The middle/late Eocene transition in the Eastern Carpathians (Romania) based on foraminifera and calcareous nannofossil assemblages

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The Mid dle/Late Eocene tran si tion in the East ern Carpathians (Ro ma nia) based on foraminifera and cal car e ous nannofossil as sem blages

Raluca BINDIU^1, *, Sorin FILIPESCU¹, Ramona BÃLC², Lavinia COCI² and Delia GLIGOR²

1 Babeº-Bolyai Uni ver sity, Fac ulty of Bi ol ogy and Ge ol ogy, De part ment of Ge ol ogy, 1 Mihail Kogãlniceanu Street, 400084 Cluj-Napoca, Ro ma nia

2 Babeº-Bolyai Uni ver sity, Fac ulty of En vi ron men tal Sci ence and En gi neer ing, 30 Fântânele Street, 400294 Cluj-Napoca, Ro ma nia

Bindiu, R., Filipescu, S., Bãlc, R., Cociº, L., Gligor, D., 2016. The Mid dle/Late Eocene tran si tion in the East ern Carpathians (Ro ma nia) based on foraminifera and cal car e ous nannofossil as sem blages. Geo log i cal Quar terly, 60 (1): 38–55, doi:

10.7306/gq.1237

Foraminiferal and cal car e ous nannofossil as sem blages from the East ern Carpathians (north ern part of the Tarcãu Nappe, Ro ma nia) were doc u mented and cor re lated in or der to re con struct the palaeonvironmental set tings and pro vide a biostratigraphic frame work of the Plopu For ma tion. The ben thic foraminiferal as sem blages are dom i nated by flysch-type ag - glu ti nated taxa, sug gest ing a bathyal palaeodepth with fre quent os cil la tions of the car bon com pen sa tion depth. The ag glu ti - nated foraminifera morphogroup anal y ses sug gest dif fer ent lev els of or ganic mat ter in flux and ox y gen a tion. Both the foraminifera and cal car e ous nannofossil as sem blages sug gest a shift be tween the warm Mid dle Eocene to the cooler Late Eocene cli mate. Biostratigraphic data based on cal car e ous nannofossils (NP15–NP19/NNTe8–NNTe12 biozones) helped to es tab lish the age of the for ma tion. Four as sem blages of ben thic ag glu ti nated foraminifera (Psammosiphonella cylindri - ca– No thia excelsa; Paratrochamminoides spp.–Trochamminoides spp.; Karrerulina spp.–Reticulophragmium amplectens;

Spiroplectammina spectabilis) cor re lated with cal car e ous nannofossil bioevents sup ported the place ment of the Middle to Late Eocene tran si tion within the Plopu For ma tion.

Key words: microfossils, biostratigraphy, palaeoecology, turbidites, Tarcãu Nappe.

INTRODUCTION

A de tailed micropalaeontological study was car ried out in the Eocene deep-wa ter de pos its of the north ern part of the East ern Carpathians (Plopu For ma tion, Tarcãu Nappe) in or der to pro vide an ac cu rate biostratigraphic frame work and palaeoenvironmental re con struc tions. Al though a sig nif i cant amount of in for ma tion on the lithostratigraphy and tec tonic set - tings of the Tarcãu Nappe in the Suceava River val ley is al ready avail able (Joja, 1952, 1955; Joja et al., 1963, 1967; Joja and Manoliu, 1978; Juravle, 2007; Juravle et al., 2008; Bindiu and Filipescu, 2011; Bindiu et al., 2013), the biostratigraphical data are very scarce. This has re sulted in pro longed dis pute re gard - ing the age of the Plopu For ma tion due to the fact that the flysch de pos its are strongly af fected by tec ton ics, and the biostratigraphical anal y ses were not con sis tent through out all of the lithostratigraphic units.

The con ti nu ity and ex ten sive de vel op ment of the de pos its from the Suceava River val ley sec tion al lowed the doc u ment ing

of the biostratigraphy of the Middle to Late Eocene in ter val and the suc ces sion of changes in the ben thic foraminifera and cal - car e ous nannofossil as sem blages as a re sult of en vi ron men tal changes in the ba sin.

LOCATION AND GEOLOGICAL SETTING

The area in ves ti gated is lo cated in the Suceava River val - ley, near the vil lage of Brodina (N 47.89052°, E 25. 43590°).

Geo log i cally, it be longs to the north ern part of the Outer Moldavides (Sãndulescu, 1984) of the East ern Carpathian flysch, more pre cisely to the Eocene part of its most im por tant unit, which is the Tarcãu Nappe (Joja, 1955; Fig. 1). The geotectonic evo lu tion of the area dur ing the Eocene (Pandele and Stãnescu, 2001; Bãdescu, 2005; Juravle, 2007) ac cel er - ated the dy nam ics of the ba sin, lead ing to more prom i nent en vi - ron men tal changes when com pared to the Paleocene. In the prox i mal ar eas re lated to the Carpathian source, sandy for ma - tions are pres ent; while the dis tal ar eas are char ac ter ized by al - ter na tions of sandy and silty/muddy de pos its with a cal car e ous char ac ter (Juravle et al., 2008). This re sulted in the oc cur rence of three dif fer ent lithofacies with dif fer ent lithologies and palaeontological con tent (Ionesi, 1971; Gigliuto et al., 2004;

Juravle et al., 2008), on go ing from west to east (Fig. 2): Tarcãu, Tazlãu, and Doamna. The Tarcãu lithofacies is de fined by the

* Corresponding author, e-mail: raluca.bindiu@ubbcluj.ro Received: March 23, 2015; accepted: June 3, 2015; first published online: June 29, 2015

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The Middle/Late Eocene transition in the Eastern Carpathians (Romania)... 39

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pre dom i nance of a sandy flysch where the per cent age of sand - stone pres ent in the lithological col umn ex ceeds 80% (Mutihac and Ionesi, 1974; Grasu et al., 1988); the Doamna lithofacies is char ac ter ized by the pres ence of sandy-cal car e ous-clay flysch in the lower part (Joja, 1960), and in the up per part the Doamna lime stone is pres ent (Athanasiu et al., 1927; Mutihac and Ionesi, 1974); the Tazlãu lithofacies has a mixed char ac ter of both the Tarcãu and Doamna lithofacies (Ionesi, 1971; Mutihac and Ionesi, 1974). In the area stud ied, the Plopu For ma tion be - longs to the Tazlãu lithofacies and is rep re sented by turbidites with a rhyth mi cal al ter na tion of green and grey cal car e ous clays with thin sand stones, and by three in ter vals of red clays in the lower part of the sec tion (Ionesi, 1971; Mutihac and Ionesi, 1974; Juravle, 2007; Juravle et al., 2008).

MATERIAL AND METHODS

Thirty-six sam ples were col lected from a con tin u ous suc - ces sion of the Plopu For ma tion in the Suceava River val ley, the Brodina sec tion (Fig. 3), in or der to in ves ti gate the foraminifera and cal car e ous nannofossil as sem blages. The sam ples were split into two sub-sam ples; the first set of sam ples was used to study foraminiferal as sem blages, while the sec ond was ana - lysed in or der to cap ture the changes in cal car e ous nannofossil as sem blages.

The sam ples for foraminifera were pre pared us ing the stan - dard micropalaeontological method; they were dried, weighed, and dis in te grated in a so lu tion of so dium car bon ate. Then the ma te rial was washed on a 63 µm-mesh sieve (Armstrong and Brasier, 2005). Wher ever pos si ble, 300 foraminiferal tests were picked and iden ti fied un der a stereomicroscope. Sev eral spec i - mens were ex am ined in de tail us ing a JSM-JEOL 5510 LV scan ning elec tron mi cro scope. Abun dant data were pro cessed at the spe cies level. Spec i mens of tu bu lar taxa (Rhizammina,

Bathysiphon, Rhabdammina, Nothia), usu ally re cov ered only as frag ments, were counted just for con sis tency. Palaeo eco - logi cal meth ods in clude the ag glu ti nated foraminifera morphogroups (Nagy et al., 1995; Van der Akker et al., 2000;

Kaminski and Gradstein, 2005; Cetean et al., 2011; Murray et al., 2011; Setoyama et al., 2011, 2013) and the di ver sity of foraminiferal as sem blages (Hulbert, 1971). The morphogroup anal y sis is based on the con cept of foraminifera mor phol ogy and the idea that in di vid u als with dif fer ent test shapes have dif - fer ent hab i tats and dif fer ent feed ing strat e gies, there fore the changes in the rel a tive abun dance of morphogroups in the as - sem blages can re flect en vi ron men tal changes (Corliss, 1985;

Jones and Charnock, 1985; Murray et al., 2011). The sam ples for cal car e ous nannofossils were pro cessed us ing the grav ity set tling tech nique (Bown and Young, 1998). The cal car e ous nannofossils study was per formed us ing a light mi cro scope at 1000x mag ni fi ca tion and the pho to graphs were cap tured with a AxioCam ERc5s dig i tal mi cros copy cam era. At least 300 spec i - mens were counted for the quan ti ta tive study. An other 1000 FOV (fields of view) were ex am ined to iden tify rare taxa. The in - di vid ual abun dance of the taxa ob served was as sessed as fol - lows: VR – very rare: 1 spec i men to more than 50 FOV; R – rare: 1 spec i men to 21–50 FOV; F – few: 1 spec i men to 11-20 FOV; C – com mon: 1 spec i men to 2–10 FOV; A – abun dant:

more than 1 spec i men per FOV.

Some re worked spec i mens (Cre ta ceous) were iden ti fied in the sam ples stud ied. This is due to ero sion pro cesses dur ing tec tonic in sta bil ity. The Late Eocene in ter val is char ac ter ized by an in creas ing num ber of spec i mens of re worked spe cies.

The biozones were de fined us ing the biozonation schemes of Mar tini (1971) and Varol (1998) for cal car e ous nannofossils, and of Bratu (1975), Geroch and Nowak (1984), Berggren et al.

(1995), Kaminski (2005) and Kaminski et al. (1989) for foraminifera. The ag glu ti nated foraminifera taxa iden ti fied are listed in Ap pen dix 1*, while the cal car e ous nannofossils are Fig. 2. Paleogene lithostratigraphic scheme of the Tarcãu Nappe (modified after Ionesi, 1971)

* Supplementary data associated with this article can be found, in the online version, at doi: 10.7306/gq.1237

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Fig. 3. Sedimentary log and biostratigraphy of the Brodina section

The biostratigraphy used the biozonation schemes of Martini (1971) and Varol (1998) for calcareous nannofossils (N) and of Kaminski et al. (1989), Kaminski (2005) and Bratu (1975) for foraminifera (F)

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listed in Ap pen dix 2. The dis tri bu tion of foraminifera within the stud ied sam ples can be ob served in the Ap pen dix 3. The method used for de ter mi na tion of the cal cium car bon ate con - tent con sisted of the fol low ing steps: the sam ple was treated with hy dro chlo ric acid, the re sulted vol ume of the car bon di ox - ide was mea sured, and the equiv a lent per cent age of cal cium car bon ate con tent was cal cu lated (STAS 7107/3-74, 1974).

The lithological logs were drawn us ing the StratDraw pro - gram (Hoelzel, 2004), while the abun dance graphics were gen - er ated by the GpalWin ap pli ca tion (Goeury, 1997).

RESULTS

PRESERVATION, SPECIES DIVERSITY AND ABUNDANCE

Foraminiferal as sem blages are quite abun dant in the sec - tion stud ied, while pres er va tion of the in di vid u als var ies from mod er ate to good. 119 spe cies of foraminifera (Ap pen dix 1) were iden ti fied, the ag glu ti nated foraminifera group be ing the most abun dant (Ap pen dix 1). The di ver sity in dex (Hulbert in - dex) var ies from 5 to 22.4 in the foraminiferal as sem blages (Fig. 4). The most com mon foraminifera are Psammosiphonella cylindrica, Karrerulina spp., Spiroplectammina spectabilis, Trochamminoides spp., Paratrochamminoides spp., Recurvoides spp., Saccammina pla centa, Reophax spp., and Reticulophragmium amplectens, which oc cur in dif fer ent pro - por tions (Fig. 5). The di ver sity of the foraminiferal as sem blages cor re lates with the CaCO3 con tent of the sam ples along the sec tion stud ied (Fig. 4).

Fifty-six cal car e ous nannofossil spe cies were iden ti fied (Fig. 6). Di ver sity var ies be tween 0 and 2.6 (Shan non_H in dex).

The pres er va tion is mod er ate to poor and the as sem blages are dom i nated by Noelaerhabdaceae, such as: Reticulofenestra dictyoda (12–58%), R. bisecta (2–9%), R. scrippsae (1–15%), and Cribrocentrum reticulatum (0.3–26.3%), fol lowed by Coccolithaceae: Coccolithus pelagicus (4–17%), C. formosus (0.3–17%), and C. eopelagicus (3–13%). Helicosphaeraceae and nannoliths are other im por tant groups: Discoasteraceae, Braarudosphaeraceae, and Sphenolithaceae (Ap pen dix 2).

Some spe cies (i.e. Chiasmolithus spp., Clausicoccus fenestratus, Discoaster spp., Lanternithus minutus, Micrantolithus spp., Pontosphaera spp., Sphenolithus spp., Zigrhablithus bijugatus) oc cur ir reg u larly along the sec tion (Fig. 6). The rel a tive abun dance of cal car e ous nannofossils is low in the sam ples with low val ues of CaCO3, prob a bly due to dis so lu tion pro cesses. Blaj et al. (2009) de scribed a sim i lar sit u - a tion from the near-equa to rial Pa cific (Ocean Driling Pro gram – Site 1218), where the rel a tive abun dance of cal car e ous nannofossils is strongly con trolled by the CaCO3 con tent. The in ter vals with low CaCO3 con tent are dom i nated by the dis so lu - tion-re sis tant spe cies, such as Coccolithus pelagicus or Cyclicargolithus floridanus, sim i larly to the sam ples stud ied (Fig. 7).

BIOSTRATIGRAPHY

The cal car e ous nannofossil as sem blages doc u ment the age of the de pos its. A se ries of bioevents were re corded in the sam ples stud ied (Fig. 3). The most im por tant are:

– LO (last oc cur rence) of Nannotetrina alata (in sam ple 5) mark ing the NNTe8/NNTe9 bound ary;

– LO of Chiasmolithus solitus (in sample10) mark ing the NP16/NP17 and NNTe10/NNTe11 bound aries;

– FO (first oc cur rence) of Chiasmolithus oamaruensis (in sam ple 14) mark ing the NP17/NP18 bound ary;

– LO of Chiasmolithus grandis (in sam ple 17) mark ing the NNTe11/NNTe12 bound ary and Middle to Late Eocene tran si tion;

– FO of Istmolithus recurvus (in sam ple 25) mark ing the NP18/NP19 bound ary.

In ad di tion, some other bioevents have been iden ti fied along the sec tion stud ied:

– FO of Cribrocentrum reticulatum (in sam ple 7);

– LO of Helicosphaera lophota (in sam ple 10);

– FO of Reticulofenestra bisecta (in sam ple 10);

– FO of Reticulofenestra lockerii (in sam ple 14);

– LO of Cruciplacolithus edwardsii (in sam ple 21);

– LO of Sphenolithus spiniger (in sam ple 22).

Based on these bioevents, the sec tion stud ied falls in the Mid dle to Late Eocene, NP15–NP19 biozone (Mar tini, 1971), which cor re sponds to NNTe8–NNTe12 zones in the biozonation scheme of Varol (1998).

The foraminiferal as sem blages com plete the biostratigraphical data pro vided by the cal car e ous nannofossil as sem blages. The base of the sec tion con tains plank tonic foraminifera, e.g., Subbotina linaperta (Finlay), and Morozovelloides lehneri (Cushman and Jarvis). The as sem - blage is not di verse but it is in dic a tive of the Middle Eocene.

Based on the to tal ranges and rel a tive abun dances of ag - glu ti nated foraminifera, four as sem blages were sep a rated on the in ter val stud ied (Fig. 5):

– Psammosiphonella cylindrica–Nothia excelsa (Middle Eocene, cor re spond ing to the NP15–NP16 biozones);

– Paratrochamminoides spp.–Trochamminoides spp.

(Middle Eocene, cor re spond ing to the NP17 Biozone);

– Karrerulina spp.–Reticulophragmium amplectens (Upper Eocene, cor re spond ing to the NP18 Biozone);

– Spiroplectammina spectabilis (Up per Eocene, cor re - spond ing to the NP 19 Biozone).

The ag glu ti nated foraminifera biozonation used fol lows the Eocene to Oligocene scheme of Kaminski (2005) and Kaminski et al. (1989) for the North At lan tic and West ern Tethys, and the Maastrichtian to early Oligocene scheme of Bratu (1975) for the East ern Carpathians. The foraminiferal biozones were es tab - lished by acmes or lo cal strati graphic ranges (Fig. 3).

The ab sence of in dex plank tonic foraminifera pre vented the ap pli ca tion of the stan dard biozonation schemes (Berggren et al., 1995) and con se quently the cor re la tion be tween cal car e ous nannofossils and foraminifera.

The Mid dle Eocene Psammosiphonella cylindrica–Nothia excelsa and Paratrochamminoides spp.–Trochamminoides spp. (Figs. 8 and 9) as sem blages are char ac ter ized by high abun dances of the nom i nal spe cies.

Two stratigraphically im por tant spe cies, Reticulophrag - mium amplectens and Spiroplectammina spectabilis (Fig. 10), are pres ent in the sec tion stud ied. R. amplectens is one of the mark ers of the Eocene, rang ing in the Carpathians from the Early to Late Eocene (Morgiel and Olszewska, 1981). A peak in Karrerulina spp. can be ob served just above the Mid dle–Late Eocene tran si tion (Fig. 5). A peak in the rel a tive abun dance of Spiroplectammina spectabilis oc curs in sam ple 25 (at the base of the NP 19 Zone; Fig. 5), reach ing 52% of the as sem blage.

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PALAEOECOLOGY

Ex cept for the flat tened ir reg u lar Ammolagena spec i mens (M3b), all the morphogroups of ag glu ti nated foraminifera de - scribed by Nagy et al. (1995), Van der Akker et al. (2000), Kaminski and Gradstein (2005), Cetean et al. (2011), Murray et al. (2011), and Setoyama et al. (2011, 2013) are pres ent in the sec tion in ves ti gated. The graphic dis tri bu tion of the morpho - groups (Fig. 4) re veals sev eral events along the sec tion:

– a dom i nance of tu bu lar foraminifera (M1) in sam ple 4;

– a neg a tive cor re la tion be tween the trocho-, streptospiral (M2b), and elon gated (M4b) ver sus tu bu lar forms (M1) in sam ples 7, 8, 20, and 34;

– peaks of elon gated forms (M4b) in sam ple 20, and of elon gated keeled forms (M2c) in sam ple 25.

Ex cept for the in ter vals con tain ing sam ples 19 and 27, an in crease of infaunal M2a and M4b morphotypes and the peak of epifaunal M2c morphotype char ac ter ize the Late Eocene.

High abun dances of Karrerulina spp. and Recurvoides spp.

(M2b and M4b morphogroups) can be ob served just above the tran si tion be tween the Mid dle and Late Eocene strata (Fig. 4), fol lowed by a peak of Spiroplectammina spectabilis (M2c – shal low taxa).

A cool ing ep i sode is high lighted by a de crease in the rel a - tive abun dance of Reticulofenestra scrippsae, Coccolithus formosus, and the nannoliths group, to gether with an in crease in the rel a tive abun dance of Reticulofenestra bisecta and Cribrocentrum reticulatum (Fig. 7) from the lower to the up per part of the sec tion.

Fig. 4. Dis tri bu tion (in per cent ages) of the ag glu ti nated foraminifera morphogroups (M1 – tu bu lar; M2a – glob u lar; M2b – rounded trochospiral and streptospiral/planconvex trochospiral; M2c – elon gate keeled; M3a – flat tened trochospiral/ flat tened planispiral and streptospiral; M3c – flat tened streptospiral; M4a – rounded planispiral; M4b – elon gate subcylindrical/elon gate ta pered), plank tonic foraminifera (in per cent ages), cal car e ous ben thic foraminifera (in per cent ages), CaCO3 con tent and di ver sity (Hurlbert in dex)

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Fig. 5. Relative abundances of characteristic foraminiferal taxa in the Middle to Late Eocene strata of the Plopu Formation from the Suceava River valley

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suoeraclac emos fo snoitautculf ecnadnuba evitaleR .7 .giFlissofonnanseiceps

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Fig. 8A – Bathysiphon sp. 1 (sam ple 1); B – Bathysiphon sp. 2 (sam ple 11); C – Bathysiphon sp. 3 (sam ple 16); D – Nothia excelsa (Grzybowski) (sam ple 17); E – Psammosiphonella discreta (Brady) (sam ple 27); F – Psammosiphonella cylindrica (Glaessner) (sam ple 27); G – Rhabdammina linearis Brady (sam ple 19); H – Psammosphaera irregularis (Grzybowski) (sam ple 19); I – Psammosphaera irregularis (Grzybowski) (sam ple 20); J – Hyperammina elongata Brady (sam ple 6); K – Ammodiscus cretaceus (Reuss) (sam ple 9); L – Ammodiscus sp.

(sam ple 18); M, N – Ammodiscus peruvianus Berry (M – sam ple 13, N – sam ple 22); O – Glomospira sp. (sam ple 30);

P,R – Glomospira charoides (Jones & Parker) (P – sam ple 22, R – sam ple 31)

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Fig. 9A – Subreophax scalaris (Grzybowski) (sam ple 31); B – Reophax du plex Grzybowski – (sam ple 22); C–E – Hormosina trinitatensis Cushman & Renz (C – sam ple 25, D – sam ple 27, E – sam ple 29); F – Lituotuba lituiformis (Brady) (sam ple 31); G, H – Paratrochamminoides heteromorphus (Grzybowski) (G – sam ple 10, H – sam ple 13); I, J – Paratrochamminoides acervulatus (Grzybowski) (I – sam ple 10, J – sam ple 11); K – Paratrochamminoides sp. 1 (sam ple 2); L – Paratrochamminoides sp. 2 (sam ple 10); M – Trochamminoides dubius (sam ple 9); N – Trochamminoides subcoronatus (Grzybowski) (sam ple 10); O – Praesphaerammina subgaleata (Vašièek) (sam - ple 6); P – Recurvoides sp. (sam ple 5)

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Fig. 10A–E – Spiroplectammina spectabilis (Grzybowski) (sample 25); F, G – Karrerulina horrida (Mjatliuk) (F – sample 20, G – sample 29); H – Karrerulina coniformis (Grzybowki) (sample 35); I–N – Reticulophragmium

amplectens (Grzybowski) (sample 24)

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DISCUSSION

BIOSTRATIGRAPHY

Based on the foraminifera and cal car e ous nannofossil as - sem blages, some au thors (Ionesi, 1967; Dicea, 1974; Dicea and Dicea, 1976, 1980; Juravle, 2007; Juravle et al., 2008) con - sid ered the Plopu For ma tion as Late Eocene (Priabonian), while oth ers (Joja et al., 1963; Agheorghiresei et al., 1967;

Sãndulescu et al., 1987; Bãdescu, 2005) claimed that the Mid - dle/Late Eocene (Bartonian/Priabonian) bound ary is ob served in this unit. The sec tion stud ied is rep re sen ta tive for this long-time age dis cus sion; the re sults ob tained sup port ing the sec ond the ory based on micropalaeontological as sem blages.

Thus, a re vi sion of the lithostratigraphical units from the north - ern part of the Tarcãu Nappe is nec es sary. Based on larger ben thic foraminifera, the Bartonian/Priabonian bound ary was traced at the first oc cur rence of Num mu lites fabianii, Assilina alpina, Discocyclina pratti mi nor, and Asterocyclina alticostata danubica (Papazzoni and Sirotti, 1995; Serra-Kiel et al., 1998;

Ionesi, 1999; Bassi et al., 2000). From the cal car e ous nannofossils point of view, the bound ary be tween the Bartonian and Priabonian is placed within the basal part of the NP18 zone, based on the LO of Chiasmolithus grandis (Varol, 1998) and/or at the low est oc cur rence of Chiasmolithus oamaruensis (Berggren et al., 1985, 1995). These events were used to ap - prox i mate the Bartonian/Priabonian bound ary, be ing con sis tent with the re sults ob tained in the Priabonian stratotype and parastratotype at Bressana (Verhallen and Romein, 1983).

The Paratrochamminoides spp.–Trochamminoides spp.

(Fig. 9) as sem blages have been no ticed in the Mid dle Eocene de pos its of the Outer Carpathians in Po land (Kender et al., 2005). These as sem blages are known to make acmes at dif fer - ent times: Morgiel and Szymakowska (1978) placed the event in the ear li est Eocene, Morgiel and Olszewska (1981) in the Paleocene of the Pol ish Carpathians, while Kaminski et al.

(1996) re ported such an event from the Late Cre ta ceous of the Nu midi an Rif. The Reticulophragmium amplectens abun dance de fines the Mid dle Eocene R. amplectens Zone men tioned by Joja et al. (1963), Agheorghiresei at al. (1967), Bratu (1975), and Sãndulescu et al. (1987) in the Ro ma nian Carpathians, and by Geroch and Nowak (1984) in the Pol ish Carpathians.

Gradstein et al. (1994) ex tended the range of the R. amplectens Zone into the late Eocene for the North Sea and Lab ra dor Shelf.

This spe cies was ob served in all sam ples stud ied, with the high est pro por tion in sam ple 24 (11%). The Karrerulina spp.

acmes were men tioned at dif fer ent strati graphic in ter vals:

Gradstein et al. (1994) and Kaminski et al. (1996) re ported it from the up per part of the Lower Eocene; B¹k (2004) and Bindiu and Filipescu (2011) from the Lower Eocene, just above the Glomospira acme; while Kaminski (2005) from the lower part of the Mid dle Eocene. In the Ro ma nian East ern Carpathians, Bratu (1975) men tioned a peak of Spiroplectammina spectabilis in the Bisericani For ma tion, which is an equiv a lent of the Plopu For ma tion. This taxon was men tioned to form acmes just above the Cre ta - ceous/Paleogene bound ary in Gubbio, south ern Spain, and in the equa to rial At lan tic (Kuhnt and Kaminski, 1996, Kuhnt et al., 1998) in the Paleocene de pos its from the Cen tral North Sea ba - sin and Lab ra dor Shelf (Gradstein et al., 1994). This al most monospecific as sem blage has been re ported from Late Eocene de pos its from At lan tic and west ern Tethyan re gions (Kaminski et al., 1989; Kaminski, 2005).

PALAEOECOLOGY

The dis tri bu tion of morphogroups shows a low or ganic mat - ter flux and mod er ate ox y gen a tion dur ing the Mid dle Eocene (dom i nance of the morphotype M1), and al ter nat ing eutrophic (low ox y gen a tion) – oligotrophic (rel a tively well-ox y gen ated) in - ter vals around the Mid dle/Late Eocene tran si tion (re flected by a neg a tive cor re la tion of M2b + M4b with M1). The in creased bot - tom cur rent ac tiv ity and bot tom wa ter ox y gen a tion are de fined by in ter vals with epifaunal and infaunal op por tun ists, ac cord ing to Kaminski and Schroder (1987) and Kaiho (1994).

The four as sem blages of foraminifera of fer the fol low ing palaeo eco logi cal in for ma tion: the Psammosiphonella cylindri - ca– Nothia excelsa (Fig. 9) as sem blage sug gests rel a tively low or ganic mat ter flux and mod er ately ox y gen ated bot tom wa ters (Ta ble 1), while the Paratrochamminoides spp.–Trocham - minoides spp. as sem blage points to a lower-en ergy deep-wa ter en vi ron ment with low sed i men ta tion rates. The Psammosipho - nella cylindri ca–No thia excelsa (Fig. 8) and Paratrocham - minoides spp.–Trochamminoides spp. (Fig. 9) as sem blages are com mon in bathyal de pos its (Schröder, 1986; Nagy et al., 1995).

The abun dance of the Karrerullina spp. in sam ple 20 sug - gests an in crease in the or ganic mat ter flux (Kaminski, 2005).

The Spiroplectammina spectabilis taxa is known to be an op - por tu nis tic “di sas ter spe cies” re lated to the trophic con tin uum (Kaminski and Gradstein, 2005); in the At lan tic and west ern Tethyan re gions (Kaminski et al., 1989; Kaminski, 2005) and an acme of Spiroplectammina spectabilis was re lated to eutrophic con di tions (Kaminski and Gradstein, 2005).

Tu bu lar forms (such as Psammosiphonella cylindrica, Nothia spp., Bathysiphon sp.), as well as glob u lar (Saccam - mina spp., Psammosphaera spp.), rounded (Recurvoides spp., Reticulophragmium spp.) or flat tened streptospiral ones (Paratrochamminoides spp., Trochamminoides spp.), to gether with coarsely ag glu ti nated taxa are typ i cal of the “flysch-type”

ag glu ti nated foraminiferal biofacies (Gradstein and Berggren, 1981; Kaminski and Gradstein, 2005). The com po si tion of the microfossil as sem blages, as so ci ated with vari able CaCO3 con - tent in all of the sam ples, in di cates an up per bathyal depositional en vi ron ment with fre quent os cil la tions of the CCD.

This is con sis tent with the hy poth e sis of Miller et al. (1982) that the flysch-type ag glu ti nated as sem blages are not re stricted only to en vi ron ments placed be low the CCD.

The dif fer ent val ues of the foraminiferal di ver sity in dex sug - gest changes in the palaeoenvironmental con di tions.

Based on the dis tri bu tion of the ag glu ti nated foraminiferal morphogroups and as sem blages, a sea level drop and a cool - ing in ter val are sug gested. This is con sis tent with the al ready known change be tween the warm Mid dle Eocene to the cool Late Eocene (Keller et al., 1987; Gedl and Garecka, 2008).

The cal car e ous nannofossil as sem blages (Fig. 11) also sug - gest a cool ing trend along the sec tion (Ta ble 1). Even if the cold-wa ter taxa (chiasmoliths, Istmolithus recurvus, Reticulo - fenestra daviesii) are not pres ent in high num bers, a cool ing ep i - sode can be in ferred due to a drop in the abun dance of warm-wa - ter taxa. The Mid dle Eocene oligotrophic con di tions and warm wa - ters are in di cated by the fol low ing taxa: Discoaster spp., Sphenolithus spp. (S. moriformis be ing an ex cep tion), and Helicosphaera compacta (Bralower, 2002; Agnini et al., 2006;

Bown and Pearson, 2009). This cool ing trend was re vealed by sev eral other au thors (e.g., Ed wards and Perch-Niel sen, 1975;

Beck mann et al., 1981; Wei and Wise, 1990; Osz czyp ko-Clow es, 2001; Bralower, 2002; Melinte, 2005; Agnini et al., 2006, 2007;

Bown and Pearson, 2009; Cascella and Dinares-Turell, 2009).

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CONCLUSIONS

Foraminifera and cal car e ous nannofossil as sem blages re - vealed new biostratigraphical and palaeoenvironmental data for the Plopu For ma tion in the north ern part of the Tarcãu Nappe, East ern Carpathians.

Biostratigraphic data as signed the sec tion stud ied to the fol - low ing biozones:

– NP15–NP16 zones (cor re spond ing with Psammo - siphonella cylindrica–Nothia excelsa foramini feral as - sem blage – Middle Eocene);

– NP17 Zone (cor re spond ing with Paratrochamminoides spp.–Trochamminoides spp. as sem blage – Middle Eocene);

– NP18 Zone (cor re spond ing with Karrerulina spp.–Reti - culo phragmium amplectens as sem blage – Late Eocene);

– NP 19 Zone (Spiroplectammina spectabilis as sem blage – Late Eocene). These cor re spond with the NNTe8–NNTe12 biozones.

Thus, it was dem on strated that the Middle–Late Eocene tran si tion is lo cated within the Plopu For ma tion.

The foraminiferal as sem blages are dom i nated by ag glu ti - nated taxa; plank tonic and cal car e ous ben thic forms oc cur spo - rad i cally and sug gest en vi ron ments placed above the CCD.

The foraminiferal as sem blages sug gest an up per bathyal set - ting with hemipelagic de po si tion, palaeoenvironmental in sta bil -

ity, os cil la tions of the CCD, and nor mal sa lin ity, as part of a

“flysch-type” biofacies.

The cal car e ous nannofossil to gether with the foraminiferal as sem blages in di cate a warm pe riod with low or ganic mat ter flux and mod er ate ox y gen a tion dur ing the Middle Eocene, fol - lowed by a cool ing ep i sode with in creas ing or ganic mat ter and siliciclastic flux during the Late Eocene.

Palaeoenvironmental in sta bil ity is sug gested by the dis tri - bu tion of the ag glu ti nated morphogroups, the foraminifera di - ver sity, the cal car e ous nannofossil as sem blages, and the CaCO3 con tent which cor re late along the sec tion stud ied.

Ac knowl edge ments. This pa per is a re sult of a doc toral re - search made pos si ble by the fi nan cial sup port of the Sec toral Op er a tional Programme for Hu man Re sources De vel op ment 2007–2013, co-fi nanced by the Eu ro pean So cial Fund, un der the pro ject POSDRU/159/1.5/S/133391 – “Doc toral and post doc - toral ex cel lence pro grams for train ing highly qual i fied hu man re - sources for re search in the fields of Life Sci ences, En vi ron ment and Earth”. The se nior au thor also grate fully ac knowl edges sup - port from the “B.J. O’Neill Schol ar ship” of the Grzybowski Foun - da tion. The field work and ad di tional re search costs were sup - ported by S.N.G.N ROMGAZ. R.B. and D.G. thanks to CNCSIS-UEFISCSU, pro ject PN II-RU_TE_ 313/2010 and PN-II-PT-PCCA-2013-4-0297 for the fi nan cial sup port. Sin cere thanks go to M. Kaminski, M. Oszczyp ko-Clowes, and an anon y - mous re viewer for their crit i cal com ments and sug ges tions, which helped us to im prove the manu script.

Spe cies\Gen era\

Group Palaeobathymetry, palaeoecology, temperature Ref er ences

Foraminifera

Psammosiphonella cylindrica Nothia excelsa

Bathyal to abys sal, low or ganic mat ter flux Bathyal to abys sal, low or ganic mat ter flux

Kaminski and Gradstein (2005)

Trochamminoides spp.

Paratrochamminoides spp.

Up per bathyal to abys sal, lower en ergy

deep-wa ter en vi ron ment, low sed i men tary rates Kender et al. (2005), Setoyama et al.

(2013) Karrerulina spp. Up per bathyal to abys sal, high or ganic mat ter

flux Kaminski and Gradstein (2005), Bindiu

et al. (2013) Reticulophragmium amplectens Bathyal to abys sal, rel a tively sta ble en vi ron -

men tal con di tions Kaminski and Gradstein (2005), Kender et al. (2008)

Spiroplectammina spectabilis Bathyal to abys sal, high or ganic mat ter flux, eutrophic con di tions, cool wa ter

Kaminski (1984, 2005), Kaminski et al.

(1989),

Kaminski and Gradstein (2005) Cal car e ous

Nannofossils

Chiasmolithus sp.

Istmolithus recurvus Reticulofenestra daviesii

Cool- or cold-wa ter taxa

Bukry (1973), Wei and Wise (1990), Firth and Wise (1992), Bralower (2002),

Persico and Villa (2004), Tremolada and Bralower (2004), Villa and Persico (2006), Villa et al. (2008), Oszczypko-Clowes and ¯ydek (2012)

Coccolithus formosus Discoaster sp.

Helicosphaera sp.

Sphenolithus sp.

Warm-wa ter taxa

Wei and Wise (1990), Aubry (1992a,b), Wei et al. (1992), Kelly et al. (1996),

Bralower (2002), Kahn and Aubry (2004), Tremolada and Bralower (2004),

Gibbs et al. (2006), Villa et al. (2008), Oszczypko-Clowes and ¯ydek (2012) T a b l e 1 Palaeo eco logi cal af fin i ties of the main spe cies iden ti fied

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Fig. 11. Calcareous nannofossils from Brodina Valley section

A – Chiasmolithus eoaltus – sam ple 7; B – Chiasmolithus grandis – sam ple 14; C – Chiasmolithus oamaruensis – sam ple 14; D – Chiasmolithus solitus – sam ple 5; E – Coccolithus eopelagicus – sam ple 21; F – Coccolithus formosus – sam ple 10; G – Coccolithus pelagicus – sam ple 32; H – Cribrocentrum reticulatum – sam ple 22; I – Cruciplacolithus edwardsii – sam ple 17; J – Discoaster barbadiensis – sam ple 5; K – Discoaster deflandrei – sam ple 10; L – Discoaster saipanensis – sam ple 7; M – Discoaster tani – sam ple 7; N – Helicosphaera bramlettei – sam ple 8; O – Helicosphaera compacta – sam ple 4; P – Helicosphaera lophota – sam ple 4; Q – Isthmolithus recurvus – sam ple 27; R – Lanternithus minutus – sam ple 34; S – Micrantholithus breviradiatus – sam ple 7; T – Micrantholithus flos – sam ple 30; U, V – Nannotetrina alata – sam ple 4; W – Neococcolithes dubius – sam ple 22; X– Pontosphaera exilis – sam ple 3; Y – Pontosphaera multipora – sam ple 30; Z – Reticulofenestra bisecta – sam ple 20; AA – Reticulofenestra dictyoda – sam ple 16; BB – Reticulofenestra minuta – sam ple 18; CC – Reticulofenestra stavensis – sam ple 16; DD, EE – Reticulofenestra umbilica – sam ple 7 and 27; FF – Sphenolithus furcatolithoides – sam ple 7; GG – Sphenolithus moriformis – sam ple 31; HH – Sphenolithus ra di ans – sam ple 6; II – Zygrablithus bijugatus – sam ple 5; the pho to graphs taken un der cross-po lar ized light; scale bar – 2µm

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