Palaeoenvironmental changes in the Transylvanian Basin during the Early Miocene revealed by the foraminifera assemblages

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Geo log i cal Quar terly, 2016, 60 (1): 167–180 DOI: http://dx.doi.org/10.7306/gq.1245

Palaeoenvironmental changes in the Transylvanian Ba sin dur ing the Early Mio cene re vealed by the foraminifera as sem blages

Szabolcs-Flavius SZÉKELY^1,*, Claudia BELDEAN¹, Raluca BINDIU¹, Sorin FILIPESCU¹ and Emanoil SÃSÃRAN¹

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

Székely, S.-F., Beldean, C., Bindiu, R., Filipescu, S., Sãsãran, E., 2016. Palaeoenvironmental changes in the Transylvanian Ba sin dur ing the Early Mio cene re vealed by the foraminifera as sem blages. Geo log i cal Quar terly, 60 (1): 167–180, doi:

10.7306/gq.1245

The evo lu tion of the Transylvanian Ba sin dur ing the Early Mio cene has been re con structed from the suc ces sion of palaeoenvironments in ferred from sedimentological trends and the suc ces sion of spe cific foraminiferal as sem blages from Lower Mio cene Tihãu sec tion in the north west ern Transylvanian Ba sin. Plank tonic foraminifera sug gest a Burdigalian age and re cord sea level changes, cli ma tic and pro duc tiv ity events. Ben thic foraminifera of fer data on the palaeoenvironmental evo lu tion, with a large-scale progradational (coars en ing up) sed i men tary suc ces sion in flu enced by re gional tec ton ics. The suc ces sion of depositional events in cludes: (1) transgressive coarse grained de pos its with typ i cal Med i ter ra nean as sem - blages of bi valves in beach en vi ron ments; (2) a glauconitic fa cies which can be as so ci ated with the max i mum flood ing sur - face of the trans gres sion; (3) sed i men ta tion con tin ued on a nar row shelf in flu enced by del tas dur ing the highstand; (4) the in flu ence of re gional tec ton ics and sub se quent fill ing with turbidites as so ci ated with fan del tas.

Key words: Early Mio cene, Transylvanian Ba sin, Cen tral Paratethys, foraminifera, palaeoenvironments.

INTRODUCTION

The Paratethys (Laskarev, 1924), as a large epicontinental sea ex tend ing from Cen tral Eu rope to Cen tral Asia since the Oligocene, grad u ally trans formed into an in land sea and fi nally into a se ries of gi ant lakes be cause of on go ing con ti nen tal col li - sion that shaped the Al pine–Hi ma la yan orogenic belt (Rögl, 1998). Tec tonic de for ma tions dur ing the Neo gene caused par - tic u lar evo lu tion of Paratethyan sub-bas ins and a pro gres sive iso la tion from the open ocean, which in duced endemism of the biota. The Transylvanian Ba sin, one of the ma jor bas ins of the Cen tral Paratethys, pre serves char ac ter is tic strati graphic fea - tures but faces the same bio- and chronostratigraphic dif fi cul - ties in cor re la tion with the stan dard zones and stages. Re cent at tempts to im prove the cor re la tion cri te ria for the Mio cene of the Transylvanian Ba sin, with im pli ca tions for the Paratethyan stra tig ra phy, were car ried out by Krézsek and Filipescu (2005), Filipescu and Silye (2008), Beldean et al. (2010), Krézsek et al.

(2010), Vasiliev et al. (2010), Filipescu et al. (2011), and de Leeuw et al. (2013).

One of the rep re sen ta tive ar eas for the Lower Mio cene is the north west ern Transylvanian Ba sin (Fig. 1), where di verse

palaeoenvironmental set tings (from con ti nen tal to shal low- and deep-ma rine – Popescu, 1975; Popescu et al., 1995; Filipescu, 2011) con trolled the dis tri bu tion of fos sil as sem blages. Due to this fa cies com plex ity and lim ited con nec tions to the ocean, ap - pli ca tion of the ex ist ing biozonation (Popescu, 1975; Beldean et al., 2010) proved dif fi cult in some cases. For this rea son we de - cided to look more care fully into the re la tion ship be tween the types of sed i men tary fa cies and their micropalaeontological con tent, as clues for palaeoenvironmental re con struc tion and for iden ti fi ca tion of im proved cor re la tion cri te ria.

The Lower Mio cene sed i men tary re cord of the Transylvanian Ba sin reaches up to 1000 m and has been pre served mainly in the flex ural ba sin de vel oped in front of the thrust ing Pienides (Krézsek and Bally, 2006). Bore hole data and re gional in ter pre - ta tions (Dicea et al., 1980; Krézsek and Bally, 2006; Tischler et al., 2008) in di cate a large-scale shallowing up ward trend. Sev - eral lithostratigraphic units were de scribed for co ex ist ing par tic u - lar sed i men tary paleoenviron ments (Fig. 2).

The su per po si tion of the par tic u lar lithofacies was pro duced due to the ini tial trans gres sion (ba sin for ma tion) and sub se - quent re gres sion (up lift of the Pienides; Beldean et al., 2012).

The stud ied sec tion from Tihãu dis plays parts of the Lower Mio - cene Coruº, Chechiº, and Hida for ma tions.

MATERIAL AND METHODS

Nine teen sam ples were col lected from fine siliciclastic sed i - ments from the Chechiº and Hida for ma tions (Fig. 3) near the

* Corresponding author, e-mail: szekelyflavius@gmail.com Received: July 17, 2015; accepted: August 20, 2015; first published online: August 24, 2015

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Tihãu lo cal ity (Lânii Val ley, Sãlaj County – 47°12’20.96”N, 23°20’34.32”E; Fig. 1). Sev en teen sam ples were re cov ered from a con tin u ous suc ces sion (Fig. 3), while two of them were col lected from a lower out crop (Fig. 3). The sedimentological in - ter pre ta tion re lies on out crop mea sure ments and ob ser va tions.

Stan dard micropalaeontological prep a ra tion meth ods were ap plied on 250 g of sam ple (boil ing in tap wa ter with one ta ble - spoon of so dium car bon ate – Na2CO3 – for approx. 1 hour, wash ing over a 63 µm brass mesh sieve and dry ing); when nec - es sary, the sed i ment was treated with 0.3% hy dro gen per ox ide (H2O2) to fur ther dis in te grate the clay min er als. More than 300 foraminifera were picked from the >63 µm frac tion. Pri mary iden ti fi ca tion was done un der a stereomicroscope, while sev - eral spec i mens were ex am ined in de tail with a scan ning elec - tron mi cro scope at the Elec tron Mi cros copy Cen ter of the Babeº-Bolyai Uni ver sity. The foraminifera were iden ti fied at spe cies-level (if pos si ble), sorted, and counted.

Plank tonic foraminifera were used to es ti mate the wa ter palaeodepth by cal cu lat ing the plank tonic/ben thic (P/B) ra tios based on the re la tion: P/B = 100(P/P + B) (Murray, 1991).

Com ple men tary data were used to re duce the pos si ble dis - tor tions in tro duced by trans port and redeposition (Van der Zwaan et al., 1990; Van Hinsbergen et al., 2005).

Some quan ti ta tive data were cal cu lated for the ben thic foraminiferal as sem blages us ing the com puter soft ware PAST (Ham mer et al., 2001) in or der to ob tain palaeo eco logi cal proxy re cords:

– Fisher’s al pha di ver sity in dex, which re mains con stant re gard less of the num ber of in di vid u als and high val ues in di cate high spe cies di ver sity (Murray, 1991);

– Shan non in dex that takes into ac count both the num ber of spe cies and the amount of in di vid u als within spe cies (Murray, 1991);

168 Szabolcs-Flavius Székely, Claudia Beldean, Raluca Bindiu, Sorin Filipescu and Emanoil Sãsãran

50°

16° 20° 24° 28°

Zagreb Vienna

Budapest Kraków

Pannonian Basin

Beograd

Bucharest

Moesian Platform Vienna

Basin

Foredeep Outer Carpathians Inner Carpathians, Alps and Dinarides units

Neogene volcanics

Cluj-Napoca

Bucharest Romania

0 5 10 km Paleogene

shallow-marine Lower Miocene deep-marine Lower Miocene

Badenian Sarmatian

metamorphics Quaternary

sampled section Transcarpathian

Basin

Trans ylvanian Basin

Ea st Eu

ropean Pla

tform

N

Fig. 1. Position of the studied area in the Transylvanian Basin (left) in the context of the Central Paratethys;

detailed geological map (right) and location of the studied outcrop (modified after Beldean and Filipescu, 2011)

Fig. 2. The correlation between the Lower and Middle Miocene biozones based on the foraminifera and calcareous nannoplankton with the lithostratigraphic units in the Transylvanian Basin (after Beldean et al., 2012)

Standard absolute ages are from Gradstein and Ogg (2004)

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Palaeoenvironmental changes in the Transylvanian Basin during the Early Miocene revealed by the foraminifera assemblages 169

Fig. 3. Sedimentary log of the studied section, position of samples and univariate statistics such as the P/B ratio, percent of agglutinated foraminifera, percent of epifauna and infauna microhabitats,

and diversity indices (Fisher alpha and Shannon indices) C – clay, Si – silt, S – sand, P – pebble

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– the rel a tive abun dance of ag glu ti nated taxa (Murray, 1991);

– the rel a tive abun dance of epifaunal (usu ally abun dant in well-ox y gen ated en vi ron ments) and infaunal (able to live with low ox y gen con tents) taxa was used to es ti mate bot tom wa ter ox y gen (Jorissen, 1999);

– the rel a tive abun dance of most im por tant ben thic foraminifera spe cies, gen era or groups with sim i lar palaeo eco logi cal af fin i ties was used to char ac ter ize the palaeoenvironmental evo lu tion.

The clas si fi ca tion of the ben thic foraminifera in epifaunal or infaunal, and as oxic, suboxic or dysoxic in di ca tors was based on lit er a ture data and the mor phol ogy of the test (e.g., Corliss and Chen, 1988; Corliss and Fois, 1990; Sen Gupta and Machain-Castillo, 1993; Kaiho, 1994, 1999; Kouwenhoven and Van der Zwaan, 2006; Jorissen et al., 2007; Kaminski, 2012).

The palaeoclimatic sig nif i cance of cer tain plank tonic foraminifera spe cies was de duced based on di rect in for ma tion from the lit er a ture (e.g., Li et al., 1992; Spezzaferri, 1994, 1995;

Spezzaferri and Æoriæ, 2001; Spezzaferri et al., 2002; Rögl and Spezzaferri, 2003; Bicchi et al., 2003, 2006; Pearson et al., 2006; Alegret et al., 2008).

RESULTS

SEDIMENTOLOGY

The Coruº For ma tion. The transgressive de pos its be long - ing to the Coruº For ma tion are rep re sented by well-sorted thick pack ages of sand stones al ter nat ing with centimetric/decimetric con glom er ates con tain ing shell lags with large molluscs (es pe - cially pectinidae) typ i cal for the lit to ral ar eas (Moisescu and Popescu, 1980).

The sand stones are char ac ter ized by cross- and par al lel lam i na tion (sub aque ous dunes). The tran si tion from the sand - stones be long ing to the Coruº For ma tion to the bioclastic silty-sandy clays with glauconite (approx. 2.5 m thick) of the Chechiº For ma tion is gradational or sharp (Fig. 3). The glauconite de pos its are grad ing up ward into grey mudstones (sam ples TH1 and TH2).

The Chechiº For ma tion. Mudstones dom i nate the Chechiº For ma tion, al though decimetric in ter ca la tions of orto- and paraconglomerates were ob served (Fig. 3). The base of the coarse grained de pos its is weakly ero sional while the top be comes gradational. The extraformational peb bles are rounded to sub-rounded, sug gest ing feed ing of the fan del tas by flu vial sys tems.

A glauconite rich in ter val is very char ac ter is tic for the lower part of the for ma tion. Glauconite is well-known to be as so ci ated with pe ri ods of trans gres sion and low de po si tion or even ero - sion of sed i ment (e.g., Rech-Frollo, 1963; McRae, 1972; Van Houten and Puruker, 1984; Har ris and Whit ing, 2000; Gon za lez et al., 2004). Cattaneo and Steel (2003) as so ci ated the max i - mum flood ing sur face (MFS) with con densed sec tions show ing re duced ox y gen val ues, high or ganic mat ter con tent, authigenic ma te rial (e.g., glauconite), abun dant and di verse plank ton, and low amounts of ben thic foraminifera. Leckie and Olson (2003) as so ci ated the glauconite rich fine-grained de pos its with the MFS, while Miller et al. (1997) as so ci ated the shelly sands with glauconite with transgressive sys tems tracts (TST) de pos ited in in ner-mid dle neritic (0 to 100 m) en vi ron ments. Other au thors re lated the MFS with: grey-brown clays with glauconite

(Danielsen et al., 1997), glauconite bear ing de pos its (Christensen et al., 1995), glauconite with peak abun dances of Uvigerina (Brown ing et al., 1997), peaks in to tal or ganic car bon (Miller and Lohmann, 1982) dur ing times of max i mum flood ing (Loutit et al., 1988), or con densed sec tions con tain ing glauconite and/or sid er ite (Posamentier and Allen, 1999;

Cãtuneanu, 2006). Con cen tra tion of glauconite and in creas ing num bers of plank tonic foraminifera were used to point to the MFS and the be gin ning of Highstand Sys tems Tracts in the Mio cene of the Vi enna Ba sin (Kováè et al., 2004).

The Coruº For ma tion was as so ci ated with the first Mio cene ma rine trans gres sion in the Transylvanian Ba sin (Popescu et al., 1995; Filipescu, 2011). The glauconite fa cies from the base of the Chechiº For ma tion was re ported by ªuraru (1967) in the Coruº–Cristolþel area. For all rea sons men tioned above, we as - sumed that the glauconitic level clearly iden ti fied at Tihãu and in other oc cur rences of the Chechiº For ma tion cor re sponds to the max i mum flood ing sur face of the first Early Mio cene trans gres - sion.

The Hida For ma tion. Turbiditic sed i men ta tion, spe cific for the Hida For ma tion, was ob served in the mid dle and up per part of the stud ied sec tion (Fig. 3). These sed i ments are char ac ter - ized by in ter vals with sands/fine grav els or sand stones with car - bon ate ce ment al ter nat ing with marly-clays. Com plete and in - com plete Bouma se quences, ero sional and deformational struc tures were rec og nized sug gest ing the de po si tion of the turbidites in mid-fan set tings.

FORAMINIFERAL ASSEMBLAGES

Foraminiferal as sem blages are abun dant in the stud ied sec tion and the pres er va tion of the in di vid u als var ies from mod - er ate to good. Among the iden ti fied foraminifera spe cies, 35 are ag glu ti nated ben thic, 123 cal car e ous ben thic, and 40 are plank - tonic (Ap pen dix 1*).

Ben thic foraminifera are well-rep re sented along the sec tion (Fig. 4), both in the Chechiº and Hida for ma tions. The ben thic as sem blages are more di verse in the mudstones of the Chechiº For ma tion and less abun dant and di verse in the fine turbidites of the Hida For ma tion (sam ples T13 to T17; Fig. 3).

Plank tonic foraminifera are rel a tively well-rep re sented in sam ples T1 to T17 (Fig. 3). The com mon spe cies are:

Globigerina angulisuturalis, G. anguliofficinalis, G. bollii, G.

bulloides (Fig. 5D), G. ciperoensis, G. dubia, G. falconensis, G.

gnaucki (Fig. 5C), G. lentiana (Fig. 5A), G. officinalis, G.

ottnangiensis, G. praebulloides, G. tarchanensis, G. wagneri, Globoturborotalita woodi (Fig. 5E), Globigerinoides trilobus (Fig. 5F and G), Glob. quadrilobatus (Fig. 5I), Paragloborotalia continuosa, P. semivera, Tenuitellinata angustiumbilicata, T.

pseudoedita, and T. juvenilis.

Plank tonic foraminifera. The plank tonic as sem blages from Tihãu are mostly dom i nated by spe cies in di cat ing cold-tem per ate wa ter and high pri mary pro duc tiv ity (Globigerina group; Globoturborotalita woodi; Tenuitellinata, Tenuitella, and Catapsydrax spe cies – Li et al., 1992;

Spezzaferri, 1994, 1995; Spezzaferri and Æoriæ, 2001;

Spezzaferri et al., 2002; Rögl and Spezzaferri, 2003; Bicchi et al., 2003, 2006; Roetzel et al., 2006). Warm-tem per ate sur face wa ters are sug gested by the pres ence of Globigerinoides (e.g., Globigerinoides trilobus, G. primordius, G. quadrilobatus) and Paragloborotalia (e.g., Paragloborotalia continuosa, P.

semivera) groups, and the spe cies Globigerina ciperoensis (Spezzaferri, 1994; Rögl and Spezzaferri, 2003; Bicchi et al., 170 Szabolcs-Flavius Székely, Claudia Beldean, Raluca Bindiu, Sorin Filipescu and Emanoil Sãsãran

* Supplementary data associated with this article can be found, in the online version, at doi: 10.7306/gq.1245

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2003; Amore et al., 2004). A sur face wa ter warm ing trend was iden ti fied in sam ples T2–T7 (Chechiº For ma tion), with grad u - ally in creas ing amounts of Globigerinoides trilobus and a de - crease in the abun dance of Globigerina ottnangiensis. The abun dance of Globigerinoides trilobus abruptly drops in the fol - low ing sam ples. The de vel op ment of plank tonic as sem blages was prob a bly in flu enced by a change in ei ther the pro duc tiv ity or tem per a ture of sur face wa ters.

The de po si tion of the Chechiº For ma tion was gen er ally cor - re lated with an Eggenburgian warm ing in ter val (char ac ter ized by the Parvamussium duodecimlamellatum–Pecten hornensis Biozone, NN2 – Discoaster druggi Biozone and also by the M1 and M2 plantkonic foraminifera zones – Nicorici et al., 1979;

Moisescu and Popescu, 1980; Chira et al., 2000). Based on microflora as sem blages, Petrescu et al. (2000) char ac ter ized this in ter val as de vel oped in a warm, sub trop i cal cli mate. Cool - ing ep i sodes in the Transylvanian Ba sin were re corded only for the Ottnangian (Moisescu and Popescu, 1980; Chira et al., 2000). The warm ing trend iden ti fied at Tihãu prob a bly ap prox i - mates the event doc u mented by palynological data by £abãrã and Chirilã (2012) for the mid dle part of the Eggenburgian.

The good rep re sen ta tion of the cool-tem per ate sur face wa ter plank tonic spe cies at Tihãu may be also re lated to other palaeo - eco logi cal fac tors such as pri mary pro duc tiv ity. Nev er the less, the scar city of Med i ter ra nean el e ments and the lack of low lat i tude plank tonic foraminifera in the Coruº and Chechiº for ma tions men tioned by Popescu et al. (1995) sug gest com plex palaeogeographic set tings due to the geotectonic evo lu tion.

Plank tonic foraminifera are gen er ally ab sent or scarce across much of the in ner and mid dle shelf and their abun dance rap idly in creases across the outer shelf and up per slope (e.g., Phleger, 1951; Grimsdale and van Morkhoven, 1955; Bandy, 1956; Gib son, 1989; Van der Zwaan et al., 1990; Leckie and Olson, 2003). The plank tonic/ben thic ra tio could be in flu enced by var i ous fac tors, such as vari a tions in sa lin ity, pro duc tiv ity, ox - y gen a tion and con nec tion with the world oceans (e.g., Ulleberg, 1974; Naidu and Malmgren, 1995; Van Hinsbergen et al., 2005). Al though, the plank tonic/ben thic ra tio is not only re lated to wa ter depth, we con sider it as an in di ca tor of changes in paleobathymetry. The plank tonic/ben thic ra tio is poorly rep re - sented in the sed i ments (sam ples TH1 and TH2) above the

glauconite rich de pos its, while the re main ing sam ples (T1–T12) be long ing to the Chechiº For ma tion dis play fre quent os cil la - tions be tween 20 to 70%. In the up per part of sec tion (the Hida For ma tion, sam ples T13–T17) the P/B ra tio (be tween 40–70%) dis plays an in creas ing trend fol lowed by a de crease (Fig. 3).

Biostratigraphic anal y sis re vealed the pres ence of the plank tonic spe cies Globigerinoides trilobus (sam ples T1–T12 and T14, T15; Fig. 5F and G), which can be as so ci ated with the Globigerinoides trilobus Biozone (Aquitanian–Burdigalian) of Popescu (1975). Ad di tion ally, ac cord ing to Cicha et al., (1998) the strati graphic range of the spe cies Globigerina ottnangiensis (sam ples TH2–T12 and T14–T17; Fig. 5B) and Globigerina dubia (sam ples TH2–T4, T7–T12 and T14–T16) in the Cen tral Paratethys is Eggenburgian–Karpatian. There fore, based on the iden ti fied plank tonic foraminifera spe cies, the stud ied in ter - val can be as signed to the Burdigalian.

Ben thic foraminifera. Iva (1971) de scribed a foraminiferal as sem blage from the type sec tion of the Coruº For ma tion, but foraminifera have not been de scribed from this unit at Tihãu.

Sam ples TH1 and TH2 were re cov ered from the base of Chechiº For ma tion (Fig. 3). The low di ver sity ben thic as sem - blage from the low er most sam ple (TH1; Fig. 3) is char ac ter ized by Reticulophragmium venezuelanum (Fig. 6I), Budashevaella multicamerata (Fig. 6G), Textularia spp., Neugeborina longi - scata, Uvigerina spp., and very rare plank tonic foraminifera.

Ac cord ing to Murray (2006), the ag glu ti nated ge nus Textularia is an epifaunal form that pre fers hard sub strates with a depth range up to 500 m. Ad di tion ally, Kaminski et al. (2005) in cluded Budashevaella multicamerata in the M2b morphogroup of shelf to deep-ma rine ag glu ti nated foraminifera, while Nagy et al.

(2000) re ported the same spe cies as dom i nant in outer neritic to up per bathyal set tings. Reticulophragmium venezuelanum has been found in deep-wa ter set tings of An gola, Cam er oon (Seiglie and Baker, 1982; Preece, 1999), Ven e zuela (Preece, 1999), and In dia (Govindan, 2004). The cal car e ous Uvigerina from the same sam ple ap pears rarely in set tings shal lower than 100 m and it is also found in low-ox y gen en vi ron ments (Spezzaferri et al., 2002; Rögl and Spezzaferri, 2003). Based on the depth range of the con stit u ent spe cies, the sed i ments cor re spond ing to sam ple TH1 were prob a bly de pos ited in a tran si tional en vi ron men tal be tween the outer neritic and up per Palaeoenvironmental changes in the Transylvanian Basin during the Early Miocene revealed by the foraminifera assemblages 171

Fig. 4. The percent (relative to total benthic abundance) of most important benthic foraminifera species, genera and groups with similar palaeoecological affinities for samples T1–T17

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Fig. 5. Planktonic foraminifera from the Tihãu section, Chechiº Formation

A – Globigerina lentiana Rögl, sam ple T4; B – Globigerina ottnangiensis Rögl, sam ple T5; C – Globigerina gnaucki Blow

& Ban ner, sam ple T10; D – Globigerina bulloides d’Orbigny, sam ple T10; E – Globoturborotalita woodi (Jenkins), sam ple T4; F – Globigerinoides trilobus (Reuss), sam ple T7; G – Globigerinoides trilobus (Reuss), sam ple T7; H – Catapsydrax unicavus (Bolli), sam ple T8; I – Globigerinoides quadrilobatus (d’Orbigny), sam ple T5; A–E, G–I – ap er tural view; F – spi - ral view; all scales rep re sent 100 mm

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Fig. 6. Benthic foraminifera from the Tihãu section (Chechiº Formation – A, C, E–O, Q–R and Hida Formation – B, D, P)

A – Bathysiphon taurinensis Sacco, sam ple TH1; B – Nothia robusta (Grzybowski), sam ple T14; C – Ammodiscus miocenicus Karrer, sam ple T4; D – Psammosphaera fusca Schultze, sam ple T14; E – Saccammina grzybowskii (Schu - bert), sam ple TH1; F – Haplophragmoides carinatus Cushman & Renz, sam ple TH1; G – Budashevaella multicamerata (Voloshinova), sam ple TH2; H – Reticulophragmium acutidorsatum (Hantken), sam ple T3; I – Reticulophragmium venezuelanum (Maync), sam ple T4; J – Karrerulina apicularis (Cushman), sam ple TH1; K – Gaudryinopsis beregoviensis (Venglinskyi), sam ple T3; L – Spirorutilus carinatus (d’Orbigny), sam ple T4; M – Vulvulina haeringensis (Gümbel), sam ple T5; N – Bigenerina agglutinans Cushman & Ellisor, sam ple TH2; O – Textularia laevigata d’Orbingy, sam ple T1; P – Cylindroclavulina rudis (Costa), sam ple T14, Hida For ma tion; Q – Karreriella chilostoma (Reuss), sam ple T5; R – Semivulvulina deperdita (d’Orbigny), sam ple T5; A–R – side views; all scales rep re sent 200 mm

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bathyal. The very low spe cies di ver sity of the ben thic as sem - blage and dom i nance of these ag glu ti nated foraminifera sug - gest a stressed palaeoenvironment, pos si bly char ac ter ized by in ter vals of high pri mary pro duc tiv ity and low-ox y gen con di tions at the bot tom wa ters.

Sam ple TH2 (Fig. 3) ex hib its a higher di ver sity of the ben - thic as sem blage, with ag glu ti nated and cal car e ous forms, sug - gest ing more sta ble con di tions on the sub strate. Cal car e ous ben thic forms are rep re sented by the highly dom i nat ing Uvigerina popescui (in di ca tor of high pri mary pro duc tiv ity – Fig. 7C), Amphicoryna (A. armata sug gest ing suboxic bot tom wa ter), Lenticulina (L. calcar, L. inornata), Marginulina (in ner to outer neritic M. hirsuta – Culver, 1988; Fig. 8R), and Sphaeroidina (S. bulloides) spe cies, and the less epifaunal oxic forms such as Cibicidoides pseudoungerianus. Spirorutilus carinatus (Fig. 6L) be longs to the M2c morphogroup of ag glu ti - nated foraminifera (Kaminski et al., 2005) and is typ i cal for the shelf en vi ron ment. The ag glu ti nated forms (Budashevaella multicamerata, Haplophragmoides spp., Spirorutilus carinatus) to gether with cal car e ous ben thic foraminifera sug gest a pos si - ble shallowing of the depositional en vi ron ment to an outer neritic set ting char ac ter ized by high pri mary pro duc tiv ity and ep i sodic ox y gen de ple tion in bot tom wa ters.

Ma rine as sem blages ob served at the base of the sec ond out crop (T1, T2; Figs. 3 and 4) in di cate shal low-ma rine en vi ron - ments, with the high est spe cies di ver sity in di ces for the Tihãu sec tion. Spirorutilus carinatus, Semivulvulina pectinata, and Vulvulina haeringensis (Fig. 6M) can be men tioned among the most abun dant ag glu ti nated forms. Cal car e ous ben thic forms are rep re sented by oxic spe cies (e.g., Cibicidoides pachy - derma – Fig. 7O; C. ungerianus, Lobatula lobatula, Heterolepa dutemplei – Fig. 7R), low-ox y gen in di ca tors as Bulimina and Bolivina (Figs. 7A and 8S), and shal low-wa ter taxa such as Am - mo nia beccarii (Fig. 7U), Asterigerinata planorbis, spe cies of Elphidium (Fig. 7S) and miliolids (Parker, 1948; Bradshaw, 1957, 1961; Bandy and Arnal, 1960; Haake, 1977; Scott et al., 1980; Poag, 1981; Albani and Serandrei Barbero, 1982;

Jorissen, 1987; Walton and Sloan, 1990; Murray, 1991;

Almogi-Labin et al., 1992, 1995; Pawlowski et al., 1995;

Debenay et al., 1998; Alve and Murray, 1999; Buck et al., 1999;

Debenay and Guillou, 2002; Hay ward et al., 2004; Mendes et al., 2004; Spezzaferri et al., 2004; PippÀr and Reichenbacher, 2010). The in crease in shal low-wa ter taxa and abrupt de crease in Uvigerina spe cies (which is rarely <100 m – Rögl and Spezzaferri, 2003) com pared to the sam ples be low sug gest a shift to ox y gen ated, low pri mary pro duc tiv ity mid dle-neritic (50–100 m) en vi ron ments. The sta ble, well-ox y gen ated en vi - ron ment prob a bly en abled the di ver si fi ca tion of the as sem - blages. Fur ther more, the P/B ra tio of this in ter val (be tween 20–35%) sup ports the mid dle neritic depositional set ting.

The fol low ing sam ples (T3, T4; Figs. 3 and 4) con tain a high pro por tion of deep-wa ter (bathyal to abys sal) ag glu ti nated foraminifera (Govindan, 2004; Kaminski et al., 2005) such as Reti culo phragmium venezuelanum, R. acutidorsatum (Fig. 6H), R. rotundidorsatum, Karrerulina conversa and fewer shelf-type taxa. Cal car e ous benthics are rep re sented by spe cies of Uvigerina (Fig. 7), Cibicidoides, Lenticulina (Fig. 8) and spec i - mens of Hansenisca soldanii. The P/B ra tio is higher com pared to the older sam ples (45–55%). These as sem blages prob a bly orig i nated in an outer neritic to up per bathyal en vi ron ment.

The P/B ra tio peaks in sam ple T7 (Fig. 3), prob a bly by reach - ing the deep est en vi ron ments on the shelf. The pres ence of miliolids and Am mo nia beccarii (Figs. 3 and 4) is prob a bly re lated to trans por ta tion of ben thic foraminifera from shal lower depths.

The up per most sam ples col lected from the Chechiº For ma - tion (T9–T12; Figs. 3 and 4) sug gest a trend of ox y gen de ple - tion (Bulimina and Bolivina spe cies) and high pri mary pro duc tiv - ity (Melonis pompilioides, Valvulineria complanata, Uvigerina popescui, Praeglobobulimina ovata – Fig. 7B), even if ep i sodes of well-ox y gen ated sub strates were pres ent.

The on set of turbiditic sed i men ta tion of the Hida For ma tion (T13–T17) changed the com po si tion of the foraminifera as sem - blages, which be came less abun dant and di verse, mostly dom i - nated by ag glu ti nated ben thic foraminifera (Fig. 3). These are rep re sented by tu bu lar (M1 morphogroup – e.g., Bathysiphon taurinensis Fig. 6A, Hyperammina spp., and Rhizammina spp.), rounded planispiral (M4a morphogroup – e.g., Cyclammina cancellata, Haplophragmoides spp., Reticulophragmium acutidorsatum, R. rotundidorsatum), rounded trochospiral (M2b morphogroup – e.g., Budashevaella multicamerata, Cribrosto - mo ides spp.), flat tened planispiral (M3a morphogroup – e.g.

Ammodiscus miocenicus – Fig. 6C; Popovia spp.), and elon - gate subcylindrical (M4b morphogroup – e.g., Cylindroclavulina rudis Fig. 6P) forms. Shal low-wa ter taxa are rare (e.g., Vulvulina haeringensis). These forms are char ac ter is tic for an up per bathyal depositional set ting.

Cal car e ous ben thic forms are rep re sented by spe cies of Cibicidoides, Lenticulina, spec i mens of Hansenisca soldanii, Melonis pompilioides, Praeglobobulimina ovata, Uvigerina popescui, U. graciliformis, Valvulineria complanata, and rare Bulimina, Bolivina, and Stilostomella (Fig. 7L and M) spe cies (Fig. 4). The pres ence of Am mo nia beccarii and other cal car e - ous ben thic spe cies in sam ples T15–T17 may be an ev i dence for ad vanc ing shal lower en vi ron ments due to an in creased progradation. The ini tial deep en ing trend fol lowed by shallowing is con firmed by the P/B ra tio (Fig. 3), with higher val ues in the lower Hida For ma tion (sam ples T13 and T14) and a sub se - quent grad ual drop (sam ples T14–T17).

SUCCESSION OF PALAEOENVIRONMENTS

The in ter pre ta tion of sedimentological trend and suc ces sion of foraminifera as sem blages al lowed the re con struc tion of palaeoenvironments suc ces sion in the Chechiº and Hida For - ma tions. The low er most ben thic foraminifera as sem blage from the Chechiº For ma tion (sam ple TH1; Fig. 3) in di cates an outer-neritic to up per bathyal palaeoenvironment (char ac ter - ized by high pri mary pro duc tiv ity) for the sed i men tary suc ces - sion above the in ter val with glauconite rep re sent ing the max i - mum flood ing sur face. The sed i ments above the glauconite can be as so ci ated to the Highstand Sys tems Tract de pos ited dur ing the late stage of the rel a tive sea level rise. A shallowing of the depositional set ting (outer neritic) was ob served in sam ple TH2.

This trend was also ob served in sam ple T2, where the palaeoenvironment was prob a bly char ac ter ized by a 50–100 m palaeodepth. Shal low en vi ron ments were char ac ter ized by a good ox y gen a tion of the bot tom wa ters and a low pri mary pro - duc tiv ity. The up per part of the Chechiº For ma tion (sam ples T3–T12) is char ac ter ized by mi nor palaeodepth os cil la tions oc - cur ring in an outer neritic en vi ron ment (an aggradational stack - ing pat tern of the parasequences), and ep i sodes of high pri - mary pro duc tiv ity. Bot tom wa ters were rel a tively well ox y gen - ated and prob a bly al ter nated with ep i sodes of ox y gen de ple - tion. In the up per most part of the Chechiº For ma tion, ben thic foraminifera as sem blages sug gest in tense high pri mary pro - duc tiv ity and en hanced ox y gen de ple tion in the bot tom wa ters.

The fre quent en vi ron men tal shifts in the Chechiº For ma tion 174 Szabolcs-Flavius Székely, Claudia Beldean, Raluca Bindiu, Sorin Filipescu and Emanoil Sãsãran

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Fig. 7. Benthic foraminifera from the Tihãu section (Chechiº Formation)

A – Bulimina striata striata d’Orbigny, sam ple T2; B – Praeglobobulimina ovata (d’Orbigny), sam ple T4; C – Uvigerina popescui Rögl, sam ple T4; D – Uvigerina posthantkeni Papp, sam ple TH2; E – Uvigerina continuosa Lamb, sam ple TH1;

F – Uvigerina graciliformis Papp & Turnovsky, sam ple TH1; G – Uvigerina acuminata Hosius, sam ple T8; H – Uvigerina farinosa (Hantken), sam ple T5; I – Lapugyina schmidi Popescu, sam ple T2; J – Fursenkoina acuta (d’Orbigny), sam ple T2; K – Siphonodosaria consobrina (d’Orbigny), sam ple T1; L – Stilostomella adolphina (d’Orbigny), sam ple T2; M – Stilostomella bradyi (Cushman), sam ple T2; N – Siphonina reticulata (Czjzek), sam ple T5; O – Cibicidoides pachyderma (Rzehak), sam ple T8; P – Cibicidoides pseudoungerianus (Cushman), sam ple T8; Q – Nonion com mune (d’Orbigny), sam ple T7; R – Heterolepa dutemplei (d’Orbigny), sam ple T8; S – Elphidium ortenburgense (Egger), sam ple T7; T – Chilostomella oolina Schwager, sam ple T4; U – Am mo nia beccarii (Linné), sam ple T7; Q, S, T – side views; O, P, R, U – spi ral views; all scales rep re sent 100 mm

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Fig. 8. Benthic foraminifera from the Tihãu section (Chechiº Formation)

A – Sigmoilopsis colomi (Glaçon & Magné), sam ple T2; B – Sigmoilopsis ottnangensis (Cicha, Ctyroka & Zapletalova), sam ple T5; C – Sigmoilopsis schlumbergeri (Silvestri), sam ple T3; D – Laevidentalina elegans (d’Orbigny), sam ple TH2;

E – Grigelis pyrula (d’Orbigny), sam ple T4; F – Dentalina acuta d’Orbigny, sam ple T5; G – Pseudonodosaria discreta (Reuss), sam ple T8; H – Lenticulina gibba (d’Orbigny), sam ple TH2; I – Lenticulina cultrata (Montfort), sam ple TH2; J – Lenticulina subpapillosa (Nuttall), sam ple T2; K – Lenticulina budensis (Hantken), sam ple TH2; L – Lenticulina reniformis (d’Orbigny), sam ple T3; M – Lenticulina sp., sam ple T8; N – Frondovaginulina tenuissima (Hantken), sam ple T7; O – Marginulinopsis tenuis (Bornemann), sam ple T2; P – Pyramidulina catesbyi (d’Orbigny), sam ple T2; Q – Marginulina similis d’Orbigny, sam ple T8; R – Marginulina hirsuta d’Orbigny, sam ple TH2; S – Bolivina antiqua d’Orbigny, sam ple T5; T – Siphogenerinoides vasarhelyi (Hantken), sam ple T8; A–T – side views; all scales rep re sent 200 mm

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were prob a bly the re sult of chang ing rates be tween rel a tive sea level and sed i men tary in put from the land (sed i men ta tion as so - ci ated with fan del tas on a nar row shelf). The sed i men tary log and suc ces sion of as sem blages con firms the tran si tion to the progradational stack ing pat tern dur ing the late highstand.

The re gional tec ton ics in flu enced the sed i men ta tion trend start ing with the de po si tion of Hida For ma tion. The tec tonic thrust of the Pienides (Krézsek and Bally, 2006) pro duced a deep en ing (up per bathyal) of the en vi ron ments from the lower Hida For ma - tion, as sug gested by deep-wa ter ag glu ti nated foraminifera as - sem blages (sim i lar to those de scribed by Filipescu and Beldean, 2008; Beldean and Filipescu, 2011; Beldean et al., 2011) and by the on set of the turbiditic sed i men ta tion. The shift to a clear progradational stack ing pat tern is dem on strated by the shallowing in ter val from the mid dle part of the for ma tion, where cal car e ous ben thic forms be come sig nif i cant. The trans port from shal lower en vi ron ments and progradational trend be come stron - ger in the up per part of the for ma tion.

CONCLUSIONS

The Early Mio cene suc ces sion of palaeonvironments ob - served in the Tihãu sec tion is re lated to the par tic u lar evo lu tion of the Transylvanian Ba sin un der global and re gional con trol.

The biostratigraphic study en ables the cor re la tion of the sed i ments with the Globigerinoides trilobus Biozone of Popescu (1975) in di cat ing a Burdigalian age for the de pos its.

A po ten tial warm ing event dur ing the sec ond part of the Eggenburgian (Chechiº For ma tion) has been ob served based on the tem per a ture pref er ences of plank tonic foraminifera as - sem blages. This event shows cor re la tion po ten tial to global events, al though a cal i bra tion is al most im pos si ble by plank tonic foraminifera only. Ad di tion ally, the pres ence of small sized plank - tonic foraminifera sug gests ep i sodic high pri mary pro duc tiv ity.

Fre quent shifts be tween mid dle neritic to up per bathyal palaeoenviromnents were ob served in the Chechiº For ma tion, while an up per bathyal depositional set ting was re stored for the Hida For ma tion. The dis tri bu tion of the cal car e ous ben thic

foraminiferal as sem blages through out the sec tion in di cate fluc - tu a tions in pri mary pro duc tiv ity and bot tom wa ter ox y gen a tion.

The sedimentology of the stud ied sec tion to gether with foraminiferal as sem blages al lowed the de lin ea tion of the evo lu - tion of the sed i men tary ba sin:

– the coarse grained lit to ral de pos its of the Coruº For ma - tion rep re sent the first term of Early Mio cene ma rine trans gres sion in the Transylvanian Ba sin;

– the glauconite fa cies from the base of the Chechiº For - ma tion can be as so ci ated with the max i mum flood ing sur face;

– the de po si tion of the sed i ments be long ing to the mid dle and up per part of the Chechiº For ma tion pro duced on a nar row shelf, prob a bly un der the in flu ence of prograding del tas dur ing the sub se quent highstand;

– the turbiditic sed i men ta tion spe cific for the Hida For ma - tion prob a bly was also as so ci ated to the highstand sys - tems tract, but in flu enced by re gional tec tonic con trol (up lift ing of the Pienides to the north).

The stud ied sec tion pro vides an over view on the dis tri bu tion in time and space of the foraminiferal as sem blages and sed i - men tary en vi ron ments from the north west ern Transylvanian Ba sin; it pro vides cri te ria for fa cies cor re la tion and al lows the re - con struc tion of a part of the re gional evo lu tion un der tec tonic con trol.

Ac knowl edge ments. We are grate ful to the re view ers M. Kaminski and A. Waœkowska, and the GQ ed i tor T.M. Peryt for their sug ges tions, com ments and cor rec tions which helped im prov ing the pa per. The re search of S-.F. Székely and R.

Bindiu was 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 Grzybowski Foun da tion’s “Brian J.

O’Neill Me mo rial Grant in-Aid” and the S.N.G.N. Romgaz (Con - tract 18/2011) are also warmly thanked for fi nan cial sup port.

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