The Ponto-Caspian basin as a final trap for southeastern Scandinavian
Ice-Sheet meltwater
Alina Tudryn a, *
, Suzanne A.G. Leroy b
, Samuel Toucanne c
, Elisabeth Gibert-Brunet a
,
Piotr Tucholka a
, Yuri A. Lavrushin d
, Olivier Dufaure a
, Serge Miska a
, Germain Bayon c
a
GEOPS, Univ. Paris-Sud, CNRS, Universite Paris-Saclay, Rue du Belvedere, B^at. 504-509, 91405, Orsay, France
b
Environmental Science, Brunel University London, Uxbridge, UB8 3PH, London, UK
c
Institut Français de Recherche pour l’Exploitation de la Mer (IFREMER), Unite de Recherche Geosciences Marines, F-29280, Plouzane, France
d
Geological Institute (GIN), Russian Academy of Sciences, Pyzhevskii per. 7, Moscow, 117036, Russia
a r t i c l e i n f o
Article history:
Received 23 December 2015
Received in revised form
23 June 2016
Accepted 29 June 2016
Available online 14 July 2016
Keywords:
Caspian sea
Black sea
SIS deglaciation
Early Khvalynian transgression
Chocolate clays
Red layers
Clay minerals
Neodymium isotopes
Pollen
Late Pleistocene
a b s t r a c t
This paper provides new data on the evolution of the Caspian Sea and Black Sea from the Last Glacial
Maximum until ca. 12 cal kyr BP. We present new analyses (clay mineralogy, grain-size, Nd isotopes and
pollen) applied to sediments from the river terraces in the lower Volga, from the middle Caspian Sea and
from the western part of the Black Sea. The results show that during the last deglaciation, the PontoCaspian
basin collected meltwater and fine-grained sediment from the southern margin of the Scandinavian
Ice Sheet (SIS) via the Dniepr and Volga Rivers. It induced the deposition of characteristic redbrownish/chocolate-coloured
illite-rich sediments (Red Layers in the Black Sea and Chocolate Clays in
the Caspian Sea) that originated from the Baltic Shield area according to Nd data. This general evolution,
common to both seas was nevertheless differentiated over time due to the specificities of their catchment
areas and due to the movement of the southern margin of the SIS. Our results indicate that in the
eastern part of the East European Plain, the meltwater from the SIS margin supplied the Caspian Sea
during the deglaciation until ~13.8 cal kyr BP, and possibly from the LGM. That led to the Early Khvalynian
transgressive stage(s) and Chocolate Clays deposition in the now-emerged northern flat part of
the Caspian Sea (river terraces in the modern lower Volga) and in its middle basin. In the western part of
the East European Plain, our results confirm the release of meltwater from the SIS margin into the Black
Sea that occurred between 17.2 and 15.7 cal kyr BP, as previously proposed. Indeed, recent findings
concerning the evolution of the southern margin of the SIS and the Black Sea, show that during the last
deglaciation, occurred a westward release of meltwater into the North Atlantic (between ca. 20 and
16.7 cal kyr BP), and a southward one into the Black Sea (between 17.2 and 15.7 cal kyr BP). After the Red
Layers/Chocolate Clays deposition in both seas and until 12 cal kyr BP, smectite became the dominant
clay mineral. The East European Plain is clearly identified as the source for smectite in the Caspian Sea
sediments. In the Black Sea, smectite originated either from the East European Plain or from the Danube
River catchment. Previous studies consider smectite as being only of Anatolian origin. However, our
results highlight both, the European source for smectite and the impact of this source on the depositional
environment of the Black Sea during considered period.
© 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license
(http://creativecommons.org/licenses/by/4.0/).
1. Introduction
Climate change in Europe during the Last Glacial Maximum
(LGM; ca. 26e19 kyr BP) and the subsequent deglaciation have been
intensively investigated through various archives leading to
recently published compilations that focus on both the extent and
timing of the last European Ice Sheet (EIS) (Hughes et al., 2015;
Stroeven et al., 2015; Toucanne et al., 2015). During the LGM and
until the complete melting of the ice sheet after 9.7 cal kyr BP
(Stroeven et al., 2015), the EIS affected environmental conditions
not only locally but also on a much wider scale. As a prominent
example of this, glacigenic sediments were deposited as far away as
the Eastern North Altantic and the Bay of Biscay through meltwater* Corresponding author.
E-mail address: alina.tudryn@u-psud.fr (A. Tudryn).
Contents lists available at ScienceDirect
Quaternary Science Reviews
journal homepage: www.elsevier.com/locate/quascirev
http://dx.doi.org/10.1016/j.quascirev.2016.06.019
0277-3791/© 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Quaternary Science Reviews 148 (2016) 29e43
pulses originating at the southern margin of the Scandinavian Ice
Sheet (SIS, itself part of the EIS system). The meltwater was
funneled from Baltic lowlands by ice-marginal valleys and by the
so-called Channel River (Toucanne et al., 2009, 2010). Part of the
meltwater from the southeastern side of the SIS could have been
evacuated into the Caspian and Black Seas via the Volga and Dniepr
Rivers respectively, as it has been postulated by many authors (e.g.
Mangerud et al., 2004; Soulet et al., 2013). Indeed, both rivers drain
the East European Plain that constitutes partly their catchment
area, and their northern extent is close to, or on the limit of the
southeastern SIS margin during the LGM and the deglaciation.
In the Western Black Sea, the so-called Red Layers form part of
the Late Quaternary sedimentary sequence (Major et al., 2002;
Strechie-Sliwinski, 2007; Soulet et al., 2013). Their formation has
been attributed to the transport of sediments into the Black Sea by
meltwaters from the southern SIS margin during the last deglaciation
(Soulet et al., 2011a). On the river terraces in the lower Volga,
the so-called Chocolate Clays are present. They constitute part of
sediments deposited during the Early Khvalynian transgression of
the Caspian Sea in the Late Pleistocene (e.g. Varuschenko et al.,
1987). Nevertheless the precise timing of this transgression, as
well as the origin of Chocolate Clays (even if considered as being
deposited in cold climatic conditions) and time of their deposition
are not clearly established, and still debated (e.g. Leonov et al.,
2002; Badyukova, 2010; Yanina, 2012; Tudryn et al., 2013a;
Sorokin et al., 2014; Arslanov et al., 2015; Bezrodnykh et al., 2015;
Makshaev and Svitoch, 2015 and papers cited therein). As
Kroonenberg et al. (1997) pointed out, accurate dating of the Early
Khvalynian transgression, and determination of the origin of the
Chocolate Clays, would aid in clarifying the relationship between
global climate (the primary driving mechanism), Caspian Sea level
and the evolution of hydrological systems on the East European
Plain, and provide major arguments for causal mechanisms.
In this context we propose a detailed sedimentological, palynological
and geochemical study based on sediments from the
western part of the Black Sea, from the river terraces in the lower
Volga and from the middle basin of the Caspian Sea. Based on our
results and on recent findings concerning the Caspian and Black
Seas as well as SIS evolution, the aim of this study is to ascertain the
source areas of clay minerals deposited in the Ponto-Caspian basin
during the last deglaciation. Further to this, we intend to identify
the origin of Chocolate Clays deposited in the Caspian Sea during
the Early Khvalynian transgression to improve the chronological
framework for this transgression and to establish its causal
mechanisms.
2. Setting
2.1. SIS southern margin at the LGM
Studies of sediments along to the southern and eastern SIS
margin reveal the complexity of the spatiotemporal evolution of
the SIS. The ice margin was marked by end moraines and hummocky
landscapes with frequent ice-dammed lakes spanning from
Lake Onega in Russia to northern Germany (Svendsen et al., 2004;
Stroeven et al., 2015).
The precise timing for SIS fluctuations is still debated; nevertheless
the timing for westward meltwater routing via ice-marginal
valleys from the Baltic lowlands is quite well known. Indeed, based
on glacigenic sediments from the southern SIS margin deposited in
the Bay of Biscay, Toucanne et al. (2015) proposed a revised chronology
for the LGM and post-glacial ice sheet evolution in this area.
According to these authors, the main Channel River meltwater releases
occurred before the LGM and during the deglaciation. They
were produced by five phases of the large-scale ice-margin
retreats: (i) during Heinrich Stadial 3 (HS3: between ~31 and
29 cal kyr BP), (ii) during HS2 (between ~26 and 23 cal kyr BP), (iii)
at ~22.5e21.3 cal kyr BP, (iv) at ~20.3e18.7 cal kyr BP and finally (v)
from ~18.2 to 16.7 cal kyr BP (first part of HS1; between 18 and
15 cal kyr BP). At around 17 cal kyr BP, the Channel River stopped its
activity; according to Toucanne et al. (2010), meltwater then flowed
towards the Nordic Seas.
In the southern part of the SIS (i.e. Baltic lowlands of Poland and
Germany), a succession of three moraine belts, the BrandenburgLeszno,
Frankfurt-Poznan and Pomeranian (Pomorska), was identified
from the LGM and dated (Rinterknecht et al., 2006, 2008;
2012, 2013; Dzier_zek and Zreda, 2007; Marks, 2015). The new
chronology proposed by Toucanne et al. (2015) identifies the
Brandenburg-Leszno ice advance between ~23.4 and ~20.3 cal kyr
BP. The Brandenburg-Leszno phase ended with a significant ice
retreat dated at ~20.3e18.7 cal kyr BP. The Frankfurt-Poznan ice
advance occurred between ~18.7 and ~18.2 cal kyr BP, while the
Pomeranian one was between ~16.7 and ~15.7 cal kyr BP.
In the southeastern part of the SIS, recent reconstructions of its
deglaciation that include the recalibration of previously published
dates (Rinterknecht et al., 2008), indicate that the south Baltic coast
was already ice free at 15À14 kyr (Stroeven et al., 2015; Hughes et al.,
2015). Stroeven et al. (2015) proposed that the local LGM was
reached at ~19 cal kyr BP in Belarus (Orsha phase), Lithuania (Gruda
phase), Latvia and Estonia. This local LGM has been correlated with
the Frankfurt-Poznan phase to the west, while in the northeastern
sector in Russia, it was reached at 17 cal kyr BP, and broadly correlates
with Pomeranian ice advance. According to Svendsen et al.
(2004) and Hughes et al. (2015), the maximum position of the ice
sheet advance was reached there at ~20e18 kyr. The outermost ice
sheet limit during its maximum formed three major lobes in the
Russian sector (Hughes et al., 2015; Stroeven et al., 2015). But the
exact extent in the area of the Rybinsk basin is still not clearly
established. As pointed out by Marks (2015), the deglaciation steps
in the Russian sector are not well known; nevertheless, at least the
Vepsian (probably corresponding to the Pomeranian phase in central
Europe), Sebezha, Luga and Neva phases of ice sheet advance
have been identified. The Luga phase was derived from the last ice
sheet margin that extended to the south of Lake Onega, and it was
considered as having occurred at ~14.2 cal kyr BP. Afterwards, the
Neva phase was dated at ~13 cal kyr BP (Marks, 2015). This is in good
agreement with data from the eastern shore of Lake Onega, which
indicate that this area was deglaciated between 14.4 and 12.0 kyr BP
(Saarnisto and Saarinen, 2001), and with recent compilation of
Hughes et al. (2015).
During the LGM, the East European Plain belonged to the zone of
continuous permafrost including the middle basins of Dniestr,
Dniepr and Don (Bogutskiy et al., 1975; Velichko et al., 1996) as well
as the Volga catchment area and the northern shoreline of the
Caspian Sea from that time (Yanina, 2012). According to
Vandenberghe et al. (2014), permafrost degradation started as early
as 17e15 kyr BP.
2.2. The Ponto-Caspian basin - study area
The Black and Caspian Seas (Fig. 1) belong to the Ponto-Caspian
region. They are relicts of the East Paratethys, and became individualized
during the Pliocene (Varuschenko et al., 1987; Forte and
Cowgill, 2013; Yanina, 2014; Van Baak, 2015). Caspian and Black
Seas are intracontinental, effectively closed and semi-closed reservoirs
of waters and thus very sensitive to climatic changes. They
have important part of their catchment areas in the East European
Plain and, during the Quaternary, were subjected to large amplitude
water-level fluctuations (more than 100 m) (e.g. Serebryanny,
1982; Varuschenko et al., 1987).
A. Tudryn et al. / Quaternary Science Reviews 148 (2016) 29e4330
2.2.1. Caspian Sea
The Caspian Sea, which today lies at 27 m below sea-level, is the
world’s largest inland water body (390,000 km2
; 66,100 km3
)
without connection to the world ocean (Fig. 1). It is a reservoir of
brackish waters, with a catchment area of 3.5 million km2
, which
extends northwards over 15 of latitude to the East European Plain.
The salinity of the Caspian Sea varies from the north to the south
within the range of 1e13.5‰; this variation is particularly strong in
the north due to the large freshwater supply by the Volga River, in
other areas average water salinity is of ~12.5‰ (Dumont, 1998). The
Volga River contributes >80% of the Sea’s total inflow (237 km3
yrÀ1
on average), drains the eastern part of the East European Plain and
has a catchment area of 1.4 million km2
(Kroonenberg et al., 1997;
Dumont, 1998).
According to many authors (Varuschenko et al., 1987;
Kroonenberg et al., 1997; Dumont, 1998; Svitoch, 1997;
Dolukhanov et al., 2009), the Late Khazarian and Khvalynian
transgressions occurred during the Late Pleistocene, from about
130 kyr. The Atelian regression (À120 to À140 m asl) occurred after
the Late Khazarian (À10to À À5 m asl), whereas the Enotayevian
regression (À80 to À100 m asl) separated the Early
(maximum þ50 m asl) and Late Khvalynian (maximum 0 m asl)
transgressions. In the Holocene, the Mangyshlak regression and
finally the Neocaspian transgression were evidenced. This general
pattern of successive transgressions and regressions was complicated
by second order variations of Caspian water level with various
time constants and by change in the hydrographic network. Today
the Caspian Sea is divided into three basins, each of about the same
area, but differing in depth and volume. These are the South (water
depth < 1020 m), middle (<900 m) and North (<15 m) basins that
represent ca. two-thirds, one-third and 1% of the total volume of
water, respectively (Chalie et al., 1997). During the Late Pleistocene
transgressions, when water level reached 0 and even þ50 m asl, the
area to the north of the Caspian Sea, which is not currently submerged,
formed an additional shallow water basin (Fig. 1).
2.2.2. Black Sea
The Black Sea is one of the largest anoxic basins in the world,
with an area of 432,000 km2
, a water volume of 534,000 km3
, a
mean depth of 1240 m, and a maximal depth of 2206 m (Ross et al.,
1974) (Fig. 1). It is nowadays connected to the Mediterranean Sea
through the Bosporus Strait, the Marmara Sea and the Dardanelle
Strait. The Black Sea is characterized by the presence of a halocline
between 100 and 200 m depth separating near-surface water
Fig. 1. Map of the Caspian and Black Seas with their present day catchment areas (red lines) and the LGM ice sheet extend at ~19 cal kyr BP (white line) after Hughes et al. (2015).
Sediment sites and dating locations - numbered red stars: (1) core GS20 (479 m water depth), (2) Tsagan Aman, (3) Kolobovka, (4) Srednaya Akhtuba, (5), Chernyi Yar, (6) Privolzh’e
settlement and cores: (7) core MD04-2754 (453 m water depth), (8) core BLKS 98-11 (500 m water depth), (9) core MD04-2790 (352 m water depth), (10) core BLKS 98-22 (2100 m
water depth). Modern εNd site locations - numbered yellow dots: Rivers (1) Ropotamo, (2) and (3) Danube, (4) Desna, (5) Upper/middle Dniepr, (6) Don, (7) Kuban, (8) Volga, (9)
Amu Darya, (10) Sefid Rud. The light blue line around the Caspian Sea at 50 m asl, indicates the maximum extent of the Caspian Sea during the Early Khvalynian transgression. Blue
arrow between Caspian and Black Seas: Kuma-Manych Strait and direction of water overflow during the Early Khvalynian Transgression. White line and the arrow to the south of
the LGM extend e westward evacuation path for meltwater. Map created using GMT freeware software (Wessel et al., 2013). (For interpretation of the references to colour in this
figure legend, the reader is referred to the web version of this article.)
A. Tudryn et al. / Quaternary Science Reviews 148 (2016) 29e43 31
having salinity of ~18‰, from a deep, more saline water of ~22.5‰.
This lower body of water is of Mediterranean origin that induces
anoxic conditions below 150 m bsl (Bahr et al., 2005; StrechieSliwinski,
2007). The north-western part of the basin drains European
rivers, the largest being the Danube (catchment area of
817,000 km2
) and the Dniepr (catchment area of 504,000 km2
). To
the South, Anatolian rivers supply today more than 33% of the total
sediment input into the Black Sea (Popescu, 2002); but they
represent only 8% of the total freshwater discharge.
The connection with the Mediterranean Sea has been interrupted
frequently over the history of the Black Sea (Deuser, 1974)
and the Black Sea’s status oscillated between lacustrine (during
glacial low stands of the ocean) and marine (during interglacial
high stands) (Badertscher et al., 2011). The connection was previously
located on the Sakarya Strait (Gürbüz and Leroy, 2010). For
the last glacialepostglacial transition, two hypotheses have been
proposed to explain the Mediterranean-Black Seas re-connection: a
catastrophic (Ryan et al., 1997) or a gradual event, with the “Black
Lake” freshwater inflow into the Mediterranean Sea at either
~17 kyr BP or ~9.5 cal kyr BP, with, after ~9.8 kyr BP possible
oscillating manner allowing a periodic migration of Mediterranean
organisms into the Black basin, and finally the marine water arrival
into the “Black Lake” at ~7.6 cal kyr BP (Aksu et al., 2002; Hiscott
et al., 2007a,b; Nicholas et al., 2011; Yanko-Hombach et al., 2007,
2014). This last reconnection was recently constrained as occurring
gradually between ~9.0 and ~8.0 cal yr BP (Soulet et al., 2011b).
2.3. The Ponto-Caspian basin - Red Layers and Chocolate Clays
The Red Layers in the Western Black Sea constitute four individualized
intervals of reddish-brown silty sediment and were
deposited between ~17.2 and ~15.7 cal kyr BP, when the Black Sea
was a giant lake due to lowstand conditions (Soulet et al., 2011a).
On the basis of neodymium isotopic values, they were interpreted
as being a consequence of spillway events from the proglacial lake
Disna into the Upper River Dniepr (Soulet et al., 2013). Before and
after this event, sediment deposited in deep basin of the Western
Black Sea was attributed to a supply by the Danube River (Lericolais
et al., 2013; Constantinescu et al., 2015).
The Chocolate Clays were deposited during the Early Khvalynian,
the largest Caspian Sea transgression recorded for the Late
Quaternary. During this transgression, the maximal Caspian Sea
water level raised up to þ50 m asl (e.g. Varuschenko et al.,
1987)(Fig. 1) implying important modifications of its shoreline,
especially in the now-emerged northern flat part, where Chocolate
Clays are known. The Chocolate Clays comprise a part of the Early
Khvalynian sequence and are mostly confined to the middle and
lower reaches of the Volga River and its delta. Their detailed
description and distribution (including, to a lesser extent, the area
of the lower Ural River, Fig. 1) are given by Makshaev and Svitoch
(2015) and in papers cited therein, the oldest has been published
in Russian already in 1856. Due to discrepancies between results
from different dating methods, the age of the Early Khvalynian
transgression is still ambiguous (14
C ages: 56.0e7.0 kyr BP, U/Th
ages: 24.2e9.6 kyr, TL ages: 71.0e16.0 kyr) (Varuschenko et al.,
1987; Mamedov, 1997; Leonov et al., 2002; Bezrodnykh et al.,
2004; Badyukova, 2007; Svitoch et al., 2008; Shkatova, 2010;
Sorokin et al., 2014 and papers cited therein). Mamedov (1997)
and Shkatova (2010) claimed that the Early Khvalynian transgression
corresponded to warming between 32 and 24 kyr BP.
Nevertheless, many authors correlate that transgression with the
LGM itself or to the last deglaciation (Leonov et al., 2002;
Chepalyga, 2003, 2005, 2007; Svitoch et al., 2008, Svitoch, 2009;
Tudryn et al., 2013a; Yanina, 2012; Arslanov et al., 2015). Large
quantities of inflowing water could have been related to icedammed
lakes formed in the southern front of the Siberian and
east European ice sheets (Grosswald, 1993; Mangerud et al., 2004;
Chepalyga, 2005). According to Chepalyga (2003, 2005; 2007),
these proglacial lakes created a “Great Proglacial Drainage System”
in Northern Eurasia with water flowing through the Aral Sea and
River Uzboy into the Caspian Sea between 21 and 17 kyr BP, and the
Caspian Sea water overflowed into the Black Sea through the KumaManych
Strait (22 m asl) between 17 and 15 kyr BP. Other authors
suggested that levels of ice-dammed lakes in northern East European
Plain in the upper Volga and Northern Dvina region were too
low to feed sufficiently the Caspian Sea to produce high water level
during the Early Khvalynian transgression. In this case the highstand
conditions of the Caspian Sea could be better explained
climatically: by high precipitations (snow) and rapid snow melting
during the spring (Sidorchuk et al., 2009) or by a low evaporation
rate during the last glaciation (Velichko et al., 1987). According to
Vandenberghe et al. (2014), permafrost degradation started as early
as 17e15 kyr BP, and thus certainly acted on supplying additional
detrital material and water into the Caspian basin. Finally, recently
published data from sediment cores collected from the northern
basin of the Caspian Sea indicate that Early Khvalynian sediment
consists of two lithologically different parts (Bezrodnykh et al.,
2015). The lower part (2.5e5.0 m thick) consists of alternation of
shelly detritus of variable size with a sandy or clayey matrix, and
clays with inclusions of shells and shelly detritus. The upper part
(8e10 m thick) is composed of clays with variably thick sand intercalations.
The base of this sequence is, after 14
C dating, of
~34 cal kyr BP (Bezrodnykh et al., 2015), or even possibly ~56 kyr BP
(Sorokin et al., 2014). 14
C ages of shells from different Chocolate
Clays sections in Volga River terraces, show values between ~14.5
and 13.3 cal kyr BP (Makshaev et al., 2015; Makshaev and Svitoch,
2015).
3. Material and methods
3.1. Material collection
3.1.1. Caspian Sea
The 995 cm long Kullenberg sediment core SR-9418 GS20
(named GS20 thereafter, but called GS18 in Leroy et al., 2014), was
collected from the middle basin of the Caspian Sea (413205300N;
510600400E; water depth of 479 m) (Fig. 1). It has already been
analyzed for chronology, magnetic mineralogy, carbonate content
and micropalaeontology (ostracods and palynology) (Boomer et al.,
2005; Leroy et al., 2014; Tudryn et al., 2014), and presents a Late
Pleistocene and Holocene record (Fig. 2a,b,c). Sediments from river
terraces in the lower Volga were sampled directly from accessible
outcrops in Srednaya Akhtuba (~20 m a.s.l., 4843000.3700N,
4451059.7200E), in Kolobovka (~10 m a.s.l., 4839021.0600N,
4528029.3400E) and in Tsagan-Aman (~0 m a.s.l., 4733002.6900N,
4640049.9900E) (Fig. 1, Photo 1b,c,d). The details of sampling (about
150 samples of 8 cm3
perspex cubes were obtained) and results of
magnetic and clay minerals, palynological studies, as well as 14
C
dating of this sequence representing part of Early Khvalynian
transgression of the Caspian Sea during the Late Pleistocene, are
reported in Tudryn et al. (2013a) and in Leonov et al. (2002). The
core from the middle basin of the Caspian Sea was collected during
a cruise that took place in 1994. Sampling of Early Khvalynian
sedimentary sequences accessible from river terraces in the lower
Volga in Srednaya Akhtuba, Kolobovka and Tsagan-Aman, was
achieved during a French-Russian field trip in September 1997. Both
were obtained as part of the multidisciplinary study of the palaeolimnology
of the Caspian Sea “Understanding the Caspian Sea
Erratic Fluctuations” (an EU-INCO-Copernicus collaboration), conducted
by a team that included five authors of this paper.
A. Tudryn et al. / Quaternary Science Reviews 148 (2016) 29e4332
3.1.2. Black Sea
The 757 cm long Kullenberg sediment core BLKS 98-11 was
collected from the slope of the NW Black Sea (4403.020N,
3053.120E; water depth 500 m), in the axis of the Danube River
during a cruise as part of the French-Romanian program Blason1 in
1998 (Fig. 1). The 32 m long Calypso core MD04-2754 (4159.230N,
2840.990E; water depth 453 m) was obtained from the slope of the
SW Black Sea, during the ASSEMBLAGE 1 cruise and as part of the
European program ASSEMBLAGE (Fig.1). Sediments from core BLKS
98-11 and seven upper meters from core MD04-2754 were previously
studied for chronology, magnetic mineralogy, carbonate
content, organic carbon and nitrogen contents and their isotopic
signatures (Strechie et al., 2002; Strechie-Sliwinski,
2007)(Fig. 2deh).
3.2. Methods
Clay minerals and grain-size analysis. Clay minerals from the
Black and Caspian Seas were identified by XRD on oriented mounts
of non-calcareous clay-sized (<2 mm) particles with PANalytical
diffractometer, following the laboratory routine at the GEOPS laboratory,
Universite de Paris Sud (Liu et al., 2007, 2008). The oriented
mounts were obtained according to a method described by Liu et al.
(2004). Three XRD runs were made, following air-drying, ethyleneglycol
solute treatment for 24 h, and heating at 490 C for 2 h.
The identification of clay minerals was mainly made according to
the position of the (001) series of basal reflections on the three XRD
diagrams. Semi-quantitative estimates of peak areas of the basal
reflections for the main clay mineral groups of smectite (including
mixed-layers) (15e17 €A), illite (10 €A) and kaolinite/chlorite (7 €A)
were carried out on the glycolated curve (Holtzapffel, 1985) using
the MacDiff software (Petschick, 2000). Relative proportions of
kaolinite and chlorite were determined based on the ratio of
3.57:3.54 €A peak areas. Based on the XRD method, the semiquantitative
evaluation of each clay mineral has an accuracy of
5%. Grain-size distribution measurements of carbonate-free sediment
from core GS20, Caspian Sea, were carried out on a Malvern
Mastersizer 2000 device, at the GEOPS laboratory, Universite de
Paris Sud.
Palynological analyses. Ninety-two samples for the top 666 cm of
core GS20 were palynologically studied for palaeoenvironmental
reconstructions, both terrestrial and aquatic (Leroy et al., 2014).
Twenty-two of them were treated at Universite Catholique de
Louvain (Belgium) by the heavy liquid method (Thoulet solution at
a density of 2.1). The remaining seventy samples were treated at
Brunel University (UK) by the HF method. On average the sample
volume was 1.1 ml. Initial processing of samples involved the
addition of sodium pyrophosphate to deflocculate the sediment.
Samples were then treated with cold hydrochloric acid (from 10% to
pure) and cold hydrofluoric acid (60%), and HCl (10%) again. The
residual organic fraction was screened through 125 and
10 mm mesh sieves. Final residues were mounted on slides in
glycerol and sealed with varnish. An additional 22 samples, below
666 cm depth (treated with the HF method), were treated but not
published in Leroy et al. (2014) because of a suspected different
taphonomy. The Pinus percentages are calculated on the sum of
terrestrial pollen grains (that includes Pinus, but not reworked
grains). The reworked percentages are calculated on the same sum,
that does not include them and hence values higher than 100% can
be reached. In the Lower Volga from the Srednaya Akhtuba outcrop,
six samples were chosen from fine-grained levels. The processing of
1.9e2.7 ml of sediment, following the HF method described for the
Fig. 2. Data from sediment cores for middle basin of the Caspian Sea (core GS20, 479 m water depth) and for the Black Sea - southwestern part (core MD04-2754, 453 m water
depth) and - northwestern part (core BLKS 98-11, 500 m water depth and core MD04-2790, 352 m water depth). a) pollen data: Pinus and reworked pollen percentages, b), d) and g)
magnetic susceptibility, c), f) and i) Ca and Mg carbonate content, e) and h) organic carbon content, j) XRF Ca intensity. Data are presented on a depth scale. For core GS20, ages (14
C
cal kyr BP) are reported on the left side of the depth scale. For cores from the Black Sea, lithological Unit I, Unit II and Unit III are shown. RL e Red Layers, YD e Younger Dryas, C1 and
C2 e carbonate peaks 1 and 2. Data for core GS20 from the Caspian Sea are presented after Boomer et al. (2005), Leroy et al. (2014) and Tudryn et al. (2014). Data for Black Sea are
presented after Strechie-Sliwinski (2007) and Tudryn et al. (2012) for cores BLKS 98-11 and MD04-2754, and after Soulet et al. (2013) for core MD04-2790. (For interpretation of the
references to colour in this figure legend, the reader is referred to the web version of this article.)
A. Tudryn et al. / Quaternary Science Reviews 148 (2016) 29e43 33
GS20 core, did not yield any palynomorphs.
Neodymium. We measured Nd isotope ratios of fine-grained
detrital fractions extracted from a series of the Caspian Sea sediments
from three key locations. Sample selection was based on
recorded changes in clay mineralogy. One measurement was made
on the Early Khvalynian Chocolate Clays sample from Srednaya
Akhtuba. Two others were made on samples from core GS20, at
970 cm and 770 cm depth. Additional analyses were performed on
recent sediments from the Kuban, Don and Ropotamo rivers, all
tributaries of the Black Sea, as well as from River Sefid Rud that
drains the southern Caspian Basin and River Amu Darya (Fig.1). The
neodymium isotopic composition of terrigenous sediment is a
powerful tracer for geographical provenance; it reflects to a large
extent the mean age of the corresponding source region and is
preserved during erosion and transport processes (Goldstein and
Jacobsen, 1988). In this study we analyzed the fine clay-silt
detrital fraction (<63 mm) of the sediment, for comparison with
the Nd isotopic compositions of sediments recently reported by
Soulet et al. (2013) and Toucanne et al. (2015). Dried fine-grained
fractions (typically ~ 0.5 g) were crushed using an agate mortar
and pestle. The terrigenous fraction of each sediment sample was
digested by alkaline fusion (Bayon et al., 2009) after removal of all
carbonates, FeeMn oxide and organic components using a
sequential leaching procedure (Bayon et al., 2002). Prior to analyses,
Nd was separated by ion exchange chromatography (see
details in Bayon et al., 2012). Isotopic measurements were performed
at the P^ole Spectrometrie Ocean, Brest (France), using a
Thermo Scientific Neptune multi-collector ICPMS. Mass bias corrections
on Nd were made with the exponential law, using
146
Nd/144
Nd ¼ 0.7219. Nd isotopic compositions were determined
using sample-standard bracketing, by analysing JNdi-1 standard
solutions every two samples. Mass-bias corrected values for
143
Nd/144
Nd were normalized to a JNdi-1 value of
143
Nd/144
Nd ¼ 0.512115 (Tanaka et al., 2000). In this study, both
measured 143
Nd/144
Nd ratios and literature data are reported using
the εNd notation, which corresponds to the deviation of any
measured Nd isotopic ratio relative to the present-day value of the
Chondritic Uniform Reservoir (CHUR): [(143
Nd/144
Nd)sample/
(143
Nd/144
Nd)CHUR À 1] Â 104
; using (143
Nd/144
Nd)CHUR ¼ 0.512638
(Jacobsen and Wasserburg, 1980). Note that the estimated uncertainty
on measured εNd values, inferred from repeated analyses of
JNdi-1 standard solution is typically of about ±0.3 ε-units.
4. Results
4.1. Lithology and chronology
4.1.1. Caspian Sea
4.1.1.1. Lithology. Core GS20: The sediment from the middle basin of
the Caspian Sea (core GS20) presents fine silty deposits described in
details in Tudryn et al. (2014) and in Leroy et al. (2014). They are
characterized as a whole by an alternation of black and grey/
brownish laminae that rapidly disappear under oxidizing conditions
(Photo 1a). These laminae reflect changes in magnetic
mineralogy between greigite (an iron sulfide Fe3S4 in black
laminae) and magnetite (an iron oxide Fe3O4 in grey/brownish
laminae), and are of early diagenetic origin, as it is the case for
sediment from the South basin of the Caspian Sea (Jelinowska et al.,
1998, 1999; Leroy et al., 2013a,b). In the lower part of core GS20,
from the bottom at 995 cme~870 cm, the sediment became
brownish or slightly pink/reddish in oxidizing conditions, while
above it became rather grey-greenish.
River terraces: Early Khvalynian sediments from river terraces in
the lower Volga studied here, are formed by chocolate-colour clays
(or silts), well known from literature as Chocolate Clays (e.g. Leonov
et al., 2002; Badyukova, 2007; Chepalyga, 2007; Svitoch, 2009;
Shkatova, 2010; Makshaev and Svitoch, 2015, and papers cited
therein). The Chocolate Clays from Srednaya Akhtuba, Kolobovka
and Tsagan-Aman are more or less regularly interbedded by thin,
horizontal sandy or silty yellow laminae (Photo 1b,c). Scarce macrobiological
remains were observed. These sediments suggest a
rather calm depositional environment, and visually may resemble
varved sediments in periglacial lakes (Tudryn et al., 2013a). This
sequence, of different thickness in each outcrop (2.0 m in Srednaya
Akhtuba, 3.4 m in Kolobovka and 1.4 m near Tsagan-Aman), begins
at the bottom with a grey/green sandy and silty sediment with
oxidation traces.
4.1.1.2. Chronology. Core GS20: Six radiocarbon dates for core GS20
were already obtained from ostracod shells and have been used to
build an age-depth model after calibration by the IntCal13.14C
curve (Reimer et al., 2013) and application of a 370 years reservoir
effect (Boomer et al., 2005; Tudryn et al., 2014; Leroy et al.,
2014)(Fig. 2). Sediments in core GS20 accumulated between ~14.6
and ~2 cal kyr BP. More specifically between ~14.6 and 12 cal kyr BP
or from the bottom to 600 cm depth, the sedimentary rate is of
~0.15 cm yrÀ1
.
River terraces: The studied here Early Khvalynian sediment in
river terraces in the lower Volga was poor in biological remains.
Nevertheless, one 14
C AMS date was obtained on total organic
carbon preserved fraction from Chocolate Clays on a sample from
Srednaya Akhtuba (Tudryn et al., 2013a), and ten 14
C AMS dates
were made on marine shells from Chocolate Clays and interbedded
silts from Srednaya Akhtuba, Kolobovka and Tsagan Aman, as well
as from two other sites - Chernyi Yar and the Privolzh’e settlement
(Fig. 1)(Leonov et al., 2002). The age obtained on total organic
carbon corresponds to ~20 cal kyr BP (Tudryn et al., 2013a). This
was obtained from sample representing the upper part of the
sequence, and is consistent with an Early Khvalynian event around
the LGM. Although the analyzed organic carbon is of non-identified
origin, it could come from the basin and thus reflect the LGM time,
or at least partly from the catchment area and thus be older than
the time of the clay deposition.
Dates obtained on mollusc shells were previously published
without application of a calibration model (Leonov et al., 2002).
After application of the calibration IntCal13.14C curve (Reimer et al.,
2013), the new chronology has become established between ~19.1
and 13.9 cal kyr BP (Table 1). Since these molluscs were living in
shallow, well-mixed and oxygenated environments (Tudryn et al.,
2013a), we assume no hard-water effect in the basin and consider
an equilibrium of water carbon system with atmosphere CO2.
4.1.2. Black Sea
4.1.2.1. Lithology. In both cores from the Black Sea, three distinct
lithostratigraphic units, previously reported by Ross and Degens
(1974) and Hay et al. (1991) for deep-sea sediments, were identified
(Fig. 2). The lowest unit, Unit III, consists of alternating light
and dark silts deposited under lacustrine conditions. They include
brownish/reddish silts (Photo 1e), named Red Layers (Major et al.,
2002; Strechie-Sliwinski, 2007; Soulet et al., 2013). These silts
present a sequence of varying thickness in both cores and are
interbedded by thin grey silty bands. The Red Layers are followed
by dark, greigite-rich, and light-coloured, carbonate-rich bands.
Unit II is a carbonate-poor, fine-grained sapropel that shows variation
in organic matter content, with high values in the lower half
and marked decrease in the upper half. The lower limit of the
sapropel indicates the beginning of the Black Sea e Mediterranean
Sea connection. The uppermost unit, Unit I, is characterized by
alternating light and dark microlaminations deposited since the
first occurrence of Emiliana huxleyi, a coccolithophore that largely
A. Tudryn et al. / Quaternary Science Reviews 148 (2016) 29e4334
comprises the light bands. Different lithological characteristics,
such as sapropel in Unit II, two carbonate rich bands in Unit III,
magnetic minerals changes, which are visible through magnetic
susceptibility variation, and Red Layers are identified here by laboratory
analyses and visually. These characteristics, that reflect
environmental changes in the Black Sea and its catchment area, are
ubiquitous in the Black Sea, as shown in numerous investigations.
For instance, carbonate and XRF-Ca analyses for cores collected on
the slope (Fig. 2f,i,j) and in the deep Black Sea, as in core BLKS 98-22
(Fig. 1), highlight similar variation in the Ca content in Unit III, with
its two peaks labeled as C1 and C2 (Major et al., 2002; Strechie et al.,
2002; Bahr et al., 2005, 2006, 2008; Strechie-Sliwinski, 2007;
Kwiecien et al., 2008; Soulet et al., 2011b).
4.1.2.2. Chronology. Recent investigations allowed chronology
establishment (Soulet et al., 2011a, 2011b, 2013). According to these
authors, the deposition of the Red Layers, identified in the lacustrine
Unit III, occurred during Heinrich stadial 1 (HS1) from ~17.2 to
~15.7 cal kyr. BP. The two following peaks in Ca intensity coincide
with the BøllingeAllerød interstadial for peak C2
(~14.70e~12.65 cal kyr BP), and with the Early Holocene for peak
C1 (~11.70e~8.99 cal kyr BP) periods. The decrease in the Ca intensity
observed between these episodes is correlated to the
Younger Dryas cold event (~12.65e~11.70 cal kyr BP). The marine
inflow from Mediterranean Sea into the Black Sea started after the
C1 peak at ~8.99 cal kyr BP, and resulted in the establishment of
marine conditions at ~8.08 cal kyr BP and the formation of
sapropel-rich sediments at the sea bottom (Unit II). The base of the
youngest Unit I is dated at ~2.72 cal kyr BP (Jones and Gagnon,
1994). All these specific parts of the sequence were well identified
in cores BLKS98-11 and MD04-2754 and allowed the establishment
of a precise chronological frame (Fig. 2dei).
4.2. Clay mineralogy, grain-size, pollen and neodymium analyses
The results are presented on a calendar age scale from 19 to
12 cal kyr BP (Fig. 3). Two cores from the Black Sea indicate a
continuous record that is shown from 18 cal kyr BP onwards. Results
from the Caspian Sea are composed of sediments from the
middle basin, which begin at ~14.6 cal kyr BP, and of sediments
from the river terraces in the lower Volga, which finish at
~13.9 cal kyr BP.
4.2.1. Caspian Sea
Pollen: In core GS20, below 666 cm, three strands of information
make us suspect a different source for the palynomorphs than for
the upper part of the core. It is i) the irregular presence of high
percentages of Pinus pollen (Fig. 2a and 3a) and the occasional
occurrence of Sphagnum spore, ii) the very high occurrence of
reworked pollen grains (loss of ornamentation, increase in opacity
and often pre-Quaternary taxa) representing at times more than
100% of the terrestrial sum of well-preserved pollen grains (Figs. 2a
and 3a), and iii) the very low palynological concentrations (below
2000 pollen and spores per ml). The absence of Pinus in the vegetation
around the middle basin of the Caspian Sea and its presence
at great distance in the south (Tagieva and Veliev, 2014) and in the
north of the area (Bolikhovskaya and Kasimov, 2010; Tudryn et al.,
2013a; Richards et al., 2014) suggest a stronger contribution from
river sources to the sediment than later on, after 12.44 cal kyr BP.
The highest values of Pinus and reworked elements are reached at
the bottom of the core below 877 cm depth (~13.83 cal kyr BP)
(Fig. 3a). Then a single peak is found at 676 cm (12.56 cal kyr BP)
and afterwards very moderate values are found upward until
383 cm or 8.19 cal kyr BP. The absence of palynomorphs in samples
from the river terraces in the lower Volga is largely related to the
oxidising environment unfavourable to palynomorph preservation.
Clay minerals and granulometry: The Early Khvalynian Chocolate
Clays on river terraces in the lower Volga are clearly dominated by
illite that reaches 80%. It is followed by kaolinite, chlorite and
smectite but these minerals present low abundances. The interbedded
silts show broadly similar contents of illite and smectite. As
contents of these minerals were measured for sediments from
Srednaya Akhtuba and Kolobovka, they are reported on Fig. 3c
(indicated as dots) taking into account ages obtained from mollusc
shells from these sites (Leonov et al., 2002) and their subsequent
calibration. In the middle basin of the Caspian Sea, the sediment,
from the bottom of core GS20 until ~14e13.8 cal kyr BP, displays
similar patterns as for the Early Khvalynian sediments, with illite as
dominant mineral (reaching 60%), and low values for kaolinite,
chlorite and smectite (Fig. 3c indicated as lines). After that, and up
to 12.0 cal kyr BP, illite decreases while smectite increases and
became the most abundant mineral. Granulometric analysis of core
GS20 sediment shows fine particles sizes (Fig. 3b).
Neodymium: Nd isotopic compositions of the sediment were
obtained for three key locations with regard to changes of clay
minerals (Table 2, Fig. 3d red stars). The measurement made on the
Early Khvalynian Chocolate Clays sample from Srednaya Akhtuba
displays a εNd value of À17.7. Two other measurements were made
on the sediment from the middle basin (core GS20) where illite was
dominant, at 970 cm depth (~14.4 cal kyr BP), and where illite
decreased and smectite become dominant, at 770 cm depth
(~13.2 cal kyr BP). The results are respectively À14.0 for the first and
À10.4 for the second sample.
4.2.2. Black Sea
Changes in contents of clay minerals are more pronounced in
Table 1
14
C dates obtained for Early Khvalynian Chocolate Clays from river terraces in the lower Volga. One date obtained on organic carbon (Tudryn et al., 2013a), and 10 dates
obtained on mollusks shells by Leonov et al. (2002) and calibrated using the atmospheric calibration curve IntCal13 (Reimer et al., 2013; Stuiver and Reimer, 1993).
Site Lat. Long. Material Measured 14C yr BP Error ± yr Age 14C cal yr BP s1 Mean 14C cal yr BP Error ± yr
Srednaya Akhtuba 48
430
00.3700
N 44
510
59.7200
E C org. 16930 120 19924e20181 20053 130
(þ22e25 m asl) 48
430
00.3700
N 44
510
59.7200
E Shell 12580 70 14763e15099 14932 169
48
430
00.3700
N 44
510
59.7200
E Shell 12120 180 13734e14277 14006 272
Kolobovka 48
390
21.0600
N 45
280
29.3400
E Shell 13240 45 15821e16011 15916 95
(þ10 m asl) 48
390
21.0600
N 45
280
29.3400
E Shell 13170 85 15689e15971 15831 142
48
390
21.0600
N 45
280
29.3400
E Shell 13070 100 15468e15835 15652 184
Tsagan Aman 47
330
02.6900
N 46
400
49.9900
E Shell 12470 80 14377e14882 14630 253
(0 - þ2 m asl) 47
330
02.6900
N 46
400
49.9900
E Shell 12445 75 14304e14775 14540 236
47
330
02.6900
N 46
400
49.9900
E Shell 12060 130 13762e14070 13917 155
Chernyi Yar (0 m asl) 48
030
N 46
070
E Shell 15800 1320 17517e20772 19145 1628
settl. Privolzh’e (þ30 m asl) 52
57.500
N 48
35.520
E Shell 14030 250 16666e17405 17036 370
A. Tudryn et al. / Quaternary Science Reviews 148 (2016) 29e43 35
Fig. 3. Data for Caspian (a, b, c, d) and Black (e,f,g) Seas sediments on an age scale from 19 to 12 cal kyr BP. a) Pinus and reworked pollen percentages, core GS20, b) mean grain size
(black line) and mode (grey line), core GS20, c) clay minerals contents, lines for core GS20 and dots for river terraces in the lower Volga, dashed line separating core GS20 and river
terraces records, d) red stars: εNd values, black crosses: 14
C cal kyr BP ages obtained on shells from Chocolate Clays (CC) in river terraces in the lower Volga (Leonov et al., 2002; this
study), e) clay minerals contents for core MD04-2754, f) clay minerals contents for core BLKS 98-11, g) εNd values for core MD04-2790 after Soulet et al. (2013), h) SIS margin
evolution: 1) timing for Channel River floods (CRF) after Toucanne et al., 2015, 2) Gr - Gruda and Ba - Baltija Moraines advances, Lithuania (Marks, 2015), 3) Os e Ostashkov, Ve e
Vepsian, Se e Sebezha, Lu e Luga and N e Neva Moraines advances, northern Russia (Marks, 2015), i) the NGRIP ice core record of d18
O (North Greenland Ice Core Project Members,
2004), YD e Younger Dryas, B - Bølling, A e Allerød, HS1 e Heinrich Stadial 1. (For interpretation of the references to colour in this figure legend, the reader is referred to the web
version of this article.)
Photograph 1. a) core GS20, details of early diagenetic lamination of the sediment and oxidation process after opening of the core (917e943 cm depth), photograph taken by M.
Destarac, Dept. of Geology, Museum d’Histoire Naturelle, Paris, b) Chocolate Clays on river terraces in the lower Volga, Srednaya Akhtuba, photograph taken by A. Tudryn, c) details
of Chocolate Clays, Srednaya Akhtuba, 200e150 cm depth, photograph taken by A. Tudryn, d) simplified cross section from Tsagan Aman, river terraces in the lower Volga, modified
from Lavrushin et al. (2014): hz e Khazarian transgression, at-1 and at-2 e Atelian regression, hv1 e Early Khvalynian transgression, CC e Chocolate Clays, 1 e clays and silts of
marine origin, 2 e sub-aerial silts, 3 e fine grained sand, 4 e sand, e) core BLKS 98-11, lithological Unit III e details of Red Layers (286e439 cm depth), (Popescu in Lericolais et al.,
2005).
A. Tudryn et al. / Quaternary Science Reviews 148 (2016) 29e4336
core BLKS 98-11 than in core MD04-2754 (Fig. 3e,f). Nevertheless
the general pattern is quite similar between 18.0 and ~15.7 cal kyr
BP. Smectite is a clearly dominant mineral at the beginning of two
sequences until ~17.2 cal kyr BP. Between 17.2 and 15.7 cal kyr BP,
when Red Layers are present in the sediment, smectite decreases
while illite became dominant, with nevertheless some short-term
and significant changes. After that, in core BLKS 98-11, smectite
dominates reaching 60%, while in core MD04-2754, smectite and
illite broadly are in equal contents. Chlorite and kaolinite present
low values. Nevertheless in core MD04-2754, chlorite is clearly
higher, and increases towards 15.7 cal kyr BP. Nd isotopic compositions
of the recent sediments from Rivers Don, Kuban and
Ropotamo present values of À14.3, -9 and À7.3 respectively
(Table 2).
5. Discussion
5.1. Caspian Sea
During the Early Khvalynian transgression, the Caspian Sea
water level varied from maximal values of þ50 m asl to 0 m asl and
several transgression phases are reported (e.g. Leontiev et al.,1977).
In the northernmost part of the Caspian Sea of that time, the very
characteristic Chocolate Clays were deposited. Today they are found
in this now-emerged area, including river terraces in the lower
Volga. Despite numerous studies on this subject, some questions
still remain open and particularly the exact timing of this transgression,
its correlation with climatic events in the northern
Hemisphere and the time and origin of the Chocolate Clays deposit.
5.1.1. Sources of detrital material for the Caspian Sea
The main change in taphonomy in core GS20 after ~13.80 cal kyr
BP suggests a shift from a period with strong river transport to a
period when pollen transport by air was dominant. Although it is
impossible to find out which was the most important river reaching
the middle basin, it is likely that the Volga played an important role
in the supply of the detrital material there. This issue of detrital
material origin is discussed below.
5.1.1.1. Clay minerals. On the whole, the grain-size of all the sequences
in the middle basin and in Chocolate Clays from the river
terraces in the lower Volga indicates a dominance of fine-grained
particles. Clay fraction mineralogy in the middle basin shows a
major change exactly at the same time as a change in pollen
transport (Fig. 3a, c line). Before ~13.8 cal kyr BP, clays are essentially
composed of illite, with kaolinite as the second mineral,
followed by chlorite, while smectite is almost absent. A similar
pattern, with a large quantity of illite is recorded for Early Khvalynian
Chocolate Clays in the river terraces in the lower Volga from
this study (Fig. 3c dots), and from other sites, such as Svetly Yar,
Torgun, Novoprivolnoye and until the moraine clay loam in the
Upper Volga (Makshaev and Svitoch, 2015). The source of the
Chocolate Clays, deposited in the northernmost part of the Caspian
Sea during the Early Khvalynian transgression, is obviously in the
catchment area of the Volga River in the East European Plain. This
suggests that the lower part of the sequence from the middle basin
recorded arrivals of Chocolate Clays which were transported by the
River Volga to this site and that this supply stopped at ~13.8 cal kyr
BP. Above, illite, kaolinite and chlorite decrease and smectite becomes
the major clay mineral.
Clay minerals in river, lacustrine and marine sediments reflect
the intensity of chemical and physical weathering of their source
area (Chamley, 1989). This weathering depends on the lithology,
climate and morphology of the considered environment and results
in surface soils or sediment. On the East European Plain, climatic
oscillations between warm and cold conditions during the Pleistocene
resulted in an alternation of subaerial and subaqueous
sediments; but alternation of soils and loess reflecting these oscillations
predominates. Almost the entire East European Plain area
is covered with these Pleistocene deposits. Under cold climates, the
production of clays essentially depends on physical weathering and
illite is the dominant mineral. Under temperate climate, chemical
weathering prevails and smectite appears. Smectite in the dominant
clay mineral in paleosols from the East European Plain and is
associated with chemical weathering during warm Pleistocene
stages (Perederij, 2001). High contents of smectite were reported in
the Permian-Triassic red clays of the middle Volga region
(Makshaev and Svitoch, 2015), in the northern Caspian Sea sediments
of the river terraces in the lower Volga deposited during the
Late Khazarian transgression (Tudryn et al., 2013a), and in the
northern Black Sea, Kerch Peninsula sediments from the Karangatian
transgression (Dodonov et al., 2000), the latter two
identified as occurring during the Eemian (Mikulin) interglacial.
The supply of the smectite must have been a result of soil erosion
during this time. Broadly the same content of smectite and illite
were reported from Ukrainian loess horizons (Perederij, 2001) that
were deposited as a result of physical weathering during cold and
dry climate. After this author, in sediments from the central part of
the East European Plain, kaolinite is present but chlorite is quite
scarce, but it is known from the lower Don and lower Dniepr
(Chamley, 1989).
Considering the above, the dominance of smectite in sediments
Table 2
Neodymium isotopic signatures of samples from Caspian Sea and some rivers from the Caspian and Black Sea catchment area.
N
Name Country/Sea Lat (N) Long (E) 143Nd/144Nd (2SD) εNd(±0.3)* Source
River terraces
1 Volga (SA175) Russia 48
430
00 44
510
59 0.511732 ± 4 À17.7 this study
River mouths
2 Ropotamo Bulgaria 42
220
10 27
160
09 0.512263 ± 5 À7.3 this study
3 Danube Romania 44
530
02 29
360
50 0.512179 ± 4 À9.0 Soulet et al., 2013
4 Danube Romania 44
530
28 29
370
33 0.512176 ± 4 À9.0 Soulet et al., 2013
5 Dniepr Ukraine 51
420
47 30
370
37 0.511917 ± 7 À14.0 Soulet et al., 2013
6 Desna Ukraine 51
110
38 30
560
40 0.511990 ± 8 À12.6 Freslon et al., 2014
7 Don Russia 47
090
33 39
240
58 0.511903 ± 7 À14.3 this study
8 Kuban Russia 45
040
50 38
350
51 0.512177 ± 40 À9.0 (0.77) this study
9 Volga Russia 45
420
47 47
550
12 0.512021 ± 8 À12.0 Soulet et al., 2013
10 Amu Darya Uzbekistan 42
130
20 60
060
55 0.512151 ± 8 À9.46 this study
11 Sefid Rud Iran 37
270
55 49
560
15 0.512302 ± 10 À6.5 this study
Sedimentary core
12 G20 (770 cm) Caspian Sea 41
320
53 51
060
04 0.512104 ± 5 À10.4 this study
13 G20 (970 cm) Caspian Sea 41
320
53 51
060
04 0.511192 ± 4 À14.0 this study
A. Tudryn et al. / Quaternary Science Reviews 148 (2016) 29e43 37
from the middle basin of the Caspian Sea after ~13.8 cal kyr BP
(Fig. 3c line) suggests the erosion of the smectite-bearing rocks
from the catchment area of the River Volga. In the Early Khvalynian
Chocolate Clays, the absence of smectite rules out this source of
detrital material. The large contents of illite indicate the mobilization
of the illite-rich area and/or physical weathering in the East
European Plain, or the supply from the Baltic Shield area during
melting of the SIS. Indeed, Chamley (1989) pointed out an abundant
occurrence of illite in Pleistocene clays in Scandinavia, which illustrates
a long physical weathering through glacier action. Both
East European and Scandinavian sources for Chocolate Clays were
already considered (e.g. Leonov et al., 2002; Tudryn et al., 2013a).
Nevertheless, as these deposits are very similar to varved clays,
Leonov et al. (2002) and Chepalyga (2007) suggested that Chocolate
Clays resulted from the formation of mudflows rather than from the
melting waters of an ice sheet. According to these authors, meltwater
should transport sediments with more scattered grain sizes
than those which were deposited. Mudflows could be related to the
degradation of permafrost in the periglacial zone, which was
widespread in the Volga catchment. Another interpretation for
Chocolate Clays deposition suggested by Badyukova (2010) is that
the deposition took place in a basin-like periglacial lake or lagoon
with varved sediments: fine deposits during winter below ice cover
and particles with various grain sizes during summer.
5.1.1.2. Neodymium isotopic compositions. To clearly identify the
source area of clays delivered into the northern and middle basins
of the Caspian Sea, and thus to ascertain their origin either from
East European Plain or Baltic Shield area meltwater-induced
deposition, we measured the neodymium isotopic composition
(εNd) on fine-grained sediments from three key locations with regard
to clay mineral changes. Old cratonic source regions typically
exhibit lower εNd values than younger rock formations. According
to geophysical and structural reconstructions, the East European
Craton that consists of three segments (Fennoscandia, Sarmatia and
Volgo-Uralia) is buried under the Upper Proterozoic and Phanerozoic
rocks. Precambrian rocks outcrop in the Baltic and Ukrainian
Shields (Bibikova et al., 2009). Recently, Toucanne et al. (2015)
showed that very low εNd values (between À23.3 and À17.6)
characterize sediments transported by rivers (Kiiminkijoki, Neva)
draining the eastern part of the Precambrian Baltic Shield; i.e. one
of the oldest geological formations in Europe (Bogdanova et al.,
2008). Slightly higher Nd isotopic signatures, between À16.4 and
À14.1, characterize the sediment carried by rivers draining the
south-east of the Baltic catchment area (Rivers Narva, Gauja, Daugava,
Neman and Vistula, North European Plain, southern side of
the SIS during the LGM). These values vary from À16.5 to À13.7 for
LGM glacigenic sediment collected alongside the SIS south margin
in Germany and Poland. This highlights both the input of Baltic
Shield material in the North European Plain by the southern SIS
margins (Kjær et al., 2003), and the westward transport of sediment
from Poland and the Baltic States in continuous, extensive
ice-marginal valleys (Krzyszkowski et al., 1999). Additional information
on εNd for the East European Plain are available for some
rivers supplying the Caspian and Black Seas today, with a value of
εNd À12 for sediments from the lower Volga, -14 for the Upper/
middle Dniepr, -9 for the lower Danube (Soulet et al., 2013) and
À12.6 for Desna (Freslon et al., 2014) (Fig. 1). Complementary data
from this study provide values of À14 for the lower Don, -9 for the
Kuban (Rivers Don and Kuban flowing into the Azov Sea), -7.3 for
River Ropotamo (southwestern Black Sea, Bulgarian coast), and
À6.5 and À9.5 for Asian rivers Sefid Rud and Amu Darya respectively
(Table 2, Fig. 1). These data clearly indicate different neodymium
isotopic compositions and thus different sediment
sources.
Early Khvalynian Chocolate Clays, from river terraces in the
lower Volga at Srednaya Akhtuba, consist essentially of illite (Fig. 3c
dots), and the sample measured for εNd, shows a very low value of
À17.7 (Fig. 3d red star). This clearly identifies its old source being in
the Baltic Shield area, implying the melting of the SIS and transport
of detrital material into the Caspian Sea by fluvioglacial waters via
the River Volga. The lower part of sediment core GS20 from the
middle basin of the Caspian Sea is rich in illite in the same way as
the Chocolate Clays from the river terraces of the lower Volga
(Fig. 3c red line between ~14.6 and 13.8 cal kyr BP). The sample
from this part of the sequence displays higher εNd value (À14.0);
nevertheless it always remains as low as for sediments related to
the Baltic Shield area (Soulet et al., 2013; Toucanne et al., 2015). This
allows the clear identification of this sediment as being deposited
during the Early Khvalynian transgression, as is the case for Chocolate
Clays on river terraces in the lower Volga. The measurement
obtained from the sediment, from the middle basin where smectite
was dominant (Fig. 3c line above ~13.8 cal kyr BP), presents εNd
value of À10.4.
Change in clay mineralogy and in measured values of εNd, as well
as change in the pollen signature, highlights the change of the
detrital material source area here. The supply from the SIS was
either too weak to transport the detrital material until the middle
basin of the Caspian Sea or was stopped. This suggests the modification
of the northern River Volga catchment area at ~13.8 cal kyr
BP and a sufficient retreat of the south margin of the SIS to the
North; so that the meltwater was no longer transported into the
Caspian Sea. After that, the East European Plain area, rich in
smectite, became the dominant provider of detrital material.
5.1.2. Chronology
The identification of the Early Khvalynian sediments in the
middle basin of the Caspian Sea shows the extent of the SIS impact
to the south and the Volga River capacity to transport glacigenic
material. Core GS20 has a continuous record from ~14.6 cal kyr BP,
and the upper limit of this impact is clearly identified at
~13.8 cal kyr BP, when illite decreases and smectite becomes
dominant. 14
C dates, obtained on shells collected in the Chocolate
Clays from river terraces in the lower Volga studied here, show ages
from ~19 to ~13.9 cal kyr BP (Fig. 3d black crosses, Table 1). A
~20 cal kyr BP 14
Cage estimate for a sample of non-identified
organic matter shows that meltwater was supplied into the Caspian
Sea, including its middle basin, during the deglaciation until
~13.8 cal kyr BP, and possibly at least from the LGM. These data, and
these of Russian scientists (Makshaev et al., 2015; Makshaev and
Svitoch, 2015), provide a clear frame for the timing of the Chocolate
Clays deposition during the Early Khvalynian transgression,
when the water level reached at least þ20e0 m asl (sites studied
here), and its ending phase at ~13.8 cal kyr BP. This timing is in very
good agreement with that recently published by Arslanov et al.
(2015). Indeed, these authors obtained ages between 16 and
14 cal kyr BP for transgressive stages of the Early Khvalynian basin
with sea levels of þ35 and þ 22 m asl. These authors point out also
that the maximum stage of þ50 m asl has remained undated until
now.
5.2. Sources of detrital material for the Black Sea
On the whole, smectite and illite alternately dominate the clay
fraction of the sediment. Their content in core BLKS 98-11, that was
collected in the axis of the Danube River on a slope of the platform
constructed by sediment supplied by the Danube and Dniepr
Rivers, is much higher than in core MD04-2754, which was
collected close to the western Turkish shoreline of the Black Sea.
This indicates that the main sources of smectite and illite must have
A. Tudryn et al. / Quaternary Science Reviews 148 (2016) 29e4338
been in the catchment area of the Danube or/and Dniepr, and that
these minerals must have been transported by these northern
rivers.
5.2.1. Red Layers 17.2e15.7 cal kyr BP
In the Black Sea sediments, the two cores BLKS 98-11 and MD04-
2754 show the dominance of illite in the Red Layers (Fig. 3e,f), as it
is the case for the Chocolate Clays in the Caspian Sea. On Fig. 3g,
results of the εNd analyses for core MD04-2790 obtained by Soulet
et al. (2013) are also presented. This core was collected from 352 m
depth, in the same area as core BLKS 98-11 (500 m depth). The very
low values of εNd, between À18.7 and À12.2, have been recorded for
the Red Layers, which were deposited in four steps. This is
expressed by changes of neodymium isotopic signatures and by
changes in clay mineralogy (Fig. 3e, f and g). Soulet et al. (2013)
interpreted low εNd values as being a result of the release of meltwater
originating from a proglacial Lake Disna linked to the SIS, and
transported into the Black Sea by the River Dniepr via the River
Berezina (Fig. 1). This interpretation does not take into account the
geological context of the River Dniepr catchment area. Indeed, its
catchment area includes partly the Ukrainian Shield, and that could
explain low εNd values obtained by Soulet and collaborators (2013)
for the Red Layers in core MD04-2790 and for sample of modern
sediment from the Upper/middle Dniepr (εNd value of À14).
Our study shows that the Red Layers deposited in the Black Sea
and the Chocolate Clays deposited in the Caspian Sea between
actual river terraces in the lower Volga and its middle basin, are the
same kind of material. That confirms the interpretation concerning
the origin of the Red Layers in the Black Sea (linked to the SIS
meltwater) proposed by Soulet et al. (2013). Indeed, no connection
between the catchment area of the River Volga and Ukrainian
Shield exists, and the low values of εNd in the Caspian Sea Early
Khvalynian sediments can only be explained by their origin close to
the Baltic Shield and in relation with the SIS activity.
5.2.2. Sediments between 18.0 and 17.2 and between 15.7 and
12.0 cal kyr BP
Before the appearance of the Red Layers at 17.2 cal kyr BP, the
neodymium isotopic compositions recorded in core MD04-2790 of
the Black Sea, display values between À12 and À11 (Fig. 3g, data
after Soulet et al., 2013). The same values are recovered after the
Red Layers deposition at 15.7 cal kyr BP. Moreover from
~14.0 cal kyr BP onwards, they increase above À11. The clay
mineralogy for these two intervals recorded on core BLKS 98-11 is
largely dominated by smectite that decreases after ~14.0 cal kyr BP
but is still dominant until 12.0 cal kyr BP (Fig. 3f). In core MD04-
2754, the smectite and illite show the same pattern before the
Red Layers deposition. After their deposition, broadly equal proportions
of smectite and illite are recorded (Fig. 3e). It should be
noted that higher contents of chlorite are present in this core on the
whole.
As observed above, the content of smectite is much higher in
core BLKS 98-11 (collected on a slope of the platform, in the near
vicinity of the Danube and Dniepr mouths), than in core MD04-
2754 (collected farther away from river mouths). This suggests
that the principal source of smectite must be related to the activity
of the Danube or Dniepr. Such European origin of the smectite in
the Black Sea sediments is generally not considered. Indeed,
Stoffers and Müller (1972) attributed smectite to an Anatolian
origin where it is common (e.g. Tudryn et al., 2013b), and illite to an
European origin, and this interpretation of clay minerals origin in
the Black Sea sediments has been accepted so far (e.g. Major et al.,
2002). In core MD04-2754, clay minerals changes until 15.7 cal kyr
BP are similar to these described for core BLKS 98-11 (Fig. 3e,f),
indicating the same main source area. After the Red Layers
deposition, smectite increases while illite decreases. They present
broadly similar contents between ~15.0 and 12.0 cal kyr BP. Contents
of chlorite are higher than before and than in core BLKS 98-11.
This difference indicates the relative decrease of the previous
source impact on this site, and the increased influence of another
one: a southwestern or southern source area, probably Bulgarian or
Anatolian, where Stoffers and Müller (1972) reported higher contents
of chlorite.
5.3. A Ponto-Caspian trap and the SIS deglaciation
Our work shows that during the last deglaciation, the PontoCaspian
basin collected meltwater and fine-grained sediment
transported from the southern margin of the SIS via the Dniepr and
Volga Rivers. It resulted in the deposition of characteristic redbrownish/chocolate
coloured illite-rich sediments that originated
from Baltic Shield area. After that, smectite-rich sediments were
deposited in the Caspian and Black Seas. This common general
evolution for the two seas was nevertheless differentiated over
time due to the specificities of their catchment areas and to the
movement of the southern limit of the SIS.
The catchment area of the Black Sea reaches Northern Belarus,
Southern Lithuania and Latvia through the Dniepr and Berezina
basins. The deglaciation started there before 18.3 cal kyr BP with
the recession of the Gruda phase ice sheet (Rinterknecht et al.,
2008; Hughes et al., 2015) (Fig. 3h-2). According to some authors,
Baltija, the youngest phase of the ice margin readvance, finished at
~14 cal kyr BP and the recession steps were definitely terminated at
~13.3 cal kyr BP (Rinterknecht et al., 2008; Marks, 2015). Meltwater
and the detrital material from this area was only partly supplied
into the Black Sea between 17.2 and 15.7 cal kyr BP (Soulet et al.,
2013; this study)(Fig. 3e,f,g). Another route for meltwater was towards
the North Atlantic via ice-marginal valleys from the Baltic
lowlands and the Channel River (Fig. 3h-1) dated between 18.2 and
16.7 cal kyr BP (Toucanne et al., 2015). Further ice-sheet readvance
during the Baltija phase did not reach the northern limit of the
Dniepr catchment area to produce the meltwater evacuation into
the Black Sea during its recession.
The southern limit of the SIS margin in Russia cuts the actual
catchment of the River Volga in the Lake Beloye, and probably even
today’s reservoir Rybinsk area (Svendsen et al., 2004; Hughes et al.,
2015; Stroeven et al., 2015), both are to the south of Lake Onega
(Fig. 1). The maximal extend of the SIS there was attained around
20e18 kyr (Svendsen et al., 2004; Hughes et al., 2015), and after
that at least four advances were identified (Fig. 3h-3). According to
Svendsen et al. (2004), only the last one (the Neva, ~13 cal kyr BP)
did not reach the River Volga catchment area; the Luga phase, i.e.
the previous phase, began its recession after ~14.2 cal yr BP. Our
study shows that this deglaciation timing from the LGM until
~14 cal kyr BP corresponds exactly with the supply of the Chocolate
Clays (via River Volga) into the Caspian Sea as far as at least its
middle basin during the Early Khvalynian transgression, and with
its end recorded at ~13.8 cal kyr BP. Recent publications proposed
that the SIS southeastern margin retreated to the north of Lake
Onega before 14 cal kyr BP (Stroeven et al., 2015; Hughes et al.,
2015). However our data indicate that it must have occurred
slightly later, since the Caspian Sea was fed by meltwater until
~13.8 cal kyr BP.
As pointed out by Arslanov et al. (2015), the beginning of the
Early Khvalynian transgression remains to be assessed. Indeed,
according to radiocarbon dating on sediments collected from
northern, shallow water basin of the Caspian Sea, it started at
~34 cal kyr BP (Bezrodnykh et al., 2015), or even possibly at ~56 kyr
BP (Sorokin et al., 2014). These sediments present the Early Khvalynian
sequence of several meters thick and offer the possibility for
A. Tudryn et al. / Quaternary Science Reviews 148 (2016) 29e43 39
future precise identification of Chocolate Clays (as those deposited
in actual river terraces in the lower Volga and in the middle Caspian
basin) there. According to Bezrodnykh et al. (2004, 2015), their
upper part (8e10 m thick), is composed of clays with variablethickness
sand intercalations and was deposited at depths of
approximately 100 m. 14
C ages on mollusk shells display values
such as ~23.8 and ~21.6 cal kyr BP. These ages are older than those
obtained on mollusk shells and on organic matter from the Chocolate
Clays in river terraces in the lower Volga (Leonov et al., 2002;
Tudryn et al., 2013a; Makshaev and Svitoch, 2015; this study) but
still correspond to LGM. In the Southern basin of the Caspian Sea,
Late Pleistocene reddish sediments were reported and suggested to
correspond to Chocolate Clays (Kroonenberg et al., 2010; Kakroodi
et al., 2015). Further clay minerals and especially neodymium isotopes
studies should allow the clear identification of this material
as transported locally or supplied from the north until the southern
basin of the Caspian Sea. Clay minerals and neodymium isotopes
studies should also allow the identification of the nature and origin
of Chocolate Clays deposited in the actual river valley in the lower
Ural, described by Makshaev and Svitoch (2015).
Our data show different timings in the meltwater supply into
two major areas of the Ponto-Caspian basin. They inform indirectly
on the southern SIS margin extent in the East European Plain and
on meltwater evacuation routes. In the western part the East European
Plain, both a westward release into the North Atlantic (between
18.2 and 16.7 cal kyr BP; Toucanne et al., 2015) and a
southward one into the Black Sea (between 17.2 and 15.7 cal kyr BP)
occurred (Soulet et al., 2013; this study). For the eastern part of the
plain, apart from a northern direction into the Barents Sea
(Svendsen et al., 2004), only a southern direction into the Caspian
Sea was possible, that led to the Early Khvalynian transgressive
stage(s) from LGM until ~13.8 cal kyr BP (this study). According to
Arslanov et al. (2015), the Early Khvalynian transgressive stages
between 16 and 14 cal kyr BP reached the water level of ~22e~35 m
asl, and that resulted in the Caspian Sea water overflowing into the
Black Sea through the Kuma-Manych Strait (22 m asl) during this
time and even until ~12.8 cal kyr BP, when water level dropped so
that it could not reach Kuma-Manych Strait. Our data from the
Caspian Sea confirm the possibility of such timing. Nevertheless the
cores studied here from the western Black Sea area show that clay
minerals originating from the SIS margin were deposited between
17.2 and 15.7 cal kyr BP and that they were transported by the River
Dniepr. Cores were thus probably collected too far from KumaManych
Strait to record the overflow from the Caspian Sea
through clay mineralogy after 16 cal kyr BP, or the overflow could
happen concurrently with meltwater arriving into the Black Sea by
the Dniepr River.
6. Conclusions
This work allowed establishment of the following conclusions:
The Early Khvalynian Chocolate Clays from the lower Volga and
middle basin of the Caspian Sea consist essentially of illite. Very low
εNd values for this sediment clearly identify its source in the Baltic
Shield area, implying the melting of the SIS and transport of this
detrital material into the Caspian Sea by fluvioglacial waters via the
Volga River.
The Early Khvalynian transgressive stage(s) leading to the
Chocolate Clays deposition in the lower Volga and middle basin of
the Caspian Sea took place during the deglaciation and possibly
from the LGM. As recorded by sediments from the Caspian Sea
(values of εNd, clay mineralogy and pollen signature), the Chocolate
Clays deposition finished at ~13.8 cal kyr BP. At that time, the
southeastern margin of the SIS has retreated back so far northward
that the meltwater was no longer transported into the Caspian Sea.
The cessation of fluvioglacial supply into the Caspian Sea
resulted in the modification of the northern part of the River Volga
catchment area and a proportionally increased influence from the
drainage of East European Plains area, its part that is rich in
smectite. Thus the latter became the dominant clay mineral in
sediments after ~13.8 cal kyr BP.
Our results show that illite is the dominant clay mineral in the
Red Layers deposited in the Black Sea between ca. 17.2 and
15.7 cal kyr P, that these Red Layers and the Chocolate Clays from
the Caspian Sea present the same kind of sediment, and confirm
that Red Layers originated from the Baltic Shield area and were
transported into the Black Sea from the southern SIS margin during
the deglaciation by Dniepr River, as proposed Soulet et al. (2013).
Before the deposition of the Red Layers in the Black Sea (between
ca. 18 and 17.2 cal kyr BP) and after the deposition of the Red
Layers/Chocolate Clays in both seas (from ~15.7 in the Black Sea and
from ~13.8 cal kyr BP in the Caspian Sea), smectite became the
dominant clay mineral until 12 cal kyr BP. The East European Plain
is identified as the source for smectite deposited in the Caspian Sea
sediments. In the Black Sea, smectite originated either from the East
European Plain or from the Danube River catchment area. This is an
important result since previous studies considered smectite as only
being of Anatolian origin.
Our investigation shows that during the last deglaciation the
Ponto-Caspian basin collected meltwater and acted as a trap for
fine-grained sediment transported from the southeastern margin
of the SIS via the Dniepr and Volga rivers. In the eastern part of the
East European Plain, the supply of meltwater from the SIS margin
into the Caspian Sea took place during the LGM and the subsequent
deglaciation. That led to the Early Khvalynian transgressive stage(s)
and so-called Chocolate Clays deposition on river terraces in the
lower Volga and until at least the middle basin of the Caspian Sea.
The meltwater supply stopped at ~13.8 cal kyr BP; this indicates
that the southeastern SIS margin retreated so far north that the
meltwater was no longer transported into the Caspian Sea. In the
western part the East European Plain, both a westward release of
meltwater into the North Atlantic (from ca. 20 to 16.7 cal kyr BP;
Toucanne et al., 2015) and a southward one into the Black Sea
(between 17.2 and 15.7 cal kyr BP) occurred (Soulet et al., 2013; this
study).
Acknowledgements
This work is part of the French INSU-CNRS-DYTEC Program and
of the European project “Understanding the Caspian Sea Erratic
Fluctuations” (EU Contract 15-CT96-0112) for Caspian Sea area investigations.
Jean-Charles Fontes, Françoise Gasse and Piotr
Tucholka were the architects of the Caspian Sea project, and
Françoise was its leader. The team included scientists from France,
Russia, Turkmenistan, Azerbaijan, Italy and Belgium. For the Black
Sea, this work is a contribution to the FrencheRomanian BLASON
Programme in the north-western part of the Black Sea, and to the
“Assessment of the Black Sea Sedimentary System Since the Last
Glacial Extreme” (ASSEMBLAGE) project funded by the European
Commission Grant EVK3-CT-2002-00090. Our gratitude goes to G.
Lericolais, project leader, and to French, Romanian, Russian, Turkmenian,
Azerbaijanian, Italian and Belgian teams working with us
on these projects for productive discussions and support. We thank
especially E. Spiridonova, M.P. Antipov, V. Lavrushin, V. Kharchenko,
F. Chalie (they sampled the Chocolate Clays with Yu. A. Lavrushin
and A. Tudryn from river terraces in the lower Volga in
Srednaya Akhtuba, Kolobovka and Tsagan-Aman during a field trip
in September 1997), F. Guichard, P.J. Giannesini, D. Badaut-Trauth,
N. Panin, C. Strechie-Sliwinski, P.N. Kuprin, H. Zeyen and Master
students, who actively contributed to this work. The present results
A. Tudryn et al. / Quaternary Science Reviews 148 (2016) 29e4340
would not have been possible without the support of the numerous
European institutions, especially IFREMER-Genavir and CEA
(France), GeoEcoMar, Bucharest (Romania), IAEA (Vienna), Russian
Academy of Sciences, and the Russian Navy, that latter allowed us to
use a military ship during the Caspian Sea expedition. We are
grateful to G. Soulet and T. Pinchuk, they collected sediments from
Rivers Ropotamo, Kuban and Don for εNd analyses. P. Collins and T.
Hoyle (Brunel University) have kindly checked the English of the
manuscript. The authors are grateful to the two anonymous reviewers
for their comments and information that allowed an
improvement of the final version.
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