GEOLOGICA CARPATHICA, 50, 1, BRATISLAVA, FEBRUARY 1999

5–20

BERRIASIAN-VALANGINIAN (EARLY CRETACEOUS) SEAWAYS

OF THE RUSSIAN PLATFORM BASIN AND THE PROBLEM

OF BOREAL/TETHYAN CORRELATION

EVGENIJ J. BARABOSHKIN

Department of Historical and Regional Geology, Geological Faculty, Moscow State University,

Vorobjovy Gory, 199899 Moscow, Russia; barabosh@geol.msu.su

(Manuscript received March 24, 1998; accepted in revised form September 1, 1998)

Abstract: 

The Russian Platform (RP) is one of the key-regions for the correlation of the Boreal and Tethyan stratigraphic

successions. Zoogeographical analysis of ammonite distribution in the RP and adjacent areas demonstrates the existence
of relations between different basins and the opening/closure of sublatitudinal and submeridional sea-connections in the
RP area. Two epochs in the development of the RP were recognized. The Berriasian–Barremian time shows a close
relation of the RP Basin to the Boreal Realm. During Aptian–Albian times the region was affected mainly by the Tethys
Ocean. It is supposed that the Upper Volgian corresponds to the Lower Berriasian. The similarity of the Western Siberia
and the Peri-Caspian–Mangyshlak fauna allows us to propose for the first time an existence of a direct connection
between those basins. Berriasian-Valanginian sea-connections of the RP Basin are discussed in this paper.

Key words: 

Lower Cretaceous, Boreal Realm, Tethyan Realm, Russian Platform, seaway, zoogeography, ammonites.

Saratov Trough and  Peri-Caspian Syneclise) and due to com-
parison with ammonite data from other regions, the following
biostratigraphic scheme (for the central parts of the RP) is pro-
posed (Fig. 1). The scheme was compiled after schemes of
Gerasimov (1969) and Sasonova & Sasonov (1979) for Lower
Berriasian (= Upper Volgian) and Valanginian, Mesezhnikov
(1984) and Sasonova (1977) for Upper Berriasian. The pro-
posed scheme, in general, is a combination of zones from both
Boreal and Tethyan schemes, because of mixing of Boreal
(prevailing) and Tethyan faunas in this region.

A similar scheme was published by Alekseev et al. (1993)

and by Shulgina (1996) within the framework of the
Interdepartmental Stratigraphic Commission of Russia. Both
schemes differ from the scheme proposed here and excludes
Upper Volgian as an equivalent of the Boreal Lower
Berriasian. Some elements of the Lower Cretaceous
biostratigraphy of the RP were included in the “Boreal
Standard scheme”, proposed by Zakharov et al. (1997).

Correlation

The author compiled the correlational scheme (Fig. 2) on the

basis of the tentative analyses of the co-distribution of zonal
indexes. As in recent cephalopods (Nessis 1985), the distribu-
tion of index ammonites was limited by (1) temperature, (2)
basin bathymetry and configuration, (3) mode of life, (4) post
mortem transportation. We can add some geological control-
ling factors: (5) selection during deposition, (6) selection dur-
ing diagenesis, (7) the existence of redeposition or condensa-
tion, (8) the recent character of the exposures (or boreholes),
and “subjective” factors. In spite of many limited factors, I
consider that the primary factors (1–4) are the most important.
One may conclude that in the places with optimal basin condi-
tions ammonite species should be numerous and occupy this
area for the longest time. It means that in the borders of am-
monite index species areas, the frequency of the index spe-

Introduction

This paper is based on long-term investigations of the Lower
Cretaceous of the Russian Platform (RP) and adjacent areas
(Crimea, North Caucasus, Peri-Caspian, Mangyshlak and the
Tuarkyr–Kopet-Dagh region) and of its ammonite fauna. Even
a brief observation of the ammonite distribution in this area
demonstrates that the Lower Cretaceous Basin of the Russian
Platform (Russian Sea — in literature) was the connecting
area between the Tethys and Arctic (Boreal) seas. This fact
was recognized a long time ago by Pavlow (1901) and
Arkhangelsky (1923), who supposed the existence of
meridional and latitudinal seaways through the Russian Plat-
form. In accordance with the appearance of new stratigraphic
data those reconstructions were modified and the sea-connec-
tions on the territory of the RP have been discussed in different
works. One of the latest is that Sasonova (1971, 1977) and Sa-
sonova & Sasonov (1967). The preliminary schemes about the
configuration of the RP Basin data were published by the au-
thor (Baraboshkin 1997b).

The Russian Platform (RP) is a relatively stable block of the

Earth crust. Its basement is heterogeneous and determines the
position and the development of different troughs, depressions
and syneclises during the Cretaceous (Milanovsky 1987). The
RP responded to external stress conditions by changes in its
relief and therefore in the shape of the existing sea basin and
its paleogeography. The paleozoogeographical model and the
model of RP seaways are proposed in the present paper.

Stratigraphy

Data for a stratigraphical scheme

Due to reinvestigation of the ammonite collections and out-

crops (in the Moscow Syneclise, Simbirsk Syneclise, Riasan-

6                                                                                            BARABOSHKIN

cies should be less than in the centre and it may co-occur
with other index species. One of the most important factors
is the water temperature, which causes some ammonites in
one bed only (for example, Hectoroceras in the RP) or in a
series of beds (Hectoroceras in Northern Siberia sections). It
is obvious that in different regions index ammonites may oc-
cupy different stratigraphic intervals, that is they may have
different ranges in different regions. Therefore, I propose to
correlate zones not in the traditional way (correlation of zon-
al names in tables), but to look at them as at 3-dimensional
zonal bodies on the basis of co-occurrence of zonal indexes
in related regions (Fig. 2 and Fig. 3) in well-investigated sec-
tions.

Paleozoogeography

Terminology

The total fauna depends on climatic conditions. Therefore,

the zonal subdivisions we used for biostratigraphical purposes
are in fact of a paleozoogeographical nature. The author
prefers the idea of the hierarchical system in paleo-
zoogeography, as developed by Makridin (Makridin & Meyen
1988). He proposed to recognize subdivisions for different
ecological types of organisms. It seems to the author, that if all
groups of fossils will be included in this scheme (as they were
traditionally), the “fine” data of short-term fauna area changes
will be lost (one should keep in mind that our calculations are
extrapolated on the geological time scale). This idea is well-
illustrated in the work of Druzchitz & Smirnova (1979), who
distinguish different subprovinces and regions for the same

time and area

 by means of different groups of animals. A

similar terminology was used by Saks et al. (1971, 1972) and
his disciples, Druzchitz & Smirnova (1979), Rawson (1981,
1993, 1995), Hoedemaeker (1990) and others, for the global
Early Cretaceous ammonite zoogeography with geographical
labels.

The author proposes the following meaning for the paleozo-

ogeographical terms for marine basins. A realm (or belt) is, in
fact, analogous to a recent climatic zone. It includes very dif-
ferent paleogeographical situations (such as continental and
marine), and it is therefore better to use it to determine climat-
ic zones. A province is a part of a climatic realm determined
by the domination of taxa of family range which are endemic.
They could be named after a family. A subprovince is a part
of a province determined by the domination of taxa of subfam-
ily

 range. They could be named after a subfamily. A region is

a part of a subprovince determined by the domination of taxa
of genera–subgenera range. They could be named after genera
(subgenera). A district is a part of a region determined by the
domination of taxa of species range. They could be named af-
ter a species (or lower taxa). It seems to me that taxonomic
names are probably better for terminology (it was developed
for the Lower Cretaceous by Owen, see for example Owen
1996) than some of the geographical names.

Seaways and paleozoogeography of the Russian Platform

in the Early Cretaceous

One of the main peculiarities of the Russian Platform (RP)

sea in the Cretaceous is the existence of two systems of
straits: (1) A sublatitudinal system, which connected the RP
with the Polish Basin and with the Carpathians in the west and

Fig. 1.

 The proposed ammonite biostratigraphic scheme for the Russian Platform, the ammonite diversity and the sea-level curves for th e

Berriasian and Valanginian. The solid sea-level curve is drawn after Haq et al. (1988) and adopted (scaled) to the zonal scheme . Dashed line
is compiled by the author for the northern part of the Moscow Syneclise. Thick lines on the scheme are the 2nd-order fluctuatio ns and fine
lines are the 3rd-order fluctuations.

BERRIASIAN -VALANGINIAN (EARLY CRETACEOUS) SEAWAYS OF THE RUSSIAN PLATFORM BASIN              7

with Western Siberia in the east, and (2) a submeridional sys-
tem, which connected the RP with the Tethys ocean in the
south and with the Arctic sea in the north. Opening or closing
of those seaways led to the prevalence of different successive
faunas in the Early Cretaceous sea of the RP. The existence of
these straits determined the penetration of Boreal ammonites
into the Tethys area, but also of Tethyan ammonites into the
Boreal area. The whole system was controlled by the tectonic
activity of the RP and the eustatic changes of sea level.

There is no agreement among specialists either in the higher

taxa systematics (families, subfamilies and higher), or in lower
taxa systematics (genera and lower) of the ammonites
discussed. For unification of terminology the author used the
system of Wright et al. (1996) only for the higher taxa and tried
to apply it to the various publications on the RP and
neighbouring regions. The author disagrees with Wright and
his colleagues in many points, especially in their attempt to
synonymize many of the Lower Cretaceous ammonite genera,
because it disagrees with stratigraphic data. The correct
number of species is really hard to calculate (it needs an
extended revision) and the author’s idea of the reality of the
taxa is reflected in Tables 1–4. The author’s work resulted in
the recognition of various paleozoogeographic regions and in
the attempt to define seaways, which were a very important
factor in water mass exchange and changes in the
configuration of ammonite areas.

Some problems of the distribution of the Lower Cretaceous

fauna of the RP and adjacent areas were observed by
Sasonova (1971, 1977; Sasonova & Sasonov 1967, 1979),
Saks et al. (1971, 1972), Shulgina  (1974), Mesezhnikov et al.
(1983). For the paleogeographical reconstructions I used
palinspastic maps, polar projection, by Rowley & Lottes
(1988), because this “mobile” pattern explains the faunal
distribution much better than the “fixed” one of Saks et al.
(1971, 1972).

The preliminary patterns of seaway changes and fluctua-

tions of ammonite areas on the RP were illustrated by the au-
thor (Baraboshkin 1997b) and in this paper I will focus more
tentatively on the Berriasian–Valanginian interval.

Early Berriasian

There is no uniform view on the subdivision of the Berria-

sian. Some authors do not like to subdivide it at all (Nikolov
1982; Luppov et al. 1988), others try to divide it into 3 sub-
stages (Hoedemaeker at al. 1995). The author prefers the
scheme, proposed by Sakharov (1984) for the North Caucasus,
where the lithostratigraphic subdivision coincides with the
biostratigraphic subdivision based on ammonites. This point is
also shared by Sasonova & Sasonov (1979), Sei & Kalacheva
(1997), Zeiss (1979), Casey et al. (1977). Two subdivisions in
the Berriasian are more useful for the RP and adjacent areas,
where Lower Berriasian (= Upper Volgian) sections are char-
acterized by a Boreal fauna whereas the Upper Berriasian suc-
cession contains a Tethyan as well as a Boreal fauna.

According to the publication of Casey (1973), Sasonova &

Sasonov (1979), Jeletzky (1984), Hoedemaeker (1987), Sei &
Kalacheva (1997), the Upper Volgian should be correlated
with the Lower Berriasian if we accept the boundary of the

Durangites spp./Berriasella jacobi Zones as the Jurassic/Creta-
ceous boundary. A very similar idea was proposed by Zeiss
(1979), but he drew the boundary at the base of the Subditus
Zone. It seems that the idea of Casey (1973), Sasonova & Sa-
sonov (1979) and Sei & Kalacheva (1997) is more reasonable
if we analyse the sea-connections of the RP and adjacent ar-
eas. The same idea was reflected in the correlation scheme of
the International Jurassic-Cretaceous Working Group (Za-
kharov et al. 1996). In the sections along the middle Volga
River (mainly Kashpir region), where the sedimentary record
of Lower Berriasian (= Upper Volgian)-Upper Berriasian (=
Ryazanian) transition is complete enough, one can see that
there are 4 major sedimentary events: at the top of the Dor-
soplanites panderi Zone, at the top of the Epivirgatites nikitini
Zone (Middle Volgian),  at the top of  the Surites tzikwinianus
Zone (Upper Berriasian) and at the top of the Lower Valangin-
ian. The Upper Volgian-Berriasian sedimentary style (sand-
stones with phosphorites) is the same. The extension of the hi-
atus between Upper Volgian (= Boreal Lower Berriasian) and
Upper Berriasian (= Ryazanain) is estimated to be one ammo-
nite zone or even less according to Casey et al. (1977),
Mesezhnikov (1979b), Mesezhnikov (1984), Sei & Kalacheva
(1997), and author’s data (Fig.  2). The range of that hiatus
was correlated with the Occitanica Zone by Hoedemaeker
(1987) i.e. with the Middle Berriasian (Hoedemaeker et al.
1995).

We have modified the zonal scheme of the Upper Volgian

and divided the Kashpurites fulgens Zone into 2 subzones:
Kashpurites fulgens s.s. and Craspedites nekrassovi
(Figs. 1, 2). The type section for this subdivision is located
on the right bank of the Volga River, Kashpir Town (Syzran
region), near to the boat station. The section and the
distribution of fossils in it were described in detail by
Gerasimov (1969, p. 26). The Kashpurites fulgens Subzone
corresponds to beds 6–8 and the Craspedites nekrassovi
Subzone to bed 5 of Gerasimov. The main peculiarity of the
new Craspedites nekrassovi Subzone is the appearance of
the first representatives of Craspedites, including the index
species and the widely distributed Craspedites okensis.

One of the key regions for clarifying the situation with the RP

Lower Berriasian is the Polish Furrow (Marek 1967–1969,
1983; Raczyńska 1967), where in the Kujawy area (Northern
Poland) it is possible to recognize traces of Tethyan Lower
Berriasian covering a Middle Volgian Succession with
Zarajskites

 and Virgatites and a Wealden Succession. Marek

recognized 2 ammonite levels (Marek et al. 1989; Marek &
Shulgina 1996): the Riasanites, Himalayites and Picteticeras
beds at the base and Surites, Euthymiceras and
Neocosmoceras

 beds at the top, which he proposed to be

equivalent to the Ryazanian horizon of the RP. Marek changed
his list of ammonite names 3 times at least (Marek 1967–1969;
Dembovska & Marek 1979; Marek et al. 1989 — with a
revision of his finds). According to his last publication on this
topic (Marek & Shulgina 1996), the lower ammonite
assemblage should be correlated with the Tethyan Tirnovella
occitanica Zone and with the Boreal Hectoroceras kochi Zone
and with a part of the Fauriella boissieri  Zone. I think that the
Boreal correlation was not correct, because Hectoroceras
occurred with Riasanites in the RP area, therefore, they cannot

8                                                                                            BARABOSHKIN

be Early Berriasian (see Fig. 2) in age. The genus  “Riasanites”
from Kujawy differs from the true Riasanites in the absence of a
ventral groove, the existence of a connection between the an-
gled secondary ribs and the high position of the point of virga-
tion. Sasonova (1977) thought that they are “not typical Riasani-
tes rjasanensis

” (p. 33) and similar to Riasanites maikopensis

from the North Caucasus.

If we look at the composition of the ammonite assemblage

for the Lower Berriasian (Table 1), we can determine the
following provinces in the region allied to the RP area.

A. Perisphinctid-Polyptychitid Province. It is character-

ized by the prevalence of Craspeditinae: Craspedites, Taimy-
roceras, Subcraspedites, Chetaites

 with rare representatives of

Perisphinctidae: Praechetaites (Sasonova & Sasonov 1979, =
Virgatosphinctes

 sensu Shulgina) and (?)Kossmatia with ex-

tremely rare Phylloceratidae: Phylloceras(?). The Province in-
cludes Western Siberia (with Polar Ural Mts.), Northern Sibe-
ria and Spitzbergen Islands. It was named North-Siberian
Subprovince of Arctic Province by Saks et al. (1971–1972)
and Shulgina (1974).

B. Polyptychitid  Province is characterized by the total

prevalence of Craspeditinae: Craspedites, Subcraspedites.
The Province includes Russian Platform and Pechora area in
the north and was referred to as the East-European Province
by Saks et al. (1971, 1972) and Shulgina (1974). Within this
area it is possible to differentiate a Platylenticeratinid
Subprovince

 (RP & Pechora Basins and eastern slope of the

Ural Mts.) and a related Craspeditinid Subprovince
(England). The Platylenticeratinid Subprovince contains en-
demic Platylenticeratinae: Garniericeras and Craspeditinae:

Kachpurites

 (typical for the RP and very rare in Pechora Basin

and in the east of Western Siberia). The Craspeditinid Sub-
province (England) is characterized by endemic Craspeditinae:
Subcraspedites (S.), S. (Swinnertonia), S. (Volgidiscus). 

Both

provinces could be placed in the Boreal climatic realm.

C. Neocomitid Province contains representatives of Berria-

sellinae (Neocomitidae): Pseudosubplanites, Retowskiceras,
Dalmasiceras?, Tirnovella, Mazenoticeras

, etc. Some rare

ammonites from the Perisphinctid-Polyptychitid Province,
may occur, but this is problematic. The Province belongs to
the northern part of Tethyan climatic realm and covers the ter-
ritory of Central Poland.

D. Olcostephanid-Neocomitid Province contains mainly

representatives of Berriasellinae: Pseudosubplanites, Retowski-
ceras, Dalmasiceras, Tirnovella, Mazenoticeras, Subalpinites

,

etc. quite frequent Olcostephanidae (Spiticeratinae: Spiticeras)
and rare representatives of Neocomitinae (Jabronella). The
Province belongs to the Tethyan climatic realm and includes
the Carpathians, Crimea and North Caucasus.

On the basis of ammonite zoogeography one may suppose

that the RP Basin had free connection with the Boreal Realm
during the Early Berriasian (= Late Volgian). The only
northern seaway  reflected on the basin reconstructions by
Sasonova (1971, 1977; Sasonova & Sasonov 1967) and Saks
et al. (1972, 1972). In 1977 Sasonova proposed an additional
reconstruction for Occitanica Chron (p. 30) with a northward
spread into the central part of the RP Basin of Malbosiceras
malbosi

 and Tirnovella sp. (samples in the collection of

Sasonova, she never illustrated them) from the Neocomitid
Province. I think that the reconstruction was not correct, be-

Fig. 2.

 Correlation of zonal index species ranges in Northern Siberia, Western Siberia, Pechora region, Russian Platform and Mangyshla k.

Legend:

 1 — Boreal zonal index species ranges; 2 — “European” zonal index ammonite ranges; 3 — Tethyan zonal index species ranges; 4

— Endemic zonal index species ranges; 5 — Absence of sediments; 6 — Limits of zonal index ammonite ranges; 7 — Supposed limits and
crossing of index species ranges.

BERRIASIAN -VALANGINIAN (EARLY CRETACEOUS) SEAWAYS OF THE RUSSIAN PLATFORM BASIN              9

cause nobody mentioned Early Berriasian Tethyan ammonite
finds from the RP. The absolute domination of a Boreal ammo-
nite fauna in the Lower Berriasian of the RP also excludes
connections with the Polish Furrow Basin. Therefore, the Rus-
sian sea was connected with the other regions only through the
Pechora Basin. In the previous model the author supposes the
existence of a Timan highland as an island chain (Baraboshkin
1997b). Recently, I accepted the idea of Gramberg & Ronkina
(1983), that the Timan region developed as a submerged high
from the Late Jurassic. The Baltic Shield was probably a high-
land during the Cretaceous.

In the Early Berriasian the basin temperature conditions of

the RP sea were different from the Arctic sea. Therefore,
many endemic species in this basin: Kachpurites,
Garniericeras

 and various endemic species of Craspedites

(Gerasimov 1969). “Garniericeras” described from Siberia
by Shulgina (in Ronkina et al. 1969) and Mesezhnikov et al.
(1983), differ significantly from the real Garniericeras in be-
ing more similar to Subcraspedites (Volgidiscus), which oc-
curs in England (Casey et al. 1977). Some of these
Craspedites

 forms were found in the Pechora Basin and the

Polar Ural Mts. The southward expansion of the Craspeditinae
also occurred during that time. In particular, Craspedites
okensis

 penetrated into the RP Basin during the second half of

the Fulgens Chron.

The southern margin of the RP Basin was located in the

Peri-Caspian region. This is supported by the finds of
Craspedites okensis

 and Kachpurites cf. subfulgens(?) in the

Koi-Kara–Kainar River area (Sokolova 1939; Vakhrameev
1952). Those “far south” finds of  fragments of Kachpurites
sp. indet. (Braduchan et al. 1986: p. 104, pl. XVI: figs. 1, 2)
from the Salyma River area in Western Siberia give us a
possibility to presume the existence of a shallow seaway
between the RP and the Western Siberia Basin. The analysis
of the paleogeographical data (Surkov 1995) shows that the
south-west marginal facies of the “Bazhenov” Basin (in the
direction of Ekaterinburg city, Middle Ural Mts.) are missing
(eroded) and fine clayey and bituminous facies are located in
the western part of this basin. In the RP Basin in its present con-
figuration the same clayey facies are located only in the Peri-
Caspian region (Sasonova 1977), whereas the other area to the
north-west is covered by shallow-water sandy facies. So, it is

Polish

Basin

Spitzber-

gen

Basin

North

Siberia

Basin

Western

Siberia

Basin

(+Polar

Urals)

Pechora

Basin

Moscow

Basin

Ulianovsk

-Saratov

Basin

Peri-

Caspian

Basin

Mangy-

shlak

Basin

North

Caucasus

Basin

Phylloceratidae

Phylloceras s.l.

1?

Perisphinctidae

Dorsoplanitinae

Chetaites

1

1

Paracraspedites

1?

Virgatosphinctinae

Praechetaites

1?

3?

1?

Polyptychitidae

Platylenticeratinae

Garniericeras

1?

1?

+

3

3

+

Craspeditinae

Taimyroceras

1

3

1

Craspedites

3

3

3

3

16

15

1?

Kachpurites

2

2

2

2

1?

Subcraspedites

1?

1

2

1?

Volgidiscus

1

Pseudocraspedites

4

Neocomitidae

Berriasellinae

Dalmasiceras

1?

1(3?)

Delphinella

1

Fauriella

2(4?)

Malbosiceras

1?

1?

Mazenoticeras

2

Pseudosubplanites

2?

2?

Retowskiceras

1?

1

Tirnovella

1?

2(1?)

Neocomitinae

Jabronella

2

Olcostephanidae

Spiticeratinae

Spiticeras

2(3?)

Table 1:

 Distribution of Lower Berriasian (= Upper Volgian) ammonite genera and subgenera.  Explanations: The data were taken from

works of Aristov & Ivanov 1971; Casey et al. 1977; Dembovska & Marek 1979; Gerasimov 1969, 1986; Golbert & Klimova 1979; Gordeev
1971; Klimova 1982, 1990; Kutek & Marcinowski 1996; Kvantaliani & Sakharov 1986; Luppov et al. 1983, 1988; Marek 1967; Mesezhnik-
ov et al. 1979a,b; Sakharov 1984; Saks et al. 1972; Sasonova 1971, 1977; Sei & Kalacheva 1997; Zakharov & Mesezhnikov 1974 and com-
pleted by the author’s data. “?” marks problematic determination of the genus. “+” indicate presence of genus without species name and fig-
ure. Numbers indicate the number of the species illustrated in publications and mentioned in the lists.

10                                                                                            BARABOSHKIN

very probable that a seaway connected Western Siberia with
the RP Basin in the Early Berriasian and that Kachpurites used
this for the eastward expansion of it area. The existence of this
strait is recognized for the first time in the Berriasian–Hau-
terivian. It probably functioned also during the Late Jurassic.
It seems that the RP Basin was the shallow shelf of the West
Siberian sea. This idea was discussed first by A.G. Olferiev
(PGO “Centrgeologia”, personal communication) as one of the
alternative possibilities to explain the peculiarities of the RP
paleogeography.

The distribution of Praechetaites in the Perisphinctid-

Polyptychitid Province provides additional data on the direc-
tion of water mass movement. The earliest finds of Praechetait-
es

 gr. tenuicostatus are mentioned from the Epivirgatites vari-

abilis Zone of North Siberia (Saks et al. 1976), where they
occurred up to the Chetaites chetae Zone (Upper Volgian). The
same species was found in the Polar Ural Mts. (Golbert & Kli-
mova 1979) in the Chetaites chetae Zone and in the Spitzbergen
Islands (Ershova 1983) from the same level (but without
Chetaites

). This shows that Praechetaites migrated from the Pa-

cific Ocean (or North-Eastern Tethys, but not from the Atlantic
(!) as was supposed by Saks et al. (1971, 1972) and invaded the
North Siberian Basin in the latest Jurassic.

Late Berriasian

The late Berriasian is characterized by shallow marine to

continental conditions in the RP Basin. Specialists agree that
the “Ryazanian Horizon” of Bogoslowsky (1897) should be
referred to as Upper Berriasian. I accept in general the bios-
tratigraphic scheme by Mesezhnikov et al. (1979) for Upper
Berriasian, but I think that Tzikwinianus Zone could be over-
builded by Simplex Zone of Sasonova (1977). I cannot agree
with the opinion of Mesezhnikov (Mesezhnikov et al. 1979;
Mesezhnikov 1984) that Surites simplex should be referred to
Nikitinoceras

 and therefore to the base of the Valanginian. I

also think that the Zone of Riasanites rjasanensis and Garni-
ericeras subclypeiforme

 of Mesezhnikov (1984) could not be

accepted at the moment, because of the debatable position of
finds of Garniericeras: are they reworked or not? On the other
hand, I agree with the existence of a level in the base of the
Rjasanensis Zone, which contains different Riasanites. It is
possible that the level one may correlate with the Sibiricus
Zone (or a part of it) of the Boreal scheme.

In the Late Berriasian we recognize the following provinces

in the region allied to the RP area (Table 2).

A. The Perisphinctid-Polyptychitid Province is character-

ized by the dominance of Tolliinae (Bojarkia, Praetollia,
Tollia, Surites, Peregrinoceras

, etc.) and Craspeditinae

(Hectoroceras) and rare Chetaites (Perisphinctidae). The
Province includes Western Siberia (with the Polar Ural Mts.),
Arctic Siberia, the Spitzbergen Islands and Greenland. It was
called the North-Siberian Province by Saks et al. (1971, 1972),
Shulgina (1974) or Siberian/North American Region by
Rawson (1981). The finding of Riasanites in the Spitzbergen
Islands (Zhirmunsky 1927) is very questionable, because this
genus is not even known from the Pechora Basin. The
distribution of Riasanites towards the north was limited by the
water temperatures.

B.  The  Polyptychitid  Province is characterized by the

prevalence of Tolliinae (Runctonia, Borealites, Paratollia,
Surites, Peregrinoceras

, etc.) and Craspeditinae (Hector-

oceras

). England is the only region within this Province.

C.  The  Neocomitid-Polyptychitid  Province contains

representatives of Tolliinae (Surites, Caseyiceras, Borealites,
Peregrinoceras, Externiceras, Subcraspedites, 

etc.), rare

Craspeditinae (Hectoroceras) and Berriasellinae (Riasanites,
Euthymiceras, Transcaspiites

) and the first Polyptychitinae

(Subpolyptychites). The only find of Chetaites (Peri-
sphinctidae) was also mentioned from this Province (Sasonova
1977). The Province includes the Russian Platform, Poland,
Mangyshlak. It was divided by Saks et al. (1971, 1972) and
Shulgina (1974) into 2 Subprovinces (Polish and East-
European) which seems very unnatural, because both basins
contain the same ammonite families.

D.  The  Olcostephanid-Neocomitid Province mainly

contains representatives of Berriasellinae (Euthymiceras, Neo-
cosmoceras, Riasanites, Fauriella, Picteticeras, Trans-
caspiites

, etc.), quite frequent Olcostephanidae (Spiticeras),

rare Himalayitinae (Himalayites) and Neocomitinae
(Jabronella). The Province forms part of the Tethyan climatic
realm and includes the Carpathians, the Crimea and the North
Caucasus. According to Rawson (1981) the last two should
still be included in the Neocomitid-Polyptychitid Province
(i.e. his European Province for the Berriasian–Early
Barremian), but this disagrees with the family distribution data
at least for Berriasian–Lower Hauterivian.

The early Late Berriasian is characterized by the expan-

sion of Tethyan ammonites towards the north. This occurred
along 2 routes (Fig. 2). One seaway connected the Polish Ba-
sin with the Crimea–Carpathians area. Sasonova (1971,
1977) supposed that there was no direct connection between
the RP Basin and the Polish Basin, because of the difference
in faunas (in contrast to the ideas of Marek 1967–1969). The
Polish “Ryazanian” fauna differs significantly from the origi-
nal Ryazanian of the RP (see above). The other seaway
passed through Mangyshlak, where the neocomitid diversity
is rather high (Table 2): Neocosmoceras, Euthymiceras,
Riasanites

, other Berriasellids and Boreal Surites. Luppov et

al. (1988) supposed an Early Berriasian age for the basal part
of this succession. A comparison with the North Caucasus
ammonite succession (Sakharov 1984; Sei & Kalacheva
1997) indicates, however, a Late Berriasian age for the
Mangyshlak ammonite assemblage. It should be noted that
the first species of Riasanites (R. cf. swistowianus, R. ex gr.
subrjasanensis

) were found together with Neocosmoceras

and Transcaspiites in this area (“Lone of Neocosmoceras
and  Septaliphoria semenovi”: Luppov et al. 1988). This
makes the distribution of the later two genera the same as in
the North Caucasus the so-called “lower Riasanites” level
(Sei & Kalacheva 1997). In this case, it would probably be
better to refer to “the upper Riasanites” level as the Taurico-
ceras

 level (Kvantaliani & Lysenko 1979) and correlated

with the “upper Riasanites” level from Mangyshlak (Riasan-
ites rjasanensis

 (p. 130, pl. XVII: figs. 4, 6); R. sp. nov. ex

gr. rjasanensis (p. 132, pl. XVII: fig. 7, Luppov et al. 1988).
The Boreal ammonites Surites cf. spasskensis and S. koza-
kowianus 

were mentioned from the basal part of the Upper

BERRIASIAN -VALANGINIAN (EARLY CRETACEOUS) SEAWAYS OF THE RUSSIAN PLATFORM BASIN              11

Berriasian of Mangyshlak (Luppov et al. 1988). This consid-
erably differs from the situation in the central part of RP,
where these species of Surites appear above the beds with the
first Riasanites, Transcaspiites and Euthymiceras (Sasonova
1977; Mesezhnikov et al. 1979b). Taking in account that both
samples were not collected by the authors themselves and
that most finds of Surites  (in situ) are known from higher
levels than those with the FO of Riasanites, Transcaspiites
and Euthymiceras, we may suppose that the given age by
Luppov et al. (1988) was provisional. Then we must con-
clude that Lons (= local Zones) of “Buchia volgensis” and
“Riasanites

 and Pygurus rostratus” correlates with the

Surites tzikwinianus Zone and with upper part of the Riasan-
ites rjasanensis Zone of the RP (according to Mesezhnikov
1984). Only Surites sp. indet. was mentioned in list from the

Neocosmoceras and Septaliphoria semenovi Lone from Dz-
harmysh section (Luppov et al. 1988, p. 25, not illustrated). If
it is a true Surites, we may expect the opening of a direct
sea-connection with the West Siberian Basin and an acceler-
ated penetration of Surites into the Peri-Caspian and Mangy-
shlak areas. In the central parts of the RP, the first Surites ap-
pears together with Riasanites, above the base of Rjasanensis
Zone and Hectoroceras level (Mesezhnikov 1984), i.e. much
higher than in the Mangyshlak. In that case Surites could ap-
pear there even earlier than in the RP. The other reason for
this suggestion is the comparison of the paleogeography of
the RP (Sasonova 1977) and Western Siberia (Sarkisian &
Protzvetalova 1968). If mainly clayey sedimentation took
place in the north-western part of Western Siberia, it was
mainly sandy sedimentation in the RP (with some exceptions

Polish

Basin

Spitzber-

gen Basin

North

Siberia

Basin

Western

Siberia

Basin

(+Polar

Urals)

Pechora

Basin

Moscow

Basin

Ulianovsk-

Saratov

Basin

Peri-

Caspian

Basin

Mangy-

shlak

Basin

North

Caucasus

Basin

Neocomitidae

Berriasellinae

Argentiniceras (?)

1

Prorjasanites

2

+?

+?

Riasanites

?

1?

4

3

1?

6

6(4?)

Berriasella

1

1

Blanfordiceras

2?

Euthymiceras

1

1

1?

Fauriella

1

Gechiceras

3

Neocosmoceras

2

4

2(2?)

Malbosiceras

2?

1?

Mazenoticeras

1

1

Picteticeras

1

3

Tauricoceras

1?

Tirnovella

1?

Transcaspiites

3

2(3?)

Neocomitinae

Jabronella

1

1

Subalpinites

3

1

Himalayitinae

Himalayites

1?

1?

Perisphinctidae

Dorsoplanitinae

Chetaites

1

2

1

Polyptychitidae

Craspeditinae

Hectoroceras

3

1

1

Tolliinae

Surites

3

1

4

2

3

10

10

+

4

?

Externiceras

1?

2

2

1

Bogoslovskia

+

2

2

+

Caseyiceras

2

3

3

+

Chandomirovia

+

1

1

1

Pronjaites

1?

+

2

2

+

Pseudocraspedites

1

Praesurites

1

Ronkinites

1

Schulginites

3

Peregrinoceras

1

1

2

Praetolia

1?

1

2

1?

Bojarkia

1

3

3

1

Borealites

1?

1

1

5

1

Tollia

1?

1

1

1

Polyptychitinae

Subpolyptychites

1

Olcostephanidae

Spiticeratinae

Spiticeras

6(3?)

Table 2:

 Distribution of Upper Berriasian ammonite genera and subgenera.  Explanations see Table 1.

12                                                                                            BARABOSHKIN

in the Peri-Caspian region). Nevertheless, an island chain in-
stead of the Ural Mts. must have existed as a natural border
separating different paleozoogeographical provinces.

Neocosmoceras

 is not known from the centre of the RP, so

the basal part of the Upper Berriasian does not exist here (see
also Sasonova & Sasonov 1979) and the Tethyan transgression
reached this region only later. Analogues of the Siberian
Chetaites chetae Zone (the Uppermost Volgian according to
Siberian scheme: Zakharov et al. 1997) are probably missing
in the RP. I agree with Casey (1973) and Sasonova (1977, not
Sasonova & Sasonov 1979) that a part of Riasanites rjasanen-
sis Zone of RP probably correlates with a part of the Chetaites
sibiricus Zone (Siberian scheme). Fortunately, rare finds of
Hectoroceras

 sp. juv. (Mesezhnikov et al. 1979a) in the

Pechora region and Hectoroceras sp. indet and H. cf. kochi
(Casey et al. 1977; Mesezhnikov et al. 1979b) near Riasan and
the author’s finds in the Moscow region mark the beginning of
a Boreal fauna expansion through the meridional strait. In this
time the RP–Polish Basin connection did not exist (possibly it
opened later). The Boreal influence became more powerful at
the end of the Berriasian, when Surites, Peregrinoceras, Bore-
alites

, etc. reached the central parts of RP, Peri-Caspian and

Mangyshlak. Some of the Boreal ammonites possibly pene-
trated into the North Caucasus Basin. One find of Surites cf.
pechorensis

 was reported by Sakharov (Sakharov & Frolova-

Bagreeva 1973, p. 130) from Gizeldon River (North Osetia). It
was found in an assemblage with Riasanites subrjasanensis,
“Paracraspedites”

 sp. and “Berriasella” aff. broussei. Unfor-

tunately, those finds are very problematic, because in the spe-
cial publication on the Boreal invasions into the Northern Cau-
casus by Sakharov (1993) he did not mention this Surites.
Nevertheless, a restricted connection is possible because of the
presence of Buchia there (Sakharov 1993).

The existence of a Late Berriasian sublatitudinal seaway in

the RP was proposed by Sasonova (Sasonova & Sasonov
1967; Sasonova 1971, 1977). She supposed that the connect-
ion between RP and Polish Basin did not appear earlier than
the Surites spasskensis Chron. It is supported by finds of
Surites 

and rare (?)Externiceras (the typical form for the RP)

in Central Poland (Marek 1967, 1968, 1983; Raczyńska 1967).
It is possible, however, that the Boreal faunas coming from the
North Sea (some of the English suritids, described by Casey
(1973) are similar to those of the RP area: Casey et al.  1977).
Anyway, this strait should have opened not long before the
Berriasian/Valanginian boundary, because it was the only way
by which Delphinites (= Pseudogarnieria), Proleopoldia and
Platylenticeras

 could have migrated from Western Europe to

the east.

Early Valanginian

The Early Valanginian was characterized by a decreasing of

the ammonite diversity in the investigated area. Shallow ma-
rine to continental conditions existed over the RP and the
southern connection was closed or was extremely restricted.
The Valanginian is one of the known good levels for
correlation. There is only a problem with the definition of the
base of the Valanginian in the RP region: the position of the

Bogoslovskia simplex Zone. Sasonova (1971, 1977; Sasonova
& Sasonov 1979) prefers to put it in the top of the Berriasian
succession and I agree.

The following ammonite provinces could be recognized for

the Early Valanginian (see Table 3):

A.  The Polyptychitid Province is characterized by the

dominance of Tolliinae: Neotollia, Nikitinoceras (= Temno-
ptychites

), Tollia, etc. and various Polyptychitinae: Amundo-

ptychites, Astieriptychites, Euryptychites, Polyptychites

, etc.

The Province includes Western Siberia (with the Polar Ural
Mts.), Arctic Siberia, the Spitzbergen Islands, Greenland and
England. It was recognized as the Arctic Region by Saks et
al. (1971, 1972) and Shulgina (1974) (or the Siberian/North
American Region by Rawson (1981)) with 3 Provinces: the
Pechora-Greenland, North Siberian and Chukotka-Canadian
Provinces. The RP was recognized by Saks et al. and
Shulgina as a separate East-European Province within the
Boreal-Atlantic Region. It coincides in principle with our
definitions: the RP should be separated as Platylenticera-
tinid-Polyptychitinid

-Tolliinid  Subprovince, because of

the dominance of Tolliinae, the presence of relatively rare
Polyptychitinae and rare Platylenticeratinae: Delphinites,
Platylenticeras 

and Proleopoldia, which passed through Pol-

ish Basin to the east. The other part of the Province should be
determined as Polyptychitinid-Tolliinid Subprovince.

B.  The  Neocomitid-Polyptychitid  Province is character-

ized by an assemblage of rare Platylenticeratinae (Platylen-
ticeras

), Tolliinae (Nikitinoceras), Polyptychitinae (Astieripty-

chites, Euryptychites, Polyptychites

) and relatively rare

Neocomitidae (Thurmanniceras, Karakaschiceras). Two Sub-
provinces could be distinguished in the Province: The Neo-
comitinid-Polyptychitinid-Tolliinid Subprovince

 (Mangy-

shlak area and Peri-Caspian) and the Neocomitinid-
Platylenticeratinid-Polyptychitinid

 Subprovince (Poland,

Germany, England).

C.  The  Neocomitid Province contains representatives of

the Neocomitidae: Kilianella and Busnardoites. The Province
includes the North Caucasus Basin and belongs to the Tethyan
Realm.

D. The Olcostephanid-Neocomitid Province contains rep-

resentatives of the Neocomitidae (Kilianella, Thurmanniceras,
Busnardoites, 

etc.), and Olcostephanidae (Olcostephanus,

Spiticeras

, etc.). The Province belongs to the Tethyan Realm

and includes the recent territory of southern Europe, Crimea
(Baraboshkin 1997a) and extends further to the south-east.

A sublatitudinal strait connecting the Polish Basin with the

RP existed at the beginning of the Early Valanginian. This is
confirmed by the distribution of the Platylenticeratinae; Platy-
lenticeras

 and possibly Proleopoldia moved from Europe

through the Polish Basin to the RP Basin. The direction of this
faunal expansion was probably opposite to that in the Late the
Berriasian. According to Saks et al. (1971) the provisional di-
rection of the faunal movement was the same as in the Berria-
sian, but this would conflict with the higher diversity of repre-
sentatives of the Platylenticeratinae in Western Europe
(mainly Germany) and their presence in Greenland. Moreover,
finds of the Platylenticeratinae are not known from the Siberi-
an-Pechora area. As to the derivation of Platylenticeras, it

BERRIASIAN -VALANGINIAN (EARLY CRETACEOUS) SEAWAYS OF THE RUSSIAN PLATFORM BASIN              13

seems that this genus penetrated the RP not because of the
“northward spread” of the sea (Rawson 1993), but because of
the opening of the latitudinal connection.

The other seaway joined the Arctic sea with the central part of

the Russian Platform. The fauna moved through the Pechora
Basin and the diversity of Nikitinoceras there is very similar to
that in the centre of the RP. In the Pechora area (Izhma River)
typically Siberian Tollia and Neotollia are common, whereas
many of the endemic ammonites (Stchirowskiceras, Suridiscus,
Luppoviceras, Costamenjaites

, etc.) were spread over the RP

Basin (Sasonova 1971, 1977). It indicates a one-way exchange
with Western Siberia. It seems that most specimens of
Polyptychites

 in the RP were found in phosphorite conglomer-

ates, they were interpreted as redeposited and mixed with in situ
Nikitinoceras

.

The diversity of Polyptychites in the Mangyshlak area (Lup-

pov et al. 1988) and the frequency of Euryptychites, Astierip-
tychites

 and Nikitinoceras in the Peri-Caspian region (Aktu-

binsk region, author’s data) are much higher than in the RP
(Table 3). Moreover, there are some finds of Tollia sp. in the

Aktyubinsk region (Moskvin 1986, p. 67). This implies the
presence of a seaway joining Western Siberia and the south-
eastern part of the RP. According to paleogeographical data
(Sarkisian & Protzvetalova 1968) this seaway should be shal-
lower and narrower.

The RP Basin had a very limited sea-connection with the

North Caucasus Basin and only Tethyan ammonites (Kilianel-
la, Busnardoites

) are known from the latter region (Sakharov

1984, 1993; Kvantaliani & Sakharov 1986). Very rare Thur-
manniceras(?)

 and Karakaschiceras(?) are mentioned from

the Mangyshlak–Peri-Caspian area (Moskvin 1986).

A movement of Boreal ammonites during the Early Valang-

inian has been recognized in Western Europe. A new seaway
could have opened through Northern France (?) or Germany
(as was supposed by Rawson 1995), because a rich ammonite
assemblage with Platylenticeras and Polyptychites is known
from southern France (Thieuloy 1973; Kemper et al. 1981;
Rawson 1981) as well as in Germany (Kemper 1961). In the
Polish Lowland (Marek & Raczyńska 1973) and in the Car-
pathians (Michalík 1995) Platylenticeras is not so frequent.

Polish

Basin

Spitzber-

gen Basin

North

Siberia

Basin

Western

Siberia

Basin

(+Polar

Urals)

Pechora

Basin

Moscow

Basin

Ulianovsk-

Saratov

Basin

Peri-

Caspian

Basin

Mangy-

shlak

Basin

North

Caucasus

Basin

Lytoceratidae

"Lytoceras"

1?

Phylloceratidae

"Phylloceras

1?

Neocomitidae

Endemoceratinae

Karakaschiceras

4

1?

Neocomitinae

Busnardoites

2

Kilianella

1

Thurmanniceras

1

1

1?

Polyptychitidae

Tolliinae

Nikitinoceras

+?

2

12

7

4

4

1

3

1

Bogoslovskia

+

+

+

+

Costamenjaites

1?

+

1

4

Stchirowskiceras

+

+

4

4

Luppoviceras

1

Suridiscus

2

Menjaites

+

1?

1

6

6

Tollia

1

1

1

1?

Neotollia

5

4

1?

Neocraspedites

1

Thorsteinssonoceras

1

Subtemnoptychites

2

1?

Bodylevskites

2

1?

Russanovia

2

2

Platylenticeratinae

Platylenticeras

2

1

+

Delphinites

3

Proleopoldia

3

Tolypeceras

+

Polyptychitinae

Polyptychites

3

7

7

2

2

2

6

Euryptychites

2

3

1

1

1

1

Astieriptychites

4

2

1

1

1

Subpolyptychites

3

Amundoptychites

3

1

Siberites

2

1

Siberiptychites

1

1

Primitiviptychites

1

Virgatoptychites

2

Table 3:

 Distribution of Lower Valanginian ammonite genera and subgenera.  Explanations see Table 1.

14                                                                                            BARABOSHKIN

Late Valanginian

Late Valanginian sediments in the RP Basin are only locally

preserved in the northern part of the Moscow Syneclise and in
the Peri-Caspian area and contain very rare Dichotomites bidi-
chotomus

 and Polyptychites petschorensis (Sasonova 1958).

The following ammonite provinces could be defined in the

studied area during the Late Valanginian (Table 4).

A.  The  Polyptychitid  Province is characterized by the

domination of the Polyptychitinae: Dichotomites, Polyptychites,
Homolsomites

 and by rare Tolliinae: Neocraspedites. The

Province embraces Western and Arctic Siberia, the Spitzbergen
Islands and RP. It could be subdivided into the Tolliinid-
Polyptychitinid

  Subprovince  (Siberia, Polar Ural Mts.,

Pechora Basin), because of the presence of Tolliinae and the
Polyptychitinid

  Subprovince s.s. (Russian Platform except

Peri-Caspian).

B. The Neocomitid-Polyptychitid Province is characterized

by an assemblage of the Polyptychitinae (Dichotomites, Polyp-
tychites, Homolsomites

), rare Tolliinae (Neocraspedites), and

Neocomitidae (Neohoploceras, Karakaschiceras). Probably,
very rare Olcostephanidae (Valanginites?) also occur there
(Mangyshlak: Luppov et al. 1988). The Province includes only
the Mangyshlak–Peri-Caspian area.

C.  The Polyptychitid-Olcostephanid-Neocomitid Province

contains mainly representatives of the Neocomitidae (Karak-
aschiceras,

 

Teschenites

, 

Neocomites

); Olcostephanidae

(Valanginites, 

Olcostephanus

, 

Saynoceras

) and quite rare Polyp-

tychitinae (Dichotomites, Polyptychites, Prodichotomites). The
Province covers the Polish Basin and the North Caucasus Basin.

D. The Olcostephanid-Neocomitid Province contains rep-

resentatives of the Neocomitidae: Karakaschiceras, Teschen-
ites

, Neocomites, Luppovella; Olcostephanidae: Valanginites,

Olcostephanus

, Saynoceras. The presence of the Polyptychiti-

nae (Dichotomites, Polyptychites) is questionable. The Prov-
ince covers the North Caucasus Basin, southern Europe and
the Crimea (Baraboshkin 1997a).

Representatives of Bochianitidae (Bochianites, Protolepto-

ceras

) could occur as a rare occasional element either in the

Polyptychitid Province and in the Polyptychitid-Olcoste-
phanid-Neocomitid Province. It betrays the existence of a
direct Boreal–Tethyan connection.

An important seaway connected the RP Basin with the

Arctic sea through the Pechora Basin. It is confirmed by the
similarity of the ammonite assemblages in these basins, but
there were a few more Boreal elements in the Pechora –
Polar Ural Mts. region than in the RP (see Table 4). The
highest sea-level position was determined for the Polar Ural
Mts.–Western Siberia in the Late Valanginian (Golbert &
Klimova 1979) and resulted in a free penetration of ammo-
nite faunas through this seaway. In spite of the co-occurrence
of Dichotomites and Homolsomites in Western Siberia (Kli-
mova 1990), it seems that in the RP (Yaroslavl region: Shul-
gina et al. 1979) both genera appear to be reworked in phos-
phorite conglomerates.

The seaway between the Polish Basin and the RP was

closed. This is confirmed by the presence of a Tethyan fauna
in the Polish furrow (Marek & Raczyńska 1973; Kutek &
Marcinowski 1996; Kutek et al.1989) and its absence in the
Russian Platform. The other argument is the general paleogeo-

Polish

Basin

Spitzberg

en Basin

North

Siberia

Basin

Western

Siberia

Basin

(+Polar

Urals)

Pechora

Basin

Moscow

Basin

Ulianovsk-

Saratov

Basin

Peri-

Caspian

Basin

Mangy-

shlak

Basin

North

Caucasus

Basin

Polyptychitidae

Tolliinae

Neocraspedites

2?

3

2

1

1

1

1?

Polyptychitinae

Dichotomites

6

3

1

3

2

1

1?

5

1?

Polyptychites

3

2

17

1

2

1

1

1?

1

1?

Prodichotomites

1?

1

2?

2

+?

Homolsomites

1

1?

1?

Olcostephanidae
Olcostephaninae

Olcostephanus

1

3

Rogersites

1

Saynoceras

1

2

Valanginites

2

1?

2

Neocomitidae

Endemoceratinae

Karakaschiceras

2

1?

2

Neohoploceras

1

1

Neocomitinae

Luppovella

1

Neocomites

1?

1

Teschenites

1

Sarasinella

1

Bochianitidae
Bochianitinae

Bochianites

1

1

Protoleptoceras

1

Haploceratidae

Neolissoceras

1

Table 4:

 Distribution of Upper Valanginian ammonite genera and subgenera.  Explanations see Table 1.

BERRIASIAN -VALANGINIAN (EARLY CRETACEOUS) SEAWAYS OF THE RUSSIAN PLATFORM BASIN              15

graphical situation in the Russian Platform (excluding the
Peri-Caspian region): the development of a shallow-water
sandy facies with rare faunal remains in the northern part (Sa-
sonova 1958; Moskvin 1986), which are missing in the central
part of the RP.

The other region with Upper Valanginian sediments is the

Peri-Caspian region, where they are developed in a sandy
facies (salt dome sections) and in a silty-clayey facies (be-
tween salt domes). The ammonite fauna is typically Boreal:
Dichotomites, Polyptychites 

(Moskvin 1986; Sasonova & Sa-

sonov 1967, and author’s data) and rare Neocraspedites (au-
thor’s data from the Aktubinsk region). The co-occurrence of
Dichotomites

 with the earliest Homolsomites: H. petschoren-

sis

 (Moskvin 1986) is important, for it makes the situation al-

most identical to Western Siberia (Klimova 1990), the
Spitzbergen Islands (Ershova 1983) and probably Poland
(Marek 1968). This co-occurrence as well as the paleogeo-
graphical data from Western Siberia (Sarkisian & Protzvetalo-
va 1968) confirm the existence of a sea-connection between
Western Siberia and the Peri-Caspian region. The central part
of the strait was located in the Middle Ural Mts. A seaway was
opened further to the south towards Mangyshlak, where a Bo-
real ammonite fauna is dominant (Luppov et al. 1983). Very
rare Upper Valanginian ammonites from the Tethys: Neohop-
loceras(?)

 (Gordeev 1971), Valanginites(?): Luppov et al.

(1983) are also known from this region.

The furthest finds of Boreal ammonites (Dichotomites bidi-

chotomus, Neocraspedites grotriani, Polyptychites eurypty-
choides

) together with North Tethyan Acanthodiscus and Le-

opoldia

 are known from the North Caucasus and were

mentioned in the paper of Egoyan & Tkachuk (1965). Unfortu-
nately, those ammonites were not illustrated and it is impossi-
ble to find out what they really are. The work of the author
during a long time in the North Caucasus did not reveal new
finds of these Boreal Upper Valanginian ammonites.

The expansion of the Boreal fauna was significant in the

Late Valanginian, probably even more significant than in the
Early Valanginian, because Boreal ammonites penetrated into
the northern margins of the Tethys not only in the regions of
Poland–Mangyshlak, but also in France, where Dichotomites
and Neocraspedites were found (Thieuloy 1973; Kemper et al.
1981).

Sea-level changes

It is hard to reconstruct the sea-level changes on the basis of

a few sections in the RP because of numerous unconformities
and stratigraphical problems. A compilation of the data from
the northern part of the Moscow Syneclise provided material
to draw a provisional sea-level curve (Fig. 1). The comparison
of this curve with the “global” curve (Haq et al. 1988) shows
that its trend is close to the fluctuations for the Lower Berria-
sian–mid-Valanginian. It is strongly confirmed by ammonite
diversity. The trend of the 2nd order curve starts to be opposite
to the ammonite diversity for the Michalskii–Bidichotomus
zones. This irregularity can be explained as being caused by
tectonic movements: the uplift of the northern part of the RP
and the attendant shallowing of the sea (Fig. 3). These data are
in contradiction to Rawson’s (1993, 1995) idea on the late Ear-

ly Valanginian and mid-Valanginian sea-level rise. But Raw-
son’s idea fits in well with sea-level rise in the southern part of
the RP (Peri-Caspian–Mangyshlak area), because of the open-
ing of the seaway to Western Siberia through the Urals. The
3rd-order curve contains more peaks than the “global” curve
because of the very shallow marine conditions of the RP. Sea-
level drops were have appeared around most of the zonal
boundaries.

An other logical conclusion can be reached when one

compares the rate of endemism with the third-order sea-level
changes (Fig. 1). Endemism rises during shallowing of the
sea. Shallowing leads to the appearance of geographical
barriers, which makes the exchange of marine fauna difficult.
The rate of endemism was very high during the Fulgens and
Nodiger chrons in the Early Berriasian, and the Simplex
Chron in the Late Berriasian. In the second half of the Fulgens
Chron a part of the West-Siberian Craspeditidae (Craspedites
okensis, for example) penetrated into the RP Basin and mixed
with the endemics there. The endemism increased during the
Subtzikwinianus and Undulatoplicatilis Chron and decreased
during the Rjasanensis Chron when Tethyan and Boreal faunas
mixed in the RP Basin. The late Early-Late Valanginian faunas
had no endemic ammonites at all because of the absence of
isolation of the RP Basin.

Recently, sea-level curves for the Jurassic–Cretaceous of

the RP were produced by Sahagian et al. (1996). Previous
works of the group of Sahagian have already been criticized
by me (Naidin & Baraboshkin 1994), but some of their mis-
takes were repeated again in their last work. I still cannot un-
derstand the reason for incorporating the data from Siberia
(why not Arctic Canada or Greenland?!) in the Valanginian
curve for the RP. It does not help to understand the complex
geological history of the RP and does not reflect the real
eustatic changes in the marine basin of the RP. Therefore,
there is no reason to discuss the Valanginian part of this
curve as the curve for the RP. The Upper Volgian-Berriasian
part (i.e. Berriasian part according to this paper) of the sea-
level curve of Sahagian et al. (1996) coincides in major fea-
tures with our data (with the exception of absence of  the
Simplex Zone in their stratigraphic frame).

Discussion

According to the proposed model we can conclude the fol-

lowing.

1. The shape of the RP Basin has changed during the Berria-

sian and Valanginian ages. There were 4 seaways functioning
in the RP Basin during that time (not 3 as was supposed be-
fore): (1) the Byelorussia Strait connecting the Polish Furrow
and the RP; (2) the Caspian Strait connecting the RP with
Mangyshlak area; (3) the Pechorian Strait connecting the RP
with the the Arctic basin and (4) the Mid-Uralian Strait con-
necting the RP–Peri-Caspian region with Western Siberia. The
latter is recognized here for the first time. It was located
probably in a gap through the Middle Ural Mts. (Ekaterinburg
region), where the distance between the RP and Western is
very short. From the latest Jurassic to the Valanginian, the
Ural Mts. developed as an island chain or partially submerged

16                                                                                            BARABOSHKIN

area. The northern part of the Ural Mts. became uplifted in the
early Late Berriasian and submerged in the Valanginian (Gol-
bert & Klimova 1979). The submergence happened as a result
of Western Siberia immersion: the connection of Western Si-

beria with the Peri-Caspian–Mangyshlak area became wider,
but the connection with the RP Basin reduced.

2. The contours of the RP Basin changed. During the Ear-

ly Berriasian (= Late Volgian) there was a fauna exchange

Fig. 3.

 Berriasian-Valanginian seaways of the Russian Platform Basin and ammonite paleozoogeography of the RP and surrounding area. 1

— Paleozoogeographical Subprovince boundaries; 2 — Paleozoogeographical Province boundaries; 3 — direction of fauna area expansion;
4 — land and areas of continental deposition; 5 — Olcostephanid-Neocomitid Province; 6 — Polyptychitid Province. The outlines of conti-
nents after Rowley & Lottes (1988), contours of the land margins after Casey (1973), Saks et al. (1971, 1972), Rawson (1973), Jeletzky
(1973), Kemper (1973), Sasonova (1977), Marek (1983), Marek & Raczyńska  (1973), Kemper et al. (1981), Ziegler (1990), Prozorovsky
(1991) and author’s own data. Early Berriasian Provinces: Pr-P — Perisphinctid-Polyptychitid Province; P — Polyptychitid Province:
P(C)

 — Craspeditinid Subprovince; P(P) — Platylenticeratinid Subprovince; N — Neocomitid Province; O-N — Olcostephanid-Neocomit-

id Province; N-P — Neocomitidm-Polyptychitid Province. Late Berriasian Provinces: Pr-P — Perisphinctid-Polyptychitid Province; P —
Polyptychitid Province; N-P — Neocomitid-Polyptychitid Province; O-N — Olcostephanid-Neocomitid Province. Early Valanginian Prov-
inces: P — Polyptychitid Province: P(Pl-P-T) — Platylenticeratinid-Polyptychitinid-Tolliinid Subprovince; P(P-T) — Polyptychitinid-Toll-
iinid Subprovince; N-P — Neocomitid-Polyptychitid Province: P(N-P-T) — Neocomitinid-Polyptychitinid-Tolliinid Subprovince, P(N-Pl-
P)

 — Neocomitinid-Platylenticeratinid-Polyptychitinid Subprovince; N — Neocomitid Province; O-N — Olcostephanid-Neocomitid

Province. Late Valanginian Provinces: P — Polyptychitid Province: P(T-P) — Tolliinid-Polyptychitinid Subprovince; P(P) — Polyptychi-
tinid Subprovince;  N-P — Neocomitid-Province; P-O-N — Polyptychitid-Olcostephanid-Neocomitid Province; O-N — Olcostephanid-
Neocomitid Province.

BERRIASIAN -VALANGINIAN (EARLY CRETACEOUS) SEAWAYS OF THE RUSSIAN PLATFORM BASIN              17

with Western Siberia and the Arctic sea only; this time is
characterized by the absolute dominance of a Boreal fauna
and a high rate of endemism (Fig. 1). The sea-connections of
the RP Basin with the Tethys and with the Polish Basin
opened during the Latest Berriasian and existed until the late
Early Valanginian. In the Late Valanginian the RP Basin was
again separated from the Tethys and had only a connection
with the Arctic sea. It became even more isolated than during
the Early Berriasian and its size was much smaller. This is
the reason why no endemic ammonites are known from the
Upper Valanginian of the RP. It should be noted that the di-
rect seaway between the young Atlantic Ocean and the Arc-
tic sea did not exist during the Berriasian. It probably ap-
peared in the Late Valanginian (Rawson 1973, 1995), but this
fact needs additional investigations. The Valanginian phyl-
loceratids and lytoceratids on Traill Island could also be of
Pacific origin. It is difficult to suppose the presence of the
“warm Atlantic stream” (Saks et al. 1971, 1972), especially
during Valanginian, when Boreal ammonites migrated south-
ward in the Tethys. Therefore, I think that the term “Boreal-
Atlantic” Province (Saks et al. 1971, 1972; Shulgina 1974) is
not a very good choice. I also think that taxonomic names for
different paleozoogeographical subdivisions are preferable to
the above geographic names.

3. It is obvious that the presence and configuration of sea-

ways was responsible for the ammonite distribution, but water
temperature was also important. For example, the RP Basin
had a free connection with both the Tethys and the Arctic sea
in the Late Berriasian, but Riasanites, which has Tethyan
roots, did not move far to the north. At the same time Surites, a
Boreal genus, did not move far to the south (the furthest region
is probably the North Caucasus). I think that changes in the
distance from the temperature optimum were, in fact, the rea-
son of Rawson’s (1973) “mass migrations” and “facultative
migrations” of ammonites, which he tries to explain by sea
connections. In my opinion it is not correct to apply the term
“migration” to changes of ammonite areas, because it really
reflects mass movements of water (and not changes in ammo-
nite mode environments). So, several natural factors formed
the limits of the provinces. They were, in general, correctly in-
terpreted by previous investigators (Saks et al. 1971, 1972,
etc.). It is easy to see that these limits do not coincide with the
latitude lines on palinspastic reconstructions (Fig. 3) and espe-
cially with their recent position (compare with reconstructions
of Saks et al.). The situation could be explained by the coinci-
dence of several factors: (1) the ammonite mode of life; (2) the
existence of warm/cool paleocurrents or (3) the precision of
the palinspastic and paleogeographic reconstructions.

4. One can see now, after this integrated analysis, where and

in  what stratigraphic interval we can try to solve the prob-
lem of the Boreal/Tethyan correlation. For the Early Berria-
sian: it is the Polish Furrow, Alaska and Far East. For the Late
Berriasian it is Mangyshlak, the Polish Furrow and Far East.
For the Early Valanginian it is again Mangyshlak, the Polish
Furrow–northern Europe and the Far East. For the Late Val-
anginian it is northern Europe and the Far East. The problem
was solved in particular by Kemper et al. (1981), and by Lup-
pov et al. (1983, 1988), but it should be done in the other re-
gions in the future.

Conclusions

The investigation of the Lower Cretaceous of the RP pro-

vides interesting data in many stratigraphical, paleozoogeo-
graphical and paleogeographical aspects; it had a strong rela-
tionship with the surrounding regions. The most important
factors of the development of the RP during the Early Creta-
ceous were intracratonic tectonic movements and sea-level
fluctuations. Tectonic movements controlled the opening of
the seaways and basin configuration and the sea-level fluctua-
tions determined the expansion/restriction of the ammonite ar-
eas. Both factors control the rate of endemism of the RP: if the
basin became extended, but partially isolated, the endemism
level was high. The endemism became low during the opening
of the seaways and completely disappeared during the shorten-
ing of the  basin. On the other hand, when the seaways were
maximally open, the opportunities for Tethyan/Boreal correla-
tion were also maximal. There were two such well-correlat-
able horizons for the Berriasian–Valanginian interval: the
Rjasanensis–Kochi zones in the Upper Berriasian and the Un-
dulatoplicatilis Zone in the Lower Valanginian.

Acknowledgements: 

I wish to acknowledge IGCP 362, the

Peri-Tethys Programme, INTAS (Grant No. 94-1805) and
RBSF Foundation (Grants No. 97-05-65567 and 98-05-
64195) for the financial support of my investigations.

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