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ACTA PALAEONTOLOGICA ROMANIAE V.5 (2005), P.423-439

PALEOGENE LITHO- AND BIOSTRATIGRAPHY OFTHE NE GETIC DEPRESSION (ROMANIA)

Relu - Dumitru ROBAN1

and Mihaela Carmen MELINTE2

Abstract: This paper presents the updated stratigraphy of the Paleogene from the NE of the GeticDepression, between the Cheia Valley (to the west) and Rul Doamnei Valley (to the east). The lithological

units are divided and correlated based on their litho- and palaeontological, as well as geochemicalfeatures. Five sections were detailed investigated in the field and analyzed from calcareous nannoplanktonpoint of view. The results of this study allow us to improve the lithostratigraphic nomenclature and to definea new lithostratigraphic unit - the Brdule Formation, which extends in the Early Oligocene-Early Mioceneinterval. Our work also brings new data on the sedimentology and stratigraphy of the Upper EoceneOlneti Formation, as well as of the Oligocene Cheia and Corbi formations. The nannofloralinvestigations point out the presence of the NP21, NP22, NP23, NP24, NP25, NN1 and NN2 calcareousnannoplankton zones, covering the latest Eocene (Late Priabonian) earliest Miocene (Early Burdigalian)interval. Fluctuation in the abundance and distribution patterns of nannofloras revealed significantpalaeoclimatic and palaeoenvironmental modifications in the studied area, during the Late Eocene,Oligocene and Early Miocene intervals, reflecting both regional and global changes of those times,including rapid and significant climatic modifications.

Keywords: Paleogene; litho- and biostratigraphy; sedimentology; palaeoenvironmental changes; CentralParatethys.

1

University of Bucharest, Faculty of Geology and Geophysics, Department of Mineralogy, Nicolae Blcescu Av., No. 1, 70111Bucharest, Romania, e-mail: [email protected] Institute of Marine Geology and Geo-ecology, Dimitrie Onciul Street, No. 23-25, RO-024053, Bucharest, Romania, e-mail:[email protected]

1. INTRODUCTION

The Paleogene is one of the most intriguingintervals in the Earth history, marked by significantchanges in palaeoclimate, marine productivity andin global carbon cycle.

During the Paleocene-Eocene thermalmaximum, reduced oceanic turnover, decreasesin global 13C and in marine productivity wereassumed (Aubry et al., 1996; Zachos et al., 2001;Braloweret al., 2002). Within the Early Oligocene

glacial maximum, intensification of deep oceancirculation, elevated 13C and high productivitywere supposed (Savin, 1977; Aubry, 1992;Zachos et al., 1996). Presumably, suddenchanges in climate and in ocean circulation mightoccur as result of gradual forcing, as certainphysical thresholds exceeded. The climate of thePaleogene seems to be a critical turning pointfrom a warm, humid and high-diversity"greenhouse" world of the Paleocene - Eoceneinterval to glacial "icehouse" conditions ofOligocene times.

Remarkably, the palaeogeography of the

European Tethys Realm significantly changesduring the Oligocene, due to the isolation of theParatethys Realm (in the Central and EasternEuropean regions - Bldi, 1980; Rusu, 1988;Rgl, 1998; 1999) from the Mediterranean Realm(in the Western and Southern part of Europe). Theevolution pattern of Paleogene marine biotas (andespecially of the most sensitive planktonic ones)mirrored the climatic deterioration and thepalaeoenvironmental changes.

Paleogene deposits are widespreadthroughout Romania, in the Carpathian belt. One

of the Romanian areas where the Paleogenedeposits are well preserved, allowing, based onthe nannofloral content to decipher theirbiostratigraphy, is the Getic Depression, locatedsouth of the Southern Carpathians (Fig.1).

Geological mapping and exploration for oil andgas in the Getic Depression drew attention forover a hundred years. Pioneer investigations ofthe geology of the Getic Depression belong totefnescu (1897), Murgeanu (1941a; 1941b),Iorgulescu (1953) and Popescu (1954). Thesepreliminary studies were followed by severalothers that elaborated on the stratigraphy of thePaleogene deposits in the Getic Depression (Fig.2; Ttrm, 1964; Popescu et al., 1976, 1977;Jipa, 1980; 1982; tefnescu, 1980; Bombi etal., 1980).

Over the last decade, the investigation in theGetic Depression continued with moresedimentological and biostratigraphical works,such as Jipa (1994), Rusu et al. (1996) and Ryer(1998).

Notably, the most reliable biostratigraphic datafor the Oligocene deposits of the Getic

Depression are offered so far by the study of thecalcareous nannofossils (Popescu et al., 1976;Rusu et al., 1996). The foraminifers appear to begood stratigraphical markers mostly for theEocene deposits (Ttrm, 1964; Bombi et al.,1980). In the Oligocene sediments they are veryscarce or even absent. Yet the Oligocenemacrofaunas present is quite rare, with a notableexception - the fish remains. The fish fossils arefrequent and quite well preserved, but becausemost often taxa having a wide range are present,


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Fig.

1.GeologicalmapoftheNEGeticDepression(modifiedafterMurgeanuetal.,1967;Popescuetal.,1976,1977;Lupuetal.,1978;Bombi

etal.,1980;

Dimitrescu

etal.,1978;MorariuandTeodorescu,1987,andRyer,1998)


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Paleogene litho- and biostratigraphy of the NE Getic Depression (Romania)

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they are not appropriate for high-resolutionbiostratigraphic studies.

The purpose of this paper is to present anupdated stratigraphy of the Paleogene successionin the NE of Getic Depression, between theVlcea county border in the west and the Argecounty border in the east (Fig. 1).

According to the sedimentological,geochemical as well as palaeontologicalevidences, the lithostratigraphy of the Paleogenesuccession in the study area is interpreted withina new biostratigraphic framework. Based on thecalcareous nannoplankton fluctuation pattern wedocument significant palaeoenvironmental andpalaeogeographical changes that characterizedthe Paleogene evolution of the Getic Depression.

2. GEOLOGICAL SETTING

The Getic Depression is situated within a

foreland basin formed in front of the SouthCarpathians, in response to the flexural loading ofthe Moesian Platform (Fig. 1). The GeticDepression covers a large part of the foredeepdepozone (DeCelles and Giles, 1996) of theSouth Carpathian foreland basin, which presentlyis highly deformed (Sndulescu, 1984, 1988;Mutihac, 1990; Mota et al., 1995; Dicea, 1996;Maenco, 1997; Rbgia and Maenco, 1999).The Pericarpathian Fault marks the boundarybetween the Getic Depression and the MoesianPlatform, while the Intra-Moesian Fault separatesthe Getic Depression from the South Carpathians

(Sndulescu, 1984).In the northern part, the basement of the GeticDepression consists of a nappe system in whichfour major tectonic units are recognized: theDanubian, Severin, Getic and Supragetic Nappes(Sndulescu, 1984). In the south, the MoesianPlatform represents the basement of the GeticDepression.

Following the Cretaceous deformation in theCarpathians (Sndulescu, 1984), the SouthCarpathians entered a phase of large-scaledextral deformation that caused E-W contractionand subsidence in the Getic Depression

(Ratschbacheret al., 1993).The Paleogene of the Getic Depression,exposed west of Olt Valley, is characterized,according to Popescu et al. (1996) by thesuccession of the following lithostratigraphic units(Fig. 2): (1) the Climneti Conglomerates, (2)the Cheia Conglomerates, (3) the Pucioasa typeMarls, and (4) the Muiereasca Sandstone. Inaddition, massive sandstones (the CorbiSandstone) are exposed in the eastern part of theOlt Valley.

3. DATA BASE AND METHODS

Several stratigraphic sections were measuredat five localities: Cheia, Olneti, Muiereasca,Vlsan and Rul Doamnei valleys (Fig. 1). A

simplified composite stratigraphic sectionmeasured at each locality is shown in Fig. 3.

Petrography of sandstones and conglomerateswas undertaken in thin-sections and acetate peelsanalized under Nikon E400-POL and Zoom NikonSMZ 800 microscopes, respectively. The organic-matter content was estimated based on thelosson ignition method of Heinri et al. (2001), where 5grams of sample are in combustion at 550C forfour hours. The carbonate content (%CaCO3) wasanalyzed with an Eijkelkamp calcimetre.

All measured successions were sampled forcalcareous nannoplankton investigations. Thenannofloral studies focused on qualitative analysisand were carried out under a microscope withcross-polarized light, at 1600x magnification. Thecalcareous nannofossil taxonomy follows Perch-Nielsen (1985).

4. RESULTS

4.1 Olneti FormationStratigraphy and sedimentologyThe Olneti Formation (Ryer, 1998), also

described as the Lower Marls (Murgeanu, 1941b)or the Olneti Marls (Popescu et al., 1976)continuously crops out between the Cheia Valleyto the west and Rul Doamnei Valley towards theEast (Fig. 1, Fig.3). The stratotype of this unit isexposed along the Olneti Valley, where thesuccession is 350 m thick. Over the entire studyarea this unit ranges in thickness from 200 m inthe Cheia Valley to a maximum of 600 m in the

Muiereasca Valley (Fig. 3).The lower boundary of the Olneti Formationshows a gradual transition to the underlyingClimneti Formation. North of the BrdetVillage, Jipa (1980, 1982) mapped a 40-50 mthick, westward thinning matrix-supportedconglomeratic unit, termed the TilloidConglomerates Level, which extends over 40 kmbetween Vlsan and Olt (Sltruc) valleys, were is~ 0.55 m thick. This unit is characterized by a verypoor sorting. Locally, it contains some very largeclasts, up to 3 m length. Notably, in theMuiereasca Valley, several thin coarse-grained

beds are scattered throughout the lower 30-50 min the lower part of the Olneti Formation. Thesebeds do not share the same characteristics thatJipa (1982, 1984) described within the TilloidConglomerates Level. The Tilloid ConglomeratesLevelcould be used as lithological marker for theboundary between the Climneti Conglome-rates and the Olneti Marls.

At the top, the Olneti Formation is bothdisconformity overlain by the Cheia Formation(towards the west) and by the Corbi Formation(towards the east). In the central part (i.e. Topologand Arge valleys), the Olneti Formation, is

paraconformity overlain by a sequence ofbituminous mudstones, described herein as theBrdule Formation.


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Fig.

2.Mainpreviousstratigraphicalschem

esofthePaleogeneoftheNEGetic

Depression


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On the Vlsan Valley, the Olneti Formationis composed of mudstones (up to 70%),sandstones (20%) and subordinateconglomerates. The lower part of the OlnetiFormation consists of approximately 45 m ofmatrix-supported conglomerates and gravelymudstone. The matrix is muddy, locally reachingup to 90% of the rock volume.

The sandstones of the Olneti Formationrange in thickness from centimeters todecimeters. In the lower 45 m of the succession,individual sandstone beds associated with clast-supported conglomerates may reach metricthickness. The sandstones are lithic to sublithicand occasionally contain abundant bioclasticmaterial (nummulite shells). The most commonsedimentary structures include massive, normalgrading as well as parallel stratification/lamination,frequently yielding current ripples (Jipa, 1980,1982, 1994, Ryer, 1998; Roban et al., 2005 b).

Trace fossil assemblages include Ophiomorphasp. and Skolithos sp. (Brustur, pers. comm.)typical of shallow marine environments.

In the Olneti Formation, the conglomerates(up to 3 m in thickness) have a lenticular shapeand display normal grading and intense scouringat their lower bounding surfaces. Their polymicticclast composition reflects the proximity to thesource area located in the rising of the SouthernCarpathians.

Thin beds of laminated mudstones representthe finest grain-size recorded in the OlnetiFormation and have 3 - 10 % CaCO3. Sometimes

they form couplets with silt laminae. The organicmater contents are of 3-5%.The Olneti Formation was divided, in the

Vlsan Valley section, into three distinctlithofacies (Morariu and Teodorescu, 1987; Robanet al., 2005 b):

(1) gravely mudstones, (45 m), occurring onlyat the base, with conglomerates and sandstonelevels;

(2) heterolithic thin-bedded sandstones andmudstones, having a recurrent character. Twosequences of this lithofacies, the oldest in themiddle part of the Olneti Formation (75 m in

thickness) and the youngest towards the top (175m in thickness) were recognized;(3) mudstones and siltstones (85 m in

thickness), with parallel lamination, interbeddedwith rare massive or parallel laminatedsandstones. This lithofacies is present in themiddle part of the Olneti Formation.

Biostratigraphy and ageBased on its foraminiferal and nannofloral

content, the Olneti Formation was previouslyassigned to the Lutetian and Priabonian stages(Popescu et al., 1976; Rusu et al., 1996). Notably,

the Eocene/Oligocene boundary (the NP21Calcareous Nannoplankton Zone of Martini, 1971)is placed in its uppermost part (Fig. 3).

The samples collected from the topmost of theOlneti Formation (Fig. 3) contain taxonomicaldiversified and very well preserved calcareousnannofloral assemblages. These assemblagesinclude, as biostratigraphical significantnannofossils, Discoaster saipanens Bramlette &Riedel, D. barbadienis Tan, Clausicoccusfenestratus (Roth & Hay) Prins, Discoaster tanii(Bramlette & Riedel) Bukry and Helicosphaerareticulata Bramlette & Wilcoxon. All these taxahave their last occurrence (LO) at the top of theEocene (lower part of the NP21 CalcareousNannoplankton Zones Martini, 1971; Perch-Nielsen, 1985; Krhovsk et al., 1993; Melinte,1995). The above-mentioned findings indicate thatthe upper part of the Olneti Formation is latestEocene age (Late Priabonian) and, theEocene/Oligocene boundary is located immedia-tely below the top of formation (Figs. 3, 4).

4.2. Cheia FormationStratigraphy and sedimentologyWe apply in this paper the name Cheia

Formation to designate a distinct lithologic unit,which could be map in the whole study area,stratigraphically overlying the Olneti Formation.Previously, the Cheia Formation was referred inthe literature as the Cheia Conglomerates(Popescu et al., 1976).

The type locality of this formation is the CheiaValley (Figs. 1, 3) where it reaches a maximumthickness of 500 m. Towards the East, the CheiaFormation thins to a minimum of 20 m at

Muiereasca Valley (Fig. 3). According to someauthors (Popescu et al., 1976; Bombi et al.,1980; Jipa, 1994), the formation completelypinches out east of Olt Valley (Fig. 1). However,Ryer (1998) described as Cheia Conglomerates apackage of 75 m, located at the base of thePucioasa like Formation in the Topolog Valley(Fig. 1).

In the Cheia and Olneti valleys, theboundary between the Cheia and Olnetiformations is a disconformity one, while in theMuiereasca valley, the Cheia Formation pinch outlaterally to the Brdule Formation (Figs. 3, 4).

The Cheia Formation is a coarse-grained unit,dominated by pebble and cobbles conglomeratesthat make up to 80 % of the entire succession.

Apart from pebbles and cobbles, the grain sizespectrum includes also, boulders and even metre-scale blocks. In general, a relation ofproportionality is observed between the grain sizeand the thickness of individual beds. Thus, thecoarsest units have the maximum thickness in thesuccession. However, there are some decimetre-thick beds that, which although can be consideredthin, and they contain decimetre-long clasts.These particular beds pinch out within several

tens of meters.


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Fig.

3.Lithologyandbiostratigraphyoftheinv

estigatedsectionsfromt

heNEGetic

Depression


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Most of the conglomeratic beds have a widerange of thickness, from 30 cm to 5 m (due toamalgamation), while their lower surface showsscouring. Most commonly, the base of these bedsis flat (Ryer, 1998).

We can suppose that the observed variation inthickness is due to the amalgamation process. Weuse herein the term amalgamation to indicate amix process, erosional-constructional, leading to adepositional unit, homogenous lithologically,yielding a bigger apparent thickness, and having amultistory deposition (sensu Clark and Pickering,1996).

Internal structures include massive, normaland reverse grading, diffuse parallel bedding andimbrications. The particularity of theseconglomerates is rapid transition, vertically andlaterally, in some meters, between types ofinternal structures of the same depositional unit.

Jipa (1982, 1994) also found oblique

stratifications, at medium and large scale.At Olneti and Cheia localities, the middlerespective upper part of the Cheia Formationconsists of several 30 cm up to 3 m, thick matrix-supported conglomerates that contain bothextrabasinal as well as muddy intraclasts (Fig. 1).The matrix is muddy.

Petrographic analysis of the conglomeratesthroughout the stratigraphic succession suggesteda polymictic origin with fragments of metamorphicand sedimentary rocks (limestones, marls andsandstones).

Associated with the conglomerates there are

massive, and diffuse parallel bedded sandstones.Mudstones interbedded with thinly beddedsiltstones and very fine-grained sandstones arepresent towards the top of the succession.

The general trend of the succession illustratedin the stratigraphic logs of Fig. 3 is fining andthinning upward. The megasequence consists offining-upward cycles composed of conglomerates,sandstones and sometime mudstones. Each cycleis about 5-10 m and has a flat or sometimescoured erosional base (Ryer, 1998; Roban,2004).

Biostratigraphy and age

Previous studies on the biostratigraphy of theconglomeratic succession, termed here the CheiaFormation, indicated that the duration of theformation extends over the entire Rupelian stageof Early Oligocene (Popescu et al., 1976; Bombiet al., 1980). Rusu et al. (1996) indicated anearliest Oligocene (Early Rupelian) age for theCheia Formation. According to the above-mentioned studies, the Late Rupelian (includingthe Rupelian/Chattian boundary interval) wascharacterized by the deposition of the LowerDysodilic Shale Formation (organic-rich,bituminous shales).

The samples collected in this study at Cheia,Olneti and Muiereasa localities (Figs. 1, 3)contain scarce calcareous nannoplankton

associations with a poor to moderatepreservation.

The nannofloras from the base of the CheiaFormation are dominated by holococcoliths, suchas Isthmolithus recurvus Deflandre in Deflandre &Fert, Zygrhablithus bijugatus (Deflandre inDeflandre & Fert) Deflandre, Orthozygus aureus(Strdaner) Brameltte & Wilcoxon and Lanternitusminutus Stradner, as well as by reticulofenestrids- Reticulofenestra hillae Bukry & Percival and R.umbilica (Levin) Martin & Ritzowski. Based on theidentified nannofloras, the base of the CheiaFormation is placed in the earliest Oligocene(Early Rupelian) - the NP22 CalcareousNannoplankton Zone (Fig. 3).

A significant change in nannofloral compositionwas noted within the lower part of the CheiaFormation. The presence of the NP23 CalcareousNannoplankton Zone of Martini (1971) is arguedby the first occurrence (FO) of the nannofossils

Reticulofenestra lockeri Mller, Dictyococcietsornatus (Mller)Bistrick, Transversopontis fibulaGheta and T. latus Mller. Remarkably, these areendemic species (Bldi-Beke, 1981; Krhovsky etal., 1992; Nagymarosy and Voronina, 1992;Melinte, 1993, 1995; Rusu et al., 1996 b), relatedto the first isolation of the Paratethys Realm.

The samples collected form the upper part ofthe Cheia Formation (in the Cheia Valley) containnannofloras dominated by cosmopolitannannofossils, as Dictyococcites bisectus (Hay etal.) Bukry & Percival, Reticulofenestra ornataMller, Cyclicargolithus floridanus (Roth & Hay)

Bukry, Pontosphaera latelliptica (Bldi-Beke &Bldi) Perch-Nielsenand Sphenolithus moriformis(Brnnimann & Stradner) Bramlette & Wilcoxon.The top of the Cheia Formation containsSphenolithus ciperoensis Bramlette & Wilcoxon,which is the marker species of the NP24Calcareous Nannoplankton, latest Rupelian earliest Chattian in age (according to Melinte,1995, 2005).

4.3 The Corbi FormationStratigraphy and sedimentologyWe apply the name Corbi Formation to

describe a 250 m thick sandstone-dominatedsuccession exposed in the Rul Doamnei Valleysection (Corbi village - Figs. 1, 3). This unit,previously referred as the Corbi Sandstone(tefnescu, 1897), is exposed between theVlsan and Rul Doamnei valleys (Murgeanu,1941: Figs. 1, 3; Jipa, 1980). Morariu andTeodorescu (1987) considered that the CorbiSandstone extends also in the Arge Valley (Fig.2).

The lower lithological boundary of the CorbiFormation with the underlying Olneti Formationis a disconformity one (Fig. 3). At the upper part,

the Corbi Formation fines upwards and has agradual contact with the overlying BrduleFormation (Fig. 3). Overall, the Corbi Formationshows a fining upward succession.


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Our study revealed that, lithologically, theCorbi Formation consists predominantly ofsandstones (50%), and subordinately ofconglomerates (35%) and mudstones (15 %).

The sandstone beds range in thickness from afew centimetres to several metres, this variationmost probably resulting from depositionalamalgamation processes. The maximumthickness measured within an amalgamated unitis 10 m. Main sedimentary structures includemassive, normal grading, current and ripples,parallel lamination/stratification and scouring (rip-up clasts). Deformational soft-sediment andliquefaction structures are abundant. Severalcentimetres pebble stringers or lenticular pebbleconglomerate beds are also present within thethick sandstones. Petrographical analysis of thesandstones revealed the predominance of lithic tosublithic types with some subordinate quartz andfeldspatic sandstones present as well.

The conglomerates are more abundant in thelower part of the Corbi Formation (Fig. 3), whereform several metres thick packages due toamalgamation. They are generally clast-supportedconglomerates. The main structures includemassive, normal grading and parallelstratification/lamination (Jipa, 1980, Ryer, 1988,Roban, 2004) and abundant scouring such as rip-up clasts. In the Vlsan Valley section (Figs. 1, 3),within the lower part of the formation, theamalgamated thickness of the conglomeratic bedsis up to 10 m. There the maximum grain sizevaries between boulders to cobbles, while the

matrix consists of medium-sorted pebbles. Thelargest clasts tend to be oriented parallel with thegeneral stratification. Above these levels as wellas in the Rul Doamnei Valley, the coarse bedsbecome thinly bedded with individual beds (oneevent) ranging between 10 cm to 1.5 m and grainsize decreases to pebbles and granules.Petrographically, the conglomerates arepolymictic with both metamorphic andsedimentary clasts.

In the Vlsan Valley section, towards the lowerpart of the Corbi Formation (the lowest 25 m), thegrain size ranges from cobbles to granules, and

has a fining upward trend. In the iei Valley, thelower 30 m of the Corbi Formation (overlaying theBrdule Formation) consists of granular to pebblyconglomerates that progressively grade verticallyinto sandstones. Thus, the middle part of theformation is sandstone-dominated and consists of2 to 10 m thick massive sandstones interbeddedwith 0.5 m thick sequences of sandstones andsiltstones. The upper part of the Corbi Formationconsists of vertically stacked fining upwardsequences, that contain 1 to 3 m thicksandstones, capped by 1 to 3 m thick heterolithicthinly bedded sandstones and dark mudstones.

The boundary between the Corbi and the Brduleformations is gradational and expressed by theprogressive increase of the mudstone interbedson the expense of sandstone beds.

Biostratigraphy and agePrevious studies (Murgeanu, 1941; Jipa, 1980,

1982; Bombiet al., 1980) considered the CorbiSandstone to be a distal facies of the Cheiaconglomerates, and consequently assigned it tothe Early Oligocene age (Rupelian). Recently,Ryer (1998) assumed that the Corbi Sandstone issynchronous with the upper part of the PucioasaFormation of Late Oligocene (Chattian).

The calcareous nannoplankton analysis of theCorbi Formation, collected at the stratotypelocality (Corbi village on Rul Doamnei, Figs. 1, 3)revealed that the base of the Corbi Formation liesin the Upper Oligocene (Chattian) within the NP24Calcareous Nannofossil Zone. This is indicated bythe common occurrence of the nannofossilsSphenolithus ciperoensis, Cyclicargolithusabisectus, Chiasmolithus altus, Dictyococcitesbisectus and Zygrhablithus bijugatus. Thenannofloras of the Corbi Formation are diversified

(up to 30 taxa were recorded), moderatelypreserved and contain mainly cosmopolitan taxasuch as Dictyococcites bisectus, Cyclicargolithusabisectus, C. floridanus, Sphenolithus moriformisand Coccolithus pelagicus (Wallich) Schiller. It isvery important to note the increase in abundanceof the genera Sphenolithus and Discoaster, whichare taxa confined mostly to warm surface waters,within the samples collected from the lower part ofthe Corbi Formation. At the upper part of this unit,the FO of the nannofossil Pontosphaera enormisindicates the base of the NP25a CalcareousNannofossil Subzone of Melinte (1995).

4.4. The Brdule FormationStratigraphy and sedimentologyThe name of Brdule Formation is firstly

introduced in this study to describe a successioncomposed of bituminous mudstones with rare andthin sandstones beds. This succession is exposedall over the study area and was measured at allfive localities (Fig. 1).

Previously, this succession was described asthe Upper Marls (Murgeanu, 1941), Pucioasa-typeMarls (Popescu, 1954), Dysodilic Shales (Morariuand Teodorescu, 1987), Pucioasa Formation

(Rusu, et al., 1996) and the Pucioasa likeFormation (Ryer, 1998).In the Muiereasca Valley, the lower part of the

Brdule Formation was separated as a distinctunit, named the Dysodilic Shale Formation (Rusuet al., 1996).

Between the Olt and the Arge valleys, a pileof rocks, predominantly muddy, lacking sandyand/or conglomeratic intercalations, wasdescribed as a distinct lithological unit - the JibleaMarls by Iorgulescu (1953). In fact, our data andthe field observations indicate that the lower partof the Jiblea Marls represents the top of the

Olneti Formation, while its upper part is thebase of the Brdule Formation, having distinctlithological features (see above).


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The stratotype of the new described BrduleFormation is situated in the Vlsan Valley section,near the Brdule village. At the type locality, theBrdule Formation is 500 m thick. Its thicknessvaries in the study area, from a maximum of 600m measured in Muiereasca Valley to a minimumof almost 300 m, recorded at Rul DoamneiValley (Fig. 3).

The Brdule Formation overlies the CheiaFormation in the western part of the study area,and the Corbi Formation in the eastern part (Fig.3). At both extremities, the lower boundary isgradational and characterized by a progressivevertical fining from the coarse Cheia and Corbiformations (Fig. 3).

As proved by the calcareous nannoplanktoncontent, the Cheia and the Corbi formations arecontemporaneous with the lower part of theBrdule Formation. Due to this lateral faciesvariation, the Brdule Formation directly overlain,

in the Muiereasca Valley, the Olneti Formation.Notably, some of the thin facies of the CheiaFormation as well as those from the upper part ofthe Corbi Formation are brownish mudstones andcalcareous clays, being similar with those of theBrdule Formation (cropping out in the iei andRul Doamnei valleys).

In the central part of the study area, betweenthe Olt and the Arge rivers (Fig. 1), we supposethat the Brdule Formation paraconformityoverlying the Olneti Formation, but the contactbetween the two units is not exposed in anyoutcrop. Probably this is the reason that

determined Iorgulescu (1953) to separate a singlelithological unit the Jiblea Marls - in the above-mentioned area, used also by Bombi et al.(1980) - Fig. 2.

At the top, the Brdule Formation isdisconformity bounded by the MuiereascaFormation (also called the Muiereasca Sandstone,Popescu et al., 1976), between the Olneti andMuiereasca valleys, conformity bounded by theGura Vii Formation in the Cheia Valley and,respectively, by the Srata Gypsum, between theVlsan and Rul Doamnei valleys. In the VlsanValley, the Brdule Formation is disconformity

overlain by the Mu Conglomerates, whichlocally eroded the Srata Gypsum (Figs. 1, 3, 4).The rock-succession of the new described by

us Brdule Formation is mudstone-dominated(80%). Sandstone and very rare conglomeratebeds add to 15%, and respectively 5% of theremaining succession. The most obvious featureobserved in outcrops is the black to dark brownishcolour of the mudstones.

The dark colour of the mudstones resultedfrom a generally high content in organic matterthat averages to 4-6% with a maximum of 27%.This suggests the development of an expanded

oxygen minimum layer in the basin at the time ofdeposition and the presence of bottom wateranoxia that facilitated the preservation of organicmatter. Gypsum efflorescences and sulphur-like

weathering are abundant within the mudstonesand probably resulted from the oxidation of theauthigenic pyrite. Fish scales, teeth and bones arealso common and they are similar to thosecommonly preserved in the Lower OligoceneDysodilic Shale Formation of the EasternCarpathians. Moreover, in the Muiereasca Valleysection several complete fish specimens ofEomyctophum sp. were recovered (Constantin,2004, pers. comm).

The carbonate content of the laminatedmudstones is relatively low between 0.5 to 10%CaCO3. Some marly levels of the BrduleFormation, from the Olneti, Muiereasca, Vlsanand Rul Doamnei valleys, yielded a content ofthe calcium carbonate between 55 to 75%. Theintervals that are richer in organic matter usuallyform cm-thick couplets with the more marlymudstones.

On the Vlsan Valley there are some cm-thick

bentonites derived from the chemical weatheringof volcanic ashes (Morariu and Teodorescu,1987). Unfortunately, these beds have no alaterally continuity and therefore could not beused as lithological markers.

The sandstones consist of 1 cm up to 30 cmthick beds, yielding a parallel lamination/stratification, current ripples, lenticular and flaserbedding. In addition, abundant soft-sedimentdeformational structures, such as load casting andballs-and-pillows are present along the lowerbounding surfaces. The sandstones are rich inlithic fragments and locally may contain abundant

carbonaceous material and wood fragments.In the iei Creek section, some of the bedsshow particular lithification and bioturbation similarto a hardground cementation (Anastasiu, 2004,pers. comm.)

The coarse-grained beds consist of 40 cmthick granular to pebbly sandstones and arecharacterized by scouring and lenticular shape,most probably representing event beds.

Besides its diagnostic lithological features,above-mentioned, large lithological variationswere recorded laterally (from west to east) withinthe Brdule Formation (Roban et al., 2005a),

particularly in its lower part.In the Cheia Valley section, the boundarybetween the Brdule Formation and theunderlying Cheia Formation is placed within a 15m thick interval consisting primarily of a matrixsupported conglomerates. These conglomeratesdisplay overwhelming evidence for mass transportsuch as soft-sediment deformation structures(slumps), chaotic grain size distribution andabundant mudstone intraclasts. Associated withthe matrix-supported conglomerates and gravelymudstones there are lenticular-shaped sandstonebeds, suggesting channel morphologies. The

main sedimentary structures include massive, butalso normal grading, and parallel stratification inconglomerates, as well as current ripples, normalgrading and parallel lamination in sandstones,


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which locally passed to massive ones (Bombietal. 1980; Jipa 1980, 1982; Ryer, 1998; Roban et.al., 2005a). Scouring is commonly found at thebase of all coarse deposits. Additionally, soft-sediment structures such as load casting andliquefaction are present. In the Cheia, Olnetiand Muiereasca sections, towards the middle partof the rock-sequence of the Br

dule

Formation

there are some lenticular matrix-supportedconglomerate and sandstone beds, up to 10 mthick, (Popescu et al., 1976; Bombiet al., 1980).

The coarse-grained lower part of the BrduleFormation, recorded in the Cheia and Muiereascasections, pinch out to the east, where thesuccession is characterized by laminated darkmudstones, locally containing several cm thick (upto 0.3 m) fine-grained sandstones. Thus, theconglomeratic packages are missing in the RulDoamnei and Vlsan valley sections (Fig. 3).

In the Muiereasca Valley, an approximately 20

m thick matrix-supported conglomerate ofdiamicton aspect represents the upper part of theBrdule Formation. The matrix consists ofmudstone and represents about 70% of thevolume of the rock. The clasts are extremely largeblocks, reaching a maximum of 5 m in length(Popescu et al., 1976). Within this coarsepackage, beds of coarse-grained sandstones andpebble-conglomerates form up to 2 m thick units(Jipa, 1994).

Biostratigraphy and ageAs evidenced by the calcareous nannofossil

investigations, the whole succession of theBrdule Formation covers a quite large interval the Early Rupelian Early Burdigalian (Ithe NP22-NN2calcareous nannofossil zones respectively).

The calcareous nannoplankton assemblagesfrom the Muiereasca Valley and Valey iei Creek(below the base of the Cheia Formation, andrespectively that of the Corbi Formation) wereassigned to the NP22-NP24 calcareousnannofossil zones (Fig. 3), covering the Rupelianstage pro parte, including the Rupelian/Chattianboundary interval. As significant nannofossilevents, the successive FO of Reticulofenestra

lockeri, Transversopontis fibula, Reticulofenestraornata, Cyclicargolithus abisectus andSphenolithus ciperoensis were observed.

It is worth mentioning that most of the previousstudies (Murgoci, 1941b; Popescu et al., 1976;Bombi et al., 1980) included the black to darkbrown bituminous mudstones of the lower part ofthe Brdule Formation in the Olneti Marls (=the Lower Marls). Rusu et al. (1996) separatedthis sequence as a distinct lithological unit andnamed it the Lower Dysodilic Formation. Theabove-mentioned authors, based on lithologicalsimilarities as well as on the age proved by

nannofloras, applied the lithological nomenclature,commonly used in the Paleogene EasternCarpathian Flysch Zone, to designate formationsof the Getic Depression. Rusu et al. (1996)

describe as Lower Dysodiles a sequence whichboth overlies the Olneti Marls (in MuiereascaValley), and the Cheia Conglomerates (in theCheia Valley). The age assigned by Rusu et al.(1996) for the Lower Dysodile Formation in theGetic Depression is Late Rupelian to EarlyChattian (covered by the NP23 and lower part ofNP24 calcareous nannoplankton zones).

As it was underlined above, the dark-brownishdeposits (cropping out in the Muiereasca Valley,between the Olneti Formation - at the base, andthe Cheia Formation - at the top), formerlyassigned by Rusu et al. (1996) to the LowerDysodiles, are included herein in the BrduleFormation.

Based on the identification of the nannofossilChiasmolithus altus, in samples collected from thetop of the Cheia Formation (just bellow the baseof the Brdule Formation, in the Cheia Valley,Fig. 3), the NP24 Calcareous Nannoplankton

Zone (Early Chattian in age) was recognized.Thus, we can assume that in the Cheia section,the base of the Brdule Formation is placedwithin the Rupelian/Chattian boundary interval.

At the Corbi locality (Rul Doamnei, Figs. 1,.3), the presence of the nannofossilsPontosphaera enormis, Sphenolithus ciperoensis,Dictyococcites bisectus, Cyclicargolithusfloridanus and C. abisectus, identified towards thelower part of the Brdule Formation, just abovethe Corbi Formation, indicates a latest Oligoceneage (Late Chattian - the NP25 CalcareousNannofossil Zone).

Based on these evidences, we can state thatthe base of the Brdule Formation isdyachronous, being situated in a large interval Rupelian Late Chattian.

In the stratigraphic succession of the BrduleFormation from the Rul Doamnei section (theCorbi village, Figs.1, 3), the successive firstoccurrence of the Triquetrorhabdulus carinatusMartini, Helicosphaera scissura Mller,Coccolithus miopelagicus Bukry andReticulofenestra pseudoumbilicus Gartnerindicates the presence of the NN25, NN1 andNN2 calcareous nannoplankton zones of Martini

(1971), Late Chattian-earliest Burdigalian in age(Melinte, 2005).As in the Eastern Carpathian area (Melinte,

1993), the base of the Miocene (the NN1Calcareous Nannoplankton Zone) is characterizedby significant reworking. Thus, only 25% of thetotal nannofloras represent in situ assemblages,the remaining 75% being Cretaceous, Eoceneand Oligocene reworked taxa.

5. PALAEOBIOGEOGRAPHY

Both the distribution pattern and fluctuation in

abundance of the Late Eocene to Early Miocenenannofloras (the NP21-NN2 CalcareousNannoplankton Zones) recorded in the NW areaof the Getic Depression reflect the environmental


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Fig.

4.Comparisonbetw

eenthestratrigraphyoftheNEpartoftheGeticDepression,identifiedinthisstudyandthestratigraphyof

Carpathianbend

area(tefnescu,1995)


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changes, both climatic and oceanographic, thatcharacterized the end of the Paleogene period.

The Late Eocene (Priabonian) nannofloras ofthe Olneti Formation are dominated by theSphenolithus and Discoaster genera, which aremostly confined to the warm and well-oxygenatedsurface waters of the Tethys Realm. Onlycosmopolitan nannofossils are present in theUpper Eocene deposits of the Getic Depressionand this is a common feature for the Late Eocenenannofloras throughout the world. An open-marineenvironment, largely communicating with theTethys Realm, characterized the area where themudstones of the Olneti Formationaccumulated.

It is widely accepted that the beginning of theOligocene is a time of palaeoclimatic cooling(Aubry, 1992, Zachos et al., 2001), that must havecaused significant paleoenvironmental and bioticchanges in the open seas. These changes are

mirrored in the Early Oligocene nanofloras of theGetic Depression. A sharp decline in abundanceof the warm water taxa Discoaster andSphenolithus was recorded within the top of theOlneti Formation, followed by thedisappearance of the discoasterids. The genusSphenolithus is represented only by the long-ranging and diagenetical-resistant species S.moriformis. Endemic taxa of the ParatethysRealm, such as Transversopontis lata, T. fibula,Dictyococcites ornatus and Reticulofenestralockeri, occur in the investigated Lower Oligocenedeposits. Moreover, monospecific assemblages

containing Braarudosphaera bigelowii (Gran &Braarud) Deflandre, a species characteristic forbrackish water environments, were observed fromsamples of Early Oligocene age, collected fromthe succession exposed in the Getic Depression.

These data argue for a decrease in salinity dueto the isolation of the studied area (that was partof to the Central Paratethys) from the TethysRealm. A progressive cooling, together with a lownutrient supply could also be assumed. Theoccurrence of the endemic nannofossils, togetherwith Braarudosphaera bigelowii, may representthe first signal of the instauration of the Early

Oligocene anoxia in the area of the GeticDepresssion.The disappearance of endemic taxa, the re-

occurrence of Sphenolithus and Discoaster and,the dominance of cosmopolitan nannofossils inthe Late Oligocene to Early Miocene assemblagessuggest a restoration of the communicationbetween the study area and the Tethys Realm.The increase in nannofloras diversity andabundance express environmental changes, likeincreased in salinity and evaporation, due tohigher temperatures at the surface of the sea and,increased nutrient supply and planktonic

productivity of the surface waters.

6. DISCUSSION AND CONCLUSION

A complex depositional history characterizedthe NE part of the Getic Depression, during theLate Paleogene. The end of the Eocene (LatePriabonian up to the Eocene/Oligocene boundaryinterval) is characterized by the deposition of themarine mudstones of the Ol

ne

ti Formation over

the entire study area. Beginning with theOligocene (the Rupelian stage), organic-richmudstones and marls of Brdule Formationaccumulated in the NE part of the GeticDepression (Fig. 4).

Our study documented that the lower part ofthe Brdule Formation, sharing some similarlithological features with the dysodilic shales ofthe Eastern Carpathians, is partly synchronouswith the Cheia Formation and with the lower partof the Corbi Sandstone. We can assume that thedeposition of this lithostratigraphic unit started

over the whole Getic Depression area in the EarlyOligocene (NP22 Calcareous Nannofossil Zone),shortly after the first isolation of the Paratethysfrom the Tethys Realm. To the west, the lowerpart of Brdule Formation is missing due toerosion (Fig. 3). This fact is indicated by theunconformity recorded between theconglomerates from the base of Cheia Formation,and the calcareous clays of the OlnetiFormation and, also by the absence of NP21(upper part) and probably lower part of NP22calcareous nannoplankton zones west ofMuiereasca Valley (Fig.3).

The anoxic organic rich mudstones (dysodilicshales), deposited during the Early Oligocene, arepresent within the whole Carpathian belt, probablyreflecting highstand conditions for that particularinterval over a large area of the Southern, Easternand Western Carpathians. However, theirabsence west of the Muiereasca Valley in theGetic Depression is best explained whenconsidering the unconformity at the base of theCheia Formation.

Despite different tectonic evolution of theCarpathian and Getic domains (Sndulescu,1984; tefnescu, 1995; Maenco, 1997), both

regions are characterized by deposition oforganic-rich mudstone-dominated episodes in theEarly and Late Oligocene. However, there areother significant lithological differences betweenthe two areas: in the Getic Depression theOligocene successions are dominated byconglomerates and sandstones, the former mainlymissing in the Carpathians. Taking into accountthese observations, we do not agree to extend thelithostratigraphic terminology from the EasternCarpathians into the area of Getic Depression.For instance, the Upper Oligocene organic-richmudstones, interbedded with thin sandstones, of

the Getic Depression area have been previouslydescribed as Pucioasa-type Marls. Our studyproves that this succession termed here theBrdule Formation extends in the entire interval


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occupied by the Pucioasa, Vineiu and the UpperDysodilic Shale formations (which is Chattian -Early Burdigalian in age, according to Melinte1993) in the inner part of the Tarcu Nappe of theEast Carpathians. The so-called dysodilic shalesof the Getic Depresssion, named here the lowerpart of the Brdule Formation, differ also in agefrom the Lower Dysodilic Shales of the EastCarpathians. The former spans over the EarlyOligocene, while the latter was deposited in ashorter interval, within the late Early Oligocene(Melinte, 1993). The basal Oligocene (the EarlyRupelian) is characterized in the East Carpathiansby other two lithological units (the Bituminous MarlFormation and the Menilitic Formation) whichwere not recognized so far in the GeticDepression.

Based on nannofloral changes in diversity,abundance and distribution, we assume that anopen-marine environment, with warm and well-

oxygenated surface waters characterizes the LateEocene, including the Eocene - Oligoceneboundary interval. A restrictive oceanic circulationpattern, leading to the establishment of an anoxicregime, and cooler surface waters, could beassumed for the Early Rupelian to early LateRupelian interval. A gradual transition from ananoxic to a hypoxic environment, together with aprogressive warming, developed in the LateOligocene (Chattian) to Early Miocene(Burdigalian) interval. The pattern of nannofloraldistribution and fluctuations, recorded from thePaleogene sediments of the Getic Depression,

reflects the global climatic deterioration fromEocene to Oligocene times.We consider that this study is only the

beginning of a systematic stratigraphicinvestigation of the Getic Depression. Furtherhigh-resolution lithological and biostratigraphicalworks (including also other groups of organisms -i.e. dinoflagellates) are to be carry out, in order todate more accurately the Paleogenelithostratigraphic units, cropping out in the wholeregion of the Getic Depression.

ACKNOWLEDGMENTS

Part of this research was supported by the GrantNo.14/2004 of the Petrom National Oil Company. Relu-Dumitru Roban acknowledges International Associationof Sedimentologists for a Postgraduate Grant. We areindebted to Prof. Dr. Nicolae Anastasiu, for discussionsand comments on an earlier version of the manuscript.We thank to Dr. Dan Jipa, for interesting remarks andcomments on earlier version of this paper, as well as forreviewing our work. Dr. Carmen Chira a kindly reviewedthis manuscript. Dr. Bogdan Vrban helped us withdiscussions and suggestions on the stratigraphy andsedimentology, also improving the English version ofthis manuscript. The authors thank for field assistanceto: Ovidiu Barbu, Ana Maria Muat, Liviu Popa andFlorin Stoican.

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PLATE 1LM, all microphotographs N+

1. Reticulofenestra pseudoumbilicus (Gartner), Early Miocene (Burdigalian), NN2 Nannofossil Zone, RulDoamnei, Sample 275.2. Cribrocentrum reticulatum (Gartner & Smith) Roth & Thierstein, Eocene/Oligocene boundary interval,NP21 Nannofossil Zone, Vlsan Valley, Sample 190.3. Coronocyclus nitescens (Kamptner) Bramlette & Wilcoxon, Early Miocene (Aquitanian), NN1 NannofossilZone, Rul Doamnei, Sample 2644. Reticulofenestra scrippsae (Bukry & Percival) Roth, Early Oligocene (Rupelian), NP22 Nannofossil Zone,Muiereasca Valley, Sample 380.5. Helicosphaera kamptneri (Hay & Mohler in Hay et al.) Locker, Early Miocene (Aquitanian), NN1

Nannofossil Zone, Rul Doamnei, Sample 257.6. Reticulofenestra hillae Bukry & Percival, Early Oligocene (Rupelian), NP22 Nannofossil Zone, OlnetiValley, sample 375.7. Cyclicargolithus abisectus (Mller) Bukry, Late Oligocene (Chattian), NP24 Nannofossil Zone, CheiaValley, sample 347.8. Reticulofenestra umbilica (Levin) Martini & Ritzkowski, Eocene/Oligocene boundary interval, NP21Nannofossil Zone, Vlsan Valley, Sample 190.9. Chiasmolithus altus Bukry & Percival, 1971, Late Oligocene (Chattian), NP24 Nannofossil Zone, CheiaValley, sample 348.10. Coccolithus miopelagicus Bukry, 1971, emend. Wise, 1973, Early Miocene (Aquitanian), NN1Nannofossil Zone, Rul Doamnei, Sample 257.11. Field of view with Rhabdosphaera clavigera Murray & Blackman - central part - and smallreticulofenestrids left down, Early Miocene (Burdigalian), NN2 Nannofossil Zone, Rul Doamnei, Sample

275.12. Thoracosphaera saxea Stradner, Early Oligocene (Rupelian), NP22 Nannofossil Zone, MuiereascaValley, Sample 380.13. Sphenolithus moriformis (Brnnimann and Stradner) Bramlette and Wilcoxon, Late Oligocene (Chattian),NP24 Nannofossil Zone, Cheia Valley, sample 347.14. Zygrhablithus bijugatus (Deflandre in Deflandre & Fert) Deflandre, Early Oligocene (Rupelian), NP22Nannofossil Zone, Olneti Valley, sample 375.15. Dictyococcites bisectus Hay, Mohler & Wade, Eocene/Oligocene boundary interval, NP21 NannofossilZone, Vlsan Valley, Sample 190.16. Reticulofenestra ornata Mller, Early Oligocene, NP23 Nannofossil Zone, Olneti Valley, sample 332.17. Helicosphaera compacta Bramlette & Wilcoxon, Eocene/Oligocene boundary interval, NP21 NannofossilZone, Vlsan Valley, Sample 190.18. Pontosphaera latelliptica Bldi-Beke & Baldi) Perch-Nielsen, Eocene/Oligocene boundary interval, NP21

Nannofossil Zone, Vlsan Valley, Sample 190.19. Pontosphaera enormis (Locker) Perch Nielsen, Late Oligocene, NP25 Nannofossil Zone, Rul Doamnei,Sample 317.20. Triquetrorhabdulus carinatus Martini, Late Oligocene, NP25 Nannofossil Zone, Rul Doamnei, Sample25.


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ROBAN & MELINTE Paleogene litho- and biostratigraphy of the NE Getic Depression (Romania)

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