FORAMINIFERAL PALEOECOLOGY OF THE GRUND FORMATION 155
GEOLOGICA CARPATHICA, 55, 2, BRATISLAVA, APRIL 2004
155164
FORAMINIFERAL PALEOECOLOGY AND BIOSTRATIGRAPHY OF
THE GRUND FORMATION (MOLASSE BASIN, LOWER AUSTRIA)
SILVIA SPEZZAFERRI
Department of Geosciences, Geology and Palaeontology, Ch. Du Musée 6, Pérolles, CH-1700 Fribourg, Switzerland;
silvia.spezzaferri@unifr.ch
(Manuscript received June 5, 2003; accepted in revised form December 16, 2003)
Abstract: This study was undertaken to solve the debate about the age of the sediments from the Grund Formation and
to propose an environmental interpretation based on benthic and planktonic foraminiferal assemblages from the profiles
excavated in 1998 and 1999 in the type locality of the Grund Formation (Lower Austria). In particular, quantitative data
of foraminifers from Profile G were statistically treated to unravel the ecological gradients subtending the samples.
Planktonic foraminiferal assemblages suggest a warm paleoclimate for this area. Benthic foraminiferal assemblages
testify to strong re-deposition processes displacing shallow-water sediments from the inner shelf to outer shelf. Re-
deposition may derive from storm events. Oxygenation of bottom waters is difficult to assess on the basis of benthic
foraminifers. In particular, it is not possible to identify the dysoxic episodes suggested by the occurrence of chemosymbiotic
bivalves living with anaerobic bacteria as in Zuschin et al. (2001). The studied sediments can be attributed to the Lower
Lagenidae Zone in the Badenian (Langhian, Middle Miocene) on the basis of the presence of index fossils like Praeorbulina
glomerosa circularis and Uvigerina macrocarinata.
Key words: Badenian, Austria, Grund Formation, ecology, stratigraphy, molasse, foraminifers.
Introduction
In 1998 and 1999, the Institute of Paleontology of the Univer-
sity of Vienna organized excavation campaigns in the type
area of the Grund Formation, at Grund, north of Hollabrunn in
Lower Austria, north of the Danube (Fig. 1). A total of 9 pro-
files were excavated and are currently described in detail in
Roetzel et al. (1999), Pervesler et al. (1999), Zuschin et al.
(2001), Pervesler & Roetzel (2002) and Roetzel & Pervesler
(2004).
Fig. 1. Locality map showing the position of Profiles A to H (after Roetzel & Pervesler 2004).
Sediments from these profiles are dominated by yellowish
fine sands and silts with thin intercalation of gray pelitic lay-
ers, with evidence of channels filled with molluscs debris,
coarser sand and fine gravel (Harzhauser et al. 1999) and bio-
turbations throughout (Fig. 2; Pervesler et al. 1999). In partic-
ular, Zuschin et al. (2001) interpreted the sedimentary succes-
sion as an alternation of fining upward sequences of tempestite
layers with the base characterized by abundant molluscan
fragments. To the west the Grund Formation is replaced by the
Gaindorf Formation, which is described by Roetzel et al.
Table 1: Distribution and abundance of benthic and planktonic foraminifers in Profile G. A abundant; C common; R rare.
156 SPEZZAFERRI
FORAMINIFERAL PALEOECOLOGY OF THE GRUND FORMATION 157
Fig. 2. Lithological section of Profile G (after Roetzel & Pervesler
2004). Indicated is also the level where Praeorbulina glomerosa cir-
cularis occurs.
Table 1: Continued
(1999) as characterized by coarser sediments and reduction of
pelitic layers.
Cicha & Rudolský (1996); Cicha (1999) and vábenická &
Ètyroká (1999), have recently attributed the Grund Formation
at its type locality to the Karpatian (BurdigalianEarly Mio-
cene). However, their age attribution contrasts with the obser-
vations of other authors, such as Weinhandl (1957) and Grill
(1958) who documented the occurrence of the planktonic fora-
minifers Praeorbulina glomerosa and Orbulina suturalis in
the Grund Formation. These microfossils are typical of the
Early Badenian (LanghianMiddle Miocene).
The aim of this study is to investigate the age of the Grund
Formation and to reconstruct the depositional and paleoenvi-
ronmental setting in the area.
Samples from Profiles E to H (Fig. 1) were analysed for
their micropaleontological content and for biostratigraphic
studies. Ecological investigation was performed on Profile G
only (Fig. 2). This profile was found to be the more suitable to
reconstruct environmental conditions because it is character-
ized by more numerous levels representing in-situ sediments,
with respect to other profiles. Here after, when mentioning
samples, the letter refers to profiles (Fig. 1) and the number to
progressive samples taken in each profile from bottom to top.
Material and methods
Samples were taken during the excavation to record the
more important sedimentary facies including autochthonous
and reworked sediments as shown in Fig. 2. Two hundred
grams of sediment for each sample were soaked in hydrogen
peroxide for several hours. Samples were then soaked in warm
water and washed under running water through >250 µm,
>125 µm and >63 µm mesh sieves. Residues from Profile EH
were analysed qualitatively. Washed residues from Profile
G were split, using the splitter described in Rupp (1986) to
obtain approximately 500 to 1000 specimens per fraction
for each split. Specimens of benthic and planktonic fora-
minifers were then identified using a binocular microscope
and counted.
Multivariate statistics were applied to quantitative data us-
ing the Software PRIMER 5 (Plymouth Marine Laboratory).
Application of this method to planktonic and benthic fora-
minifers is extensively discussed in Basso & Spezzaferri
(2000) and Spezzaferri & Æoriæ (2001). Hierarchical
agglomerative clustering is based on the Bray-Curtis Similar-
ity (Clifford & Stephenson 1975). Complete linkage was
used for benthic foraminifers. On the basis of the same simi-
larity matrix, samples were ordered by non-metric
MultiDimensional Scaling nMDS (Kruskal 1977). Clus-
ters identified both in the dendrograms and nMDS plots, at
the same similarity level, were further investigated through
the Similarity and Dissimilarity Term Analyses, to highlight
the contribution of each species to the total average similar-
ity and dissimilarity within each group and between differ-
ent groups and thus, to better characterize the assemblages.
Planktonic foraminifers
Sam
pl
es
G
lobi
geri
na
p
raebul
lo
id
es g
r.
G
lobi
geri
na
s
p.
G
lobi
geri
na
tarchanensi
s
G
lobi
geri
ne
lla
obesa
g
ro
up
G
loboqua
dri
na
langhi
ana
G
loborot
al
ia
b
ykovae
Pa
ragl
obo
rot
al
ia
acrost
om
a
Pa
ragl
obo
rot
al
ia
inaequi
conica
Pr
aeorbuli
na
gl
om
erosa
ci
rcul
ari
s
Pr
aeorbuli
na
s
p.
Zeagl
obi
ge
ri
na
w
oodi
Tot
al
Pl
ankt
on
ic
F
.
Re
wo
rk
in
g
Acari
ni
na
bul
brooki
M
orozove
lla
s
p.
C
assi
geri
ne
lla
s
p.
G
lobot
run
cana
s
p.
Bol
ivi
noi
de
s
draco
Bol
boform
a
R
adi
ol
ar
ia
ns
M
ol
lu
scs
G-14 -
G-13 2 2 4
G-12 -
G-11 -
G-10 -
G-9 6 1 9 16 R
G-8 8 12 1 12 1 34 C
G-7 1 1 2 R
G-6 18 2 8 3 64 2 97 1 1 1 C
G-5 5 1 1 1 1 9 1 A
G-4 2 1 4 7 A
G-3 3 1 7 11 A
G-2 3 1 4 1 1 R/C A
G-1 1 1 A
158 SPEZZAFERRI
Results
Micropaleontology and biostratigraphy
Benthic foraminifers are generally abundant in all samples.
The abundance and presence of planktonic foraminifers varies
from sample to sample from absent to common (Table 1). The
quantitative study performed on benthic foraminiferal assem-
blages from Profile G revealed that the levels characterized by
coarser lithology contain high abundance of the Ammonia, El-
phidium and Asterigerinata groups, whereas, Amphistegina
sp., Reussella spp., and Glabratellina sp. are rarer. These
forms are generally corroded and often broken. The accompa-
nying assemblages include common to abundant Pappina
spp., Bolivina spp., Bulimina spp., Caucasina spp., He-
terolepa spp., Lenticulina spp., Uvigerina graciliformis and
Table 2: Bray-Curtis Similarity and Dissimilarity of benthic foraminifers. Lentic. Lenticulina group; Saracen. Saracenaria sp.;
Avg. Ab. average abundance; Avg. Dis. average dissimilarity; Contrib. contribution, Cum cumulative.
Nonion commune. Specimens from the Globobulimina pyru-
lapupoides group, Cassidulina sp., Baggina arenaria, Vir-
gulopsis tuberculatus and Valvulineria complanata are rare.
Uvigerina macrocarinata was found in Sample F-10. De-
formed shells of benthic foraminifers and, in particular, Am-
monia spp. are observed in several samples.
Planktonic foraminifers are generally small-sized and in-
clude specimens from the Globigerina praebulloides group,
Globigerinella obesa, Globorotalia bykovae, Paragloborota-
lia sp. Praeorbulina glomerosa circularis occurs in Samples
G-9 and F-6. Clearly reworked species include rare Acarinina
sp. (Eocene), Globotruncana sp. (Cretaceous) and Cassiger-
inella sp. (Oligocene). Table 1 shows the distribution and
abundance of benthic and planktonic foraminifers in Profile G
together with the distribution of molluscan fragments and ra-
diolarians.
Cluster 1
Average similarity = 55.52
Average dissimilarity = 58.71
Avg. Ab. Avg. Sim. Contrib.% Cum%
Group 2
Group 1
Caucasina gr.
30.33
10.21
18.40
18.40
Avg. Ab. Avg. Ab. Avg. Dis. Contrib.% Cum%
A. viennesis
47.67
8.36
15.05
33.45
A. viennesis
169.80
47.67
16.65
28.37
28.37
A. parkinsoniana
19.67
4.28
7.71
41.16
Elphidium gr.
84.60
19.67
9.13
15.55
43.92
Cibicidoides gr.
12.33
2.99
5.38
46.55
Lentic.-Saracen. gr.
42.80
6.33
5.05
8.59
52.52
A. perlucida
8.67
2.58
4.66
51.20
H. dutemplei
39.60
12.33
3.96
6.74
59.26
Elphidium gr.
19.67
2.58
4.65
55.85
Caucasina gr.
5.40
30.33
3.47
5.90
65.16
N. commune
12.33
2.25
4.06
59.91
A. parkinsoniana
39.40
19.67
2.96
5.04
70.20
H. dutemplei
12.33
2.18
3.92
63.83
Bolivina gr.
1.20
10.33
1.44
2.46
72.66
Pappina gr.
10.67
2.12
3.82
67.65
Asterigerinata gr.
15.00
11.67
1.26
2.15
74.80
Asterigerinata gr.
11.67
2.10
3.79
71.44
Pappina gr.
1.80
10.67
1.17
1.99
76.79
P. granosum
6.67
1.82
3.29
74.73
B. elongata group
0.60
8.00
1.08
1.84
78.63
H. boueana
7.67
1.69
3.04
77.77
A. perlucida
1.20
8.67
1.03
1.76
80.39
A. tepida
9.67
1.58
2.85
80.62
Average dissimilarity = 31.90
Cluster 2
Average similarity = 75.28
Group 2
Group 3
Avg. Ab. Avg. Sim. Contrib.% Cum%
Avg. Ab. Avg. Ab. Avg. Dis. Contrib.% Cum%
A. viennesis
169.80
25.69
34.13
34.13
A. viennesis
169.80
282.40
10.90
34.17
34.17
Elphidium gr.
84.60
15.34
20.38
54.51
Elphidium gr.
84.60
124.80
4.06
12.72
46.89
H. dutemplei
39.60
7.82
10.39
64.90
A. parkinsoniana
39.40
66.20
2.36
7.41
54.30
A. parkinsoniana
39.40
7.75
10.29
75.19
N. commune
8.40
31.80
1.72
5.40
59.69
Lentic.-Saracen. gr.
42.80
7.64
10.15
85.34
H. dutemplei
39.60
56.80
1.32
4.14
63.83
Lentic.-Saracen. gr.
42.80
49.60
1.29
4.03
67.86
Cluster 3
Average similarity = 73.22
Cibicidoides gr.
5.60
18.20
1.10
3.44
71.30
Avg. Ab. Avg. Sim. Contrib.% Cum%
Asterigerinata gr.
15.00
28.20
1.07
3.35
74.65
A. viennesis
282.40
26.78
36.57
36.57
Caucasina gr.
5.40
18.40
1.00
3.13
77.78
Elphidium gr.
124.80
10.84
14.81
51.38
Pappina gr.
1.80
10.00
0.65
2.04
79.81
A. parkinsoniana
66.20
7.77
10.61
61.99
P. granosum
2.20
9.40
0.60
1.87
81.68
H. dutemplei
56.80
6.34
8.65
70.64
A. tepida
3.20
11.20
0.59
1.86
83.54
Lentic.-Saracen. gr.
49.60
5.25
7.17
77.82
Amphistegina spp.
4.00
8.40
0.58
1.81
85.35
Asterigerinata gr.
28.20
2.98
4.07
81.89
Average dissimilarity = 61.60
Group 1
Group 3
Avg. Ab. Avg. Ab. Avg. Dis. Contrib.% Cum%
A. viennesis
47.67
282.40
21.85
35.47
35.47
Elphidium gr.
19.67
124.80
9.54
15.49
50.95
A. parkinsoniana
19.67
66.20
4.85
7.87
58.83
Lentic.-Saracen. gr.
6.33
49.60
4.29
6.97
65.80
H. dutemplei
12.33
56.80
4.27
6.94
72.73
N. commune
12.33
31.80
1.73
2.82
75.55
Asterigerinata gr.
11.67
28.20
1.73
2.81
78.36
Caucasina gr.
30.33
18.40
1.39
2.26
80.62
FORAMINIFERAL PALEOECOLOGY OF THE GRUND FORMATION 159
Table 3: Bray-Curtis Similarity and Dissimilarity of planktonic foraminifers.
Ecology
The ecology of benthic and planktonic foraminifers is here
retained following sources such as Spezzaferri & Æoriæ
(2001). A summary of the ecological preference of Miocene
Paratethyan foraminifers is also given in Rögl & Spezzaferri
(2003) together with the ecological interpretation of the Gain-
dorf Formation equivalent to the Grund Formation outcrop-
ping at Mühlbach.
Statistical treatment
To identify the biological relationship between the samples
from the Grund Formation from Profile G in the temporal
framework of sediment deposition we have performed the sta-
tistical treatment of data. Statistical testing in this context en-
ables identification and characterization of changes in com-
munity structures through time and allows us to relate them to
changing environmental conditions (Clark & Warwick 1994).
Species with phylogenetic affinities and similar environmen-
tal significance were grouped to better interpret the distribu-
tion patterns.
Benthic foraminifers
At 64 % of the Bray-Curtis Similarity, three clusters sepa-
rate (Fig. 3A,B; Table 2). Cluster 1 is represented by samples
G-6, G-8 and G-9; thirteen species and/or groups account for
the 80.62 % of the average similarity within this group. Clus-
ter 2 groups samples G-7, G-11, G-12, G-13 and G-14; five
species and/or groups account for the 85.34 % of the average
similarity within this group. Cluster 3 groups G-1, G-2, G-3,
G-4, and G-5; six species and/or groups account for 81.89 %
of the average similarity within this group.
Planktonic foraminifers
At 44 % of the Bray-Curtis Similarity, four clusters separate
(Fig. 4A,B; Table 3). Cluster 1 groups samples G-2 and G-4;
the G. obesa group accounts for the 100 % of the average sim-
ilarity. Cluster 2 groups samples G-1 and G-7; the G. praebul-
loides group accounts for the 100 % of the average similarity.
Cluster 3 groups samples G-6 and G-8; three species and/or
groups account for 96.55 % average similarity within this
group. Cluster 4 groups samples G-3; G-5, G-9 and G-13; two
species and/or groups account for 97.60 % average similarity
within this group.
Discussion
Ecology
Paleodepth estimate
An important parameter for paleoenvironmental reconstruc-
tion of marine environments is the paleodepth of the sedimen-
tary basin. However, estimation of paleodepth for the Grund
Cluster 1
Average similarity = 54.55
Average dissimilarity = 70.76
Avg. Ab. Avg. Sim. Contrib.% Cum%
Group 4
Group 3
G. obesa gr.
3.50
54.55
100.00
100.00
Avg. Ab. Avg. Ab. Avg. Dis. Contrib.% Cum%
G. bykovae
4.75
38.00
36.41
51.67
51.67
Cluster 2
Average similarity = 66.67
G. tarchanensis
0.50
10.00
16.76
23.79
75.46
Avg. Ab. Avg. Sim. Contrib.% Cum% G. praebulloides gr.
4.00
14.00
12.25
17.38
92.84
G. praebulloides gr.
1.00
66.67
100.00
100.00 Average dissimilarity = 75.88
Group 4
Group 2
Cluster 3
Average similarity = 44.27
Avg. Ab. Avg. Ab. Avg. Dis. Contrib.% Cum%
Avg. Ab. Avg. Sim. Contrib.% Cum% G. bykovae
4.75
0.00
38.44
50.66
50.66
G. bykovae
38.00
18.32
41.38
41.38 G. praebulloides gr.
4.00
1.00
25.28
33.32
83.98
G. praebulloides gr.
14.00
12.21
27.59
68.97 G. tarchanensis
0.50
0.50
5.00
6.58
90.57
G. tarchanensis
10.00
12.21
27.59
96.55 Average dissimilarity = 75.88
Group 3
Group 2
Cluster 4
Average similarity = 51.59
Avg. Ab. Avg. Ab. Avg. Dis. Contrib.% Cum%
Avg. Ab. Avg. Sim. Contrib.% Cum% G. bykovae
38.00
0.00
49.39
52.39
52.39
G. praebulloides gr.
4.00
28.28
54.91
54.91 G. tarchanensis
10.00
0.50
20.02
21.23
73.63
G. bykovae
4.75
21.98
42.69
97.60 G. praebulloides gr.
14.00
1.00
19.51
20.69
94.32
Average dissimilarity = 84.90
Group 4
Group 1
Avg. Ab. Avg. Ab. Avg. Dis. Contrib.% Cum%
G. bykovae
4.75
0.00
28.35
33.39
33.39
G. obesa gr.
0.00
3.50
24.57
28.94
62.33
G. praebulloides gr.
4.00
1.00
19.39
22.84
85.18
Average dissimilarity = 89.44
Group 3
Group 1
Avg. Ab. Avg. Ab. Avg. Dis. Contrib.% Cum%
G. bykovae
38.00
0.00
46.44
51.92
51.92
G. tarchanensis
10.00
0.50
18.26
20.42
72.35
G. praebulloides gr.
14.00
1.00
18.20
20.35
92.69
Average dissimilarity = 82.64
Group 2
Group 1
Avg. Ab. Avg. Ab. Avg. Dis. Contrib.% Cum%
G. obesa gr.
0.00
3.50
51.11
61.85
61.85
G. praebulloides gr.
1.00
1.00
15.07
18.24
80.08
160 SPEZZAFERRI
Fig. 3. A Hierarchical agglomerative clustering based on the
Bray-Curtis Similarity, and B non-metric MultiDimensional
Scaling (nMDS) plot of benthic foraminifers from Profile G.
Formation based on benthic foraminiferal assemblages is very
difficult. The presence of stilostomellids (including the genus
Siphonodosaria) together with Pullenia bulloides, Melonis
pompilioides, and costate uvigerinids (U. graciliformis and U.
macrocarinata) indicate a relatively deep-water of about
100 meters corresponding to the outer shelf. This depth attri-
bution disagrees with the interpretation of Zuschin et al.
(2001), who inferred a water depth of much less than
100 meters based on molluscan assemblages and shell-beds
geometry suggesting proximal tempestites. The presence
throughout Profile G of shallow-water species like the Ammo-
nia group, Aubignyna perlucida, Porosononion granosum,
Asterigerinata and Amphistegina groups may indicate shal-
low water depth. However, tests of these taxa appear always
broken and/or corroded with respect to the well preserved
deeper-water species. Therefore, mixing of shallow-water
benthic foraminifers and deeper-water species indeed, indi-
cates re-deposition processes displacing the upper shelf sedi-
ments into the deeper part of the sedimentary basin.
Statistical treatment
As demonstrated in Rögl & Spezzaferri (2003) the distribu-
tion in space and time of benthic and planktonic foraminifers
Fig. 4. A Hierarchical agglomerative clustering based on the
Bray-Curtis Similarity, and B non-metric MultiDimensional
Scaling (nMDS) plot of planktonic foraminifers from Profile G.
and their ecology can provide important information to char-
acterize the sediments in term of displacement and reworking.
Combining the ecological data reported in the literature and
partially summarized in Rögl & Spezzaferri (2003), with the
distribution patterns of benthic and planktonic foraminifers
(Table 1) and the statistical parameters (Tables 23), allows
us to reconstruct the paleoenvironments in which the sedi-
ments from Profile G (Grund Formation) were deposited.
Benthic foraminifers
Cluster 1 includes Samples G-6, G-8 and G-9 collected
from the thin pelitic layers and is characterized by infaunal el-
ements consisting of Caucasina, Pappina, Bolivina and Bu-
limina (Tables 1, 2) which are very rare in the other clusters.
The Uvigerina group is also present in this cluster but not
abundant (Table 1). Kaiho (1994) considers Uvigerina spp.
and Lenticulina spp. as suboxic indicators of Group B (be-
tween the extremes of oxic and dysoxic) and Bulimina as sub-
oxic indicators of Group C (between group B and dysoxic in-
dicators). Since the genus Caucasina is morphologically and
phylogenetically related to the Bulimina group, specimens be-
longing to this genus are here retained as suboxic indicators of
Group C. On the contrary Kaiho (1994) includes bolivinids in
FORAMINIFERAL PALEOECOLOGY OF THE GRUND FORMATION 161
the dysoxic indicators group. Oxic indicators such as Cibici-
doides and Hanzawaia boueana are scarce in this cluster (Av-
erage abundance = 12.33 % and 7.67 % respectively). Almost
all the taxa identified in this cluster are mud-preferring species
(Rögl & Spezzaferri 2003). Therefore, this cluster represents
the autochthonous sediments deposited on a suboxic to dys-
oxic sea floor with oxygen-depletion down to the first centi-
meters of the sediments.
Cluster 2 (Samples G-7, G-11, G-12, G-13 and G-14) is
characterized by high abundance of shallow-water elements
like the Ammonia and Elphidium groups. Their contribution
to the total average similarity is up to 64.7 %. Amphistegina
spp. (also shallow-water species) is present and displays an
average similarity of 4 %. Lenticulina spp. (Suboxic species
B) is relatively abundant and contributes 10.15 % of the aver-
age similarity within this cluster. Caucasina, Bulimina and
Bolivina belonging to the Suboxic Group C are very rare (Ta-
ble 2). This cluster includes samples collected from coarse sedi-
ments with high abundance of probably transported shallow-
water species. The absence of molluscs in these layers may
indicate deposition during the terminal phase of storm events.
Cluster 3 (Samples G-1, G-2, G-3, G-4, and G-5) is very
similar to Cluster 2 and is characterized by the highest abun-
dance of shallow-water elements such as Ammonia, Elphidi-
um, Asterigerinata groups. Their contribution to the total av-
erage similarity is 66.04 %. Amphistegina spp. is present and
displays an average similarity of 8.4 %. Lenticulina spp. con-
tribute 7.17 % of the average similarity within this cluster
(Table 2). The difference between Clusters 2 and 3 is the high-
est abundance in Cluster 3 of Caucasina, Bulimina and Bolivi-
na belonging to the Suboxic Group C. This Cluster includes
samples from the levels containing high abundances of mol-
luscs and plants (Table 1, Fig. 1) and possibly represents mol-
luscan and plant debris at the base of the tempestites layers.
These observations allow us to interpret the non-metrical
MultiDimensional Scaling (nMDS) plot and to identify the
displacement gradient subtending the samples (Fig. 3B). The
gradient representing the bottom water oxygenation could not
be clearly identified as a result of secondary oxygenation due
to remobilization of sediments during storm events. Sample
G-12 (Cluster 2) roughly corresponds to a level where the bi-
valve Thyasira michelottii was found in life position (Fig. 2).
This species is currently interpreted as having a chemosymbi-
otic mode of life by comparison with the ecology of modern
thyasirid bivalves (Tyson & Pearson 1991). Zuschin et al.
(2001) interpreted the sediments from Profiles CE as a dys-
aerobic biofacies on the basis of the occurrence of a monospe-
cific macrofauna consisting of Thyasira michelottii in life po-
sition within bioturbated clay-silt sediments. On the basis of
these data, Sample G-12, but also the other samples from
Cluster 2 collected near the tyasirid horizon, should include
high abundance of dysoxic indicators. However, in these sam-
ples, benthic foraminifers do not show evidence of strong ox-
ygen depletion. On the contrary low oxygen-preferring spe-
cies are less abundant in Cluster 2 (and in Sample G-12) than
in Clusters 1 and 3. To explain this paradox, three interpreta-
tions are suggested: (1) bottom waters were only slightly sub-
oxic. Thyasira michelottii was searching through the sedi-
ments for short-life pockets of sulphide material which is un-
stable in the presence of oxygen. This search explains the con-
spicuous tunnelburrow-system which could be extended up
to 300 mm into the sediments (Zuschin et al. 2001). The bi-
valve monospecific assemblage was due to currently un-
known environmental conditions preferred by thyasirid but
unsuitable for other molluscan taxa. (2) Dysoxic condition
dominated the sea floor but dysoxic benthic foraminiferal in-
dicators were removed or diluted by other processes (e.g. bio-
turbation and/or storm events). Occurrence of infaunal dysox-
ic indicators like bolivinids and buliminids in Clusters 1 and 3
together with the occurrence of deformed specimens of Am-
monia spp., throughout the section (Fig. 5), may support the
interpretation of dysoxia also in shallower water. In fact, in
the presence of environmental stress like anoxia benthic fora-
minifers may produce abnormal and deformed shells in fora-
minifers (e.g. Yanko et al. 1994). (3) The dysoxic layer in
which the thyasirid bivalves proliferated was very thin and is
not represented in the studied samples.
Planktonic foraminifers
Clusters 1 and 2 (Samples G-2 and G-4; and G-1 and G-7)
are characterized by the Globigerinella obesa (temperate-wa-
ter indicator) and Globigerina praebulloides groups (cool-wa-
ter indicators) respectively. Their contribution of up to 100 %
to the average similarity is an artifact due to the scarcity of
planktonic foraminifers in the samples. Cluster 3 (Samples G-
6 and G-8) is characterized by Globorotalia bykovae, G. prae-
bulloides groups and Globigerina tarchanensis. Globorotalia
bykovae is considered a warm-temperate indicator. Its contri-
bution to the average similarity within this Cluster is 41.38 %.
Globigerina praebulloides and G. tarchanensis may indicate
increased nutrient input (e.g. Rögl & Spezzaferri 2003).
Cluster 4 (Samples G-3, G-5, G-9 and G-13) is character-
ized by G. praebulloides group with contribution to the aver-
age similarity of 54.91 %. Globorotalia bykovae is also abun-
dant.
Due to the scarcity of planktonic foraminifers in the sam-
ples from Profile G the identification of the paleoclimate is
only tentatively done (left side of Fig. 4B). The relatively
warmer paleoclimate apparently occurred in Grund in the in-
terval from Sample G-3 to G-13. The displacement and deple-
tion of planktonic foraminifers gradients are more clearly
identified as at the right side of Fig. 4B. However, the absence
of planktonic foraminifers in samples G-10, G-11, G-12 and
G-14 prevents a fully reliable interpretation of the data set.
Biostratigraphy
The biostratigraphy of the studied portion of the Grund For-
mation is based on the standard zonation for the Paratethys
(see e.g. Rögl et al. 2002 for a synthesis). Although plankton-
ic foraminifers are scarce in the analysed samples, the pres-
ence of Praeorbulina glomerosa circularis in Samples F-6
(Profile F) and G-9 (Profile G) from the pelitic layers (Fig. 5),
enable the correlation with the Early Badenian (Langhian
Middle Miocene). The occurrence of Uvigerina macrocarina-
162 SPEZZAFERRI
Fig. 5. 1 Marginulina hirsuta dOrbigny. Sample G-1. Magnification
×
100. 2. Uvigerina macrocarinata Papp et Turnovský. Sample F-
10. Magnification
×
100. 3 Guttulina austriaca dOrbigny. Sample F-10. Magnification
×
100. 4 Pappina primiformis (Papp et Turn-
ovský). Sample F-10. Magnification
×
150. 5 Ammonia viennensis (dOrbigny). Sample G-11. Magnification
×
70. Broken specimen. 6
Ammonia tepida (Cushman). Sample G-9. Magnification
×
250. Deformed specimen. 7 Elphidiella minuta (Reuss). Sample G-1. Magnifi-
cation
×
150. 8 Uvigerina graciliformis Papp et Turnovský. Sample G-9. Magnification
×
150. 9 Elphidium crispum (Linné). Sample G-
11. Magnification
×
70. Broken specimen. 10 Elphidium flexuosum (dOrbigny). Sample G-13. Magnification
×
70. Broken specimen.
11 Lenticulina inornata (dOrbigny). Sample G-11. Magnification
×
70. Broken specimen. 12 Lenticulina inornata (dOrbigny). Sam-
ple G-11. Magnification
×
600. Particular of a broken chamber. Visible are rounded elements that resemble gametes. 13 Praeorbulina
glomerosa circularis (Blow). Sample F-6. Magnification
×
150. 14 Praeorbulina glomerosa circularis (Blow). Sample F-6. Magnification
×
150. 15 Praeorbulina glomerosa circularis (Blow). Sample G-9. Magnification
×
150. 16 Globorotalia bykovae (Aisenstat). Sample
G-6. Magnification
×
200. Scale bars = 100
µ
m.
FORAMINIFERAL PALEOECOLOGY OF THE GRUND FORMATION 163
ta, index species of the Lower Lagenidae Zone (Papp & Turn-
ovský 1953) in Sample F-10 (Profile F) support this age attri-
bution (Fig. 5). An Early Badenian age is also indicated by the
presence of Bolboforma reticulata (protophyta incertae sedis)
in Sample G-8 (Spezzaferri & Rögl in print). This event is cal-
ibrated with the time scale of Berggren et al. (1995) and
equated to Zone NN5 of Martini (1971) by Spiegler & Gürs
(1996).
Nannofossil assemblages indicate a Badenian age (Zone
NN5) for the excavated sections based on the presence of
Helicosphaera waltrans, as also in Cicha (1999) and váben-
ická & Ètyroká (1999).
Summary and conclusion
This study contributes to solving the debate about the
age of the Grund Formation. Foraminiferal analyses suggest a
Badenian age (LanghianMiddle Miocene), for the sediments
recovered from profiles excavated by the Institute of Paleon-
tology, University Vienna. In particular, the presence of P.
glomerosa circularis and U. macrocarinata enable the corre-
lation with the Lower Lagenidae Zone.
Massive re-deposition processed possibly due to stormy
events displaced shallower-water sediments into the deeper
parts of the basin as indicated by mixing of abundant and gen-
erally broken shallow-water species like Ammonia, Elphidi-
um, Asterigerinata groups, and Amphistegina spp. with better
preserved deeper-water species. The high abundance of bro-
ken shallow-water specimens (Fig. 5) testifies to the intense
re-deposition.
Different phases in the storm events can be identified
combining micro- and macrofauna. Coarse bioclasts (domi-
nantly molluscs) dominate at the base of the tempestites layers
indicating the strongest pulse of the stormy event. Finer ele-
ments like foraminifers dominate in the middle part and at the
top, indicating decreased intensity.
Paleodepth estimation based on benthic foraminiferal as-
semblages indicates that the sediments from Profile G were
deposited in the outer shelf.
A relatively warm paleoclimate characterized the inter-
val of the deposition of the sediments from Profile G at least
from Sample G-3 to G-13 based on the presence of warm-wa-
ter indicators such as Globorotalia bykovae and P. glomerosa
circularis. The scarcity of planktonic foraminifers, however,
prevents a more reliable and detailed interpretation of data.
The oxygenation of the bottom waters is difficult to as-
sess. Dysoxic episodes in sediments with chemosymbiotic bi-
valves living with anaerobic bacteria are not identified based
on benthic foraminiferal assemblages.
Acknowledgments: This investigation is part of FWF Project
P-13743-BIO focused on the ecology of the Austrian marine
Miocene (Austrian Science Fund). I thank the University of
Vienna for support during my stay there. For discussion, in-
formation, and provision of samples I am grateful to R. Roet-
zel (Geological Survey, Vienna), P. Pervesler, M. Zuschin
and the students from the University of Vienna participating
in the excavations. For technical assistance at the SEM,
thanks to Ch. Baal and S. Æoriæ (University of Vienna). I also
thank the reviewers K. Holcová and A. Gasiñski for their
comments, which improved this manuscript. Especially thank
to F. Rögl, his friendship, help and advice have represented an
important contribution to all my work since I have started my
career.
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