GeolCarp_Vol69_No3_264

GEOLOGICA CARPATHICA

, JUNE 2018, 69, 3, 264–282

doi: 10.1515/geoca-2018-0016

www.geologicacarpathica.com

The Rupelian – Chattian transition in the north-western

Transylvanian Basin (Romania) revealed by calcareous

nannofossils: implications for biostratigraphy and

palaeoenvironmental reconstruction

MĂDĂLINA – ELENA KALLANXHI

, RAMONA BĂLC

2, 3,



STJEPAN ĆORIĆ

SZABOLCS – FLAVIUS SZÉKELY

and SORIN FILIPESCU

Babeș–Bolyai University, Department of Geology, M. Kogălniceanu 1, 400084 Cluj–Napoca, Romania; madalina_kallanxhi@yahoo.com,

szekelyflavius@gmail.com, sorin.filipescu@ubbcluj.ro

Babeș–Bolyai University, Department of Environmental Science, Fântânele 30, 400294 Cluj–Napoca, Romania

Interdisciplinary Research Institute on Bio–Nano Sciences, Babeș–Bolyai University, 42 Treboniu Laurian Street, 400271 Cluj–Napoca,

Romania;



ramona.balc@ubbcluj.ro

Geological Survey of Austria, Neulinggasse 38, A–1030 Vienna, Austria; Stjepan.Coric@geologie.ac.at

(Manuscript received November 13, 2017; accepted in revised form April 16, 2018)

Abstract: Sediments belonging to the Oligocene Vima Formation (located in the north-western part of the Transylvanian

Basin, Romania) have been investigated for calcareous nannofossils content. Biostratigraphically, the sedimentary

succession is late Rupelian–Chattian in age, belonging to the NP24 — Sphenolithus distentus and NP25 — Sphenolithus

ciperoensis biozones, to CP19a — Cyclicargolithus floridanus and CP19b — Reticulofenestra bisecta Subzones and to

the interval from CNO4 — Sphenolithus distentus / Sphenolithus predistentus CRZ to CNO5 — Sphenolithus ciperoensis

TZ. The palaeoenvironment of the Fântânele section was reconstructed by means of calcareous nannofossils and statistics.

Multivariate statistics were applied to the composition of autochthonous assemblages and the obtained clusters were used

to assess the palaeoecological preferences of the nannofossils. We document changes from more stable open-marine

regime, with temperate sea-surface temperatures interfering locally with influx of cooler water and enriched cool-nutrient

supply for the late Rupelian–earliest Chattian (NP24), to shallower and possibly warmer near-shore marine eutrophic

environment, with salinity fluctuations, increased terrigenous material run-off and freshwater influx for the remaining

early Chattian (NP25).

Keywords: Rupelian–Chattian transition, Central Paratethys, Transylvanian Basin, calcareous nannofossils, biostratigraphy,

palaeoenvironment, statistics.

Introduction

The Oligocene–Early Miocene interval is characterized by

important palaeogeographical changes, due to intense tectonic

activity, uplifting of the alpine mountain chains, all these

bringing the reconfiguration of the area into two marine

domains: the intracontinental Paratethys to the north and

the Mediterranean to the south (Laskarev 1924; Báldi 1969,

1980; Rusu 1988; Săndulescu & Micu 1989; Rögl 1998,

1999). Distinct marine conditions associated with the above

mentioned changes are reflected in the composition of macro-

and micro-palaeontological assemblages, by the appearance of

Paratethyan endemic assemblages, immediately after the first

isolation of the Paratethys in the Early Oligocene (early

Rupelian or early Kiscellian in the terms of Paratethyan

stages). Within the NP23 biozone, blooms of endemic species

Pontosphaera fibula and of other taxa such as Reticulo fenestra

ornata and Braarudosphaera bigelowii, are recorded all over

the area (Gheţa et al. 1976; Krhovský et al. 1992; Haczewski

1989; Nagymarosy & Voronina 1992; Rusu et al. 1996;

Nagymarosy 2000; Schultz et al. 2004; Melinte 2005;

Melinte-Dobrinescu & Brustur 2008; Soták 2010; Oszczypko-

Clowes & Żydek 2012), reflecting restricted basin palaeo-

environment characterized by anoxic conditions, reduced

salinities and colder surface sea waters. All these environ-

mental features can be attributed to the reduced seaway

connection to the Mediterranean region (Rögl 1998, 1999).

The Early to Late Oligocene interval (late Rupelian to

Chattian, or late Kiscellian to Egerian, in terms of Paratethyan

stages), corresponding to the upper NP23 to NP25 biozones, is

characterized by the re-establishment of normal marine con-

ditions due to the opening of the sea-way connection with

the Mediterranean Sea via the Slovenian corridor (Báldi 1986;

Nagymarosy 1990; Rögl 1998, 1999; Popov et al. 2004). In

the northern part of the basin a connection with the North Sea

probably existed through the Rhine Graben (Berger 1996;

Sissingh 1997; Rögl 1998, 1999; Popov et al. 2004), while to

the south a well developed marine gateway through the eastern

Mediterranean provided access from the Indo–Pacific realm

(Rögl & Steininger 1983). These palaeogeographical and

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palaeoclimatic changes during the Oligocene (Kiscellian–

early Egerian), are also reflected in the composition of calca-

reous nannofossil assemblages, and well documented by many

authors, from several areas of the Paratethyan domain.

The aims of this study are: 1) to bring new contributions to

the regional Oligocene biostratigraphy; 2) to investigate and

record the calcareous nannofossil assemblages and bioevents,

their diversity and abundance patterns; 3) to investigate

the palaeoecology of the calcareous nannofossils, to recon-

struct the palaeoenvironment based on the most abundant taxa

and to compare the studied deposits to other localities on

the regional and global scales.

Geological setting

The Transylvanian Basin is a major sedimentary basin sur-

rounded by the Eastern and Southern Carpathians to the south

and east, the Apuseni Mountains to the west and the Preluca–

Țicău metamorphic massifs to the north. From a stratigraphic

point of view, the Transylvanian Basin comprises sedimentary

sequences extending from the Late Cretaceous to the Late

Miocene (Krézsek & Bally 2006). The Oligocene sediments

from the north-western part of the Transylvanian Basin were

deposited into three distinct sedimentation areas (Rusu 1970),

all named after the neighbouring crystalline massifs, which

from the north-east to south-west are: the Preluca, the Meseş

and the Gilău areas. The lateral extension of the formations

from the Preluca area is lithologically uniform, in the Meseş

and Gilău areas the lateral variations are characteristic

(Rusu 1977).

The investigated sediments (Fântânele section) are part of

the terrigenous Vima Formation (Lăzărescu 1957, emend.

Rusu 1969), located south of the Preluca Massif, in the NW

Transylvanian Basin (Fig. 1) and represent a continuous marine

sedimentary succession spanning the Oligocene to Early

Miocene (Popescu 1975; Mészáros 1991; Krézsek & Bally

2006; Filipescu 2011). Hofmann (1887) described the sedi-

ments from the north-western part of the Transylvanian Basin

as “a deep water clay facies of Aquitanian age” with molluscs.

Majzon (1950) mentioned foraminifera assemblages from

deposits “similar to Kiscell clays”. Lăzărescu (1957) sug-

gested a Late Oligocene age for these sediments and similari-

ties to the boreal fauna. Mészáros & Marosi (1957) described

molluscs from the “grey claystones and marlstones horizon”.

Rusu (1969) included under the description of “Vima strata”

all the sedimentary succession between the Ileanda Formation

(of Rupelian age) and Hida Formation (of Early Miocene age).

Rusu (1977) assigned the Vima Formation to the Egerian (late

Rupelian–Chattian) in the Vima Syncline and to the Egerian–

Eggenburgian (late Rupelian to Aquitanian) in the Glod

Anticline. Additional data were published on foraminifera

(Popescu 1971, 1972, 1975; Popescu & Iva 1971; Popescu &

Brotea 1989), molluscs (Rusu 1977), ostracods (Olteanu 1980,

2002), and palinomorphs (Ionescu & Popescu 1995). Recent

studies on the Vima Formation (Fântânele section) were

focussed on planktonic and benthic foraminiferal biostrati-

graphy and palaeoecology (Székely & Filipescu 2015, 2016).

Mészáros (1991) traced the Oligocene / Miocene boundary

within the Fântânele section, and considered the age of the Vima

Formation as Oligocene to Early Miocene. Previous studies on

Oligocene calcareous nannofossils from the NW Transylvanian

Basin were done by: Popescu & Gheţa (1972), Mészáros et al.

(1973, 1979), Martini & Moisescu (1974), Mészáros & Ghergari

(1979), Mészáros (1984, 1991), Mészáros & Ianoliu (1989).

Melinte-Dobrinescu & Brustur (2008) traced the Oligocene/

Miocene boundary in the Vima Formation based on the first

occurrence (FO) of Sphenolithus capricornutus.

Material and methods

Studied sections

The sampled outcrops consist of claystones, marlstones,

siltstones, and thin sandstone intercalations. In all, 75 samples

were collected from three outcrops (47.41477º N, 23.82699º E;

47.41356º N, 23.82637º E and 47.41195º N, 23.82692º E)

of the Fântânele section (Fig. 1; Székely & Filipescu 2016),

in order to analyse the calcareous nannofossil assemblages.

The studied outcrops are labelled A, B and C, where the

Transect A represents the oldest one and Transect C the youn-

gest. Transect A represents a thick sequence (16 m thickness)

of finely laminated silty claystones and marlstones, siltstones

with thin intercalations of clayey fine grained sandstones.

In the uppermost part compact coarse grained sandstone is

present. The sampling resolution for Transect A is at intervals

of 0.50 m. Transect B has an approximate thickness of 3 m and

is mainly composed by fine laminated marly siltstones. Four

samples were collected at a resolution of 0.50 m. Transect C

has an approximate thickness of 7.5 m, and is lithologically

composed of silty claystones and marlstones, intercalated with

clayey siltstones and sandstones. High resolution sampling at

intervals of 10–30 cm was applied.

Investigation methods

Smear slides, for all samples, were prepared using the stan-

dard smear slide technique (Bown & Young 1998) and were

examined under the light microscope at 1000× magnification,

in polarized light. Quantitative data were obtained from 34

samples by counting at least 300 specimens per sample (Bown

& Young 1998), while for less abundant samples (20 samples)

at least 100 specimens were counted. Due to the low calca-

reous nannofossil abundance, only qualitative investigations

were done on 8 samples (FA1, FA4, FA9, FA29, FA36,

FB10, FB25 and FB55) which have a very low amount of

calcareous nannofossils, while 12 samples are barren in cal-

careous nannofossils (FB1, FB4, FB28, FB31, FB34, FB37,

FB40, FB58, FB61, FB64, FB66 and FB70). The overall

abundance of calcareous nannofossils per field of view (FOV)

in each sample was assessed as follows: A — abundant

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(>21 specimens per FOV), C — common (11–20 specimens

per FOV), F — few (1–10 specimens per FOV), R — rare

(1–10 nannofossils per 10 FOV), VR — very rare (1 specimen

in >10 FOV), B — barren (no nannofossils were found) and

“Bloom” when >90 % of the assemblage is represented by

a single species/group.

Preservation was considered as follows: G — good (all

the specimens can be identified at species level and less than

10 % of the assemblage shows fragmentation, etching and/or

overgrown), M — moderate (25 % of the specimens show

fragmentation, etching and overgrowth, but the species are

easily to identify) and P — poor (>25 % of the specimens are

broken, sometimes it was not possible to identify some

fragments; the exceptions were the single segments of

Braarudosphaera bigelowii and fragments of Pontosphaera

spp.). The standard zonations (Fig. 2) implemented in this

study follow the concepts of Martini (1971), Okada & Bukry

(1980) and additionally, tentative correlation is made to

the low to middle latitudes zonation of Agnini et al. (2014).

The PAST software (Hammer et al. 2001) was used for statis-

tical treatment of the counts. Multivariate Hierarchical Clus-

tering by Ward’s Method and Non-metric Multidimensional

Scaling (Hammer & Harper 2006) have been applied to all

the counted samples. Before statistical treatment, percentages

of the counts were calculated and the Arcsine SQRT (Square

Root) formula was applied on the obtained data. The general

taxonomy follows the concepts of Perch-Nielsen (1985a, b)

and the Nannotax3 website (Young et al. 2017).

Results

Assemblage composition and species diversity

Forty-nine calcareous nannofossil species (Table 1, electr.

sup plement) were identified in the studied outcrops, 38 of them

Fig. 2. Biochronological Time Scale for the Oligocene and the Central Paratethys regional stages (Gradstein et al. 2012). The standard calca-

reous nannofossils follow: NP — Martini (1971); CP — Okada & Bukry (1980); CNO — Agnini et al. (2014).

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were in situ while 11 species were reworked from Mesozoic

and lower stages of the Palaeogene. The long ranging species

such as Braarudosphaera bigelowii, Coccolithus pelagicus,

Sphenolithus moriformis and Zygrhablithus bijugatus are con-

sidered the autochthonous component. The examined material

contains well to poorly preserved calcareous nannofossil assem-

blages, dominated in order of abundance by: Cyclicargolithus

floridanus, Reticulofenestra minuta, Braarudosphaera bigelowii,

Pontosphaera multipora, Coccolithus pelagicus, Reticulo

fenestra gr. 3–5 µm, Reticulofenestra bisecta, Cyclicargolithus

abisectus, Reticulofenestra lockeri, Pontosphaera pygmaea,

Reticulofenestra daviesii, Reticulofenestra stavensis, Helico

sphaera recta, Sphenolithus moriformis and Pontosphaera

desueta. Species with rarer and irregular distribution are:

Coronocyclus sp., Helicosphaera euphratis, H. intermedia,

Pontosphaera cf. enormis, Pyrocyclus orangensis, Reticulo

fenestra callida, R. dictyoda, R. scrippsae, Sphenolithus

akropodus, S. ciperoensis, S. distentus, Sphenolithus predis

tentus, Sphenolithus sp. and Zygrhablithus bijugatus. Other

important biostratigraphical species such as Chiasmolithus

altus, Sphenolithus dissimilis and Triquetrorhabdulus longus

are extremely rare and appear in few samples. Reworked

taxa represent 0.2 % of the whole assemblage and include

species (Table 1, electr. sup plement) with their FO (first

occurrence) and LO (last occurrence) in the Mesozoic and

lower stages of the Palaeogene.

The taxa diversity is expressed as the number of autochtho-

nous species per sample and here it is considered as moderate

to low. The maximum diversity of 26 autochthonous species

was recorded in sample FA20, in the first outcrop, decreasing

in the second one up to a maximum of 17 autochthonous

species in sample FA34, while in the last one the maximum

diversity of 22 species is recorded in samples FB19 and FB43.

A drastic decrease in the number of species (5 species) is

recorded in the upper part of the last transect in the samples

containing blooms of Braarudosphaera bigelowii and Reticulo 

fenestra minuta. Microphotographs of the most representative

nannofossil taxa are included in Figs. 3 & 4.

Calcareous nannofossils biostratigraphy

Biostratigraphically, the calcareous nannofossil assem-

blages suggest a late Rupelian to Chattian age (Fig. 2) for

the whole sedimentary succession. This attribution is sup-

ported by the absence of index species Reticulofenestra umbi

licus, ranging from the base of NP16 (Middle Eocene) to

the lower NP23 (Gradstein et al. 2012). The lowermost part of

the Fântânele section (Transect A and partially Transect B)

belongs to the NP24 — Sphenolithus distentus biozone (Martini

1971) and CP19a — Cyclicargolithus floridanus Subzone

(Okada & Bukry 1980) of late Rupelian–early Chattian age.

The boundary between NP24 (Sphenolithus distentus Zone)

— NP25 (Sphenolithus ciperoensis Zone of Chattian age)

biozones is tentatively traced between samples FA34–FA35

from the second transect, where the LO of Sphenolithus

distentus, was recorded. Above this level the presence of this

marker is not observed anymore. The upper part of the second

transect and the whole of Transect C belong to the NP25 —

Sphenolithus ciperoensis biozone of Martini (1971) and to

CP19b — Reticulofenestra bisecta Subzone of Okada &

Bukry (1980). Correlation with the new zonation for low to

middle latitudes, proposed by Agnini et al. (2014) suggest that

the investigated transects would fall within the interval from

CNO4 — Sphenolithus distentus / Sphenolithus predistentus

CRZ to CNO5 — Sphenolithus ciperoensis TZ.

The Upper Oligocene–Lower Miocene markers Sphenolithus

delphix and Sphenolithus capricornutus, used to define

the Oligocene/Miocene boundary in the Mediterranean area

and other Lower Miocene taxa such as Helicosphaera carteri,

H. mediterranea and Discoaster druggii were not recorded in

the investigated samples.

Abundance patterns of the selected coccolith taxa for

palaeoecology

The palaeoecological preferences (Table 2, electr. sup-

plement) of the most abundant species and taxonomical groups

were investigated and the following were considered for

palaeo environmental reconstruction: Cyclicargolithus spp.

(Cy. flori danus with an average of 26.06 %. and Cy. abisectus

with a total of 3.42 %), small reticulofenestrids (Reticulofenestra

minuta comprise coccoliths < 3 µm; 14.78 % from total;

Reticulofenestra gr. 3–5 µm including small specimens with

a pore or a small central opening — total of 4.26 %), Ponto

sphaera spp. (14.55 %), Braarudosphaera bigelowii (12.70 %),

Reticulofenestra spp. (coccoliths > 5 µm; 11.57 % from total),

Coccolithus pelagicus (7.44 %), Sphenolithus spp. (2.54 %)

and Helicosphaera spp. (1.54 %). The abundance patterns of

the above mentioned species and groups are plotted along

the sampling interval (m) in Figs. 5, 6 and 7.

Multivariate statistics

The Multivariate Hierarchical Clustering (Fig. 8) indicates

four main clusters and eight sub-clusters which are well diffe-

rentiated and are described below. Samples belonging to

the first and second outcrops are noted with FA and samples

belonging to the third outcrop with FB.

Cluster 1 (assemblages with Pontosphaera spp.) comprises

9 samples and groups the highest proportions of Pontosphaera

spp. with values between 13.21 and 99.34 %. Two sub-clusters

1a and 1b are differentiated by the fluctuations in the amount

of Pontosphaera spp. Sub-cluster 1a (samples FA3, FA10,

FA23, FA24, FB12 and FB41) includes assemblages with

Pontosphaera spp. in association with increased amounts of

C. pelagicus (from 12.38 to 61.32 %) and in two samples with

Helicosphaera spp. (up to 25.23 %). The average participation

of the rest of the taxa is less than 6 % per group. Sub-cluster 1b

(samples FB9, FB11 and FB13) is characterized by the highest

amount of Pontosphaera spp. (from 81.41 to 99.34 %).

Cluster II (Cyclicargolithus spp. assemblages) concentrates

the highest number of samples (in total 28) belonging to

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Transect A (FA5–FA8, FA11, FA15–FA19, FA26, FA30–FA32),

all positive samples from the second (FA33 to FA35) and

some from the third outcrop (FB7–FB8, FB16, FB19,

FB22–FB24, FB42, FB46, FB49, FB52). It contains

the highest amount of Cyclicargolithus spp. (Cy. floridanus),

which has an average participation in the assemblage of

47.64 % (from 0.31 up to 73.29 %), followed in moderate

amounts by Reticulofenestra spp. (17.68 %) and by small

reticulofenestrids (16.29 %). Low participation in the assem-

blage was registered for C. pelagicus (7.58 %) and for Ponto

sphaera spp. (6.1 %). Very low average quantities occur of

Sphenolithus spp. (2.9 %), Helicosphaera spp. (1.74 %) and

B. bigelowii (0.69 %). The three sub-clusters identified (2a, 2b

and 2c) are defined by the fluctuations in abundance and

intra-cluster shifts of the main autochthonous taxa. Sub-cluster

2a exhibits the lowest amounts of Cy. floridanus (32.44 %)

and the highest amount of small reticulofenestrids (24.70 %),

followed by Reticulofenestra spp. (17.35 %), C. pelagicus

(11.99 %), less Pontosphaera spp. (6.47 %) and Sphenolithus

spp. (6.43 %). Increasing of the amount of Cy. floridanus

(average 48.25 %) and shift in small reticulofenestrids

(decrease to 17.84 %) and Reticulofenestra spp. (increase to

22.84 %) is noticed in sub-cluster 2b, coupled with a very low

amount of the rest of the taxa with group average participation

less than 4 %. Sub-cluster 2c exhibits the highest quantity of

Cy. floridanus (58.96 %), slightly increase of C. pelagicus

(11.63 %) and Pontosphaera spp. (10.35 %) and noticeable

decrease of Reticulofenestra spp. (8.91 %) and small reticulo-

fenestrids (7.61 %).

Cluster III (small reticulofenestrids assemblages) has 13

samples belonging to Transect A and to Transect C and dis-

plays the highest amounts of small reticulofenestrids which

account for an average of 47.69 %, followed by Cyclicargolithus

spp. (Cy. floridanus) with a mean of 21.23 %, Reticulo fenestra

spp. (10.72 %), B. bigelowii (9.31 %), C. pelagicus (6.24 %),

Pontosphaera spp. (5.46 %), Sphenolithus spp. (2.06 %) and

Helicosphaera spp. (1.92 %). Three sub-clusters (3a, 3b and

3c) were distinguished based on the participation of small

reticulofenestrids to the assemblages, with gradual increase

from sub-cluster 3a to 3c. Sub-cluster 3a (FA4, FA12–FA14,

FA22) is dominated by an association of small reticulo-

fenestrids (36.84 %) and Cy. floridanus (33.18 %), with

an additional contribution of B. bigelowii (12.60 %) and less

Reticulofenestra spp. (7.87 %), Pontosphaera spp. (7.23 %)

and C. pelagicus (6.90 %). Sub-cluster 3b (FA20-FA21, FA25,

FA27–FA28 and FB43) exhibits abundant small reticulo-

fenestrids (53.26 %), with smaller numbers of Cy. floridanus

(17.97 %), Reticulofenestra spp. (13.66 %) and C. pelagicus

(7.55 %). The rest of the taxa do not reach more than 4.5 % per

group. Sub-cluster 3c (FB67–FB68) displays the highest

amount of small reticulofenestrids (58.11 %) and additionally

B. bigelowii (26.13 %).

Cluster IV includes only 4 samples (FB69, FB71–FB73)

from the uppermost part of Transect C. It is clearly distin-

guished from the others due to the blooms of a single species

Braarudosphaera bigelowii (from 91.88 to 96.33 %).

Discussions

Biostratigraphy and calcareous nannofossil bioevents

The sediments from the Vima Formation were previously

investigated by Mészáros & Ghergari (1979) and Mészáros

(1984), who identified the following zones: the NP24 biozone

based on the co-occurrence of Cyclicargolithus floridanus,

Reticulofenestra dictyoda, Sphenolithus moriformis, Ponto

sphaera fibula, and Reticulofenestra ornata; the NP25 biozone

with dominant species: Cyclicargolithus floridanus, Cocco

lithus formosus, Coccolithus pelagicus, Sphenolithus cipe

roensis, Cyclicargolithus abisectus, Sphenolithus moriformis,

Pontosphaera desueta, P. multipora, P. obliquipons, P. fibula,

Syracosphaera clathrata and R. ornata; the NN1 biozone

based on the presence of marker species Triquetrorhabdulus

carinatus, and the NN2 biozone based on the sporadic appea-

rance of index species Discoaster druggii, Helicosphaera

ampliaperta, H. cf. carteri, H. euphratis, R. lockeri and

R. pseudoumbilica.

The assignments of the Fântânele section deposits to

the NP24–NP25 biozones (Martini 1971), to CP19 (Okada &

Bukry 1980) and additionally to CNO4–CNO5 (Agnini et al.

2014) are based on the presence of several primary and

secondary bioevents considered for the Oligocene biostrati-

graphical subdivision schemes. Whether or not they can be

applied in the present study is discussed below. Several authors

(Mészáros 1984; Rusu et al. 1996; Melinte 2005; Melinte-

Dobrinescu & Brustur 2008) investigated various locations

where the Vima Fm. crops out, in more complete successions

compared to the Fântânele section. A recent study on plank-

tonic and benthic foraminifera from the Vima Formation

(Székely & Filipescu 2016) indicates an Early Oligocene

(Rupelian) age for the base of the first sampled transect, more

precisely the Biozone O4 (based on the co-occurrence of

Chiloguembelina cubensis together with Paragloborotalia

opima), while for the third investigated transect a Late

Oligocene (Chattian) age is suggested, or the foraminiferal

biozone O5 (based on co-occurrence of Paragloborotalia

opima and Globigerina ciperoensis).

In the Fântânele section, the marker species Sphenolithus

ciperoensis appears in the Transect A at 7 m (FA15).

The absence of this species from the lower part of the studied

section raises the question whether the NP23 zone of Martini

(1971) and CP18 of Okada & Bukry (1980) are present or not.

The presence of the NP23 and CP18–lower CP19a biozones

would be in disagreement with the planktonic foraminifera

data (Székely & Filipescu 2016) which point to the O4 zone of

Wade et al. (2011) of late Rupelian age. In conclusion, it is

difficult to consider this event as a first occurrence and its

absence from the lowermost part of Transect A might be due to

unfavourable environmental conditions or to its scarcity and in

general to the reduced number of sphenoliths.

The species Cyclicargolithus abisectus displays low abun-

dance patterns, both sizes being present (<10 μm and >10 μm).

The medium-sized specimens (<10 μm) appear from samples

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Fig.

Transect

—

lithology

, sample

positions

and

abundance

patterns

the

most

important

species

and

taxonomic

groups

plotted

along

the

sampling

interval

(m):

—

Standard

Zonations

Martin

i (1971),

Okada

Bukry

(1980)

and

Agnini

al.

(2014);

—

Lithology;

—

Samples

position;

—

Braarudosphaera

bigelowii

; e

—

Coccolithus pelagicus

; f

—

Cyclicar

golithus

floridanus

+ Cyclicar

golithus

abisectus

;

—

Helicosphaera

spp.;

—

Pontosphaera

spp.;

—

Reticulofenestra

3–5 +

Reticulofenestra

minuta

;

—

Reticulofenestra

spp.

>5;

k —

Sphenolithus

spp.

273

OLIGOCENE TRANSITION IN TRANSYLVANIAN BASIN REVEALED BY CALCAREOUS NANNOFOSSILS

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, 2018, 69, 3, 264–282

FA3 upwards and are more continuously

distributed along the section than the

large- sized ones which are present star-

ting from the middle of Transect A

(FA17), in a few samples above this level.

In this study the FO is not recognized due

to the fact that the above mentioned spe-

cies has a continuous distribution along

the investigated section. Rich assem-

blages, dominated by Cy. abisectus and

R. bisecta, are mentioned for the late

Rupelian (Van Simaeys et al. 2004), from

several boreholes in the Belgium Basin

(Belgium and Germany). From the Central

Paratethys realm, the NP24 zone and

assemblages containing this taxon were

men tioned from: the Magura Basin

(Poland) by Oszczypko-Clowes (2001,

2010), Oszczypko-Clowes & Ślączka

(2006), Oszczypko-Clowes & Żydek

(2012), the Subtatric Group (Slovakia) by

Ozdínová (2013), the Podhale flysch

(Poland) by Garecka (2005), from the

Skole Unit (Poland) by Garecka (2012),

from the Magura Basin (Poland) by

Kopciowski & Garecka (1996), Garecka

et al. (1998), Garecka & Szydlo (2011,

2015), from the South Slovakian Basin

by Ozdínová & Soták (2014), from the

NW Transylvanian Basin and from the

central and southern Eastern Carpathians

(Gheţa et al. 1976; Mészáros & Ghergari

1979; Mészáros 1991; Rusu et al. 1996;

Melinte 2005; Melinte-Dobrinescu &

Brustur 2008).

The species Sphenolithus distentus is

very scarce in the first two transects, and

is absent from the third one. Its LO is ten-

tatively placed at the level of sample

FA34 in Transect B.

The LO of Sphenolithus predistentus

is not used in the standard zonations of

Martini (1971) and Okada & Bukry

(1980), but its biostratigraphical impor-

tance was pointed out by several authors

(Fornaciari et. al. 1990; Olafsson & Villa

1992; Agnini et. al. 2014). Gradstein et al

(2012) indicate that its LO is located at

26.93 Ma, below the LO of Sphenolithus

distentus. This bioevent is recorded in

the Fântânele section at 13.5m (between

FA28–FA29) from Transect A. Its absence

from Transects B and C makes it suitable

to be considered as a possible LO event.

The species Helicosphaera recta is

more or less continuously present in

Fig.

ransect

—

lithology

, sample

positions

and

abundance

patterns

the

most

important

species

and

taxonomic

groups

plotted

along

the

sampling

interval

(m):

—

Standard

Zonations

Martini

(1971),

Okada

Bukry

(1980)

and

Agnini

al.

(2014);

—

Litho

logy;

—

Sample

positions;

—

Coccolithus

pelagicus

; e

—

Cyclicar

golithus

floridanus

+ Cyclicar

golithus

abisectus

;

f —

Helicosphaera

spp.;

g —

Pontosphaera

spp.;

h —

Reticulofenestra

. 3–5 +

Reticulofenestra minuta

; i

—

Reticulofenestra

spp. >5;

j —

Sphenolithus

spp.

274

KALLANXHI , BĂLC , ĆORIĆ, SZÉKELY and FILIPESCU

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, 2018, 69, 3, 264–282

Transects A and B (from sample FA5 of the first

outcrop, upwards), and sporadically in Transect

C and due to this continuity its FO was not traced

in this interval. In other areas of the Central

Paratethys domain, this species has been mentio-

ned from the NP24–NP25 zones by Mărunţeanu

(1992; from the Romanian Carpathians),

Oszczypko-Clowes (2001, 2010), Garecka

(2005), Garecka & Szydlo (2011, 2015), and

Ozdínová & Soták (2014).

Pontosphaera cf. enormis (first observed in

sample FA7 from Transect A) occurs rarely and

discontinuously. It appears to have a lower

occurrence (within NP24) compared to other

studies which mention it near the NP24/NP25

boundary (von Benedek & Müller 1974; Martini

& Müller 1975; Martini 1981) and from the

NP25 Zone (Van Simaeys et al. 2004; Garecka

2005; Melinte 2005; Melinte-Dobrinescu &

Brustur 2008; Ozdínová & Soták 2014).

The species Chiasmolithus altus is very rare

and sporadic and is present only in Transect A

(samples FA20 and FA30). Previous reports

from similar sections in Romania, mentioned its

FO in the late Rupelian (Melinte-Dobrinescu &

Brustur 2008).

The species Triquetrorhabdulus longus has

a biostratigraphical range from NP24 to NN3

Zones, and a well marked acme in the Late

Oligocene (Blaj & Young 2010). It is present in

the studied material in only one sample from

the third outcrop (FB43).

Rupelian / Chattian boundary

The historically acknowledged Rupelian–

Chattian boundary as defined from its typical

stratotypes in the North Sea Basin, is associated

with several benthic foraminiferal and dinocists

events (Köthe 1990; Berggren et al. 1995;

De Man et al. 2004; Van Simaeys et al. 2004,

2005a, b; Pross et al. 2010; Wade et al. 2011).

New data on the reliability of marker species

foraminifer Chiloguembelina cubensis as bio-

event for defining the R/C boundary were

brought by King & Wade (2017). The base of the

Chattian at the Monte Cagnero section (Umbria-

Marche Basin, Apennines, Italy) was calibrated

at 27.82 Ma at the HCO (Highest Common

Occur rence) of Chiloguembelina cubensis

(Coccioni et al. 2017). In terms of calcareous

nannofossils the Rupelian–Chattian boundary

falls within the upper part of the NP24 biozone

(Berggren et al. 1995; Coccioni et al. 2008,

2017). The R/C boundary in the North Sea Basin

(Van Simaeys et al. 2004) is marked by cooler

Fig.

ransect

–

lithology

, sample

positions

and

abundance

patterns

the

most

important

species

and

taxonomic

groups

plotted

along

the

sampling

interval

(m):

—

Standard

Zonations

Martini

(1971),

Okada

Bukry

(1980)

and

Agnini

al.

(2014);

—

Lithology;

c —

Sample

positions;

d —

Braarudosphaera bigelowii

; e

—

Coccolith

us pelagicus

; f

—

Cyclicar

golithus

floridanus

+ Cyclicar

golithus abisectus

; g

—

Helicosphaera

spp.;

h —

Pontosphaera

spp.;

i —

Reticulofenestra

. 3–5 +

Reticulofenestra minuta

; j

—

Reticulofenestra

spp. >5;

k —

Sphenolithus

spp.

275

OLIGOCENE TRANSITION IN TRANSYLVANIAN BASIN REVEALED BY CALCAREOUS NANNOFOSSILS

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, 2018, 69, 3, 264–282

climate and more open marine conditions for the late Rupelian,

while the lower Chattian is associated with shallower, warmer

climate and warmer sea-surface water temperatures and

hyposaline shallow marine environments, as documented also

by the calcareous nannofossil assemblages (at the base of

Chattian) with presence in higher quantities of Ponstosphaera

spp., Zygrhablithus bijugatus and B. bigelowii. Generally,

the calcareous nannofossil assemblages from the Fântânele

section, assigned to the NP24 / CP19a zones are comparable in

species composition to many other Paratethyan localities,

where the NP24 Biozone was identified, being considered as

late Rupelian to Chattian. The acknowledgement of NP24 /

CP19a is associated with the presence of several primary and

secondary index species with overlapping ranges which cross

the R/C boundary, such as Sphenolithus ciperoensis, S. distentus,

S. predistentus, H. recta and Cy. abisectus. The identification

of the NP25 / CP19b biozones (of Chattian age) is given by

the absence of S. distentus and S. predistentus in the last part

of the second transect and in the third one. The R/C boundary

is difficult to trace in the investigated sediments, and this is

mainly due to the gaps between the outcrops, areas covered by

vegetation, where sampling was not possible. Detailed age

assignment and separation of the nannofossil assemblages, to

only late Rupelian or to the Chattian part of the NP24 biozone,

was also difficult to perform due to the similarities in their

composition. The first investigated transect and to the half

of the second one, is given a general late Rupelian–early

Chattian age (NP24 Zone), while for the second half of

Transect B and Transect C, the Chattian age was assumed

(NP25 Zone).

Calcareous nannofossils palaeoecology, palaeoenvironment

and statistical interpretation

Palaeoenvironmental changes during the deposition of the

Fântânele sedimentary succession are recorded here through

the variations in calcareous nannofossil abundance and assem-

blage composition, all together connected to the distinct

climatic conditions and to the changed palaeogeographical

configuration during the Oligocene (Rögl 1998, 1999; Popov

et al. 2004). The calcareous nannofossil assemblages from

the Fântânele section indicate similar palaeoenvironmental

conditions as recorded by many other authors in other

Paratethyan areas, with a temperate to cooler late Rupelian

interval and slightly warmer conditions in the Chattian (Báldi-

Beke 1984; Rögl 1998; Soták 2010). Similar variations in

temperatures and salinities were mentioned by Van Simaeys et

al. (2004) as prevailing during the early Chattian in the North

Sea Basin, assumed to be connected to the beginning of the

Late Oligocene Warming Event (Zachos et al. 2001).

Based on our statistical model (Fig. 9) and calcareous

nanno fossil trophic preferences (Table 2, electr. sup plement),

the palaeoenvironmental regime under which the Fântânele

section sediments were deposited, can be considered as more

open-marine for the latest Rupelian to earliest Chattian

interval, with normal salinity, with little or no fluctuations in

the nutrient supply content, and temperate to cool sea-surface

temperatures, while for the youngest part of the section (NP25,

early Chattian) this study confirmed the near-shore shallow to

brackish palaeoenvironment identified by Székely & Filipescu

(2016), characterized by temperate to slightly warmer SSTs,

stronger salinity fluctuations, increased terrigenous material

runoff and freshwater influx and fluctuations of the distance to

the shore.

As a general trend, the first sampled transect assigned to

the NP24 / CP19a Zone (late Rupelian–early Chattian) is domi-

nated by two types of assemblages, while those belonging to

Clusters 2 and 3 (Figs. 5, 8, 9) are characterized by high

amounts of Cyclicargolithus spp. (always prevailing Cy. flori

danus) and small reticulofenestrids (especially R. minuta),

coupled locally with moderate amounts of temperate — cool

and cold-water taxa such as Reticulofenestra spp. (R. bisecta

and R. daviesii groups), C. pelagicus and B. bigelowii

(Table 2, electr. sup plement). The temperate–warm and sub-

tro pical water taxa, such as Pontosphaera spp., Helicosphaera

spp. and Spheno lithus spp. (Table 2, electr. sup plement)

display moderate to very low amounts.

Fig. 8. Multivariate Clustering Analysis by Ward’s Method.

276

KALLANXHI , BĂLC , ĆORIĆ, SZÉKELY and FILIPESCU

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The intervals with prevailing Cy. floridanus (FA4–FA8,

FA11–FA19, FA22) are associated with stable, meso- to eutro-

phic open-marine conditions, nutrient-rich waters (Aubry

1992; Monechi et al. 2000), without too much water turbu-

lence and no fluctuations in temperature, salinity and nutrient

content (Auer et al. 2014), while those with increased small

reticulofenestrids, known to flourish along continental mar-

gins (Haq 1980), reflect eutrophic conditions (Wade & Bown

2006) and high primary productivity under increased stress

factors such as higher contents of terrigenous material derived

from the continent (Auer et al. 2014). As indicated in Figs. 5

and 9, intervals with equal participation of Cy. floridanus and

R. minuta contents (Sub-cluster 3a), are displayed in some

samples, where apparently a slight decrease in Cy. floridanus

amount is balanced by an increase in R. minuta, possibly due

to a moderate run off of continental material.

Contrasting the general stable open-marine conditions

reflected by the diverse nannofossil assemblages of this tran-

sect, supported also by recent data on foraminifera (Székely &

Filipescu 2016), several short intervals (Fig. 5) reflect a dras-

tic decrease in the calcareous nannofossil content (samples

FA1–FA2, FA9 and FA29), while those occupied by the

assemblages of sub-cluster 1a, suggest a slight deviation from

the normal marine stable palaeoenvironmental conditions,

associated with the increased amounts of C. pelagicus,

Pontosphaera spp. and Helicosphaera spp. The presence of

the above mentioned taxa as the main components within

the sub-cluster 1a assemblage, are not easily connected to each

other’s palaeoecological preferences. The highest amount of

C. pelagicus, a species known to occupy eutrophic surface

waters and upwelling areas (Haq 1980; Rahman & Roth 1990;

Kameo & Sato 2000), was recorded in sample FA3 and is

associated with the increase of Pontosphaera spp. These two

species characterize this level before the establishment of

the stable marine conditions with dominating Cy. floridanus.

The next intervals occupied by the sub-cluster 1a assemblage,

are at the level of sample FA10, and in samples FA23–FA24,

being marked by the replacement of Cy. floridanus — small

reticulofenestrids assemblages with C. pelagicus–Helico

sphaera spp.–Pontosphaera spp. associations. Higher amounts

with the open-marine species C. pelagicus suggest periods

with less surface water column stratification (Auer et al.

2014), connected to fluctuations in upwelling intensity, possi-

ble increasing of cool-nutrient availability and increased wave

driven surface water turbulence or seasonal marine oscilla-

tions. The high amounts of Pontosphaera spp. known to thrive

under shallow, warmer conditions (Perch-Nielsen 1985b; Firth

1989), considered to tolerate salinity fluctuations (Krhovský

et al. 1992; Nagymarosy 2000), in samples with higher

amounts of C. pelagicus (sub-cluster 1a), might indicate

an opportunistic behaviour of this group and increased tole-

rance of stress factors, such as variation in the type of nutrient

available (possible cooler nutrient), column-water mixing and

increased upwelling conditions. The highest amounts of

Helicosphaera spp. at this level, a taxonomical group with

preference for shallow hemipelagic, near-shore upwelling

conditions (Bukry et al. 1971; Krhovský et al. 1992), supports

our assignment of Pontosphaera spp. group, to adapt to

increased nutrient supply, increased upwelling and nutrient

mixing. A slightly increased water salinity as a stress factor

is not excluded for both Pontosphaera spp. and C. pelagicus

and goes somehow along with the position of the sub-cluster

1a samples on the left upper side of the nMDS plot (Fig. 9).

The terminal part of Transect A (FA30–FA32) containing

samples assigned to sub-cluster 2b (Figs. 5, 9), is marked

by domi nance of temperate–cool to cold water species

of Reticulofenestra spp. and Cy. floridanus, indicative

for more meso- to eutrophic sea-surface waters and full

marine conditions. Assemblages with Cy. floridanus,

Reticulofenestra bisecta and Zygrhablithus bijugatus were

described by Melinte (2005) as occurring together within

the Oligocene deposits from Romania and were considered to

be indicative for warmer conditions with increased nutrients

available.

The stable open-marine palaeoenvironment which charac-

terize Transect A, continue also in the second outcrop (Fig. 6).

The nannofossil assemblages of sub-cluster 2c are characte-

rized by high amounts of the open-ocean species Cy. flori

danus, accompanied by the moderate amounts of C. pelagicus,

Reticulofenestra spp. and less small reticulofenestrids, indi-

cating more stable marine meso-eutrophic conditions,

decreased influx of terrigenous material and implicitly higher

distance from the shore.

The depositional regime and palaeoenvironment of Transect C

(Fig. 7) indicates in general meso- to eutrophic conditions,

with strong fluctuations in calcareous nannofossil abundance

and diversity. High-resolution sampling at intervals from 10 to

30 cm was applied, providing more detailed information.

As represented on the nMDS plot (Fig. 9), the samples of this

transect are scattered, indicating highest variability in calca-

reous nannofossil composition and abundance, coupled with

the most variable palaeoenvironmental conditions. The calca-

reous nannofossil assemblages are dominated by sub-cluster

1b & 2b & 2c, and cluster 4 (less Cluster 3), indicating abrupt

short-term variations in basin conditions, reflected also in

the blooms of low diverse monospecific assemblages, domi-

nated by one species or genus, coupled additionally with

the presence of more barren intervals (Fig. 7) and supported

also by the foraminifera data (Székely & Filipescu 2016).

The intervals barren of nannofossils and all those where no

counting was possible (FB1–FB4, FB25–FB40, FB55–FB66

and FB70), and only qualitative data were collected, corre-

spond to those of infrequent foraminifera intervals (Székely &

Filipescu 2016).

Similar assemblages to those of Transects A and B, domi-

nated by the open-ocean species Cy. floridanus (sub-clusters

2b & 2c) are met at several levels (FB7–FB8, FB16–FB24,

FB42, FB46–FB52). The highest peaks of this species (FB8,

FB16, FB49) are associated with Reticulofenestra spp. >5 µm

(highest amount in FB22 and FB52), with Cy. abisectus

(highest amount in FB8, FB16 and FB46), with Reticulofenestra

gr. 3–5 µm (in FB7 and FB43), less R. minuta, Pontosphaera

277

OLIGOCENE TRANSITION IN TRANSYLVANIAN BASIN REVEALED BY CALCAREOUS NANNOFOSSILS

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spp. and Sphenolithus spp. (highest peaks in FB22 and FB46).

Restoration of short term eutrophic marine conditions, with

seasonal high primary productivity is also recorded by

the foraminiferal data (Székely & Filipescu 2016).

The short intervals belonging to sub-cluster 1b comprise

the most intriguing low diverse assemblages, due to the blooms

of Pontosphaera spp. (Fig. 7h). Among this genus, P. multi

pora is the dominant species of sub-cluster 1b, while P. pyg

maea of sub-cluster 1a. It is acknowledged that this genus

thrives in shallow, near shore warmer marine environments

(Perch-Nielsen 1985b; Firth 1989, present study), under stable

marine conditions (Melinte 2005; Bartol et al. 2008; Garecka

2012) and tolerates some salinity fluctuations (Krhovský et al.

1992; Nagymarosy & Voronina 1992, Nagymarosy 2000;

Garecka 2012). Several authors indicate adaptability to

increased salinity (Báldi-Beke 1984; Melinte 2005; Bartol et

al. 2008; Garecka 2012) while others identify adaptation to more

hyposaline conditions (Van Simaeys et al. 2004). The shallo-

wing trend indicated by calcareous nannofossil abundance

fluctuations were recognized also by means of low abundance

and low diverse foraminiferal assemblages (Székely & Filipescu

2016). This interval is comprised between two periods of fully

marine, meso-eutrophic palaeoenvironment, and indicative of

high nutrient availability, temperate to warmer SSTs and

normal to slightly increased salinity (Fig. 9). The presence of

Pontosphaera spp. in association with the Cy. floridanus–

abisectus group, indicates that this genus can also adapt to

more stable marine eutrophic conditions, with normal salinity.

The timing of these blooms, immediately before and after such

conditions might be due to regional or local seasonal varia-

tions. Two regime models might explain the slightly increased

sea surface water salinity and the increased amounts of this

genus. The first one might be associated with the prevailing of

a warmer drier climate, with reduced connectivity of the area

to the more marine palaeo-environment, with no/or very little

continental riverine input into the basin. Seasonal warming

and intense evaporation might have triggered the creation of

shallower intervals with increased sea-surface water salinity,

eutrophic near shore palaeoenvironment, as indicated by

the posi tioning of samples FB9, FB11, FB 12 and FB13 on

the nMDS plot (Fig. 9). The second possibility might be due to

the combination of reduced seasonal fluvial input, with up wel-

ling of denser more saline nutrient-rich waters to the surface.

The intriguing and opportunistic behaviour of this genus is

Fig. 9. Non–Metric Multidimensional Scaling (nMDS) showing the clusters distribution according to palaeo-environmental variables.

278

KALLANXHI , BĂLC , ĆORIĆ, SZÉKELY and FILIPESCU

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given by the many assemblage combinations where it has been

found in our material. In the Fântânele section, excepting

the cases when this genus is associated with Cy. floridanus–

abisectus and when found alone, it was recorded in association

with high amounts of C. pelagicus and less B. bigelowii,

co-occurring together in sample FB41, which might reflect

a certain tolerance to dense cooler nutrient influx (P. pygmaea

dominates this interval) caused by the increased upwelling,

nutrient mixing, not necessarily connected to cooler SSTs

waters. The salinity ranges from normal to slightly hypersa-

line. The co-occurrence together with R. minuta in sample

FB43, and the positioning on the nMDS plot (Fig. 9), does not

necessarily imply a near-shore environment with very shallow

water depth, but it seems to be more marine and within the

normal sea surface water salinity, with moderate continental

material influx and high tolerance of environmental stress.

The uppermost part of this outcrop belonging to cluster 4

(FB69, FB71–FB73) is associated with blooms of monospe-

cific assemblages of B. bigelowii. Approximately 10 cm of

non-calcareous interval is present at the level of sample FB70.

The position of samples FB67–FB68 on the nMDS plot

(Fig. 9) marks the beginning of the shallowest period recorded

in the Fântânele section, with extreme eutrophication due to

increased seasonal terrigenous nutrient and fresh water influx,

near shore high energy wave dominated palaeoenvironment,

cool nutrient available due to mixing and seasonal upwelling

and increased precipitation. All these variables taken together,

might have contributed to the lowered sea-surface waters as

indicated by the blooms of B. bigelowii. In additional,

the sample FB68, displays abundant R. minuta, a species asso-

ciated with high productivity eutrophic environment and

increased continental influx. B. bigelowii displays opportu-

nistic behaviour and flourishes under reduced concurrence and

together with R. minuta, are considered indicator taxa for

tolerance of high environmental stress (Wade & Bown 2006;

Bartol et al. 2008; Auer et al. 2014; present study). Samples

FB67–FB68 also display a very low abundance of forami-

nifera, while samples FB69–FB73 are barren in foraminifera

(Székely & Filipescu 2016). The absence of planktonic and

benthic foraminifera could be explained by the fresh-water

influence and lower salinity (Székely & Filipescu 2016), as

also suggested by the calcareous nannofossils. The calcareous

nannofossil fluctuations from the last outcrop can be con-

nected to increased proximity to the shore, shallowing, and

terrigenous material influx and not least to fluctuations in

salinity. In the Central Paratethys Realm, blooms of

Braarudosphaera bigelowii in the Oligocene were considered

to have been caused by the partial separation of the Paratethys

from the Mediterranean and were connected to the existence

of anoxic environmental conditions (Nagymarosy 1991).

Monospecific assemblages of B. bigelowii are mentioned from

the early Rupelian (Rusu et al. 1996; Melinte 2005), in both

the Eastern Carpathians and Transylvanian areas.

The absence of the warm open marine Discoaster genus

(Lohmann & Carlson 1981; Aubry 1992; Young 1998; Villa et

al. 2008) coupled with the low amounts of autochthonous

subtropical warm water taxa (Sphenolithus spp., Helicosphaera

spp. and Zygrhablithus bijugatus) indicate shallow marine

conditions, with temperate to cooler SSTs for the first and

second outcrops, and with a slightly warmer and shallow

marine environment for the youngest one.

Palaeogeographical considerations

The Transylvanian Palaeogene formations crop out and are

widespread around the northern parts of the Transylvanian

Basin, in the Pienide nappes (Krézsek & Bally 2006). Starting

with the late Rupelian the emplacement of the Pienide nappes

took place (Sãndulescu et al. 1981), resulting in the deposition

of coarse-grained siliciclastic sediments (Tischler et al. 2008).

Differences in depositional settings from area to area are

acknowledged for the late Rupelian–Chattian interval.

The southern part of the basin was exposed and the central part

was dominated by continental, inner to outer shelf palaeoenvi-

ronments (Petrescu et al. 1989; Rusu 1995; Filipescu 2001).

The situation in the northern part of the basin was totally

different, a deeper marine environment (Vima Formation) and

slope/outer to middle fan dominated (Valea Carelor, Birţu and

Borşa Formations) (Mészáros et al. 1971; Dicea et al. 1980).

The more marine character of these deposits and the north-

ward thickening of the Oligocene successions in the area are

due to a flexural down-bending caused by the emerging of

the Pienides nappes (Săndulescu & Micu 1989; Aroldi 2001;

Tischler et al. 2008). Several authors considered the late

Rupelian sediments to be transgressive (Rusu 1989; Popescu

& Brotea 1994; De Broucker et al. 1998; Ciulavu et al. 2000),

but the Chattian siliciclastic sediments to be progradational

(Krézsek & Bally 2006). During the Chattian, important sedi-

mentary changes occurred in relation to the climate cooling

(Abreu & Haddad 1998) and to the global eustatic sea-level

fall (Hardenbol et al. 1998).

The palaeoenvironmental reconstruction of the Fântânele

section highlights the development of the north-western

Transylvanian Basin in the Paratethyan settings during

the Oligocene (Székely & Filipescu 2016). Tischler et al.

(2008) pointed out that the late Rupelian–early Chattian pro-

gradational phases do not match to the global eustatic sea-

level changes of Haq et al. (1987). Székely & Filipescu (2016)

connected the foraminifera abundances within the Fântânele

section with high-frequency sequences associated with 4

order relative sea-level oscillations for Transects A and B,

while the strong progradational trend observed in Transect C

suggests an increased continental influence. These data are

also supported by the calcareous nannofossil changes along

the section, changes which might be due to episodic isolation

of the basin and to tectonic activity in the area. A sedimentary

hiatus was observed at the top of the Vima Formation

(Hofmann 1887; Majzon 1950; Popescu 1971; Popescu & Iva

1971), highlighting the possibility that these sediments could

have been eroded as a result of a sea-level fall (Székely &

Filipescu 2016) which gave a diachronic upper boundary for

the Vima Formation.

279

OLIGOCENE TRANSITION IN TRANSYLVANIAN BASIN REVEALED BY CALCAREOUS NANNOFOSSILS

GEOLOGICA CARPATHICA

, 2018, 69, 3, 264–282

Conclusions

Biostratigraphically, based on the presence and overlapping

ranges of several marker species, the investigated sediments

were dated as belonging to the late Rupelian–Chattian interval.

Correlation to the following biozones was possible: the NP24

— Sphenolithus distentus Zone, the NP25 — Spheno lithus

ciperoensis Zone, the CP19a — Cyclicargolithus floridanus

Subzone, the CP19b — Dictyococcites bisectus Subzone,

the CNO4 — Sphenolithus distentus / Sphenolithus predistentus

CRZ, and the CNO5 — Sphenolithus ciperoensis TZ.

Several bioevents for the Oligocene subdivision were

discussed and the following were considered as reliable for

the investigated interval: the LO of Sphenolithus predistentus,

the LO of Sphenolithus distentus, the FO of Pontosphaera cf.

enormis. Important marker species such as Helicosphaera

recta and Sphenolithus ciperoensis were recorded.

Variations in the abundance of autochthonous calcareous

nannofossils and the clusters distribution along the investi-

gated interval, allowed the palaeoenvironmental reconstruc-

tion of the Fântânele Section. Alternations from open marine

to shallower conditions are documented here.

Intervals with short-term abrupt changes in nannofossil

composition and abundance are associated with the blooms of

Pontosphaera spp. and B. bigelowii. New insights on

Pontosphaera genus palaeoecology indicates opportunistic

behaviour, quick response to fast changes in the environment,

increased tolerance of stress factors and great adaptability

to a wide range of palaeoenvironmental conditions, from

normal fully marine to shallower, to the type and availability

of nutrient content, normal to increased salinity, nutrient

mixing and increased upwelling intensity in the upper water

column.

Acknowledgements: This work was possible due to the finan-

cial support of the Sectoral Operational Program for Human

Resources Development 2007–2013, co-financed by

the European Social Fund, under the project number POS-

DRU/159/1.5/S/132400 with the title “Young successful

researchers — professional development in an international

and interdisciplinary environment”, and to the “Erasmus +

Traineeship” mobility in the period March–June 2016, at

the Montanuniversität Leoben, Austria. The work of Székely

Szabolcs–Flavius is a result of doctoral research made possi-

ble by the financial support of the Sectoral Operational

Programme for Human Resources Development 2007–2013,

co-financed by the European Social Fund, under the project

POSDRU/159/1.5/S/133391 — “Doctoral and postdoctoral

excellence programs for training highly qualified human

resources for research in the fields of Life Sciences, Environ-

ment and Earth”. Ramona Bălc thanks the CNCSIS–

UEFISCSU, project PN–III–P3–3.6–H2020–2016–0015 for

the financial support. We would like to express our gratitude to

Marta Oszczypko-Clowes and Mihaela Carmen Melinte-

Dobrinescu, for their suggestions which improved the quality

of our manuscript.

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OLIGOCENE TRANSITION IN TRANSYLVANIAN BASIN REVEALED BY CALCAREOUS NANNOFOSSILS

GEOLOGICA CARPATHICA

, 2018, 69, 3, 264–282

a) Autochtonous calcareous nannofossils

Number of specimens / specie

Blackites sp.

Braarudosphaera bigelowii (Gran & Braarud, 1935) Deflandre, 1947

1677

Calcidiscus pataecus (Gartner, 1967) de Kaenel & Villa, 1996

Chiasmolithus altus (Bukry & Percival, 1971)

Coccolithus pelagicus (Wallich, 1877) Schiller, 1930

983

Coronocyclus sp. (Hay, Mohler & Wade, 1966)

Cyclicargolithus abisectus (Muller, 1970) Wise, 1973

452

Cyclicargolithus floridanus (Roth & Hay, in Hay et al., 1967) Bukry, 1971

3441

Discoaster deflandrei (Bramlette & Riedel, 1954)

Helicosphaera euphratis (Haq, 1966)

Helicosphaera intermedia (Martini, 1965)

Helicosphaera recta (Haq, 1966) Jafar & Martini, 1975

163

Helicosphaera sp.

Pontosphaera desueta (Müller, 1970) Perch-Nielsen, 1984

134

Pontosphaera cf. enormis (Locker, 1967) Perch-Nielsen, 1984

Pontosphaera multipora (Kamptner, 1948 ex Deflandre in Deflandre & Fert, 1954) Roth, 1970

1300

Pontosphaera pygmaea (Locker, 1967) Bystricka & Lehotayova, 1974

433

Pyrocyclus orangensis (Bukry, 1971) Backman, 1980

Reticulofenestra bisecta (Hay, Mohler & Wade, 1966) Roth, 1970

467

Reticulofenestra callida (Perch-Nielsen, 1971) Bybell, 1975

Reticulofenestra daviesii (Haq, 1968) Haq, 1971

199

Reticulofenestra dictyoda (Deflandre in Deflandre & Fert, 1954) Stradner in Stradner & Edwards, 1968

Reticulofenestra lockeri (Müller, 1970)

476

Reticulofenestra minuta (Roth, 1970)

1952

Reticulofenestra scissura (Hay, Mohler & Wade, 1966)

Reticulofenestra scrippsae (Bukry & Percival, 1971)

Reticulofenestra stavensis (Levin & Joerger, 1967) Varol, 1989

202

Reticulofenestra gr. 3-5 μm (Hay, Mohler & Wade, 1966)

563

Sphenolithus akropodus (de Kaenel & Villa, 1996)

Sphenolithus ciperoensis (Bramlette & Wilcoxon, 1967)

Sphenolithus dissimilis (Bukry & Percival, 1971)

Sphenolithus distentus (Martini, 1965) Bramlette & Wilcoxon, 1967

Sphenolithus moriformis (Bronnimann & Stradner, 1960) Bramlette & Wilcoxon, 1967

136

Sphenolithus predistentus (Bramlette & Wilcoxon, 1967)

Sphenolithus sp. (Deflandre in Grassé, 1952)

Thoracosphaera sp. (Kamptner, 1927)

Triquetrorhabdulus longus (Blaj & Young, 2010)

Zygrhablithus bijugatus (Deflandre in Deflandre &Fert, 1954) Deflandre, 1959

Total

13180

b) Reworked calcareous nannofossils
Calculites obscurus (Deflandre, 1959) Prins & Sissingh in Sissingh, 1977

Cyclagelosphaera reinhardtii (Perch-Nielsen, 1968) Romein, 1977

Cyclicargolithus luminis (Sullivan, 1965) Bukry, 1971

Neochiastozygus sp. (Perch-Nielsen, 1971)

Pontosphaera distincta (Bramlette & Sullivan, 1961) Roth & Thierstein, 1972

Prediscosphaera cretacea (Arkhangelsky, 1912) Gartner, 1968

Prinsius sp. (Hay & Mohler, 1967)

Rhabdosphaera sp. (Haeckel, 1894)

Sphenolithus obtusus (Bukry, 1971)

Toweius rotundus (Perch-Nielsen in Perch-Nielsen et al., 1978)

Watznaueria barnesiae (Black in Black & Barnes, 1959) Perch-Nielsen, 1968

Total

Supplementum

Table 1: List of calcareous nannofossils species present in the Fântânele Section together with their counts.

KALLANXHI , BĂLC , ĆORIĆ, SZÉKELY and FILIPESCU

GEOLOGICA CARPATHICA

, 2018, 69, 3, 264–282

Species versus their known
palaeoecology

Palaeoenvironment
(eutrophic,
mesotrophic,
oligotrophic)

Type of nutrient t /
Trophic preferences

Temperature:
warm, temperate,
cold

Salinity:
brackish–hyposaline,
normal, hypersaline

Geological setting

Others

Braarudosphaera bigelowii Eutrophic

(1, 7, 9,

30, 41, 46, 59, 61,
70, 73, 82, 85)

High-nutrient input

(23, 65, 77)

Warmer

(63)

Hyposaline–brackish

(1, 3, 7, 9, 23, 28, 46,
51, 60, 77, 81, 85)

Neritic

(1, 7, 9)

Increased
environmental stress

(1, 7, 9, 73, 81, 85)

Terrigenous material
influx

(47, 81, 85)

Cool

(85)

Hypersaline

(83)

Shallow / increased
proximity to the
shore

(23, 28, 51, 64,

73, 81, 85)

Opportunistic /
reduced competition

(30, 46, 59, 61, 65,
70, 73, 85)

Cold nutrient-rich
waters (

60)

Absent in high-salinity

(9)

Open-marine

(30,

46, 59, 61, 70)

Coastal areas

(46)

Coccolithus pelagicus

Eutrophic

(21, 57)

Cool high-nutrient
input

(2, 13, 34, 48,

60, 81)

Cold

(13, 35, 57, 67)

Hyposaline

(2)

Open-ocean

(2, 81,

84)

Middle–high
latitudes

(11, 22, 43,

48)

Oligotrophic

(82)

High terrigenous
material influx

(57)

Temperate

(55, 63,

71, 75, 82)

Different salinity
ranges

(76)

Turbulence / mixing
/ non-stratification

(57, 74, 81)

Warm

(22)

Upwelling

(21, 32,

33, 60, 81, 84)

Cyclicargolithus genus

Eurytopic

(77)

Cy. floridanus

Eutrophic

(22, 25,

50, 81, 82)

No changes in
temperature / no to
reduced mixing in
nutrient

(81, 83, 85)

Temperate

(22, 55,

82, 85)

Open-marine

(14,

80, 81)

Mid-latitudes

(20)

Eurytopic

(78, 85)

No / reduced
turbulence

(81, 85)

Mesotrophic to
eutrophic

(85)

Decrease in
abundance when
influx of warm, low
nutrient

(53)

Temperate–cold

(25)

No-temp affiliation

(63)

Warm

(69)

Discoaster spp.

Oligotrophic

(14, 15,

18, 19, 25, 26, 31,
44, 45, 75)

Absent / rare in high
fertility waters (

19,

40)

Warm

(14, 15, 18,

19, 25, 26, 31, 44,
45)

Deep-marine, stable

(14, 15, 18, 19, 25,
26, 31, 39, 44, 45,
75)

Absent in marginal
seas

(17)

Table 2: Published references emphasising species known palaeoecological preferences and the findings from this study

Gran & Braarud

(1935);

McIntyre & Bé (1967);

Bukry (1971);

Bukry & Percival (1971);

Bukry et al. (1971);

Haq & Lipps (1971);

Takayama (1972);

Okada & Honjo (1973);

Bukry (1974);

Roth & Berger (1975);

Haq et al. (1977);

Schmidt (1978);

Okada & McIntyre (1979);

Haq (1980);

Lohmann & Carlson (1981);

Báldi-Beke (1984);

Perch-Nielsen (1985b);

Flores & Sierro (1987);

Chepstow-Lusty

et al. (1989);

Firth (1989);

Rahman & Roth (1990);

Wei & Wise (1990);

Nagymarosy (1991);

Wei & Thierstein (1991);

Aubry

(1992);

Chepstow-Lusty et al. (1992);

Krhovský et al. (1992);

Nagymarosy & Voronina (1992);

Pujos (1992);

Sissier et al. (1992);

Wei et al. (1992);

Giraudeau et al. (1993);

Giraudeau & Rogers (1994);

Roth (1994);

Winter et al. (1994);

Flores et al. (1995);

Ziveri et al. (1995);

Fornaciari et al. (1996);

De Kaenel & Villa (1996);

Chapman & Chepstow-Lusty (1997);

Cunha & Shimabukuro

(1997);

Flores et al. (1997);

Wells & Okada (1997);

Aubry (1998);

Young (1998);

Peleo-Alampay et al. (1999);

Svábenická (1999);

Cachão & Moita (2000);

Kameo & Sato (2000);

Monechi et al. (2000);

Nagymarosy (2000);

Negri & Villa (2000);

Pagani

et al.

(2000);

Takahashi & Okada (2000);

Oszczypko-Clowes (2001);

Bralower (2002);

Geisen et al. (2002);

Kameo (2002);

Kelly et al.

(2003);

Ćorić & Rögl (2004);

Eisenach & Kelly (2004);

Gibbs et al. (2004);

Persico & Villa (2004);

Van Simaeys et al. (2004);

Thierstein et al. (2004);

Tremolada & Bralower (2004);

Ziveri et al. (2004);

Flores et al. (2005);

Melinte (2005);

Gamboa &

Shimabukuro (2006);

Villa & Persico (2006);

Wade & Bown (2006);

Bartol et al. (2008);

Ćorić & Hohennegger (2008);

Villa et al.

(2008);

Silva et al. (2008);

Narciso et al. (2010);

Shcherbinina (2010);

Garecka (2012);

Plancq et al. (2013);

Auer et al. (2014);

Ozdínová & Sotak (2014);

Kallanxhi et al. (2016);

Holcová (2017);

present study.

Note: some of the references from table 3 of Villa

et al. (2008) are included here.

iii

OLIGOCENE TRANSITION IN TRANSYLVANIAN BASIN REVEALED BY CALCAREOUS NANNOFOSSILS

GEOLOGICA CARPATHICA

, 2018, 69, 3, 264–282

Species versus their known
palaeoecology

Palaeoenvironment
(eutrophic,
mesotrophic,
oligotrophic)

Type of nutrient t /
Trophic preferences

Temperature:
warm, temperate,
cold

Salinity:
brackish–hyposaline,
normal, hypersaline

Geological setting

Others

Helicosphaera spp.

Eutrophic

(17, 72)

High-productivity
waters

(17, 29, 67,

68, 69, 77)

Warm

(5, 6, 52, 69,

82)

Hyposaline–brackish

(29, 68, 72, 77)

Shallow /
hemipelagic / near
continental

(5, 6, 17,

20, 27, 51, 67)

Oligotrophic

(81)

High terrigenous
nutrient influx

(5,

77)

Warm–temperate

(17, 22, 67, 85

)

Normal to slightly
increased salinity

(85)

Upwelling

(17, 37,

67, 79, 85)

Pontosphaera spp.

Eutrophic

(25, 85)

Nutrient mixing and
sea surface
turbulence

(85)

Warm

(64,79)

Tolerate slight salinity
fluctuations

(27, 28,

79, 82)

Shallow/ near shore

(17, 20, 27, 28, 51,
64, 79, 85)

Eurytopic

(85)

Temperate–warm

(85)

Hyposaline

(64)

Stable marine
conditions

(69, 73,

79)

Opportunistic

(85)

Hypersaline

(16, 73,

79, 82)

Normal–hypersaline

(85)

Pontosphaera multipora

Adapt to nutrient
mixing and sea
surface turbulence

(85)

Warm

(64)

Normal

(28)

Shelf areas

(17)

Opportunistic

(85)

Temperate–warm

(85)

Normal–hypersaline

(85)

Shallow/ near shore

(51, 85)

Pontosphaera pygmaea

Adapt to nutrient
mixing and sea
surface turbulence

(85)

Warm

(64)

Temperate–warm

(85)

Normal–hypersaline

(85)

Shallow/ near shore

(51, 85)

Opportunistic

(85)

Reticulofenestra genus

Eutrophic

(52, 68,

73)

Cold high-nutrient
input

(14, 49)

Eurytopic

(78)

Reticulofenestra bisecta

Eutrophic

(82, 85)

High-nutrient input

(69, 85)

Warm

(52, 69)

Neritic / near-
continental

(27, 69)

High latitudes

(11,

20)

Warm–temperate

(22)

Temperate

(31,

55,63, 71, 75, 82)

Temperate–cool

(85)

Cold

(51)

Reticulofenestra callida

Cold

(22, 51)

Reticulofenestra daviesii

Cold

(24)

Cool

(31, 50, 63, 71,

75)

Reticulofenestra lockeri

Eutrophic

(51)

High-nutrient input

(51, 79)

Cold

(22, 51, 82)

Hypersaline

(79)

Shallow

(79)

Oligotrophic

(82)

Reticulofenestra minuta

Eutrophic

(14, 72,

85)

Terrigenous
high-nutrient input

(14, 72, 81, 85)

Warmer

(60, 72, 74)

Brackish to
hypersaline

(72)

Near-shore / shallow
/ continental margin

(5, 14, 27, 72, 81)

Better stratified
column water / stable

(60, 74)

More oligotrophic

(60, 74)

Oscillations in
nutrient

(42, 43, 58,

83)

Hyposaline

(74)

Environmental stress
/ instability

(72, 81,

84, 85)

High productivity
environments

(72,

85)

Normal to hyposaline

(85)

Opportunistic
behaviour

(72)

Small Reticulofenestra (<5) Eutrophic

(58, 85)

High-nutrient input

(8, 25, 36, 54, 85)

Environmental stress
/ instability

(84, 85)

Table 2 (continued)

KALLANXHI , BĂLC , ĆORIĆ, SZÉKELY and FILIPESCU

GEOLOGICA CARPATHICA

, 2018, 69, 3, 264–282

Species versus their known
palaeoecology

Palaeoenvironment
(eutrophic,
mesotrophic,
oligotrophic)

Type of nutrient t /
Trophic preferences

Temperature:
warm, temperate,
cold

Salinity:
brackish–hyposaline,
normal, hypersaline

Geological setting

Others

Reticulofenestra scrippsae

Neritic + open-marine

(4)

Sphenolithus genus

Oligotrophic

(17,

22,44, 62, 63)

Nutrient input

(81)

Warm

(17, 22, 38,

44, 56, 63, 75)

Deep-marine

(38,

39)

Eutrophic

(72)

Shallow,
near-continental,
stable

(17, 72)

S. moriformis

Oligotrophic

(62)

Warm

(25, 31, 50,

62, 66, 71, 75)

Near-shore

(81)

Zygrhablithus bijugatus

Oligotrophic

(22)

Warm

(62, 64, 69)

Near-shore

(27, 50,

51, 69)

Eutrophic

(66, 75)

Temperate

(75)

Cool

(66)

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