GEOLOGICA CARPATHICA, FEBRUARY 2009, 60, 1, 59—70 doi: 10.2478/v10096-009-0006-3
www.geologicacarpathica.sk
Introduction
The development of the Vienna Basin (part of the epicontinen-
tal sea, called Central Paratethys) was mainly influenced by
local geotectonic movements and global sea-level fluctuations
(Hudáčková & Kováč 1997; Kováč 2000; Kováč et al. 2007).
The most distinctive changes occurred in the Middle Miocene.
These processes caused the formation of marine and terrestrial
phases in the Paratethys area with occasional connections with
the Mediterranean and Eastern Paratethys. The closing and re-
activating of seaways, especially during the Miocene, pro-
duced changes of environmental conditions (see Rögl 1998).
A significant global change affecting the Paratethys was the
gradual temperature decline, which followed the warm period
of Miocene Climatic Optimum occurring between 17 and
15 Ma (Gonera et al. 2000; Ivanov et al. 2002; Böhme 2003;
Bicchi et al. 2003; Hudáčková et al. 2003a; Báldi 2006). A
cooling event in the Central Paratethys was observed first in
the Late Badenian (Early Serravallian) marine microfauna as-
semblages (Hudáčková & Spezzaferri 2002; Spezzaferri et al.
2004). Usually, this cooling step reflects the formation of a
permanent ice cap on Antarctica around ~ 14 Ma (late Mid-
dle Badenian, Upper Langhian) and is well documented from
the deep-sea records (e.g. Shackleton & Kennett 1975a;
Berger et al. 1981; Savin et al. 1985; Miller et al. 1991; Pa-
gani et al. 2000; Zachos et al. 2001; Billups & Schrag 2002).
Late Badenian foraminifers from the Vienna Basin
(Central Paratethys): stable isotope study
and paleoecological implications
PATRÍCIA KOVÁČOVÁ
1*
and NATÁLIA HUDÁČKOVÁ
1
1
Department of Geology and Paleontology, Faculty of Sciences, Comenius University in Bratislava, Mlynská dolina G, 842 15 Bratislava,
Slovak Republic; *patriciakovacova@yahoo.com; hudackova@fns.uniba.sk
(Manuscript received November 8, 2007; accepted in revised form June 12, 2008)
Abstract: Paleoecological interpretations based on stable isotope study of benthic (Uvigerina semiornata) and planktonic
(Globigerina bulloides, Globigerinoides trilobus) foraminiferal shells from the Paratethys Vienna Basin (southwestern
Slovakia) are presented. The study was performed on sediments of the Devínska Nová Ves-clay pit deposited during the
Middle and Late Badenian (Middle Miocene). Our
δ
13
C data show an enhanced nutrient input to the water column and the
organic matter accumulation at the bottom of the Vienna Basin. The remineralization of accumulated organic matter on the
sea floor resulted in the formation of oxygen-depleted zones, where no oxic indicators but the oxygen-deficiency tolerant
species were found. Positive benthic
δ
18
O signal can be attributed to the influence of the global cooling recognized in the
world-ocean during the Middle Miocene. At the same time, variations observed in the water column are interpreted as
reflecting the local temperature and salinity changes resulting from the fluvial and rain inflow. The differences between
surface and bottom water temperature reflect the stratification of the water column. Such stratification might be related to
the isolation process of Central Paratethys in the Badenian. This study confirms that
δ
13
C and
δ
18
O are not always in
isotopic equilibrium with the ambient water but are also influenced by vital effects (respiration, symbiont photosynthe-
sis ...). The vital effects led to the incorporation of isotopically light metabolic CO
2
into Globigerina bulloides resulting in
high similarity between
δ
13
C values of Uvigerina and Globigerina. It has been shown that the extremely high
δ
13
C and
very low
δ
18
O of Globigerinoides trilobus clearly imply the influence of algal photosymbionts.
Key words: Middle Miocene, Central Paratethys, Vienna Basin, paleoecology, stable isotopes, planktonic and benthic
foraminifers.
During the time span considered in the present work (Bade-
nian, 16.3—12.7 Ma; Kováč et al. 2007) the Paratethys region
became more and more isolated due to tectonic movements
in the Carpathian Arc. The Late Badenian (13.6—12.7 Ma) is
regarded as the last period of marine connection between the
Paratethys and Mediterranean Tethys.
Stable oxygen and carbon isotope records of foraminifers
are essential proxies for the paleoceanographic and paleocli-
matic evaluation of the sedimentary record. The interpretation
of paleoecological conditions from isotope analyses of shells
is based on the assumption that the isotopic signal of foramin-
iferal tests should reflect the isotopic composition of ambient
water where the organism was growing. In general,
δ
13
C and
δ
18
O are independent of each other and reflect rather different
environmental conditions. The oxygen isotope ratio mainly
reflects fluctuations of global ice volume and sea-surface and
deep-water temperature changes (e.g. Shackleton 1967, 1987;
Shackleton & Opdyke 1973; Shackleton & Kennett 1975b).
The
13
C signal of foraminifers provides information on the
carbon cycling and the origin of organic matter in the oceans
and is widely used to reconstruct past changes of marine-water
properties and organic matter fluxes (e.g. Emrich et al. 1970;
Kroopnick et al. 1970; Duplessy 1972; Renard 1986; Zahn et
al. 1986; McConnaughey et al. 1997; Corliss et al. 2002).
There are several isotope studies that were performed on Mio-
cene foraminifers in the Paratethys region (Šutovská & Kan-
60
KOVÁČOVÁ and HUDÁČKOVÁ
tor 1992; Durankiewicz et al. 1997; Hladilová et al. 1998;
Gonera et al. 2000; Hudáčková & Krá 2002; Báldi 2006).
Some other isotope studies in the Paratethys area were ori-
ented towards gastropod (Latal et al. 2004, 2006a,b), pec-
tinid and brachiopod (Bojar et al. 2004) research.
In the present work, we focus on the stable isotope (
δ
13
C,
δ
18
O) composition of planktonic and benthic foraminiferal
shells from Devínska Nová Ves-clay pit (DNV) because it has
the most complete profile of Badenian age outcrops in the
Vienna Basin. A few stable isotope measurements on foramin-
iferal shells from this area were performed first in the work of
Hudáčková et al. (2003a). In our previous study (Kováčová et
al. 2008), we did geochemical research on foraminifers from
several localities in the Vienna Basin, including DNV. The
present study focuses on confirming paleoecological and
paleoclimatological trends indicated on the basis of the previ-
ous data from the profile. For the more detailed stable isotope
analyses on foraminiferal tests more than 60 new samples
were evaluated from the uppermost part of the DNV profile,
using the most modern measuring technology.
Geological setting
The Vienna Basin (Fig. 1) represents a typical pull-apart
basin situated within the Alpine-Carpathian mountain belt,
between the Eastern Alps and Western Carpathians. The ba-
sin Neogene fill comprises Early to Late Miocene, and
Pliocene-Quaternary deposits. The Early and Middle Mio-
cene sediments were mostly deposited in marine environ-
ments. The uppermost Middle Miocene and Upper Miocene
sediments were deposited in brackish water conditions and
the youngest ones in the freshwater, limnic to fluvial envi-
ronments (Kováč 2000).
The studied area near the Devínska Nová Ves (DNV, Fig. 1)
represents the Slovak part of the Vienna Basin, situated at the
foothills of the Devínske Karpaty (subunit of the Malé Kar-
paty Mts). DNV profile uncovers several stages of the late
Middle/Late Badenian sedimentary sequence. The studied in-
terval consists of over 15 meters thick sequence of laminated
grey clays to claystones and green-grey marls to marlstones
rich in fossil remnants: calcareous nannoplankton, planktonic
and benthic foraminifers, molluscs, fish skeletons and otho-
lites as well as a rare flora fragments. The lower part of section
(15 m—12.2 m) belongs to the Middle Badenian CPN8 Glo-
boturborotalita druryi-Globoturborotalita decoraperta Zone
(Cicha et al. 1975). The Late Badenian age of the Studienka
Formation was determined in the middle and upper part (from
12.2 m up to top) by the foraminiferal assemblages belonging
to the Bulimina/Bolivina Zone (Grill 1941) and nannofossils
of NN6 Zone (Hudáčková & Kováč 1997; Hudáčková et al.
2003a). The Upper Badenian (13.54 Ma) in the upper part of
the transect at 7 m has been documented by
87
Sr/
86
Sr age
based on Pappina neudorfensis (Toula) shells (Hudáčková &
Krá 2000; Hudáčková et al. 2003b). The fauna support sedi-
mentation in middle-outer neritic environment (Hudáčková et
al. 2003a).
Materials and methods
For the paleoecological and paleoclimatological interpre-
tation 108 samples were taken from the DNV profile, in gen-
eral every 10 cm in the upper 9 m. In the lower part, the in-
terval used was 40 cm. In sample preparation we followed
the standard laboratory methods adopted at the Department
of Geology and Paleontology at Comenius University in
Bratislava to separate foraminiferal shells from the sediment.
About two hundred grams of sediment for each sample were
soaked in water and diluted hydrogen peroxide (3%) for sev-
eral hours to desegregate the sediments without damaging
the specimens and to retain the original faunal composition.
Samples were then washed under running water through
200 µm, 125 µm and 71 µm mesh sieves. Approximatelly
200—300 specimens for each sample were picked, identified
with a binocular microscope and counted. The raw data were
transformed into percentages over the total abundance and
percent abundance curves were plotted (Fig. 2 for planktonic
taxa, Fig. 3 for benthic taxa). Species with phylogenetic af-
finities and similar environmental significance were grouped
to better interpret their distribution patterns.
The best-preserved planktonic and benthic foraminiferal
shells were picked for stable isotope measurements. The
benthic stable isotope data were obtained from individuals of
Uvigerina semiornata (Fig. 4.21). In some cases, several
species of uvigerinids (e.g. U. semiornata, U. aculeata) oc-
cupying the same environment were used for analyses. In gen-
eral, the representatives of these taxa inhabit the upper 0—2 cm
in the sediment and are believed to precipitate their tests in
oxygen isotopic equilibrium with the ambient water (Woo-
druff et al. 1980). The planktonic stable isotope data were
Fig. 1. Location of the Vienna Basin and the investigated Devínska
Nová Ves-clay pit (DNV) in the Central Paratethys.
61
STABLE ISOTOPE STUDY OF LATE BADENIAN FORAMINIFERS (CENTRAL PARATETHYS)
achieved from analysis of the intermediate-water dweller
Globigerina bulloides (Fig. 4.1,2), in some samples mixed
with G. diplostoma (Fig. 4.4) or G. praebulloides. In two
samples (65 and 71) the isotope ratio were measured on pre-
vailing tests of Globigerinoides trilobus (Fig. 4.10). This
species occupies predominantly the surface-water layers.
G. trilobus hosts photosymbionts whereas G. bulloides is an
algal
symbiont-barren species (Bé & Tolderlund 1971). In
the uppermost two meters of profile, only the planktonic for-
aminifers have been analysed because of scarcity of benthic
specimens.
The use of stable oxygen isotopic measurements as a
proxy for past paleothermometry began with Urey’s (1947)
theoretical prediction that the
18
O/
16
O ratio in calcite varies
as a function of the temperature in which the mineral precipi-
tated. Since that time, various forms of the paleotemperature
equation have been generated (e.g. Erez & Luz 1983) but all
generally follow Epstein et al.’s (1953) original determina-
tion. In the present work, we used the adapted version of pa-
leotemperature equation as modified by Shackleton (1974)
for calculation of the surface and bottom water temperature:
T = 16.9—4.38 (
δ
18
O
c
—
δ
18
O
w
) + 0.10 (
δ
18
O
c
—
δ
18
O
w
)
2
where T is the paleotemperature (°C),
δ
18
O
c
=
δ
18
O of the
carbonate and
δ
18
O
w
is the isotopic composition of the sea-
water where the carbonate was precipitated.
The first one is relative to the Vienna-PDB (VPDB – Vien-
na PeeDee Belemnite) standard, while the water value in
which the carbonate precipitated is on Standard Mean Ocean
Water (SMOW) scale. The later must be further corrected by
—0.27 ‰ (see in Hut 1987 or Bemis et al. 1998). If
δ
18
O
w
of
—0.24 ‰ is applied for Middle Miocene seawater (Lear et al.
2000) the above equation can be rewritten as follows:
Fig. 2. Relative abundance (percent value) of planktonic foraminifers with estimation of the CPN8/CPN9 planktonic Zones (according to
Cicha et al. 1975) boundary. Absolute age according to Hudáčková & Krá (2002).
62
KOVÁČOVÁ and HUDÁČKOVÁ
Fig. 3. Relative abundance (percent value) of benthic foraminifers with estimation of the CPN8/CPN9 planktonic Zones (according to
Cicha et al. 1975) boundary.
63
STABLE ISOTOPE STUDY OF LATE BADENIAN FORAMINIFERS (CENTRAL PARATETHYS)
T = 16.9—4.38 [
δ
18
O
c
—(—0.51)] + 0.10 [
δ
18
O
c
—(—0.51)]
2
The VPDB standard replaced after intercalibration the older,
no longer available standard PDB, which refers to the Creta-
ceous belemnite formation at PeeDee in South Carolina, USA.
When using Shackleton’s equation with the above men-
tioned corrections, the final temperature values are about
2.2 °C lower than the results without any corrections.
The isotope measurements were performed on a Finnigan
MAT 251 mass spectrometer at the GSM laboratory of Ber-
gen University, Norway, adapting the standard method used
in that laboratory. The number of specimens analysed at a
single measurement varied between 1 and 3 for benthic
shells ( ~ 85 µg) and between 6 and 10 for planktonic individ-
uals ( ~ 70 µg). Foraminiferal tests were ultrasonically
cleaned in ethanol for 10 s. Gas for isotope measurements
was produced by reaction with orthophosphoric acid at
70 °C in an automated on-line system, where the acid was
added to the sample in individual reaction chambers. Results
are reported with respect to the VPDB standard through cali-
bration against CM03 standards. The reproducibility of the
system is ± 0.06 ‰ for
δ
13
C and ± 0.07 ‰ for
δ
18
O, based on
replicate measurements of an internal carbonate standard.
Results
On the basis of the 89 identified foraminiferal taxa – (39
planktonic ones) from 108 samples we suggest that water
depth during the sedimentation fluctuated from the inner to
outer shelf.
The planktonic assemblages indicate a paleoclimatic trend
from warm to more temperate conditions from the bottom to
the top of the section, based on lower abundance of the Glo-
bigerinoides and Orbulina-Praeorbulina group (Fig. 2).
The benthic foraminiferal assemblages suggest, indeed,
that the sea floor was characterized by suboxic episodes, as
indicated by positive excursions in the abundance of the Uvi-
gerina group (Fig. 3). Suboxic and dysoxic episodes also oc-
curred, documented by drastic decrease in the abundance of
benthic foraminifers.
105 stable isotope measurements on benthic and plankton-
ic foraminiferal shells from DNV profile have been pro-
duced. The stable isotope results are shown in Table 1.
Changes in the isotope ratios of planktonic and benthic fora-
miniferal tests along the profile are shown in Fig. 5 for both
carbon and oxygen stable isotopes.
The benthic
δ
18
O values are between + 1.7 ‰ and + 2.3 ‰
with an average of + 1.9 ‰. The curve records a slight in-
creasing trend towards the upper part of the studied section.
The
δ
13
C values demonstrate a narrow range of values from
—1.06 ‰ to —0.05 ‰ (averaging —0.64 ‰). The record is
well balanced and no distinct variances were observed.
The
δ
18
O values measured in the shells of planktonic Globi-
gerina taxa range from —1.11 ‰ to + 1.39 ‰ (mean value
+ 0.25 ‰) and the
δ
13
C values range from —1.37 ‰ to
+ 0.20 ‰ (mean value —0.65 ‰). The
δ
18
O values show larger
variations with a negative trend towards the top in contrast to
δ
13
C data, which tend to have positive values, most visible in
Table 1: Stable isotope results of oxygen (
δ
18
O) and carbon (
δ
13
C)
of analysed planktonic and benthic foraminiferal shells in the DNV
section. G.b. – Globigerina bulloides, G.tr. – Globigerinoides
trilobus, U – Uvigerina semiornata.
64
KOVÁČOVÁ and HUDÁČKOVÁ
Fig. 4. SEM pictures of the most frequent species in DNV. 1 – Globigerina bulloides d’Orbigny, spiral side, 70
×, 80 cm. 2 – Globigerina
bulloides d’Orbigny, apertural side, 72
×, 80 cm. 3 – Globigerina ex. gr. bulloides d’Orbigny, apertural side, 75×, 40 cm. 4 – Globigerina
diplostoma Reuss, 62
×, 120 cm. 5 – Globigerina concinna Reuss, 75×, 80 cm. 6, 7 – Globigerina concinna Reuss, 77.5×, 95×, 40 cm. 8 –
Globigerinoides cf. bulloideus Crescenti, 110
×, 1420 cm. 9 – Globigerina concinna Reuss, 87×, 80 cm. 10 – Globigerinoides trilobus (Re-
uss), 55
×, 1520 cm. 11 – Globigerinella obesa (Bolli), 75×, 120 cm. 12 – Globigerinella cf. obesa (Bolli), 77.5×, 120 cm. 13 – Pavonitina
styriaca Schubert, 31
×, 1125 cm. 14 – Valvulineria complanata (d’Orbigny), 52.5×, 1125 cm. 15 – Valvulineria complanata (d’Orbigny)
with microbial cover, 72.5
×, 1125 cm. 16 – Detail of microbial cover on the V. complanata test, 350×, 1125 cm.
65
STABLE ISOTOPE STUDY OF LATE BADENIAN FORAMINIFERS (CENTRAL PARATETHYS)
Continued from previous page:
17 – Uvigerina venusta Franzenau with microbial cover, 45
×, 1125 cm. 18 – Budashevaella wilsoni
(Smith), 77.5
×, 1125 cm. 19 – Hanzawaia crassiseptata (Łuczkowska) umbilical side, with microbial cover, 85×, 1125 cm. 20 – Spirolocu-
lina badenensis d’Orbigny, 72.5
×, 1125 cm. 21 – Uvigerina semiornata d’Orbigny, 57×, 1125 cm. 22 – Cassidulina carinata Silvestri,
142
×, 320 cm. 23 – Uvigerina bellicostata Łuczkowska, 65×, 420 cm. 24 – Uvigerina accuminata Hosius, 62.5×, 420 cm. 25 – Uvigerina
venusta Franzenau, 47
×, 380 cm. 26 – Bolivina viennensis Marks, 77×, 740 cm. 27 – Bolivina pokornyi Cicha et Zapletalova, 60×, 740 cm.
28 – Bolivina dilatata maxima Cicha et Zapletalova, 60
×, 740 cm. 29 – Bolivina dilatata maxima Cicha et Zapletalova, 57.5×, 720 cm.
30 – Bulimina elongata d’Orbigny, 50
×, 980 cm. 31 – Uvigerina venusta Franzenau, wall detail, 450 cm. 32 – Uvigerina venusta Fran-
zenau, wall detail, 450 cm. 33 – Pappina neudorfensis (Toula), wall detail, 450 cm. 34 – Sediment microlayer structure, 520 cm. 35 – Sed-
iment microlayer structure, 535 cm. 36 – Uvigerina venusta Franzenau, wall detail, 450 cm. 37 – Uvigerina venusta Franzenau, 50
×,
450 cm. 38 – Pappina neudorfensis (Toula), 50
×, 450 cm. 39 – Sediment microlayer structure, 740 cm. The scale bars = 100 µm.
the middle and upper part of the section. On samples 65 and 71,
planktonic isotope measurements were carried out on the pre-
dominant species Globigerinoides trilobus. The measured val-
ues of this taxon reached ~ + 1.10 ‰ for
δ
13
C and ~ —1.41 ‰
for
δ
18
O. Considering the
δ
18
O differences between Globigeri-
na and Globigerinoides taxa, it was observed that the deeper-
water dweller Globigerina gives a more positive
δ
18
O signal
than the shallow living Globigerinoides. Towards the top of
the section increasing differences between the
δ
18
O data of
planktonic and benthic taxa are recorded.
The calculated paleotemperature (Fig. 6) of bottom waters
(benthic Uvigerina) ranges from 5.2 °C to 7.7 °C (averaging
at 6.8 °C). Planktonic Globigerina bulloides indicate quite a
large temperature range from a minimal value of 9 °C to a
maximal value of 19.4 °C (average 13.7 °C). The near-sur-
face living Globigerinoides trilobus has been analysed in
two samples where the values of 19.7 °C and 21.6 °C (aver-
age 20.6 °C) were obtained.
Discussion
Carbon isotopes
The
δ
13
C values recorded in foraminiferal tests reflect the
δ
13
C values of dissolved inorganic carbon (DIC) of ambient
water masses in the ocean. Foraminiferal
δ
13
C values, there-
fore, are usually used as the major tracer for nutrients (Sarn-
thein et al. 1994). The
δ
13
C in the ocean is inversely correlated
to nutrient concentration; the higher nutrient concentration in
seawater produces more depleted
δ
13
C of calcareous shells.
When the
12
C-rich organic matter is transported to the sea
floor, its remineralization causes release of
12
C and depletion
of
13
C in water. Consequently, the ambient water exhibits nu-
trient enriched values and causes low
δ
13
C values in foramin-
iferal shells. However, the carbon isotopic composition often
deviates from equilibrium (Mulitza et al. 1999). These offsets
have been attributed to “vital effects” involving biologically,
physically and chemically controlled processes, which cause
disequilibrium between the
δ
13
C
DIC
and
δ
13
C of foraminiferal
shells (Peters 2000).
Our benthic and planktonic
δ
13
C data indicate that the nutri-
ent-rich water conditions occurred in the investigated Vienna
Basin during the late Middle/Late Badenian (Late Langhian/
Early Serravallian). The
δ
13
C measurements on foraminifers
show that the subsurface species of Globigerina recorded
lighter values of ~ 1.73 ‰ than the near-surface Globige-
rinoides (Fig. 5, Table 1). In many cases it is also lighter than
benthic
δ
13
C, even if the mean values are very close (—0.65 ‰
for Globigerina, —0.64 ‰ for Uvigerina). G. bulloides is a
typical high biological productivity indicator (Naidu & Niitsu-
ma 2004). When the specimens of G. bulloides calcify in fer-
tile waters, their
δ
13
C signal should be lower resulting from
the fractionation pattern of carbon isotopes. The negative
δ
13
C
values of Globigerina, thus, imply an increasing nutrient input
to the water column of the Vienna Basin.
An accessible reservoir of light carbon
12
C is represented
mainly by continental organic matter (Berger et al. 1981).
Therefore, the most probably nutrient source bringing the or-
ganic matter to the water column of the Vienna Basin was pro-
vided by terrestrial input. During the Middle Miocene, an
important paleogeographical change in the Vienna Basin was
the formation of a new drainage pattern resulting in a wide
deltaic system of the paleo-Danube on the northern edge of
the basin (Jiříček 1990). Thus, we suppose that the paleo-
Danube river inflow might have increased the productivity in
the surface waters of the Vienna Basin and have caused the
δ
13
C-depleted values in planktonic shells (Kováčová et al.
2008). At this time, the marine connection of Central Parat-
ethys was closing and the river input was probably the only pos-
sible source providing the nutrient supply to the water column.
The negative carbon isotopic ratio (—0.64 ‰) extracted from
benthic Uvigerina shells indicates an increased organic carbon
supply to the sea floor. The benthic
δ
13
C curve exhibits a neg-
ative trend towards the top (Fig. 5), which is probably related
to enhanced benthic eutrophication, especially pronounced in
the Late Badenian, first recognized by Báldi (2006). Such con-
ditions can arise when the remaining organic matter, not con-
sumed by the microorganisms or bigger faunal elements in the
water column, falls down to the bottom. Accumulated organic
matter, rich in
12
C, on the sea floor and within the sediment is
subject to decomposition, which depletes the carbon isotope
ratio of ambient water (McCorkle et al. 1990).
The Uvigerina species analysed in the DNV are consid-
ered to be shallow-infaunal and so are influenced by the iso-
topic composition of pore water (Schmiedl et al. 2004). Un-
der the nutrient-rich conditions, the pore water DIC, even in
the upper millimeter, may be depleted in
13
C relative to that
of the bottom water. Thus, the negative
δ
13
C of Uvigerina
analysed in DNV might reflect the nutrient-rich and
13
C de-
pleted pore water conditions in the Vienna Basin. At the
same time, the remineralization of accumulated organic mat-
ter at the bottom can produce oxygen-depleted zones. In the
Vienna Basin, an insufficient oxygenation of the sea floor is
indicated by abundance of low-oxygen benthic foraminiferal
indicators, dominated by the following taxa: Uvigerina (U. ve-
66
KOVÁČOVÁ and HUDÁČKOVÁ
nusta, Fig. 4.31,32,36,37; U. bellicostata, Fig. 4.23; U. semi-
ornata, Fig. 4.21), Bolivina (B. dilatata maxima, Fig. 4.28, 29;
B. pokornyi, Fig. 4.27) and Bulimina (B. elongata, Fig. 4.30;
B. subulata). The sub/dysoxic conditions are also reflected by
absence of oxic indicators reported in previous studies (Fig. 3;
Kováč & Hudáčková 1993; Hudáčková & Kováč 1997). Our
benthic
δ
13
C data correspond to the observations, based on
benthic foraminiferal species distribution, and support the
high nutrient and low oxygen concentrations at the bottom of
the Vienna Basin during the late Middle/Late Badenian.
Multi-species measurements of fossil and recent foramini-
fers revealed that the stable isotope composition of calcare-
ous tests of many species exhibits deviations from the calcite
precipitated in equilibrium with the ambient water (Gross-
man 1987; Spero & Lea 1996; Peeters et al. 2002; Naidu &
Niitsuma 2004; Schmiedl et al. 2004). These deviations are
most expressed in the
δ
13
C signal and are called vital effects.
Vital effects include the incorporation of metabolic CO
2
into
the shells during calcification, calcification rate rising, phys-
iological changes during ontogenesis, kinetic effects and the
photosynthetic activity of symbionts (Erez 1987; McCon-
naughey 1989; McConnaughey et al. 1997). The high simi-
larity between the
δ
13
C values of Uvigerina and Globigerina
from DNV can be regarded as a vital effects implication for
G. bulloides. The increased productivity in surface water
evocates a higher calcification rate and consequently higher
respiration of CO
2
(Berger et al. 1978) in the eutrophic spe-
cies G. bulloides. CO
2
comprises the light carbon isotope
12
C. Under the favourable conditions, which apparently oc-
curred in the Vienna Basin, G. bulloides could involve more
CO
2
enriched in
12
C (Naidu & Niitsuma 2004). Consequent-
ly, this process led to slightly more negative
δ
13
C compared
to benthic Uvigerina from the same area.
Another process affecting foraminifer
δ
13
C is algal photo-
symbiosis. Planktonic foraminifers with photosymbionts dis-
play higher
δ
13
C values than nonsymbiotic species (e.g.
Spero & Williams 1988; McConnaughey 1989). This could
be the case of the analysed symbiont-bearing species Globi-
gerinoides trilobus, whose carbon isotope results are surpris-
ingly positive (~ + 1.10 ‰). The difference between
Globigerina and Globigerinoides is about 1.5 ‰. During
photosynthesis, the algal symbionts preferentially use the
lighter version of carbon isotope (
12
C) and so elevate the
13
C/
12
C ratio in the ambient water. The production rate of
symbionts and the degree of
δ
13
C increase in foraminifers
vary directly as a function of light intensity (see Spero et al.
1991). Consequently, the near-surface dweller G. trilobus
with photosymbionts should yield the heaviest carbon iso-
tope values. The results from DNV show a distinctive sym-
biotic influence on the
δ
13
C signal of G. trilobus. The
analysed foraminiferal taxa Uvigerina and Globigerina do not
host any symbiotic algae in the cytoplasm and their stable iso-
tope carbon signal is not changed by photosynthetic activity.
Oxygen isotopes
The ratio of the stable oxygen isotopes
18
O and
16
O is one of
the most important tools in paleoceanography and paleoclima-
tology. In marine sediments, the oxygen isotopic composition
of foraminiferal shells is used as a proxy for the temperature
(e.g. Emiliani 1954; Erez & Luz 1983; McConnaughey 1989;
Bemis et al. 1998). In addition to temperature, sea surface sa-
linity changes also affect foraminiferal
δ
18
O distribution. The
benthic foraminifer
δ
18
O is controlled by water temperature
because salinity seems to be constant in deeper parts of the
oceans (Cheng et al. 2004). On the other hand, the planktonic
δ
18
O appears to have been controlled by both, temperature of
surface waters and salinity (Kennett 1986).
Water temperature decreases with increasing water depth
and this trend is observed by the foraminiferal
δ
18
O data in
this work (Fig. 5, Table 1). As expected, the most positive
oxygen isotope values have been recorded from benthic Uvi-
gerina (average + 1.9 ‰). It has been shown that the oxygen
isotopic composition of Uvigerina is in equilibrium with the
surrounding seawater (Shackleton 1973). Thus, we can as-
sume that the oxygen isotope signal of shallow-infaunal Uvi-
gerina reflects the
δ
18
O conditions of pore water in the Vien-
na Basin during the late Middle to Late Badenian. The
benthic
δ
18
O from DNV is comparable to results of many
cores from the Pacific and Atlantic oceans during 14—13 Ma
(e.g. Shackleton & Kennett 1975b; Woodruff et al. 1981;
Savin et al. 1981; Kennett 1986; Boersma 1986). The mean
values from those studies range approximately between
+ 1.9 ‰ and + 2.6 ‰. Our benthic data from DNV are also
positive ranging between + 1.7 ‰ and + 2.3 ‰ and are ap-
parently very close to the open ocean signal.
An increase in
δ
18
O values of benthic foraminifers may re-
flect several processes: a cooling of ocean water tempera-
ture, an increase in global ice volume, an increase in salinity,
or some combination. The Middle Miocene
δ
18
O increase
between 16.5 and 13.2 Ma (Kennett 1986) has generally
been accepted as representing a major permanent buildup of
the East Antarctic ice sheet (Savin et al. 1975; Shackleton &
Kennett 1975a). Our positive benthic
δ
18
O record, suggest-
ing colder bottom-water temperature, might be interpreted as
result of global cooling influence recognized in world ocean
and also affecting the Central Paratethys. Benthic
δ
18
O val-
ues between approximately + 1.9 ‰ and +3 ‰ are interpret-
ed as ice periods (see Williams et al. 1988) and we believe
that our results of + 1.7 ‰ — + 2.3 ‰ represent the influence
of ice-buildup. Because the Vienna Basin was an intramoun-
tain shallow (neritic) basin, the bottom-water environment
was evidently warmer than in the open ocean. Therefore the
benthic oxygen isotope data from DNV are lower and do not
show strong variations. However, in the DNV oxygen iso-
tope profile we cannot see the distinct positive trend. We sup-
pose that this is caused by the fact that the investigated profile
from DNV represents only a small part of cooling phase.
The oxygen isotope results of Globigerina from DNV
show a wide range between —1.11 ‰ and + 1.39 ‰ (Fig. 5,
Table 1). In general, we observe two directions of oxygen
isotope signal: a tendency to more positive data (averaging
+ 0.6 ‰) in the lower part of the profile up to 7 m; and a
trend to more negative values (average + 0.04 ‰) from 7 m
to the top of DNV. The planktonic
δ
18
O data obtained from
the Middle Miocene show that the most positive/coolest val-
ues between + 0.6 ‰ and + 1.9 ‰ were observed in the Pa-
cific (Shackleton & Kennett 1975a; Kennett 1986); slightly
67
STABLE ISOTOPE STUDY OF LATE BADENIAN FORAMINIFERS (CENTRAL PARATETHYS)
less positive data of —0.2 ‰ to + 1.5 ‰ were observed in the
Atlantic (Keigwin 1983; Vergnaud-Grazzini 1985) and the
most negative/warmest values ranging between —1 ‰ and
+ 0.6 ‰ were obtained in the Mediterranean Sea (Van der
Zwaan & Gudjonsson 1986).
Our values from DNV are close to the Mediterranean level
and show a slight negative trend. This trend could imply
warming of surface water or slight decreasing of salinity or a
combination of both. Since the Vienna Basin represents a
shallow environment, the water temperature, in general, is
expected to be higher than in the open ocean area. On the
other hand, the surface water in the basin was affected by
isotopically depleted meltwater arriving from the paleo-
Danube delta. The frequent variations shown by
δ
18
O signal
of planktonic taxa might thus reflect the temperature and sa-
linity changes caused by both, river and rain inflow. We sug-
gest that in the case of the Vienna Basin, the local effects
played an important role and the
δ
18
O signal recorded by
planktonic foraminifer Globigerina is influenced by both,
the local temperature and salinity changes.
The use of stable isotope ratios is limited by a number of
problems.
δ
18
O measurements on living and laboratory cul-
tured foraminifers show distinct deviations with respect to
the isotopic equilibrium (e.g. Grossman 1987). These devia-
tions are presumably influenced by life processes including
the vital effects. A perfect example of taxa displaying a devia-
tion due to vital effect in this work is Globigerinoides trilobus
(as already shown from the carbon isotope signal). This spe-
cies exhibits the most negative
δ
18
O values (average —1.41 ‰)
and is associated with dinoflagellate symbionts that are dis-
tributed between and on spines in a halo around the calcitic
shell (Wolf-Gladrow et al. 1999). The photosynthetic activity
of algal symbionts affects shell
δ
18
O values; an increase in
symbiont photosynthetic activity results in a decrease in shell
δ
18
O values (e.g. Bemis et al. 1998). Species exhibiting vital
effects generally have compositions 0.5—1.5 ‰ depleted in
18
O relative to equilibrium (Grossman 1987). G. trilobus from
DNV displays a strong deviation of ~ 1.7 ‰ compared to G.
bulloides. Such difference between two planktonic species in-
habiting roughly the same environment, regarding the shallow
water environment of the Vienna Basin, clearly implies the in-
fluence of symbionts in the case of G. trilobus. We suppose
that the depleted oxygen isotope ratio and enriched
δ
13
C sig-
nal observed at the same time in G. trilobus do not reflect the
isotopic composition of ambient water but represent the devia-
tion due to vital effects.
We calculated paleotemperature from our benthic and
planktonic
δ
18
O values using the equation of Shackleton
(1974) described in the methodology part (Fig. 6). The bot-
tom water temperature records variations of about 2 °C and
represents relatively cold conditions averaging ~ 6.8 °C. The
temperature of the water column calculated from
δ
18
O values
of G. bulloides recorded bigger variations than in the sea
floor. In general, we recognize two tendencies: a distinctive
trend to cooler temperature (shift of ~ 6 °C) in the lower part
of the profile up to 11 m and the tendency to warmer temper-
atures (shift of ~ 7 °C) from 11 m towards the top. However,
the temperature in the water column (mean value ~ 13.7 °C)
was very variable and we observe a lot of small shifts to-
wards cooler or warmer conditions. According to our as-
sumptions, the surface water was more influenced by the
temperature changes, related to the warmer fluvial and rain-
water input, than the sea bottom. Furthermore, the seasonal
temperature changes affecting only the near-surface layers
could play a role. In the Vienna Basin, temperature stratifica-
tion has been reported in previous paleoecological works
(e.g. Kováč & Hudáčková 1993; Hudáčková & Kováč
Fig. 5. The Badenian oxygen and carbon stable isotope record of
planktonic and benthic foraminifers from the Vienna Basin. Ma
ages agree with: 13.54 Ma (radiometric dating
87
Sr/
86
Sr, Hudáč-
ková & Krá 2002), 13.65 Ma (Middle/Late Badenian boundary ac-
cording to Kováč et al. 2007).
68
KOVÁČOVÁ and HUDÁČKOVÁ
1997). This stratification trend is probably related to the
closing of the Central Paratethys Sea, which culminated in
the Late Badenian. The difference of ~ 7 °C between the bot-
tom and surface water temperature shown in this study
agrees with previous observations.
The paleotemperature obtained from the oxygen isotope ra-
tio of symbiont-bearing G. trilobus is evidently the highest
(average at 20.6 °C), as we expected, since it is a near-surface
dwelling species. However, as has been previously reported,
in consideration of the assumed paleodepth of Vienna Basin
(150—200 m), a difference of ~ 7.5 °C between the G. bul-
loides and G. trilobus is enormous. In the shallow basin, these
two genera are supposed to have roughly the same habitat-
depth, and even in the stratified water, the temperature should
not be very different. There are, however, also suggestions
that a species like Globigerina bulloides may calcify as a ju-
venile at depth and migrate to shallower depths in later growth
stages (Spero & Lea 1996; Bemis et al. 1998). This opinion
could explain the strong contrast between the water tempera-
ture indicated by
δ
18
O of G. bulloides and G. trilobus. Never-
theless, in this case, we believe that, as well as the
δ
13
C signal,
the
18
O/
16
O ratio was influenced and changed by the vital ef-
fect due to symbiotic algae, which depleted and consequently
suggested a higher temperature.
Conclusions
The stable isotope signal of foraminiferal shells from the
Vienna Basin (Central Paratethys) was influenced by the
global temperature changes, but the local factors also played
an important role. Stable isotope analyses were done on
planktonic and benthic foraminiferal shells from the upper
Middle to Upper Badenian (Middle Miocene) sediments of
the Devínska Nová Ves-clay pit (DNV) in the Vienna Basin
(in Slovakia). The most frequent foraminiferal taxa (benthic
Uvigerina semiornata and planktonic Globigerinoides trilo-
bus and Globigerina bulloides) have been selected for stable
isotope measurements.
A nutrient enrichment in the water column and in the sea
floor of the Vienna Basin was observed. The enhanced accu-
mulation of organic matter at the sea floor followed by de-
composition produced an oxygen deficiency in the bottom
indicated by the low-oxygen tolerant taxa Uvigerina, Bolivi-
na, Bulimina and mainly by the absence of oxic indicators.
The global cooling phase, recognized in the world ocean
during the Middle Miocene, also affected the Vienna Basin.
Positive benthic
δ
18
O values represent the influence of ice-
buildup. The planktonic
δ
18
O record is apparently influenced
by isotopically depleted freshwater arriving from the paleo-
Danube runoff.
Calculated paleotemperatures showed the differences be-
tween the bottom and the water column. The bottom-water
temperature indicates stable conditions whereas the surface
water was apparently influenced by the temperature changes,
related to the warmer fluvial and rain input. We cannot ex-
clude the seasonal temperature changes affecting the surface
water. The difference between the bottom-water and surface-
water temperature could represent a stratification of the wa-
ter column, which might relate to the isolation process of the
Central Paratethys sea during the Badenian.
Acknowledgments: We thank the GMS Laboratory at the
University of Bergen (Norway) for running the mass spec-
trometers. We are grateful to ubomír Sliva for comments
on sedimentology and technical help. We also thank our re-
viewers Katalin Báldi, László Kocsis and Otília Lintnerová
for the useful comments and suggestions. This study was fi-
nancially supported by Slovak Grant Agency (Grants VEGA
1/2035/05, APVV-51-011305 and APVV-028007).
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