskaya Pristan and Memei-1 and 2. The
septarian concretions yielded Orthaspidoceras liparum
(oppel) (Fig. 11B).
Some 1.5 km northwards of the T2 section at Tarkh-
anovskaya Pristan, Bathonian silts covered by Callo-
vian marls and Lower Oxfordian clays, and overlain by
Kimmeridgian deposits, were exposed in the sections
described by Mitta et al. (2014).
Very quick changes in the completeness and thick-
ness of the Lower/Upper Kimmeridgian boundary beds
in a distance of a few kilometers as well as the same
variability in structure of the underlying Middle Juras-
sic deposits as shown in descriptions of the sections
given above (see also Mitta et al. 2014) in the area
of study suggest a significant role of synsedimentary
tectonics in the development of sedimentation in this
part of basin. The tectonic phenomena were especially
active during the late Cymodoce Chron, and especially
during the formation of the beds with Crussoliceras
which show large differences in thickness and sedi-
mentological character between the Tarkhanovskaya
Pristan and the Memei localities (Figs. 4-5; see also
chapter on ammonite stratigraphy). An active tectonic
setting during the Jurassic in this area was also as-
sumed by k
orolev
et al. (2012) to explain the occur
-
rence of the barite-rich concretions in the Kimmeridg-
ian deposits. As suggested by korolev et al. (2012), the
origin of barite in these concretions occurred through
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Fig. 5. Ammonite distribution and stratigraphical correlation of the sections between Memei and Tarkhanovskaya Pristan
(section T5).
eschweizerbart_xxx
168 M.A. Rogov et al.
fault-controlling underwater hydrothermal vents. Bar-
ite concretions from Southern Tatarstan were also re-
ported previously in the Callovian deposits (korcHagin
1962), which suggest repeated tectonic activity during
the Middle and Late Jurassic.
2.2. Ammonite stratigraphy
The oldest ammonites have been discovered in a lag-
deposit, in reworked, mostly crushed, phosphorite nod-
ules, at the base of the Upper Jurassic succession in
section T1. Some phosphorites yielded imprints of am-
monites of the subfamily Cadoceratinae – of the genus
Cadoceras and its close allies. These findings indicate
the original presence of deposits (mostly of Lower
Callovian age) which have been completely washed out
during the Late Jurassic. However, a few kilometers
eastwards, Lower and Upper Callovian deposits, which
overlie the poorly fossiliferous Bajocian (?) to Batho-
nian strata, are well developed (Mitta et al. 2014).
The Upper Jurassic succession is composed of six
main ammonite assemblages (Figs. 4-5). The oldest
Kimmeridgian assemblage was discovered by Hantz-
pergue et al. (1998) in the the Memei-1 section, where
unfigured Rasenia cf. cymodoce (d’orBigny) and Zo-
novia cf. uralensis (dorBigny) together with the Bo-
real bivalve Buchia concentrica (
v
. B
ucH
) have been
mentioned. The Subboreal ammonite assemblage with
Rasenia is replaced upwards by a new assemblage
dominated by drastically different ammonites of Sub-
mediterranean affinity. This assemblage occurring in
sections Memei 1-2, and at Tarkhanovskaya Pristan
(section T1 and a lower part of section T3) in deposits
strongly contrasted in their thickness (from about 0,3
m to 3.5 m thick), consists mostly of the Submediter-
ranean representatives of the genus Crussoliceras – C.
atavum (scHneid) [M] and C. lacertosum (fontannes)
[m], representing possibly a dimorphic pair. The occur-
rence of these forms in the described ammonite suc-
cession is indicative of the Divisum Zone of the Sub-
mediterranean zonal scheme; and the occurrence of C.
atavum suggests additionally the upper part of this zone
(e.g., scHick 2004) although the species shows a wide
stratigraphical range from the upper part of the Divi-
sum Zone up to the Acanthicum Zone and the Eudoxus
Zone (see enay et al. 2014, and earlier papers cited
therein). The Boreal ammonites of the genus Amoebites
– such as Amoebites kitchini (salfeld) and Amoebites
sp. – occur additionally in the middle-upper parts of
the stratigraphical interval discussed. These ammonites
are indicative of the upper part of the Kitchini Zone –
the Modestum Subzone (see WierzBoWski & sMelror
1993; WierzBoWski et al. 2002).
A younger ammonite assemblage is composed of
Rasenioides sp. found in deposits about 0.1 m thick in
section T3 (member 3 – middle part). This assemblage
could nearly correspond to the Rasenioides-bearing
beds of the Tver (B
uev
2012) and Kaluga (Fig. 12N)
areas. These ammonites are indicative of the upper
part of the Subboreal Cymodoce Zone, an upper part
of the Chatelaillonensis Subzone of the “Biome Franco-
Germanique” (after presence of Rasenioides, see e.g.,
Hantzpergue 1989; Matyja & WierzBoWski, 2000;
coMMent et al. 2015).
The ammonite assemblage composed of numerous
representatives of the genus Aulacostephanoides oc
-
curs in a narrow interval about 1 m in thickness in
section T2 (upper part) and in section T3 (member 3
– upper part, and member 4 – lower part). The fauna
with Aulacostephanoides is indicative of the Subboreal
Mutabilis Zone in its traditional (and accepted herein)
interpretation. It should be remembered that the de-
posits of this interval in section T2 are possibly strati-
graphically condensed as shown by their small thick-
ness, common occurrence of ammonites, as well as the
presence of numerous burrows and phosphorites. The
section T2 has yielded additionally a single specimen of
a rasenoid – Eurasenia or strongly ribbed Involuticeras
which range up at least into higher part of the Lower
Kimmeridgian (cf. M
atyja
& W
ierzBoWski
1998, 2000;
see also c
oMMent
et al. 2015), being thus a link with
the underlying ammonite assemblage described here-
in. Additionally, a few specimens of the Boreal genus
Amoebites including Amoebites kitchini (s
alfeld
) as
well as the recently described small-sized species A.
peregrinator r
ogov
have been found in the assemblage
in question. They are indicative of the uppermost part
of the Boreal Kitchini Zone – the Modestum Subzone.
Amoeboceras peregrinator is also typical of this as-
semblage.
The Boreal aulacostephanid Zenostephanus sachsi
(MesezHnikov) was found above the discussed ammo-
nite assemblage. This species is indicative of the sachsi
horizon, which is widely distributed in the Arctic (cf.
rogov 2016).
The ammonite assemblage occurring in section T4
from the marl unit of the topmost part of member 4 up
to the black-shale member 6 is composed of numerous
Aulacostephanoides still indicating the presence of the
Subboreal Mutabilis Zone, but with a marked admix-
ture of the ammonites of Tethyan origin (mainly badly
eschweizerbart_xxx
Ammonite assemblages in the Lower to Upper Kimmeridgian boundar y interval 169
preserved aspidoceratids and oppeliids).
A single record of Orthaspidoceras liparum (o
p
-
pel
), indicative of the Lallierianum Subzone of the Mu-
tabilis Zone, was made in section T5 in a bed of clay
with septarian concretions, difficult to correlate litho-
logically with other sections at Tarkhanovskaya Pristan
and Memei. The ammonite Orthaspidoceras lallieria-
num (
d
’o
rBigny
) originally described as Aspidoceras
liparum by p
avloW
(1886, pl. 9, fig. 3; see H
antzpergue
1989: 305) coming from the neighbouring outcrops on
the Volga river near Goridischi (now covered by wa-
ter of the Kuybyshev reservoir) possibly belongs to the
same ammonite assemblage. The assemblage of the
Lallierianum Subzone is characterized by dominance
of “an endemic and monotaxic Orthaspidoceras fauna
originating from the Submediterranean stock” (H
antz
-
pergue
1995), although Aulacostephanoides records are
also known from this subzone (e.g., saMson et al. 1996).
Because the group of O. lallierianum is strictly related
to the Mediterranean Aspidoceras of the A. acanthicum
group (Hantzpergue 1989, fig. 136), the discussed as-
semblage of ammonites may be also compared with
the Submediterranean Acanthicum Zone (although the
detailed correlation between the Mutabilis Zone and
the Acanthicum Zone is still an open question); an oc-
currence of Orthaspidoceras is known also from one
of the famous Crussol sections being the typical local-
ity of the Acanthicum fauna (Baudouin et al. 2011). It
should be noted that Aulacostephanoides ranges up into
the Acanthicum Zone (ziegler 1962; Borrelli 2014).
Thus, the occurrence of O.lallierianum may be treated
as indicative of the uppermost ammonite assemblage
of those distinguished herein in the succession studied.
3. Discussion
The changes in the character of the ammonite faunas
in the succession studied are of biogeographical na-
ture. They are the result of migrations of the ammonite
groups which occupied various areas from the oceanic
Tethyan basins to shallow epicontinental seas during
the Late Jurassic. The distribution of special ammonite
groups in Eurasia was strictly confined to particular
areas, each of them related to environmental – palaeo-
climatic conditions. These areas (bioprovinces) were
characterized during the Kimmeridgian by the develop-
ment of different ammonite groups: the families Atax-
ioceratidae, Aspidoceratidae and Oppeliidae for the
Submediterranean Province, the Aulacostephanidae for
the Subboreal Province and the Cardioceratidae for the
Boreal Province. In the Subboreal Province all these
groups co-occurred during the Kimmeridgian in some
levels, whereas their joint records were also known in
the Submediterranean Province, while aulacostepha-
nids were widely distributed in the Boreal Province
except some high-latitude sites.
Above the Rasenia cf. cymodoce – Zonovia cf. ura-
lensis assemblage of Hantzpergue et al. (1998), repre-
sented by Subboreal ammonites, the oldest assemblage
in the succession studied is characterized by the oc-
currence of Submediterranean Ataxioceratidae of the
genus Crussoliceras. The appearance of the ammonite
group of Crussoliceras and the closely related Garni-
erisphinctes at the end of Early Kimmeridgian over
wide areas of the Submediterranean Province had most
possibly the character of migration from the Mediterra-
nean Province. During this time an older assemblage of
Ataxioceratinae (from Orthosphinctes to Ataxioceras)
was replaced by a new wave of Ataxioceratidae, repre-
senting possibly a new subfamily, and having their roots
in forms related to Passendorferiinae in the Mediter-
ranean basins (see pavia et al. 1987). Such an interpre-
tation seems to be in full agreement with the character
of the inner whorls of Crussoliceras specimens from
Tatarstan, which reveal typical passendorferiid very
evolute coiling showing the common occurrence of
simple ribs. The suggestion postulating the origin of the
Crussoliceras group directly from Passendorferiinae
seems thus more plausible for the present authors than
an alternative assumption according to which the roots
of the Crussoliceras group have been in the Lithaco-
sphinctes – Orthosphinctes group of strictly Submedi-
terranean origin (see also enay et al 2014, where both
these interpretations are discussed).
It should be noted that Crussoliceras occurs in other
Subboreal areas such as Northern Poland (WierzBoWski
et al. 2015), and is widely distributed in the European
part of Russia. This genus is known from the histori-
cal sections of the Yaroslavl region (Perisphinctes pra-
lairei in n
ikitin
, 1884, pl. 3, fig. 17, refigured here at
Fig. 10A), as well as from pebbles of the re-worked
deposits at the base of the Middle Volgian of the Un-
zha river, Kostroma area (Figs. 9G, 10D). Specimens
of Crussoliceras associated with Rasenioides have
been reported from the Kaluga region, where they are
known from highly condensed glauconitic sand with
whitish phosphorite concretions. Crussoliceras records
are also known from the Moscow region (Fig. 10B).
They are mainly noted in reworked phosphorites at the
base of the Middle Volgian, but there is at least one
section near to Ignatievo village, in which clays with
eschweizerbart_xxx
170 M.A. Rogov et al.
Crussoliceras-bearing phosphorites occur below the
Autissiodorensis Zone (the latter is characterized by
Sarmatisphinctes subborealis kutek & zeiss and Au-
lacostephanus spp.). Additional Crussoliceras records
were made recently by the amateur palaeontologist
dMitry Buev at the Volga river coast near to Kimry
town, ca 150 km north of Moscow (Buev 2012). These
ammonites were found in a thin band (0.1-0.2 m) of
black clay with occasional phosphorite nodules. The as-
semblage described is mainly dominated by Crussoli-
ceras cf./aff. lacertosum (B
uev
2012, pl. 1, figs. 1-10; pl.
2, figs. 3-8) with uncommon Amoebites kitchini (B
uev
2012, pl. 2, fig. 1) and Aspidoceras binodum (Buev
2012, pl. 2, fig. 2). One additional ammonite record,
figured under the name Vineta cf. jaeckeli (B
uev
2012,
pl. 2, fig. 9) is of a special interest, as it could represent
Rasenioides (Semirasenia) discoides, the index species
of the uppermost horizon of the Askepta Subzone in
France (Hantzpergue 1989).
The sudden appearance of the new ataxioceratid
ammonites (Crussoliceras – Granierisphinctes) dur-
ing the late Early Kimmeridgian (at the boundary of
the Hypselocyclum and Divisum chrons) over wide
areas of the Submediterranean Province in the south
has its time equivalent in the sudden appearance of a
new group of aulacostephanids (Rasenioides) at the
Askepta horizon of the Chatelaillonensis Subchron in
the Subboreal Province in the north (as well as some
transitional areas called “Biome franco-germanique”)
(Matyja & WierzBoWski 2000; see also Hantzpergue
1989, 1995). This phenomenon is often interpreted in
sequence stratigraphic terms as corresponding to the
beginning of the transgressive phase of the eustatic cy-
cle (Hantzpergue 1995), but possibly it may be better
interpreted as a consequence of tectonically enhanced
changes over wide areas of the northern Tethyan shelf.
The synsedimentary tectonic activity recognized at
the stratigraphical interval with Crussoliceras ammo-
nites in the Tatarstan (central European Russia) section
seems to confirm such an interpretation.
Study of the Tatarstan succession indicates that
after an initial dominance of Submediterranean am-
monites of the Crussoliceras group of the oldest am-
monite assemblage, a new assemblage of ammonites
composed of Aulacostephanidae of Subboreal character
has appeared. It marks the replacement of the Submedi
-
terranean ammonites by Subboreal ones. These Sub-
boreal ammonites are late Rasenioides, and co-occur
with finely ribbed cardioceratids showing a transitional
character between A. modestum and Amoebites (or
Euprionoceras) kapffi (o
ppel
). Additionally, a single
specimen of Eurasenia or heavily ribbed Involuticeras
indicative of the areas transitional between the Sub-
boreal and Submediterranean provinces (Matyja &
W
ierzBoWski
2000) is known also from the Tatarstan
succession at the transition into a younger assemblage
with Aulacostephanoides. A “mixed character” of
rasenioid ammonites, representing different lineages
of the Aulacostephanidae (genera Rasenia, Eurasenia
and Rasenioides), with some Submediterranean am-
monites like Crussoliceras and Progeronia, was recog-
nized in a similar stratigraphical position at the end of
the Cymodoce Zone in northern areas of the Jura Mts.
in Switzerland (coMMent et al. 2015). The occurrence
of such an assemblage composed of various rasenoids
in the Tatarstan succession, indicates a high gradient of
diversity of the local environmental factors and/or the
opening of the migration pathways during the sea-level
highstand which resulted in the existence of a highly
diversified ammonite fauna.
The subsequent Aulacostephanoides ammonite
assemblage had a fairly uniform character over wide
areas of the Subboreal, and partly Submediterranean
areas. It indicates generally similar environmental
conditions which favoured the strong development
of a single aulacostephanid stock having its roots in
older Rasenioides. The only other ammonites were
representatives of the Boreal genus Amoebites which
occurred nearly continuously from the upper part of
the Crussoliceras assemblage at the base of the suc-
cession studied in Tatarstan, although always in sub-
ordinate numbers, but nevertheless indicating an open
sea connection with the Boreal Province. Among the
cardioceratids the presence of small-sized coarsely
ribbed Amoebites (A. peregrinator r
ogov
) being the
late representative of the genus has a special interest,
as this species as recently recognized is characterized
by wide geographic and narrow stratigraphic ranges
Fig. 6. Ammonites from the Lower-Upper Kimmeridgian transitional beds. ACrussoliceras atavum (scHneid), Tarkha-
novskaya Pristan, locality T1, member 1, 0.35 m above the base, specimen SGM MK4047. BCrussoliceras lacertosum
(f
ontannes
): Tarkhanovskaya Pristan, locality T1, member 2, 0.45 m above the base, specimen MWG UW ZI/80/03. All
specimens depicted in Figs. 6-13 are coated with ammonium chloride except indicated otherwise.
eschweizerbart_xxx
Ammonite assemblages in the Lower to Upper Kimmeridgian boundar y interval 171
Fig. 6.
eschweizerbart_xxx
172 M.A. Rogov et al.
(rogov 2016). Slightly above these cardioceratids and
within the Aulacostephanoides range a remarkable
record of Zenostephanus is especially important for
correlation with Boreal succession. Although the first
Zenostephanus originated during the late Cymodoce
Chron (MesezHnikov 1984; WierzBoWski & rogov
2013), Z. (Z.) sachsi (MesezHnikov) – typical of the
so-called sachsi horizon of the Mutabilis Zone – was
characterized by wide geographic distribution in high-
latitude sites (r
ogov
2016), and a closely related Ze-
nostephanus penetrated that time to British Columbia
(r
ogov
& p
oulton
2015). It is very possible that the
historical record of Zenostephanus (Xenostephanoides)
fraasiformis (n
ikitin
) in the Yaroslavl region (=Peri-
sphinctes fraasiformis nikitin, 1881, pl. V, figs. 42-43,
refigured here at Fig. 13J) should be assigned to the
sachsi horizon. This species was found at the same
site as “Perisphinctes pralairei” mentioned above
(and interpreted herein as Crussoliceras), which came
from the phosphorite nodules at the top of the “Ox-
fordian clay” below the Middle Volgian Nikitini Zone
of Koprino village. These ammonites were mentioned
among the other Oxfordian and Lower Kimmeridgian
taxa from the 10-m thick clayey succession, which is
now unavailable through flooding by Rybinsk reser-
voir. Re-worked Zenostephanus are also known from
the phosphorite pebbles of the basal Middle Volgian of
Unzha river (collection by A. stupacHenko, Moscow).
In contrast to multiple occurrences of Crussoli-
ceras and Zenostephanus in the European part of Rus-
sia, Aulacostephanoides are virtually missing outside
Southern Tatarstan, except for the single record of A.
mutabilis (s
oWerBy
) from the Valanginian phosphorite
conglomerate of the Belgorod region (rogov 2015, pl.
2, fig. 1).
The decline of the Aulacostephanoides group at
the end of the Mutabilis Chron was proceeded by the
appearance of a new Submediterranean group of am-
monites (especially Aspidoceratidae with development
of the special group of Orthaspidoceras), indicating
the beginning of a new “transgressive phase” (Hantz-
pergue 1995).
4. Systematic palaeontology
The following abbreviations are used in description of the
ammonites: D – diameter of specimen in mm; Wh – whorl
height as a percentage of D; Ud – umbilical diameter as a
percentage of D; Wb – whorl breadth as a percentage of D;
PR – number of primary ribs per whorl (PR/2 on a half a
whorl); SR/PR – number of secondary ribs per one umbili-
cal ribs (usually counted on 5 neighbouring primary ribs at
diameter given).
Family Ataxioceratidae
Several large macroconch specimens are referred to the
genus Crussoliceras (according to the original defini-
tion of enay 1959; see also enay et al. 2014). These
specimens attaining about 200-300 mm in diameter are
preserved in clays which makes their extraction from
the rock difficult. Some of the better preserved of them
were photographed in the field and their larger frag-
ments were collected. The most carefully studied was
a specimen from locality T1 – member 1 (0.35 m above
the base; Fig. 6A). It attains about 270 mm in diameter;
the coiling is evolute (at D = 210 mm, Wh = 28; Ud
= 54); the ribbing is fairly dense on the inner whorls
and consists of numerous, prominent, almost rectira-
diate primary ribs which are regularly bifurcated; PR
equals 40 at D = 90 mm, and 43 at D between 120-160
mm, and markedly decreases thereafter, attaining about
35 at D = 200 mm. The ribs on the outer whorl are
swollen, initially branched high on the whorl side into
three secondaries, then becoming simple. The speci-
men shows marked similarities to the type specimens
of Crussoliceras atavum (s
cHneid
) as illustrated and
described by scHneid (1915: 94-95, pl. 2, fig. 2; pl. 9,
fig. 1) which corresponds strictly to Ammonites divisum
coronatus of q
uenstedt
(1888, pl. 106, figs. 6-8), a very
characteristic species showing the dense biplicate ribs
on the inner whorls, and the polygyrate and single ribs
on the outer whorl with a coronate whorl section (see
geyer 1961; scHick 2004). An allied form is Crusso-
liceras petitclerci e
nay
, g
allois
& e
tcHes
whose vari-
ability is unknown because the species is based on a
single specimen (see e
nay
et al. 2014: 319-320, pl. 7, fig.
1); thus the name may even appear a younger synonym
of C. atavum.
Another specimen from member 1 (0.85 m above
the base) although not so well preserved is of similar
size (up to about 300 mm in diameters), shows fairly
densely ribbed inner whorls (PR/2 is about 25 at 150
mm diameter) and swollen simple ribs on the outer
whorl (PR/2 is about 10 at about 300 mm diameter).
It seems generally similar to that described below and
may be referred to as Crussoliceras cf. atavum. An-
other specimen from member 2 (0.3 m above the base)
was photographed in the field, and only fragments of
its inner whorls were collected. The specimen is about
190 mm in diameter and shows only biplicate ribbing
very close to that of the specimens described above
(PR equals: 32 at D = 80 mm, 35 at D = 95 mm, 37 at
eschweizerbart_xxx
Ammonite assemblages in the Lower to Upper Kimmeridgian boundar y interval 173
Fig. 7. Crussoliceras atavum (scHneid), Tarkhanovskaya Pristan, locality TP, loose, specimen SGM MK2905. A1 – lateral
view; A2 – ventral view.
eschweizerbart_xxx
174 M.A. Rogov et al.
Fig. 8.
eschweizerbart_xxx
Ammonite assemblages in the Lower to Upper Kimmeridgian boundar y interval 175
D = 120 mm, 38 at D = 140 mm, and about 42 at D =
190 mm). It represents possibly the same form as the
above, although the specimen is not fully grown (or not
completely preserved) because of the absence of single
swollen ribs typical of the outer whorl of Crussoli-
ceras macroconchs. Similar big-sized macroconchs of
Crussoliceras were found loose some 500 m westwards
from the T4 section (Figs. 7A, 8A).
Smaller-sized, fairly densely ribbed specimens rep-
resent either Crussoliceras microconchs, or the inner-
most whorls of the macroconch of the genus and are
difficult for closer identification. The better preserved
specimen (Fig. 6B) found in locality T1 – member 2
(0.45 m above the base) is the phragmocone about 95
mm in diameter. The whorl section is trapezoidal (Wh
= Wb = about 30 at D = 90 mm) with a larger whorl
breadth directly above the umbilical wall, and a wide
ventral side; the coiling is evolute (Ud = 49.5 at D =
90 mm). The ribs are distinct, somewhat prorsiradiate,
splitting high into two secondary ribs showing a weak
forward sweep, and regularly joining the secondary
ribs of the corresponding rib on the opposite side of
whorl. PR equals 36 at D = 70 mm, and 42 at D = 95
mm. The specimen may be compared with the type
specimen of Crussoliceras lacertosum (fontannes),
differing only in its somewhat more dense ribbing
(duMortier & fontannes 1886: 100, pl. 15, fig. 1; cf.
geyer 1961: 49). Smaller-sized specimens found in
members 1 and 2 of locality T1 represent the phrag-
mocone or phragmocone with initial part of the body
chamber. The specimens show evolute coiling, low oval
to trapezoidal whorl sections (at D = 40 mm, Wb =
36-42), and moderately dense ribbing (at D = 20-40
mm, PR = 28-31). They may be referred to as C. cf.
lacertosum (fontannes). The species C. lacertosum is
akin to Crussoliceras lotharingicum enay, gallois &
etcHes (enay et al. 2014: 324-325, pl. 7, fig. 2) but it
differs in its less evolute coiling and smaller number
of primary ribs in the early whorls. Because the forms
Crussoliceras petitclerci and C. lotharingicum have
been interpreted by e
nay
et al. (2014: 325) as dimor-
phic counterparts, a similar relation between closely
related forms referred to herein as C. atavum and C.
lacertosum seems also plausible. Additional C. lacer-
tosum were found also in member 1 of the Memei 2
section (Figs. 9B, 10C, F). Among these ammonites
a few specimens are especially interesting: a piece of
the body chamber, showing a few single ribs, and two
well preserved specimens, in which the cross-section is
clearly visible. One juvenile specimen (D = 50 mm) is
characterized by a very low cross section with Wb/Wh
ratio 1.42, while a bigger specimen with body chamber
(D~92 mm) is characterized by nearly equal Wb and
Wh. Well-preserved macroconchs of Crussoliceras (C.
atavum) found loose at locality TP, between sections T5
and T3-4 (Figs. 7A, 8A) show additional features not
seen clearly in crushed specimens from Tarkhanovs-
kaya Pristan. One of these ammonites is represented
by part of the terminal body chamber (Wh = 81 mm),
covered by thick primaries, which branch into 4-5 thin
secondaries at the ventrolateral margin; it is charac-
terized by a very thick cross-section (Wb/Wh = 1.51).
Another ammonite (D = 200 mm) has the same pattern
of ribbing on the body chamber and a similar cross-
section. It should be noted, that in at least some cases
significant changes of ribbing from dense biplicate to
distant ribs with a higher rib ratio and lowering of the
cross-section occur in C. atavum before the terminal
body chamber. Such a specimen from the Unzha river
shows a similar “adult” morphology on the fully septate
part of the whorl (Fig. 9G).
Family Aspidoceratidae
Aspidoceratid ammonites from the clayey deposits
of the Mutabilis Zone in the Tarkhanovskaya Pristan
are generally very badly preserved and cannot be de-
termined at the species level. For example, Aspido-
ceras sp. indet. from the black shale member (Fig. 12C,
D) and numerous Aspidoceras sp. indet. collected at
2.6-2.8 m below the black shales (Fig. 12A, B) of the
T4 section are recognized by the presence of spines
on the midflanks and their general shell outline, but
other shell features are unclear. The only exception is
a well-preserved Orthaspidoceras collected from a
big septarian concretion from section T5. This speci-
men (D = 192 mm), ascribed to O. liparum (oppel)
shows the periumbilical spines, which were well vis-
Fig. 8. ACrussoliceras atavum (s
cHneid
), Tarkhanovskaya Pristan, locality TP, loose, specimen SGM MK2906. A1 –
lateral view; A2 – ventral view. B – Oppeliidae sp. indet: Tarkhanovskaya Pristan, locality T3, member 4, 6.5 m above the
base of the section, specimen SGM MK4206.
eschweizerbart_xxx
176 M.A. Rogov et al.
Fig. 9.
eschweizerbart_xxx
Ammonite assemblages in the Lower to Upper Kimmeridgian boundar y interval 177
Fig. 10.
eschweizerbart_xxx
178 M.A. Rogov et al.
ible when specimen was fractured during the prepara-
tion (Fig. 11B). An historical record of O. lallierianum
(
d
’o
rBigny
) was given by p
avloW
(1886) possibly from
the same level near Gorodischi (north of Ulianovsk re-
gion), but now these deposits are flooded by the Kuyby-
shev reservoir. The ammonite from p
avloW
s collection
(refigured herein, Fig. 11A) belongs to a small-sized
morphotype of Orthaspidoceras (described as ‘micro-
conchs’ by Hantzpergue 1989). This specimen shows
clearly visible periumbilical nodes (4 node per quarter
of whorl), which split into very fine and poorly devel-
oped secondaries on the body chamber.
Family Oppeliidae
A single oppeliid ammonite with a narrow umbilicus
and completely smooth whorls was recorded from the
uppermost part of the T3 succession (Fig. 8B).
Family Aulacostephanidae
Several specimens from locality T2 may be attributed
to the genus Aulacostephanoides s
cHindeWolf
, 1925.
The specimens are generally of small-size, from about
25 mm to 45 mm in diameter, having short swollen
umbilical ribs, and numerous secondary ribs and all
of them reveal a well developed ventral smooth band.
Some of them are more evolute (although the specimens
are often badly deformed which precludes very detailed
measurements), including one with the final peristome
preserved with lappets. They can be safely attributed to
Aulacostephanoides eulepidus (scHneid) (Fig. 12H) –
well characterized by ziegler (1962: 44-48, pl. 1, figs.
1-16) and recognized as the type of the new microconch
subgenus Aulacostephanites. It is highly probable that
the pyritized nuclei showing weakly evolute coiling,
and the presence of thick short umbilical ribs (PR =
16-18, SR = 3.4-4 at D = 15 mm) represent the inner
whorls of A. eulepidus. Two larger specimens attaining
34 mm, and 45 mm in diameter, respectively (Fig. 12I,
R), show more involute coiling (Wh = 44-47, Ud = 20-
22) with a higher number of secondary ribs at a larger
diameter (at D = 45 mm, SR is about 7-8), and may
be referred to as Aulacostephanoides cf. desmonotus
(o
ppel
) (see z
iegler
: 50-52, pl. 2, figs. 13-15). It should
be remembered that the occurrence of specimens show-
ing a similar variability in a single bed and referred to
as Aulacostephanoides eulepidus (scHneid) and A. cf.
desmonotus (oppel), but representing possibly the “end-
members in the variability of the same species”, has
been described by B
irkelund
et al. (1983, fig. 5F-H) in
the English sections.
Members of the genus Aulacostephanoides from
sections T3 and T4 are mainly represented by small
badly preserved incomplete specimens, showing clearly
visible rib interruption at the ventral side. One speci-
Fig. 9. A-CCrussoliceras cf. lacertosum (fontannes), A, C – Tarkhanovskaya Pristan, loose; B – Memei-2, 0.25-0.3 m
below the top of member 1. A – specimen SGM MK4; B – specimen SGM MK3001; C – specimen SGM MK 3000. D-F
Crussoliceras lacertosum (fontannes), Tarkhanovskaya Pristan, loose; D – specimen SGM MK7; E – specimen SGM
MK12; F – specimen SGM MK 10. GCrussoliceras atavum (s
cHneid
): right bank of the Unzha river near to Burdovo
village, specimen SGM 3-873. G1 – lateral view; G2 – ventral view.
Fig. 10. A-D, F, GCrussoliceras lacertosum (fontannes), A – Koprino section, Yaroslavl region (refigured from nikitin
1884, pl. 3, figs. 17-18), specimen CNIGR 36-373, A1 – lateral view; A2 – apertural view, A3 – ventral view; B – Ignatievo
section, Moscow area, bed 2; specimen GIN MK4615, B1 – lateral view, B2 – apertural view; C – Memei-2 section, 0.25 m
below the top of member 1, specimen SGM MK3002, C1 – apertural view, C2 – lateral view; D – Unzha river, 2 km below
Yakovlevo village, specimen SGM 3-941, D1 – lateral view, D2 – ventral view; F – Memei 2 section, member 1, 2.2 m be-
low base of member 3; specimen SGM MK 2935; G – Tarkhanovskaya Pristan, locality T 1, 0.15 m above the base of the
Kimmeridgian. ECrussoliceras sp., Memei 2 section, 0.25-0.3 m below the top of member 1; specimen SGM MK3003.
Fig. 11. A. Orthaspidoceras lallieranum (d’orBigny), Gorodischi near Undory, Ulyanovsk region; specimen CNIGR 11/312
(pavloW 1886, pl. 9, fig. 3), not coated with ammonium chloride; A1– lateral view, A2 – cross-section of the body chamber;
BOrthaspidoceras liparum (o
ppel
), Tarkhanovskaya Pristan, locality T 5, 0.7 m above the base of the Kimmeridgian;
specimen SGM MK 4519.
last doublepage
right page
eschweizerbart_xxx
Ammonite assemblages in the Lower to Upper Kimmeridgian boundar y interval 179
Fig. 11.
eschweizerbart_xxx
180 M.A. Rogov et al.
Fig. 12.
eschweizerbart_xxx
Ammonite assemblages in the Lower to Upper Kimmeridgian boundar y interval 181
men from the black shales can be tentatively assigned
to as A. aff. mutabilis (soWerBy). Additional well-pre-
served pyritized moulds of Aulacostephanoides were
collected loose near T3 section by Dr. v
ladiMir
e
fiMov
(Undory). Among these specimens A. mutabilis is rep-
resented by the relatively big-sized septate whorls (Fig.
12O) (D~69 mm), with PR = 7 and SR/PR = 5.6, whorl
section with flattened ventral side, Wb/Wh = 0.86. The
inner septate whorls of Aulacostephanus cf. desmono-
tus (Fig. 12L-M) (D = 38 mm) are characterized by
short primaries (PR = 10), which split into numerous
secondaries (slightly rursiradiate to rectiradiate) below
the midflanks (SR/PR = 4.9). Other specimens collect-
ed in the rubble include: A. cf. eulepidus (oppel) (Fig.
12J) and A. cf. peregrinus (ziegler) (Fig. 12K).
A single strongly compressed specimen from local-
ity T2, attaining about 80 mm in diameter (Fig. 12P)
shows strongly involute coiling (at D = 54 mm, Wh =
44.4, Ud = 25.9). The ribbing is stout and consists of
short well developed primary ribs and markedly thin-
ner secondary ribs which appear low on the whorl side
and cross the ventral side without any weakening: PR
= 21 at D = 80 mm, and 23 at D = 50 mm; number of
secondary ribs is fairly high (SR/PR = 4.0 at D = 55-
80 mm). The presence of strongly developed primary
ribs is often recognized in the genus Eurasenia g
eyer
,
1961, whereas the involute coiling and the presence of
fairly numerous, markedly thinner, secondary ribs is a
feature of the genus Involuticeras salfeld, 1917, and
the specimen in question may be informally referred to
as Eurasenia/Involuticeras sp.
A single crushed specimen of Zenostephanus (Z.)
sachsi (MesezHnikov) was found in section T4 (Fig.
13K). It is characterized by strongly evolute coiling
(at D = 129 mm, Ud = 48.5), thus both primaries and
secondaries are easily visible in the umbilicus, includ-
ing the innermost whorls. The ribbing is typical of Ze-
nostephanus and consists of short node-like primaries,
clearly separated from numerous thin secondaries. Due
to poor preservation of the primary ribs on the outer
whorls they cannot be precisely counted. In the inner
whorls PR/2 = 10, SR/PR = 4 (at D = 40 mm). Addi-
tional moulds of pyritized Zenostephanus (Z.) sachsi
were found loose near Tarkhanovskaya Pristan by the
authors as well as similar derived specimens from the
Dr. vladiMir efiMov (Undory) collection (Fig. 13G-I).
These well-preserved ammonites show the well-de-
veloped interruption of ribs at the ventral side, which
along with the mode of coiling, cross-section and type
of ribbing are typical of Zenostephanus. The specimens
are characterized by a gradual increase of the SR/PR
ratio through ontogeny, from 2.5-3 (at D = 20-30 mm)
to 4 in full-grown specimens.
One badly preserved and crushed aulacostephanid
ammonite, which has been found at 2.4 m below the
black shales of the T4 section, is characterized by rela-
tively distant and coarse ribs with prominent ventrolat-
eral nodes. Although imperfectly preserved, in can be
tentatively ascribed to the poorly-known genus Sarygu-
lia. This name is here accepted for the ammonite group
usually referred to the genus Pararasenia. The type
species of Pararasenia (Aulacostephanus zacataca-
nus BurckHardt) is known from a single record from
the Idoceras Beds of Mexico, and differs from Aula-
costephanus in its smaller size and septal suture. The
generic name Sarygylia (nomen nudum) has been pub-
lished by k
Hudyaev
(1932) in the figure caption only
for S. pischmae kHudyaev, while in his text this species
Fig. 12. A-DAspidoceras sp. indet., Tarkhanovskaya Pristan, locality T4. A – member 4, 2.8 m below the black shales,
specimen SGM MK4216; B – member 4, 2.8 m below the black shales, specimen SGM MK7634; C, D – member 6 (black
shales), C – specimen SGM MK4235, D – specimen SGM MK 4233. E-GAulacostephanoides sp. indet. E – Tarkha-
novskaya Pristan, locality T4, member 6 (black shales), specimen SGM MK 4234; F, G – Tarkhanovskaya Pristan, locality
T3, member 3; F – 3.4 m above the base of the section, specimen SGM MK4227; G – 2.1 m above the base of the section,
specimen SGM MK4224. HAulacostephanoides eulepidus (oppel), Tarkhanovskaya Pristan, locality T2, top of the sec-
tion, specimen MWG UW ZI/80/13, with lappet preserved. I, L, M, RAulacostephanoides cf. desmonotus (oppel): I,
R – Tarkhanovskaya Pristan, locality T2, top of the section: I – specimen MWG UW ZI/80/08; R – specimen MWG UW
ZI/80/02; L, M – Tarkhanovskaya Pristan, loose; L – specimen SGM TP 5, L1 – apertural view, L2 – lateral view; M –
specimen SGM TP 6, M1 – lateral view, M2 – apertural view. JAulacostephanoides cf. eulepidus (oppel): Tarkhanovs-
kaya Pristan, loose, specimen SGM TP6/2, J1 – apertural view, J2 – lateral view. KAulacostephanoides cf. peregrinus
(ziegler), Tarkhanovskaya Pristan, loose, specimen SGM TP3, K1 – apertural view, K2 – lateral view. NRasenioides sp.
indet., Lipitsy, Kaluga region, base of the bed 5; specimen GIN MK 4756. OAulacostephanoides mutabilis (j. soWerBy),
Tarkhanovskaya Pristan, loose, specimen SGM TP2, O1 – lateral view, O2 – ventral view. PEurasenia or Involuticeras
sp., Tarkhanovskaya Pristan, locality T2, top of the section, specimen MWG UW ZI/80/01.
eschweizerbart_xxx
182 M.A. Rogov et al.
Fig. 13.
eschweizerbart_xxx
Ammonite assemblages in the Lower to Upper Kimmeridgian boundar y interval 183
was assigned to the genus Aulacostephanus. Later N.T.
sasonov (1960) provided a full diagnosis of the genus
Sarygulia, and he should be considered as the author
of this genus.
Family Cardioceratidae
Four specimens coming from locality T1 – member 2
(0.25 m, and 0.55 m, above the base, Fig. 13B, C), and
locality T2 (Fig. 13L) show fairly uniform features, in-
dicating affiliation to the genus Amoebites BuckMan,
1925. The specimens are very coarsely ribbed with
short primaries (PR = 23-27 at D = 25-45 mm), strongly
accentuated at two/thirds of the whorl height, and sepa-
rated on the outer whorl by a smooth spiral band from
heavy ventrolateral nodes which become fused into
clavi with growing diameter; the strongly crenulated
keel is bordered by well developed ventral sulci. The
small-size of the specimens and their involute coiling
(at D = 28-44 mm, Wh = 43-44.6, Ud = 27-33) indicate
their close relation to Amoebites kitchini (s
alfeld
) (see
Salfeld 1915; see also Birkelund & calloMon 1985:
20-22, fig. 6 – where the lectotype of the species has
been designated).
Still another specimen found loose in the rubble but
in the stratigraphical interval of locality T3 is a frag-
mentarily preserved specimen showing markedly pror-
siradiate and simple ribbing, and a well developed keel
bordered by distinct ventral sulci. This finely-ribbed
cardioceratid ammonite, co-occurring with Rasenioi-
des in the lower portion of T3 section, is closely related
to A. kapffi (o
ppel
) but it differs in the presence of well
developed ventral sulci along the keel (Fig. 13A).
Aptychi
In addition to the ammonites a few aptychi were col-
lected from a level 2.55 m below the black shales in
section T4. These includes a few partially preserved
pyritized Laevaptychus and small elongated Praestri-
aptychis sp. (Fig. 13F). The latter could belong to an
aulacostephanid ammonite.
Acknowledgements
vladiMir efiMov (Undory), andrey sHkolin (Moscow) and
denis gulyaev (Yaroslavl) are acknowledged for providing
additional ammonite specimens for this paper. The authors
are grateful to G. s
cHWeigert
for valuable discussion. The
study was supported by the National Science Centre Poland
(project no. 2014/13B/ST10/02511) and Russian Foundation
of Basic Researches (projects no. 15-05-03149 and 15-05-
06183); it is also a part of the project of the Geological Insti-
tute of RAS no. 0135-2014-0064. The authors are grateful to
joHn WrigHt for linguistic correction. The authors are also
thankful to Guenter Schweigert for his valuable comments
and for the financial support of colour figures printing.
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sHcHepetova, e.v. & rog ov, M. (2013): Organic carbon
rich horizons in Upper Kimmeridgian of the northern
part of Ulyanovsk-Saratov trough (Russian Platform):
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nite and dinoflagellate cysts in the Upper Oxfordian and
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WierzboWski, A., smoleń, J. & iWAńczuk, J. (2015): The
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DOI: 10.1127/njgpa/2015/0496
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Manuscript received: April 11th, 2017.
Revised version accepted by the Stuttgart editor: June 6th,
2017.
Addresses of the authors:
MikHai l a. rogov, elena sHcHepetova, Geological Insti-
tute of RAS, 7, Pyzhevski lane, 119017 Moscow, Russia;
e-mail: russianjurassic@gmail.com
a
ndrzej
W
ierzBoWski
, Institute of Geology, University of
Warsaw, 93, Żwirki i Wigury Str., 02-089 Warszawa, Poland;
Polish Geological Institute – National Research Institute, 4,
Rakowiecka Str., 00-975 Warszawa
e-mail: andrzej.wierzbowski@uw.edu.pl
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... Как и в случае с более древними отложениями, из-за существования разных данных об объеме её мощность может быть определена лишь приблизительно. В наиболее полных разрезах на севере Ульяновской области она достигает 30-40 м [9,20,21]. ...
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... Инфразональное расчленение зоны пока недостаточно устоявшееся, последовательность биогоризонтов неполна и прослеживается неповсеместно. Снизу вверх в зоне могут быть намечены биогоризонты bayi, subkitchini, kapffi, peregrinator, salfeldi (Рогов, 2016;Rogov et al., 2017). Из этих биогоризонтов на юге Московской синеклизы достоверно устанавливается только биогоризонт bayi. ...
... II, фиг. 9-12), чьи находки, как показали недавние исследования (Rogov et al.,2017) широко распространены в европейской части России. В фосфоритах зоны Panderi иногда встречаются также аммониты, характерные для средней части верхнего кимериджа, такие как Euprionoceras (Табл. ...
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... Very characteristic ammonite faunal communities occurred during late Early Kimmeridgian, and the early Late Kimmeridgian (the Mutabilis Chron) along the middle of the European shelf and these have been originally distinguished by Hantzpergue (1989) as a characteristic faunal assemblage of the "franco-germanique" biome. This characteristic paleobiogeographic unit (biome or ecotone) continues further east to central Poland (Kutek & Zeiss 1997), and even more eastward to central part of European Russia (Rogov et al. 2017). The wide transgression affecting this area resulted also in the abrupt appearance of Subboreal ammonites of the family Aulacostephanidae, mostly of the genus Rasenioides which evolved here subsequently into a genus Aulacostephanoides, as well as the Tethyan representatives of the family Ataxioceratidae, and a marked northward distribution of Aspidoceratidae ranging into Subboreal Province (see e.g. ...
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Today in the course of active updating and development (on the basis of the GSSP and GSSA concept) International Chronostratigraphic Chart in general and, the Mesozoic in a particular, among the most relevant and sharp stratigraphy problems still there is a level division of a Cretaceous system (GTS–2012) and J/K boundary in particular. For almost 200 years, an attempt to solve this problem has been raised by researchers at the regional and global levels, discussed at numerous symposiums, colloquiums, meetings, conferences and covered in a number of publications by several generations of stratigraphs around the world. In the last three decades Subcommission on Cretaceous Stratigraphy (SCS) with the Working Groups that make important decisions on global questions of level division, carrying out boundaries between systems, series, stages and making GSSP. It was not succeeded to solve this problem at the regional and global level yet (Hoedemaeker 1987; Grabowski 2011; Schnabl et al. 2015; Wimbledon et al. 2017). But it is nearing completion (Wimbledon 2017). At the present stage more than 300 section are studied worldwide, more than 3500 taxons and the marking layers are established, but making decision on the choice of GSSP for unratified stages of the Jurassic and Cretaceous systems remains the Working Groups relevant (Granier et al. 2019). Considering emergence of new actual material and new researches techniques the problem remains unresolved. It is as follows. Despite almost 200-year history of studying of a Сretaceous system, stages of lower department and partially top (except for Cenomanian, Turonian, Santonian and Maastrichtian) have the status of unratified. It concerns also stages of the Upper Jurassic (Oxfordian, Tithonian). Boundaries Lower Cretaceous and partially the Upper Cretaceous of stages have no approved stratotype. Stages and substages of Cretaceous systems as the main subdivisions of International Chronostratigraphic Chart have the status of unratified. There is debatable a boundary problem between Jurassic and Cretaceous systems and also the provision of a Berriassian stage in International Chronostratigraphic Chart (System boundary has to correspond to boundary of the lower stage).
... Very characteristic ammonite faunal communities occurred during late Early Kimmeridgian, and the early Late Kimmeridgian (the Mutabilis Chron) along the middle of the European shelf and these have been originally distinguished by Hantzpergue (1989) as a characteristic faunal assemblage of the "franco-germanique" biome. This characteristic paleobiogeographic unit (biome or ecotone) continues further east to central Poland (Kutek & Zeiss 1997), and even more eastward to central part of European Russia (Rogov et al. 2017). The wide transgression affecting this area resulted also in the abrupt appearance of Subboreal ammonites of the family Aulacostephanidae, mostly of the genus Rasenioides which evolved here subsequently into a genus Aulacostephanoides, as well as the Tethyan representatives of the family Ataxioceratidae, and a marked northward distribution of Aspidoceratidae ranging into Subboreal Province (see e.g. ...
... Lowermost level A, belonging to the bayi horizon of the lower Kimmeridgian, is known from the Kostroma region only (Głowniak et al. 2010). Level B, characterized by both aspidoceratid ammonites and laevaptychi expands over the upper Kimmeridgian mutabilis Zone, with exception of its presence in lowermost part (Rogov et al. 2017). Most well-recognizable level C is also characterized by numerous occurrences of Aspidoceras spp., and is spanning across the upper part of the eudoxus Zone. ...
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During the construction of the A16 Transjurane highway (Canton Jura, Switzerland), the Paléontologie A16 team (Project funded by the Swiss Confederation and the République et Canton du Jura) had the opportunity to document and sample numerous new Kimmeridgian sections. The historical description of stratigraphical units and their synonyms, as well as the different lithofacies and dominant faunal assemblages of the Reuchenette Formation (Kimmeridgian, Upper Jurassic) are completely reviewed. The upper part of the Reuchen- ette Formation (Upper Kimmeridgian) is the new Chevenez Member. A description of local lithostratigraphic members and their cor- relation with regional geological units is proposed. The observed facies correspond to marine deposits of a shallow, more or less open carbonate platform. Sedimentary beds are rich in fossils of typical intertidal to subtidal zones. During the fieldwork, 630 specimens of ammonites were discovered. This new material, in addition to the historical collections of the JURASSICA Museum (Porrentruy) and the “Fondation paléontologique jurassienne” (FPJ, Glovelier) completes previous studies of the Kimmeridgian of the Swiss and French Jura. Thirteen ammonite-bearing horizons have been recognized and correlated with the Franco-Germanic biochronological scale. A new ammonite species from the Member of Courtedoux, Progeronia bruntrutense nov. sp., is described. These new data improve the biostratigraphic calibration of the lithostratigraphical units of the Reuchenette Formation and allow correlations between successions of the Ajoie and the nearby French outcrops (Montbéliard region).
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Shallow cores drilled in the southwestern Barents Sea have revealed Kimmeridgian strata with a fairly complete succession of species of the ammonite genus Amoehoceras. The taxonomical problems of these ammonites are discussed, and the new species Amoehoceras (Euprionoceras) norvegicum WIERZBOWSKI, sp.n., is established. The recognized ammonite succession is compared with these described previously from East Greenland and Spitsbergen, and the new zonal scheme based entirely on the representatives of the genus Amoehoceras is proposed for the Boreal Kimmeridgian. In this scheme four zones are distinguished: the Bauhini Zone, the Kitchini Zone (with the Subkitchini horizon, and the Modestum horizon), the Kochi Zone (with the Norvegicum horizon, and the Kochi horizon), and the EJegans Zone.
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Palaeontological study of the ammonite collection of the Oxfordian and Lower Kimmeridgian in the Kcynia IG IV borehole in northern Poland has resulted in biostratigraphical revision of the succession and allowed the recognition of the Submediterranean Zones and Subzones. Although Submediterranean ammonites overdominate in the succession, Subboreal and Boreal ammonites increase proportionally in the lower Bimammatum Zone and the uppermost Hypselocyclum Zone reflecting significant ammonite invasions from the north. The co-occurrence of the ammonites indicative of different bioprovinces in the same intervals of the studied succession permits closer correlation of the zonal schemes. The new results of the correlation are as follows: (1) the lower boundary of the Baylei Zone of the Subboreal zonal scheme corresponding therein to the lower boundary of the Kimmeridgian lies within the upper part of the Submediterranean Bimammatum Zone, (2) the lower boundary of the Subboreal Mutabilis Zone (sensu Birkelund et al., 1983) lies within the uppermost part of the Submediterranean Hypselocyclum Zone. Palaeoecological analysis of the distribution of ammonites representing the particular Submediterranean families in Poland has shown that during the earliest Kimmeridgian there existed a direct marine connection between northern Poland and the Franconian and Swabian Albs enabling free migration of ammonites through the areas presently devoid of Upper Jurassic deposits.
Ammonites and dinoflagellate cysts recovered from Upper Oxfordian and Kimmeridgian deposits in a core 6814/04-U-01 from offshore northern Nordland, Norway, allow a detailed biostratigraphic subdivision of the studied sequence. The numerous ammonites of the families Cardioceratidae and Aulacostephanidae found in the Kimmeridgian strata show both Boreal and Subboreal affinities and allow a correlation with the standard Boreal and Subboreal biostratigraphic zonations. The Kimmeridgian ammonite fauna from offshore northern Nordland shows an intermediate character between the Subboreal fauna of Northwest Europe and the Boreal fauna of the southern Barents Shelf and Svalbard. The dinoflagellate cyst assemblages are typically of low diversity and are related to the Upper Jurassic Boreal/ Arctic Paragonyaulacysta borealis assemblage. They apparently seem to show the same type of provincialism within the "Kimmeridge Clay Sea" as the ammonites.
Article
Extensive new collections of ammonites made bed by bed in many sections through the Kimmeridgian (Lower Kimmeridgian sensu anglico) of Milne Land are described. These are used to revise and amplify the earlier accounts in a classical monograph of 1935 by Spath. The ammonites occur at ten sharply defined and well separated faunal horizons in the Bays Elv, Cardioceraskløft and Gråkløft Members of the Kap Leslie Formation. These horizons are readily correlated with the well-known successions of NW Europe, and their precise stratigraphical positions within the framework of the standard NW European Sub-Boreal zonation are discussed. All five Zones – Baylei, Cymodoce, Mutabilis, Eudoxus and Autissiodorensis – are represented. The more tenuous correlations with the analogous successions of the Barents Shelf and northern Siberia are also discussed. The faunas belong almost wholly to the two Sub-Boreal families Cardioceratidae and Aulacostephanidae. In the former, eight species of Amoeboceras are described, one of them new: A. (Amoebites) bayi sp. nov., closely related to European A. (A.) bauhini . In the latter family ten species of the genera Pictonia, Rasenia, Pachypictonia?, Aulacostephanoides and Aulacostephanus are described. Those of Pictonia and Rasenia are particularly significant in comparison with European and Siberian forms. Other families continue to be represented by but a single specimen of the Oppeliidae, Streblites? cf. S. taimyrensis Mesezhnikov. Some key sections of stratigraphical importance are recorded in an Appendix.