GeolCarp_Vol48_No5_325

GEOLOGICA CARPATHICA, 48, 5, BRATISLAVA, OCTOBER 1997

325–334

LOWER BADENIAN SEA-LEVEL DROP ON THE WESTERN BORDER

OF THE TRANSYLVANIAN BASIN: FORAMINIFERAL

PALEOBATHYMETRY AND STRATIGRAPHY

SORIN FILIPESCU

and

RADU GÎRBACEA

“Babes-Bolyai” University, Department of Geology, Str. Kogalniceanu nr. 1, RO-3400 Cluj-Napoca, Rumania, and University College

London, Department of Geological Sciences, Gower Street, WC1E 6BT London, U.K.

Institute of Geology and Paleontology, University of Tübingen, Sigwartstr. 10, 72076 Tübingen, Germany

(Manuscript received December 2, 1996; accepted in revised form June 24, 1997)

Abstract:

The marine Lower Badenian deposits from the western border of the Transylvanian Basin belong to the

Gârbova de Sus Formation, lithologically dominated by algal-bioclastic limestones. The rich and well preserved fora-
miniferal assemblages correspond to planktonic foraminiferal Zone M5b-M6 (Berggren et al. 1995) and the “Upper
Lagenid Zone” of the Central Paratethys. The sediments are set in two sequences of about 20 m in thickness, the first
mostly siliciclastic, displaying coastal onlap, and the second mainly carbonatic, with a regressive character. The
sedimentary and paleontological features reflect sea level changes, the main event — recorded between the first and
the second sequence — probably being correlable with a global sea-level drop in the Middle Miocene (15.5–16 Ma).

Key words:

Transylvanian Basin, Badenian, sequence stratigraphy, lithostratigraphy, foraminifera.

Introduction

The molasse sedimentation in the Transylvanian Basin start-
ed during the Middle Miocene (Badenian/Langhian), over the
post-tectogenetic (Senonian–Burdigalian) cover.

The Middle Miocene sedimentary formations from the

western border of the Transylvanian Basin have been studied
since the second part of the 19th century, particularly by the
fossil faunas of echinids and bivalves. Most of these deposits
belong to the Gârbova de Sus Formation (Langhian/Bade-
nian — Upper Lagenid Zone, Filipescu & Gîrbacea, in press).

The purpose of this study is to emphasize some particular

events in the biostratigraphical and sedimentological record of
the Gârbova de Sus Formation. The observations on the fora-
miniferal assemblages and sedimentary sequences have fo-
cused on the main sections and especially the type section of
Gârbova de Sus (Pârâul Pietrii Creek). The results of our in-
vestigations enable us to make correlations with the corre-
sponding intervals of the Central Paratethys.

Lithostratigraphy

The type section of the Gârbova de Sus Formation is locat-

ed close to the northwestern limit of the Gârbova de Sus vil-
lage. The locality is situated southwest of the city of Aiud,
8 km west of the E81 European road (Fig. 1).

The lithology consists of lower Badenian carbonate sands

and especially algal-bioclastic limestones. The most typical
sequences occur at Gârbova de Sus, Lopadea Veche, Podeni,
and Moldovene ti. The formation is about 35–40 m thick,
and extends along the common border of the Transylvanian
Basin and the Apuseni Mountains for more than 40 km, be-
tween the Arie and Ampoi rivers.

Fig. 1.

Geological map of the western border of the Transylvanian

Basin (after Lupu et al. 1967).

326 FILIPESCU and GÎRBACEA

The formation, synchronous with the upper part of the Dej

Formation (Popescu 1970), lies transgressively over the Be-
deleu Nappe (late Jurassic–early Cretaceous) or the post-aus-
tric Râme i Formation s.l. (late Cretaceous), of the eastern
part of the Apuseni Mountains (Fig. 1, Fig. 2). It is usually
overlain by the Pannonian siliciclastic deposits with brackish
to fresh-water faunas of the Lopadea Formation (Lubenescu
& Lubenescu 1977). The hiatus associated with the unconfor-
mity between the Badenian and the Pannonian strata dimin-
ishes or disappears laterally. Thus, in the Podeni area reef and
coastal sabkha deposits are observed, which are separated
here as the Cheia Formation (Filipescu 1996) — middle Bad-
enian/latest Langhian (see also Ghergari et al. 1991). The
Cheia Formation corresponds to the salt deposits from the
middle part of the Transylvanian Basin. The following marine
Kossovian deposits are separated here as the Pietroasa For-
mation (Filipescu 1996), overlain by brackish Sarmatian de-
posits belonging to the Măhăceni Formation (Filipescu
1996). Taken together, the Cheia and Pietroasa formations are
equivalent to Mire Formation of Popescu (1972).

The distinctive algal-bioclastic limestones from the upper

and middle part of the formation can be separated as a mem-
ber — the Podeni Limestone of Mészáros (1991); the Buha
Limestone of Popescu et al. (1995). The most representative
sections of the member are situated at Podeni and Lopadea
Veche, north of Gârbova. The member is delimited by the si-
liciclastites from the lower part of the formation and by the
fine sediments with foraminifers and bivalves from its top.
Sometimes it is directly overlain by the younger formations.

Fig. 2.

Lithostratigraphy of the Neogene formations from the west-

ern border of the Transylvanian Basin.

Fig. 3.

Lithology and sedimentary sequence of the Gârbova de Sus

Formation type section. After Hosu & Filipescu (1996). 1 — bio-
clastic limestone; 2 — microconglomerate and calcarenite; 3 —
marl, clay; 4 — turbidites; 5 — microfauna abundance; 6 — mac-
rofauna abundance; 7 — ripples; 8 — cross-bedding; 9 — channels;
U

— unconformity; TST — transgressive stand; MFS — maximum

flooding surface; HST — high stand; FU — finig upward tendency;
CU

— coarsening upward tendency.

LOWER BADENIAN SEA-LEVEL DROP ON THE WESTERN BORDER OF THE TRANSYLVANIAN BASIN 327

Fauna — composition, biostratigraphy, environment

The most complete synthesis of geological and palaeonto-

logical data from the Gârbova de Sus Formation was carried
out by Koch (1900). Vadász (1915) studied the rich echinoid
fauna from Gârbova, and in the last decades Gábos & Ghi-
urcă (1969) documented the small echinids, Nicorici (1975)
the pectinids, and Ghiurcă (1974) the bryozoans.

Although Koch (1900) mentioned the existence of several

foraminiferal species, no significant studies have been made
on this group until the present.

The foraminiferal associations are very rich and diverse, espe-

cially in the lower part of the sequence, where sublittoral spe-
cies prevail in fine sediments. The associations are similar to
those described by d’Orbigny (1846) from the Vienna Basin.

Among benthics, a large abundance of the lagenids is ob-

served (Pl. III–V). Many of the species are in common with
the “Upper Lagenid Zone” (Papp & Turnovski 1953) of the
Badenian, thus allowing correlation of the sequences with the
corresponding interval in the Central Paratethys.

In addition to Lagenidae, the benthic associations include a

large number of other calcareous species (Pl. II, IV–VI), and also
agglutinated taxa (Pl. I). The benthic associations are accompa-
nied by a large number of planktonics, belonging to the “Orbuli-
na suturalis

Biozone” M5b-M6 Zone (Berggren 1995).

The microfauna also includes other fossil groups, such as

the bryozoans (Cellaria, Crisia), brachiopods (Argyrotheca,
Megerlea

) and ostracods (Aurila, Parakrithe, Xestoleberis).

The macrofauna usually consists of brachiopods, echinoids,

and especially bivalves (pectinids and ostreids) belonging to
the “Neopycnodonte navicularis Biozone” (Lubenescu et al.
1977). The uppermost level with macrofauna contains a large
number of Terebratula grandis Blum. and Isocardia cor Linné.

Fig. 4.

Benthic and planktonic

O and

C fluctuations during Middle Miocene and biostratigraphic zonation for calcareous nannoplank-

ton and planktonic foraminifers in SE Pacific (after Kenett 1985). The shifts of

O and

C ratios indicate a sea-level drop between 15.5

and 16 Ma, possibly recorded on the western border of the Transylvanian Basin.

Sequence stratigraphy

According to Hosu & Filipescu (1996), the Gârbova de Sus

Formation is bound by two unconformities (Fig. 3). The sedi-
ments comprise two sequences: the lower (15–20 m thick)
mostly siliciclastic, displaying coastal onlap, and the upper
(15–20 m thick) mainly carbonatic, with a regressive pattern.
The sediments of both sequences belong to the inner plat-
form, indicating the presence of the transgressive and high
stands, separated by maximum flooding surfaces.

In the lower sequence, the sediments belong mainly to

the transgressive systems track, and are grouped in pro-
gressively thinner parasequences with a retrogradational
stacking pattern, as a response to an important sea level
rise. The first recorded fossils are algae, echinids and mol-
luscs. The abundance of microfauna in this sequence is as-
sociated with the maximum flooding surface, correspond-
ing to a major condensation sequence. Towards the upper
part of the sequence, a progradational tendency has been
attributed to a high stand, which leads to the end of the
first sequence.

The upper sequence, starts with siliciclastic deposits

(transgressive lag), followed by upper shoreface to lagoonal
algal-bioclastic deposits. The maximum flooding surface is
represented by fine sediments with foraminifers. The follow-
ing pattern of the parasequences suggests the progradation ten-
dency in a mainly carbonatic environment.

The sea-level change observed between the lower and up-

per sequences may be the expression of an important global
event. The unconformity probably can be associated with the
sea-level drop at 15.5–16 Ma (Fig. 4) — according to the
eustatic curve of Kennett (1985) — as a response to global
cooling and ice growth in Antarctica.

Orbulina suturalis

Brönnimann 1951 = Candorbulina universa Jedlicka 1934 (Orbulina universa d’Orbigny 1846, non 1839)

328 FILIPESCU and GÎRBACEA

Plate I:

Foraminifera from Gârbova de Sus Formation. Gârbova de Sus (Figs. 1, 3, 4), Moldovene ti (Figs. 2, 5) — marker length

0.1 mm. Fig. 1. Vulvulina pennatula (Batsch). Fig. 2. Reticulophragmium crassum (Reuss). Fig. 3. Karreriella bradyi (Cushman). Fig. 4.
Textularia mariae

d’Orbigny. Fig. 5. Paragaudryina mayeriana (d’Orbigny). Fig. 6. Martinottiella communis d’Orbigny.

The Badenian sedimentation in this area commenced with

coarse and fine sands, typical of a nearshore or beach environ-
ment. As the process continued, the sands became interfin-
gered with marls and limestones, very rich in foraminifera (the
planktonic taxa reach about 20 %). The fossil associations of
the carbonate facies also include oysters and rhodolites.

Agglutinated foraminifera occur in all depths, as well as

on all types of substratum, representing approximately 20 %
of the benthic associations. Intraspecific variations in the
type and the dimensions of the agglutinated granules are also
observed. At certain levels pseudopored species (e.g.
Spirorutilus

) are found, probably related to the increased

LOWER BADENIAN SEA-LEVEL DROP ON THE WESTERN BORDER OF THE TRANSYLVANIAN BASIN 329

Plate II:

Foraminifera from Gârbova de Sus Formation. Gârbova de Sus (Figs. 1, 3, 5), Geoagiu de Sus (Figs. 2, 4) — marker length

0.1 mm. Fig. 1. Adelosina longirostra (d’Orbigny). Fig. 2. Dendritina haueri d’Orbigny. Fig. 3. Cycloforina reticulata (Karrer). Fig. 4.
Lachlanella incrassata

(Karrer). Fig. 5. Cycloforina vermicularis (Karrer).

needs in gas exchanges, due to a slight deepening of the sub-
stratum.

The miliolids (Pl. II) lived mainly as epiphytic forms, either

on hard and soft substratum or in interstitial spaces at the sed-
iment — water interface. Species associated with a soft sub-

stratum (fine sediments) have an elongated, ovoidal, smooth
shape, while those that lived on hard substrata have a
flatenned discoidal shape. The heavy ornamentation, result-
ing in the occurrence of irregular forms, is typical of mobile
coarse sediment. In the Gulf of Aqaba, Reiss & Hottinger

330 FILIPESCU and GÎRBACEA

Plate III:

Foraminifera from Gârbova de Sus Formation. Gârbova de Sus — marker length 0.1 mm Fig. 1. Laevidentalina elegans

(d’Orbigny). Fig. 2. Nodosaria pyrula d’Orbigny. Fig. 3. Stilostomella adolphina (d’Orbigny). Fig. 4. Marginulina hirsuta d’Orbigny.
Fig. 5.

Neugeborina longiscata (d’Orbigny). Fig. 6. Dimorphina variabilis (Neugeboren). Fig. 7. Amphicoryna hispida (Soldani).

(1984) registered a severe reduction in miliolids at the 50 m
isobath (from 50 % to less than 10 % in the foraminiferal asso-
ciations). A similar significant reduction has been recorded
next to the unconformity surface separating the two sequenc-
es of the Gârbova de Sus Formation.

The lagenids are very frequent close to the interval of maxi-

mum flooding in the lower sequence, their presence usually
suggesting depths up to 70 m. Their frequency is severely di-
minished above the unconformity surface, along with most of
the subtropical species. This suggests a temperature drop asso-

LOWER BADENIAN SEA-LEVEL DROP ON THE WESTERN BORDER OF THE TRANSYLVANIAN BASIN 331

ciated with the unconformity surface, which can probably be
related to the global sea-level event mentioned above.

The bolivinids reach 10–15 % and the uvigerinids do not ex-

ceed 10 % of the benthic assemblage. Only in the marls above
the Podeni Limestone (Lopadea Veche) the Uvigerina species

are more abundant (20 %), a consequence of brief deepening
of the substratum.

The sea-level drop in the middle part of the formation

brought favourable life conditions for larger foraminifera —
Planostegina costata

d’Orbigny, Amphistegina hauerina d’Orbigny,

Plate IV:

Foraminifers from Gârbova de Sus Formation. Gârbova de Sus (Figs. 1–4), Moldovene ti (Fig. 5) — marker length 0.1 mm

Fig. 1. Lenticulina calcar

(Linne). Fig. 2. Anomalinoides farctus (Fichtel & Moll). Fig. 3. Bitubulogenerina reticulata Cushman. Fig. 4.

Globulina spinosa

d’Orbigny. Fig. 5. Planostegina costata (d’Orbigny).

332 FILIPESCU and GÎRBACEA

Plate V:

Foraminifera from Gârbova de Sus Formation. Gârbova de Sus (Figs. 1, 3–5), Moldovene ti (Fig. 2) — marker length 0.1 mm.

Fig.

1. Lenticulina vortex (Fichtel & Moll). Fig. 2. Lingulina costata d’Orbigny. Fig. 3. Uvigerina bellicostata Luczkowska. Fig. 4. Loxos-

tomum digitalis

(d’Orbigny). Fig. 5. Uvigerina pygmoides Papp & Turnovski.

Amphistegina mammilla

(Fichtel & Moll) — which occur in

large quantities in carbonate sands and sandstones, sometimes
forming exclusive beds. Those forms lived in the interstitions
between clasts in subtidal areas, and are also present within the
lagoonal laminated marls. The levels containing thick-walled

Amphistegina

suggest high energy, shallow water environ-

ments in front of marginal reefs or in channels. Thin walled
specimens are usually associated with the lower sequence
“Lagenid” interval, having analogs in modern seas at depths
of 40–80 m. The species of Amphistegina usually share the

LOWER BADENIAN SEA-LEVEL DROP ON THE WESTERN BORDER OF THE TRANSYLVANIAN BASIN 333

Plate VI:

Foraminifera from Gârbova de Sus Formation. Gârbova de Sus (Figs. 1, 2, 4, 5), Moldovene ti (Fig. 3) — marker length

0.1 mm. Fig. 1. Candorbulina universa Jedlicka. Fig. 2. Lobatula lobatula (Walker & Jakob). Fig. 3. Elphidium fichtelianum (d’Orbigny).
Fig.

4. Nonion commune (d’Orbigny). Fig. 5. Neoeponides schreibersi (d’Orbigny).

hard substratum with other larger foraminifers, such as Pla-
nostegina

. Their modern distribution is usually delimited by

depths of 20–70 m, but in our case they can also occur in con-
centration levels at greater depths. The ratio between richly
and poorly ornamented Planostegina decreases in the upper

part of the formation, probably as an effect of a change in the
environmental parameters, or another change related to the
sea-level event mentioned above.

We notice a change in the aspect of the faunas owing to the

establishment of shallow carbonate sedimentation (mainly al-

334 FILIPESCU and GÎRBACEA

gal limestone) in the upper part of the section. The lagenids
are scarce, but the “cibicids”, elphidiids and some large fora-
minifers become more abundant.

Branched foraminifer (of Miniacina type) have been identi-

fied, especially on hard bottom. They are the short lived pio-
neers of the substratum, and are overlain by succeeding comu-
nities of bryozoa and algae.

The elphidiids lived in significant communities only in the

upper, shallower part of the formation. Their major frequency
in modern seas is registered between 20 and 50 m.

The upper part of the Lower Badenian sequence also in-

cludes some planktonic foraminiferal levels (mainly with
Candorbulina universa

Jedlicka), but their frequency is lower

than in the lower sequence.

Conclusions

The Gârbova de Sus Formation is the most distinctive

lithostratigraphic unit of the Middle Miocene (early Badenian
—Upper Lagenid Zone) on the western border of the Transyl-
vanian Basin. It consists mainly of shallow water algal-bio-
clastic limestones associated with epiclastic deposits, all
structured in two sequences, a lower transgressive one, most-
ly clastic, and a regressive upper one, mainly carbonatic.

The micropaleontologic and sedimentologic features clear-

ly indicate a drop of the sea level at the middle part of the for-
mation, probably related to global eustacy. A comparison of
the observed paleobathymetric indicators with the global
eustatic curves suggests a possible calibration of the se-
quence within the interval 15.5–16 Ma.

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