Barremian – Early Aptian Urgonian Limestones from the south-eastern Ku ~ aj Mountains ( Carpatho-Balkanides , eastern Serbia )

The newest results of sedimentological and paleontological investigations of part of the Urgonian Limestones studied in the surrounding of Boljevac on the SE slopes of the Ku~aj Mts. (Carpatho-Balkanides, eastern Serbia) are presented. On two localities, near the village Faca Vajali, four types of microfacies and one subtype within the bioclastic limestones were separated. The characteristics of the depositional environments of the investigated Urgonian Limestones were studied and are discussed. At the base of the established rich microassociations of foraminifera and algae, the vertical distribution of foraminiferal species was precisely defined which enabled the determination the the age of this part of the Urgonian Limestones as Late Barremian–Early Aptian.


Introduction
The rocks of Lower Cretaceous age, belonging to the eastern Serbian Carpatho-Balkanides, are widely distributed and facially heterogeneous.It refer to the Barremian and Aptian sediments and their special type known as Urgonian, Urgonian facies or Urgonian development.The mentioned sediments are most often in the mountainous area of the middle eastern Serbian Carpatho--Balkanides, which extend as an elongated arc from the Danube in the north southwards, then twist toward southeast and east until the Serbian-Bulgarian boundary.
A detailed summary of investigations of the Urgonian sediments of the eastern Serbian Carpatho-Balkanides until 1974 was given by JANKI^EVI] (1978).In addition, his monograph contains numerous new and comprehensive data about the paleontology, stratigraphy, and lithology of the Urgonian.Hence in further investigations, just a few authors in Serbia paid attention to the study of these sediments.In addition to papers of MA-RAN (1996,1998), which dealt mostly with Urgonian echinids of the Ku~aj Mts., the Master Thesis of RADU-LOVI] (2003) could be mentioned, in which, together with Upper Barremian and Lower Aptian brachiopods, microassociations from the Urgonian of the Ku~aj were separated.It is also necessary to emphasize the paper of JANKI^EVI] (1996) who studied the Urgonian of the Carpatho-Balkanides using formational analysis and suggested the name Tupi`nica Formation for these carbonate-terrigenous deposits of Upper Barremian and Lower Aptian (Bedoulien and possibly also lower Middle Aptian -Gargasian) time/stratigraphic position.
During field investigations for the Master Thesis of A. MARAN in the period 1994-1995, a few geological columns were made at localities near Boljevac (southeastern slope of the Ku~aj Mts.) and macrofossils and material for thin sections were collected.The investigated sites were: Faca Vajali-Izvor, Faca Vajali-U{}e Arnaute, Faca Vajali-Vidikovac, Mali Izvor/1, Mali Izvor/2, Bogovina-Kamenolom and Bogovina-Pe}ina.At that time, relatively poor sedimentological and micropaleontological studies were used for the determination and explanation of the paleoecological characteristics of the established microassociations, and on that way, indirectly for the analysis and solutions of paleoecological problems of echinoid macrofauna (MARAN 1996).
Afterwards, the complex of the Faca Vajali sections were chosen and proposed for protection within the frame of the Cretaceous Geosite Conservation Program in Serbia as being representative, accessible and available for the geological science (MARAN 1999, MARAN et al. 2005).
As part of an ongoing project, in past decade, the localities Faca Vajali-Izvor and Faca Vajali-U{}e Arnaute were investigated several times and new material was collected.The aim of this paper is to present the results of the new detailed micropaleontological and sedimentological studies and evaluate these results in order to contribute to a better understanding of this part of the Urgonian sediments of eastern Serbia.In this way, the fund of our geological knowledge and practice is enriched, which is very important because a 40 m high dam will be built on the Crni Timok River close to locality Faca Vajali-Izvor, the main purpose of which will be to supply regional water to towns in the Timok Region (the towns Bor and Zaje~ar).As a result, the closest area surrounding the village together with all the geological localities will be submerged and lost forever.
The Ku~aj Terrane had a long (Proterozoic to Neogene) and very complex geological evolution.The western boundary of the Unit is an Alpine eastward thrust, the eastern boundary is mostly of the same character.The time of the docking of the Ku~aj Terrane to the Stara Planina-Pore~ Terrane at the East is the end of the Viséan.
In the Ku~aj Unit, the oldest rocks (Osanica metamorphics) are of Proterozoic age, metamorphosed under amphibolite facies conditions, and represent part of the old crystalline basement.The following Upper Proterozoic to Lower Cambrian rocks are volcanic-sedimentary rocks metamorphosed under greenschists facies conditions.Over this basement, Upper Cambrian to Lower Carboniferous sediments of the Caledonian-Variscan Cycle were deposited: shallow marine clastics (Upper Cambrian-Ordovician), deep-sea black shales (Upper Ordovician-Lower Devonian), pre-flysch (Lower and Middle Devonian) and flysch (Upper Devonian-Lower Carboniferous).
The post-Variscan overstep sequence begins with the Stephanian Limnic sediments grading into the Permian Red Sandstone Formation formed in intramountain depressions.In the Lower until the Middle or even in a part of the Upper Triassic, mainly shallow water carbonate rocks were deposited.In the Bajocian, basal clastics and oolitic limestones were formed transgressively.After that, in the eastern parts of the terrane, shallow water sediments of a carbonate platform (inclusively Urgonian Limestones were deposited up to the end of Lower Aptian.In the western regions of the Unit, Callovian-Valanginian deep water deposits are present.From the Cenomanian to the Maastrichtian, in places to the Paleocene, identical pelagic clastics and carbonate sediments occur, accompanied by a multistage magmatism (the Timok area).Brackish Upper Maastrichtian sediments represent the final stage of the marine regime.Lacustrine Paleogene sediments unconformably ovelie the Upper Cretaceous formations.The Middle and Upper Miocene limnic rocks are a post-Alpine overstep sequence.
The Lower Cretaceous sediments belonging to the Ku~aj Unit/Terrane are widely distributed and thick.Differentiation of the sea bottom started in the Upper Jurassic, and continued in the Lower Cretaceous.The main rock types of the Neocomian are different kinds of shallow water limestones, but sandstones and sandy marlstones are also present.The rocks are characterized by rich association of bivalves, gastropods, brachiopods, echinoids, foraminifera and algae.A small flysch depression located in the southwestern part was formed in theUpper Jurassic and was present to the Valanginian.After the flysch sediments post-flysch marlstones and marly limestones were deposited.Over the whole area, Urgonian rocks of Barremian and Aptian age are MILAN SUDAR, DIVNA JOVANOVI], ALEKSANDRA MARAN & SVETLANA POLAVDER represented by carbonate sediments with three facies (limestone facies with rudists, facies of bioclastic limestones with orbitolinids and facies of bioclastic limestones with a terrigenous component and orbitolinids) and terrigenous non-carbonatic rocks with three/four facies (facies of sandstones and marlstones with orbitolinids, sandstone facies with ostreids and sandstone facies with plant detritus) (JANKI^EVI] 1978, 1996).Their total thickness is circa 450-500 m and fossils are abundant, especially representatives of rudists (and other bivalves), corals, echinoids, brachiopods, orbitolinids, other foraminifera and algae.The lower boundary of these sediments is not sharp but is undertaken because of the presence of a rich microassociation of Barremian age.The previously mentioned fauna of Neocomian age is very poor.In addition, it is almost impossible to divide the sediments of Barremian and of Aptian age, and the boundary is the most often located conditionally because only a gradual transition exists.The upper boundary is sharp.The Upper Aptian is not found, hence directly over the Lower Aptian lie conglomerates and glauconitic sandstones of Albian age or some other rocks of Upper Cretaceous age.

Microfacial analysis of Urgonian Limestones in the investigated sections
The Urgonian sediments located in the vicinity of Boljevac were sampled in detail southwestern from Bogovina near the village Faca Vajali on two sections: Faca Vajali-Izvor and Faca Vajali-U{}e Arnaute (Fig. 1).In both sections are present only a part of the Urgonian Limestones, which are macroscopically, i.e., lithologically, represented with two groups of limestones: thick-bedded to massive grey limestones with visible sections of macrofauna and thin-to decimeter thick-bedded friable, disintegrated partly, sandy-marly grey-yel- Fig. 2. Geologic column and vertical distribution of the determined foraminifera species in the Late Baremian-Early Aptian of the Faca Vajali-Izvor Section, eastern Serbian Carpatho-Balkanides (for the symbols, see Fig. 5).lowish limestones with the whole forms of fossils.In these rocks, it was possible, on the basis of sedimentological, macro-and micropaleontological features (depositional textures, biota, etc.), to define four microfacies types (MFT 1-4) and one subtype (MFT 2A).The extended version of the DUNHAM (1962) and the methods described by WILSON (1975) andFLÜGEL (2004) were used for the microfacies analysis.
The thin sections are housed in the collection of M. SUDAR (Department of Paleontology, Faculty of Mining and Geology, University of Belgrade, Belgrade, Serbia), under the numbers MS 3000-3041.

The Faca Vajali-Izvor Section
The geological column from this locality is located westward of the village Faca Vajali.It begins from the middle parts of a temporary flow which from level 350 descends to the Crni Timok River and continues eastward, on the left side of the local road leading to the center of the village (coordinates: x 4859050, y 7574470).The locality is named by the spring (in Serbian = Izvor) which is situated close below the section, directly along the Crni Timok River.
At the locality Faca Vajali-Izvor, the studied column has a thickness 51.9 m (Fig. 2).It is possible to distinguish the lower and upper part of the column on the field.The lower part (3 units, 12.4 m thickness) is composed of compact, grey thick-bedded to massive limestones with a good visible extracted macrofauna on the surfaces -colonial and solitary corals, stromatoporoids, chaetetids, gastropods, bryozoans and other forms.In the upper part of the column (thickness 39.5 m, units 4-10) predominate friable thick-to thin-bedded carbonate sediments, partially enriched by clayey and sandy fractions and with a yellowish weathering of the surfaces.Only sporadically are harder beds, thick to a few dm, visible (Fig. 3).This part of the.column is abundant with whole forms of fossils: bivalves (no rudists), echinoids, gastropods, brachiopods, orbitolinids, etc.
On the the Faca Vajali-Izvor Section column are separated the.following two characteristic microfacies types and one subtype, the photomicrographs of which are given in Fig. 4: MFT 1 -bioclastic wackestone with transitions to packstone, grainstone or floatstone; MFT 2A -bioclastic wackestone with transition to packstone, rare boundstone; and MFT 4 -orbitolinid packstone.
MFT 1. Bioclastic wackestone with transitions to packstone, grainstone or floatstone (Fig. 4, 5-7) are present in rocks, around 70 %, mostly from the upper parts of the column (units 4-10).In addition to rich macrofaunal biota, the microassociation is represented by fragments (bioclasts) of bivalves (but no rudists), gastropods, corals, algae, foraminifera, echinoids, brachiopods, crinoids, etc.The bioclasts are unequally distributed in micrite, rarely microsparite, sporadically enriched by Fe-pigment or fine siliciclastic detritus (quartz predominates).Their size varies from 0.1 mm and less to over 2 mm and more.The bioclastic and another allochems (coated grains, grapestone, rarely ooids, pelloids etc., sometimes with geopetal fillings) are well rounded, mostly middle to bed sorted.Very often they have micritic envelopes as a result of work of cyanobacterias, fungi etc., which are characteristic for protected shoals and lagoons of higher salinity.
These sediments were deposited in a shallow subtidal, and/or rather deeper intertidal area (carbonate platform margin, i.e., open shelf lagoon behind a platform margin; WILSON 1975;FLÜGEL 2004).
MFT 4. Orbitolinid packstone is present in the rocks of the both parts of the column in an amount of 10 %.Higher contents of sandy-clayey, hence ferruginous matter, is typical in microsparite-micrite.In addition to numerous agglutinated orbitolinids (only Palorbitolina, Fig. 4, 8), they contain small coated bioclasts with a core of dasycladaceans, stromatoporoids, and other organisms, whole tiny foraminifera and microgastropods, tiny organic debris (echinoid spines, etc.), etc.
Their microfossil community is monotonous because of the presence of terrigenous matter which reduced flourishing of the organic world.In addition orbitolinids, Nezzazata, Nezzazatinella, Everticyclammina, and calcareous perforate genera Neotrocholina, Lenticulina and some miliolids were determined.Algae are present only with rare Boueina (Udoteaceae).
These microfacies types were probably formed in the shallow subtidal of a partially protected lagoon in a carbonate platform.

The Faca Vajali-U{}e Arnaute Section
The section is located in the eastern part of the village, on the slope of Cukloj, 200 m SW from the confluence (in Serbian = U{}e) of the Arnauta River into the Crni Timok River (coordinates: x 4858950, y 7576175).The column, thick 45.5 m contains 10 units (Fig. 5).At the base (3 units, thickness 6.2 m) are yellow friable sandy-marly limestones without macrofauna.They are followed by thick-bedded to massive grey limestones (units 4-9, thickness 37 m), which represent thicker and a more imposing part of the column with surfaces where numerous concentrations are visible, coquinas of the rudists and very rare other macrofaunas -corals, stromatoporoids, gastropods, bryozoans, etc. (Fig. 6).The highest part of the column (unit 10, thickness 2.3 m) is made.up of yellowish disintegrated sandymarly limestones, identical to the sandstones at the base of the section and also without fauna.
On the geological column of the Faca Vajali-U{}e Arnaute Section the following characteristic three microfacies types are present and their photomicrographs are given in Fig. 7: MFT 2 -bioclastic wackestone with transition to packstone; MFT 3 -bioclastic grainstone and MFT 4 -orbitolinid packstone.
The MFT 2 microfacies (Fig. 7, 1, 3-6) from the middle part of column and the friable MFT 3, which is present in the lowest and final part of the Faca Vajali-U{}e Arnaute Section (Fig. 7, 2) are dominant.In adition to these, in the whole column also exist rocks with the MFT 4, but with much fewer and rarer microfossils than in the same MFT of the Faca Vajali-Izvor Section.
In parts with an unequal presence of a sandy fraction, the development of an abundant organic world was enabled but it was also suitable for agglutinated foraminifera (orbitolinids).They rarely appear together with algae in the bioclastic packstone (MFT 4).
These rocks have two main characteristics: an abundance of rudists (and rare specimens of other reef macrofaunas) and a bioclastic character.Although the first characteristic indicates reef origin, the fauna present in the bioclastic, very fragmented limestones is not sufficient to mark the limestone of MFT 2 and MFT 2A as reefal.This was confirmed with their view, manner of appearance, structure, etc.For the other characteristics of these limestone with rudists and an interpretation of their depositional nature see in the penultimate chapter of this paper.
MFT 3. Bioclastic grainstone appears subordinately in yellowish, partially friable and thicker limestone beds without macrofauna but with a relatively rich and diverse microfossil community.
Limestone of this microfacial type were deposited in intertidal (WILSON 1975, washed grains of a platform margin; LOGMAN 1981, backreef sands).

* * *
For comparison with the given investigated sections, existing results of sedimentological and paleontological analyses from a few other localities near to Boljevac were used but the given data will not be presented separately.These localities are: Faca Vajali-Vidikovac, Mali Izvor/1, Mali Izvor/2, Bogovina-Pe}ina and Bogovina-Kamenolom.The established microfacial types and subtype are distingished on the following sections.
MFT 1 and especially MFT 4: Faca Vajali-Izvor (units 4-10), Bogovina-Pe}ina, and Mali Izvor (both fossiliferous sites).MFT 3 is found only in the lower and higher part of the Faca Vajali-U{}e Arnaute Section (units 1-3 and 10).MFT 4 is also present in remaining sections but in smaller amounts than other microfacial types.
MFT 2 is the most common in the middle part of the Faca Vajali-U{}e Arnaute Section (units 4-9) and at the locality Bogovina-Kamenolom.MFT 2A, characterized by rarer presence or almost without rudists, is found in the lower units (1-3) of the Faca Vajali-Izvor Section and at the site Faca Vajali-Vidikovac.

Summary and conclusions
The herein presented results of a detailed sedimentological and paleontological (especially micropaleontological) study of a part of the Urgonian bioclastic limestones from near to the village Faca Vajali, the Boljevac Area on the SE slopes of the Ku~aj Mts.(Carpatho--Balkanides, eastern Serbia), some summary discussions and conclusions in relation to the interpretation of their depositional environment and stratigraphy can be made.

Interpretation of the depositional environment
Sedimentological and paleontological data of the Late Barremian-Early Aptian Urgonian Limestones of the studied area of eastern Serbia confirmed shallow water carbonate sedimentation of a platform type under conditions of a tropical to subtropical climate on a wide unstable shelf of developed relief in a warm sea of the Tethyan areal.In French literature, this area is traditionally known as the "carbonate (Urgonian) platform" (ARNAUD-VANNEAU 1980; MASSE & PHILIP 1981; MAS-SE 1993, etc. and many other earlier and newer references) and in Serbian literature, it is defined as the "paraplateforme carbonatique" (GRUBI] & JANKI^EVI] 1973) or the "shelf carbonate platform" (JANKI^EVI] 1978, 1996).
GU[I] & JELASKA (1990) while establishing some depositional environments of the Upper Cretaceous of the Bra~ Island made comparisons with the ambients of the middle shelf in sense of WILSON & JORDAN (1983).The investigated biotop of part of the Urgonian sediments near to Boljevac could be correlated with the ambient and characteristics of that area.It represents an extensive and morphologically differentiated backreef platform, partially opened (presence of sceletal carbonate sands of higher water energy formed in sandy shoals, beaches, tidal accumulations, submarine rises -bioclastic grainstone), with a depth from shallow low and/or high energy infralittoral (subtidal less than 10 m) to littoral (intertidal, tidal flat).Different microfacies rich with carbonate mud from the protected shelf lagoon of limited circulation below the wave base are very frequent.
Bioclasts (whole or fragmented fossil specimens) mostly derived from rudist shells and also from other reef fauna: corals, chaetetids, stromatoporoids, etc. indicate the interspersing of these organisms on the platform or accumulation in coquinas.According to WIL- SON & JORDAN (1983) and MASSE (1990MASSE ( , 1993)), the Urgonian forms of rudists were formed on the middle shelf, i.e., on the internal parts of the external platform margin and in an intraplatform lagoon (margin or inside), in which occupy different paleoecological niches.
These small ecologic reefs (small biostromes, carbonate build-up or patch reefs) built by the mentioned bioclasts and other reef organisms were formed as elevations a few meters over the sea bottom (3-6 m in recent analogues, JAMES 1983) in the interior of the platform.In addition, they represented immature ecosystems in the initial stabilization/colonization stadium and because of their fast destruction, nowadays, just products of their erosion and disintegration are found, such us in the limestone B group, i.e., in MFT 2.
A special characteristic of the sedimentary area of the investigated Urgonian Limestones of the Faca Vajali area is the exclusive presence of bioclastic varieties of all the included limestones.In addition, some fauna was found in an abnormal position, as an example the overturned coral colony in the beginning of the Fa-caVajali-Izvor section (Fig. 8).Chaotical distribution of the rest of macrofauna (especially rudists), recognizable transport and erosion of allochems (for example many of the orbitolinids have not a top with an embryonic chamber).All this points to constant transport, i. e., to parautochthonity of all the presented biota and other Late Barremian-Early Aptian Urgonian Limestones from the south-eastern Ku~aj Mountains ... 23 Fig. 8. Overthurned colonial coral from the lower part (unit 3) of the Faca Vajali-Izvor Section, eastern Serbian Carpatho--Balkanides. material in a depositional marine environment of very shallow subtidal and/or somewhat deeper intertidal.
Hence, it can be concluded that all these paleoenvironments, essentially infralittoral to partially or rarely littoral, with a more or less distinct water energy, probably occupy an area linked either just before the outer edge of a platform or just inside, i. e., also before the inner open, to more of less protected parts of the platform lagoon.

Stratigraphy
The age of the Urgonian sediments from eastern Serbia is of great importance.Usually it is determined as Barremian-Aptian, Upper Barremian-Lower Aptian, etc.As is shown in the geological setting, their boundaries are distinctly determined, the upper more than the lower.In spite of the presence of rich fossil material, especially macrofauna and the absence of lithological variabilities, the precise determination of Barremian--Aptian boundary is not always sure and simple.For this reason, during earlier geological investigations of the Lower Cretaceous of eastern Serbia, the presence of Urgonian sediments and their Barremian and/or Aptian age was mostly established.
In the Serbian geological literature attempts were made to subdivide the mentioned stages.The first results were given by V. PETKOVI] who considered that the boundary between the Barremian and the Aptian on the Tupi`nica Mt. lies "eventually between limestones with pachydont shells and orbitolinid limestones" (PETKOVI] 1908 from JANKI^EVI] 1978, p. 161).The question of boundary in the investigated Urgonian complex of eastern Serbia was of special interest for JANKI^EVI] (1978).The same author defined the whole complex as Barremian-Lower Aptian, although he considered all separated limestone facies as Barremian (whole, or only their upper part) to Lower Aptian, and other terrigenous non-carbonate sediments as only Lower Aptian.Also of interest is part from his conclusion: "The boundary between the Barremian and Aptian stage is most often provisory undertaken, because exists a gradual transition.But, the fossil association of organisms, in which are numerous Palorbitolina lenticularis (Blum.),surely confirms Lower Aptian" (op.cit., p. 183).A very similar is opinion is shared by RADULOVI] (2003).She decided that the parts of the columns of Urgonian sediments at the localities Faca Vajali and Mali Izvor with a defined microassociation of Palorbitolina lenticularis and Neotrocholina aptiensis are of Lower Aptian age.Unfortunately, their conclusions were not confirmed with detailed defined stratigraphic characteristics of the whole microassociation and their members.In addition, the mentioned foraminifera have a range from the Late Barremian to the earliest Late Aptian (ARNAUD--VANEAU et al. 1991, and many other earlier and newer papers).
A large part of the mentioned interval belongs to the Palorbitolina lenticularis Zone according to the range of this foraminifera, one of the most important taxon and geographically widespread in the Tethys.Since detailed investigations and a more exact dating of the whole Urgonian geologic column of eastern Serbia are missing, their later biostratigraphic sudivision was not possible.Also, real knowledge about the lower and upper boundary of the investigated Late Baremian-Early Aptian Urgonian Limestone in the Boljevac area does not exist.