calcareous nannofossils at the paleogene – neogene boundary

ACTA PALAEONTOLOGICA ROMANIAE V. 7 (2011), P. 87-92
CALCAREOUS NANNOFOSSILS AT THE PALEOGENE – NEOGENE BOUNDARY IN BUCOVINA,
ROMANIA: RÂŞCA – VATRA MOLDOVIŢEI AREA
CARMEN M. CHIRA 1 , DORU T. JURAVLE 2 , ALIN IGRIŢAN 1 & MIRELA V. POPA 1
Abstract. A new section was investigated in order to establish the Paleogene/Neogene boundary in northern Moldavia,
Bucovina, i.e. Loba Valley section, located between Raşca and Vatra Moldoviţei localities. The new section was
compared with the one from Dumbravnic Brook, nearby Vatra Moldoviţei. The presence of Sphenolithus conicus (NP23-
NN2), which proves the presence of Lower Miocene, was remarked starting with the second part of the section besides
Helicosphaera scissura, Coccolithus pelagicus, Reticulofenestra spp. etc.
Triquetrorhabdulus carinatus (NN1), Discoaster drugii (NN2) and Helicosphaera cf. ampliaperta were also
identified;,thus, the Lower Miocene age for these deposits could be well documented.
Keywords: Nannofossils, Paleogene-Neogene Boundary, northern Eastern Carpathians, Romania.
INTRODUCTION
Calcareous nannofossils include calcareous
nannoplankton, calcareous dinoflagellates and ascidian
spicules. The calcareous nannoplankton is represented by
unicellular, micron-sized golden-brown algae belonging to
Haptophyte, and it constitutes the calcareous
phytoplankton that provides the largest amounts of
calcified organisms.
This study is focused on the calcareous nannofossils
identified across the Paleogene–Neogene boundary (PNB)
in the sediments of the Loba Valley section (Fig. 1). The
results were compared with the Dumbravnic Valley section
(placed in the same area of the northern Eastern
Carpathians), one of the currently most detailed studied
section for the remarkable results obtained concerning the
Paleogene–Neogene boundary in the northern Romanian
province of Moldavia (Chira et al, in press).
The investigated area, situated between Raşca and
Vatra Moldoviţei localities (Figs. 1, 2), belongs to the
northern Paleogene–Early Miocene flysch units of the
Eastern Carpathians, respectively to the Tarcău Nappe,
part of the Moldavidian Realm (Săndulescu, 1984).
CALCAREOUS NANNOFOSSIL ASSEMBLAGES
ACROSS THE PALEOGENE–NEOGENE BOUNDARY IN
MOLDAVIA, ROMANIA
Calcareous nannofossils across the Paleogene–Neogene
boundary were previously studied from other Eastern
Carpathian areas, situated south from the section of
Moldoviţa Valley Basin investigated by us, such as Tarcău
Basin (Martini & Lebenzon, 1971, Lebenzon, 1973),
Tazlău Basin (Ionesi & Gheţa, 1978; Dicea & Dicea,
1980), or Trotuş Valley (Melinte-Dobrinescu & Brustur,
2008), a.o.
Around the Oligocene–Miocene boundary interval,
shaly turbidites – i.e. the Vineţişu Formation in the inner
facies, and the Podu Morii Formation in the outer facies
(Melinte & Brustur, 2008), were deposited. The Oligocene-
Miocene boundary was identified based on calcareous
nannoplankton investigations, towards the base of the two
above-mentioned units (Melinte, 1988; Ionesi & Mészàros,
1989; Ionesi et al., 1999; Mărunţeanu, 1999; Melinte &
Brustur, 2008, Chira et al., in press, a.o.), within the NN1
Nannofossil Zone of Martini (1971). In the southern and
central areas of the Eastern Carpathians, Melinte &
Brustur (2008) identified the NN1 biozone based on the
concurrent ranges of Sphenolithus capricornutus and
Sphenolithus delphix.
Mărunţeanu (1999) considered that in Romania, in
general, the Oligocene–Miocene boundary is
represented by the FO of Helicosphaera mediterranea.
Species with Oligocene–Miocene distribution ranges
have been remarked in the Outer Moldavides:
Coccolithus pelagicus, C. eopelagicus, Cyclicargolithus
abisectus, C. floridanus, Discoaster adamanteus, D.
deflandrei, Helicosphaera euphratis, H. intermedia, H.
paleocarteri, Sphenolithus conicus, Reticulofenestra
minuta, R. minutula (Mărunţeanu, 1999).
The calcareous nannofossils from Moldoviţa Basin
had been previously investigated (Ionesi & Mészàros,
1989), but from another area - the Izvor Brook section,
nearby Gura Humorului locality.
In the Moldoviţa Basin, the Oligocene/Miocene
boundary was remarked in the northern part of the
Tarcău Nappe, within the Vineţişu Formation.
The studied (Ionesi & Mészàros, 1989) calcareous
nannofossils from the Izvor Brook were separated from
the pelitic intervals of the limestones belonging to the
Jaslo Limestone. The presence of the NP25 Biozone –
with Sphenolithus ciperoensis was documented. In the
succession from Izvor Brook that crosses the Dîlma–
Deia and Palamania–Ascuţita synclines, the subsequent
biozone is represented by NN1 - with Triquetrorhabdulus
carinatus (Ionesi & Mészàros, 1989, Juravle, 2007). The
previous studies mainly focused on the Upper Member
of the Jaslo Limestone and on the Vineţişu Formation
from the Tarcău Nappe – Moldoviţa Lithofacies.
From the Upper Member of the Jaslo Limestone, an
assemblage with Sphenolithus ciperoensis, typical for
the NP25 Biozone was identified.
From the Vineţişu Formation, the studied calcareous
nannofossils assemblages provided the following
biozones:
1
Babeş-Bolyai University, Department of Geology, 1 Kogălniceanu St., 400084 Cluj-Napoca, Romania. e-mail: carmen.chira@ubbcluj.ro
2
Al. I. Cuza University, Faculty of Geography and Geology, Carol I St., 700506 Iaşi, Romania.e-mail: jdorut@yahoo.com
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CARMEN M. CHIRA, DORU T. JURAVLE, ALIN IGRIŢAN & MIRELA V. POPA
Fig. 1 - Geological map of Suceviţa-Moldoviţa area, with location of the studied section.
- Sphenolithus ciperoensis Biozone - NP25 – in the
lower part, and an assemblage with Helicosphaera
euphratis, H. recta, Reticulofenestra bisecta,
Pontosphaera enormis (NP25 or NN1);
- NN1 Biozone, with Triquetrorhabdulus carinatus in
the middle part;
- no specifications were identified in the upper part.
Thus, the Oligocene–Miocene boundary was
evidenced in the top of the lower part of the Vineţişu
Formation (Ionesi & Mészàros, 1989).
The Vinetişu Formation represents the last term of the
Moldoviţa Lithofacies and it consists of sandstones and
clays, 100–120 m thick. The calcareous sandstones form
30–40 m-thick beds (Grasu et al., 2007).
MATERIALS AND METHODS
A number of 68 samples were investigated from Loba
Valley–Raşca for their calcareous nannofossils content.
About 130 vertical meters were sampled, the resolution of
sampling being about one meter. A more detailed
sampling for the Vinetişu Formation, at the Paleogene-
Neogene boundary, was also accomplished meanwhile.
The smear slides were studied under the optical
microscope, with 1000x magnification.
RESULTS AND DISCUSSIONS CONCERNING THE
CALCAREOUS NANNOFOSSIL ASSEMBLAGES
ACROSS THE PALEOGENE–NEOGENE BOUNDARY
FROM LOBA VALLEY SECTION
Our previous study was realised in Moldoviţa Basin,
nearby the locality with the same name, along
Dumbravnic Brook, an affluent of Secrăieş Valley, which
is tributary of Moldoviţa Valley (Fig. 1).
In the Dumbravnic Brook section that crosses the
Dilma–Deia and Palamina–Ascutita synclinal structures,
the sediments belong to the Vineţişu Formation.
About 100 samples were investigated in order to
establish the Paleogene/Neogene boundary along
Dumbravnic Brook (Chira et al., 2008; Chira et al., in
press).
In the first part of the section, almost all taxa of the
calcareous nannofossils assemblages have a large
distribution in the Eocene and Oligocene.
The most frequent Paleogene species, present in the
oldest part of the succession, are basically
representative for the Lower Oligocene: NP21–22 zones
of Martini (1971): Reticulofenestra umbilica, Lanternitus
minutus, Coccolithus formosus, Cyclicargolithus
floridanus and Upper Oligocene NP23– 24 zones of
Martini (1971): Helicosphaera ethologa, H. compacta, H.
cf. wilcoxonii, a.o.
In the youngest part of the section, the calcareous
nannofossils assemblages contain species that are
present also on the top of the Oligocene/Miocene
boundary, which are frequent in the Lower Miocene:
Helicosphaera scissura (NP24 – NN4), H. recta (NP24 –
NN4), Discoaster deflandrei (NP11 – NN7), Sphenolithus
moriformis (NP12 – NN9), a.o.; also Paleogene species
are present.
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CALCAREOUS NANNOFOSSILS AT THE PALEOGENE – NEOGENE BOUNDARY IN BUCOVINA, ROMANIA
Fig. 2 - The Paleogene–Lower Neogene lithostratigraphic units of the Tarcău and Vrancea Nappes.
Fig. 3 - Lithologic succession of the Loba section, with samples location.
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CARMEN M. CHIRA, DORU T. JURAVLE, ALIN IGRIŢAN & MIRELA V. POPA
The presence of Triquetrorhabdulus carinatus was
remarked in the youngest part of the section, while
topmost also Helicosphaera ampliaperta was present.
Thus, the presence of the Paleogene/Neogene
boundary could be certainly documented in the section
from the Dumbravnic Brook in the Moldoviţa Basin.
Our present study was realised north from Dumbravnic
Brook, along Loba Valley, which is a left affluent of
Moldoviţa Valley in the surroundings of Raşca locality.
These results are only preliminary, meanwhile the section
has been studied in detail for the Paleogene-Neogene
boundary.
The Loba Valley section (Fig. 3) was studied starting
from the confluence of Loba and Moldoviţa valleys, which
is located in Raşca locality (Fig. 1).
In the oldest deposits of the investigated Loba Brook
section, the nannofossil assemblages are rich in Upper
Oligocene taxa: reticulofenestrids, sphenoliths,
Zygrablithus bijugatus a.o.
The presence of Sphenolithus conicus (NP23-NN2)
was until now remarked starting with the second part of the
section, besides Helicosphaera scissura, Coccolithus
pelagicus, Reticulofenestra spp., etc., proving the
presence of Lower Miocene (between samples 32 and 33).
Triquetrorhabdulus carinatus (NN1), Discoaster drugii
(NN2) and Helicosphaera cf. ampliaperta were also
identified, thus the presence of Lower Miocene deposits
could be well documented.
Sometimes also coccospheres of Reticulofenestra
were observed. Very frequent are ascidian spicules, and in
same cases also taxa of the calcareous dinoflagellate
genus Thoracosphera.
Holcova (2005) has studied the relative abundances of
seventeen calcareous nannoplankton species around the
Oligocene/Miocene boundary interval (NP25–NN2 Zones)
in the northern part of the Buda Basin (Central
Paratethys). She has documented a succession of four
bioevents present in all the studied sections, as follows:
first appearance datum (FAD) of Helicosphaera carteri,
FAD of Reticulofenestra cf. pseudoumbilica, and FADs of
Discoaster druggii and Helicosphaera scissura, followed
by FAD of Helicosphaera ampliaperta. The
Oligocene/Miocene boundary was established between
the FAD of Reticulofenestra cf. pseudoumbilica and FADs
of Discoaster druggii and Helicosphaera scissura. Other
nannofossil events known to approximate this limit, such
as the total range of Sphenolithus delphix and the last
occurrence of Sphenolithus capricornutus, were not
recognized.
CONCLUSIONS
The Loba Valley section was investigated starting from the
confluence of Loba and Moldoviţa valleys, located in
Raşca locality (Fig. 1).
In the first part of the investigated Loba Brook section,
the nannofossil assemblages are rich in Upper Oligocene
forms: reticulofenestrids, sphenoliths, Zygrablithus
bijugatus a.o.
The presence of Sphenolithus conicus (NP23-NN2)
which proves the presence of Lower Miocene was until
now remarked starting only from the second part of the
section, besides Helicosphaera scissura, Coccolithus
pelagicus, Reticulofenestra spp., etc. Thus, the
Paleogene-Neogene boundary in this section could be
established between samples 32 and 33.
Acknowledgments
This work was supported by CNCSIS –UEFISCSU,
project number 382 PNII – IDEI 496/2007.
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PLATE CAPTIONS
PLATE I
Calcareous nannofossils from Loba section.
1. Helicosphaera ethologa BOWN, 2005
2. Helicosphaera scissura MILLER, 1981
3. Helicosphaera cf. ampliaperta BRAMLETTE & WILCOXON, 1967
4a, 4b. Helicosphaera recta (HAQ, 1966) JAFAR & MARTINI, 1975
5,6,7. Cyclicargolithus floridanus (ROTH et al., 1967) BUKRY, 1971
8. Coccolithus pelagicus (WALLICH, 1877) SCHILLER, 1930
9. Coccolithus eopelagicus (BRAMLETTE & RIEDEL, 1954) BRAMLETTE & SULLIVAN, 1961
10. Reticulofenestra bisecta (HAY ET AL., 1966) ROTH, 1970
11. Reticulofenestra lockeri MÜLLER, 1970
12,13. Reticulofenestra minuta ROTH, 1970
14. Reticulofenestra umbilica (LEVIN, 1965) MARTINI & RITZKOWSKI, 1968
15. Reticulofenestra dictyoda (DEFLANDRE IN DEFLANDRE & FERT, 1954) STRADNER IN STRADNER & EDWARDS, 1968
16. Sphenolithus spiniger BUKRY, 1971
17,18,19. Sphenolithus conicus BUKRY, 1971
20a,20b. Triquetrorhabdulus carinatus MARTINI, 1965
21. Discoaster druggii BRAMLETTE & WILCOXON, 1967
22. Discoaster sp.
23. Coccosphere of Reticulofenestra sp.
24. Ascidian spicules
25,26,27,28. Calcispheres.
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PLATE I
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